[Federal Register Volume 67, Number 149 (Friday, August 2, 2002)]
[Proposed Rules]
[Pages 50374-50383]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 02-19419]


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 Proposed Rules
                                                 Federal Register
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 This section of the FEDERAL REGISTER contains notices to the public of 
 the proposed issuance of rules and regulations. The purpose of these 
 notices is to give interested persons an opportunity to participate in 
 the rule making prior to the adoption of the final rules.
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  Federal Register / Vol. 67, No. 149 / Friday, August 2, 2002 / 
Proposed Rules  

[[Page 50374]]



NUCLEAR REGULATORY COMMISSION

10 CFR Parts 50 and 52

RIN 3150-AG76


Combustible Gas Control in Containment

AGENCY: U.S. Nuclear Regulatory Commission.

ACTION: Proposed rule.

-----------------------------------------------------------------------

SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) proposes to amend 
its regulations for combustible gas control in power reactors 
applicable to current licensees and to set and consolidate combustible 
gas control regulations for future applicants and licensees. The 
proposed rule eliminates the requirements for hydrogen recombiners and 
hydrogen purge systems and relaxes the requirements for hydrogen and 
oxygen monitoring equipment to make them commensurate with their risk 
significance. This action stems from the Commission's ongoing effort to 
risk-inform its regulations, and is intended to reduce the regulatory 
burden on present and future power reactor licensees.
    In addition to the rulemaking and its associated analyses, the NRC 
is also proposing a draft regulatory guide, a draft standard review 
plan revision, and a Consolidated Line Item Improvement Process (CLIIP) 
for draft technical specifications changes to implement the proposed 
rule. The NRC is requesting comments on these documents as well as the 
proposed rulemaking.

DATES: Submit comments by October 16, 2002. Comments received after 
this date will be considered if it is practical to do so, but the 
Commission is able to ensure consideration only for comments received 
on or before this date.

ADDRESSES: Submit comments to the Secretary, U.S. Nuclear Regulatory 
Commission, Washington, DC 20555-0001, Attention: Rulemakings and 
Adjudications Staff.
    Deliver comments to: 11555 Rockville Pike, Rockville, Maryland, 
between 7:30 a.m. and 4:15 p.m. on Federal workdays.
    You may also provide comments via the NRC's interactive rulemaking 
Website at http://ruleforum.llnl.gov. This site provides the capability 
to upload comments as files (any format) if your Web browser supports 
that function. For information about the interactive rulemaking 
Website, contact Ms. Carol Gallagher, (301) 415-5905 (e-mail: 
[email protected]).
    Certain documents related to this rulemaking, including comments 
received, may be examined at the NRC Public Document Room, 11555 
Rockville Pike, Rockville, Maryland. Some of these documents may also 
be viewed and downloaded electronically via the rulemaking Website.

FOR FURTHER INFORMATION CONTACT: Anthony W. Markley, Office of Nuclear 
Reactor Regulation, U.S. Nuclear Regulatory Commission, Washington, DC 
20555-0001, telephone (301) 415-3165, e-mail [email protected].

SUPPLEMENTARY INFORMATION:

I. Background
II. Rulemaking Initiation
III. Proposed Action
    A. Retention of Inerting, BWR Mark III and PWR Ice Condenser 
Hydrogen Control Systems, Mixed Atmosphere Requirements, and 
Associated Analysis Requirements
    B. Elimination of Design-Basis LOCA Hydrogen Release
    C. Oxygen Monitoring Requirements
    D. Hydrogen Monitoring Requirements
    E. Combustible Gas Control Requirements for Future Applicants
    F. Clarification and Relocation of High Point Vent Requirements 
From 10 CFR 50.44 to 10 CFR 50.46a
    G. Elimination of Post-Accident Inerting
IV. Section-by-Section Analysis of Substantive Changes
V. Plain Language
VI. Voluntary Consensus Standards
VII. Finding of No Significant Environmental Impact: Environmental 
Assessment
VIII. Paperwork Reduction Act Statement
IX. Regulatory Analysis
X. Regulatory Flexibility Certification
XI. Backfit Analysis

I. Background

    On October 27, 1978 (43 FR 50162), the Commission adopted a new 
rule, 10 CFR 50.44, specifying the standards for combustible gas 
control systems. The rule requires the applicant or licensee to show 
that during the time period following a postulated loss-of-coolant 
accident (LOCA), but prior to effective operation of the combustible 
gas control system, either: (1) An uncontrolled hydrogen-oxygen 
recombination would not take place in the containment, or (2) the plant 
could withstand the consequences of an uncontrolled hydrogen-oxygen 
recombination without loss of safety function. If neither of these 
conditions could be shown, the rule required that the containment be 
provided with an inerted atmosphere to provide protection against 
hydrogen burning and explosion. The rule defined a release of hydrogen 
involving up to 5 percent oxidation of the fuel cladding as the amount 
of hydrogen to be assumed in determining compliance with the rule's 
provisions. This design-basis hydrogen release was based on the design-
basis LOCA postulated by 10 CFR 50.46 and was multiplied by a factor of 
five for added conservatism to address possible further degradation of 
emergency core cooling.
    The accident at Three Mile Island, Unit 2 involved oxidation of 
approximately 45 percent of the fuel cladding [NUREG/CR-6197, dated 
March 1994] with hydrogen generation well in excess of the amounts 
required to be considered for design purposes by Sec. 50.44. In the 
aftermath of the Three Mile Island accident, the Commission reevaluated 
the adequacy of the regulations related to hydrogen control to provide 
greater protection in the event of accidents more severe than design-
basis LOCAs. The Commission reassessed the vulnerability of various 
containment designs to hydrogen burning, which resulted in additional 
hydrogen control requirements adopted as amendments to Sec. 50.44. The 
1981 amendment, which added paragraphs (c)(3)(i), (c)(3)(ii), and 
(c)(3)(iii) to the rule, imposed the following requirements: (1) An 
inerted atmosphere for boiling water reactor (BWR) Mark I and Mark II 
containments, (2) installation of recombiners for light water reactors 
that rely on a purge or repressurization system as a primary means of 
controlling combustible gases following a LOCA, and (3) installation of 
high point vents to relieve noncondensible gases from the reactor 
vessel (46 FR 58484, December 2, 1981).
    On January 25, 1985 (50 FR 3498), the Commission published another 
amendment to Sec. 50.44. This

[[Page 50375]]

amendment, which added paragraph (c)(3)(iv), required a hydrogen 
control system justified by a suitable program of experiment and 
analysis for BWRs with Mark III containments and pressurized water 
reactors (PWRs) with ice condenser containments. In addition, plants 
with these containment designs must have systems and components to 
establish and maintain safe shutdown and containment integrity. These 
systems must be able to function in an environment after burning and 
detonation of hydrogen unless it is shown that these events are 
unlikely to occur. The control system must handle an amount of hydrogen 
equivalent to that generated from a metal-water reaction involving 75 
percent of the fuel cladding surrounding the active fuel region.
    When Sec. 50.44 was amended in 1985, the NRC recognized that an 
improved understanding of the behavior of accidents involving severe 
core damage was needed. During the 1980s and 1990s, the Commission 
sponsored a severe accident research program to improve the 
understanding of core melt phenomena, combustible gas generation, 
transport and combustion, and to develop improved models to predict the 
progression of severe accidents. The results of this research have been 
incorporated into various studies (e.g., NUREG-1150 and probabilistic 
risk assessments performed as part of the Individual Plant Examination 
(IPE) program) to quantify the risk posed by severe accidents for light 
water reactors.
    The result of these studies has been an improved understanding of 
combustible gas behavior during severe accidents and confirmation that 
the hydrogen release postulated from a design-basis LOCA was not risk-
significant because it would not lead to containment failure, and that 
the risk associated with hydrogen combustion was from beyond design-
basis (e.g., severe accidents) accidents. These studies also confirmed 
the assessment of vulnerabilities that went into the 1981 and 1985 
amendments which required additional hydrogen control measures for some 
containment designs.

II. Rulemaking Initiation

    In a June 8, 1999, Staff Requirements Memorandum (SRM) on SECY-98-
300, Options for Risk-informed Revisions to 10 CFR part 50--``Domestic 
Licensing of Production and Utilization Facilities,'' the Commission 
approved proceeding with a study of risk-informing the technical 
requirements of 10 CFR part 50. The NRC staff provided its plan and 
schedule for the study phase of its work to risk-inform the technical 
requirements of 10 CFR part 50, in SECY-99-264, ``Proposed Staff Plan 
for Risk-Informing Technical Requirements in 10 CFR part 50'' dated 
November 8, 1999. The Commission approved proceeding with the plan for 
risk-informing the part 50 technical requirements in a February 3, 
2000, SRM. Section 50.44 was selected as a test case for piloting the 
process of risk-informing 10 CFR part 50 in SECY-00-0086, ``Status 
Report on Risk-Informing the Technical Requirements of 10 CFR part 50 
(Option 3).''
    Mr. Christie of Performance Technology, Inc. submitted letters, 
dated October 7 and November 9, 1999, that requested changes to the 
regulations in Sec. 50.44. He requested that the regulations be amended 
to: reflect that the hydrogen source term be based on realistic 
calculations for accidents with a high probability of causing severe 
reactor core damage; eliminate the requirement to monitor hydrogen 
concentration; eliminate the requirement to control combustible gas 
concentration resulting from a postulated-LOCA; retain the requirement 
to inert Mark I and II containments; retain the requirement for high 
point vents; require licensees with Mark III and ice condenser 
containments to have hydrogen control systems capable of meeting a 
specified performance level; and specify that facilities with other 
types of containments ``must demonstrate that the reactor containment 
(based on realistic calculations) can withstand, without any hydrogen 
control system, a hydrogen burn for accidents with a high probability 
of causing severe core damage.''
    These letters have been treated by the NRC as a petition for 
rulemaking and assigned the Docket No. PRM-50-68. The NRC published a 
document requesting comment on the petition in the Federal Register on 
January 12, 2000 (65 FR 1829). The issues associated with Sec. 50.44 
raised by the petitioner were discussed in SECY-00-0198, Status Report 
on Study of Risk-Informed Changes to the Technical Requirements of 10 
CFR part 50 (Option 3) and Recommendations on Risk-Informed Changes to 
10 CFR 50.44 (Combustible Gas Control). The proposed rule and the 
petition are consistent in most areas, with the following exceptions 
proposed by the NRC: a functional requirement for hydrogen monitoring, 
the capability for ensuring a mixed atmosphere, and the expectation 
that future plants preclude concentrations of hydrogen below limits 
that may support detonation. The Commission's basis for including these 
requirements in the proposed rule is addressed in the subsequent 
sections of this supplementary information.
    The Commission also received a petition for rulemaking filed by the 
Nuclear Energy Institute. The petition was docketed on April 12, 2000, 
and has been assigned Docket No. PRM-50-71. The petitioner requests 
that the NRC amend its regulations to allow nuclear power plant 
licensees to use zirconium-based cladding materials other than zircaloy 
or ZIRLO, provided the cladding materials meet the requirements for 
fuel cladding performance and have received approval by the NRC staff. 
The petitioner believes the proposed amendment would improve the 
efficiency of the regulatory process by eliminating the need for 
individual licensees to obtain exemptions to use advanced cladding 
materials which have already been approved by the NRC. The proposed 
rule would remove the restrictive language in 10 CFR 50.44 that 
precludes the use of zirconium-based cladding materials other than 
zircaloy or ZIRLO. The change requested by the petitioner is unrelated 
to the risk-informing of 10 CFR 50.44. The Commission is addressing 
this petition in this rulemaking for effective use of resources. The 
NRC published a document requesting comment on the petition in the 
Federal Register on May 30, 2000 (65 FR 34599).
    In SECY-00-0198, dated September 14, 2000, the NRC staff proposed a 
risk-informed voluntary alternative to the current Sec. 50.44. 
Attachment 2 to that paper, hereafter referred to as the Feasibility 
Study, used the framework described in Attachment 1 to the paper and 
risk insights from NUREG-1150 and the IPE programs, to evaluate the 
requirements in Sec. 50.44. The Feasibility Study found that 
combustible gas generated from design-basis accidents was not risk-
significant for any containment type, given intrinsic design 
capabilities or installed mitigative features. The Feasibility Study 
also concluded that combustible gas generated from severe accidents was 
not risk significant for (1) Mark I and II containments provided that 
the required inerted atmosphere was maintained, (2) Mark III and ice 
condenser containments provided that the required igniter systems were 
maintained and operational, and (3) large, dry and sub-atmospheric 
containments because the large volumes, high failure pressures, and 
likelihood of random ignition help prevent the build-up of hydrogen 
concentrations.
    The Feasibility Study did conclude that the existing requirements 
for

[[Page 50376]]

combustible gas mitigative features were risk-significant and must be 
retained. Additionally, the Feasibility Study also indicated that some 
mitigative features may need to be enhanced beyond current 
requirements. This was identified as Generic Issue (GI) 189. The 
resolution of GI-189 will assess whether improvements to safety can be 
achieved and the costs and benefits of enhancing combustible gas 
control requirements for Mark III and ice condenser containment 
designs. The resolution of GI-189 will proceed independently of this 
rulemaking.
    The staff incorporated Mr. Christie's petition into the effort to 
risk-inform Sec. 50.44. A comparison of Mr. Christie's petition for 
rulemaking to the staff's recommended alternative was provided in 
Attachment 3 to SECY-00-0198. In an SRM dated January 19, 2001, the 
Commission directed the NRC staff to proceed expeditiously with 
rulemaking on the risk-informed alternative to Sec. 50.44.
    In SECY-01-0162, Staff Plans for Proceeding with the Risk-informed 
Alternative to the Standards for Combustible Gas Control Systems in 
Light-water-cooled Power Reactors in 10 CFR 50.44, dated August 23, 
2001, the NRC staff recommended a revised approach to the rulemaking 
effort. This revised approach recognized that risk-informing part 50, 
Option 3 was based on a realistic reevaluation of the basis of a 
regulation and the application of realistic risk analyses to determine 
the need for and relative value of regulations that address a design-
basis issue. The result of this process necessitates a fundamental 
reevaluation or ``rebaselining'' of the existing regulation, rather 
than the development of a voluntary alternative approach to rulemaking. 
Lastly, upon its own initiative, the staff incorporated the relevant 
portions of the NEI petition into this rulemaking. On November 14, 
2001, in response to Commission direction in an SRM dated August 2, 
2001, the staff published draft rule language on the NRC web site for 
stakeholder review and comment. In an SRM dated December 31, 2001, the 
Commission directed the staff to proceed with the revision to the 
existing Sec. 50.44 regulations.

III. Proposed Action

    The Commission proposes to retain existing requirements for 
ensuring a mixed atmosphere, inerting Mark I and II containments, and 
hydrogen control systems capable of accommodating an amount of hydrogen 
generated from a metal-water reaction involving 75 percent of the fuel 
cladding surrounding the active fuel region in Mark III and ice 
condenser containments. The Commission proposes to eliminate the 
design-basis LOCA hydrogen release from Sec. 50.44 and to consolidate 
the requirements for hydrogen and oxygen monitoring into Sec. 50.44 
while relaxing safety classifications and licensee commitments to 
certain design and qualification criteria. The Commission also proposes 
to relocate without change the hydrogen control requirements in 
Sec. 50.34(f) to Sec. 50.44. The Commission proposes to relocate the 
high point vent requirements from Sec. 50.44 to Sec. 50.46a with a 
change that eliminates a requirement prohibiting venting the reactor 
coolant system if it could ``aggravate'' the challenge to containment. 
The NRC received comments on the draft rule language published on the 
Web site from seven members of the public which included both 
petitioners, four utilities, and a law firm that represents the Nuclear 
Utility Group on Equipment Qualification. The comments were 
overwhelmingly supportive of the draft proposed rule language. The 
Commission used stakeholder comments on the draft rule language, 
information provided in licensee exemption submittals, in the petitions 
for rulemaking, and in the Boiling Water Reactor Owners Group (BWROG) 
topical report to inform its deliberations and decisions with respect 
to specific rule language and positions taken.
    The Commission also received feedback on several issues for which 
comments were specifically requested in the draft rule language. The 
existing rule provides detailed, prescriptive instructions using 
American Society of Mechanical Engineers (ASME) references for the 
performance of boiling water reactor (BWR) Mark III and pressurized 
water reactor (PWR) ice condenser containments. The staff provided an 
option for a more performance-based approach for stakeholder 
consideration, which received positive public comment. Based upon 
stakeholder input, the proposed rule eliminates the existing references 
to ASME and prescriptive requirements and the proposed regulatory 
guide, attached to this paper, includes the ASME approach as one in 
which the intent of the regulations could be satisfied which simplifies 
the proposed regulations.
    The staff also requested feedback on the utility of post-accident 
inerting as a means of combustible gas control. To date, no current 
licensee facility has exercised this alternative to address the control 
of combustible gas nor has any new reactor design opted for this 
approach. The major concerns involved with post-accident inerting of 
containment are expense and the issues associated with its adverse 
effects and actuation. Stakeholder feedback during public meetings and 
in the comments received on the draft rule language supported 
elimination of this option. Based upon stakeholder input, the proposed 
rule eliminates the post-accident inerting option which also simplifies 
the proposed regulations.
    Substantive changes in rule language that resulted from 
consideration of public comments are addressed in the following subject 
sections.

A. Retention of Inerting, BWR Mark III and PWR Ice Condenser Hydrogen 
Control Systems, Mixed Atmosphere Requirements, and Associated Analysis 
Requirements

    The Commission proposes to retain the existing requirement in 
Sec. 50.44(c)(3)(i) to inert Marks I and II type containments. Given 
the relatively small volume and large zirconium inventory, these 
containments, without inerting, would have a high likelihood of failure 
from hydrogen combustion due to the potentially large concentration of 
hydrogen that a severe accident could cause. Retaining the requirement 
maintains the current level of public protection, as discussed in 
section 4.3.2 of the Feasibility Study.
    The Commission proposes to retain the existing requirements in 
Sec. 50.44(c)(3) (iv), (v), and (vi) that BWRs with Mark III 
containments and PWRs with ice condenser containments provide a 
hydrogen control system justified by a suitable program of experiment 
and analysis. The amount of hydrogen to be considered is that generated 
from a metal-water reaction involving 75 percent of the fuel cladding 
surrounding the active fuel region (excluding the cladding surrounding 
the plenum volume). The analyses must demonstrate that the structures, 
systems and component necessary for safe shutdown and maintaining 
containment integrity must perform their functions during and after 
exposure to the conditions created by the burning hydrogen. 
Environmental conditions caused by local detonations of hydrogen must 
also be included, unless such detonations can be shown unlikely to 
occur. A beyond design-basis accident generating significant amounts of 
hydrogen (on the order of Three Mile Island, Unit 2, accident or a 
metal water reaction involving 75 percent of the fuel cladding 
surrounding the active fuel region) would pose a severe threat to the 
integrity of these containment types in the absence of the

[[Page 50377]]

installed igniter systems. Section 4.3.3 of the Feasibility Study 
concluded that hydrogen combustion is not risk-significant, in terms of 
the framework document's quantitative guidelines, when igniter systems 
installed to meet Sec. 50.44(c)(3) (iv), (v), and (vi) are available 
and operable. The Commission proposes to retain these requirements. 
Previously reviewed and approved licensee analyses to meet the existing 
regulations constitute compliance with this proposed section. The 
results of these analyses must continue to be documented in the plant's 
Updated Final Safety Analysis Report in accordance with Sec. 50.71(e).
    The Commission proposes to retain the Sec. 50.44(b)(2) requirement 
that all containments ensure a mixed atmosphere. A mixed containment 
atmosphere prevents local accumulation of combustible or detonable 
gases which could threaten containment integrity or equipment operating 
in a local compartment. The current regulation ensures that features 
that promote atmospheric mixing, either active systems and/or 
containment internal structures that have design features which promote 
the free circulation of the containment atmosphere, are provided.

B. Elimination of Design-Basis LOCA Hydrogen Release

    The proposed rule would remove the existing definition of a design-
basis LOCA hydrogen release and eliminate requirements for hydrogen 
control systems to mitigate such a release. The installation of 
recombiners and/or vent and purge systems required by Sec. 50.44(b)(3) 
was intended to address the limited quantity and rate of hydrogen 
generation that was postulated from a design-basis LOCA. The Commission 
finds that this hydrogen release is not risk-significant. This finding 
is based on the Feasibility Study which found that the design-basis 
LOCA hydrogen release did not contribute to the conditional probability 
of a large release up to approximately 24 hours after the onset of core 
damage. The requirements for combustible gas control that were 
developed after the Three Mile Island Unit 2 accident were intended to 
minimize potential additional challenges to containment due to long 
term residual or radiolytically generated hydrogen. The Commission 
found that containment loadings associated with long term hydrogen 
concentrations are no worse than those considered in the first 24 hours 
and are, therefore, not risk-significant. The Commission believes that 
accumulation of combustible gases beyond 24 hours can be managed by 
licensee implementation of the severe accident management guidelines 
(SAMGs) or other ad hoc actions because of the long period of time 
available to take such action. Therefore, the Commission proposes to 
eliminate the hydrogen release associated with a design-basis LOCA from 
Sec. 50.44 and the associated requirements that necessitated the need 
for the hydrogen recombiners and the backup hydrogen vent and purge 
systems.
    In plants with Mark I and II containments, the containment 
atmosphere is required to be maintained with a low concentration of 
oxygen, rendering it inert to combustion. Mark I and II containments 
can be challenged beyond 24 hours by the long-term generation of oxygen 
through radiolysis. The regulatory analysis for this proposed 
rulemaking found the cost of maintaining the recombiners exceeded the 
benefit of retaining them to prevent containment failure sequences that 
progress to the very late time frame. The Commission believes that this 
conclusion would also be true for the backup hydrogen purge system even 
though the cost of the hydrogen purge system would be much lower 
because the system is also needed to inert the containment.
    The Commission continues to view severe accident management 
guidelines as an important part of the severe accident closure process. 
Severe accident management guidelines are part of a voluntary industry 
initiative to address accidents beyond the design basis and emergency 
operating instructions. In November 1994, the U.S. nuclear industry 
committed to implement severe accident management at their plants by 
December 31, 1998, using the guidance contained in NEI 91-04, Revision 
1, ``Severe Accident Issue Closure Guidelines.'' Generic severe 
accident management guidelines developed by each nuclear steam system 
supplier owners group includes either purging and venting or venting 
the containment to address combustible gas control. On the basis of the 
industry-wide commitment, the Commission is not proposing to require 
such capabilities, but continues to view purging and/or controlled 
venting of all containment types to be an important combustible gas 
control strategy that should be considered in a plant's severe accident 
management guidelines.

C. Oxygen Monitoring Requirements

    The Commission proposes to amend Sec. 50.44 to codify the existing 
regulatory practice of monitoring oxygen in containments that use an 
inerted atmosphere for combustible gas control. Standard technical 
specifications and licensee technical specifications currently require 
oxygen monitoring to verify the inerted condition in containment. 
Combustible gases produced by beyond design-basis accidents involving 
both fuel-cladding oxidation and core-concrete interaction would be 
risk-significant for plants with Mark I and II containments if not for 
the inerted containment atmosphere. If an inerted containment was to 
become de-inerted during a beyond design-basis accident, then other 
severe accident management strategies, such as purging and venting, 
would need to be considered. The oxygen monitoring is needed to 
implement these severe accident management strategies, in plant 
emergency operating procedures and is also used as an input in 
emergency response decision making.
    The Commission proposes reclassifying oxygen monitors as not 
safety-related components. Currently, as recommended by the 
Commission's Regulatory Guide (RG) 1.97, oxygen monitors are classified 
as Category 1. Category 1 is defined as applying to instrumentation 
designed for monitoring variables that most directly indicate the 
accomplishment of a safety function for design-basis events. By 
eliminating the design-basis LOCA hydrogen release, the oxygen monitors 
are no longer required to mitigate design-basis accidents. The 
Commission finds that Category 2, defined in RG 1.97, as applying to 
instrumentation designated for indicating system operating status, to 
be the more appropriate categorization for the oxygen monitors, because 
the monitors will still continue to be required to verify the status of 
the inerted containment. Further, the staff concludes that sufficient 
reliability of oxygen monitoring, commensurate with its risk-
significance, will be achieved by the guidance associated with the 
Category 2 classification. Because of the various regulatory means, 
such as orders, that were used to implement post-TMI requirements, this 
proposed relaxation may require a license amendment. Licensees would 
also need to update their final safety analysis report to reflect the 
new classification and RG 1.97 categorization of the monitors in 
accordance with 10 CFR 50.71(e).

D. Hydrogen Monitoring Requirements

    The Commission proposes to maintain the existing requirement in 
Sec. 50.44(b)(1) for monitoring hydrogen in the containment atmosphere 
for all plant designs. Section 50.44(b)(1),

[[Page 50378]]

standard technical specifications and licensee technical specifications 
currently contain requirements for monitoring hydrogen, including 
operability and surveillance requirements for the monitoring systems. 
Licensees have also made commitments to design and qualification 
criteria for hydrogen monitors in NUREG-0737, Item II.F.1, Attachment 6 
and in RG 1.97. The hydrogen monitors are required to assess the degree 
of core damage during a beyond design-basis accident and confirm that 
random or deliberate ignition has taken place. Hydrogen monitors are 
also used, in conjunction with oxygen monitors in inerted containments, 
to guide response to emergency operating procedures. Hydrogen monitors 
are also used in emergency operating procedures of BWR Mark III 
facilities. If an explosive mixture that could threaten containment 
integrity exists, then other severe accident management strategies, 
such as purging and/or venting, would need to be considered. The 
hydrogen monitors are needed to implement these severe accident 
management strategies.
    The Commission proposes to reclassify the hydrogen monitors as not 
safety-related components. With the proposed elimination of the design-
basis LOCA hydrogen release (see Item B. earlier), the hydrogen 
monitors are no longer required to mitigate design-basis accidents and, 
therefore, the hydrogen monitors do not meet the definition of a 
safety-related component as defined in Sec. 50.2. This is consistent 
with the Commission's proposal that oxygen monitors that are used for 
beyond-design basis accidents need not be safety grade.
    Currently, RG 1.97 recommends classifying the hydrogen monitors in 
Category 1, defined as applying to instrumentation designed for 
monitoring key variables that most directly indicate the accomplishment 
of a safety function for design-basis accident events. The hydrogen 
monitors no longer meet the definition of Category 1 in RG 1.97 and, 
therefore, the Commission believes that licensees' current commitments 
are unnecessarily burdensome. The Commission believes that Category 3, 
as defined in RG 1.97, is an appropriate categorization for the 
hydrogen monitors because the monitors are required to diagnose the 
course of beyond design-basis accidents. Category 3 applies to high-
quality, off-the-shelf backup and diagnostic instrumentation. As with 
the revision to oxygen monitoring, this proposed relaxation may require 
a license amendment. Licensees would also need to update their final 
safety analysis report to reflect the new classification and RG 1.97 
categorization of the monitors in accordance with 10 CFR 50.71(e).

E. Combustible Gas Control Requirements for Future Applicants

    The Commission proposes to set forth combustible gas control 
requirements for all future applicants for or holders of a construction 
permit or an operating license under part 50, and to all future 
applicants for design approval, design certification, or a combined 
license under Part 52. These requirements would consolidate combustible 
gas requirements for existing and future light water reactors in 
Sec. 50.44. Section 52.47(a)(ii) requires demonstration of compliance 
with the technically relevant portions of the Three Mile Island 
requirements in Sec. 50.34(f). Section 50.34(f)(2)(ix) requires a 
system for hydrogen control that can safely accommodate hydrogen 
generated by the equivalent of a 100 percent fuel-clad metal-water 
reaction. In addition, the regulation requires this system to be 
capable of precluding uniform concentrations of hydrogen from exceeding 
10 percent (by volume), or providing an inerted atmosphere within the 
containment. The Commission is proposing requirements for future light 
water reactors that are consistent with the criteria currently 
contained in Sec. 50.34(f)(2)(ix) to preclude local concentrations of 
hydrogen collecting in areas where unintended combustion or detonation 
could cause loss of containment integrity or loss of appropriate 
mitigating features. These requirements are in keeping with the 
Commission's expectation that future designs will achieve a higher 
standard of severe accident performance (50 FR 32138; August 8, 1985). 
Additional advantages of providing hydrogen control mitigation features 
(rather than reliance on random ignition of richer mixtures) include 
the lessening of pressure and temperature loadings on the containment 
and essential equipment.

F. Clarification and Relocation of High Point Vent Requirements From 10 
CFR 50.44 to 10 CFR 50.46a

    The Commission proposes to remove the current requirements for high 
point vents from Sec. 50.44 and to transfer them to a new Sec. 50.46a. 
The Commission proposes relocating these requirements because high 
point vents are relevant to emergency core cooling system (ECCS) 
performance during severe accidents, and Sec. 50.44 does not address 
ECCS performance. The requirement to install high point vents was 
imposed by the 1981 amendment to Sec. 50.44. This requirement permitted 
venting of noncondensible gases which may interfere with the natural 
circulation pattern in the reactor coolant system. This process is 
regarded as an important safety feature in accident sequences that 
credit natural circulation of the reactor coolant system. In other 
sequences, the pockets of noncondensible gases may interfere with pump 
operation. The high point vents could be instrumental for terminating a 
core damage accident if ECCS operation is restored. Under these 
circumstances, venting noncondensible gases from the vessel allows 
emergency core cooling flow to reach the damaged reactor core and thus 
prevents further accident progression.
    The Commission proposes to amend the language in current 
Sec. 50.44(c)(3)(iii) by deleting the statement, ``the use of these 
vents during and following an accident must not aggravate the challenge 
to the containment or the course of the accident.'' For certain severe 
accident sequences, the use of reactor coolant system high point vents 
is intended to reduce the amount of core damage by providing an 
opportunity to restore reactor core cooling. While the release of 
noncondensible and combustible gases from the reactor coolant system 
will, in the short term, ``aggravate'' the challenge to containment, 
the use of these vents will positively affect the overall course of the 
accident. The release of any combustible gases from the reactor coolant 
system has been considered in the containment design and mitigative 
features that are required for combustible gas control. Any venting is 
highly unlikely to affect containment integrity; however, such venting 
will reduce the likelihood of further core damage. Inasmuch as the 
overall safety is increased by venting through high point vents, the 
Commission proposes elimination of this statement in Sec. 50.46a.

G. Elimination of Post-Accident Inerting

    The proposed rule would no longer provide an option to use post-
accident inerting as a means of combustible gas control. Although post-
accident inerting systems were permitted as a possible alternative for 
mitigating combustible gas concerns after the accident at Three Mile 
Island, Unit 2, these systems have never been implemented to date. 
Concerns with a post-accident inerting system include: corrosion (if 
halon gas is used as the inerting agent), increase in containment 
pressure with use, limitations on emergency response personnel access, 
and cost. Sections 50.44(c)(3)(iv)(D) and 50.34(f)(ix)(D)

[[Page 50379]]

were promulgated to address these concerns. On November 14, 2001, draft 
rule language was made available to elicit comment from interested 
stakeholders. The draft rule language recommended eliminating the 
option to use post-accident inerting as a means of combustible gas 
control and asked stakeholders if there was a need to retain these 
requirements. Stakeholder feedback supported the staff recommendation 
to eliminate the post-accident inerting option and indicated that 
licensees do not intend to convert existing plants to use post-accident 
inerting. Because there is no need for the regulations to support an 
approach that is unlikely to be used, post-accident inerting 
requirements are being eliminated.

IV. Section-by-Section Analysis of Substantive Changes

Section 50.44--Combustible Gas Control in Containment

    Paragraph (a) [Definitions]. Paragraph (a) adds definitions for two 
previously undefined terms, ``mixed atmosphere,'' and ``inerted 
atmosphere.''
    Paragraph (b) [Requirements for currently-licensed reactors]. This 
paragraph would set forth the requirements for control of combustible 
gas in containment for currently-licensed reactors. All BWRs with Mark 
I and II type containments will be required to have an inerted 
containment atmosphere, and all BWR Mark III type containments and PWR 
s with ice condenser type containments would be required to include a 
capability for controlling combustible gas generated from a metal water 
reaction involving 75% of the fuel cladding surrounding the active fuel 
region (excluding the cladding surrounding the plenum volume) so that 
there is no loss of containment integrity. Current requirements in 
Sec. 50.44(c) (i), (iv), (v), and (vi) would be incorporated in to the 
proposed amended regulation without substantial change. Previously 
reviewed and installed combustible gas control mitigation features to 
meet the existing regulations are considered in compliance with this 
proposed section. Because these proposed requirements address beyond 
design-basis combustible gas control, it is acceptable for structures, 
systems, and components provided to meet these requirements to not be 
safety-related and may be procured as commercial grade items.
    Proposed paragraph (b)(1) [Mixed atmosphere]. The requirement for 
capability ensuring a mixed atmosphere in all containments is 
consistent with the current requirement in Sec. 50.44(b)(2) and would 
not require further analysis or modifications by current licensees. The 
intent of this requirement is to maintain those plant design features 
(e.g., availability of active mixing systems or open compartments) that 
promote atmospheric mixing. The requirement could be met with active or 
passive systems. Active systems could include a fan, a fan cooler or 
containment spray. Passive capability could be demonstrated by 
evaluating the containment for susceptibility to local hydrogen 
concentration. These evaluations have been conducted for currently 
licensed reactors as part of the IPE program.
    Proposed paragraph (b)(3) retains the existing requirements for BWR 
Mark III and PWR ice condenser facilities that do not use inerting to 
establish and maintain safe shutdown and containment structural 
integrity to use structures, systems, and components capable of 
performing their functions during and after exposure to hydrogen 
combustion.
    Proposed paragraph (b)(4)(i) would codify the existing regulatory 
practice of monitoring oxygen in containments that use an inerted 
atmosphere for combustible gas control. The proposed rule would not 
require further analysis or modifications by current licensees but 
certain design and qualification criteria would be relaxed. The 
proposed rule requires that equipment for monitoring oxygen be 
functional, reliable and capable of continuously measuring the 
concentration of oxygen in the containment atmosphere following a 
beyond design-basis accident. Equipment for monitoring oxygen is 
expected to perform in the environment anticipated in the severe 
accident management guidance. The oxygen monitors are expected to be of 
high-quality and may be procured as commercial grade items. Existing 
oxygen monitoring commitments for currently licensed plants are 
sufficient to meet the intent of this rule.
    Proposed paragraph (b)(4)(ii) would retain the requirement in 
Sec. 50.44(b)(1) for measuring the hydrogen concentration in the 
containment. The proposed rule would not require further analysis or 
modifications by current licensees but certain design and qualification 
criteria would be relaxed. The proposed rule requires that equipment 
for monitoring hydrogen be functional, reliable and capable of 
continuously measuring the concentration of hydrogen in the containment 
atmosphere following a beyond design-basis accident. Equipment for 
monitoring hydrogen is expected to perform in the environment 
anticipated in the severe accident management guidance. The hydrogen 
monitors may be procured as commercial grade items. Existing hydrogen 
monitoring commitments for currently licensed plants are sufficient to 
meet the intent of this rule.
    Paragraph (c) [Requirements for future applicants and licensees]. 
Proposed paragraph (c) would promulgate requirements for combustible 
gas in containment control for all future construction permits or 
operating licenses under part 50 and to all design approvals, design 
certifications, combined licenses or manufacturing licenses under part 
52. The current requirements in Sec. 50.34(f)(2)(ix) and (f)(3)(v) 
would be retained. Proposed paragraph (c)(2) would require all 
containments to have an inerted atmosphere or limit hydrogen 
concentrations in containment during and following an accident that 
releases an equivalent amount of hydrogen as would be generated from a 
100 percent fuel-clad coolant reaction, uniformly distributed, to less 
than 10 percent and maintain containment structural integrity and 
appropriate mitigating features. Structures, systems, and components 
(SSCs) provided to meet this requirement must be designed to provide 
reasonable assurance that they will operate in the severe accident 
environment for which they are intended and over the time span for 
which they are needed. Equipment survivability expectations under 
severe accident conditions should consider the circumstances of 
applicable initiating events (such as station blackout \1\ or 
earthquakes) and the environment (including pressure, temperature, and 
radiation) in which the equipment is relied upon to function. The 
required system performance criteria will be based on the results of 
design-specific reviews which include probabilistic risk-assessment as 
required by 10 CFR 52.47(a)(v). Because these requirements address 
beyond design-basis combustible gas control, SSCs provided to meet 
these requirements need not be subject to the environmental 
qualification requirements of 10 CFR Section 50.49; quality assurance

[[Page 50380]]

requirements of 10 CFR part 50, Appendix B; and redundancy/diversity 
requirements of 10 CFR part 50, Appendix A. Guidance such as that found 
in Appendices A and B of RG 1.155, ``Station Blackout,'' is appropriate 
for equipment used to mitigate the consequences of severe accidents. 
Proposed paragraph (c) would also promulgate requirements for ensuring 
a mixed atmosphere and monitoring oxygen and hydrogen in containment, 
consistent with the requirements for current plants set forth in 
proposed paragraphs (b)(1), and (b)(4)(i) and (ii).

Section 50.46a--Acceptance Criteria for Reactor Coolant System Venting 
Systems

    Proposed Sec. 50.46a would be a new section which relocates the 
requirements for high point vents currently contained in Sec. 50.44. 
The amendment includes a change that eliminates a requirement 
prohibiting venting the reactor coolant system if it could 
``aggravate'' the challenge to containment. Any venting is highly 
unlikely to affect containment integrity; however, such venting will 
reduce the likelihood of further core damage. Commission continues to 
view use of the high point vents to be an important strategy that 
should be considered in a plant's severe accident management 
guidelines.
---------------------------------------------------------------------------

    \1\ The Proposed Section 50.44 does not require the deliberate 
ignition systems used by BWRs with Mark III type containments and 
PWRs with ice condenser type containments to be available during 
station blackout events. The deliberate ignition systems should be 
available upon the restoration of power. Additional guidance 
concerning the availability of deliberate ignition systems during 
station blackout sequences is being developed as part of the staff's 
review of Generic Safety Issue 189: ``Susceptibility of Ice 
Condenser and Mark III Containments to Early Failure from Hydrogen 
Combustion During a Severe Accident.''
---------------------------------------------------------------------------

Section 52.47--Contents of Applications

    Sec. 52.47 would be amended to eliminate the reference to 
subsections within Sec. 50.34(f) for technically relevant requirements 
for combustible gas control in containment for future design approval, 
design certification, or license applicants. These applicants would 
reference Sec. 50.44 for technical requirements for combustible gas 
control in containment.

V. Plain Language

    The Presidential memorandum dated June 1, 1998, entitled ``Plain 
Language in Government Writing'' directed that the Government's writing 
be in plain language. This memorandum was published on June 10, 1998 
(63 FR 31883). In complying with this directive, editorial changes have 
been made in these proposed revisions to improve the organization and 
readability of the existing language of the paragraphs being revised. 
These types of changes are not discussed further in this document. The 
NRC requests comments on the proposed rule specifically with respect to 
the clarity and reflectiveness of the language used. Comments should be 
sent to the address listed under the ADDRESSES caption of the preamble.

VI. Voluntary Consensus Standards

    The National Technology Transfer and Advancement Act of 1995, Pub. 
L. 104-113, requires that Federal agencies use technical standards that 
are developed or adopted by voluntary consensus standards bodies unless 
using such a standard is inconsistent with applicable law or is 
otherwise impractical. In this proposed rule, the NRC proposes to use 
the following Government-unique standard: 10 CFR 50.44, U.S. Nuclear 
Regulatory Commission, October 27, 1978 (43 FR 50163), as amended. The 
NRC is not aware of any voluntary consensus standard that could be used 
instead of the proposed Government-unique standard. The NRC will 
consider a voluntary consensus standard if an appropriate standard is 
identified. If a voluntary standard is identified for consideration, 
the submittal should explain how the voluntary consensus standard is 
comparable and why it should be used instead of the proposed 
Government-unique standard.

VII. Finding of No Significant Environmental Impact: Environmental 
Assessment

    The Commission has determined under the National Environmental 
Policy Act of 1969, as amended, and the Commission's regulations in 
Subpart A of 10 CFR Part 51, that this rule, if adopted, would not be a 
major Federal action significantly affecting the quality of the human 
environment and, therefore, an environmental impact statement is not 
required. The basis for this determination reads as follows:
    This action endorses existing requirements and establishes 
regulations that reduce regulatory burdens for current and future 
licensees and consolidates combustible gas control regulations for 
future applicants and licensees. This action stems from the 
Commission's ongoing effort to risk-inform its regulations. The 
proposed rule would reduce the regulatory burdens on present and future 
power reactor licensees by eliminating the LOCA design-basis accident 
as a combustible gas control concern. This change eliminates the 
requirements for hydrogen recombiners and hydrogen purge systems and 
relaxes the requirements for hydrogen and oxygen monitoring equipment 
to make them commensurate with their safety and risk significance.
    The proposed action would not significantly increase the 
probability or consequences of an accident. No changes are being made 
in the types or quantities of radiological effluents that may be 
released off site, and there is no significant increase in public 
radiation exposure since there is no change to facility operations that 
could create a new or affect a previously analyzed accident or release 
path. There may be a reduction of occupational radiation exposure since 
personnel will no longer be required to maintain or operate, if 
necessary, the hydrogen recombiner systems which are located in or near 
radiologically controlled areas.
    With regard to non-radiological impacts, no changes are being made 
to non-radiological plant effluents and there are no changes in 
activities that would adversely affect the environment. Therefore, 
there are no significant non-radiological impacts associated with the 
proposed action.
    The primary alternative to this action would be the no action 
alternative. The no action alternative would continue to impose 
unwarranted regulatory burdens for which there would be little or no 
safety, risk, or environmental benefit.
    The determination of this environmental assessment is that there 
will be no significant offsite impact to the public from this action. 
However, the general public should note that the NRC is seeking public 
participation. Comments on any aspect of the environmental assessment 
may be submitted to the NRC as indicated under the ADDRESSES heading.
    The NRC has sent a copy of this proposed rule to every State 
Liaison Officer and requested their comments on the environmental 
assessment.

VIII. Paperwork Reduction Act Statement

    This proposed rule decreases the burden on new applicants to 
complete the hydrogen control analysis required to be submitted in a 
license application, as required by sections 50.34 or 52.47. The public 
burden reduction for this information collection is estimated to 
average 720 hours per request. Because the burden for this information 
collection is insignificant, Office of Management and Budget (OMB) 
clearance is not required. Existing requirements were approved by the 
Office of Management and Budget, approval numbers 3150-0011 and 3150-
0151.

Public Protection Notification

    The NRC may not conduct or sponsor, and a person is not required to 
respond to, a request for information or an information collection 
requirement unless the requesting document

[[Page 50381]]

displays a currently valid OMB control number.

IX. Regulatory Analysis

    The Commission has prepared a draft regulatory analysis on this 
proposed regulation. The analysis examines the costs and benefits of 
Commission alternatives for updating the existing rule to accommodate 
technological advances while addressing regulatory relaxation issues. 
From an overall safety and value impact perspective, the analysis 
recommends removing hydrogen recombiner requirements and relaxing 
hydrogen and oxygen monitoring requirements.
    The Commission requests public comment on the draft regulatory 
analysis. The regulatory analysis may be viewed and downloaded, and 
comments may be submitted at the NRC Rulemaking Web site. Single copies 
of the analysis are also available from Anthony Markley, Office of 
Nuclear Reactor Regulation, (301) 415-3165, e-mail [email protected]. 
Comments on the draft analysis may be submitted to the NRC as indicated 
under the ADDRESSES heading.

X. Regulatory Flexibility Certification

    As required by the Regulatory Flexibility Act, as amended, 5 U.S.C. 
605(b), the Commission certifies that this proposed rule, if adopted, 
would not have a significant economic impact on a substantial number of 
small entities. This proposed rule would affect only licensees 
authorized to operate nuclear power reactors. These licensees do not 
fall within the scope of the definition of ``small entities'' set forth 
in the Regulatory Flexibility Act, or the Size Standards established by 
the Nuclear Regulatory Commission (10 CFR 2.810).

XI. Backfit Analysis

    The NRC has determined that the backfit rule does not apply to this 
proposed rule; therefore, a backfit analysis is not required for this 
proposed rule because these amendments do not impose more stringent 
safety requirements on 10 CFR part 50 licensees. For current licensees, 
the proposed amendments either maintain without substantive change 
existing requirements or reduce current regulatory requirements. For 
future applicants and future licensees, the proposed requirements do 
not involve backfitting as defined in 10 CFR 50.109(a)(1). This is 
because any changes will have only a prospective effect on future 
design certification applicants and future applicants for licensees 
under 10 CFR part 50 and 52. As the Commission has indicated in other 
rulemakings, sec., e.g., 54 FR 15372, April 18, 1989 (Final Part 52 
Rule), the expectations of future applicants are not protected by the 
Backfit Rule. Therefore, the NRC has not prepared a backfit analysis 
for this rulemaking.

List of Subjects

10 CFR Part 50

    Antitrust, Classified information, Criminal penalties, Fire 
protection, Intergovernmental relations, Nuclear power plants and 
reactors, Radiation protection, Reactor siting criteria, Reporting and 
recordkeeping requirements.

10 CFR Part 52

    Administrative practice and procedure, Antitrust, Backfitting, 
Combined license, Early site permit, Emergency planning, Fees, 
Inspection, Limited work authorization, Nuclear power plants and 
reactors, Probabilistic risk assessment, Prototype, Reactor siting 
criteria, Redress of site, Reporting and recordkeeping requirements, 
Standard design, Standard design certification.
    For the reasons set out in the preamble and under the authority of 
the Atomic Energy Act of 1954, as amended; the Energy Reorganization 
Act of 1974, as amended; and 5 U.S.C. 553, the NRC is proposing to 
adopt the following amendments to 10 CFR Parts 50 and 52.

PART 50--DOMESTIC LICENSING OF PRODUCTION AND UTILIZATION 
FACILITIES

    1. The authority citation for Part 50 continues to read as follows:

    Authority: Secs. 102, 103, 104, 105, 161, 182, 183, 186, 189, 68 
Stat. 936, 938, 948, 953, 954, 955, 956, as amended, sec. 234, 83 
Stat. 444, as amended (42 U.S.C. 2132, 2133, 2134, 2135, 2201, 2232, 
2233, 2239, 2282); secs. 201, as amended, 202, 206, 88 Stat. 1242, 
as amended, 1244, 1246 (42 U.S.C. 5841, 5842, 5846).
    Section 50.7 also issued under Pub. L. 95-601, sec. 10, 92 Stat. 
2951, as amended by Pub. L. 102-486, sec. 2902, 106 Stat. 3123 (42 
U.S.C. 5851). Section 50.10 also issued under secs. 101, 185, 68 
Stat. 936, 955, as amended (42 U.S.C. 2131, 2235); sec. 102, Pub. L. 
91-190, 83 Stat. 853 (42 U.S.C. 4332). Sections 50.13, 50.54(dd), 
and 50.103 also issued under sec. 108, 68 Stat. 939, as amended (42 
U.S.C. 2138). Sections 50.23, 50.35, 50.55, and 50.56 also issued 
under sec. 185, 68 Stat. 955 (42 U.S.C. 2235). Sections 50.33a, 
50.55a and Appendix Q also issued under sec. 102, Pub. L. 91-190, 83 
Stat. 853 (42 U.S.C. 4332). Sections 50.34 and 50.54 also issued 
under Pub. L. 97-415, 96 Stat. 2073 (42 U.S.C. 2239). Section 50.78 
also issued under sec. 122, 68 Stat. 939 (42 U.S.C. 2152). Sections 
50.80-50.81 also issued under sec. 184, 68 Stat. 954, as amended (42 
U.S.C. 2234). Appendix F also issued under sec. 187, 68 Stat. 955 
(42 U.S.C. 2237).

    2. In Sec. 50.34, paragraph (a)(4) is revised, paragraph (g) is 
redesignated as paragraph (h), and a new paragraph (g) is added to read 
as follows:


Sec. 50.34  Contents of applications; technical information.

    (a) * * *
    (4) A preliminary analysis and evaluation of the design and 
performance of structures, systems, and components of the facility with 
the objective of assessing the risk to public health and safety 
resulting from operation of the facility and including determination of 
the margins of safety during normal operations and transient conditions 
anticipated during the life of the facility, and the adequacy of 
structures, systems, and components provided for the prevention of 
accidents and the mitigation of the consequences of accidents. Analysis 
and evaluation of ECCS cooling performance and the need for high point 
vents following postulated loss-of-coolant accidents must be performed 
in accordance with the requirements of Sec. 50.46 and Sec. 50.46a of 
this part for facilities for which construction permits may be issued 
after December 28, 1974.
* * * * *
    (g) Combustible gas control. All applicants for a construction 
permit or operating license under part 50 of this chapter, and all 
applicants for design approval, design certification, or license under 
part 52 of this chapter, whose application was submitted after 
[EFFECTIVE DATE OF RULE], shall include the descriptions of the 
equipment, systems, and analyses required by Sec. 50.44 as a part of 
their application.
* * * * *
    3. Section 50.44 is revised to read as follows:


Sec. 50.44  Combustible gas control in containment.

    (a) Definitions. (1) Inerted atmosphere means a containment 
atmosphere with less than 4 percent oxygen by volume.
    (2) Mixed atmosphere means that the concentration of combustible 
gases in any part of the containment is below a level that supports 
combustion or detonation that could cause loss of containment 
integrity.
    (b) Requirements for currently-licensed reactors. Each boiling or 
pressurized light-water nuclear power reactor with an operating license 
on [EFFECTIVE DATE] must comply with

[[Page 50382]]

the following requirements, as applicable:
    (1) Mixed atmosphere. All containments must have a capability for 
ensuring a mixed atmosphere.
    (2) Combustible gas control. (i) All boiling water reactors with 
Mark I or Mark II type containments must have an inerted atmosphere.
    (ii) All boiling water reactors with Mark III type containments and 
all pressurized water reactors with ice condenser containments must 
have the capability for controlling combustible gas generated from a 
metal-water reaction involving 75 percent of the fuel cladding 
surrounding the active fuel region (excluding the cladding surrounding 
the plenum volume) so that there is no loss of containment structural 
integrity.
    (3) Equipment survivability. All boiling water reactors with Mark 
III containments and all pressurized water reactors with ice condenser 
containments that do not rely upon an inerted atmosphere inside 
containment to control combustible gases must be able to establish and 
maintain safe shutdown and containment structural integrity with 
systems and components capable of performing their functions during and 
after exposure to the environmental conditions created by the burning 
of hydrogen. Environmental conditions caused by local detonations of 
hydrogen must also be included, unless such detonations can be shown 
unlikely to occur. The amount of hydrogen to be considered must be 
equivalent to that generated from a metal-water reaction involving 75 
percent of the fuel cladding surrounding the active fuel region 
(excluding the cladding surrounding the plenum volume).
    (4) Monitoring. (i) Equipment must be provided for monitoring 
oxygen in containments that use an inerted atmosphere for combustible 
gas control. Equipment for monitoring oxygen must be functional, 
reliable, and capable of continuously measuring the concentration of 
oxygen in the containment atmosphere following a beyond design-basis 
accident for combustible gas control and accident management, including 
emergency planning.
    (ii) Equipment must be provided for monitoring hydrogen in the 
containment. Equipment for monitoring hydrogen must be functional, 
reliable, and capable of continuously measuring the concentration of 
hydrogen in the containment atmosphere following a beyond design-basis 
accident for accident management, including emergency planning.
    (5) Analyses. Each holder of an operating license for a boiling 
water reactor with a Mark III type of containment or for a pressurized 
water reactor with an ice condenser type of containment, shall perform 
an analysis that:
    (i) Provides an evaluation of the consequences of large amounts of 
hydrogen generated after the start of an accident (hydrogen resulting 
from the metal-water reaction of up to and including 75 percent of the 
fuel cladding surrounding the active fuel region, excluding the 
cladding surrounding the plenum volume) and include consideration of 
hydrogen control measures as appropriate;
    (ii) Includes the period of recovery from the degraded condition;
    (iii) Uses accident scenarios that are accepted by the NRC staff. 
These scenarios must be accompanied by sufficient supporting 
justification to show that they describe the behavior of the reactor 
system during and following an accident resulting in a degraded core.
    (iv) Supports the design of the hydrogen control system selected to 
meet the requirements of this section; and,
    (v) Demonstrates, for those reactors that do not rely upon an 
inerted atmosphere to comply with paragraph (b)(2)(ii) of this section, 
that:
    (A) Containment structural integrity is maintained. Containment 
structural integrity must be demonstrated by use of an analytical 
technique that is accepted by the NRC staff in accordance with 
Sec. 50.90. This demonstration must include sufficient supporting 
justification to show that the technique describes the containment 
response to the structural loads involved. This method could include 
the use of actual material properties with suitable margins to account 
for uncertainties in modeling, in material properties, in construction 
tolerances, and so on; and
    (B) Systems and components necessary to establish and maintain safe 
shutdown and to maintain containment integrity will be capable of 
performing their functions during and after exposure to the 
environmental conditions created by the burning of hydrogen, including 
local detonations, unless such detonations can be shown unlikely to 
occur.
    (c) Requirements for future applicants and licensees. The 
requirements in this paragraph apply to all construction permits or 
operating licenses under this part, and to all design approvals, design 
certifications, combined licenses or manufacturing licenses under part 
52 of this chapter, any of which are issued after [EFFECTIVE DATE].
    (1) Mixed atmosphere. All containments must have a capability for 
ensuring a mixed atmosphere.
    (2) Combustible gas control. All containments must have an inerted 
atmosphere or limit hydrogen concentrations in containment during and 
following an accident that releases an equivalent amount of hydrogen as 
would be generated from a 100 percent fuel clad-coolant reaction, 
uniformly distributed, to less than 10 percent and maintain containment 
structural integrity and appropriate mitigating features.
    (3) Equipment survivability. Containments that do not rely upon an 
inerted atmosphere to control combustible gases must be able to 
establish and maintain safe shutdown and containment structural 
integrity with systems and components capable of performing their 
functions during and after exposure to the environmental conditions 
created by the burning of hydrogen. Environmental conditions caused by 
local detonations of hydrogen must also be included, unless such 
detonations can be shown unlikely to occur. The amount of hydrogen to 
be considered must be equivalent to that generated from a fuel clad-
coolant reaction involving 100 percent of the fuel cladding surrounding 
the active fuel region.
    (4) Monitoring. (i) Equipment must be provided for monitoring 
oxygen in containments that use an inerted atmosphere for combustible 
gas control. Equipment for monitoring oxygen must be functional, 
reliable, and capable of continuously measuring the concentration of 
oxygen in the containment atmosphere following a beyond design-basis 
accident for combustible gas control and accident management, including 
emergency planning.
    (ii) Equipment must be provided for monitoring hydrogen in the 
containment. Equipment for monitoring hydrogen must be functional, 
reliable, and capable of continuously measuring the concentration of 
hydrogen in the containment atmosphere following a beyond design-basis 
accident for accident management, including emergency planning.
    (5) Analyses. An applicant shall perform an analysis that 
demonstrates containment structural integrity. This demonstration must 
use an analytical technique that is accepted by the NRC staff and 
include sufficient supporting justification to show that the technique 
describes the containment response to the structural loads involved. 
The analysis must address an accident that releases hydrogen generated 
from 100

[[Page 50383]]

percent fuel clad-coolant reaction accompanied by hydrogen burning. 
Systems necessary to ensure containment integrity must also be 
demonstrated to perform their function under these conditions.
    4. Section 50.46a is added to read as follows:


Sec. 50.46a  Acceptance criteria for reactor coolant system venting 
systems.

    Each nuclear power reactor must be provided with high point vents 
for the reactor coolant system, for the reactor vessel head, and for 
other systems required to maintain adequate core cooling if the 
accumulation of noncondensible gases would cause the loss of function 
of these systems. High point vents are not required for the tubes in U-
tube steam generators. Acceptable venting systems must meet the 
following criteria:
    (a) The high point vents must be remotely operated from the control 
room.
    (b) The design of the vents and associated controls, instruments 
and power sources must conform to appendix A and appendix B of this 
part.
    (c) The vent system must be designed to ensure that:
    (1) The vents will perform their safety functions, and
    (2) There would not be inadvertent or irreversible actuation of a 
vent.

PART 52--EARLY SITE PERMITS; STANDARD DESIGN CERTIFICATIONS; AND 
COMBINED LICENSES FOR NUCLEAR POWER PLANTS

    5. The authority citation for Part 52 continues to read as follows:

    Authority: Secs. 103, 104, 161, 182, 183, 186, 189, 68 Stat. 
936, 948, 953, 954, 955, 956, as amended, sec. 234, 83 Stat. 444, as 
amended (42 U.S.C. 2133, 2201, 2232, 2233, 2236, 2239, 2282); secs. 
201, 202, 206, 88 Stat. 1242, 1244, 1246, as amended (42 U.S.C. 
5841, 5842, 5846).
    6. In Sec. 52.47, paragraph (a)(1)(ii) is revised to read as 
follows:


Sec. 52.47  Contents of applications

    (a) * * *
    (1) * * *
    (ii) Demonstration of compliance with any technically relevant 
portions of the Three Mile Island requirements set forth in 10 CFR 
50.34(f) except paragraphs (f)(1)(xii), (f)(2)(ix) and (f)(3)(v);
* * * * *

    Dated at Rockville, Maryland, this 26th day of July , 2002.
    For the Nuclear Regulatory Commission.
Annette Vietti-Cook,
Secretary of the Commission.
[FR Doc. 02-19419 Filed 8-1-02; 8:45 am]
BILLING CODE 7590-01-P