[Federal Register Volume 69, Number 62 (Wednesday, March 31, 2004)]
[Notices]
[Pages 16980-16987]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 04-7164]


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NUCLEAR REGULATORY COMMISSION


Proposed Generic Communication; Potential Impact of Debris 
Blockage on Emergency Recirculation During Design Basis Accidents at 
Pressurized Water Reactors

AGENCY: Nuclear Regulatory Commission.

ACTION: Notice of opportunity for public comment.

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SUMMARY: The U.S. Nuclear Regulatory Commission (NRC) is proposing to 
issue a generic letter (GL) to request that addressees submit 
information to the NRC concerning the status of their compliance with 
10 CFR 50.46(b)(5), which requires long-term reactor core cooling be 
available following a design basis loss of coolant accident, and with

[[Page 16981]]

the additional plant-specific licensing basis requirements listed in 
this generic letter, in accordance with 10 CFR 50.54(f). This request 
is based on the identified potential susceptibility of pressurized-
water reactor (PWR) recirculation sump screens to debris blockage 
during design basis accidents requiring recirculation operation of the 
emergency core cooling system (ECCS) or containment spray system (CSS) 
and the potential for additional adverse effects due to debris blockage 
of flowpaths necessary for ECCS and CSS recirculation and containment 
drainage
    This Federal Register notice is available through the NRC's 
Agencywide Documents Access and Management System (ADAMS) under 
accession number ML040830518.

DATES: Comment period expires June 1, 2004. Comments submitted after 
this date will be considered if it is practical to do so, but assurance 
of consideration cannot be given except for comments received on or 
before this date.

ADDRESSES: Submit written comments to the Chief, Rules and Directives 
Branch, Division of Administrative Services, Office of Administration, 
U.S. Nuclear Regulatory Commission, Mail Stop T6-D59, Washington, DC 
20555-0001, and cite the publication date and page number of this 
Federal Register notice. Written comments may also be delivered to NRC 
Headquarters, 11545 Rockville Pike (Room T-6D59), Rockville, Maryland, 
between 7:30 a.m. and 4:15 p.m. on Federal workdays.

FOR FURTHER INFORMATION, CONTACT: David Cullison at 301-415-1212 or by 
e-mail at [email protected] or Ralph Architzel at 301-415-2804 or by e-mail 
at [email protected].

SUPPLEMENTARY INFORMATION:

Draft NRC Generic Letter 2003-XX: Potential Impact of Debris Blockage 
on Emergency Recirculation During Design Basis Accidents at Pressurized 
Water Reactors

Addressees

    All holders of operating licenses for pressurized-water nuclear 
power reactors, except those who have ceased operations and have 
certified that fuel has been permanently removed from the reactor 
vessel.

Purpose

    The U.S. Nuclear Regulatory Commission (NRC) is issuing this 
generic letter to:
    (1) Request that addressees submit information to the NRC to 
confirm compliance with 10 CFR 50.46(b)(5), which requires long-term 
reactor core cooling, and other existing regulatory requirements listed 
in this generic letter. This request is based on the identified 
potential susceptibility of pressurized-water reactor (PWR) 
recirculation sump screens to debris blockage during design basis 
accidents requiring recirculation operation of the emergency core 
cooling system (ECCS) or containment spray system (CSS) and the 
potential for additional adverse effects due to debris blockage of 
flowpaths necessary for ECCS and CSS recirculation and containment 
drainage.
    (2) Require addressees to provide the NRC a written response in 
accordance with 10 CFR 50.54(f).

Background

    In 1979, as a result of evolving staff concerns related to the 
adequacy of PWR recirculation sump designs, the NRC opened Unresolved 
Safety Issue (USI) A-43, ``Containment Emergency Sump Performance.'' To 
support the resolution of USI A-43, the NRC undertook an extensive 
research program, the technical findings of which are summarized in 
NUREG-0897, ``Containment Emergency Sump Performance,'' dated October 
1985. The resolution of USI A-43 was subsequently documented in Generic 
Letter (GL) 85-22, ``Potential for Loss of Post-LOCA Recirculation 
Capability Due to Insulation Debris Blockage,'' dated December 3, 1985. 
Although the staff's regulatory analysis concerning USI A-43 did not 
support imposing new sump performance requirements upon licensees of 
operating PWRs or boiling-water reactors (BWRs), the staff recommended 
in GL 85-22 that all affected reactor licensees replace the 50-percent 
blockage assumption (under which most nuclear power plants had been 
licensed) with a comprehensive, mechanistic assessment of plant-
specific debris blockage potential for future modifications related to 
sump performance, such as thermal insulation changeouts. The 50-percent 
screen blockage assumption does not require a plant-specific evaluation 
of the debris-blockage potential and may result in a non-conservative 
analysis for screen blockage effects. The staff also updated the NRC's 
regulatory guidance, including Section 6.2.2 of the Standard Review 
Plan (NUREG-0800) and Regulatory Guide 1.82, ``Water Sources for Long-
Term Recirculation Cooling Following a Loss-of-Coolant Accident,'' to 
reflect the USI A-43 technical findings documented in NUREG-0897. 
Following the resolution of USI A-43 in 1985, several events occurred 
that challenged the conclusion that no new requirements were necessary 
to prevent the clogging of ECCS strainers at operating BWRs:
     On July 28, 1992, at Barseb[auml]ck Unit 2, a 
Swedish BWR, the spurious opening of a pilot-operated relief valve led 
to the plugging of two containment vessel spray system suction 
strainers with mineral wool and required operators to shut down the 
spray pumps and backflush the strainers.
     In 1993, at Perry Unit 1, two events occurred 
during which ECCS strainers became plugged with debris. On January 16, 
ECCS strainers were plugged with suppression pool particulate matter, 
and on April 14, an ECCS strainer was plugged with glass fiber from 
ventilation filters that had fallen into the suppression pool. On both 
occasions, the affected ECCS strainers were deformed by excessive 
differential pressure created by the debris plugging.
     On September 11, 1995, at Limerick Unit 1, 
following a manual scram due to a stuck-open safety/relief valve, 
operators observed fluctuating flow and pump motor current on the A 
loop of suppression pool cooling. The licensee later attributed these 
indications to a thin mat of fiber and sludge which had accumulated on 
the suction strainer.
    In response to these ECCS suction strainer plugging events, the NRC 
issued several generic communications, including Bulletin 93-02, 
Supplement 1, ``Debris Plugging of Emergency Core Cooling Suction 
Strainers,'' dated February 18, 1994, Bulletin 95-02, ``Unexpected 
Clogging of a Residual Heat Removal (RHR) Pump Strainer While Operating 
in Suppression Pool Cooling Mode,'' dated October 17, 1995, and 
Bulletin 96-03, ``Potential Plugging of Emergency Core Cooling Suction 
Strainers by Debris in Boiling-Water Reactors,'' dated May 6, 1996.
    These bulletins requested that BWR licensees implement appropriate 
procedural measures, maintenance practices, and plant modifications to 
minimize the potential for the clogging of ECCS suction strainers by 
debris accumulation following a loss-of-coolant accident (LOCA). The 
NRC staff has concluded that all BWR licensees have sufficiently 
addressed these bulletins.
    However, findings from research to resolve the BWR strainer 
clogging issue have raised questions concerning the adequacy of PWR 
sump designs. In comparison to the technical findings of the USI A-43 
research program concerning PWRs, the research findings demonstrate 
that the amount of debris generated by a high-energy line break (HELB) 
could be greater, that the debris could be finer (and, thus, more 
easily transportable), and that certain

[[Page 16982]]

combinations of debris (e.g., fibrous material plus particulate 
material) could result in a substantially greater head loss than an 
equivalent amount of either type of debris alone. These research 
findings prompted the NRC to open Generic Safety Issue (GSI) 191, 
``Assessment of Debris Accumulation on PWR Sump Performance.'' The 
objective of GSI-191 is to ensure that post-accident debris blockage 
will not impede or prevent the operation of the ECCS and CSS in 
recirculation mode at PWRs during LOCAs or other HELB accidents for 
which sump recirculation is required.
    On June 9, 2003, having completed its technical assessment of GSI-
191 (summarized below in the Discussion section of this generic 
letter), the NRC issued Bulletin 2003-01, ``Potential Impact of Debris 
Blockage on Emergency Recirculation During Design-Basis Accidents at 
Pressurized-Water Reactors.'' As a result of the emergent issues 
discussed therein, the bulletin requested an expedited response from 
PWR licensees as to the status of their compliance on a mechanistic 
basis, with regulatory requirements concerning the ECCS and CSS 
recirculation functions. Addressees who were unable to assure 
regulatory compliance pending further analysis were asked to describe 
any interim compensatory measures that have been implemented or will be 
implemented to reduce risk until the analysis could be completed. All 
licensees have since responded to Bulletin 2003-01. In developing 
Bulletin 2003-01, the NRC staff recognized that it may be necessary for 
addressees to undertake complex evaluations to determine whether 
regulatory compliance exists in light of the concerns identified in the 
bulletin and that the methodology to perform such evaluations was not 
currently available. As a result, that information was not requested in 
the bulletin but addressees were informed that the staff was preparing 
a generic letter that would request this information. This generic 
letter is the follow-on information request referenced in the bulletin.
    In response to Bulletin 2003-01, PWR licensees that were unable to 
confirm regulatory compliance implemented or plan to implement 
compensatory measures to reduce risk or otherwise enhance the 
capability of the ECCS and CSS recirculation functions. During the 
process of resolving the potential concerns identified in this generic 
letter, the revised analysis of sump performance may affect addressees' 
understanding of their facilities' ECCS and CSS recirculation 
capabilities. In accordance with GL 91-18, Revision 1, ``Information to 
Licensees Regarding NRC Inspection Manual Section on Resolution of 
Degraded and Nonconforming Conditions,'' dated October 8, 1997, 
addressees may find it necessary to reevaluate the adequacy of their 
compensatory measures in light of the new information and take further 
action as appropriate and necessary. Upon resolution of the potential 
concerns identified in this generic letter and the completion of any 
corrective actions resulting from that resolution, addresses may 
consider continuing, revising, or retiring their compensatory measures 
as appropriate.
    The NRC has developed a Web page to keep the public informed of 
generic activities on PWR sump performance (http://www.nrc.gov/reactors/operating/ops-experience/pwr-sump-performance.html). This page 
provides links to information on PWR sump performance issues, along 
with documentation of NRC interactions with industry (industry 
submittals, meeting notices, presentation materials, and meeting 
summaries). The NRC will continue to update this Web page as new 
information becomes available.

Discussion

    In the event of a HELB inside the containment of a PWR, energetic 
pressure waves and fluid jets would impinge upon materials in the 
vicinity of the break, such as thermal insulation, coatings, and 
concrete, causing them to become damaged and dislodged. Debris could 
also be generated through secondary mechanisms, such as severe post-
accident temperature and humidity conditions, flooding of the lower 
containment, and the impact of containment spray droplets. In addition 
to debris generated by jet forces from the pipe rupture, debris can be 
created by the chemical reaction between the chemically reactive spray 
solutions used following a LOCA and the materials in containment. These 
reactions may result in additional debris such as disbonded coatings 
and chemical precipitants being generated. Through transport methods 
such as entrainment in the steam/water flows issuing from the break and 
containment spray washdown, a fraction of the generated debris and 
foreign material in the containment would be transported to the pool of 
water formed on the containment floor. Subsequently, if the ECCS or CSS 
pumps were to take suction from the recirculation sump, the debris 
suspended in the containment pool would begin to accumulate on the sump 
screen or be transported through the associated system. The 
accumulation of this suspended debris on the sump screen could create a 
roughly uniform covering on the screen, referred to as a debris bed, 
which would tend to increase the head loss across the screen through a 
filtering action. If a sufficient amount of debris were to accumulate, 
the debris bed would reach a critical thickness at which the head loss 
across the debris bed would exceed the net positive section head (NPSH) 
margin required to ensure the successful operation of the ECCS and CSS 
pumps in recirculation mode. A loss of NPSH margin for the ECCS or CSS 
pumps as a result of the accumulation of debris on the recirculation 
sump screen, referred to as sump clogging, could result in degraded 
pump performance and eventual pump failure. Debris could also plug or 
wear close tolerance components within the ECCS or CSS systems. The 
effect of this plugging or wear may cause a component to degrade to the 
point where it may be unable to perform its designated function ( i.e. 
pump fluid, maintain system pressure, or pass and control system flow.)
    Assessing the likelihood of the ECCS and CSS pumps at domestic PWRs 
experiencing a debris-induced loss of NPSH margin during sump 
recirculation was the primary objective of the NRC's technical 
assessment of GSI-191. The NRC's technical assessment culminated in a 
parametric study that mechanistically treated phenomena associated with 
debris blockage using analytical models of domestic PWRs generated with 
a combination of generic and plant-specific data. As documented in 
Volume 1 of NUREG/CR-6762, ``GSI-191 Technical Assessment: Parametric 
Evaluations for Pressurized Water Reactor Recirculation Sump 
Performance,'' dated August 2002, the GSI-191 parametric study 
concludes that recirculation sump clogging is a credible concern for 
domestic PWRs. As a result of limitations with respect to plant-
specific data and other modeling uncertainties, however, the parametric 
study does not definitively identify whether or not particular PWR 
plants are vulnerable to sump clogging when phenomena associated with 
debris blockage are modeled mechanistically.
    The methodology employed by the GSI-191 parametric study is based 
upon the substantial body of test data and analyses that are documented 
in technical reports generated during the NRC's GSI-191 research 
program and earlier technical reports generated by the NRC and the 
industry during the resolution of the BWR strainer clogging issue and 
USI A-43. These pertinent technical reports, which cover debris 
generation, transport, accumulation, and

[[Page 16983]]

head loss, are incorporated by reference into the GSI-191 parametric 
study:
     NUREG/CR-6770, ``GSI-191: Thermal-Hydraulic 
Response of PWR Reactor Coolant System and Containments to Selected 
Accident Sequences,'' dated August 2002.
     NUREG/CR-6762, Vol. 3, ``GSI-191 Technical 
Assessment: Development of Debris Generation Quantities in Support of 
the Parametric Evaluation,'' dated August 2002.
     NUREG/CR-6762, Vol. 4, ``GSI-191 Technical 
Assessment: Development of Debris Transport Fractions in Support of the 
Parametric Evaluation,'' dated August 2002.
     NUREG/CR-6224, ``Parametric Study of the 
Potential for BWR ECCS Strainer Blockage Due to LOCA Generated 
Debris,'' dated October 1995.
    In light of the credibility of the concerns identified above, the 
NRC staff has determined that it is appropriate to request that 
addressees submit information to confirm their plant-specific 
compliance with NRC regulations and other existing regulatory 
requirements listed in this generic letter pertaining to post-accident 
debris blockage. If addressees perform an analysis to confirm 
compliance, the NRC staff recommends the use of an analysis method that 
mechanistically accounts for debris generation and transport, post 
accident equipment and systems operation with debris laden fluid.
    In addition to demonstrating the potential for debris to clog 
containment recirculation sumps, operational experience and the NRC's 
technical assessment of GSI-191 have also identified three integrally 
related modes by which post-accident debris blockage could adversely 
affect the sump screen's design function of intercepting debris that 
could impede or prevent the operation of the ECCS and CSS in 
recirculation mode.
    First, as a result of the 50-percent blockage assumption, most PWR 
sump screens were designed assuming that relatively small structural 
loadings would result from the differential pressure associated with 
debris blockage. Consequently, PWR sump screens may not be capable of 
accommodating the increased structural loadings that would occur due to 
mechanistically determined debris beds that cover essentially the 
entire screen surface. Inadequate structural reinforcement of a sump 
screen may result in its deformation, damage, or failure, which could 
allow large quantities of debris to be ingested into the ECCS and CSS 
piping, pumps, and other components, potentially leading to their 
clogging or failure. The ECCS strainer plugging and deformation events 
that occurred at Perry Unit 1 (further described in Information Notice 
(IN) 93-34, ``Potential for Loss of Emergency Cooling Function Due to a 
Combination of Operational and Post-LOCA Debris in Containment,'' dated 
April 26, 1993, and LER 50-440/93-011, ``Excessive Strainer 
Differential Pressure Across the RHR Suction Strainer Could Have 
Compromised Long Term Cooling During Post-LOCA Operation,'' submitted 
May 19, 1993), demonstrate the credibility of this concern for screens 
and strainers that have not been designed with adequate reinforcement.
    Second, in some PWR containments, the flowpaths by which 
containment spray or break flows return to the recirculation sump may 
include ``choke-points,'' where the flowpath becomes so constricted 
that it could become blocked with debris following a HELB. Examples of 
potential choke-points are drains for pools, cavities, isolated 
containment compartments, and constricted drainage paths between 
physically separated containment elevations. Debris blockage at certain 
choke-points could hold up substantial amounts of water required for 
adequate recirculation or cause the water to be diverted into 
containment volumes that do not drain to the recirculation sump. The 
holdup or diversion of water assumed to be available to support sump 
recirculation could result in an available NPSH for ECCS and CSS pumps 
that is lower than the analyzed value, thereby reducing assurance that 
recirculation would successfully function. A reduced available NPSH 
directly concerns sump screen design because the NPSH margin of the 
ECCS and CSS pumps must be conservatively calculated to determine 
correctly the required surface area of passive sump screens when 
mechanistically determined debris loadings are considered. Although the 
parametric study (NUREG/CR-6762, Volume 1) did not analyze in detail 
the potential for the holdup or diversion of recirculation sump 
inventory, the NRC's GSI-191 research identified this phenomenon as an 
important and potentially credible concern. A number of LERs associated 
with this concern have also been generated, which further confirms its 
credibility and potential significance:
     LER 50-369/90-012, ``Loose Material Was Located 
in Upper Containment During Unit Operation Because of an Inappropriate 
Action,'' McGuire Unit 1, submitted August 30, 1990.
     LER 50-266/97-006, ``Potential Refueling Cavity 
Drain Failure Could Affect Accident Mitigation,'' Point Beach Unit 1, 
submitted February 19, 1997.
     LER 50-455/97-001, ``Unit 2 Containment Drain 
System Clogged Due to Debris,'' Byron Unit 2, submitted April 17, 1997.
     LER 50-269/97-010, ``Inadequate Analysis of ECCS 
Sump Inventory Due to Inadequate Design Analysis,'' Oconee Unit 1, 
submitted January 8, 1998.
     LER 50-315/98-017, ``Debris Recovered from Ice 
Condenser Represents Unanalyzed Condition,'' D.C. Cook Unit 1, 
submitted July 1, 1998.
    Third, debris blockage at flow restrictions within the ECCS 
recirculation flowpath downstream of the sump screen is a potential 
concern for PWRs. Debris that is capable of passing through the 
recirculation sump screen may have the potential to become lodged at a 
downstream flow restriction, such as a high-pressure safety injection 
(HPSI) throttle valve or fuel assembly inlet debris screen. Debris 
blockage at such flow restrictions in the ECCS flowpath could impede or 
prevent the recirculation of coolant to the reactor core, thereby 
leading to inadequate core cooling. Similarly, debris blockage at flow 
restrictions in the CSS flowpath, such as a containment spray nozzle, 
could impede or prevent CSS recirculation, thereby leading to 
inadequate containment heat removal. Debris may also accumulate in 
close tolerance sub-components of pumps and valves. The effect may 
either be to plug the sub-component thereby rendering the component 
unable to perform its function or to wear critical close tolerance sub-
components to the point at which component or system operation is 
degraded and unable to fully perform its function. Considering the 
recirculation sump screen's design function of intercepting potentially 
harmful debris, it is essential that the screen openings are adequately 
sized and that the sump screen's current configuration is free of gaps 
or breaches which could compromise the ECCS and CSS recirculation 
functions. It is also essential that system components are designed and 
evaluated to be able to operate with debris laden fluid as necessary 
post-LOCA.
    To assist in determining on a plant-specific basis whether 
compliance exists with 10 CFR 50.46(b)(5), addressees may use the 
guidance contained in Regulatory Guide 1.82 (RG 1.82), Revision 3, 
``Water Sources for Long-Term Recirculation Cooling Following a Loss-
of-Coolant Accident,'' dated November 2003. Revision 3 enhanced the 
debris blockage evaluation guidance

[[Page 16984]]

for pressurized water reactors provided in Revision 1 of the regulatory 
guide. The NRC staff determined after the issuance of Revision 2 that 
research for PWRs indicated that the guidance in that revision was not 
comprehensive enough to ensure adequate evaluation of a PWR plant's 
susceptibility to the detrimental effects caused by debris accumulation 
on debris interceptors (e.g., trash racks and sump screens). Revision 2 
altered the debris blockage evaluation guidance found in Revision 1 
following the evaluation of blockage events, such as the Barseb[auml]ck 
Unit 2 event mentioned above, but for BWRs only. Revision 1 replaced 
the 50-percent blockage assumption in Revision 0 with a comprehensive, 
mechanistic assessment of plant-specific debris blockage potential for 
future modifications related to sump performance, such as thermal 
insulation changeouts. This was in response to the findings of USI A-
43. In addition, the NRC staff is reviewing generic industry guidance 
and will issue a safety evaluation report endorsing portions or all of 
the generic industry guidance, if found acceptable. Once approved, this 
guidance may also be used to assist in determining the status of 
regulatory compliance. Individual addressees may also develop 
alternative approaches to those named in this paragraph for determining 
the status of their regulatory compliance; however, additional staff 
review may be required to assess the adequacy of such approaches. If 
the industry guidance will not be available when the generic letter is 
issued, the NRC will provide additional guidance for determining on a 
plant-specific basis whether compliance exists with 10 CFR 50.46(b)(5).
    The time frames for addressee responses in this generic letter were 
selected to (1) allow adequate time for addresses to perform an 
analysis, if they opt to do so, (2) allow addressees to properly design 
and install any identified modifications, (3) allow addresses adequate 
time to obtain NRC approval, as necessary, for any licensing basis 
changes, and (4) allow for the closure of the generic issue in 
accordance with the published schedule. These time frames are 
appropriate since all addresses have responded to Bulletin 2003-01 and 
will, if necessary, implement compensatory measures until the issues 
identified in this generic letter are resolved.

Applicable Regulatory Requirements

    NRC regulations in Title 10, of the Code of Federal Regulations 
Section 50.46,(10 CFR 50.46), require that the ECCS must satisfy five 
criteria, one of which is to provide the capability for long-term 
cooling of the reactor core following a LOCA. The ECCS must have the 
capability to provide decay heat removal, such that the core 
temperature is maintained at an acceptably low value for the extended 
period of time required by the long-lived radioactivity remaining in 
the core. For PWRs licensed to the General Design Criteria (GDCs) in 
Appendix A to 10 CFR Part 50, GDC 35 specifies additional ECCS 
requirements.
    Similarly, for PWRs licensed to the GDCs in Appendix A to 10 CFR 
Part 50, GDC 38 provides requirements for containment heat removal 
systems, and GDC 41 provides requirements for containment atmosphere 
cleanup. Many PWR licensees credit a CSS, at least in part, with 
performing the safety functions to satisfy these requirements, and PWRs 
that are not licensed to the GDCs may similarly credit a CSS to satisfy 
licensing basis requirements. In addition, PWR licensees may credit a 
CSS with reducing the accident source term to meet the limits of 10 CFR 
Part 100 or 10 CFR 50.67.
    Criterion XVI (Corrective Action) of Appendix B to 10 CFR Part 50 
states that measures shall be established to assure that conditions 
adverse to quality are promptly identified and corrected. For 
significant conditions adverse to quality, the measures taken shall 
include root cause determination and corrective action to preclude 
repetition of the adverse conditions.
    If, in the course of preparing a response to the requested 
information, an addressee determines that its facility is not in 
compliance with the Commission's requirements, the addressee is 
expected to take appropriate action in accordance with requirements of 
Appendix B to 10CFR Part 50 and the plant technical specifications to 
restore the facility to compliance.

Applicable Regulatory Guidance \1\

    Regulatory Guide 1.82, Revision 3, ``Water Sources for Long-Term 
Recirculation Cooling Following a Loss-of-Coolant Accident,'' November 
2003.
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    \1\ The NRC staff is currently reviewing evaluation guidance 
developed by the industry. The NRC staff will document its review in 
a safety evaluation which licensees can reference as regulatory 
guidance.
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Requested Information

    All addressees are requested to provide the following information:
    1. Within 60 days of the date of this generic letter, addressees 
provide information regarding their planned actions and schedule to 
confirm their compliance with 10 CFR 50.46(b)(5) and other existing 
regulatory requirements listed in this generic letter. The provided 
information should include the following:
    (a) A description of the methodology used or that will be used to 
analyze the susceptibility of the ECCS and CSS recirculation functions 
for your reactor to adverse effects of post-accident debris blockage 
and operation with debris laden fluids identified in this generic 
letter. Provide the completion date of any analysis that will be 
performed.
    (b) If a mechanistic analysis was or will be performed to confirm 
compliance, provide a statement of whether or not you plan to perform a 
containment walkdown surveillance in support of the analysis of the 
susceptibility of the ECCS and CSS recirculation functions to the 
adverse effects of debris blockage identified in this generic letter. 
Provide justification if no containment walkdown surveillance will be 
performed. If a containment walkdown surveillance will be performed, 
state the planned methodology to be used and the planned completion 
date. If a containment walkdown surveillance has already been 
performed, state the methodology used, the completion date, and the 
results of the surveillance.
    2. Addresses are requested to provide no later than April 1, 2005, 
information that confirms their compliance with the regulatory 
requirements listed in the Applicable Regulatory Requirements section 
of this generic letter.
    (a) Provide confirmation that the ECCS and CSS recirculation 
functions under debris loading conditions are or will be in compliance 
with the regulatory requirements listed in the Applicable Regulatory 
Requirements section of this generic letter. This submittal should also 
address the configuration of the plant that will exist once all 
modifications required for regulatory compliance have been made.
    (b) A general description of and implementation schedule for all 
corrective actions, including any plant modifications that may be 
necessary to ensure compliance with the regulatory requirements listed 
in the Applicable Regulatory Requirements section of this generic 
letter. Provide justification for any corrective action that will not 
be completed by the end of the first refueling outage after April 1, 
2005.
    (c) A submittal that describes the methodology that was used to 
perform an analysis of the susceptibility of the ECCS and CSS 
recirculation functions to the adverse effects of post-accident debris 
blockage and operation with

[[Page 16985]]

debris laden fluids. The submittal may reference a guidance document 
(e.g. Regulatory Guide 1.82, industry guidance) or other methodology 
previously submitted to the NRC. If a mechanistic analysis was 
performed to confirm compliance, the documents to be submitted or 
referenced should include the methodology for conducting a supporting 
containment walkdown surveillance used to identify potential debris 
sources and other pertinent containment characteristics.
    (d) If a mechanistic analysis was performed to confirm compliance, 
the submittal should include, at a minimum, the following information:
    (i) The minimum available NPSH margin for the ECCS and CSS pumps 
with an unblocked sump screen.
    (ii) The extent of submergence of the sump screen (i.e., partial or 
full) at the time of the switchover to sump recirculation, and the 
submerged area of the sump screen at this time.
    (iii) The maximum head loss postulated from debris accumulation on 
the submerged sump screen, and a description of the primary 
constituents of the debris bed that result in this head loss. In 
addition to debris generated by jet forces from the pipe rupture, 
debris created by the resulting containment environment (thermal and 
chemical) and CSS washdown should be considered in the analyses. 
Examples of this type of debris are disbonded coatings in the form of 
chips and particulates or chemical precipitants caused by chemical 
reactions in the pool.
    (iv) The basis for concluding that water inventory required to 
ensure adequate ECCS or CSS recirculation would not be held up or 
diverted by debris blockage at choke-points in containment 
recirculation sump return flowpaths.
    (v) The basis for concluding that inadequate core or containment 
cooling would not result due to debris blockage at flow restrictions in 
the ECCS and CSS flowpaths downstream of the sump screen, such as a 
HPSI throttle valve, pump bearings and seals, fuel assembly inlet 
debris screen, or containment spray nozzles. The discussion should 
consider the adequacy of the sump screen's mesh spacing and state the 
basis for concluding that adverse gaps or breaches are not present on 
the screen surface.
    (vi) Verification that close tolerance sub-components in pumps, 
valves and other ECCS and CSS components are not susceptible to 
plugging or excessive wear due to extended post accident operation with 
debris laden fluids.
    (vii) If an active approach (e.g. back flushing, powered screens, 
etc.) is selected in lieu of or in addition to a passive approach to 
mitigate the effects of the debris blockage, describe the approach and 
associated analyses.
    (e) A general description of and planned schedule for any changes 
to the plant licensing bases resulting from any analysis or plant 
modification done to ensure compliance with the regulatory requirements 
listed in the Applicable Regulatory Requirements section of this 
generic letter.
    (f) A description of any existing or planned programmatic controls 
that will ensure that, in the future, potential sources of debris 
introduced into containment (e.g., insulations, signs, coatings, and 
foreign materials) will be assessed for potential adverse effects on 
the ECCS and CSS recirculation functions. Addressees may reference 
their responses to GL 98-04 to the extent that their responses address 
these specific foreign material control issues.

Required Response

    In accordance with 10 CFR 50.54(f), the subject PWR addressees are 
required to submit written responses to this generic letter. This 
information is sought to verify licensees' compliance with current 
licensing basis for the subject PWR addressees. The addressees have two 
options:
    (1) Addressees may choose to submit written responses providing the 
information requested above within the requested time periods, or
    (2) Addressees who choose not to provide information requested or 
cannot meet the requested completion dates are required to submit 
written responses within 15 days of the date of this generic letter. 
The responses must address any alternative course of action proposed, 
including the basis for the acceptability of the proposed alternative 
course of action.
    The required written responses should be addressed to the U.S. 
Nuclear Regulatory Commission, Attn: Document Control Desk, 11555 
Rockville Pike, Rockville, Maryland 20852, under oath or affirmation 
under the provisions of Section 182a of the Atomic Energy Act of 1954, 
as amended, and 10 CFR 50.54(f). In addition, a copy of a response 
should be submitted to the appropriate regional administrator.
    The NRC staff will review the responses to this generic letter and 
will notify affected addressees if concerns are identified regarding 
compliance with NRC regulations and their current licensing bases. The 
staff may also conduct inspections to determine addressees' 
effectiveness in addressing the generic letter.

Reasons for Information Request

    As discussed above, research and analysis suggests that (1) the 
potential for the failure of the ECCS and CSS recirculation functions 
as a result of debris blockage is not adequately addressed in most PWR 
licensees' current safety analyses, and (2) the ECCS and CSS 
recirculation functions at a significant number of operating PWRs could 
become degraded as a result of the potential effects of debris blockage 
or extended operation with debris laden fluids identified in this 
generic letter. An ECCS that is incapable of providing long-term 
reactor core cooling through recirculation operation would be in 
violation of 10 CFR 50.46. A CSS that is incapable of functioning in 
recirculation mode may not comply with GDCs 38 and 41 or other plant-
specific licensing requirements or safety analyses. Bulletin 2003-01 
requested information to verify addressees' compliance with NRC 
regulations and to ensure that any interim risks associated with post-
accident debris blockage are minimized while evaluations to determine 
compliance proceed. This generic letter is the follow-on generic 
communication to Bulletin 2003-01 which is requesting information on 
the results of the evaluations referenced in the bulletin. Therefore, 
the information requested in this generic letter is necessary to 
confirm plant-specific compliance with 10 CFR 50.46 and other existing 
regulations.
    The NRC staff will also use the requested information to (1) 
determine whether a sample auditing approach is acceptable for 
verifying that addressees have resolved the concerns identified in this 
generic letter, (2) assist in determining which addressees would be 
subject to the proposed sample audits, (3) provide confidence that any 
nonaudited addressees have addressed the concerns identified in this 
generic letter, and (4) assess the need for and guide the development 
of any additional regulatory actions that may be necessary to address 
the adequacy of the ECCS and CSS recirculation functions.

Related Generic Communications

     Bulletin 2003-01, ``Potential Impact of Debris 
Blockage on Emergency Recirculation During Design-Basis Accidents at 
Pressurized-Water Reactors,'' June 9, 2003.
     Bulletin 96-03, ``Potential Plugging of 
Emergency Core Cooling Suction Strainers by Debris in Boiling-Water 
Reactors,'' May 6, 1996.

[[Page 16986]]

     Bulletin 95-02, ``Unexpected Clogging of a 
Residual Heat Removal (RHR) Pump Strainer While Operating in the 
Suppression Pool Cooling Mode,'' October 17, 1995.
     Bulletin 93-02, ``Debris Plugging of Emergency 
Core Cooling Suction Strainers,'' May 11, 1993.
     Bulletin 93-02, Supplement 1, ``Debris Plugging 
of Emergency Core Cooling Suction Strainers,'' February 18, 1994.
     Generic Letter 98-04, ``Potential for 
Degradation of the Emergency Core Cooling System and the Containment 
Spray System After a Loss-of-Coolant Accident Because of Construction 
and Protective Coating Deficiencies and Foreign Material in 
Containment,'' July 14, 1998.
     Generic Letter 97-04, ``Assurance of Sufficient 
Net Positive Suction Head for Emergency Core Cooling and Containment 
Heat Removal Pumps,'' October 7, 1997.
     Generic Letter 85-22, ``Potential For Loss of 
Post-LOCA Recirculation Capability Due to Insulation Debris Blockage,'' 
December 3, 1985.
     Information Notice 97-13, ``Deficient Conditions 
Associated With Protective Coatings at Nuclear Power Plants,'' March 
24, 1997.
     Information Notice 96-59, ``Potential 
Degradation of Post Loss-of-Coolant Recirculation Capability as a 
Result of Debris,'' October 30, 1996.
     Information Notice 96-55, ``Inadequate Net 
Positive Suction Head of Emergency Core Cooling and Containment Heat 
Removal Pumps Under Design Basis Accident Conditions,'' October 22, 
1996.
     Information Notice 96-27, ``Potential Clogging 
of High Pressure Safety Injection Throttle Valves During 
Recirculation,'' May 1, 1996.
     Information Notice 96-10, ``Potential Blockage 
by Debris of Safety System Piping Which Is Not Used During Normal 
Operation or Tested During Surveillances,'' February 13, 1996.
     Information Notice 95-47, ``Unexpected Opening 
of a Safety/Relief Valve and Complications Involving Suppression Pool 
Cooling Strainer Blockage,'' October 4, 1995.
     Information Notice 95-47, Revision 1, 
``Unexpected Opening of a Safety/Relief Valve and Complications 
Involving Suppression Pool Cooling Strainer Blockage,'' November 30, 
1995.
     Information Notice 95-06, ``Potential Blockage 
of Safety-Related Strainers by Material Brought Inside Containment,'' 
January 25, 1995.
     Information Notice 94-57, ``Debris in 
Containment and the Residual Heat Removal System,'' August 12, 1994.
     Information Notice 93-34, ``Potential for Loss 
of Emergency Cooling Function Due to a Combination of Operational and 
Post-LOCA Debris in Containment,'' April 26, 1993.
     Information Notice 93-34, Supplement 1, 
``Potential for Loss of Emergency Cooling Function Due to a Combination 
of Operational and Post-LOCA Debris in Containment,'' May 6, 1993.
     Information Notice 92-85, ``Potential Failures 
of Emergency Core Cooling Systems Caused by Foreign Material 
Blockage,'' December 23, 1992.
     Information Notice 92-71, ``Partial Plugging of 
Suppression Pool Strainers at a Foreign BWR,'' September 30, 1992.
     Information Notice 89-79, ``Degraded Coatings 
and Corrosion of Steel Containment Vessels,'' December 1, 1989.
     Information Notice 89-79, Supplement 1, 
``Degraded Coatings and Corrosion of Steel Containment Vessels,'' June 
29, 1990.
     Information Notice 89-77, ``Debris in 
Containment Emergency Sumps and Incorrect Screen Configurations,'' 
November 21, 1989.
     Information Notice 88-28, ``Potential for Loss 
of Post-LOCA Recirculation Capability Due to Insulation Debris 
Blockage,'' May 19, 1988.

Backfit Discussion

    Under the provisions of Section 182a of the Atomic Energy Act of 
1954, as amended, and 10CFR 50.54(f), this generic letter transmits an 
information request for the purpose of verifying compliance with 
existing applicable regulatory requirements (see the Applicable 
Regulatory Requirements section of this generic letter). Specifically, 
the required information will enable the NRC staff to determine whether 
the emergency core cooling system (ECCS) and containment spray system 
(CSS) at reactor facilities are able to perform their safety functions 
following all postulated accidents for which ECCS or CSS recirculation 
is required while taking into account the adverse effects of post-
accident debris blockage and operation with debris laden fluids. No 
backfit is either intended or approved by the issuance of this generic 
letter, and the staff has not performed a backfit analysis.

Small Business Regulatory Enforcement Fairness Act

    The NRC has determined that this generic letter is not subject to 
the Small Business Regulatory Enforcement Fairness Act of 1996.

Federal Register Notification

    The NRC published a notice of opportunity for public comment on 
this generic letter in the Federal Register on ------. In addition, the 
NRC has provided opportunities for public comment at several public 
meetings. As the resolution of this matter progresses, the NRC will 
continue to provide opportunities for further public involvement.

Paperwork Reduction Act Statement

    This generic letter contains information collections that are 
subject to the Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et 
seq.). These information collections were approved by the Office of 
Management and Budget (OMB) under approval number XXXX-XXXX which 
expires on XXX XX, XXXX.
    The burden to the public for these mandatory information 
collections is estimated to average 1000 hours per response, including 
the time for reviewing instructions, searching existing data sources, 
gathering and maintaining the necessary data, and completing and 
reviewing the information collections. Send comments regarding this 
burden estimate or any other aspect of these information collections, 
including suggestions for reducing the burden, to the Records 
Management Branch, Mail Stop T-6 E6, U.S. Nuclear Regulatory 
Commission, Washington, DC 20555-0001, or by Internet electronic mail 
to [email protected]; and to the Desk Officer, Office of Information 
and Regulatory Affairs, NEOB-10202 (3150-0011), Office of Management 
and Budget, Washington, DC 20503.
Public Protection Notification
    The NRC may neither conduct nor sponsor, and an individual is not 
required to respond to, an information collection unless the requesting 
document displays a currently valid OMB control number.

End of Draft Generic Letter

    Documents may be examined, and/or copied for a fee, at the NRC's 
Public Document Room at One White Flint North, 11555 Rockville Pike 
(first floor), Rockville, Maryland. Publicly available records will be 
accessible electronically from the Agencywide Documents Access and 
Management System (ADAMS) Public Electronic Reading Room on the 
Internet at the NRC Web site, http://www.nrc.gov/NRC/ADAMS/index.html. 
If you do not have access to

[[Page 16987]]

ADAMS or if you have problems in accessing the documents in ADAMS, 
contact the NRC Public Document Room (PDR) reference staff at 1-800-
397-4209 or 301-415-4737 or by e-mail to [email protected].

    Dated at Rockville, Maryland, this 24th day of March 2004.

    For the Nuclear Regulatory Commission.
William D. Beckner,
Chief, Reactor Operations Branch, Division of Inspection Program 
Management, Office of Nuclear Reactor Regulation.
[FR Doc. 04-7164 Filed 3-30-04; 8:45 am]
BILLING CODE 7590-01-U