[Federal Register Volume 65, Number 106 (Thursday, June 1, 2000)]
[Rules and Regulations]
[Pages 34913-34921]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-13745]


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NUCLEAR REGULATORY COMMISSION

10 CFR Part 50

RIN 3150-AG26


Emergency Core Cooling System Evaluation Models

AGENCY: Nuclear Regulatory Commission.

ACTION: Final rule.

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SUMMARY: The Nuclear Regulatory Commission (NRC) is amending its 
regulations to allow holders of operating licenses for nuclear power 
plants to reduce the assumed reactor power level used in evaluations of 
emergency core cooling system (ECCS) performance. This amendment 
provides licensees the option to apply a reduced margin for ECCS 
evaluation or to maintain the value of reactor power that had been 
mandated in the regulation. This action allows interested licensees to 
pursue small, but cost-beneficial, power uprates and reduces 
unnecessary regulatory

[[Page 34914]]

burden without compromising the margin of safety of a facility.

EFFECTIVE DATE: The rule becomes effective July 31, 2000.

ADDRESSES: The final rule and any related documents are available on 
the NRC's rulemaking website at http://ruleforum.llnl.gov. For 
information about the interactive rulemaking website, contact Ms. Carol 
Gallagher, (301) 415-5905 (e-mail: [email protected]).

FOR FURTHER INFORMATION CONTACT: Mr. Joseph E. Donoghue, Office of 
Nuclear Reactor Regulation, U.S. Nuclear Regulatory Commission, 
Washington, DC 20555-0001; telephone: 301-415-1131; or by Internet 
electronic mail to [email protected].

SUPPLEMENTARY INFORMATION:

Background

    A holder of an operating license (i.e., the licensee) for a light-
water power reactor is required by regulations issued by the NRC to 
submit a safety analysis report that contains an evaluation of 
emergency core cooling system (ECCS) performance under loss-of-coolant 
accident (LOCA) conditions. 10 CFR 50.46, ``Acceptance criteria for 
emergency core cooling systems for light-water nuclear power 
reactors,'' requires that ECCS performance under LOCA conditions be 
evaluated and that the estimated performance satisfy certain criteria. 
Licensees may conduct an analysis that ``realistically describes the 
behavior of the reactor system during a LOCA'' (often termed a ``best-
estimate analysis''), or they may develop a model that conforms with 
the requirements of Appendix K to 10 CFR part 50. Most ECCS evaluations 
are based on Appendix K requirements. Before this revision, the opening 
sentence of Appendix K specified that a power level of 102 percent be 
assumed when conducting ECCS analyses. Licensees have proposed using 
instrumentation that would reduce the uncertainties associated with 
measurement of reactor power when compared with existing methods of 
power measurement. This development could justify a reduced margin 
between the licensed power level and the power level assumed for ECCS 
evaluations. This final rule amends this provision in Appendix K and 
allows licensees the option of using a value lower than 102 percent of 
licensed power in their ECCS analyses where justified.
    Several licensees have expressed interest in using updated 
feedwater flow measurement technology discussed later in ``Calorimetric 
Uncertainty and Feedwater Flow Measurement'' as a basis for seeking 
exemptions from the Appendix K power level requirement and to implement 
power uprates. One licensee, TXU Electric Company, obtained an 
exemption from the Appendix K requirement for Comanche Peak Units 1 and 
2 as well as an increase in licensed power based, in part, on more 
accurate feedwater flow measurement capability. The prospect of 
additional exemption requests from other licensees provides the impetus 
for the final rule.
    The objective of this rulemaking is to reduce an unnecessarily 
burdensome regulatory requirement. Appendix K was originally issued to 
ensure an adequate performance margin of the ECCS in the event a 
design-basis LOCA were to occur. The margin is provided by conservative 
features and requirements of the evaluation models and by the ECCS 
performance criteria. The original regulation did not require that the 
power measurement uncertainty be demonstrated, but rather mandated a 2-
percent margin. The final rule allows licensees to justify a smaller 
margin for power measurement uncertainty. Because there will continue 
to be substantial conservatism in other Appendix K requirements, 
sufficient margin to ECCS performance in the event of a LOCA will be 
preserved, which is the underlying purpose of Appendix K. The final 
rule does not significantly affect plant risk, as discussed in the 
section entitled, ``ECCS Evaluation Conservatism.''
    Another objective is to avoid unnecessary exemption requests. A 
licensee has obtained an exemption from the 2-percent margin 
requirement in 10 CFR part 50, Appendix K. The final rule eliminates 
the need for licensees to obtain exemptions.
    The final rule gives licensees the option of applying a reduced 
margin between the licensed power level and the assumed power level for 
ECCS evaluation, or maintaining the current margin of 2-percent power. 
As discussed in the section entitled ``ECCS Evaluation Conservatism,'' 
the NRC has concluded that the 2 percent power margin requirement in 
the original rule appeared to be based solely on considerations 
associated with power measurement extant at the time of the original 
ECCS rulemaking. The original rule unnecessarily restricted operation 
for licensees that can show that the uncertainties associated with 
power measurement instrumentation errors are less than 2 percent.
    This amendment gives licensees the opportunity to use a reduced 
margin if they determine that there is a sufficient benefit. Licensees 
may apply the margin to gain benefits from operation at higher power, 
or the margin could be used to relax ECCS-related technical 
specifications (e.g., pump flows). Another potential benefit could be 
in modifying fuel management strategies (e.g., possibly by altering 
core power peaking factors). However, the final rule, by itself, does 
not allow increases in licensed power levels. Because licensed power 
level for a plant is a technical specification limit, proposals to 
raise the licensed power level must be reviewed and approved under the 
license amendment process. The license amendment request should include 
a justification of the reduced power measurement uncertainty and the 
basis for the modified ECCS analysis, including the justification for 
reduced power measurement uncertainty, should then be included in 
documentation supporting the ECCS analysis (see Section-by-Section 
Analysis).
    As licensees apply the final rule and the NRC gains experience 
reviewing related license amendment requests, the NRC will consider the 
need for specific guidance to help licensees appropriately account for 
power measurement uncertainty in safety analyses. In the absence of 
specific guidance, the NRC expects that power uprate amendment requests 
based on this amendment to the regulations will address the suitability 
of non-LOCA analyses for operation at proposed higher power levels. 
Licensees can refer to available instrumentation guidance such as the 
Instrument Society of America Standard ISA 67.04, 1982, ``Safety-
Related Instrumentation Used in Nuclear Power Plants,'' and NRC 
Regulatory Guide 1.105, Revision 2, ``Instrument Setpoints for Safety-
Related Systems.''

Conservatisms in Appendix K ECCS Evaluation Model

    Appendix K defines conservative analysis assumptions for ECCS 
performance evaluations during design-basis LOCAs. Large safety margins 
are provided by conservatively selecting the ECCS performance criteria 
as well as conservatively establishing ECCS calculational requirements. 
The major analytical parameters and assumptions that contribute to the 
conservatisms in Appendix K are set forth in sections A through D of 
the rule: (A) ``Sources of Heat During the LOCA'' (the 102-percent 
power provision is a key factor); (B) ``Swelling and Rupture of the 
Cladding and Fuel Rod Thermal Parameters;'' (C) ``Blowdown Phenomena;'' 
and (D) ``Post-Blowdown Phenomena: Heat Removal by ECCS.'' In each of 
these areas, several assumptions are typically used to ensure 
substantial conservatism in the analysis results. For

[[Page 34915]]

instance: under ``Sources of Heat During the LOCA,'' decay heat is 
modeled on the basis of an American Nuclear Society standard with an 
added 20-percent penalty, and the power distribution shape and peaking 
factors expected during the operating cycle are chosen to yield the 
most conservative results. In ``Blowdown Phenomena,'' the rule requires 
use of the Moody model and the discharge coefficient that yields the 
highest peak cladding temperature. ``Post-Blowdown Phenomena; Heat 
Removal by the ECCS,'' requires that the analysis assume the most 
damaging single failure of ECCS equipment.
    One of several conservative requirements in section A of the 
original Appendix K was to assume that the reactor was operating at 102 
percent power when the LOCA occurred ``to allow for such uncertainties 
as instrumentation error * * *.'' (Appendix K, section I.A., first 
sentence, emphasis added). The phrase, ``such as,'' suggested that the 
two percent power margin was intended to address uncertainties related 
to heat source considerations beyond instrument measurement 
uncertainties. However, the basis for the required assumption of 102 
percent power (2 percent power margin) does not appear to be contained 
in the rulemaking record for the ECCS rules, 10 CFR 50.46 and Appendix 
K. These rules were adopted in 1974 (39 FR 1001; January 4, 1974), and 
were preceded by a formal rulemaking hearing which ultimately resulted 
in a Commission decision on the proposed rulemaking, CLI-73-39, 6 AEC 
1085 (December 28, 1973). Neither the statement of considerations (SOC) 
for the final rule nor the Commission decision appear to provide 
specific basis for the required assumption of 102 percent power.
    The SOC for the January 4, 1974, final rule discusses the 102 
percent power assumption in general terms, and does not mention 
instrumentation uncertainty:

    The Commission believes that the implementation of the new 
regulations will ensure an adequate margin of performance of the 
ECCS should a design basis LOCA ever occur. This margin is provided 
by conservative features of the evaluation models and by the 
criteria themselves. Some of the major points that contribute to the 
conservative nature of the evaluations and the criteria are as 
follows:
    (1) Stored heat. The assumption of 102 percent of maximum power, 
highest allowed peaking factor, and highest estimated thermal 
resistance between the UO2 and the cladding provides a 
calculated stored heat that is possible but unlikely to occur at the 
time of a hypothetical accident. While not necessarily a margin over 
the extreme condition, it represents at least an assumption that an 
accident happens at a time which is not typical. 39 FR at 1002 
(first column).\1\

    \1\ This statement in the SOC was taken unchanged from section I 
of the Commission's ECCS decision. See CLI-73-39, 6 AEC 1085, 1093-
94 (December 28, 1973).

Thus, while the pre-accident power level assumption is connected with 
the modeling of the rate of heat generation after the LOCA occurs, a 
clear basis for the 102 percent assumed power level requirement is not 
provided, nor does the SOC explain whether there are other 
uncertainties besides instrumentation uncertainties for which the 102 
percent assumed power level is intended to compensate.
    The Commission's decision in the ECCS rulemaking hearing also does 
not explain whether the 102 percent assumed power level was intended to 
address uncertainties other than instrumentation uncertainties. Section 
I of the Commission decision was the basis for the SOC discussion on 
the 102 percent assumed power level (see 6 AEC at 1093-94). Section 
III. A. of the Commission's decision, ``Required and Acceptable 
Features of the Evaluation Model,'' does not offer a detailed technical 
basis for the power level chosen, but instead uses the language 
ultimately adopted in the original Appendix K rule:

    For the heat sources listed in paragraphs 1 to 4 below it shall 
be assumed that the reactor has been operating continuously at a 
power level at least 1.02 times the licensed power level (to allow 
for such uncertainties as instrumentation error), with the maximum 
peaking factor allowed by the technical specifications (6 AEC at 
1100).

Thus, the Commission's decision does not shed further light on the 
basis for the 102 percent assumed power level, nor whether the 
Commission had in mind uncertainties other than those associated with 
the instrumentation for measurement of power level.
    NRC review of the ECCS rulemaking hearing record did not disclose 
presentations relating to quantification of power measurement 
uncertainties, or the magnitude of other uncertainties that the 102 
percent assumed power level may have been intended to address. The 
Commission decision (CLI-73-39, 6 AEC 1085, December 28, 1973) cited 
three documents in the rulemaking hearing record.
    The first, cited in the Commission decision as Exhibit 1113, was 
``Supplemental Testimony of the AEC Regulatory Staff on the Interim 
Acceptance Criteria for Emergency Core Cooling Systems for Light-Water 
Cooled Power Reactors'' (filed October 26, 1972). In section 10 of the 
document, stored energy in the fuel was considered, specifically the 
expected power distributions in fuel rods. The 102-percent power 
analysis requirement is not discussed.
    The second item, cited in the Commission decision as Exhibit 1137 
was ``Redirect and Rebuttal Testimony of Dr. Donald H. Roy on Behalf of 
Babcock & Wilcox,'' (October 26, 1972) in which the characteristic of 
the decay heat release following reactor shutdown was discussed. In 
this document, the 102-percent assumption is associated with the 
predicted decay heat generation rate. The over-power condition is 
associated with a ``design-basis maneuvering operation,'' but the basis 
for the value of power chosen for the analysis (i.e., 102 percent) is 
not disclosed.
    Finally, in the ``Concluding Statement of Position of the 
Regulatory Staff--Public Rulemaking Hearing on: Acceptance Criteria for 
Emergency Core Cooling Systems for Light-Water Cooled Nuclear Power 
Reactors,'' April 16, 1973 (the Concluding Statement), the power level 
assumption is included as part of the proposed rule itself. The 
proposed rule language clearly states that the power level assumption 
is to ``allow for instrumentation error.'' The term ``such as'' does 
not appear here. It is unclear when or why the proposed language in 
this regard was changed to its current form. The power level assumption 
is mentioned again in the Concluding Statement indirectly in 
association with power level changes before the LOCA and the effect on 
decay heat generation. But it is discussed most directly with regard to 
initial stored energy in the fuel. In the discussion on stored energy, 
the 102-percent assumption is attributed to ``uncertainties inherent in 
the measurement of the operating power level of the core'' (page 144 of 
the Concluding Statement). Reasons for choosing 102-percent as the 
value are not discussed.
    When Appendix K was first issued, as is the case today, the thermal 
power generated by a nuclear power plant was determined by steam plant 
calorimetry, which is the process of performing a heat balance around 
the nuclear steam supply system (called a calorimetric). The heat 
balance depends upon measurement of several plant parameters, including 
flow rates and fluid temperatures. The differential pressure across a 
venturi installed in the feedwater flow path is a key element in the 
calorimetric measurement. Licensees have proposed using instrumentation 
other than a venturi-

[[Page 34916]]

based system to obtain feedwater flow rate for calorimetrics. The lower 
uncertainty associated with the new instrumentation is information that 
was apparently not available during the original Appendix K rulemaking.
    In view of the regulatory history for Appendix K, the Commission 
now believes that the 2-percent margin embodied in the requirement for 
a 102-percent assumed power level in Appendix K was based solely on 
uncertainties associated with the measurement of reactor power level.

Reduction in 102 Percent Assumed Power Level

    The Commission believes that other requirements of Appendix K 
modeling contain substantial conservatisms of much greater magnitude 
than the 2 percent margin embodied in the requirement for a 102 percent 
assumed power level. This point was discussed in ``Conservatisms in 
Appendix K ECCS Evaluation Model,'' above.
    The Commission is also aware of new information gained since the 
1974 rulemaking which shows that the Appendix K model contains 
additional conservatisms not recognized in 1974. Evidence from 
experiments designed to simulate LOCA phenomena suggest that these 
conservatisms added hundreds of degrees Fahrenheit to the prediction of 
peak fuel cladding temperature than would actually occur during a LOCA. 
The significant conservatism was necessary when the rule was written 
because of a lack of experimental evidence at that time with respect to 
the relative effects of analysis input parameters, including pre-
accident power level. Since that time, there has been substantial 
additional research on LOCA. NUREG-1230, ``Compendium of ECCS Research 
for Realistic LOCA Analysis,'' December 1988, contains the technical 
basis for improved understanding of LOCA progression and ECCS 
evaluation gained after the ECCS rule was issued. The NUREG includes a 
discussion of the basis for uncertainties in detailed fuel bundle power 
calculations as part of the consideration of overall calculational 
uncertainty inherent in best-estimate evaluations. Chapters 7 and 8 of 
the NUREG include consideration of the changes in licensed power level 
that could result from application of best-estimate evaluation methods. 
The discussion includes an estimated sensitivity of predicted peak clad 
temperature (PCT) associated with changes in pre-accident power level. 
From that estimate, the NRC expects peak cladding temperature changes 
of approximately 15  deg.F to result from 1-percent changes in plant 
power level that could result from the final rule.
    In view of: (i) Substantial conservatisms known in 1974 that were 
embodied in the Appendix K requirements for ECCS evaluations; (ii) new 
information developed since the 1974 rulemaking which shows additional 
conservatism in the Appendix K modeling requirements beyond that 
understood by the Commission when it adopted the 1974 rule; and (iii) 
the relative insensitivity of the calculated clad temperatures to 
assumed power level, the Commission concludes that it is acceptable to 
allow a reduction in the currently-required 102 percent power level 
assumption if justified by the actual power level measurement 
instrumentation uncertainty. Accordingly, the Commission is amending 
the Appendix K requirement for an assumed 102 percent power level. This 
amendment allows a licensee to use an assumed power level of less than 
102 percent (but not less than 100 percent), if the licensee has 
determined that the uncertainties in the measurement of core power 
level justifies the reduced margin.

Calorimetric Uncertainty and Feedwater Flow Measurement

    The NRC staff has approved an exemption to the 102-percent power 
level requirement for Comanche Peak Units 1 and 2. The basis for the 
action is application of upgraded feedwater flow measurement technology 
at the plant. As indicated, the prospect of additional licensees 
requesting similar action has prompted the final rule. Other methods, 
systems, or analyses could be used as the basis for demonstrating 
reduced power measurement uncertainty.
    In most nuclear power plants, operators obtain a continuous 
indication of core thermal power from nuclear instruments that provide 
a measurement of neutron flux. The nuclear instruments must be 
periodically calibrated to counteract the effects of changes in flux 
pattern, fuel burnup, and instrument drift. Steam plant calorimetry, 
which is the process of performing a heat balance around the nuclear 
steam supply system (called a calorimetric), is used to determine core 
thermal power and is the basis for the calibration. The differential 
pressure across a venturi installed in the feedwater flow path is a key 
element in the calorimetric measurement. Some plants use this 
calorimetric value directly to indicate thermal power; the nuclear 
instruments are used as anticipatory indicators for transients and for 
reactivity adjustments made with the control rods.
    The system in use at Comanche Peak Units 1 and 2 is the Leading 
Edge Flowmeter (LEFM), manufactured by Caldon, Inc. The LEFM system is 
an ultrasonic flow meter that measures the transit times of pulses 
traveling along parallel acoustic paths through the flowing fluid. LEFM 
technology has been employed in non-nuclear applications, such as 
petroleum, chemical, and hydroelectric plants for several years. This 
operating experience will provide reliability data, supplementing data 
from nuclear applications. Additional information on the Comanche Peak 
Appendix K exemption and on the Caldon, Inc. LEFM system appears in 
safety evaluations issued by the NRC staff on March 8, 1999, and May 6, 
1999.
    The NRC issued a safety evaluation on March 20, 2000, on the ABB 
Combustion Engineering ultrasonic flow-measuring system known as 
Crossflow. The Crossflow system is expected to be part of a licensee 
amendment request for power uprate in the near future.

Public Comment

    In the proposed rulemaking (64 FR 53270; October 1, 1999), the NRC 
sought comments from the public on four issues related to the revision 
of Appendix K. The NRC received comments from four utility companies, 
the Nuclear Energy Institute (NEI), and Caldon, Inc., manufacturer of 
the LEFM system. All of the commenters supported the proposed rule. NEI 
and Caldon offered comments on the four issues that the Commission 
included in the proposed rule. NEI and the New York Power Authority 
commented on several other issues as well.
    The issues that accompanied the proposed rule were:
    1. The current rule states that the required 2-percent analysis 
margin is to account for ``such uncertainties as instrumentation error 
* * *.'' (emphasis added). This suggests that the 2-percent margin was 
intended to account for other sources of uncertainty in addition to 
instrumentation error. However, explicit documentation of the basis for 
the value of the margin does not appear to be contained in the 
rulemaking record for the original 1974 ECCS rulemaking. The Commission 
was interested in whether there were other sources of uncertainty, 
relevant to sources of heat following a LOCA, that should be considered 
when licensees seek to reduce the margin in the Appendix K requirement 
for assumed power.

[[Page 34917]]

    As discussed in the section entitled, ``Conservatisms in Appendix K 
ECCS Evaluation Model,'' the Commission considered the rulemaking 
historical record for Appendix K and concluded that instrument 
uncertainty was likely the only source of uncertainty that was to be 
accounted for by the 2-percent margin. NEI and Caldon have not 
identified other sources of uncertainty, relevant to sources of heat 
following a LOCA, that are connected with the power level assumption.
    2. Were there rulemaking alternatives to the proposed rule that 
were not considered in the regulatory analysis?
    The Commission considered rulemaking alternatives in the 
accompanying regulatory analysis. The alternatives were: (i) No rule 
change; (ii) removal of the 102 percent requirement while requiring 
justification of a power level margin; (iii) the approach taken in the 
amended rule to maintain the 102 percent requirement and offer the 
option to reduce the margin; (iv) elimination of the power level 
margin; and (v) broad revision of Appendix K addressing all analysis 
requirements. Additional alternatives were not identified in the 
comments received for the proposed rule.
    3. What criteria should be used for determining whether a proposed 
reduction in the 2 percent power margin has been justified, based upon 
a determination of instrumentation error? For example, should a 
demonstrated instrumentation error of 1 percent in power level be 
presumptive of an acceptable reduction in assumed power margin of 1 
percent?
    The comments from NEI on this point emphasized that any criteria 
developed to evaluate proposed reductions in ECCS analysis power margin 
should be based only on the instrumentation error associated with power 
measurement. NEI said that the conservatism inherent in the ECCS 
analysis requirements embodied in Appendix K provide sufficient margin 
to maintain safety so that instrumentation uncertainty should be the 
only basis for the power level assumption. The comments also stated 
that the overall impact on safety should be considered and that 
degradation in safety should not be allowed.
    The Commission agrees that the main criteria determining the 
suitability of proposed power level margin reductions should be the 
details associated with uncertainties in power level measurement. The 
Commission also agrees that the overall impact on plant safety should 
be considered, preferably in a risk-informed manner. However, the 
commenter contended that a lower probability of exceeding the analyzed 
power level translates to an overall improved level of safety at a 
facility. The Commission does not necessarily equate a lower 
probability of exceeding an analysis limit with improved safety for 
facilities that obtain approvals to increase reactor thermal power or 
make other changes based on the amendment. For example, when plants 
obtain power uprates in conjunction with the relaxation in the amended 
rule, other factors come into play that may reduce the overall margin 
of safety, albeit probably only slightly for the small power increases 
anticipated with the amendment. Such changes in safety margin, if small 
and controlled, can be acceptable in light of other substantial 
conservatisms or associated risk-related information.
    Caldon offered detailed comments on this issue. Their comments went 
beyond general instrumentation uncertainty considerations by proposing 
a list of criteria that appeared to be based on application of the LEFM 
to power measurement at a plant. Although the Commission considers the 
criteria provided by Caldon to be helpful, the Commission is not yet 
prepared to formalize any criteria for evaluating reductions in the 
power level margin for ECCS analysis. The safety evaluations associated 
with the Appendix K exemption and power uprate for Comanche Peak 
granted to TXU Electric Company set forth basic review criteria, 
including many of those proposed by Caldon. In those reviews, the NRC 
staff referred to available instrumentation guidance such as the 
Instrument Society of America Standard ISA 67.04, 1982, ``Safety-
Related Instrumentation Used in Nuclear Power Plants,'' and NRC 
Regulatory Guide 1.105, Revision 2, ``Instrument Setpoints for Safety-
Related Systems.''
    The NRC staff intends to gain further experience with licensee 
proposals that pursue the relaxation offered by the amendment before 
deciding whether a regulatory guide providing detailed acceptance 
criteria needs to be developed. Licensee proposals may involve use of 
advanced flow measurement systems or other approaches to determine the 
level of power measurement uncertainty and to reduce it. However, the 
Commission does not believe that generic acceptance criteria should be 
too closely based on any particular measurement technology or analysis 
method.
    4. How should the rule address cases in which licensees determine 
that power measurement instrument error is greater than 2 percent?
    Both NEI and Caldon offered comments on this issue. Caldon 
maintained that current regulatory processes provide a sufficient basis 
for dealing with such situations. NEI recommended that licensees should 
conduct Appendix K ECCS evaluations at rated thermal power level plus 
the value of power measurement uncertainties, regardless of the 
magnitude of the uncertainty. The comments clearly stated that this 
position also applies for uncertainties determined to be greater than 2 
percent. NEI considered the need for licensees to ensure that safety 
analyses are valid for their facility. According to NEI, if the 
required margin for power level measurement were found to be 
insufficient to account for actual uncertainty levels, then licensees 
must take appropriate action, including lowering the operating power 
level. NEI offered alternatives for licensees to accommodate 
uncertainties above 2 percent, including demonstration that the PCT 
margin for a facility could accommodate greater-than-expected 
uncertainty. Also, NEI indicated that other conservatisms in Appendix K 
methodologies could be applied to ``offset'' the excessive power 
measurement uncertainty.
    The Commission agrees that licensees who find that the power 
measurement uncertainty for their facilities is greater than expected 
should take action to ensure that their plant is operated within the 
assumptions used in safety analyses. This follows from the requirement 
in 10 CFR 50 Appendix B, section III, ``Design Control.'' The Appendix 
B requirement states that design control measures will be applied to 
items such as accident analyses, and that design changes shall be 
subject to design control measures. Therefore, licensees must take 
action if the power measurement uncertainty is greater than typically 
expected or as determined in a plant-specific analysis. The expected 
magnitude of uncertainty at a facility could be the 2-percent margin 
that is preserved in the final rule, or it could be based on a plant-
specific analysis supporting a smaller value. As already considered, 
the basis for the value in the rule is not clearly illuminated in the 
rulemaking history of Appendix K. However, the Commission believes that 
the Appendix K value represents a typical value for power measurement 
uncertainty, unless demonstrated otherwise for a particular facility.
    The Commission does not believe that it is necessary to allow 
application of safety margins based on other conservative factors in an 
Appendix K ECCS evaluation to offset excessive uncertainties discovered 
in power measurement for a plant. By proposing

[[Page 34918]]

to use safety margin ``offsets'' to justify higher-than-expected power 
measurement uncertainties, NEI is proposing an alternative to Appendix 
K ECCS evaluation methods already permitted by Sec. 50.46. The 
Commission considers the available analysis alternatives offered by 
Sec. 50.46 (i.e., those based on Appendix K and the so-called best 
estimate methods) to offer sufficient flexibility to licensees without 
introducing large complexities to the review and approval process that 
could be anticipated if Appendix K were to be applied in a 
``piecemeal'' fashion.
    The Commission originally instituted the ECCS evaluation 
requirements with the understanding that substantial conservatisms 
existed. Later, the relative contributions of various conservative 
factors were estimated on a largely generic basis to demonstrate the 
feasibility of best-estimate evaluations. However, when the revisions 
to Sec. 50.46 were considered in 1988, the Commission deliberately 
maintained two distinct options: (i) Licensees could use the method 
defined by Appendix K; or (ii) they could develop a best-estimate 
approach. The alternatives discussed in the NEI comment can be 
accommodated by a licensee using the best-estimate option offered by 
Sec. 50.46, rather than applying Appendix K in a ``piecemeal'' fashion.
    On the basis of the ``best-estimate'' alternative to Appendix K 
requirements available in Sec. 50.46, the Commission takes the position 
that Appendix K requirements should not be applied in a ``piecemeal'' 
fashion, as discussed in the NEI comment. Rather than searching for 
customized adjustments to Appendix K requirements, licensees should 
develop a ``best-estimate'' method, as permitted in Sec. 50.46. The 
Commission position does not present licensees with an onerous burden. 
Licensees discovering that actual power measurement uncertainty at 
their plant is greater than the uncertainty assumed in safety analysis 
can take corrective action to address the problem while continuing 
plant operation. For example, plant power level may be reduced while 
the problem is addressed. Therefore, in the final rule the Commission 
has not adopted the NEI approach of applying offsetting uncertainties.
    The comments received from NEI addressed four additional areas:
    1. Uncertainties from additional heat sources. NEI commented that 
utilities would be able to use the amended rule to reduce the decay 
heat input used in Appendix K evaluations. NEI proposed that licensees 
could use the power measurement uncertainty to, ``ensure that the 
expected decay heat bounds the full rated plant power plus the 
uncertainty value.''
    The NEI comment expands the scope of the proposed revision to 
Appendix K, bringing into consideration decay heat uncertainty, which 
is a separate analysis requirement in the rule. The Commission agrees 
that the decay heat level used in the Appendix K analysis could be 
reduced commensurate with a lower assumed power level. However, the 
reduced power level assumption must be justified by an acceptable 
analysis of the power measurement uncertainty. Also, the decay heat 
level used in the analysis must continue to meet the requirement in 
Appendix K(I)(A)(4), ``Fission Product Decay.'' Discussion of the 
uncertainty involved with decay heat value required by Appendix 
K(I)(A)(4) is beyond the scope of this rulemaking. Licensees who wish 
to address the uncertainty of the decay heat level in their ECCS 
analysis should develop a ``best-estimate'' method which addresses 
uncertainties of all of the ECCS analysis parameters.
    2. Consistency among NRC documents. NEI pointed out that other 
Commission documents besides Appendix K contain the 1.02 power level 
multiplier. In the regulatory analysis accompanying the rule, the 
Standard Review Plan sections and Regulatory Guide 1.49 are listed as 
part of the current regulatory framework considered during the 
rulemaking.
    The NRC staff agrees with the comment that changes to guidance 
documents may be necessary and will make the necessary revisions to 
these documents to maintain consistency with the amended rule.
    3. Requirement for upgrade to feedwater flow measurement. NEI 
commented that the proposed rule appeared to be based upon application 
of upgraded feedwater flow technology. NEI recommended that the rule or 
associated guidance make clear that availability of the relaxation 
offered by the final rule is not restricted to licensees applying 
upgraded flow measurement technology.
    The preamble for the proposed rule does indeed discuss application 
of improved flow measurement technology. This discussion is appropriate 
because this new technology is the impetus for the exemption granted to 
one licensee and is a key justification for the Commission action in 
amending the current rule. In the section, ``Calorimetric Uncertainty 
and Feedwater Flow Measurement,'' the Commission pointed out that 
methods other than application of improved flow measurement technology 
could be used as the basis for demonstrating reduced power measurement 
uncertainty. Also, in its discussion of the Caldon comments on issue 
number 3, the Commission acknowledged that licensee proposals may 
involve use of advanced flow measurement systems or other approaches. 
To prevent misinterpretation of the rule, the Section-by-Section 
analysis has been modified to reiterate that other methods not 
considered in the rulemaking could be used to justify a reduced power 
measurement uncertainty allowance. Although various approaches to 
reduce the uncertainty involved with PCT calculation may be used, the 
only uncertainty considered under this amendment is that associated 
with power level measurement.
    4. Reportability under 10 CFR 50.46(a)(3). NEI cited the Section-
by-Section analysis of the proposed rule, where the Commission stated 
that, ``estimated changes in ECCS performance due to final analysis 
inputs are reported under section 50.46 (a)(3), at least annually.'' 
NEI recommended clarification of the statement to reflect an 
interpretation of Sec. 50.46 so as to relate only to evaluation model 
parameters, but not to plant design parameters. NEI contended that 
plant parameters change from cycle to cycle and that changes in PCT 
caused by plant specific input parameter changes to design information 
fall outside the scope of reportability under 10 CFR 50.46(a)(3).
    Although the Commission accepts that the results of ECCS 
evaluations could change as a result of cycle specific variations in 
model inputs, the Commission does not agree with NEI on this point. In 
their comment, NEI drew a distinction between design inputs and model 
inputs to ECCS evaluations. The amended rule does not change the 
reporting requirements of 10 CFR 50.46 for changes to ECCS evaluations. 
The regulations are clear on the definition of an ECCS evaluation model 
and when reports are required. 10 CFR 50.46 (c)(2) defines ECCS 
evaluation models and provides a list of the elements including, ``one 
or more computer programs and all other information necessary for 
application of the calculational framework to a specific LOCA, such as 
* * * values of parameters, and all other information necessary to 
specify the calculational procedure.'' In other words, the ECCS 
evaluation model is comprised of the computer code or codes, the input 
parameters (including plant-specific design parameters), and the 
calculational results. The Commission should be informed as described 
in 10

[[Page 34919]]

CFR 50.46(a)(3) when even a relatively small change to the 
calculational framework is made, especially when the PCT result is 
affected. As discussed in the statement of considerations to the 
September 16, 1988, final rule (53 FR 35996), the Commission needs to 
be cognizant of such changes to be able to confirm licensee or vendor 
assessments of the significance of the changes and to ensure that 
approved models continue to be used.
    10 CFR 50.46 (a)(ii) contains an unambiguous requirement that 
changes to the ECCS evaluation must be reported at least annually: 
``For each change to or error discovered in an acceptable evaluation 
model or in the application of such a model that affects the 
temperature calculation, the applicant or licensee shall report the 
nature of the change or error and its estimated effect on the limiting 
ECCS analysis to the Commission at least annually as specified in 
Sec. 50.4.'' Therefore, on the basis of the definition of an evaluation 
model in Sec. 50.46, the Commission does not accept the distinction 
made by NEI between ``model parameters'' and ``design parameters.'' 
Based on the requirements of Sec. 50.46, changes to the ECCS evaluation 
model under the amended Appendix K rule which affect the temperature 
calculation must be reported at least annually.
    The comments from one licensee, the New York Power Authority 
(NYPA), considered two areas not already discussed:
    1. Other potential benefits. NYPA commented that licensees could 
seek benefits other than increasing licensed power under the amended 
rule. The commenter offered two examples of such benefits--revised 
containment analyses conducted at power levels below 102 percent power 
and relaxation of operating restrictions on ultimate heat sink 
temperatures.
    The Commission agrees that licensees could request the relaxation 
offered by the amended rule while not pursuing a power level increase. 
In the Background section the Commission recognized that other benefits 
are available to licensees and that power level increase is just one 
option. The examples offered by the NYPA comments may be suitable to a 
licensee, depending on plant characteristics and plant-specific safety 
analyses.
    2. Changes to technical specifications. NYPA interpreted statements 
in the proposed rule to suggest that licensees pursuing the relaxation 
offered in the amendment would need to change their plant technical 
specifications to include a limiting condition for operation for new 
feedwater flow instrumentation. Further, the comments suggested that 
clarification was needed to address when license amendments were 
required for changes associated with the rule.
    In the Section-by-Section Analysis, the Commission discusses 
technical specification modifications that might be necessary when a 
power measurement uncertainty reduction is used in safety analyses. 
Typically, when an ECCS methodology is changed, a revision is made to 
the technical specification list of references associated with plant 
safety analysis methods. Technical specifications for nuclear power 
plants do not contain explicit requirements for feedwater flow 
instrumentation. The Commission does not believe that technical 
specification requirements for feedwater flow instruments are necessary 
for licensees to use the relaxation offered by the amended rule. 
Clarification regarding this point has been added to the Section-by-
Section Analysis.

Section-by-Section Analysis

Appendix K to Part 50--ECCS Evaluation Models (I)(A)--Sources of Heat 
During the LOCA

    This section is amended by removing words from the first sentence 
in the section to specifically associate the power level requirement 
with instrumentation error, and by adding a sentence immediately 
following the first sentence in the section. The new sentence indicates 
that licensees may assume a power level lower than 102 percent, but not 
less than 100 percent, if the proposed lower alternative value can be 
shown to account for core thermal power measurement instrumentation 
uncertainty. Licensee proposals may involve use of advanced flow 
measurement systems or other approaches to determine the level of power 
measurement uncertainty and to support reduction of the power level 
assumption. Only the uncertainty associated with power level 
measurement is considered in this amendment.
    Appendix K, part II (1)(a) requires that the values of analysis 
parameters or their basis be sufficiently documented to allow NRC 
review. The requirement applies to all analysis input parameters, 
including those related to other plant instrumentation, such as 
temperature and pressure. Changes to other inputs are documented in the 
same manner as the power measurement uncertainty would be documented 
under the final rule. NRC review and approval is not needed to change a 
parameter in an approved ECCS evaluation model unless the change is 
associated with technical specification or license condition 
modfications, or a final safety analysis report change not covered by 
Sec. 50.59, ``Changes, tests and experiments.'' Estimated changes in 
ECCS performance due to revised analysis inputs are reported under 
Sec. 50.46 (a)(3), at least annually. As discussed in the Statement of 
Considerations for a final rule amending Appendix K (53 FR 36001; 
September 16, 1988), the annual reports keep NRC apprised of changes. 
This should ensure that the NRC staff can evaluate a licensee's 
assessment of the significance of changes and maintain cognizance of 
modifications made to NRC-approved evaluation models. The licensee must 
include revised parameters and other changes in the ECCS evaluation 
model as required by Sec. 50.46 (a)(3) when a single change or an 
accumulation of changes is expected to affect peak cladding temperature 
by 50 deg.F or more. The basis for the revised analysis parameter 
(i.e., the assumed power level) should be included in documentation of 
the evaluation model, as required by Appendix K, Part II (1)(a).
    Licensees could take advantage of the amended rule without a change 
to technical specifications or to the plant license by simply updating 
the ECCS analysis and following the reporting requirements of 
Sec. 50.46. However, in most cases the NRC expects that the analysis 
supporting the power measurement uncertainty, as well as the 
description of the relevant instrumentation and associated plant-
specific parameters involved in the uncertainty analysis, would be 
submitted for NRC review and approval before being used. These requests 
are expected because most licensees have adopted Generic Letter 88-16, 
``Removal of Cycle-Specific Parameter Limits from Technical 
Specifications.'' The generic letter provided guidance for licensees to 
transfer cycle-specific parameters from their technical specifications 
to a Core Operating Limits Report (COLR). Licensees following the 
generic letter guidance added an administrative requirement to their 
technical specifications that specifically identifies NRC-reviewed and 
approved methods used to determine core operating limits (e.g., topical 
reports). Because a number of core operating limits are based on LOCA 
analysis results, ECCS evaluation methods are included in the technical 
specification list. Therefore, most licensees opting to use the 
relaxation in the final rule will need to amend technical 
specifications to include a reference to an NRC-approved topical report 
that includes the uncertainty

[[Page 34920]]

analysis justifying reduced power measurement uncertainty. However, a 
technical specification requirement specifically related to feedwater 
flow measurement system operability is not needed.
    An additional technical specification consideration for licensees 
pursuing changes based on the final rule could involve nuclear 
instrument (NI) requirements. Existing plant technical specifications 
include surveillance requirements to calibrate the power range NIs 
based on the calorimetric measuring reactor thermal power. The NIs 
provide the indication of reactor power used as an input for safety 
systems. Licensees obtaining the relaxation offered in the final rule 
are expected to change some operating parameter of the plant, whether 
it be power level, required ECCS flow, etc. By incorporating the 
justification of reduced uncertainty in power measurement in the basis 
for their ECCS analysis, licensees would be placing a condition on an 
input to the calorimetric. The NI calibration required by the plant 
licensee would then be based on a calorimetric assuming the reduced 
power measurement uncertainty. If, for some reason, during the course 
of plant operation the reduced uncertainty did not apply (e.g., the new 
feedwater flow meter was no longer operating), the calorimetric would 
no longer be a valid source of calibration for the NIs. Licensees would 
need to take action to maintain compliance with their technical 
specification, for example, by using an alternate input to the 
calorimetric. The power measurement uncertainties associated with the 
alternate input would then apply and the plant would need to adjust its 
operating condition (possibly lower its operating power level) to 
satisfy the final rule and to maintain the validity of applicable 
safety analyses. A change to technical specifications for NIs is not 
required in this situation.

Referenced Documents

    Copies of GL-88-16, and CLI-73-39, and ``Supplemental Testimony of 
the AEC Regulatory Staff on the Interim Acceptance Criteria for 
Emergency Core Cooling Systems for Light-Water Cooled Power Reactors,'' 
and ``Redirect and Rebuttal Testimony of Dr. Donald H. Roy on Behalf of 
Babcock & Wilcox,'' and ``Concluding Statement of Position of the 
Regulatory Staff--Public Rulemaking Hearing on: Acceptance Criteria for 
Emergency Core Cooling Systems for Light-Water Cooled Nuclear Power 
Reactors,'' and NRC safety evaluations are available for inspection and 
copying for a fee at the NRC Public Document Room, 2120 L Street, NW. 
(Lower Level), Washington, DC. GL-88-16 is also available via the 
Internet at http://www.nrc.gov/NRC/GENACT/GC/index.html#GL.
    NUREG-1230 is available from the Superintendent of Documents, U.S. 
Government Printing Office, Post Office Box 37082, Washington, DC 
20013-7082 or from the National Technical Information Service, 
Springfield, VA 22161.

Voluntary Consensus Standards

    The National Technology Transfer 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 the 
use of such a standard is inconsistent with applicable law or otherwise 
impractical. In this final rule, the NRC provides holders of operating 
licenses for nuclear power plants the option of reducing the assumed 
reactor power level used in ECCS evaluations. This action constitutes a 
modification to an existing government-unique standard, 10 CFR part 50, 
Appendix K issued by the NRC on January 4, 1974. The NRC is not aware 
of any voluntary consensus standard that could be adopted instead of 
the government-unique standard. The NRC considered using a voluntary 
consensus standard. However, an appropriate standard was not 
identified.

Finding of No Significant Environmental Impact: Availability

    The NRC has determined under the National Environmental Policy Act 
of 1969, as amended, and the NRC's regulations in subpart A of 10 CFR 
part 51, that this regulation is not a major Federal action 
significantly affecting the quality of the human environment and, 
therefore, an environmental impact statement is not required.
    The action is likely to result in relatively small changes to ECCS 
analyses or to the licensed power of nuclear reactor facilities. The 
NRC staff expects that no significant environmental impact will result 
from the final rule, because licensee actions based on the rule should 
not significantly increase the probability or consequences of 
accidents; no changes will be made in the types of any effluents that 
may be released off site; and there should be no significant increase 
in occupational or public radiation exposure. Therefore, there are no 
significant radiological environmental impacts associated with the 
action. The action does not involve non-radiological plant effluents 
and has no other environmental impact. Therefore, there are no 
significant non-radiological environmental impacts associated with the 
final rule.
    The determination of the environmental assessment is that there 
will be no significant offsite impact on the public from this action. 
Also, the NRC has committed itself to complying in all its actions with 
Executive Order (E.O.) 12898, ``Federal Actions To Address 
Environmental Justice in Minority Populations and Low-Income 
Populations,'' dated February 11, 1994. The NRC has determined that 
there are no disproportionately high and adverse impacts on minority 
and low-income populations. The NRC uses the following working 
definition of environmental justice: Environmental justice means the 
fair treatment and meaningful involvement of all people, regardless of 
race, ethnicity, culture, income, or educational level with respect to 
the development, implementation and enforcement of environmental laws, 
regulations, and policies. In the letter and spirit of E.O. 12898, the 
NRC requested public comments on environmental justice considerations 
or other questions related to this rule, but none were received.

Paperwork Reduction Act Statement

    This final rule increases the burden on licensees opting to use a 
reduced power level assumption for ECCS analysis (i.e., below 102 
percent) to include the change in their annual report required under 10 
CFR 50.46 (a)(3)(ii). The public burden to modify the annual report is 
estimated to average one-half hour per response. The estimated public 
burden for record keeping, analysis, and other effort associated with 
this information collection will be included in the Office of 
Management and Budget FY2000 Information Collection Budget. Existing 
requirements were approved by the Office of Management and Budget, 
approval number 3150-0011.

Public Protection Notification

    If a means used to impose an information collection does not 
display a currently valid OMB control number, the NRC may not conduct 
or sponsor, and a person is not required to respond to, the information 
collection.

Regulatory Analysis

    The Commission has prepared a regulatory analysis on this 
regulation. Copies of the regulatory analysis may be obtained as 
indicated in the ADDRESSES section.

[[Page 34921]]

Regulatory Flexibility Certification

    As required by the Regulatory Flexibility Act of 1980, 5 U.S.C. 
605(b), the Commission certifies that this final rule does not have a 
significant economic impact on a substantial number of small entities. 
This final rule would affect only the licensing and operation of 
nuclear power plants. The companies that own these plants do not fall 
within the definition of ``small entities'' found in the Regulatory 
Flexibility Act or within the size standards established by the NRC in 
10 CFR 2.810.

Backfit Analysis

    The NRC has determined that the backfit rule in 10 CFR 50.109 does 
not apply to this final rule and that a backfit analysis is not 
required for this amendment because the change does not involve any 
provisions that impose backfits as defined in 10 CFR 50.109(a)(1). The 
final rule establishes an alternative approach for ECCS performance 
evaluations that may be voluntarily adopted by licensees. Licensees may 
continue to comply with existing requirements in Appendix K. The final 
rule does not impose a new requirement on current licensees and 
therefore, does not constitute a backfit as defined in 10 CFR 
50.109(a)(1).

Small Business Regulatory Enforcement Fairness Act

    In accordance with the Small Business Regulatory Enforcement 
Fairness Act of 1996, the NRC has determined that this action is a 
major rule and has verified this determination with the Office of 
Information and Regulatory Affairs of`OMB.

List of Subjects in 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.

    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. 552 and 553, the NRC is adopting 
the following amendments to 10 CFR part 50.

PART 50--DOMESTIC LICENSING OF PRODUCTION AND UTILIZATION 
FACILITIES

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

    Authority: Sections 102, 103, 104, 105, 161, 182, 183, 186, 189, 
68 Stat. 936, 937, 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, 2236, 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 (42 U.S.C. 5851). Section 50.10 also issued under secs. 101, 
185, 68 Stat. 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 sec. 204, 88 Stat. 1245 (42 U.S.C. 5844). Sections 50.58, 
50.91, and 50.92 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. Appendix K to part 50 is amended by revising the introductory 
paragraph of I. A., ``Sources of heat during the LOCA,'' to read as 
follows:

Appendix K to Part 50--ECCS Evaluation Models

I. Required and Acceptable Features of the Evaluation Models

    A. Sources of heat during the LOCA. For the heat sources listed 
in paragraphs I.A.1 to 4 of this appendix it must be assumed that 
the reactor has been operating continuously at a power level at 
least 1.02 times the licensed power level (to allow for 
instrumentation error), with the maximum peaking factor allowed by 
the technical specifications. An assumed power level lower than the 
level specified in this paragraph (but not less than the licensed 
power level) may be used provided the proposed alternative value has 
been demonstrated to account for uncertainties due to power level 
instrumentation error. A range of power distribution shapes and 
peaking factors representing power distributions that may occur over 
the core lifetime must be studied. The selected combination of power 
distribution shape and peaking factor should be the one that results 
in the most severe calculated consequences for the spectrum of 
postulated breaks and single failures that are analyzed.
* * * * *


    Dated at Rockville, Maryland, this 26th day of May 2000.

    For the Nuclear Regulatory Commission.
J. Samuel Walker,
Acting Secretary of the Commission.
[FR Doc. 00-13745 Filed 5-31-00; 8:45 am]
BILLING CODE 7590-01-P