ML20217G762

Forwards Ltr for Recipient Use to Solicit Comments Re Proposed Rule Rev to App K of 10CFR50 from State Liaison Officers

ML20217G762
Person / Time
Issue date:	09/23/1999
From:	Wermiel J NRC (Affiliation Not Assigned)
To:	Lohaus P NRC OFFICE OF STATE PROGRAMS (OSP)
Shared Package
ML20217G757	List: ML20217G754 ML20217G762
References
NUDOCS 9910210350
Download: ML20217G762 (31)

Text

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_ sp "'=f p 4 UNITED STATES g

.i e j NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20666 4 001

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's., h o , * / September 23, 1999 j i

MEMORANDUM TO: Pasi H.= Lohaus, Dl rector ;

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i Offi6s of State Projirsms FROM: Jared S. Wermiel, Chief Reactor Systems Branch k [

Division of Systems Safety a(nd Analysis

SUBJECT:

STATE CONSULTATION ON PROPOSED REVISION TO APPENDIX K, 10 CFR PART 50 By memorandum dated September 17,1999, the Secretary of the ComtWssion approved the I proposed rule on emergency core cooling systems analysis requirements.

Attached is a letter for your use to solicit comments regarding the proposed rule from State Liaison Officers. Copies of the Federal Register notice and the Environmental Assessment associated with the proposed rule accompany the letter. Please note that the proposed rule will be published on or about October 1,1999, startir g the 75-day public comment period. '

Contact Joe Donoghue of my staff at 415-1131 if you have any questions about the proposed rule, cc: G. Holahan (w/o Attachment)

Attachment:

As stated IS f4

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9910210350 991001 PDR STPRO ESGOEN PDR l

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I STATE LIAISON OFFICERS

SUBJECT:

. Emergency Core Cooling System Evaluation Models l

The United States Nucice ag:latory Commission (NRC) has sent to the Office of the Federal

- Register for publication the enclosed proposed amendment to the Commission's rules in 10 CFR Part 50. The amendment, if adopted, would allow licensees of nuclear power plants l for which an operating license has been granted to justify the assumed reacte,r power used in i emergency core cooling system analyses. The current rule requires that the Analyses use j 102 percent of the licensed power level, therefore, the change will provide re actor licensees an  !

option to reduce the' assumed power level. The amendment resulted from the prospect of I multiple requests for exemptions from the existing rule by nuclear power plant licensees seeking a reduction in the assumed power level for analysis. The proposed action would allow 4 interes,'ed licensees to pursue small, but cost-beneficial, power uprates and would reduce  ;

unneomary regulatory burden without compromising the margin of safety for their facilities. l

- Also enclosed is an Environmental Assessment (EA) that has been prepared in support of this proposed rule. The conclusion of the EA is the Commission's finding that no significant l environmental impact will result from the proposed rule. The EA and FRN are provided for your review and comment. If you have any comments on the rule and its environmental impact, please send them within 75 days of the date of this letter. Comments after this 75 day comment period will be considered if it is practical to do so, but the Commission is able to assure consideration only for comments received during the comment period.

. You can use the following methods to transmit your comments: (1) you can mail your written comments to: Secretary, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001,  !

Attention: Rulemakings and Adjudications Staff, (2) you can fax your comments to i

(301) 415-1672, and (3) you can transmit your comments electronically to the NRC's ,

interactive rulemaking Web site, "Rulemaking Forum," through the NRC home page i

(http://ruleforum.lini. gov).

Sincerely,

. Pau! H. Lohaus, Director )

' Office o,' State Programs Ii

Enclosures:

' As stated .

Attachment 1

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NUCLEAR REGULATORY COMMISSION -

p i 10 CFR Pad 50 RIN 3150 - AG26 Emergency Core Cooling System Evaluation Models AGENCY: Nuclear Regulatory Commission.

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ACTION: Proposed rule.

SUMMARY

The Nuclear Regulatory Commission (NRC)is proposing to amend its regulations to allow holdera of operating licenses for nuclear power plants to reduce the assumed reactor power level used in esaluations of emergency core cooling system (ECCS) performance.

Under the proposed rule, licensees would be given the option to apply a reduced margin for ECCS evaluation or to maintain the value of reactor power currently mandated in the

! regulation. This action would allow interested licensees to pursue small, but cost-beneficial,

' power uprates and would reduce unnecessary regulatory burden without compromising the margin of safety of the facility.

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. DATES: The comment period expires on (75 days afterpublication in the Federal Register).

Comments received after this daie will be considered if it is practical to do so but the NRC is

- able to assure consideration only for comments received on or before this date, i

L ADDRESSES: Mail written comments to: Secretary, U.S. Nuclear Regulatory Commission, Washington,' D.C. 20555-0001, Attention: Rulemakings and Adjudications Staff, Mail Stop O-16C1.

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. Deliver written comments to: One White Flint North,11555 Rockville Pike, Rockville, Maryland between 7:30 a.m. and 4:15 p.m. on Federal workdays.

Documents related to this rulemaking may be examined at the NRC Public Document 1

Room,2120 L Street, NW. (Lower Level), Washington, D.C. Documents also may be viewed I I

and downloaded electronically via the interactive rulemaking Web site established by NRC for i

this rulemaking (see the discussion under Electronic Access in the Supplementary Information i

section). .Obtain single copies of the environmental assessment and the regulatory analysis from the NRC contact given below.

. FOR FURTHER INFORMATION CONTACT: Mr. Joseph E. Donoghue, Office of Nuclear

5 actor Regulation, U.S. Nuclear Regulatory Commission, Washington, D.C. 20555-0001; l . telephone

301-415-1131; or by Internet electronic mail to jed1@nrc. gov.

SUPPLEMENTARY INFORMATION:-

Background

A holder of an operating license (i.e!, the licensee) for a light-water power reactor is I 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 i

- 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.

s LOCA" (often termed a ,"best-estimate analysis"), or they may develop a model that conforms L s.

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with the requirements of Appendix K to 10 CFR Part 50. Most ECCS evaluations are based on

. Appendix K requirements. The opening sentence of Appendix K establishes the requirement

l. l l . to conduct ECCS analyses at a specified power level: "It shall be assumed that the reactor has i been operating continuously at a power level at least 1.02 times the licensed power level (to

. allow for such uncertainties as instrumentation error)." 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 would justify a reduced margin between the licensed power level and the power level assumed for ECCS

. evaluations. The proposed rule would revise this provision in Appendix K, thereby allowing j licensees the option of using a value lower than 102 percent of licensed r ower in their ECCS  !

I analyses m justified.

Several licensees have expressed interest in using updated feedwater flow measurement technology discussed later in " Calorimetric Uncertainty and Feedwater Flow  ;

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Measurement" as a basis for seeking exemptions from the Appendix K power level requirement and to implement power uprates. One licensee, Texas Utilities Electric Company

. (TUE), has obtained an exemption from the Appendix K requirement for Comanche Peak Units  ;

1 and 2 and is pursuing an increase in licwsmi 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 proposed rule.

L The objective of this rulemaking is to reduce an unnecessarily burdensome regulatory

requirement. Appendix K was 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 1

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features and requirements of the evaluation models and by the ECCS performance criteria.  ;

LThe existing regulation does not require that the power measurement uncertainty be demonstrated, but rather mandates a 2-percent margin to account for uncertainties, including I those expected to be involved with measuring reactor power. By allowing licensees to justify a smaller margin for power measurement uncertainty, the proposed rule does not violate the i

underlying purpose of Appendix K.' The intent of Appendix K, to ensure sufficient margin to  !

ECCS performance in the event of a LOCA', would still be met because of the substantial I conservatism of other Appendix K requirements. The proposed rule would not significantly i

affect plant risk, as discussed in the section entitled, "ECCS Evaluation Conservatism."  !

- Another objective is to avoid unnecessary exemption requests. As discussed above, a licensee has obtained an exemption from the 2-percent margin requirement in 10 CFR Part 50, Appendix K. It is likely that additional exemption requests will be submitted. Revising the rule i

to remove the need for licensees to obtain exemptions is considered by the NRC to be a l

l prudent regulatory action.

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If adopted, the proposed rule would give licensees the option of applying a reduced l; - margin between the licensed power level and the assumed power level for ECCS evaluation, I

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 existing rule appears to be based solely on considerations associated with

. - power measurement extant at the time of the original ECCS rulemaking. If licensees can show that the uncertainties associated with power measurement instrumentation errors are less than

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2 percent, thereby justifying a smaller margin, then the curront rule unnecessarily restricts operation.

Making this change to the rule would give licensees the opportunity to use a reduced margin if they determine that there is a sufficient benefit. Licensees could 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 would be in modifying fuel management strategies (e.g., possibly by altering core power peaking factors).

However, the proposed 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).

In the short term, the NRC intends to grant exemptions to the assumed power level provision of Appendix K for properly supported exemption requests. In addition to satisfying the provisions of 10 CFR 50.12, properly supported exemption requests are expected to quantify the uncertainties associated with measuring reactor thermal power that are associated with the current 2-percent power margin.

i in the longer term, the NRC intends to review the affected safety analysis guidance and L

will evaluate the impact of the proposed rule on those safety analyses. Further, the NRC is

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considteg the need for specific guidance to help licensees appropriately account for power measurement u.1 certainty in safety analyses. However, the NRC expects that power uprate amendment requests based on the proposed rule will address the suitability of non-LOCA analyses for operation at proposed higher power levels.

In addition to comments on the proposed rule, the NRC is seeking comments on the specific issues set forth below under " Issues for Public Comment."

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 assumptlons 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),

(S)" 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 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 Maody model and the discharge coefficient that yields the highest peak j l

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 is to assume that the reactor is operating at 102 percent power when the LOCA occurs "to allow for such uncertainties as instrumentation error... " { Appendix K,Section I.A., first sentence, emphasis added). The phrase, "such as," suggests 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, CLl-73-39,6 AEC 1085 (December 28, 1973)' Neither the statement of considerations (SOC) for the final rule nor the Commissian i

l decision appear to provide specific basis for the required assumption of 102 percent power.

The SOC for the final 1974 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 l

, 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

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contribute to the conservative nature of the evaluations and the criteria are as follows:

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(1) Stored heat. The assumption of 102 percent of maximum l power, highest allowed peaking factor, and highest estimated l thermal resistance between the UO2 and the cladding provides a calculated stored heat that is possible but unlikely to occur at the j time of a hypothetical accident. While not necessarily a margin

.. over the extreme condition, it represents at least an assumption l that an accident happens at a time which is not typical.

l 39 FR at 1002'(first column)'. 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 l

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 l the 102 percent assumed power level is intended to compensate.

l 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 l than instrumentation uncertainties.Section I of the Commission decision was the basis for the SOC discussion on the 102 percent assumed power level (Sa; 5 KEC at 1093-94). Section 111. A. of the Commission's decision," Required and Acceptable Features of the Evaluation j

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

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~ Model," does not offer a detailed technical the basis for the power level chosen, but instead uses the language ultimately adopted in the final Appendix K rule :

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L 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 I

other than those associated with the instrumentation for measurement of power level.

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.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 (CLl-73-39,6 AEC 1085, December 28,1973) citeJ 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

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decision as Exhibit 1137 was " Redirect and Rebuttal Testimony of Dr. Donald H. Roy on L

y 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 .

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. 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 1C' percent assumption is attributed to " uncertainties inherent in the measurement of the operating powerlevel of the core,"(page 144 of the Concluding Statement). Reasons for choosing 102-percent as the value are not discussed.

When Appendix K vias first issued, as is the case today, the thermal power generated by a nuclear power plant was determined by steam plant calorimetrv, which is the process of j l

performing a heat balance around the nuclear steam supply system (called a calorimetric). j The heat balanca depends upon measurement of several plant parameters, including flow rates and fluid temperatures. The dif arential pressure across a venturi installed in the feedwater flow path is a key element in the calorimetric measurement. Licensees have 1 l

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. proposed using instrumentation other than a venturi-based system to obtain feedwater flow

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rate for calorimetrics. The lower uncertainty associated with the new instrumentation is information that was apparently not available during the original Appendix K rulemaking.

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- 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.

Proposed Reduction in 102 Percent Assumed Power Level The Commission believes that other requirements of Appendix K modeling include 1 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 substantial conservatisms. 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 L

Research for Realistic LOCA Analysis," December 1988, contains the technical basis for

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L 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 evaluatio'ns. Chapters 7 and 8 of the NUREG incinde consideration 4

' of the changesJn licensed power level that could result from application of best-estimate i

- evaluation methods. The discussion includes an estimated sensitivity of predicted peak clad i 1

temperature associated with changes in pre-accident power level. From that estimate, the NRC expects peak cladding temperature changes of approximately 15'F to result from 1-percent changes in plant power level that could result from the proposed rule.

In view of: (i) substantial conservatisms embodied in the Appendix K requiremerts 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 temperhtures to assumed power level, the Commission concludes that it is )

i 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

Commisejon proposes tc amend the Appendix K requirement for an assumed 102 percent power level. The propossa rule would allow a licensee to use an assumed power level of less than 102 percent (but not less than 100 pc rent), provided that the licensee has determined  !

that the uncertainties in the measurement of core power level justifies the reduced margin. l l

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l l Calorimetric Uncertainty and Feedwater Flow Measurement i

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! 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 l

l feedwater flow measurement technology at the plant. As indicated, the prospect of additional licensees requesting similar action has prompted the proposed 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 nuclearinstruments, that provide a measurement of neutron flux. The nuclear instruments must be periodically calibrated to counteract the effects of changes in flux pattem, fuel bumup, 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 l determine core thermal power and is the basis for the calibration. The differential pressure I

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.

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i The system in use at Comanche Peak Units 1 and 2 is the Leading Edge Flowmeter l

(LEFM), manufactured by Caldon, Inc. The LEFM system i.s an ultrasonic flow meter that l ,

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 t

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I 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 l

safety evaluations issued by the NRC staff on March 8,1999, and May 6,1999.

ABB Combustion Engineering has expressed interest in the proposed rule because its flow-measuring systero, known as Crosstlow (which is also an ultrasonic flow-measuring device), is expected to be part of a licensee exemption request in the near future.

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issues for Public Comment The NRC is seeking comments from the public on the following issues related to this proposed rule:

1. The current rule states that the required 2-percent analysis margin is to account 1

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for "such uncertainties as instrumentation error...." (emphasis added). Thb suggests that the 2-percent margin was intended to account for other sources of uncertainty in addition to instrumentation error. However, explicit i 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 l Commission is interested !n whether there are other sources of uncertainty, j i

relevant to sources of heat following a LOCA, that should be considered when j i

licensees seek to reduce the margin in the Appendix K requirement for assumed power. If other contributors ste suggested, a clear technicaljustification should accompany the suggestion.

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2.' - Are there rulemaking attematives to this proposed mie that were not considered in the regulatory analysis for this 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 j error of 1 percent in power level be presumptive of an acceptable reduction in assumed power margin of 1 percent?

4. How should the proposed rule address cases in which licensees determine that power measurement instrument error is greater than 2 percent?

Section-by-Section Analysis i

Appendix K to Part 50 - ECCS Evaluation Models (I)(A) - Sourres of heat during the LOCA This section would be amended by romoving words from the first sentence in the I 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  !

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- indicates that licensees may assume a power level lower than 102 percent, but not less than I

100 percent, provided that the proposed lower attemative value can be shown to account for I core thermal power measurement instrumentation uncertainty. l i

App 4ndix K, Part ll (1)(a) requires that the values of analysis parameters or their basis be sufficientiv documented to allow NRC' review. The requirement applies to all analysis input parameters, including'those related to other plant instrumentation, such as temperature and

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16-pressure. Changes to other inputs are documented in the same manner as the power measurement uncertainty would be documented under the proposed rule. NRC review and approval is not necessarily needed to change a parameter in an approved ECCS evaluation model. Estimated changes in ECCS performance due to revised analysis inputs are reported l

' under $ 50.46 (a)(3), at least annually. As discussed in the Statement of Considerations for

Appendix K (53 FR 36001, September 16,1988), the annual reports keep NRG apprised of l changes. This should ensure that the NRC staff can judge a licensee's assessment of the

~s ignificance of changes and maintain cognizance of modifications made to NRC-approved evaluation models. The licensee must include revised parameters and other changes in the I l

! ECCS evaluation as required by 9 50.46 (a)(3) when a single change or an accumulation of l

l changes is expected to affect peak cladding temperature by 50*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).

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 pararneters involved in the uncertainty analysis, would be submitted for NRC review l

_ and approval before being used. These requests are expected because most licensees have adopted Generic Letter 88-16, " Removal of Cycle-Specific Parameter i imits from Technical Specifications.". The generic letter provided guidance for licensees to trar-'or cycle-specific h

. 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 leantifies NRC-reviewed and approved methods used  ;

to determine core' operat;ng limits (e.g., topical reports). Because a number of core operating

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. limits are based on LOCA analysis results, ECCS evaluation methods are included in the technical specification listc Therefore, most licensees opting to use the relaxation in the

, proposed rule would need to revise technical specifications to include a reference to an NRC-approved topical report that includes the uncertainty analysis justifying reduced power measurement uncertainty.

. An additional technical specification consideration for licensees pursuing changes

- based on the proposed rule could involve nuclear instruments (NI) requirements. Existing plant technical specifications include surveillance requirements to calibrate the power range Nis based on the calorimetric measuring reactor thermal power. The Nls pr. vide the indication

- of reactor power used as an input for safety systems. Licensees obtaining the relaxation offered in the proposed 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  ;

i would be placing a condition on an input to the calorimetric. The Nl calibration required by the i

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 became inoperable), the calorimetric would no longer be a valid source of calibration for the Nls. Licensees would need to take action to maintain compliance with their technical specification, for example, by using

.- i an attemate input to the calorimetric. The power measurement uncertainties associated with the attemate input would then apply and the plant would need to adjust its operating condition I (possibly lower its operating power level) to satisfy the proposed rule and to maintain the

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validity'of applicable safety analyses.

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-18 Referenced Documents Copies of GL-88-16 and CLI-73-39 are available for inspection and copying for a fee at

. the NRC Public Document Room,2120 L Street, NW. (Lower Level), Washington, D.C.

Electronic Access You may a!so submit comments via the NRC's interactive rulemaking Web site, "Rulemaking F9 rum " through the NRC home page (http://ruleforum.llnl. gov). This site enables people to transmit comments as files (in any format, but Wordperfect version 6.1 is preferred),

if your Web browser supports that function. Information on the use of the Rulemaking Forum is available on the Web site. For additional assistance on the use of the interactive rulemaking site, contact Ms. Carol Gallagher, telephone: 301-415-5905; or by Intemet electrcnic mail to i cag@nrc. gov.

I Plain Language The Presidential memorandum dated June 1,1998, entitled, " Plain Language in l 1

Government Writing,' directed that the govemment's writing be in plain language. This memorandum was published June 10,1998 (63 FR 31883). In complying with this directive, editorial char'oes have been made in this proposed amendment to improve readability of the l existing language of the provisions being revised. These types of changes are not discussed l

- further in this documed. The NRC requests comment on the proposed rule specifically with )

respect to the clarity and effectiveness of the language used. Comments should be sent to the address listed under the ADDRESSES caption of the preamble.

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Voluntary Consensus Standards The National Technology Transfer Act of 1995, Pub. L.104-113, requires tnat Federal I

l agencies use tech :ical standards that are developed or adopted by voluntary consensus standards bodies unless the use of such a standard is inconsistent with applicable law or l l

l otherwise impractical. In this proposed rule, the NRC is proposing to provide holders of operating licenses for nuclear power plants with the option of reducing the assumed reactor 1

power level used in ECCS evaluations. This proposed action constitutes a modification to an l l

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;nstead of the proposed government-unique standard. The NRC will consider using a voluntary consensus standard if an appropriate standard is identified. If a voluntary consensva standard is identified for consideration, the submittal must explain how the voluntary consensus standard is comparable and why it should be used instead of the proposed govemment-unique standard.

Finding of No Significant EnvironmentalImpact: Availability The NRC has determined under the National Environmental Policy Act of 1969, as I amended, and the NRC's regulations in Subpart A of 10 CFR Part 51, that this regulation, if adopted, would not be a major Federal action significantly affecting the quality of the human environment and, therefore, an environmental impact statement is not required.

i The proposed 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 would result from the proposed rule, because licensee actions based on r

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the proposed rule would not significantly increase the probability or consequences of

' accidents; no changes would be made in the types of any effluents that may be released off site; and there would be no significant increase in occupational or public radiation exposure.

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Therefore, there are no significant radiological environmental impacts associated with the proposed action. The proposed action does not involve non-radiological plant effluents and  !

has no other environmental impact. Therefore, there are no significant non-radiological environmentalimpacts associated with the proposed action.

The determination of the environmental assessment is that there would be no l

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significant offsite impact on the public from this action. However, the general public should note that the NRC welcomes public participation. 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

-l February 11,1994. . The NRC has determined that there are no disproportionately high and adverse impacts on minority and low-income populations, in the letter and spirit of E.O.

12898,' the NRC is requesting public comments on any environmental justice considerations or l

questions that the public thinks may be related to this proposed rule, but that somehow were I not addressed. The NRC uses the following working definition of environmentaljustice:

i Environmenta/ 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 environmentallaws, regulations, and policies. Comments on any aspect of the environmental assessment, including environm6r. tai justice, may be submitted to the NRC as indicated under the ADDRESSES heading.

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- The draft environmental assessment is available for inspection at the NRC Pub';c Document Room,2120 L Street NW. (Lower Level), Washington, D.C.' Single copies of the environmental assessment are available from Mr. Joseph Donoghue, Office of Nuclear Reactor Regulation, U.S. Nuclear Regulatory Commission, Washington, D.C. 20555-0001, telephone: 301-415-1131, or by Internet electronic mail to JEDi@nrc. gov, Paperwork Reduction Act Statement This proposed rule increases the burden on licensees opting to use a reduced power level assumption for ECCS analysis (i.e., below 102%) to include the change in their annual report required under 10 CFR 50.46 (a)(3)(ii). The public burden for this information collection is estimated to average one-half hour per response. Because the burden for this information collection is insignificant, Office of Management and Budget (OMB) clearance is not required.

- Existing requirements were approved by the Office of Management and Budget, approval number 3150-0011.

Public Protection Notification If a means used to impose an information collection does not display a currently valid 1

OMB control number, the NRC may not conduct or sponsor, and a person is not required to '

respond to, the information collection.

Regula%ry Analysis The Commission has prepared a regulatory analysis on this regulation. Interested persons may examine a copy of the regulatory analysis at the NRC Public Document Room,

-2120 L Street NW. (Lower Level), Washington, D.C. Single copies of the analysis are )

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! available from Mr. Joseph Donoghue, Office of Nuclear Reactor Regulation, U.S. Nuclear Regulatory Commission, Washington, D.C. 20555-0001, telephone: 301-415-1131, or by Internet electronic mail to JED1@NRC. GOV.-

i Regulatory Flexibility Certification As required by the Regulatory Flexibility Act of 1980, 5 U.S.C. 605(b), the Commission ceitifies that this proposed rule, if adopted, would not have a significant economic impact on a substantial number of small entities. This proposed rule would affect only the licensing and operation of nuclear power plants. The companies that own these plants do not fall within the i 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 proposed rule and that a backfit analysis is not required for this proposed rule because the

change does not involve any provisions that would impose backfits as defined in 10 CFR 50.109(a)(1). The proposed rule would establish 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 proposed rule does not i

impose a new requirement on current licensees and therefore, does not constitute a backfit as I

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' defined in 10 CFR 50.109(a)(1).-

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. .. c 23-List of Subjects in 10 CFR Part 50 Antitrust, Classified Information, Criminal Penalties, Fire Protaction, Intergovernmental Relations, Nuclear Power Plants and Reactors, Radiation Protection, Reactor Siting Criteria, Reporting and Recordkeeping Requirements.

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). 1 l

Section 50.7 also issued under Pub. L.95-601, sec.10,92 Stat. 2951 (42 U.S.C. l 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 abo issued under sec. 204, 88 Stat.124u (42 U.S.C. 5844). Sections 50.58,50.91, and 50.92 also issued under Pub. L.  ! 415,96 Stat. 2073 (42 U.S.C. 2239) . Section 50.78 also issued under sec.122,68 Stat. i

- 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)..

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2. Appendix K to Part 50 is amended by revising the beginning of paragraph I. A.,

? Sources of heat during the LOCA," to read as follows -

Appendix K to Part 50 - ECCS Evaluation Models

1. Required and Acceptable Features of the Evaluation Models 1

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 j 1

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 tht Mvpsed altemative value has been demonstrated to account for uncertainties due to power level instrumentation error. A range of power distribution shapes -

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and peaking factors representing power distributions that may occur over the core lifetime i

must be studied. The selected combination of power distribution shape and peaking factor-should be the one that results in the r.ast severe calculated consequences for the spectrum of

< postulated breaks and single failures that are analyzed. l Dated at Rockville, Maryland, this,_ day of .1999.

For the Nuclear Regulatory Commission.

Annette Vietti-Cook,

. Secretary of the Commission.

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ENVIRONMENTAL ASSESSMENT REVISION OF 10 CFR PART 50, APPENDIX K -

This document examines the environmental impacts of its regulatory actions in

- accordance with 10 CFR Part 51, for a rulemaking addressing NRC's current emergency core cooling systems (ECCS) evaluation requirements for nuclear power reactors. NRC is proposing to modify these requirements, which are contained in Appendix K to 10 CFR Part

.50. The proposed rule would provide a voluntary option for licenseps to appiy a reduced margin between the licensed power level and the assumed power level for ECCS evaluation.

The currently required analysb margin is 2 percent of licensed reactor power.

NRC's regulations for implementing Section 102(2) of the National Environmental Policy Act of 1969 (NEPA), as amended, are contained in Subpart A of 10 CFR Part 51.

These regulations require that an environmental impact statement or an environmental assessment be prepared for all licensing and regulatory actions that are not classified as

" categorical exclusions"in accordance with 10 CFR 51.22(c) and are not identified in 10 CFR 51.22(d) as other actions not requiring environmental review.

This document presents the findings of NRC's environmental assessment of the proposed rule.

Identification of the Proposed Action 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 ECCS performance under accident conditions. Section 50.46," Acceptance criteria for emergency core cooling systems for light-water nuclear power reactors," requires that ECCS performance under loss-of-coolant accident (LOCA) conditions be evaluated and that the estimated performance satisfy certain criteria. Licensees mey conduct an analysis

. that " realistically describes the behavior of the reactor system durir.g a LOCA" (often termed a "best-estimate analysis"), or they may develop a model that conforms with the required and u . acceptable features of Appendix K to 10 CFR Pari 50. Most ECCS evaluations are based on Appendix K requirements. The opening sentence of Appendix K establishes the requirement to conduct ECCS analyses at a specified power level: "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)."

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L The proposed rule would give licensees the option to apply a reduced margin between i the licensed power level and the assumed power level for ECCS evaluation. The current margin of 2 percent power may be maintained, if preferred. If licensees can show that the uncertainties associated with power measurement instrumentation errors are less than 2 percent, and a smaller margin can be justified, then the current rule unnecessarily restricts operation of some faci!ities by limiting their ability to operate at higher power levels, and in  !

other cases by imposing unnecessary requirements on ECCS performance.

- Appendix K to 10 CFR Part 50 was written to define conservativa analysis assumptions  !

- for ECCS performance evaluations during' design-basis LOCAs. Large margins for important l I

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safety parameters were provided by conservatively selecting the ECCS performance criteria as well as conservatively establishing ECCS calculational requirements. The staff has long recognized that Appendix K incorporated substantial conservatisms and previously had considered methods that would acceptably reduce safety margins. The conservatisms were necessary when the rule was written because of a lack of experimental evidence at that time.

When the NRC adopted changes to 10 CFR 50.46 to allow "best-estimate" modeling, it concluded that experimental evidence gained since the original rule was implemented and analysis advances allowed the consideration of alternative approaches. In the proposed rule,

. the staff is extending the application of its understanding of ECCS evaluation conservatism to allow relaxation of one of several conservative analysis features.

i The current analytical approach of assuming 102 percent of licensed power for ECCS evaluation is adequate to protect public health and safety; therefore, the NRC does not intend to backfit a change to the regulation on operating reactors. Because the proposed revision would not constitute a backfit, the bases for current ECCS evaluations mest be preserved.

Therefore, the revision will retain the current requirement as an option for licensees.

Need for the Proposed Action The objective of this rulemaking is to allow the voluntary relaxation of an unnecessarily burdensome regulatory requirement. Appendix K was 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. By allowing a smaller margin for power measurement uncertainty, the proposed rule does not undermine the underlying purpose of Appendix K.

A secondary objective is to avoid unnecessary exemption requests. The staff has previously sought rule changes to avoid the prospect of multiple exemption requests. In the i case'of this proposed change to Appendix K, the staff is anticipating recurrent exemptions and has determined that revising the rule at this early stage will be the best course. ,

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Environmentalimpacts of the Proposed Action The proposed rule would affect an analysis assumption for ECCS evaluation, not actual -

' LOCA effects. Use of a reduced power margin alone cannot affect core damage frequency, the large early release frequency, or actual accident release consequences. The actual accident sequence ano progression of a LOCA are not changed unless the licensee modifies its facility. However, the proposed rule may have indirect effects on the environment by allowing licensees to pursue changes to their facilities such as increases to licensed power.

The most obvious change a licensee might pursue under the proposed rule is to increase the licensed power of the facility without conducting ECCS evaluations at a higher 7 power level. Licensees requesting higher licensed power levels are required to assess b . environmental effects of the change. However, the NRC expects only neglyjible effects on the environment from small power level changes, such as those that are likely to result from the proposed rule. The NRC previously considered the effects of smallincreases in licensed

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power level and concluded that such changes would present little change in risk. In NUREG-1230 (Reference 2), the staff considered the risk impact of changes associated with -

the revised ECCS rules allowing best-estimate analyses, including power increases, and determined that a power level increase of 5 percent or less had little risk significance. This conclusion was, in part, based on the staff's estimate that a small power level increase would only slightly increase the fission product inventory. Also, the staff judged that a slightly higher power would not appreciably alter the potential for LOCAs or affect predicted accident

- progression.

The staff also considered the risk impact from boiling water reactor extended power -

' uprates, which are much greater than the marginal power change expected under the proposed rule. In these cases, the staff concluded (Reference 3) that extended power uprates are expected to only slightly affect the risk profile of a plant. The staff also stated that marginal power uprates, of about 1 percent, were not expected to require an assessment of plant risk.

An overall affect of a power uprate for a large number of plants is the possible increase

. In the amount of spent fuel generated by operating at higher power. For the purposes of this assessment, the staff assumed a linear relationship between power level and amount of fuel discharged, and a 1-percent power level increase for 50 plants. Using information on predicted fuel discharges contained in the " Generic Environmental Impact Statement for License Renewal of Nuclear Plants"(Reference 4), the staff estimated that a marginal power increase for half the operating plants would amount to a total of approximately 70 additional discharge fuel bundles per year. This is less than the number of fuel bundles discharged during a typical reactor refueling for a plant. There is a potsntial cumulative effect associated with the anticipated annual increase in discharged fuel.' However, it is not conside*ed significant in light of the cumulative level of all fuel discharges during the lifetime of an operating facility._

Under the proposed rule, some licensees could realize savings without seeking power uprates.. By revising their ECCS analysis based on a lower assumed power level, licensees could gain margin that could lead to a relaxation in requirements for LOCA mitigation system (i.e., ECCS) performance or in core operating parameters. Changes to technical specifications requirements for ECCS system performance will require license amendments and licensees will need to determine environmental impactsc in these cases involving relatively small changes to ECCS analyses', the staff expects that no significant environmental impact would result.

The proposed action, as well as its indirect and cumulative effects, would not increase the probability or consequences of accidents; no changes are being made in the types of any

~ effluents that may be released off site; and there is no significant increase in occupational or public radiation exposure. Therefore, there are no significant radiological environmental impacts associated with the proposed action. The proposed 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 proposed action.

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l Alternatives to the Proposed Action l

As required by Section 102(2)(E) of the NEPA (42 U.S.C.A. 4332(2)(E)), the NRC has l considered possible altematives to the proposed action. The staff considered the following rulemaking options: (1) maintain the provision requiring an analysis margin to account for l uncertainty in power measurement but remove the specification of the 2-percent value for the )

margin and require licensees to assess power measurement uncertainty; (2) eliminate the requirement for a margin between power level and assumed power, disregarding power ,

measurement uncertainty; and (3) broadly revise Appendix K, addressing several conservative i parameters.

The altemative of retaining the existing assumed power requirement (i.e., no-action altemative) would essentially have the same environmental impact as rulemaking altematives 1 and 2 if licensees pursued exemptions from the current Appendix K requirement. Under the j no-action attemative, licensees could also consider the more costly altemative of implementing a best-estimate ECCS evaluation under 6 50.46. However, fewer licensees are expected to take this course, because if there currently were sufficient benefit, they would have already done so. The potential power increase under a best-estimate evaluation is expected to be ,

greater than the marginal power increase associated with the proposed rule. However, the I fewer licensees that would use this option reduces the resulting overall environmental impact.

The staff assumed that the environmental impact for either scenario under the no-action attemative would be roughly equivalent.

The environmental effects for the first two attematives would be roughly equivalent, because about the same number of licensees would seek benefits under any change that would allow a relaxation in the requirement. The main distinction between these attematives is the course taken to revise the rule. But the end result is the sa ne, in that a marginal power increase would be an indirect result. As discussed earlier, the staff considers marginal power increases to present little risk on a plant-specific basis and the overall effect of increased spent fuel generation is considered small.

The final rulemaking option, to broadly revise Appendix K requirements, could allow greater increases in licensed power for operating plants. However, since there is not a clear understanding of the magnitude of the changes that might result, the staff can only speculate that such a revision would lead to power uprates somewhat greater than those expected under the proposed rule change. The resulting power increases may be commensurate with those

. associated with previous changes considered by the staff, such as those discussed in NUREG-1230, which were not considered risk-significant.

Therefore, none of the attematives considered by the staff is expected to significantly  ;

affect the environment.  !

I Agencies and Persons Consulted The NRC developed the proposed rule and this environmental assessment. The proposed rule will be published in the Federal Register for all interested parties to review. All

comments received within the stated time limit will be considered in developing the final rule.

The NRC is sending this environmental assessment to all State liaison officers for comment.

Finding of No Significant impact

.On the basis of the environmental assessment, the Commission concludes thet the proposed action will not have a significant effect on the human environment. Accordingly, the Commission has determined not to prepare an environmental impact statement for the proposed action.

Also, the NRC is committed to following Executive Order 12898, " Federal Actions To Address Environmental Justice in Minority Populations and Low-Income Populations," dated February 11,1994. Since there are no significant offsite impacts on the public from this action, the NRC has determined that there are no disproportionately high and adverse impacts on minority and low-income parties. The NRC uses the following working definition of environmental justice: Environmentaljustice 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.

References

1. . Code of Federal Regulations, Title 10, Chapter I, Parts 50 and 51.

2. U.S. Nuclear Regulatory Commission, " Compendium of ECCS Research for Realistic LOCA Analysis," NUREG-1230, Washington, D.C., December 1988.

3. U.S. Nuclear Regulatory Commission, Letter from EDO to ACRS, " Staff Response to

'ACRS Letter of July 24,1998 on General Electric Nuclear Energy Extended Power Uprate Program and Monticello Nuclear Generating Plant Extended Power Level increase Request," September 14,1998.

4. U.S. Nuclear Regulatory Commission, " Generic Environmental impact Statement for License Renewal of Nuclear Plants," NUREG-1437, Volume 1, Washington, D.C.,

May 1996.

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