ML20206H206

SER Accepting Exemption to App K Re Leading Edge Flowmeter for Plant,Units 1 & 2

ML20206H206
Person / Time
Site:	Comanche Peak
Issue date:	05/06/1999
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20206H174	List: ML20206H170 ML20206H188 ML20206H206
References
NUDOCS 9905110089
Download: ML20206H206 (11)

Text

ps at:vq O t UNITED STATES

~'

jp j

t NUCLEAR REGULATORY COMMISSION Y*ASHINGTON. D.C. 30666 4001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION EXEMPTION TO APPENDIX K - LEADING EDGE FLOWMETER TEXAS UTILITIES ELECTRIC COMPANY COMANCHE PEAK STEAM ELECTRIC STATION (CPSESL UNITS 1 AND 2 DOCKET NOS. 50-445 AND 50-446

)

1.0 INTRODUCTION

I By letter dated August 13,1998 (Reference 1), as supplemented December 17,1998 (Reference 2), Texas Utilities Electric Company (TU Electric, the licensee) requested approval of a request for exemption from a requirement in Appendix K to Title 10 of the Code of Federal Reoulations o (10 CFR) Part 50. Based on the proposed use of a new feedwater flow measurement system to allow more accurate measurement of thermal power, the request seeks l an exemption to reduce the power level margin assumed for the emergency core cooling system i (ECCS) analysis required by Appendix K from the current value of 1.02 times the licensed power l level, to not less than 1.01 times the licensed power level.

2.0 DISCUSSION 2.1 Backoround in most nuclear power plants, operators obtain a continuous indication of core thermal power from nuclear instruments, which provide a measurement of neutron flux. The nuclear instruments must be periodically calibrated to counteract the effects of flux pattern changes, fuel burnup, and instrument drift. Steam plant calorimetry, which is the process of performing a heat balance around the nuclear supply system (i.e., 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 to measure flow is a key input to the calorimetric measurement.

The Caldon, Inc., Leading Edge Flowmeter (LEFM) System is an ultrasonic flow meter that measures the transit times of pulses traveling along parallel (chordal) acoustic paths through the flowing fluid. The LEFM System consists of spool pieces mounted in the feedwater lines. Each spool piece has four chordal acoustic paths to measure fluid velocity and sound velocity. One electronic unit serves up to four spool pieces and is specifically designed to provide flow and temperature measurements, as well as online verification of system performance. The LEFM technology has been employed in nonnuclear applications, such as the petroleum industry, 9905110089 990506 pDR ADOCK 05000445 PDR

~' ~

, chemical plants, and hydroelectric plants. Caldon, Inc.'s, Topical Report, ER-80P, " Improving Thermal Power Accuracy and Plant Safety While increasing Operating Power Level Using the

)

LEFM System," provides information on operating experience, reliability data, and instrument i uncertainty analysis to supplement its assessment of the safety impact of using the LEFM  !

System.  !

1 2.2 LEFM System History l Westinghouse Electric Corporation (Westinghouse) developed the LEFM System in the early 1970s, and it was first installed at Prairie Island Unit 2 to measure reactor coolant flow. ,

Westinghouse also sold LEFM systems to U.S. nuclear plants during the 1980s for use in correcting feedwater flow venturi readings, since corrosion and fouling can degrade venturi meter performance. Caldon, Inc., purchased the technology from Westinghouse in 1989 and developed an upgraded system capable of detecting degraded transducer signals and compensating for errors. The upgraded system was used to replace most of the originally installed Westinghouse systems. Caldon, Inc., developed an externally mounted version of the i system employing the same principles as the chordal system but not providing the same  ;

l accuracy.

In March 1997 (Reference 3), Caldon, Inc., submitted its topical report detailing the LEFM System (Reference 4) and requested that the Nuclear Regulatory Commission (NRC) review the I report to support power reactor licensee applications to increase licensed power levels.

On July 14,1998, the staff met with representatives of TU Electric and Caldon, Inc., to discuss licensing submittals for proposed power uprate license amendments. The licensee presented an overview of its proposed hcense amendments and submitted its request for an exemption to Appendix K (Reference 1). The licensee recently submitted a power uprate amendment l request.

2.3 Accendix K Backaround The Appendix K rule was written to ensure that adequate margin for ECCS performance would be available if a design-basis loss-of-coolant accident (LOCA) ever occurred (39 FR 1002, January 4,1974). The margin was provided by incorporating several conservative features into l

- the ECCS performance criteria as well as maintaining conservative requirements and  ;

recommendations for evaluation models. One conservative requirement is the 102 percent power assumption, which is part of the set of factors used to represent the souices of heat during the accident. The opening sentence of Appendix K,Section I.A., establishes the requirement to conduct ECCS analyses at a specified power level, stating that "it shall be assumed that the reactor has been operating continuously at a power level at least 1.02 times j the licensed power level (to allow for such uncertainties as instrumentation error)." As stated parenthetically in the rule itself, the requirement is imposed to account for uncertainties.

The basis for the requirement is discussed in the regulatory history for the rule, such as the  !

Statement of Consideration for Appendix K (39 FR 1002, January 4,1974). The 102 percent assumption is one of several items listed as conservative factors used to model the energy available from reactor operation. The Statement of Consideration also associates the

m preaccident power level assumption with the modeling of the rate of heat generation after the LOCA occurs. A comparison is made between the estimated uncertainty associated with the decay heat assumption (i.e.,20 percent above the American Nuclear Society (ANS) standard) and the estimated effect on heat generation resulting from the 102 percent power assumption.

This is a natural connection since the preaccident power level directly affects the decay heat

. generation rate after reactor shutdown.

When it was considering changes to Appendix K to accept the use of best-estimate evaluations, the staff understood that the rule incorporated substantial conservatisms (see SECY 83-472, Emergency Core Cooling System Analysis Methods," November 17,1983). These conservatisms were necessary when the rule was written because of limited experimental evidence. The major analysis inputs and assumptions that contribute to the conservatism in Appendix K are grouped together under Sections A through D of the rule: (A) Sources of Heat During the LOCA (the 102 percent power provision is one 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 assure conservatism in the analysis results. For instance, under sources of heat during the LOCA, in addition to the 102 percent requirement, decay heat is modeled on the basis of an ANS 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. As discussed in SECY-83-472, experimental programs provided ample data, which shed light on the considerable margin provided by Appendix K, giving the staff confidence to consider alternative ECCS evaluation models.

2.4 Current Licensina Basis CPSES conforms to the Appendix K requirement since the analyses of ECCS performance for the plant were conducted assuming that the reactor had been operated at a power level of 102 percent of licensed power. The licensing-basis analysis for a LOCA is discussed in

' Sections 4 and 15 of the CPSES Final Safety Analysis Report (FSAR), which references topical reports that describe the analysis methods and assumptions. The FSAR cites a TU Electric topical report (Reference 5) and FSAR Section 15.6 that both state that the assumption used for reactor analysis during the large break LOCA is 1.02 times reactor power level. The licensing basis for small break LOCA analysis is contained in another TU Electric topical report

. (Reference 6), which uses the analysis assumption of 1.02 times reactor power level. The peak cladding temperatures (PCTs) given in the FSAR for each unit are listed as follows:

Peak Cladding Temperature Results from LOCA Analyses Unit 1 Unit 2  !

Small Break LOCA 1695*F 1781 'F Large Break LOCA 2013 'F 2119 'F

~

. a i- .

. ' 4-e:

3.0 EVALUATION

. 3.1 Acceptance Criteria The staff reviewed the exemption request against the criteria in 10 CFR 50.12, " Specific

. Exemptions," as well as applicable portions of Regulatory Guide 1.174, "An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Current Licensing Basis,". and Standard Review Plan (SRP) Chapter 19, "Use of Probabilistic

' Risk Assessment in Plant-Specific, Risk-Informed Decision Making: General Guidance."

. Section 50.12 allows exemptions to be granted to NRC regulations when specific criteria are

' met. These criteria are given in two parts in the rule, Sections 50.12(a)(1) and 50.12(a)(2).

Section 50.12(a)(1) gives basic requirements that the exemption must meet. It must:

. be authorized by law,

. not result in an undue risk to public health and safety, and-

. - be consistent with common defense and security.

Section'50.12(a)(2), provides six instances that are considered special circumstances warranting consideration of a rule exemption. The licensee's submittal addressed three of the special circumstcaces in Section 50.12(a)(2) of the rulp: (ii) application of the rule is not needed to achieve its underlying purpose, or (iv) the exemptich would result in a benefit to public health -

and safety that outweighs any potential safety degradation, or (vi) circumstances are present I which were not conaldered when the regulation was adopted. I In the licensee's submittal, information was providet vtisfying criteria (ii), (iv), and (vi), and ,

meeting the requirements of 10 CFR 50.12. Although only one of the instances demonstrating I special circumstances needs to be illustrated, the staff's evaluation considered each instance addressed in the licensee's submittal. l Since the exemption request constitutes a change to the licensing basis for CPSES, and the licensee submittal depends on risk insights in a limited fashion, the staff's evaluation used criteria contained in Regulatory Guide 1.174 and SRP Chapter 19 to determine the acceptability 1 of the safety impact of the proposed licensing basis change. Specifically, the staff determined that the proposed change:

. is consistent with the defense-in-depth philosophy, e maintains sufficient safety margins, and

'. results in only a small change in the risk of plant operation and is consistent with the intent of the Commission's safety goals.

3.2 Staff Evaluation L

l ' The licensee's exemption request offers four main points in support of the proposed action:

l>

. The requested exemption is authorized by law,

• No undue risk to public health and safety would result by allowing the exemption, l

, . 5-L

• Common defense and security would not be endangered,

. Special circumstances exist, in that:

_ (a) the underlying purpose of Appendix K will stiC be served under the exemption, (b) Allowing the exemption will benefit public health and safety that compensates for any decrease in safety that may result from the grant of the exemption, and (c) A material circumstance exists which was not considered when the rule was j adopted for which it would be in the public interest to grant an exemption. l

. The first three items address Section 50.12(a)(1) and the fourth item addresses Section 50.12(a)(2).

l The licensee uses the Caldon, Ir.c., topical report (Reference 4) throughout its submittal as the 1 basis for the technical arguments associated with the exemption request, and as the source of l much of the information to support the safety impact argument. In response to staff questions, the licensee supplemented its submittal (Reference 2), and included plant-specific information that was not included in the topical report. The staff evaluated the merits of each point raised in the licensee's submittal as discussed in the following paragraphs.' The staff's consideration of information presented in the Caldon, In :., topical report is discussed later in this safety

- evaluation.

3.2.1 Authorized by Law in explaining that the proposed exemption is authorized by law, the licensee stated that installation and use of the LEFM System is not prohibited. Appendix K and Section 50.46 do not prescribe how reactor power is to be measured, only that a certain power level be assumed for analysis. The licensee then provided instances where the Commission stated its understanding that Appendix K contained substantial conservatism, and that advances in technology would lead to reconsideration of the margins provided by Appendix K requirements. Further, the licensee stated that the exemption would be consistent with the approach used in Section 50.46,

" Acceptance criteria for emergency core cooling systems for light-water nuclear power reactors."

The staff has reviewed the applicable regulations and the regulatory history for Appendix K as )

well as for Section 50.46, and finds that those regulatory documents do not prohibit the licensee from using the LEFM System instrument. No other parts of the regulations require the power margin assumption, and the supporting materials for Appendix K (e.g., References 7-9) indicate that the Commission expected requests such as the one submitted by TU Electric and expected the staff to consider them.

3.2.2 Mo_ Undue Risk The licensee cites analyses in the Caldon, Inc., topical report (Reference 4) to support the claim I that use of the LEFM System instrument leads to a lower likelihood that plant power would be  ;

. above prescribed limits at the onset of a LOCA. The licensee concludes that relative to f conventional venturi-based flow measuring devices, there would be an overall increase in the j level of safety using the LEFM System, even while operating at a higher licensed power level.  !

s- The staff's evaluation of the safety impact of the proposed exemption appears in Section 3.3 of this evaluation.

4

g I'

L g

i l ..

l 3.2.3 Common Defense and Security Based on its review of the licensee's submittals, the staff concludes that use of the LEFM L System and an exemption from the 2 percent power margin requirement in Appendix K will not -

jeopardize the nation's common defense and security.

L 3.2.4 Underivina Purpose of Anoendix K By seeking to apply a smaller margin for power measurement uncertainty, the exemption does not violate the underlying purpose of Appendix K. Indeed, by quantifying a contributor to the uncertainty, which previously was not specifically known, the exemption may better serve the underlying purpose of the requirement. As discussed in Section 2.3 of this evaluation considering the background of Appendix K. the rule was devised to incorporate conservatisms in several areas of the analysis. The pwvv3el margin requirement is one factor involved with the sources of heat assumed for the 1./ 6 analysis. The current regulation does not require that the power measurement uncertainty be demonstrated. The regulation presupposes that the mandated margin is sufficient to account for uncertainties expected to be involved with measuring reactor power. Since the exemption request seeks only to reduce the specification in the requirement, and not to eliminate all margin accounting for uncertainty, the proposal does not undermine the purpose of the provision. In fact, by seeking the exemption, the licensee is undertaking to quantify the feedwater flow measurement accuracy, a contributor to the uncertainty in power measurement.

' ~

3.2.5 Safety Benefit As discussed in Sections 3.2.2 and 3.2.4 of this evaluation, the use of the LEFM System and the quantification of power measurement uncertainty appear to offer safety benefits in that they eliminate some of the uncertainty in the ECCS safety analysis.

Although there is a small safety impact expected from the associated power increase, it is not considered significant, as discussed later in this evaluation.

3.2.6 Material Circumstance The LEFM System and the quantification of power measurement uncertainty associated with use of the LEFM System constitute material circumstances that did not exist when the rule was written. The current Appendix K rule presumes that the 2 percent margin accounts for uncertainties associated with measurement of thermal power. Contributors to the uncertainty were not identified and the magnitude of the uncertainty was not demonstrated by experiment or analysis. As discussed earlier, the rule does not require quantification of actual uncertainties nor did the regulatory history for the rule discuss any detailed technical basis for the choice of a 2 percent margin.-

i 3.3 Risk Considerations l'

The staffs evaluation sought to determine if the licensee submitted information sufficient to satisfy the no " undue risk to the public health and safety" criterion of 10 CFR 50.12(a)(1)

n  ;

discussed in Section 3.1 of this evaluation. The staff structured this portion of the review following guidance in Regulatory Guide 1.174 and SRP Chapter 19; however, the application was not considered a risk-informed application as defined by the staff in Reference 10.

SRP Chapter 1g directs the staff to determine if licensee submittals meet the principles of risk-informed decision making. There are five principles listed in Section 11 of the SRP chapter, which are summarized below;

. The proposed change meets current regulations unless an exemption is requested,

. . The change is consistent with the defense-in-depth philosophy,

. The change maintains sufficient safety margin, If a proposed change results in a risk increase, that the increase be small and , >

consistent with the Commission safety goals, and j

= The impact of the change should be monitored.  !

l Because the submittal is an exemption request, and due to the limited nature of the submittal and the focus of the staff review, the staff evaluation considered only the second, third, and fourth items. I The exemption request seeks a reduction in an analysis margin mandated by the rule. The licensee submitted an assessment that is limited in scope, in that it addressed only the probability of the plant operating above a certain power level at the time of a LOCA. A power levelincrease could impact plant risk in several ways. The increased heat source can have an effect on anticipated transient without scram progression, containment analyses, ECCS analysas, and other accidents. The staff did not conduct a review of these areas as yet, but will consider them in conjunction with a review of the licensee's expected power uprate amendment request. Also, when the licensee requests an increased operating power level, the safety margin for other events, which may have also used the 1.02 power level assumption, will be reviewed in context of the overall impact on pient risk.

Additionally, the staff did not consider overall risk impacts in terms of influences on Individual l

. Plant Examination results that might result from utilization of the exemption to facilitate a power uprate. Again, such a broad consideration of plant risk effects is more appropriate during a review of a license amendment seeking a change to the licensed power level.

3.3.1 Defense-in-deoth -

SRP Chapter 19 discusses defense-in-depth in terms of maintaining a balance among core damage prevention, containment failure, and consequence mitigation, in the context of the requested exemption to Appendix K, consequence mitigation as considered in a LOCA analysis is most directly affected. To maintain consistency with the defense-in-depth philosophy, the proposed exemption should not result in a substantial change in the effectiveness of barriers to fission product release that could result from a LOCA.

A principal effect of increased power would be an increase in fission product inventory, primarily the inventory of short-lived isotopes. This issue was considered when Section 50.46 was

e

. amended to allow alternative ECCS analysis methods (see 53 FR 35996, September 16,1988).

. Fission product inventory is a complex function of power level and time at power, but to a first approximation, the inventory increase will be proportional to the increase in power level.

Therefore, a 1 percent power increase could be expected to result in a 1 percent increase in fission products available for reiesse. Although fission product inventories can be predicted l reasonably accurately, analysis ut fission product transport from the fuel to the environment involves uncertainties, which are considered large with respect to the change in source term

- anticipated from a small power level increase. LOCA analysis release assumptions given in Regulatory Guides 1.3 and 1.4 are quite conservative and are expected to account for such a smallinventory change.

A slightly higher power level will result in a small increase in decay heat load that could affect required response time of the ECCS and the available operator response time following -

transients and accidents. Results of core and containment consequence analyses from higher l power levels could also be affected. However, NUREG-1230 (Reference 11) considered the I risk impact of changes associated with the revised ECCS rules, including a power increase, and considered a power change of 5 percent or less to have little risk significance.

I Another aspect of defense-in-depth concems the ability of the plant to safely sustain a failure of l a component or system. Information presented by the licensee concerning failure effects of the system were not integral to the staff evaluation of the exemption request. However, although

. the LEFM System is not considered a safety-related system, the staff's evaluation of a power uprate request may need to consider failure effects to determine the overall risk implications of the proposed power increase. l 3.3.2 Safety Marain Since the licensee's proposal centers on a margin used in safety analyses, the effect on safety margin is central to the staff's consideration of the proposed exemption. SRP Chapter 19 directs that any reduction in margin should appropriately reflect understanding of the ]

uncertainties involved and the potentialimpact of the proposed change. The licensee submitted information in the Caldon topical report (Reference 4) and in responses to staff questions (Reference 2) regarding the expected effect of employing the LEFM System and reducing the safety analysis margin.

)

3.3.2.1 LEFM System Benefit The staff reviewed applicable portions of the topical report (Reference 4), particularly those conceming the determination of uncertainty for the LEFM System and venturi-based flow i instruments and the comparison of the effect of associated uncertainties on the determination of l thermal power. The staff's review in this area focused on Sections 5,7, and 8 as well as j Appendices A, D, E, and G of the tepical report. The licensee's responses to questions conceming materialin Section 5 were also used.

A key component of the submittalis the safety benefit claimed by quantification of the power measurement uncertainty attributed to using the LEFM System. In Section 5 of the topical report and in the licensee's response to questions 31,32, and 34 contained in Reference 2, ,

i m.

i 3 ,- .

,~, . information is presented showing that, even if the plant is operated at a power level 1 percent higher than the current limit, the likelihood of the plant exceeding the assumed power level for

- analysis at the onset of a LOCA is reduced using the LEFM System. This is solely a result of quantification of the power measurement uncertainties and treatment of the contributors to the uncertainties associated with the LEFM System and venturi meters as normally distributed parameters.

The staff accepted the licensee's claims regarding the uncertainty values associated with the two types of flow measurement instruments at CPSES as stated in the staff's March 8,1999, safety evaluation (Reference 12) of the Caldon, Inc., topical report (Reference 4). The staff also accepted the statistical treatment of contributors to the uncertainty in its comparison used to demonstrate a safety benefit.L However, the conditions given in Section 8 of the topical report are not sufficient by themselves to allow use of the LEFM System as the basis for a power increase. The licensee will need to determine how to include the plant-specific LEFM uncertainty values in the licensing basis for the plant when seeking a power uprate. The proposed change to the plant licensing basis will depend upon the power measurement 1 uncertainties for CPSES, and assurance that they are no greater than the values claimed in the  !

licensee's submittal.

3.3.3 Consistency with Commission Safety Goal )

l To make a final determination of the consistency of the licensee's proposal to increase plant I power with the Commission safety goals, the overall impact on plant risk must be considered.

As already stated, such an evaluation was not conducted for this exemption request, but would be part of the staff's review of a proposed increase in licensed power level. A review of the j

'information provided in the licensee's exemption submittal leads the staff to conclude that use of the LEFM System and quantification of power measurement uncertainty do not raise inconsistencies with the Commission's safety goals.

4.0 CONCLUSION

S The information provided by the licensee supports a finding, pursuant to Section 50.12, to allow the proposed exemption to the requirement in Appendix K to 10 CFR Part 50 that ECCS evaluation analyses be conducted at 1.02 times licensed power, to authorize use of an analysis  ;

for not less than 1.01 times licensed power level. Specifically, the exemption is authorized by J law, does not present an undue risk to public health and safety, and is consistent with the common defense and security. Further, the licensee has demonstrated that special l circumstances exist warranting the exemption. The underlying purpose of Appendix K will be satisfied under the exemption, and material circumstances now exist that were not considered when the rule was adopted. The exemption allows the licensee to utilize a reduction in the margin required to account for power measurement uncertainty. Further, the use of the Caldon LEFM system and the quantification of power measurement uncertainty appear to offer safety benefits.

In this evaluation, the staff concluded that use of the LEFM System and quantification of power measurement uncertainty do not pose undue risks to public health and safety. Although the staff expects that the risk from the associated power level increase would be small, the staff did 4

r-

, not reach a conclusion regarding the overall risk impact of using the LEFM System and increasing licensed power. The staff accepts the safety assessment provided by the licensee i showing that using the LEFM System at CPSES provides a safety benefit, but until other I aspects of the proposed power uprate are evaluated, the staff cannot reach a conclusion that using the LEFM System along with an increased licensed power would provide a safety benefit l outweighing any potential degradation in safety. However, satisfaction of the other special circumstances criteria are sufficient to support the proposed exemption.

The staff evaluation dated March 8,1999 (Reference 12), included a review of the Caldon, Inc.,

topical report (Reference 4). The staff examined those portions of the report supporting the claimed safety benefit. The staff accepts the statistical treatment of uncertainties attributed to l the LEFM System and venturi-based flow measurement instruments. The staff also accepts the l methods used in the comparison of the power measurement uncertainties derived from the flow instrument uncertainties that form the basis of the licensee's safety benefit argument. However, this determination for CPSES is based on plant-specific uncertainty information for both types of instruments, which were provided by the licensee. The conclusion reached by the staff in this  ;

evaluation is not necessarily generically applicable, and would not apply to other facilities until '

plant-specific information can be reviewed.

Principal Contributor: J.Donoghue i Date: May 6, 1999 I

i w.

g -

[ REFERENCES

1. Letter from C. L Terry (TU Electric) to NRC, TXX-98183, Request for Exemption from Appendix K, to 10 CFR Part 50 ECCS Evaluation Models, August 13,1998.

2. Letter from C. L. Terry (TU Electric) to NRC, TXX-98274, Submittal of Responses to Request for Additional Information Regarding Caldon Topical Report ER-80P, December 17,1998.

3. Letter from Calvin R. Hastings (Caldon) to NRC, Submittal of Topical Report, " Improving Thermal Power Accuracy and Plant Safety While increasing Operating Power Level Using the LEFM/ System," Caldon, Inc., Engineering Report-80P, March 10,1997.  !

4. Caldon, Inc., Engineering Report-80P, " Improving Thermal Power Accuracy and Plant Safety While Increasing Operating Power Level Using the LEFM/ System," Revision 0, March 1997.

5. TU Electric Topical Report, "Large Break Loss of Coolant Accident Analysis Methodology,"

Report No. RXE-90-007-A, April 2,1993.

6. TU Electric Topical Report,"Small Break Loss of Coolant Accident Analysis Methodology,"

Report No. RXE-95-001-P-A, September 1996.

7. SECY-83-472, " Emergency Core Cooling System Analysis Methods," November 17,1983.

' 8. Atomic Energy Commission Interim Policy Statement, " Criteria for Emergency Core Cooling Systems for Light-Water Power Reactors," 36 FR 12247, June 29,1971.

9. Opinion of the Commission, "Rulemaking Hearing - Acceptance Criteria for Emergency Core Cooling Systems for Light-Water-Cooled Nuclear Power Reactors," CLI-73-39, December 28,1973.

10. Memorandum from Gary M. Holahan to NRR Staff and Management, " Interim Guidance on Implementation of Risk-Informed Review Process," October 30,1998,

11. NUREG-1230, ? Compendium of ECCS Research for Realistic LOCA Analysis,"

December 1988.

12. Letter and Safety Evaluation from J. N. Hannon (NRC), to C. L. Terry (TU Electric),

" Review of Caldon Engineering Topical Report ER 80, P, ' improving Thermal Power Accuracy and Plant Safety While increasing Power Level Using the LEFM System,'"

March 8,1999.

l l