3F0698-09, Requests Exemption from 10CFR50,App K,Section I.D.1, Single Failure Criterion, as It Relates to 10CFR50.46(b)(5), Long-Term Cooling, for Plant.Detailed Justification for Request Encl
| ML20248K993 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 06/04/1998 |
| From: | Cowan J FLORIDA POWER CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 3F0698-09, 3F698-9, TAC-M99892, NUDOCS 9806100367 | |
| Download: ML20248K993 (14) | |
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June 4,1998 3F0698-09 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001
Subject:
Request for Exemption from 10 CFR Part 50, Appendix K, Section I.D.1 - Crystal j
River Unit 3 (NRC TAC Number M99892) i
References:
1.
FPC to NRC letter (3F0498-17) dated April 24,,1998, " Clarification of Post-l LOCA Boron Precipitation Prevention - Licens?. Amendment Request #223 (NRC TAC Number M99892) - Crystal River Ur.it 3" 2.
FPC to NRC letter (3F0298-07) dated February 27,1998, " Request for NRC Approval of Topical Report - Boron Dilution by Reactor Coolant System Hot leg injection - Crystal River Unit 3" 3.
FPC Calculation M97-0146, Revision 2, " Post-LOCA Boron Concentration Management for CR-3" (provided as attachment to Refgrence 1) 4.
NRC to FPC letter (3N0896-12) dated August 23,1996, " Crystal River Unit 3 Integrated Performance Assessment Process (IPAP) Final Assessment Report (NRC Inspection Report No. 50-302/96-201)"
5.
FPC to NRC letter (3F0997-28) dated September 12, th97, " Post LOCA Boron Precipitation Mitigation Plan" Ltar Sir:
Pursuant to 10 CFR 50.12, Florida Power Corporation (FPC) is hereby requesting an exemption from 10 CFR Part 50, Appendix K, Section I.D.1, " Single Failure Criterion," as it relates to 10 CFR 50.46(b)(5), "Imng-term cooling " for the Crystal River Unit 3 (CR-3) Nuclear Plant. The detailedjustification for this request is provided as Attachment A to this letter.
Appendix K Section I.D.1 requires accident evaluation using the combination of Emergency Core Cooling System (ECCS) subsystems assumed to be operative "... after the most damaging single failure of ECCS equipment has tsken place." 10 CFR 50.46(b)(5) requirt.s that the ECCS be capable of providing long-term core cooling. Post-accident boron precipitation is a potential, but unlikely, challenge to maintain.:.g long-term core cooling. In the NRC's Integrated Performance g/
Assessment Process (IPAP) Final Assessment Report (Reference 4), a pr:liminary safety evaluation determined that continued CR-3 operation is safe until the post-accident boron precipitation issue could be resolved.
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'vvvD Dl CRYSTAL RIVER ENERGY CoMPl.Ex: 15760 W. Power Line Street = Crystal River, Florida 34428 4 708 (352)7954 488 9806100367 980604 S Florida Progress Company PDR ADOCK 05000302 L __ __
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- U S. Nuclear Regulatory Commission' l
- 3F0698-09 Page 2 of 2 The exemption is needed because, with the postulation of a single failure of Engineered Safeguards (ES) Motor Control Center (MCC) 3AB, both approved active methods for boron precipitation control (de:ay heat Dump-to-Sump and Auxiliary Pressurizer Spray) will not be available until manual repair actions are completed. In the event of this low probability sequence of events, the-passive dilution methods of Reactor Vessel Vent Valve overflow and hot leg nozzle gap flow to mitigate boron precipitation will be available and will provide boron dilution until necessary
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equipment is restored. As detailed in Attachment A, the conservatism present in the calculations
- that validate the active methods, the effectiveness of the passive methods,'and the timely actions FPC would take to restore an active mitigation method assure adequate long term core cooling is maintained.'.nerefore, loss of ES MCC 3AB until repair actions can be implemented will not -
endanger public health and safety.
A third analyzed active method, Hot Leg Injection (Reference 2), is currently in NRC review. This active method is also affected by the failure of ES MCC 3AB. This information is provided to the.
NRC for consideration in their review of Reference 2.
If this exemption is granted, FPC will revise the Final Safety Analysis Report to reflect the exemption. This commitment is provided in Attachment B.
If you have any questions regarding this submittal, please contact Ms. Sherry Bernhoft, Manager,.
Nuclear Licensing at (352) 563-4566.
l" Sincerely, MOQ John Paul Cowan Vice President Nuclear Operations JPC/rer.
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Regional Administrator, Region II Senior Resident inspector NRR Project Manager
.- Attachments: A.
Request for Exemption from Title 10 CFR 50, Appendix K, Section I.D.1 for Crystal River Unit 3 (CR-3)
B.
List of Regulatory Commitments C. - Acronyms and Abbreviations L-
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i U.S. Nuclear Regulatory Commission Attachment A l
3F0698-09 Page 1 of 10 ATI'ACIIMENT A REQUEST FOR EXEMPTION FROM TITLE 10 CFR 50, APPENDIX K SECTION I.D.1 FOR CRYSTAL RIVER UNIT 3 (CR-3)
This attachment provides the technical justification for the exemption request from 10 CFR 50, Appendix K, Section I.D.1, Single Failure Criterion, as it relates to 10 CFR 50.46(b)(5),
Long-tenn cooling.
BACKGROUND 10 CFR 50.46(a)(1)(i) requires that each nuclear power reactor have an Emergency Core Ccoling System (ECCS) that complies with the criteria set forth in 10 CFR 50.46(b). Pursuant to 10 CFR 50.46(a)(1)(ii), CR-3's ECCS performance is evaluated with the required and acceptable features of 10 CFR 50, Appendix K.
Section I.D.1, Single Failure Criterion, of Appendix K requires an analysis of possible ECCS equipment failure modes and their effects on ECCS performance during the post-blowdown phase of the postulated accident. In addition, it requires that the combination of ECCS subsystems assumed to be operative shall be those available after the most damaging single
' failure of ECCS equipment has taken place.
The CR-3 Reactor Coolant System (RCS) has boron in solution as boric acid, a soluble neutron poison. CR-3 has both active and passive methods of mitigating post-accident boron precipitation.
The two NRC-approved active methods are decay heat Dump-to-Sump (DTS) and Auxiliary Pressurizer Spray (APS). The system alignments for these active methods are depicted on attached Figures 1 through 4.
Dump-to-Sump (DTS) Method The DTS Method is currently part of the CR-3 licensing basis. The DTS alignment provides a Dow path from the RCS decay heat drop line to the reactor building (RB) emergency sump.
One ECCS train must be stopped or not operating to establish this connguration. To protect the RB sump screens from potential damage due to reverse flow through the drop line, valves DHV-42 or DHV-43, depending on which train is used to establish the DTS How path, must be throttled.
Auxiliary Pressurizer Spray (APS) Method Another method that is part of the current CR-3 licensing basis is the APS method. This method involves an alignment that provides a flow path from an operating low Pressure Injection (LPI) pump to the pressurizer (PZR). Dilution How is developed from the PZR through the hot leg and into the reactor core via the hot leg nozzle.
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U.S. Nuclear Pagulatory Commission Attachment A
. 3F0698-09' Page 2 of 10 CR-3's passive methods, which are inherent in the plant design, are Reactor Vessel Vent Valve (RVVV) overflow and hot leg nozzle gap flow. It has been postulated that, in the unlikely event the active methods are unavailable and the passive methods are not credited, the core region concentration might reach the coolant solubility limit, resulting in boron precipitation. The precipitate could hypothetically cause blockage of the core coolant flow Uannels and thereby potentially result in overheating of the fuel and consequent fuel clad damage. However, only a loss of coolant accident (LOCA) that results in the RCS reaching an inadequately sub-cooled state for a given period of time can concentrate boric acid in the core region and cause n to potentially reach its solubility limit. As discussed in more detail below, it is very unlikely that boron precipitation would occur without operator awareness using the existing prescribed guidance and preventive actions. Technical Support Center (TSC) procedure EM-225B provides the guidance necessary to prevent boron precipitation. Operational strategies for recognizing the precipitation phenomenon and the system alignments for the active methods are included in this procedure.
The analytical methods and results of the calculations that quantified the effectiveness of these methods were provided to the NRC by letter dated April 24,1998 (Reference 1). In FTI Document 51-5000519-00, included with Reference 5, FTI provided information regarding the hot leg nozzle gaps at CR-3 and discusses that the gaps will be open and provide sufficient boron dilution flow.
REASON FOR REQUEST To address single failure issues associated with License Amendment Request #n3, FPC performed a single failure analysis to determine single failures of ECCS equipment that affect long-term core cooling in accordance with Appendix K,Section I.D.I. Because of the potential for post-accident boron precipitation, the single failure analysis identified those failures that affect CR-3's ability to implement its active boron precipitation control methods.
FPC systematically examined the configurations associated with each active method to determine the impact of a single failure on the individual active methods. Figures 1 through 4 show the configurations for these methods. The examination identified. active end-device failures and failures to supply electrical power to end-devices.
The identified active end-device failures include valves failing to respond to an opening, closing, or throttling signal. Consideration was also given to their initial state prior to the occurrence of the single failure. LPI pump or train availability had been explicitly factored into the development and l
analytical validation of the active methods. The analysis concluded that given a postulated single active end-device failure, there would always be one approved ' active method for dilution.
However, a short-term reliance on passive methods may be necessary to provide dilution' flow until the available active method becomes effective, chus precluding a challenge to the solubility limit.
The failure to supply electrical power to an end-device has a much broader impact. The analysis identified a single failure that is common to both active dilution methods. ES MCC 3AB powers 1
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U.S. Nuclear Regulatory Commission Attachment A 3F0698-09 Page 3 of 10 valves used in both active methods. The valves required for boron precipitation mitigation which could be rendered unavailable upon the MCC failure are as follows:
DlIV this valve is located in the decay heat drop line and must be opened for DTS, and DHV-91 and RCV These valves are located in the APS line and must be opened for e
APS, either Train A or Train B Cow.
For completeness, other electrical and instrumentation single failures were also investigated. These included the failures of each train's DC electrical distribution system, the failure of an emergency diesel generator to start and load, and the failure of flow indication. The impact of these identi0ed single failures is similar to the impact considered in the analysis of train-dependent active methods.
For example, if the "B" emergency diesel generator fails to start, DTS flow through LPI Train B would not be available, but APS Cow through LPI Train A would remain available.
To summarize, the single failure analysis identified one single failure, that of ES MCC 3AB, which affects both of CR-3's approved methods (i.e., DTS and APS). This failure requires a reliance on the passive dilution methods of RVVV overnow and hot leg nozzle gap flow until an active method
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is restored.
i JUSTIFICATION FOR EXEMPTION 10 CFR 50.12 states that the Commission may grant an exemption from requirements contained in 10 CFR Part 50 provided that: (1) the exemption is authorized by law; (2) the exemption will not present an undue risk to the public health and safety; (3) the exemption is consistent with the 1
common defense and security; and (4) special circumstances, as defined in 10 CFR 50.12(a)(2), are present. The requested exemption from the single failure requirement of Appendix K,Section I.D.1 satisfies these requirements as described below.
- 1. The requested exemption is authorized by law NRC's authority to grant exemptions from the requirements of Title 10 of the Code of Federal Regulations, Part 50, is codified in 10 CFR 50.12. Since the exemption request does not present an undue risk to the public health and safety and will not endanger the common defense and security, as discussed below, the NRC is authorized to issue the exemption.
- 2. The requested exemption will not presemt an undue risk to the public health and safety A risk evaluation showed the very low probability of tne combination of the accident and the single failure of ES MCC 3AB that renders both active methods unavailable for a short period of time. In the event this does occur, FPC will initiate repair actions that will reactivate these active methods in a timely manner. The calculations that vtlidated the effectiveness of the active methods also contained numerous conservative assumptions, and took no credit for the
U.S. Nuclear Regulatory Commission Attachment A 3F0698-09 Page 4 of 10 passive dilution methods that are inherent in the plant's design. These conservatism, in addition to the conservatism imposed by Appendix K, provide the necessary time to address a single failure. As such, there would be no undue risk to the public health and safety.
In Reference 4, the NRC determined post accident boron precipitation is an issue that would not preclude continued operation of CR-3.
From a risk perspective, an evaluation was performed to comprehensively address the identified failure modes of the required equipment.
The active mechanical failures, which include valves failing to open, throttle, or close, were evaluated to have a probability on the order of 10.
When combined with accident
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3 probabilities, the order of magnitude is reduced to 10'" or lower. The frequency of the ES MCC 3AB failure coinciding with the accident has been evaluated as 10"/ year.
(The frequency of this was previously quantified as 10*/ year in Reference 1). Other electrical failures result in similar combined probabilities. These extremely low probabilities demonstrate that these events need not be further evaluated.
Moreover, the analysis which validated the effectiveness of the active methods (Reference 3),
contained conservative assumptions which assure the methods' effectiveness for bounding scenarios. This analysis conservatively demonstrated the effectiveness of the active methods for the entire range of post-accident conditions for which boron precipitation is a potential concern.
For instance, no credit was taken for the passive dilution methods of RVVV overflow and hot leg nozzle gap flow. Also, no credit was taken for the presence of buffer compounds that increase margins to the solubility limit. In addition, the solubility limit itself, as represented in the sump-delta concentration curve used in procedure EM-225B was conservatively lowered by 25% to further ensure the timely implementation of an active method.
Also, it is important to note that the Appendix K,Section I.A.4 requirement to assume 1.2 times the American Nuclear Society (ANS), October 1971, " Decay Energy Release Rates Following Shutdown of Uranium-Fueled Thermal Reactors" for an infinite operating time is also a source of conservatism. Elevated decay heat levels provide a more effective boron concentrating mechanism than do lower levels. Calculations have shown that conservative decay heat levels of 1.0 times ANS 1971 iraprove the effectiveness of each active method. A corollary is that more realistic decay heat levels provide more time to address the effects of a single failure. Tables 8 and 9 of Reference 3 show the times to reach a solubility limit for both Appendix K and more realistic decay heat assumptions.
Thus, the conservatism inherent in tne analysis are a source of margin to the solubility limit.
It follows that operating within the bounds established by these conservatism would provide additional time to address a single failure. In the unlikely event of the ES MCC 3AB single failure, steps can be taken to repower and operate affected end-devices. Such steps will take time, requiring interim reliance on the passive dilution methods described previously. Once the steps are completed, one or more active methods would then be available.
FPC has evahiated the radiological conditions that might exist in the areas of the plant that would be involved in the repowering activities. The objective of the boron precipitation
U.S. Nuclear Regulatory Commission Attachment A 3F0698-09 Page 5 of 10 mitigation is to prevent fuel overheating and damage. Therefore FPC considers it reasonable to expect that large amounts of failed fuel will not exist during the efforts to repower ES MCC 3AB or the affected end-devices. Mission dose evaluations confirm repowering activities are achievable with no additional fuel failures occurring as a result of the LOCA.
It is important to note that a failure of ES MCC 3AB would be evident during accident mitigation earlier in the event and prior to the time when boron precipitation is a potential. The actions to restore power to the affected end-devices needed to activate an active method are described in procedure EM-225B and would be promptly initiated when the MCC failure is i
recognized. The time to complete the repowering is bounded by the time to reach the solubility limit by several hours. This is demonstrated by the following:
the analysis performed by Framatome Technologies, Inc. (FTI) of the time to reach the solubility limit (at 1.0 times ANS 1971 Decay Heat) documented in Reference 1, and estimates made by FPC personnel of the time to repower the required valves and reactivate an active method of boron dilution.
The FTI analysis did not credit the passive methods which are inherent to the reactor internals design. With credit given for these passive methods, the time will be increased.
In summary, the extremely low probability of ES MCC 3AB failure concurrent with the accident and the conditions that result in boron precipitation, and the conservatism used in the effectiveness calculations, provide assurance that post-accident long-term core cooling will be maintained. Although the unlikely failure of ES MCC 3AB to power the required valves hinders the implementation of an active method for boron precipitation mitigation, necessary actions will be taken in a timely manner to restore an active method. Passive dilution methods are inherent in the plant design and will function to limit the risk of a long-term core cooling challenge. In addition, conservatism in the calculations are a source of considerable margin to address the MCC single failure. Based on the above, this exemption does not pose an undue risk to the health and safety of the public.
- 3. The requested exemption will not endanger the common defense and security To ensure that the common defense and security are not endangered, the exemption request must demonstrate that the loss or diversion of Special Nuclear Material (SNM) is precluded. CR-3 has systems and processes in place which provide protection for the public from diversion of SNM that CR-3 is licensed to possess. Yhese systems and processes are those embodied in the CR-3 Physical Security Plan, the Safeguards Contingency Plan, and the Training and Qualification Plan for security personnel.
The request for exemption from the single failure criterion of Appendix K,Section I.D.1 does not affect the systems and processes discussed above. Therefore, this exemption does not affect the common defense and security.
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- U.S. Nuclear Regulatory Commission Attachment A 3FM98-09 Page 6 of 10
- 4. Special circumstances are present which require issuance of the exemption to 10 CFR 50, Appendix K.Section I.D.1, as it reiates to 10 CFR 50.46 (b)(5) 10 CFR 50.12(a)(2) states that the NRC will not consider granting an exemption to the regulations unless special circumstances are present. The requested exemption meets the special circumstance of 10 CFR 50(a)(2)(ii), in that application of these regulations in this circumstance is not necessary to achieve the underlying purpose of the regulations.
The ur.derlying purpose of Appendix K,Section I.D.1, as it relates to 10 CFR 50.46(b)(5), is to assure long-term cooling performance of the ECCS in the event of the "most damaging single failure of ECCS equipment."
As discussed above, CR has the active boron precipitation mitigation _ methods of. DTS and APS in place.. These active methods are susceptible to a single failure that is common to both active methods. Through repair efforts, these methods can be reactivated thereby assuring long-term core cooling. The conservative analysis that.- validated the effectiveness of these methods to prevent boron mitigation demonstrate that under realistic conditions, sufficient time would be available to perform repairs. Additionally, the passive dilution methods are inherent in'the reactor internals design and can be relied upon to provide boron dilution in the short term until restoration activities are.
complete. The possibility of this single failure and the need for repair actions are described in procedure EM-225B. Although the single failure cri:erion is not satisfied, measures will be taken to reactivate the active methods, thereby assuring long-term core cooling.
Based on the above, FPC concludes that the underlying purpose of Appendix K,Section I.D.1, as it relates to 10 CFR 50.46(b)(5), is achieved by assuring long-term core cooling through passive dilution methods, timely recognition of boron precipitation as provided in procedure EM-225B, and prompt operator actions to restore an active method in the event of the ES MCC 3AB failure.
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U.S. Nuclear Regulatory Commission Attachment A 3F0698-09 Page 7 of 10 FIGURE 1 CR-3 DECAY HEAT DROP LINE DUMP TO SUMP (DTS) FLOW PATH WITH THE DECAY HEAT PUMP A (DHP-1 A) OPERATING HotLeg RB i
oss To PZR Aux Spray j
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1P From To HPl BWST NOTE 1 - DHV-43 position is shown as throttled.
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U.S. Nuclear Regulatory Commission Attachment A 3F0698-09 Page 8 of 10 FIGURE 2 CR-3 DECAY HEAT DROP LINE DUMP TO SUMP (DTS) FLOW PATH WITH THE DECAY HEAT PUMP B (DHP-1B) OPERATING l
Hot Leg RB Inwa To PZR Aux Spray oe*4
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BV'ST tuns *,9 P
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Deve-is t>was D** '3 RB u
From To HPl BWST NOTE 1 DHV-42 position is shown as throttled.
U.S. Nuclear Regulatory Commission Attachment A 3F0698-09 Page 9 of 10 FIGURE 3 CR-3 AUXILIARY PRESSURIZER SPRAY (APS) FLOW PATH USING THE DECAY HEAT PUMP /. (DHP-1 A)
Hot Leg RB To PZR Aux Spray 9 r a6 J k DHN1 U
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DHW 110 oHW 2 T
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1r From To HPl BWST NOTE 1 - DHV 5 posmon is shown as throttled.
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e U.S. Nuclear Regulatory Commission Attachment A 3F0698-09 Page 10 of 10 FIGURE 4 CR-3 AUXILIARY PRESSURIZER SPRAY (APS) FLOW PATH USING THE DECAY HEAT PUMP B (DHP-1B)
Hot Leg RB To PZR Aux Spray 9 F J'
d k DHv 41 U
N VM J
To HR From d'
BWST a6 DHv et p11 J k D*8 oHv.iio X
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RB ir Frorn To HPt BWST NOTE 1 - DHV4 position is shown as throttled.
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U.S. Nuclear Regulatory Commission Attachment B 3F0698-09 Page 1 ofI ATTACIIMENT 11 LIST OF REGULATORY COMMITMENTS i
The following table identifies those actions committed to by Florida Power Corporation in this document. Any other actions discussed in the submittal represent intended or planned actions by Florida Power Corporation. They are described to the NRC for the NRC's info:.:ation and are not regulatory commitments. Please notify the Manager of Nuclear Licensing of any questions regarding this document or any associated regulatorv commitments.
COMMITMENT DUE DATE FPC will revise the CR-3 Final Safety Analysis Report to Subsequent to receipt of the reflect the exemption from 10 CFR 50, Appendix K, exemption in accordance with Section I.D.l.
the requirements of 10 CFR 50.71(e).
1 U.S. Nuclear Regulatory Commission Attachment C 3F0698-09 Page1 of1 i
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ATTACIIMENT C ACRONYMS AND ABBREVIATIONS i
ANS............... American Nuclear Society l
APS................ Auxiliary Pressurizer Spray (mitigation method)
BWST............. Borated Water Storage Tank -
CFT................ Core Flood Tank CR-3............... Crystal River Unit 3 DTS................ Dump-to-Sump (mitigation method)
ECCS.............. Emergency Core Cooling System ES.................. Engineered Safeguards FPC................ Florida Power Corporation 11PI................ High Pressure Injection system IPAP............... Integrated Performance Assessment Process LOCA............. less of Coolant Accident LPI................. Low Pressure Injection system MCC............... Motor Control Center NRC............... U.S. Nuclear Regulatory Commission l
PZR................ Pressurizer RB.................. Reactor Building RCS................ Reactor Coolant System i
RVVV............. Reac'.or Vessel Vent Valve SNM............... Special Nuclear Material l
TSC................ Technical Support Center
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