ML20276A135

From kanterella
Jump to navigation Jump to search
TSTF Proposal to Reevaluate Application of 10 CFR 50.36(c)(2)(ii) Criterion 4
ML20276A135
Person / Time
Site: Technical Specifications Task Force
Issue date: 10/02/2020
From:
Technical Specifications Task Force
To:
Office of Nuclear Reactor Regulation
Honcharik, M., NRR/DSS, 301-415-1774
References
Download: ML20276A135 (28)
v • d • e


Text

Technical Specifications Task Force A Joint Owners Group Activity TSTF 1

Proposal to Reevaluate Application of 10 CFR 50.36(c)(2)(ii)

Criterion 4

Technical Specifications Task Force A Joint Owners Group Activity TSTF Introduction

  • 10 CFR 50.36(c)(2)(ii) states that a TS LCO must be established for each item meeting one or more of four criteria.
  • The fourth criteria states, "A structure, system, or component

[SSC] which operating experience or probabilistic risk assessment has shown to be significant to public health and safety."

  • The Commissions Final Policy Statement on Technical Specifications Improvements for Nuclear Power Reactors, lists the following systems as satisfying Criterion 4:

- Residual Heat Removal (RHR),

- BWR Reactor Core Isolation Cooling (RCIC)/Isolation Condenser,

- BWR Standby Liquid Control (SBLC), and

- BWR Recirculation Pump Trip (RPT).

2

Technical Specifications Task Force A Joint Owners Group Activity TSTF Introduction

  • In addition to the systems above, the STS includes other LCOs that the Bases state satisfy Criterion 4:

- Remote Shutdown (All)

- Pressurizer PORV (B&W)

- Hydrogen Control (W Ice Condenser, BWR/4, BWR/6)

- RPV WIC (BWR/4, BWR/6)

  • The determination of which STS LCOs satisfy Criterion 4 was based on late-1980's industry operational experience (including new plants) and initial PRA development.

- Average nuclear capacity factors were less than 60% (> 92% today)

- PRA was just beginning to be used at plants for IPE and IPEEE development.

3

Technical Specifications Task Force A Joint Owners Group Activity TSTF Introduction

  • There are also many plant-specific LCOs that were retained during ITS conversion due to satisfying Criterion 4.
  • The Owners Groups initiated a project to evaluate whether the existing LCOs retained based on satisfying Criterion 4 would satisfy the Criterion 4 definition of SSCs that operating experience or probabilistic risk assessment has shown to be significant to public health and safety, when examined using modern PRA tools and operating experience.

4

Technical Specifications Task Force A Joint Owners Group Activity TSTF

Background

  • Reexamining what should be in the TS is not a new idea.
  • There has been an ongoing effort for over 50 years to define and refine what limitations should be included in the TS:

- 1953, the original 10 CFR 50 mentions TS without a definition

- 1961, 50.36 was revised and added Appendix A, Content of TS

- 1968, 50.36 was revised to add Safety Limits, LCOs, Surveillance Requirements, Design Features, and Administrative Controls

- 1972, The NRC starts the Standard Technical Specifications program to increase consistency

- 1975, First STS were issued 5

Technical Specifications Task Force A Joint Owners Group Activity TSTF

Background

- 1979, ANSI/ANS-58.4-1979, Criteria for Technical Specifications for Nuclear Power Stations

- 1979, ASLB Trojan Decision on the purpose of TS

  • Technical Specifications are to be reserved for those matters as to which imposition of rigid conditions or limitations upon reactor operation is deemed necessary to obviate the possibility of an abnormal situation or event giving rise to an immediate threat to the public health and safety.

- 1980, NRC issues an ANPR requesting ideas on standards for determining which items should be in TS

- 1982, NRC issues a proposed rulemaking with criteria to separate TS and Supplemental Specifications

- 1984, NRC and the Atomic Industrial Forum (AIF) form the Technical Specifications Improvement Project (TSIP) 6

Technical Specifications Task Force A Joint Owners Group Activity TSTF

Background

- 1986, SECY-86-10, Recommendations for Improving Technical Specifications

- 1987, NRC issues the Interim Policy Statement on Technical Specifications Improvements for Nuclear Power Reactors

- 1987, Owners Groups submit reports applying interim policy statement criteria to current STS

- 1988, NRC issues "split report" on application of interim policy statement criteria to current STS

- 1989, Owners Groups submit proposed improved STS

- 1992, NRC issues Revision 0 of STS

- 1993, NRC issues Final Policy Statement

- 1995, Criteria added to 10 CFR 50.36 7

Technical Specifications Task Force A Joint Owners Group Activity TSTF Development of Criterion 4

  • The 1987 Interim Policy Statements Criteria 1, 2, and 3 are the same as those in the Final Policy Statement.
  • The Interim Policy didnt include Criterion 4 but stated:

In addition to the above criteria, it is the Commissions policy that licensees retain in their Technical Specifications LCOs, action statements, and Surveillance Requirements for the following systems (as applicable) which operating experience and probabilistic risk assessment have generally shown to be important to public health and safety:

Reactor Core Isolation Cooling (RCIC)/Isolation Condenser, Residual Heat Removal (RHR),

Standby Liquid Control (SBLC), and Recirculation Pump Trip (RPT).

8

Technical Specifications Task Force A Joint Owners Group Activity TSTF Development of Criterion 4

  • In the Final Policy Statement, this discussion was added as Criterion 4.
  • There is no discussion in the Interim or Final Policy Statements or any of the other discovered documents what operating experience or PRA made these four systems important to public health and safety.

- It appears they were systems that were considered to be important based on late 1980s OE; for example NUREG-1269, "Loss of Residual Heat Removal System - Diablo Canyon, Unit 2, April 10, 1987."

  • The 1987 Owners Group split reports concluded that none of the systems satisfy Criterion 1, 2, or 3, or were risk significant, but they were retained because of the policy statement.

9

Technical Specifications Task Force A Joint Owners Group Activity TSTF Owners Group Project

  • The Final Policy Statement stated that the NRC will continue to consider methods to make better use of risk and reliability information for defining future generic TS requirements part of the ongoing program of improving TS.
  • The industry and the NRC have pursued many risk-informed TS improvements since the Final Policy Statement was issued, such as:

- Missed Surveillance (SR 3.0.3)

- Increase Flexibility in MODE Restraints

- Preferred End States

- Surveillance Frequency Control Program

- Risk Informed Completion Times 10

Technical Specifications Task Force A Joint Owners Group Activity TSTF Owners Group Project

  • However, there has been no effort to reexamine that first risk-informed TS decision on which LCOs should be retained.
  • The PWROG and BWROG initiated a project to evaluate whether the existing LCOs retained under Criterion 4 would satisfy the Criterion 4 definition of SSCs that operating experience or probabilistic risk assessment has shown to be significant to public health and safety, if examined using modern PRA tools and evaluated using recent operating experience.
  • The Owners Groups selected two systems applicable to PWRs and BWRs for reevaluation as a pilot project:

- The Remote Shutdown System, and

- The Residual Heat Removal System 11

Technical Specifications Task Force A Joint Owners Group Activity TSTF Remote Shutdown System (RSS)

  • The RSS provides the control room operator with sufficient instrumentation and controls to place and maintain the unit in a safe shutdown condition from locations other than the control room, should the control room become inaccessible.

- Not all RSS equipment is operated from the remote shutdown panel. Some equipment is operated locally at the switchgear, motor control panels, or other local stations.

- The list of RSS functions and equipment is in the TS Bases.

- The Required Action for one or more inoperable RSS functions is to restore it within 30 days.

12

Technical Specifications Task Force A Joint Owners Group Activity TSTF Remote Shutdown System (RSS)

  • The NRC 1988 review of the Owners Groups Split Reports stated, Because fires (either inside or outside the control room) can be a significant contributor to the core melt frequency and because the uncertainties with fire initiation frequency can be significant, the staff believes that this LCO should be retained in the STS at this time. The staff will consider relocation of Remote Shutdown Instrumentation on a plant-specific basis.

13

Technical Specifications Task Force A Joint Owners Group Activity TSTF Remote Shutdown System (RSS) Operating Experience

  • The Licensee Event Reports (LERs) for events that occurred since January 1, 2010 were reviewed.

- All LERs with "remote shutdown" in the title were reviewed.

- The abstracts of LERs with "remote shutdown" in the text were reviewed.

- The majority of the LERs documented failures of equipment required to be operable by other TS as well as the RSS TS or documented issues that did not affect that ability of the RSS to perform its function.

  • There were no instances in which the issue documented in the LER would have prevented a safe shutdown using the RSS.
  • Based on the LER review, operating experience does not show that the RSS is significant to public health and safety.

14

Technical Specifications Task Force A Joint Owners Group Activity TSTF Remote Shutdown System (RSS) Risk Assessment

  • Examining the detailed results of one PRA model and talking with analysts familiar with other models to validate the observations, greater than 75% of the fire-induced CDF is attributed to a fire requiring abandonment of the control room.
  • However, the subsequent failure of any portion of the Remote Shutdown System appears in a very small fraction of the risk significant cutsets (slightly over 1% of the fire-induced CDF).
  • In other words, the failure of the reactor operators to successfully perform the required abandonment procedures within the required time is much more risk significant than any equipment failure of the Remote Shutdown System.

15

Technical Specifications Task Force A Joint Owners Group Activity TSTF Remote Shutdown System (RSS) Risk Assessment

  • Relocating the RSS from the TS would not change these observations as appropriate configuration and corrective action controls will be maintained, consistent with relocating any other TS LCO to licensee control.

- Note that an existing Operating License Condition prohibits changes that would adversely affect the ability to achieve and maintain safe shutdown in the event of a fire.

16

Technical Specifications Task Force A Joint Owners Group Activity TSTF Remote Shutdown System (RSS) Other Considerations RSS is only risk significant in fire scenarios. Generic Letter 88-12 relocated all fire protection related requirements from the TS to licensee control. The RSS should be treated consistently.

GDC 19 requires the plant design to include remote shutdown capabilities and the RSS is credited in fire protection programs.

There is no plan to eliminate the RSS if relocated from the TS.

Per the Commission's policy statement, the TS are for the imposition of rigid conditions or limitations upon reactor operation.

- However, the current RSS TS does not impose rigid conditions or limitations. The list of RSS functions is in the TS Bases and under licensee control. If one or more RSS functions are inoperable, a 30 day Completion Time is provided.

17

Technical Specifications Task Force A Joint Owners Group Activity TSTF Remote Shutdown System (RSS)

  • Based on the operating experience, PRA, and other considerations, the RSS does not satisfy Criterion 4 or any of the other criteria for inclusion in the TS.

18

Technical Specifications Task Force A Joint Owners Group Activity TSTF Residual Heat Removal (RHR) System

- B&W STS Decay Heat Removal (DHR) System

- Westinghouse STS Residual Heat Removal (RHR) System

- Combustion STS Engineering Shutdown Cooling (SDC)

System

- BWR STS Residual Heat Removal (RHR) Shutdown Cooling (SDC) System

  • The RHR system is used to remove decay heat after shutdown and is not credited in any accident analysis

- For some PWR designs and modes, the RCS flow rate during shutdown modes is an input into the boron dilution analysis.

19

Technical Specifications Task Force A Joint Owners Group Activity TSTF Residual Heat Removal (RHR) System

  • The TS contain notes permitting RHR to be stopped for a significant period (e.g., 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> in any 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period) with some conditions.

20

Technical Specifications Task Force A Joint Owners Group Activity TSTF Residual Heat Removal (RHR) System

Criterion 1, 2, or 3.

  • The NRC review of the Owners Groups Split Reports did not justify retention of the RHR System in the TS, and simply stated, Policy Statement.
  • Because it was required by the Policy Statement, the Owners Groups did not evaluate whether the RHR System was risk significant in their criteria evaluations.

21

Technical Specifications Task Force A Joint Owners Group Activity TSTF Residual Heat Removal (RHR) System Operating Experience

"shutdown cooling," and "SDC." 746 LERs were found.

  • The abstract of each LER was reviewed to find events related to failure of the RHR system. 60 LERs were identified and reviewed in further detail.

- LERs related only to failure of a TS support system, loss of AC power, or containment isolation valve failures were removed from consideration as those systems are not proposed to be relocated to licensee control.

- LERs related only to the ECCS mode operation of the RHR System were removed from consideration as the TS on those modes of operation are not proposed to be relocated to licensee control.

22

Technical Specifications Task Force A Joint Owners Group Activity TSTF Residual Heat Removal (RHR) System Operating Experience

  • Twenty LERs met the criteria and were evaluated.
  • Three events affected all RHR trains or subsystems.

- Two events were related to a crack in a relief line on common RHR piping (leakage rates of 3 and 30 drops per minute, respectively). The ability of RHR to remove decay heat was not affected.

- One event was due to a momentary pressure spike from coolant flashing to steam that resulted in the isolation valves closing. The RHR systems were not damaged and RHR was quickly restored to operation.

  • In all of the events, the ability of the RHR System to remove decay heat was retained.

23

Technical Specifications Task Force A Joint Owners Group Activity TSTF Residual Heat Removal (RHR) System Operating Experience

  • The review did not identify any instances in which the event represented a threat to public health and safety.
  • Therefore, based on the LER review, operating experience does not show that the RHR System is significant to public health and safety.

24

Technical Specifications Task Force A Joint Owners Group Activity TSTF Residual Heat Removal (RHR) System Risk Assessment

  • Operating plants do not have PRA models for shutdown modes.
  • Qualitatively, it is assumed that RHR is needed during shutdown modes, but it is not a significant risk contributor.
  • The industry has implemented programs in accordance with NUMARC 91-06, Guidelines for Industry Actions to Assess Shutdown Management, to manage risk during shutdown, and to prevent loss of decay heat removal.
  • Therefore, the risk assessment has determined that the RHR System is not significant to public health and safety.

25

Technical Specifications Task Force A Joint Owners Group Activity TSTF Residual Heat Removal (RHR) System Other Considerations

- Both are required to reach cold shutdown

- Neither are credited in the accident analysis

  • The PWR boration systems were relocated to licensee control but the RHR Systems were retained in TS.
  • After issuance of the interim policy statement and the NRCs review of the Owners Groups Split Reports, the industry issued NUMARC 91-03 and implemented a robust program to ensure decay heat removal capability is available.

26

Technical Specifications Task Force A Joint Owners Group Activity TSTF Residual Heat Removal (RHR) System

  • Based on the operating experience, PRA, and other considerations, the RHR System does not satisfy Criterion 4 or any of the other criteria for inclusion in the TS.

27

Technical Specifications Task Force A Joint Owners Group Activity TSTF Next Actions

  • The industry believes there are opportunities to further focus the TS on requirements that are needed to avoid an immediate threat to public health and safety by reevaluating those systems that were previously determined to satisfy Criterion 4.
  • This could take the form of TSTF travelers that justify relocation of specific TS that were previously determined to meet Criterion 4 as well as industry/NRC agreement on the type of evaluations needed for a license amendment request to relocate plant-specific LCOs that were determined to satisfy Criterion 4.

28

Retrieved from "https://kanterella.com/w/index.php?title=ML20276A135&oldid=3848946"