ML090210242

Licensee Slides, January 15, 2009, Category 1 Meeting with Wolf Creek Nuclear Operating Corporation to Discuss Changes to Post Fire Shutdown Unresolved Items Analysis Methods Pre-Application for Wolf Creek Generating Station

ML090210242
Person / Time
Site:	Wolf Creek
Issue date:	01/15/2009
From:	Wolf Creek
To:	Office of Nuclear Reactor Regulation
Shared Package
ML090210167	List: ML090210206 ML090210242
References
TAC ME0280
Download: ML090210242 (39)

Text

Post Fire Safe Shutdown Analysis Unresolved Items Wolf Creek Nuclear Operating Corporation January 15, 2009

• Introductions/Purpose of Meeting

• Fire Induced Closure of Reactor Coolant Pump Seal Injection Valves

• Method Used for Cable Analysis of PressurizerPower Operated Relief Valves (PORVs)Meeting Agenda 2

Purpose of Meeting

• Describe WCNOC'sintent to request approval to change the Post Fire Safe Shutdown

Analysis Method for Two Fire Induced

Failures*Obtain NRC comment and feedback whether

presented methods are reasonable 3

Reactor Coolant Pump Seal Injection Valves

• Describe WCNOC'sintent to pursue operation with the Reactor Coolant Pump (RCP) Seal

Injection Valves de-energized in the open

position*Provide a description of the design and operation of the RCP Seal Injection Valves

• Provide a description of the analysis supporting RCP Seal Injection Valves operability

• Discuss associated Technical Specification compliance 4

Reactor Coolant Pump Seal Injection Valves (cont)

• WCNOC intends to pursue opening the electrical breakers with the RCP seal

injection containment is olation valves in the open position during normal operation

• Certain fires at WCGS could cause spurious closure of these valves with resulting loss of

RCP seal injection, increasing risk of RCP

seal damage 5

Reactor Coolant Pump Seal Injection Valves (cont)

• Operators must diagnose and mitigate the spurious closure of the RCP seal injection

valves in a timely manner

• Diagnostic instrumentation is available, but difficult to recognize

• Compensatory measures are in place 6

Simplified Schematic of RCP Seal Injection Penetrations 7

Seal Injection Valves Description and Operation

• One Motor Operated Valve (MOV) installed in each of the four seal injection penetration lines (outboard)

• These valves are considered remote-manual containment isolation valves

• One Check Valve is installed in each of the four seal injection penetration lines (inboard) to provide containment isolation valves

• RCP seal injection valves have no automatic closure function (essential penetration) (Westinghouse Systems Stan dard Design Criteria 1.14 and NUREG 0881) 8 Seal Injection Valves Description and Operation (cont)

• RCP seal injection valves have no required closure time (Westinghouse Systems Standard Design

Criteria 1.14)

• RCP seal injection valves can be remote-manually closed by operator when charging pump has

completed its safety function. (Westinghouse

Systems Standard Design Criteria 1.14)

• RCP seal injection valves are tested per Appendix J, type C testing (USAR Fig. 6.2.4-1, pages 18, 29, 30 and 31) 9 Seal Injection Valves Description and Operation (cont)

• Reactor Coolant Pump Seals

• Among most vulnerable components in a PWR (Generic Safety Issues 23 and 65)

• Seals require cooling to avoid failure and possible unisolable seal LOCA

• Seal Injection from charging pump provides one method of cooling the seals

• Thermal Barrier Cooling provides a second method of cooling the seals 10 Seal Injection Valves PSA review

• WCGS PSA models the RCP Seal Injection Valves only for a failure in the closed position

• Spurious closure is possible du e to fire damage on control cables*Spurious closure has minimal impact on risk of CDF due to existence of thermal barrier cooling

• Same fire can cause thermal barrier cooling to be lost

• Simultaneous loss increases risk of CDF (half order of magnitude increase above baseline at-power CDF)

• PSA does not model the RCP seal injection valves as containment isolation valves 11 Seal Injection Valves Design Basis

• Containment isolation valves in the Chemical and Volume Control System (CVCS) are selected, tested and located in accordance with the requirements of 10CFR50, GDC 55 and Appendix J (USAR Section 9.3.4.1.1)

• CVCS is able to continuously supply filtered water to each reactor coolant pump seal, as required by the reactor coolant pump design and as specified in USAR Table 9.3-8 (USAR Section 9.3.4.1.2)

• Seal water supply flow rate, for all four reactor coolant pumps, nominal, 32 gpm (Table 9.3-8) 12 Seal Injection Valves Design Basis(cont)

• Westinghouse Systems Standard Design Criteria 1.14 states that the seal injection line

penetrations are a special case for plants where

charging pumps are used for safety injection (i.e., WCGS)

• Flow to the RCP seals will be provided by the charging pumps following an accident

• Due to the high pressure inflow, there is no need to provide trip valves in the seal injection lines 13 Seal Injection Valves Design Basis(cont)

• WCGS SER -NUREG 0881 (by reference to the Callaway SER) states:

• RCP seal water supply lines are classified as essential and provisions have been made to detect possible leakage from these lines outside containment, thereby allowing remote-manual

instead of automatic isolation valves

• Staff finds that the containment isolation provisions for the specific penetration is an acceptable alternative to the requirements of GDC 55 14 Seal Injection Valves Design Basis(cont)

• USAR Table 18.2-2 identifies the containment penetrations for the seal injection valves as

essential

• Essential is defined as th ose systems required to have isolation valves open for either post

accident safe shutdown or mitigation of the

consequences of an accident

• CVCS piping inside and outside containment is designed to ASME Boiler and Pressure Vessel Code,Section III, class 2 requirements (Same

design requirements as piping in the

containment penetration piping) 15 16 RCP Seal Injection Valves Safety Analysis Review

• Safety Analysis calculations do not model these valves for containment isolation function

• Analyses assume that seal injection is in service and water is flowing into the containment

through these essential penetrations

• On loss of power, these valves will fail-as-is

• Under accident conditions, these valves stay open*There is no specified closure time for these valves in the safety analyses 17 RCP Seal Injection Valves Safety Analysis Review (cont)

• Four Operations Emergency procedures call for closure of the seal injection isolation valves

• To allow restart of charging pump following loss of all charging and loss of all seal cooling

• To avoid thermal shock damage to the RCP seals

• Meets Westinghouse Emergency Response Guidelines for restoring seal injection 18 RCP Seal Injection Valves Technical Specifications

• Section 3.6.3, Condition A, states that if one containment isolation valv e is inoperable in a penetration flow path, the penetration must be

isolated by a closed manual valve, blind flange, or closed and de-activated automatic valve, or a check valve with flow through the valve secured

• Section 1.1 (definitions) states:

A component-shall be OPERABLE-when it is capable of performing its specified safety function(s) and when all necessary attendant instrumentation, controls, normal or emergency electrical power-that are required for the component to perform its specified safety function-are

also capable of performing their related support function(s) 19 RCP Seal Injection Valves Technical Specifications (cont)

• Based on the Technical Sp ecification definition of OPERABLE/OPERABILITY, removing

electrical power to the RCP seal injection

valves would make the valve inoperable

• Operation with the power removed to the seal injection valves is an acceptable approach, as

a safe plant condition will be maintained

• Plant Operators can energize the breakers and remote-manually close the valves when specified in procedures 20 RCP Seal Injection Valves Conclusion

• Proposed change to TS 3.6.3, "Containment Isolation Valves"will be submitted to allow

operation with the RCP seal injection

containment isolation valves in the open

position and power removed from them

• This would prevent a fire from causing the valves to spuriously close

• Operators will not need to take actions to avoid seal LOCA due to fire

• No other impacts to operation of plant 21 RCP Seal Injection Valves Conclusion

• Questions*Comments and Feedback 22

• Describe WCNOC's intent to reclassify the PORVs as non high-low pressure interface

• Provide a description of the design and operation of the PORVs

• Provide a discussion of the origin of the high-low pressure interface concern

• Proposed change would alleviate burden of operator manual actions following fire

induced opening of PORVs

• Compensatory measures are in place Pressurizer Power Operated Relief Valves (PORV) 23 Pressurizer Power Operated Relief Valves (PORV)

• For post-fire safe shutdown purposes, the PORVs have been classified as high-low pressure

interfaces

• Increases the circuit fault scenarios that can result in a fire induced open PORV

• Increases burden of operator manual actions

• Based on review, WCNOC does not consider this classification to be correct and desires to re-classify these valves as non high-low pressure interfaces 24 PORV Simplified Diagram 25 PORV Description and Operation

• PORVshave electrical solenoid actuators

• They are operated automatically based on RCS pressure or by remote manual control (USAR Section 5.1.4.f)

• PORVsdesigned to limit Pressurizer pressure to a value below the fixed high pressure Reactor trip

point *PORVsdesigned to fail to the closed position on loss of power (USAR Section 5.4.13.1) 26 PORV Description and Operation (cont)*PORVsassist administrative controls to prevent violation of pressure limits during low

temperature operation (USAR Section 5.2.2.10)

• PORVsprovide the safety related means for Reactor Cooling System depressurization to

achieve cold shutdown (USAR Section 5.4.13.3)

• Discharged steam from the PORVs is piped to the Pressurizer Relief Tank (inside containment) where it is condensed and cooled by mixing with water (USAR Section 5.1.2) 27 PORV High-Low Pressure Interface History

• WASH-1400, Reactor Safety Study (NUREG-75/014, October 1975)

• Identified an intersystem LOCA in a PWR which is a significant contributor to risk from core melt accident (Event V)

• Investigated piping systems that connect to the RCS and also go through the containment

• Such connections have the potential to cause a LOCA in which the interior of the Reactor Vessel may communicate to the environment 28 PORV High-Low Pressure Interface History (cont)

• WASH-1400 (cont)

• Paragraph 5.3.2.5 discusses interfacing systems LOCA.*The concern is stated, "-the break in the system will lead into a safeguards building outside the

containment so there will be a direct path for radioactive release to the atmosphere,-"

• All RCS connections except the low pressure injection system (LPIS) (RHR System) were

dismissed due to one or more reasons

• One reason for dismissal was "Failure of the

barriers would involve a LOCA into the containment-"(Appendix I, Paragraph 4.1.6) 29 PORV High-Low Pressure Interface History (cont)

• Task Action Plan Item B-63, "Isolation of Lower Pressure Systems Connected to the Reactor Coolant Pressure Boundary"[NUREG-0471, Sept

78]*States, "Each low pressure system connected to the reactor coolant pressure boundary and penetrating the containment will be examined"

• This issue was resolved and requirements were issued (ref.-NUREG-0933, Prioritization of Generic Safety Issues -11/83) 30 PORV High-Low Pressure Interface History (cont)

• 2/23/80 -NRC issued letter to LWR Licensees, "LWR Primary Coolant System Pressure Isolation Valves"(subsequently designated as Generic

Letter 80-14)

• References the WASH-1400 report -Concerned with an overpressurizationand ru pture of the LPIS (RHR) low pressure piping which results in a LOCA that bypasses containment

• Requested Licensees to describe the valve configuration and indicate if Event V isolation valve configuration exists (e.g., two check valves in series, or two check valves in series with an MOV) 31 PORV High-Low Pressure Interface Licensing Basis

• April 1981 -SNUPPS FSAR Question Q280.5 -

received as part of review of Appendix 9.5B (SNUPPS final fire hazards analysis) -Information

requested:

• Identify each high-low pressure interface that

uses redundant electrically controlled devices

• Identify each devices essential cabling

• Identify cable separation 32 PORV High-Low Pressure Interface Licensing Basis (cont)

• SNUPPS FSAR Question Q280.5 (cont.)

• Question indicates compliance with BTP RSB 5-1 and BTP ICSB 3

• BTP RSB 5-1 discusses the design of the RHR System only*BTP ICSB 3 discusses over pressurization of the low

pressure system and "-loss of integrity of the low

pressure system and possible radioactive releases" NOTE: Radioactive releases would occur only if containment was penetrated or compromised 33 PORV High-Low Pressure Interface Licensing Basis (cont)

• SNUPPS FSAR Question Q280.5 (cont.)

• SNUPPS response of 5/18/81 stated the RHR letdown isolation valves and the PressurizerPORVsand

associated PORV isolation valves are high/low

pressure interfaces

• Stated FSAR Appendix 9.5B (to be submitted in June 1981) demonstrates no single credible fire could cause spurious opening of these valves

• Question 280.5 and response subsequently incorporated into SNUPPS FSAR and maintained in

WCGS USARNOTE: as previously shown -the piping downstream ofPORVsis wholly contained inside containment 34 PORV High-Low Pressure Interface Licensing Basis (cont)

• September 1981 -SNUPPS submitted Event V Program (program for testing the isolation between

low pressure systems and the reactor coolant

pressure boundary)

• Submitted based on request from NRC at a June 1981 meeting with SNUPPS

• Identified only two subsystems that satisfy Event V valve configuration -cold leg injection system and hot leg injection system

• PressurizerPORVs and isolation valves are not identified as high-low pressure interfaces 35 PORV High-Low Pressure Interface Licensing Basis (cont)

• April 1982 -NUREG-0881 (WCGS SER) Section 1.8

• Confirmatory Item B.3 (Section 3.9.6) -have addressed leak testing of only those check valves with

an Event V configuration

• In addition to the above check valves, required that leaktight integrity of the accumulator discharge check valves, the boron injection system PIVs, and the

MOVS in the RHR System

• June 1983 -Supplement 2 to NUREG 0881 (WCGS SER) -"After review of the list of pressure isolation valves, we find it acceptably complete and consider

the confirmatory item complete" 36 PORV High-Low Pressure Interface Licensing Basis (cont)

• Generic Letter 87-06, "Periodic Verification of Leak Tight Integrity of Pressure Isolation Valves"

• Request submittal of list of PIVs and description of periodic tests to assure integrity of the valve

• June 5, 1987 -WCNOC response referred to the listing of PIVs in TS Table 3.4-1 and associated surveillance testing requirements (PORVs and

isolation valves not included in TS Table)

• NRC Inspection Report 92-09 -reviewed PIVs in IST Program and the response to GL 87-06 and no

issues identified 37 PORV Conclusion

• PORVs do not constitute a high-low pressure interface as intended by WASH 1400

• PORVsare not identified as a high-low pressure interface in WCGS SER (NUREG 0881)

• Response to FSAR question Q280.5 is in error

• Proposed change will be submitted to the NRC, iaw 10 CFR 50.90, as a change that could

adversely affect the ability to achieve and

maintain safe shutdown in the event of a fire (License Condition 2.C.(5))

• PFSSD Analysis of PORVsand isolation valves would utilize less severe methodology 38 PORV Conclusion

• Questions*Comments and Feedback 39