IR 05000482/2011007
| ML13101A301 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 03/29/2013 |
| From: | Broschak J P Wolf Creek |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| ET 13-0012, IR-11-007 | |
| Download: ML13101A301 (15) | |
Text
W*.L, F CR EE KNUCLEAR OPERATING CORPORATIONJohn P. BroschakVice President EngineeringMarch 29, 2013ET 13-0012U. S. Nuclear Regulatory CommissionATTN: Document Control DeskWashington, DC 20555Reference: Letter dated December 27, 2011, from J. Mateychick, USNRC, toM. W. Sunseri, WCNOC, "Wolf Creek Generating Station -NRCTriennial Fire Inspection Report (05000482/2011007)"Subject: Docket No. 50-482: Request for Review of Information to SupportResolution of Example 2 of Non-cited Violation 05000482/2011007-03, "Failure to Ensure Post-Fire Safe Shutdown ComponentsRemain Free of Fire Damage"Gentlemen:The purpose of the letter is to request Nuclear Regulatory Commission (NRC) Region IV reviewof the information provided in the Attachment for the resolution of Example 2 of Non-citedViolation (NCV)0500482/2011007-03, "Failure to Ensure Post-Fire Safe ShutdownComponents Remain Free of Fire Damage." The NCV was identified during the October 17,2011, through December 12, 2011, triennial fire protection inspection as documented in theReference.The NRC identified that Wolf Creek Nuclear Operating Corporation (WCNOC) had failed toproperly analyze for fire damage in the form of shorts-to-ground related to the pressurizerpower-operated relief valves (PORV). Certain postulated shorts-to-ground could spuriouslyactuate these valves such that safe shutdown would be impacted. This deficiency wasdocumented in Condition Report 00045452. Subsequent to this inspection, the NRC issuedadditional information based on fire testing results. Utilizing this information in conjunction withthe guidance in Nuclear Energy Institute (NEI) 00-01, Revision 2, "Guidance for Post Fire SafeShutdown Circuit Analysis," WCNOC has determined that the PORV circuits had been properlyanalyzed and that further modification to these circuits is not required.WCNOC requests that NRC Region IV review the attached information for resolution ofExample 2 of NCV 0500482/2011007-03 and provide the results of the review by September 1,2013. The information in the Attachment was discussed with NRC Region IV personnel onJanuary 8 and 28, 2013, and with the NRC Project Manager for the Wolf Creek GeneratingStation on February 13, 2013.P.O. Box 411 / Burlington, KS 66839 / Phone: (620) 364-8831An Equal Opportunity Employer M/FIHC/VET ET 13-0012Page 2 of 2This letter contains no commitments. If you have any questions concerning this matter, pleasecontact me at (620) 364-4085, or Mr. Michael J. Westman at (620) 364-8831 ext. 4009.
Sincerely,IJohn P. BroschakJPB/rltAttachment IEnclosure-Request for Review of Information to Support Resolution of Example 2 ofNon-cited Violation 05000482/2011007-03-Drawing E-13BB40: Schematic Diagram Pressurizer Power Relief Valvescc: E. E. Collins (NRC), w/a, w/eC. F. Lyon (NRC), w/a, w/eG. B. Miller (NRC), w/a, w/eN. F. O'Keefe (NRC), w/a, w/eSenior Resident Inspector (NRC), w/a, w/e Attachment I to ET 13-0012Page 1 of 11Request for Review of Information to Support Resolution of Example 2 of Non-citedViolation 05000482/2011007-03The Nuclear Regulatory Commission (NRC) identified in NRC Triennial Fire Inspection Report05000482/2011007 (Reference 1) that Wolf Creek Nuclear Operating Corporation (WCNOC)had failed to properly analyze for fire damage in the form of shorts-to-ground related to thepressurizer power-operated relief valves (PORV). Certain postulated shorts-to-ground couldspuriously actuate these valves such that safe shutdown would be impacted. This deficiencywas documented in Condition Report 00045452. Subsequent to this inspection, NUREG/CR-7150, Vol. 1/EPRI 1026424 (Reference 10), "Joint Assessment of Cable Damage andQuantification of Effects from Fire (JACQUE-FIRE)," was issued and provided additionalinformation based on fire testing results. Utilizing this information in conjunction with theguidance in Nuclear Energy Institute (NEI) 00-01, Revision 2 (Reference 2), "Guidance for PostFire Safe Shutdown Circuit Analysis," WCNOC has determined that the PORV circuits hadbeen properly analyzed and that further modification to these circuits is not required. Providedbelow is WCNOC's basis for this determination.Wolf Creek Generating Station (WCGS) Renewed Facility Operating LicenseThe Wolf Creek Generating Station (WCGS) Renewed Facility Operating License NPF-42,Section 2.C.(5) conditions the operating license as follows regarding fire protection:(5) Fire Protection (Section 9.5.1, SER, Section 9.5.1.8, SSER #5)(a) The Operating Corporation shall maintain in effect all provisions of theapproved fire protection program as described in the SNUPPS Final SafetyAnalysis Report for the facility through Revision 17, the Wolf Creek siteaddendum through Revision 15, and as approved in the SER throughSupplement 5, Amendment No. 191, and Amendment No. 193 subject toprovisions b and c below.(b) The licensee may make changes to the approved fire protection programwithout prior approval of the Commission only if those changes would notadversely affect the ability to achieve and maintain safe shutdown in theevent of a fire.(c) Deleted.Removal of High/Low Pressure Interface Designation for Pressurizer Power Operated ReliefValves (PORVs)Wolf Creek Nuclear Operating Corporation (WCNOC) letter ET 10-0013 (Reference 3)submitted a license amendment request that proposed the removal of the high/low pressureinterface designation from the pressurizer power operated relief valves (PORVs) and theirassociated block valves.WCNOC submitted letter WM 10-0016 (Reference 4) in response to a request for supplementalinformation concerning Reference 1. The response stated, in part:
Attachment I to ET 13-0012Page 2 of 11For non-high/low pressure interface components, the WCGS PFSSDA [post-firesafe shutdown analysis] considers one proper polarity inter-cable hot short and anynumber of proper polarity intra-cable hot shorts within multi-conductor cables associatedwith the component.""... The non-high/low pressure interface criteria requires consideration of a single properpolarity hot short on ungrounded DC circuits. Furthermore, the Wolf Creek PFSSDAconsiders any number of intra-cable hot shorts on any circuit regardless of itsclassification. Therefore, upon approval of this request, Wolf Creek will analyze thepressurizer PORVs by considering any-and-all intra-cable hot shorts in conjunction withone proper polarity inter-cable hot short."De-energizing both polarities ensures a single proper polarity hot short will notprevent operators from de-energizing the AR [auxiliary relay] using the hand switch inthe control room.""... In addition, the contactor panel will be re-wired to insert open contacts on thenegative side of the '72' relay and the PORV solenoid to maintain both the positive andnegative sides de-energized. This will ensure a single proper polarity hot short will notenergize the '72' relay or the PORV solenoid and open the PORV.""... The modifications will ensure that a single proper polarity inter-cable hot short incombination with any number of intra-cable hot shorts will not prevent closure of thePORVs from the control room or will prevent spurious operation of the PORVs."The Nuclear Regulatory Commission (NRC) issued License Amendment No. 193 (Reference 5)that approved the removal of the high/low pressure interface designation for the PORVs. TheSafety Evaluation for Amendment No. 193, states, in part (page 9):"The only fire-induced failure that could circumvent the proposed plant modification istwo simultaneous independent proper polarity (positive-to-positive and negative-to-negative) inter-cable hot shorts."The Safety Evaluation for Amendment No. 193, concludes, in part (page 10):"The proposed modifications would allow operating a control room switch to prevent ormitigate a fire-induced spurious opening of the PORVs. The only scenario that wouldremain that could cause the PORVs to open would involve two simultaneous inter-cableproper polarity cable failures. ... Changing the high-low pressure commitments will allowthe licensee to analyze PORV cables for a single proper polarity hot short between twocables (inter-cable) in combination with any number of internal cable (intra-cable) hotshorts. .... The proposed modifications and control room operator actions provide anadequate level of protection as described in Section III.G.2 of Appendix R to 10 CFRPart 50."Based on the information in the NRC Safety Evaluation for License Amendment No. 193, theanalysis of the PORV circuitry required consideration of a single proper polarity hot shortbetween two cables in combination with any number of internal cable hot shorts. Multiple shortsto ground that impress a voltage on one side of the circuit in conjunction with a proper polarityexternal hot short is not a circuit failure combination that is required to be analyze Attachment I to ET 13-0012Page 3 of 11Analysis and Modification of PORV CircuitsDuring Refueling Outage 18 in Spring, 2011, WCNOC implemented design change package(DCP) 12944, "PORV BBPCV0455A and BBPCV0456A Circuit PFSSD Modifications." Thismodification re-wired the control circuit associated with both pressurizer PORVs to ensure asingle proper-polarity hot short and/or multiple intra-cable hot shorts could either be mitigatedfrom the control room or would not cause the PORVs to spuriously open. Prior to themodification, the PORV circuits were of the "single break" design. In a single break circuit, oneside of the circuit is always "hot" while the other side requires contact closure to complete thecircuit. The PORV modification implemented per DCP 12944 created a "double break" circuit,where both sides of the circuit are de-energized. A double break circuit requires a minimum oftwo contact closures, one on the positive side and one on the negative side, to energize thecircuit. Therefore, a double break circuit requires two proper polarity hot shorts to open thePORV and maintain it in the open position. The Enclosure provides drawing E-13BB40,"Schematic Diagram Pressurizer Power Relief Valves," that depicts the modified circuit.NRC Triennial Fire Inspection Report (05000482/2011007)From October 17, 2011 through December 12, 2011 the NRC conducted a triennial fireprotection inspection with the results being documented in inspection report05000482/2011007. Provided below are excerpts associated with Non-cited Violation (NCV)0500482/2011007-03, "Failure to Ensure Post-Fire Safe Shutdown Components Remain Freeof Fire Damage."Introduction. The team identified a Green non-cited violation of License Condition2.C(5) because the licensee failed to implement and maintain in effect all provisions ofthe approved fire protection program. Specifically, the licensee failed to properlyanalyze for fire damage in the form of shorts-to-ground related to the residual heatremoval Train B refueling water storage tank suction valve and the pressurizer power-operated relief valves. Certain postulated shorts-to-ground could spuriously actuatethese valves such that safe shutdown would be impacted. The licensee documentedthese deficiencies in Condition Reports 044912 and 045452, respectively.Description. The licensee conducted a circuit analysis to identify circuit vulnerabilitiescreated by fire damage affecting post-fire safe shutdown components. The teamindependently assessed the licensee's circuit analysis of several components. Theteam identified two examples where the licensee failed to properly evaluate fire damagein the form of shorts-to-ground. The affected components included Valve BNHV8812B,refueling water storage tank to residual heat removal Pump B suction valve, and ValvesBBPCV0455A and BBPCV0456A, pressurizer power-operated relief valves.Example 2: Failure to Analyze the Effects of Grounds on the Pressurizer Power-Operated Relief ValveBy letter dated March 9, 2011, the NRC approved License Amendment No. 193 thatchanged the categorization of the pressurizer power-operated relief valves and blockvalves to non-high/low pressure interface valves. Changing the categorization allowedthe licensee to consider a single hot short rather than two hot shorts when evaluatingthe possible circuit failures. Since a portion of the defense-in-depth basis for thisdeclassification included a circuit modification to the power-operated relief valve circuits, Attachment I to ET 13-0012Page 4 of 11the team selected these valve circuits for additional review. Change Package 012944,"Power-Operated Relief Valve BBPCV0455A and BBPCV0456A Circuit Modifications,"modified the control circuit by adding contacts that isolated the positive and negativesides of the actuation relays and solenoids. The modification prevented a single hotshort from causing Valves BBPCV0455A and BBPCV0456A from spuriously openingand provided the operators the capability to close the power-operated relief valves fromthe control room.The team identified that the licensee limited the failure modes review to a single hotshort without considering the hot short coincident with other types of fire damage (i.e.,open circuits or shorts to ground) to cables in the cable tray. The team postulated a firethat would cause a single inter-cable hot short combined with fire damage creatingmultiple grounds of remaining cables in the cable tray. With this fire damage present,the pressurizer power-operated relief valve solenoid would energize and the operatorswould be unable to close the pressurizer power-operated relief valve from the controlroom. The pressurizer block valves can normally be used to isolate a pressurizer poweroperated-relief valves; however, the pressurizer block valve cables were routed abovethe pressurizer power-operated relief valve cables in the fire areas and would be subjectto the same fire damage caused by the same fire.The licensee did not implement any modifications to protect the circuits for thepressurizer power-operated relief valve block valves nor did they instruct operators toclose the block valves. Consequently, if a pressurizer power-operated relief valvespuriously opened because of fire damage, operators would not have the ability toisolate the power-operated relief valves. This unisolable path would result in a loss ofreactor coolant inventory and loss of pressure control that exceeded the plant responseto a loss of normal ac power. The team identified areas in the plant with cables routedfor both the pressurizer power-operated relief and block valves that could be damagedduring a fire.For both of the circuit issues, the team determined that the licensee did not follow theguidelines contained in NEI 00-01, "Guidance for Post-Fire Safe Shutdown CircuitAnalysis," Revision 2 and Regulatory Guide 1.189, "Fire Protection for Nuclear PowerPlants," Revision 2, Section 5.3. Section 5.3 identifies that licensees should considercircuit faults in at least two adjacent, external cables and all interactions within the targetcable. Specifically, the licensee did not correctly account for the interactions amongcables for all types of fire damage. This failure requires a hot short combined with ashort to ground of the target cable and a short to ground on one additional cable. Thelicensee implemented a fire watch as a compensatory measure for the deficiencies.Generic Letter 86-10Generic Letter 86-10 (Reference 6), "Implementation of Fire Protection Requirements (GenericLetter 86-10)," provides NRC Staff interpretations of 10 CFR 50, Appendix R. Enclosure 2 toGL 86-10 provides NRC Staff answers to industry questions related to implementation of 10CFR 50, Appendix R. Question 5.3.1, "Circuit Failure Modes," states the following:"What circuit failure modes must be considered in identifying circuits associated byspurious actuation."
Attachment I to ET 13-0012Page 5 of 11The NRC Staff response to this question is as follows:"Sections III.G.2 and III.L.7 of Appendix R define the circuit failure modes as hot shorts,open circuits, and shorts to ground. For consideration of spurious actuations, allpossible functional failure states must be evaluated, that is, the component could beenergized or de-energized by one or more of the above failure modes. Therefore,valves could fail open or closed; pumps could fail running or not running; electricaldistribution breakers could fail open or closed. For three-phase AC circuits, theprobability of getting a hot short on all three phases in the proper sequence to causespurious operation of a motor is considered sufficiently low as to not require evaluationexcept for any cases involving Hi/Lo pressure interfaces. For ungrounded DC circuits, ifit can be shown that only two hot shorts of the proper polarity without grounding couldcause spurious operation, no further evaluation is necessary except for any casesinvolving Hi/Lo pressure interfaces."The pressurizer PORV circuit is an ungrounded DC circuit. Based on License Amendment No.193, the PORVs are not designated as high/low pressure interfaces. Therefore, WCNOC is notrequired to consider two or more proper polarity hot shorts causing spurious actuation of thePORVs.NEI 00-01, Revision 2NEI 00-01, "Guidance for Post Fire Safe Shutdown Circuit Analysis," Revision 2, Section3.5.1.1, "Circuit Failure Criteria," specifies criteria that addresses the effects of multiple-fireinduced circuit failures impacting circuits for components classified as either "required for hotshutdown" or "important to safe shutdown." Section 3.5.1.1 states, part:"A hot short may result from a fire-induced insulation breakdown between conductors ofthe same cable, a different cable or from some other external source resulting in acompatible but undesired impressed voltage or signal on a specific conductor. A hotshort may cause a spurious operation of safe shutdown equipment.""A short-to-ground may result from a fire-induced breakdown of a cable insulationsystem, resulting in the potential on the conductor being applied to ground potential. Ashort-to-ground may have all of the same effects as an open circuit and, in addition, ashort-to-ground may also cause an impact to the control circuit or power train of which itis a part. A short-to-ground may also result in a change of state for normally energizedequipment."From the guidance in NEI 00-01, for "important to safe shutdown" components (i.e., thepressurizer PORVs), multiple shorts to ground are to be evaluated for their impact onungrounded circuits as explained in Figure 3.5.2-3. Figure 3.5.2-3 (see page 7 below) showsexamples of the effects of shorts to ground on ungrounded DC circuits and illustrates that asingle short to ground anywhere in the circuit will not cause a loss of control power to the circuit.In order for control power to be lost, another short to ground would have to exist somewhere inthe circui Attachment I to ET 13-0012Page 6 of 11An important distinction between hot shorts and shorts to ground is that hot shorts can causespurious operation of equipment whereas shorts to ground can only result in loss of power orchange of state for normally energized equipment. Multiple shorts to ground that causespurious equipment operation are treated in traditional circuit analysis as hot shorts.NEI 00-01, Section 3.5.2.2, "Circuit Failures Due to a Short-to-Ground," provides guidance foraddressing the effects of a short to ground on circuits for "required for hot shutdown" or"important to safe shutdown." Section 3.5.2.2 states, in part:"A short-to-ground is a fire-induced breakdown of a cable insulation system resulting inthe potential on the conductor being applied to ground potential. A short-to-ground cancause a loss of power to or control of required safe shutdown equipment. In addition, ashort-to-ground may affect other equipment in the electrical power distribution system inthe cases where proper coordination does not exist.There is no limit to the number of shorts-to-ground that could be caused by the fire.Consider the following consequences in the post-fire safe shutdown analysis whendetermining the effects of circuit failures related to shorts-to-ground:* A short to ground in a power or a control circuit may result in tripping one or moreisolation devices (i.e. breaker/fuse) and causing a loss of power to or control ofrequired safe shutdown equipment.* In the case of certain energized equipment such as HVAC dampers, a loss of controlpower may result in loss of power to an interlocked relay or other device that maycause one or more spurious operations."None of the potential consequences discussed in the above bullets involve energizing thecircuit. The short to ground concern is focused on loss of power to the circuit or loss of powerto upstream power supplies in the event of improper circuit coordination.Figure 3.5.2-3 in NEI 00-01 illustrates how a short to ground fault may impact an ungroundedcircui Attachment I to ET 13-0012Page 7 of 11Fuse (Typ.)Short-to-Ground Control SwitchSNo.1 Short-to-Ground2 No. 2 I0UEnergizet Energize toOpen/Start CloseieStopf Short-to-Ground-No. 3Figure 3.5.2-3: Short to Ground(Ungrounded Control Circuit)"Short-to-.qround No. 1A short-to-ground at location No. 1 will result in the control power fuse blowing and aloss of power to the control circuit if short-to-ground No. 3 also exists either within thesame circuit or on any other circuit fed from the same power source. This will result inan inability to operate the equipment using the control switch. Depending on thecoordination characteristics between the protective device on this circuit and upstreamcircuits, the power supply to other circuits could be affected. If multiple grounds canoccur in a single fire area, they should be assumed to occur simultaneously unlessjustification to the contrary is provided.""Short-to-.qround No. 2A short-to-ground at location No. 2 will have no effect on the circuit until the close/stopcontrol switch is closed. Should this occur, the effect would be identical to that for theshort-to-ground at location No. 1 described above. Should the open/start control switchbe closed prior to closing the close/stop control switch, the equipment will still be able tobe opened/started. If multiple grounds can occur in a single fire area, they should beassumed to occur simultaneously unless justification to the contrary is provided. Notethat a simultaneous short-to-ground at locations No. 1 and No. 2 could result in aspurious close/stop. This condition is identical to that portrayed in Figure 3.5.2-5 shoulda hot short occur on the ungrounded circuit shown in Figure 3.5.2-5 at location No. 1."
Attachment I to ET 13-0012Page 8 of 11Fuse (Typ.)00~000.'0F--No. 2Energize to Energize toOpen/Start Close/StopKm.iFigure 3.5.2-5: Hot Short(Ungrounded Control Circuit)Regqulatory Guide 1.189, Revision 2Regulatory Guide (RG) 1.189, Revision 2 (Reference 7), "Fire Protection for Nuclear PowerPlants," Section 5.3, "Fire Protection of Safe-Shutdown Capabilities," indicates, with someexceptions, that Chapter 3 of NEI 00-01 provides an acceptable deterministic methodology forthe analysis of post fire safe-shutdown circuits, when applied in conjunction with the RG. Thissection of the RG further indicates that the seventh bullet in Section 3.5.1.1 of NEI 00-01 titled"Circuits for important to safe shutdown components" is not endorsed by the NRC. Theseventh bullet in Section 3.5.1.1 of NEI 00-01 states:"Conversely, multiple fire-induced circuit failures affecting separate conductors inseparate cables with the potential to cause a spurious operation of an "important tosafe shutdown" component need not be assumed to exist concurrently when the effectof the fire-induced circuit failure is not sealed-in or latched. This criterion applies toconsideration of concurrent hot shorts in secondary circuits and to their effect on acomponents primary control circuit. It is not to be applied to concurrent single hotshorts in primary control circuit for separate components in an MSO combination."In lieu of the seventh bullet in Section 3.5.1.1 of NEI 00-01, RG 1.189, Section 5.3 addressescircuits not sealed in or latched as follows:"For circuits not sealed-in or latched for equipment important to safe shutdown, licenseesshould consider multiple fire-induced circuit failures in at least two separate cables. Forcircuits not sealed-in or latched for equipment important to safe shutdown that involveshigh-low pressure interfaces, licensees should consider circuit failures in at least threecables."
Attachment I to ET 13-0012Page 9 of 11As indicated on page 4 above, NRC Triennial Fire Inspection Report (05000482/2011007)states, in part:"Section 5.3 [RG 1.189] identifies that licensees should consider circuit faults in at least twoadjacent, external cables and all interactions within the target cable. Specifically, thelicensee did not correctly account for the interactions among cables for all types of firedamage. This failure requires a hot short combined with a short to ground of the targetcable and a short to ground on one additional cable. The licensee implemented a fire watchas a compensatory measure for the deficiencies."The NRC Triennial Fire Inspection Report specified that RG 1.189 identified that licenseesshould consider circuit faults in at least two adjacent, external cables and all interactions withinthe target cable. This implies that three cables would need to be affected. The RG specifiesthat licensees should consider multiple fire-induced circuit failures in at least two separatecables for non high-low pressure interfaces.The pressurizer PORV circuits are not sealed in or latched. In the modified PORV circuitdesign shown in the Enclosure, consideration was given for multiple fire-induced circuit failuresin at least two separate cables, consistent with the guidance in RG 1.189. The WCNOC designconsiders any number of intra-cable hot shorts combined with a single proper polarity inter-cable hot short on cables located in the fire area of concern. Therefore, WCNOC meets theguidance specified in RG 1.189, Section 5.3.Regulatory Guide 1.189 defines hot short and short to ground as follows:Hot short -Individual conductors of the same or different cables that come in contactwith each other and that may result in an impressed voltage or current on the circuitbeing analyzed.Short-to-ground -A short circuit between a conductor and a grounded reference point(e.g., grounded conductor, conduit or other raceway, metal enclosure, shield wrap, ordrain wire within a cable).From these definitions, as well as the definitions in NEI 00-01, a circuit failure that causes animpressed voltage is a hot short. Furthermore, a multiple short-to-ground that impresses anunwanted voltage on the circuit is a hot short. Since the pressurizer PORVs are designated asnon-high/low pressure interfaces, multiple shorts to ground that impress unwanted voltagealong with a single proper polarity hot short does not have to be analyzed since this is the sameas two proper polarity hot shorts.Fire TestingThe NRC conducted fire testing of energized DC circuits and reported the results inNUREG/CR-7100 (Reference 8), "Direct Current Electrical Shorting in Response to ExposureFire (DESIREE-Fire): Test Results" in April, 2012. The test results were analyzed in draftNUREG-2128 (Reference 9), "Electrical Cable Test Results and Analysis During Fire Exposure(ELECTRA-FIRE)." Based on the data analysis reported in draft NUREG-2128, the followingobservations were made during the test Attachment I to ET 13-0012Page 10 of 11* Shorts through the ground plane or common conductors are possible, provided thatthe circuits involved are ungrounded and use a common power supply.* Seventeen tests were conducted to evaluate the likelihood of proper-polarity inter-cable (cable-to-cable) shorting. Of these tests, only one showed weak signs ofmultiple external shorts to separate conductors. This test, identified as penlight #47, used thermoplastic PE/PVC insulated cable.* None of the tests resulted in a proper polarity ground fault equivalent hot short incombination with an inter-cable proper polarity hot short.A Phenomena Identification and Ranking Table (PIRT) panel was assembled made up of NRCand Nuclear Industry representatives. The objective of the PIRT was to identify phenomenathat can affect the fire-induced failure modes of electrical circuits after cables are damaged byfire. The PIRT panel used the results of recent NRC, NEI and EPRI tests to identify circuitconfigurations that are vulnerable to fire-induced circuit failures that can cause spuriousoperation of components. The results of the PIRT panel are documented in NUREG/CR-7150,Vol. 1/EPRI 1026424 (Reference 10), "Joint Assessment of Cable Damage and Quantificationof Effects from Fire (JACQUE-FIRE)."The final disposition of the PIRT panels evaluation on some specific issues was characterizedas "incredible" or "implausible." The definition of each is as follows:Incredible -The event will not occur.Implausible -The event, while theoretically possible, would require the convergence ofa combination of factors that are so unlikely to occur that the liklihood of thephenomenon can be considered statistically insignificant.Table 3-7 in NUREG/CR-7150 summarizes the PIRT panel results for a double breakungrounded DC circuit. Based on Table 3-7, an inter-cable hot short combined with a groundfault equivalent hot short involving thermoset cables is considered incredible. This circuit failurecombination was postulated by the NRC during the 2011 Triennial Fire Protection Inspectionand resulted in example 2 of NCV 05000482/2011007-03. An intra-cable hot short combinedwith a ground fault equivalent hot short involving thermoset cables is considered possible andhas been addressed in Change Package 012944 for the pressurizer PORVs. For WCGS, anintra-cable hot short combined with a ground fault equivalent hot short will result in either thePORV remaining closed or the PORV opening with mitigating action available from the controlroom.ConclusionsBased on the above information, WCNOC has determined that the PORV circuits had beenproperly analyzed and that further modification to these circuits is not required. Consistent withthe guidance in RG 1.189, a single proper polarity inter-cable hot short in combination with twoshorts to ground that impresses a voltage on the opposite polarity is effectively two hot shorts,does not have to be analyzed for non-high/low pressure interface components. Furthermore,industry testing does not support the claim that a ground fault equivalent hot short incombination with a proper-polarity inter-cable hot short can occur. A PIRT panel composed ofNRC and Industry experts concluded in NUREG/CR-7150 that this combination of failures will Attachment I to ET 13-0012Page 11 of 11not occur. Therefore, further analyses or modification of the PORV circuits is not required forthe resolution of Example 2 of NCV 05000482/2011007-03.References1. Letter from J. Mateychick, USNRC, to M. W. Sunseri, WCNOC, "Wolf Creek GeneratingStation -NRC Triennial Fire Inspection Report 05000482/2011007," December 27, 2011.ADAMS Accession No. ML11361A427.2. Nuclear Energy Institute (NEI) 00-01, Revision 2, "Guidance for Post Fire Safe ShutdownCircuit Analysis," May 2009.3. WCNOC letter ET 10-0013, "License Amendment Request (LAR) to the Approved FireProtection Program to Remove the High/Low Pressure Interface Designation from thePressurizer Power Operated Relief Valves (PORVs) and their Associated Block Valves,"April 13, 2010. ADAMS Accession No. ML101100479.4. WCNOC letter WM 10-0016, "Response to Supplemental Information Request for LicenseAmendment Request to Remove the High/Low Pressure Interface Designation from thePressurizer Power Operated Relief Valves (PORVs) and their Associated Block Valves,June 1, 2010. ADAMS Accession No. ML101590671.5. Letter from B. K. Singal, USNRC, to M. W. Sunseri, WCNOC, "Wolf Creek GeneratingStation -Issuance of Amendment re: Removing High/Low Pressure Designation from thePressurizer Power-Operated Relief Valves (TAC NO. ME3766)," March 9, 2011. ADAMSAccession No. ML110530183.6. Generic Letter 86-10, "Implementation of Fire Protection Requirements (Generic Letter86-10)," April 24, 1986.7. Regulatory Guide 1.189, Revision 2, "Fire Protection for Nuclear Power Plants," October2009.8. NUREG/CR-7100, "Direct Current Electrical Shorting in Response to Exposure Fire(DESIREE-Fire): Test Results," April 2012.9. Draft NUREG-2128, "Electrical Cable Test Results and Analysis During Fire Exposure(ELECTRA-FIRE)," June 2012.10. NUREG/CR-7150, Vol. 1/EPRI 1026424, "Joint Assessment of Cable Damage andQuantification of Effects from Fire (JACQUE-FIRE)," October 201 Enclosure to ET 13-0012Drawing E-13BB40Schematic Diagram Pressurizer Power Relief Valves(1 page)