ML061230107
| ML061230107 | |
| Person / Time | |
|---|---|
| Site: | Kewaunee  |
| Issue date: | 05/05/2006 |
| From: | Hackett E Plant Licensing Branch III-2 |
| To: | Satorius M Division Reactor Projects III |
| jaffe D, NRR/ADRO/DORL, 415-1439 | |
| References | |
| TAC MC8937 | |
| Download: ML061230107 (9) | |
Text
May 5, 2006MEMORANDUM TO:Mark A. Satorius, DirectorDivision of Reactor Projects Region IIIFROM:Edwin M. Hackett, Deputy Director /RA/ Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation
SUBJECT:
FINAL RESPONSE TO TASK INTERFACE AGREEMENT 2005-10RELATING TO IMPACT OF FLOODING ON RESIDUAL HEAT REMOVAL (RHR) PUMPS AT KEWAUNEE POWER STATION (TASK INTERFACE AGREEMENT (TIA) 2005-10)(TAC NO. MC8937)By memorandum dated November 17, 2005, Region III submitted Task Interface Agreement(TIA) 2005-10, which requested assistance from the Office of Nuclear Reactor Regulation (NRR) to resolve the following three issues related to RHR pump vulnerability to flooding whichmay result due to seismically induced or random failures of non-seismically qualified piping at Kewaunee Power Station (Kewaunee):*Does Kewaunee's licensing basis require the RHR system to be protected fromseismically induced or random flooding to maintain its at-power operable status in accordance with Technical Specifications?*Does Kewaunee's licensing basis require the RHR system to be protected fromseismically induced or random flooding to maintain its below-hot-shutdown operable status in accordance with Technical Specifications?*Is RHR operability mode specific? If the RHR system is inoperable below hot shutdown,is the system inoperable above hot shutdown? If it is determined that the RHR systemis operable above hot shutdown but inoperable below hot shutdown, what would be therequired licensee action?By memorandum dated April 5, 2006, NRR issued a draft TIA response prepared by NRR'sDivision of Safety Systems, Balance-of-Plant Branch which Region III was requested to reviewand provide its comments to NRR's Division of Operating Reactor Licensing within 30 days. OnApril 21, 2006, NRR held a telephone conference with Region III to discuss the draft TIAresponse. By memorandum dated April 26, 2006, Region III provided comments on the draftTIA response. This final TIA reflects Region III's comments.Docket No. 50-305
Enclosure:
NRR Staff AssessmentCONTACT: David H. Jaffe, NRR/DORL (301) 415-1439 MEMORANDUM TO:Mark A. Satorius, DirectorDivision of Reactor Projects Region IIIFROM:Edwin M. Hackett, Deputy Director /RA/ Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation
SUBJECT:
FINAL RESPONSE TO TASK INTERFACE AGREEMENT 2005-10RELATING TO IMPACT OF FLOODING ON RESIDUAL HEAT REMOVAL (RHR) PUMPS AT KEWAUNEE POWER STATION (TASK INTERFACE AGREEMENT (TIA) 2005-10)(TAC NO. MC8937)By memorandum dated November 17, 2005, Region III submitted Task Interface Agreement(TIA) 2005-10, which requested assistance from the Office of Nuclear Reactor Regulation (NRR) to resolve the following three issues related to RHR pump vulnerability to flooding whichmay result due to seismically induced or random failures of non-seismically qualified piping at Kewaunee Power Station (Kewaunee):*Does Kewaunee's licensing basis require the RHR system to be protected fromseismically induced or random flooding to maintain its at-power operable status in accordance with Technical Specifications?*Does Kewaunee's licensing basis require the RHR system to be protected fromseismically induced or random flooding to maintain its below-hot-shutdown operable status in accordance with Technical Specifications?*Is RHR operability mode specific? If the RHR system is inoperable below hot shutdown,is the system inoperable above hot shutdown? If it is determined that the RHR systemis operable above hot shutdown but inoperable below hot shutdown, what would be therequired licensee action?By memorandum dated April 5, 2006, NRR issued a draft TIA response prepared by NRR'sDivision of Safety Systems, Balance-of-Plant Branch which Region III was requested to reviewand provide its comments to NRR's Division of Operating Reactor Licensing within 30 days. OnApril 21, 2006, NRR held a telephone conference with Region III to discuss the draft TIAresponse. By memorandum dated April 26, 2006, Region III provided comments on the draftTIA response. This final TIA reflects Region III's comments.Docket No. 50-305
Enclosure:
NRR Staff AssessmentCONTACT: David H. Jaffe, NRR/DORL(301) 415-1439DISTRIBUTION
- PUBLICRidsNrrDorlSJones LPL3-1 R/FRidsNrrLplcSBurton, RIII RidsNrrAdroRidsNrrPMDJaffePLouden, RIII RidsRgn3MailCenter RidsNrrLATHarrisRidsNrrPMSMonarqueADAMS Accession Number: ML061230107 OFFICEDSS/SBPBDSS/SPWB/BCDSS/SBPB/BCLPL3-1/PMLPL3-1/LALPL3-1/BCDORL/DDDIRS/ITSBNAMESJonesJNakoskiDSolorioDJaffeTHarrisLRaghavanCMillerTKobetzDATE05/4/0605/ 4/0605/4/0605/5/0605/5/0605/4/0605/5/065/4/06OFFICIAL RECORD COPY ENCLOSUREFINAL STAFF ASSESSMENTOFFICE OF NUCLEAR REACTOR REGULATIONIMPACT OF FLOODING ON RESIDUAL HEAT REMOVAL PUMPS AT THE KEWAUNEEPOWER STATIONTASK INTERFACE AGREEMENT 2005-1
01.0 INTRODUCTION
The Kewaunee Power Station (Kewaunee) licensee (currently Dominion Energy Kewaunee,Inc.) completed an internal flooding analysis in June 2005, as part of an extent of condition review for the station's response to flooding in the auxiliary building under the licensee'scalculation 2005-05708, "Internal Flood Levels Due to Postulated Piping Ruptures In GeneralPipe Lines In Auxiliary Building" Revision 1. Region III inspectors noted that this evaluationidentified several potential flooding sources, including a non-seismically mounted service water pipe and non-seismically mounted condensate line, which could result in both residual heat removal (RHR) pump pits being filled with water to over 8 feet and cause both RHR pumpmotors to fail.Given that both pumps were vulnerable to flooding from a single-failure, the inspectorsquestioned the operability of the RHR system in the emergency core cooli ng system mode. The licensee asserted that this condition was known and is acceptable because the plant is a "hot shutdown" plant and no credit for RHR is given in reaching and maintaining hot shutdown,in accordance with the licensee's response to unresolved safety issue (USI) A-46, following a seismic event. The licensee also stated that a loss-of-coolant accident (LOCA) is not assumed coincident with a seismic event or flood. The inspectors also questioned the operability of RHRin the decay heat removal mode. The licensee asserted that flooding events were not part ofthe licensing basis for RHR which is based on hot shutdown conditions and concluded that bothRHR trains were operable. The initial questions by the residents were characterized as anUnresolved Item in the 2nd quarter integrated inspection report (05000305/2005008). No performance deficiency was identified pending resolution of the issue.
2.0 BACKGROUND
The issues identified by the inspectors involve the definition of operability. Technical guidanceprovided in Part 9900 of the Nuclear Regulatory Commission (NRC) Inspection Manual lists thefollowing principal criteria for technical specification operability requirements that are relevant tothe issue:The system operability requirements that are based on safety analysis ofspecific design-basis events for one mode or condition of operation may not be the same for all modes or conditions of operation. The system operability requirements extend to necessary support systemsregardless of the existence or absence of support system requirements. Theoperability of necessary support systems includes regulatory requirements. Itdoes not include consideration of the occurrence of multiple (simultaneous) design-basis events.Section 1.3.1, "Overall Plant Requirements," of the Kewaunee Updated Safety Analysis Report (USAR) states that those systems and components vital to safe shutdown and isolation of thereactor or whose failure might cause or increase the severity of an accident or result in an uncontrolled release of substantial amounts of radioactivity are designated Class I. In Appendix B to the USAR, Table B.2-1 lists the RHR system as a Class I System. USAR,Appendix B, Section B.5, "Protection of Class I Items," states that Class I items are protectedagainst damage from "Rupture of a pipe or tank resulting in serious flooding or excessive steam release to the extent that the Class I function is impaired." Thus, the protection against damagefrom rupture of a pipe is limited to those conditions where t he system is needed to perform itsClass I function. The need for the subsequent performance of the Class I function is informed by earlier licensing basis documents related to pipe rupture or failure.Section 9.3.3, "System Evaluation," of the Kewaunee USAR describes specific design featuresprotecting the RHR pumps from flooding. The design features include separate, shieldedcompartments with floor drains. The floor drains direct water to the RHR pump pit sump, where two 60 gpm sump pumps are provided to pump collected water to the waste holdup tank or the deaerated drains tank. Each drain line has a remotely operated valve that automatically closeson high level within the RHR pump compartment, which would indicate either massive failure or the inability of the sump pumps to handle the leakage. The RHR pump pit sump has a highlevel alarm which will cause an alarm in the main control room on high water level. Each line from the containment sump to the respective RHR pump suction has two remotely operatedisolation valves to isolate RHR following a failure of an RHR pump seal or minor pipe break within the RHR pump room. These features provide protection during performance of the Class I function of the RHR system to provide long-term post-LOCA recirculation cooling.The earliest documents pertaining to seismically-induced or random pipe failure andsubsequent flooding were developed in 1972, following the failure of a circulating water systemexpansion joint at Quad Cities. These documents were concerned with the failure of non-seismic piping systems and the potential flooding of equipment needed for safe shutdown. By letter dated September 26, 1972, the NRC requested Wisconsin Public Service Corporation(a previous Kewaunee licensee) to review Kewaunee to determine whether the failure of any non-Category I (seismic) equipment could result in a condition, such as flooding, that might adversely affect the performance of safety-related equipment required for safe shutdown of the facility or to limit the consequences of an accident. In its response dated October 31, 1972, thelicensee stated that the failure of reactor makeup water and demineralized water lines in the auxiliary building basement could potentially adversely affect the performance of engineeredsafety systems. However, the licensee also stated that, because of safety system redundancyand design arrangement, the functional purpose of the safety equipment would not be jeopardized. The criteria used to make this assessment were not documented.By letter dated November 7, 1972, the licensee responded to an oral NRC staff request toaddress random pipe breaks in systems containing high-energy fluids. Sections I through III ofthe enclosure to that letter provided analyses of postulated breaks in the main steam and main feedwater piping within the auxiliary building, and Section IV of that enclosure describedanalyses of miscellaneous piping systems. The analyses of miscellaneous pipi ng systemsincluded evaluations of potential flooding effects from failures of the service water, component cooling, demineralized water, and reactor makeup water systems. For these evaluations, thelicensee determined that either the system has too low a volume to endanger engineered safetyfeatures or the rate of rise of water level was low enough to allow operator action before affecting safeguards equipment. Again, the specific criteria used in these assessments, such as the break size and the operator response time, were not documented. In their comments on the draft TIA response, Region III staff asked whether a September 23,1971, letter to Wisconsin Public Service Corporation from the staff was part of the staff review of the TIA and whether the contents of the letter are relevant to the questions in the TIA. Thishistorical reference contained a question (Kewaunee Final Safety Analysis Report (FSAR)
Question 8.16) regarding the potential failure of service water piping in proximity to the emergency diesel generator rooms. This question requested that the licensee provide an analysis of the effect of a rupture of one of the service water lines on the emergency power systems. The response to FSAR Question 8.16 was included with Amendment No. 13 to theApplication for Construction Permit and Operating License for the Kewaunee Nuclear Power Plant, issued December 15, 1971. The response stated that the rupture of a service water pipein an emergency diesel generator room could result in loss of the generator or safeguards electrical bus in that room. In addition, the response stated that operation of service watervalves from the control room would isolate the break and, if required, operators would realignservice water supplies through intact piping. This response is consistent with the licensing basis defined in the later letters dated October 31 and November 7, 1972, in that designarrangement would limit the immediate effects and operator action would limit the later effects such that the functional capability of essential safety equipment would be retained. However,the emergency power system is an essential system in achieving hot shutdown, and the staffquestioned the potential failure of the seismically qualified service water lines in the vicinity of the emergency diesel generators based on their safety significance. The later documents establish the licensing basis with respect to pipe failures elsewhere. To further assess protection from pipe breaks in high-energy systems, the NRC issued a letterto Wisconsin Public Service Corporation dated December 15, 1972. This letter was generic in the sense that identical requests for information were sent to all plants operating or underconstruction, and it is commonly referred to as the Giambusso letter. The review criteria included with the Giambusso letter are available as an attachment to Standard Review Plan Section 3.6.1. The Giambusso letter only addressed failure of high-energy piping systems;flooding concerns associated with moderate-energy piping systems such as service water werenot within the scope of the requested review.The final analyses of postulated pipe breaks in high-energy systems were largely described inAmendment No. 24 to the Kewaunee Final Safety Analysis Report, with additional information provided in Amendment Nos. 25, 27, and 28. The NRC staff evaluation of these analyses weredocumented in Supplement 2 to the Licensing Safety Evaluation Report for the Kewaunee Nuclear Power Plant, dated May 10, 1973. The NRC staff's evaluation of pipe breaks outsideof containment did not encompass the flooding issues of concern in the TIA because the evaluation focus was on pipe breaks in high-energy systems. The NRC staff's evaluationclearly stated that the RHR system was not essential to bring the plant to a safe, cold shutdown, in the event of a pipe break in a high-energy system. However, the NRC staff noted that the equipment used to achieve cold shutdown under normal plant operating conditions,which includes the RHR system, would also be used following a high-energy pipe rupture, if theequipment were still available.Two generic safety issues were also relevant to the licensing basis for protection againstinternal flooding. These issues were USI A-17, "Systems Interactions in Nuclear Power Plants,"
and USI A-46, "Seismic Qualification of Equipment in Operating Nuclear Power Plants." Theresolution of USI A-17, as presented in Generic Letter (GL) 89-18, expected licensees to evaluate the potential for water intrusion and flooding from internal sources in the Individual Plant Examination (IPE) process requested by GL 88-20. The Kewaunee IPE did not identify any significant risk associated with internal flooding, and, therefore, no modifications addressing internal flooding vulnerabilities were implemented. The resolution of USI A-46involved the verification of seismic adequacy of mechanical and electrical equipment in nuclear power plants, as documented in GL 87-02. The scope of the seismic verification was limited to components whose failure could damage equipment necessary to maintain the plant in a safe shutdown condition for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. This criterion excludes protection of the RHR system coldshutdown functions from the scope of seismic verification.3.0 BALANCE-OF-PLANT Branch (SBPB) RESPONSE TO REGION III REQUESTSRegion III requested the Office of Nuclear Reactor Regulation to respond to three questions. The SBPB response is summarized below.Question 1:Does Kewaunee's licensing basis require the RHR system to be protected fromseismically induced or random flooding to maintain its at-power operable status in accordance with Technical Specifications?SBPB Response:
The licensing basis of the RHR system in the power operation, startup, and hot standby modesof operation includes protection of the RHR system function from failures of non-seismicallyqualified piping, consistent with the licensee's statements in the letter dated October 31, 1972. In addition, the RHR system function in these operating modes is required to be protected froma single random failure of an RHR pump seal or an unspecified minor piping failure within theRHR pump pits during the long-term post-accident recirculation phase. The licensing basisincludes a general statement that operator action or the limited system volume would precludefailure of engineered safety features as a result of other random pipe breaks, but this statement does not imply that the RHR system is protected from these other random pipe failures.Operability of the RHR system at Kewaunee in the power operation, startup, and hot standbymodes of operation is based on the RHR system performing its emergency core cooling andlong-term post-accident recirculation cooling functions. These functions are clearly specified as Class I functions of the system, and the RHR system must be capable of performing thesefunctions assuming a failure of non-seismic piping. However, the licensing basis includes a statement that the design arrangement and redundancy of the safety systems ensure thesystem function can be performed following failure of a non-seismic pipe. Therefore, the design basis of the RHR system must include a provision that the trains be separated in a manner that prevents simultaneous damage to both trains from a failure of a non-seismic pipe. However, protection of both trains from any failure of non-seismic piping is not necessary to satisfy the licensing basis.The design basis for the RHR system includes ensuring that a failure of the RHR pump seal orother unspecified passive failure in one loop of the RHR system during the long-term, post-LOCA recirculation mode of operation would not result in failure of the opposite RHR l oop. Section 9.3.3 of the Kewaunee USAR identifies specific flood protection features for the RHRpump pit rooms. These features include the drain lines from each room to the sump, the automatic isolation of the drain line on high level in the associated pump room, the operation oftwo sump pumps to transfer collected water from the sump to the liquid radioactive waste system, t he capability to remotely isolate individual lines from the containment sump to the RHRpump suction to limit the inventory of water that can leak into a room, and alarms in the main control room actuated by high sump or high pump room levels. Consistent with the criteria for operability, the ability of these flood protection features to perform their design functions isnecessary to maintain the RHR system operable. These features may also be credited whenevaluating the potential for failure of a non-seismic pipe to simultaneously affect both RHR trains such that the system function is lost.Although the features described above provide some protection against other random failuresof piping that may lead to flooding of the RHR pump rooms, the c apability to mitigate thesetypes of events was not included in the design basis of those features. The operability of theRHR system in these operating modes is based on LOCA mitigation, and the NRC staff hasgenerally concluded a coincident random failure of seismically qualified piping was sufficiently unlikely that it could be excluded from the design basis of emergency core cooling systemcomponents. Therefore, the potential for random piping failures to overwhelm these protectivefeatures and flood the RHR pump rooms does not affect the at-power operable status of theRHR system. The plant is safe because alternate systems can perform the RHR function necessary for safe shutdown.In their comments on the draft TIA response, Region III staff suggested that the licensing basisrequires that the RHR trains be protected in a manner which ensures that the Class 1 functionis maintained for both trains. The NRR staff agrees that this criteria applies to systemsnecessary to achieve safe shutdown following a pipe or tank failure that occurs as an initiating event, such as the auxiliary feedwater system and the emergency power system, becausethese systems must perform their function following an additional single failure as described inSection B.5 of the Kewaunee USAR. However, in licensing the Kewaunee plant, the staff specifically accepted exclusion of the RHR system from the set of systems necessary to achieve safe shutdown following such an event, which effectively means the RHR system hasno Class I function following a random break in a seismically qualified pipe.The licensing basis, as documented in Section IV of the attachment to the licensee's letterdated November 7, 1972, includes the statement that the rate of rise of water level from anypiping failure would be low enough to allow operator action before affecting safeguards equipment. Conformance with this licensing basis capability may involve development of alarmresponse procedures for alarm conditions associated with pipe failures (e.g., the RHR pumproom high level alarm) to ensure operator actions are completed quickly enough to avoid anadverse affect on safeguards equipment. In summary, the answer to the first question is "yes" with respect to failure of non-seismic pipingto the extent the failure threatens the RHR system function (protection against flooding thatcould result in loss of a single train is not required) and "no" with respect to random pipe breaks in the auxiliary building since the Kew aunee RHR system function is only required to beprotected from a single random failure of an RHR pump seal or an unspecified minor pipingfailure within the RHR pump pits during the long-term post-accident recirculation phase.Question 2:Does Kewaunee's licensing basis require the RHR system to be protected fromseismically-induced or random flooding to maintain its below-hot-shutdown operable status in accordance with Technical Specifications?SBPB Response:
Similar to the licensing basis of the RHR system in the power operation, startup, and hotstandby modes of operation, the Kewaunee licensing basis includes protection of the RHR system shutdown cooling function from failures of non-seismically qualified piping, consistentwith the licensee's statements in the letter dated October 31, 1972. The Kewaunee licensingbasis for the RHR system in the shutdown cooling mode of operation includes no discussionregarding protection from the effects of random, moderate-energy pipe breaks.Wisconsin Public Service Corporation stated in the letter dated October 31, 1972, that thefunctional purpose of safety equipment would not be jeopardized by the failure of non-seismic piping in the auxiliary building because of safety equipment redundancy and designarrangement. In the cold shutdown and refueling modes of operation, the RHR systemperforms an essential safety function that cannot readily be performed by other systems orcomponents. Therefore, the determination of RHR system operability in the cold shutdown andrefueling modes of operation involves an assessment of whether the failure of non-seismic piping would result in failure of both RHR trains. In completing this assessment, the licensing basis allows the consideration of design features that separate the RHR system trains.In summary, the answer to the second question is "yes" with respect to failure of non-seismicpiping to the extent the failure threatens the RHR system function (protection against floodingthat could result in loss of a single train is not required) and "no" with respect to random pipe breaks in the auxiliary building since the Kewaunee licensing basis for the shutdown coolingmode of operation includes no discussion regarding protection from the effects of random, moderate-energy pipe breaks.Question 3:Is RHR operability mode specific? If the RHR system is inoperable below hotshutdown, is t he system inoperable above hot shutdown? If it is determined thatthe RHR system is operable above hot shutdown, but inoperable below hotshutdown, what would be the required licensee action? SBPB Response:The basis for determining operability is mode-specific because some design-basis events arecredible only in certain operating modes, and operability is based on the c apability to completethe required system function during design-basis events. The NRC technical guidanceregarding operability describes that requirements based on safety analyses do not necessarilyhave to be the same for all modes of operation. The required actions are specified by the relevant technical specification. In the case of the RHR system, operability in the coldshutdown and refueling modes of operation is based on the shutdown cooling function, and operability above the hot shutdown modes is based on the emergency core cooling and long-term, post-accident recirculation cooling functions. These functions have different safety analyses, so inoperability in one mode does not translate to inoperability in another mode. Operability is determined by evaluating functional capability in each m ode.If the RHR system is inadequately protected from failures of non-seismic piping (i.e., the systemprotection is degraded to the ex tent that t he system is inoperable), the plant must bemaintained in a mode where the RHR function could be performed by other systems that areadequately protected from failures of non-seismic piping. This translates to maintaining the plant in the hot shutdown mode, where the LOCA mitigation functions are not required and theRHR function can be performed by the steam generators and the auxiliary feedwater system.In summary, the answers to the multi-part Question 3 are as follows:
Part 1: Is RHR operability mode specific? "Yes"Part 2:If the RHR system is inoperable below hot shutdown, is the system inoperableabove hot shutdown? "Not necessarily" since inoperability in one mode does not translate toinoperability in another mode.Part 3:If it is determined that the RHR system is operable above hot shutdown, butinoperable below hot shutdown, what would be the required licensee action? If the plant is in hot shutdown or above, it must remain in a mode other than coldshutdown or refueling until operability in those modes is restored. In the case ofinoperability below hot shutdown, the only option is to promptly restore thesystem to operable status since it is unreasonable to require the licensee toincrease the operational mode level. Operability may be restored by seismicallyqualifying the piping, providing protection for one train from the potential failure,or isolating the flow to the unqualified piping segment.Principal Contributor: S. Jones Date: