ML061230107

Region III Comments on Draft Response to Task Interface Agreement 2005-10 Relating to Impact of Flooding on Residual Heat Removal (RHR) Pumps at Kewaunee Power Station

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, 2006 MEMORANDUM TO: Mark A. Satorius, Director Division of Reactor Projects Region III FROM: Edwin M. Hackett, Deputy Director /RA/

Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation

SUBJECT:

FINAL RESPONSE TO TASK INTERFACE AGREEMENT 2005-10 RELATING 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 which may result due to seismically induced or random failures of non-seismically qualified piping at Kewaunee Power Station (Kewaunee):

• Does Kewaunees licensing basis require the RHR system to be protected from seismically induced or random flooding to maintain its at-power operable status in accordance with Technical Specifications?

• Does Kewaunees licensing basis require the RHR system to be protected from seismically 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 system is operable above hot shutdown but inoperable below hot shutdown, what would be the required licensee action?

By memorandum dated April 5, 2006, NRR issued a draft TIA response prepared by NRRs Division of Safety Systems, Balance-of-Plant Branch which Region III was requested to review and provide its comments to NRRs Division of Operating Reactor Licensing within 30 days. On April 21, 2006, NRR held a telephone conference with Region III to discuss the draft TIA response. By memorandum dated April 26, 2006, Region III provided comments on the draft TIA response. This final TIA reflects Region IIIs comments.

Docket No. 50-305

Enclosure:

NRR Staff Assessment CONTACT: David H. Jaffe, NRR/DORL (301) 415-1439

MEMORANDUM TO: Mark A. Satorius, Director Division of Reactor Projects Region III FROM: Edwin M. Hackett, Deputy Director /RA/

Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation

SUBJECT:

FINAL RESPONSE TO TASK INTERFACE AGREEMENT 2005-10 RELATING 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 which may result due to seismically induced or random failures of non-seismically qualified piping at Kewaunee Power Station (Kewaunee):

• Does Kewaunees licensing basis require the RHR system to be protected from seismically induced or random flooding to maintain its at-power operable status in accordance with Technical Specifications?

• Does Kewaunees licensing basis require the RHR system to be protected from seismically 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 system is operable above hot shutdown but inoperable below hot shutdown, what would be the required licensee action?

By memorandum dated April 5, 2006, NRR issued a draft TIA response prepared by NRRs Division of Safety Systems, Balance-of-Plant Branch which Region III was requested to review and provide its comments to NRRs Division of Operating Reactor Licensing within 30 days. On April 21, 2006, NRR held a telephone conference with Region III to discuss the draft TIA response. By memorandum dated April 26, 2006, Region III provided comments on the draft TIA response. This final TIA reflects Region IIIs comments.

Docket No. 50-305

Enclosure:

NRR Staff Assessment CONTACT: David H. Jaffe, NRR/DORL (301) 415-1439 DISTRIBUTION:

PUBLIC RidsNrrDorl SJones LPL3-1 R/F RidsNrrLplc SBurton, RIII RidsNrrAdro RidsNrrPMDJaffe PLouden, RIII RidsRgn3MailCenter RidsNrrLATHarris RidsNrrPMSMonarque ADAMS Accession Number: ML061230107 OFFICE DSS/SBPB DSS/SPWB/BC DSS/SBPB/BC LPL3-1/PM LPL3-1/LA LPL3-1/BC DORL/DD DIRS/ITSB NAME SJones JNakoski DSolorio DJaffe THarris LRaghavan CMiller TKobetz DATE 05/4/06 05/ 4/06 05/4/06 05/5/06 05/5/06 05/4/06 05/5/06 5/4/06 OFFICIAL RECORD COPY

FINAL STAFF ASSESSMENT OFFICE OF NUCLEAR REACTOR REGULATION IMPACT OF FLOODING ON RESIDUAL HEAT REMOVAL PUMPS AT THE KEWAUNEE POWER STATION TASK INTERFACE AGREEMENT 2005-10

1.0 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 stations response to flooding in the auxiliary building under the licensees calculation 2005-05708, Internal Flood Levels Due to Postulated Piping Ruptures In General Pipe Lines In Auxiliary Building Revision 1. Region III inspectors noted that this evaluation identified 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 pump motors to fail.

Given that both pumps were vulnerable to flooding from a single-failure, the inspectors questioned the operability of the RHR system in the emergency core cooling 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 licensees 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 RHR in the decay heat removal mode. The licensee asserted that flooding events were not part of the licensing basis for RHR which is based on hot shutdown conditions and concluded that both RHR trains were operable. The initial questions by the residents were characterized as an Unresolved 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 guidance provided in Part 9900 of the Nuclear Regulatory Commission (NRC) Inspection Manual lists the following principal criteria for technical specification operability requirements that are relevant to the issue:

The system operability requirements that are based on safety analysis of specific design-basis events for one mode or condition of operation may not be the same for all modes or conditions of operation.

ENCLOSURE

The system operability requirements extend to necessary support systems regardless of the existence or absence of support system requirements. The operability of necessary support systems includes regulatory requirements. It does 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 the reactor 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 protected against 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 damage from rupture of a pipe is limited to those conditions where the system is needed to perform its Class 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 features protecting the RHR pumps from flooding. The design features include separate, shielded compartments 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 closes on 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 high level 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 operated isolation 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 and subsequent flooding were developed in 1972, following the failure of a circulating water system expansion 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, the licensee stated that the failure of reactor makeup water and demineralized water lines in the auxiliary building basement could potentially adversely affect the performance of engineered safety systems. However, the licensee also stated that, because of safety system redundancy and 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 to address random pipe breaks in systems containing high-energy fluids. Sections I through III of the 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 described analyses of miscellaneous piping systems. The analyses of miscellaneous piping systems included evaluations of potential flooding effects from failures of the service water, component cooling, demineralized water, and reactor makeup water systems. For these evaluations, the licensee determined that either the system has too low a volume to endanger engineered safety features 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. This historical 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 the Application 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 pipe in 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 water valves from the control room would isolate the break and, if required, operators would realign service 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 design arrangement 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 staff questioned 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 letter to 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 under construction, 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 were not within the scope of the requested review.

The final analyses of postulated pipe breaks in high-energy systems were largely described in Amendment 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 were documented in Supplement 2 to the Licensing Safety Evaluation Report for the Kewaunee Nuclear Power Plant, dated May 10, 1973. The NRC staffs evaluation of pipe breaks outside of 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 staffs evaluation clearly 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 the equipment were still available.

Two generic safety issues were also relevant to the licensing basis for protection against internal 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. The resolution 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-46 involved 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 cold shutdown functions from the scope of seismic verification.

3.0 BALANCE-OF-PLANT Branch (SBPB) RESPONSE TO REGION III REQUESTS Region III requested the Office of Nuclear Reactor Regulation to respond to three questions.

The SBPB response is summarized below.

Question 1:

Does Kewaunees licensing basis require the RHR system to be protected from seismically 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 modes of operation includes protection of the RHR system function from failures of non-seismically qualified piping, consistent with the licensees statements in the letter dated October 31, 1972.

In addition, the RHR system function in these operating modes is required to be protected from a single random failure of an RHR pump seal or an unspecified minor piping failure within the RHR pump pits during the long-term post-accident recirculation phase. The licensing basis includes a general statement that operator action or the limited system volume would preclude failure 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 standby modes of operation is based on the RHR system performing its emergency core cooling and long-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 these functions 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 the system 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 or other 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 loop.

Section 9.3.3 of the Kewaunee USAR identifies specific flood protection features for the RHR pump 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 of two sump pumps to transfer collected water from the sump to the liquid radioactive waste system, the capability to remotely isolate individual lines from the containment sump to the RHR pump 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 is necessary to maintain the RHR system operable. These features may also be credited when evaluating 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 failures of piping that may lead to flooding of the RHR pump rooms, the capability to mitigate these types of events was not included in the design basis of those features. The operability of the RHR system in these operating modes is based on LOCA mitigation, and the NRC staff has generally 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 system components. Therefore, the potential for random piping failures to overwhelm these protective features and flood the RHR pump rooms does not affect the at-power operable status of the RHR 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 basis requires that the RHR trains be protected in a manner which ensures that the Class 1 function is maintained for both trains. The NRR staff agrees that this criteria applies to systems necessary 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, because these systems must perform their function following an additional single failure as described in Section 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 has no 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 licensees letter dated November 7, 1972, includes the statement that the rate of rise of water level from any piping failure would be low enough to allow operator action before affecting safeguards equipment. Conformance with this licensing basis capability may involve development of alarm response procedures for alarm conditions associated with pipe failures (e.g., the RHR pump room high level alarm) to ensure operator actions are completed quickly enough to avoid an adverse affect on safeguards equipment.

In summary, the answer to the first question is yes with respect to failure of non-seismic piping to the extent the failure threatens the RHR system function (protection against flooding that 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 RHR system function is only required to be protected from a single random failure of an RHR pump seal or an unspecified minor piping failure within the RHR pump pits during the long-term post-accident recirculation phase.

Question 2:

Does Kewaunees licensing basis require the RHR system to be protected from seismically-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 hot standby modes of operation, the Kewaunee licensing basis includes protection of the RHR system shutdown cooling function from failures of non-seismically qualified piping, consistent with the licensees statements in the letter dated October 31, 1972. The Kewaunee licensing basis for the RHR system in the shutdown cooling mode of operation includes no discussion regarding protection from the effects of random, moderate-energy pipe breaks.

Wisconsin Public Service Corporation stated in the letter dated October 31, 1972, that the functional 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 design arrangement. In the cold shutdown and refueling modes of operation, the RHR system performs an essential safety function that cannot readily be performed by other systems or components. Therefore, the determination of RHR system operability in the cold shutdown and refueling 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-seismic piping to the extent the failure threatens the RHR system function (protection against flooding that 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 cooling mode 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 hot shutdown, is the system inoperable above hot shutdown? If it is determined that the RHR system is operable above hot shutdown, but inoperable below hot shutdown, what would be the required licensee action?

SBPB Response:

The basis for determining operability is mode-specific because some design-basis events are credible only in certain operating modes, and operability is based on the capability to complete the required system function during design-basis events. The NRC technical guidance regarding operability describes that requirements based on safety analyses do not necessarily have 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 cold shutdown 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 mode.

If the RHR system is inadequately protected from failures of non-seismic piping (i.e., the system protection is degraded to the extent that the system is inoperable), the plant must be maintained in a mode where the RHR function could be performed by other systems that are adequately 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 the RHR 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 inoperable above hot shutdown?

Not necessarily since inoperability in one mode does not translate to inoperability in another mode.

Part 3: If it is determined that the RHR system is operable above hot shutdown, but inoperable 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 cold shutdown or refueling until operability in those modes is restored. In the case of inoperability below hot shutdown, the only option is to promptly restore the system to operable status since it is unreasonable to require the licensee to increase the operational mode level. Operability may be restored by seismically qualifying 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: