ML20238B191
| ML20238B191 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 09/02/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20238B139 | List: |
| References | |
| NUDOCS 8709090558 | |
| Download: ML20238B191 (9) | |
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, A. f "Ecoq'o,, UNITED STATES
- 8 o NUCLEAR REGULATORY COMMISSION
,E ;j WASHINGTON, D. C. 20555
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SAFETY EVALUATION BY THE OFFICE 0F NUCLEAR REACTOR REGULATION RELATING TO EXTENSION OF THE TEMPORARY EXEMPTION FROM THE SINGLE FAILURE CRITERION (GENERAL DESIGN CRITERION N0.35)
CONNECTICUT YANKEE ATOMIC POWER COMPANY HADDAM NECK PLANT DOCKET NO. 50-213 i
1.0 INTRODUCTION
On Mcrch 25, 1986, Connecticut Yankee Atomic Power Company (CYAPC0) reported that results for small break loss of coolant accident (LOCA) analyses at the Haddam Neck Plant indicated that the safety injection flow during the high pressure recirculation mode could be inadequate for long term core cooling.
By letter dated April 10,1986, CYAPC0 proposed a temporary high pressure safetyinjection(HPSI)recirculationmodetoprovideadequatecorecooling.
To implement the HPSI recirculation mode, CYAPC0 requested, by letter dated April 22,1986, a temporary exemption from the single failure criteria for two emergency core cooling system (ECCS) valves. These valves are located outside of containment and would be used under procedurally defined conditions to respond to small break LOCAs. By [[letter::B11409, Responds to IE Bulletin 80-06, ESF Reset Control. Trip Signal to Containment Air Activity Pump & Containment Sump Pump Provided.Removal of Safety Injection Actuation Signals from RHR Valves Being Evaluated|letter dated April 28, 1986]], the Commission granted a temporary exemption from the single failure criterion for the operation of the Haddam Neck Plant during Cycle 14.
On September 30, 1986, CYAPC0 proposed system modifications to meet the single failure requirements for the ECCS. The submittal. included a proposed schedule for the completion of ali the modifications. Because of facility limitations, some ECCS safety related electrical equipment would have to be installed in a new switchgear room. Since the switchgear room is to be completed by the end of 8709090550 070902 PDR ADOCK 05000213 P PDR
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the Cycle 15 outage, CYAPC0 requested a one cycle extension to the exemption ]
granted on April 28, 1986.
By letter dated December 17,-1986, CYAPC0 advised that the original design for i low pressure sump recirculation through the Core Deluge System was reexamined for other breaks. That review identifiet: an intermediate break LOCA in the core j deluge lines for which adequate core cooling during sump recirculation would j not be provided. CYAPC0 proposed an interim solution for the intermediate break i LOCA which would allow blocking flow control valve FCV-796 in a throttled position'to assure adequate core injection flow during sump recirculation. By letter dated December 24', 1986, the staff concurred with the interim modification.
On April 1, 1987 CYAPC0 proposed system modifications to assure adequate core cooling for small and intermediate break LOCAs. This included a description of the modifications to the ECCS with supporting single failure analysis for the spectrum of small to large breaks. The licensee reiterated the. difficulty in completing the modifications in the Cycle 14 outage and the need for extension of the exemption granted on April 28, 1986.
By letter dated June 1, 1987, CYAPC0 proposed Technical Specification (TS) changes for the ECCS. These changes were requested because hardware modifications to the ECCS related to the long term system modifications are being made during the Cycle 14 outage. The TS changes would require the newly installed motor-operated valves (MOVs) to remain in fixed positions so as to not change the present ECCS flow configuration during injection and sump recirculation. In addition, the four newly installed High Pressure Injection System (HPSI) manual valves would be locked in their proper throttled position.
2.0 EVALUATION 2.1 Permanent Modifications To Meet GDC 35 CYAPC0 proposed changes to the ECCS to provide a single failure proof means to mitigate potential small and intermediate break LOCAs.
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The existing HPSI pump suction would be cross-connected with the Residual Heat Removal (RHR) pump discharge. This will allow a redundant means for high pressure injection into the Reactor Coolant System (RCS) from the containment sump in series with.'the RHR pump (s) acting as a booster pump for the HPSI pumps.
The core deluge line would also be provided with a redundant motor-operated valve which, in the event of a core deluge line break, would allow its
. isolation from the ECCS. .This is necessary during long tenn recirculation to prevent RHR pump runout.
The proposed changes to the ECCS require permanent modifications and are described in detail below.
- 1. The existing HPSI pump suction manual valves will be replaced with motor-operated valves (MOVs) 845A and 8548. These valves are in parallel lines and are required to close during HPSI operation in the recirculation mode to assure a series flow path from the containment sump to the RCS via the RHR and HPSI pumps. An existing valve, SI-MOV-24, will provide redundancy for either of these valves. The required closure of these valves also prevents backflow of potentially contaminated water to the RWST. We find this acceptable.
- 2. An eight inch cross-tie connection between the RHR pump discharge and the HPSI pump suction will be added. This piping addition will allow HPSI operation during recirculation. We find this acceptable.
- 3. A three inch manual throttle valve will be installed in each of the four HPSI injection lines. The injection flow path after leaving the throttle valve (s) is via a check valve and M0V to the reactor. In the event of LOCA, a safety actuation signal will cause all four MOVs to proceed to the full open position. During sump recirculation with HPSI operation, two of the injection lines will be blocked closed by remote operator action. The throttle valves in the remaining two available lines are installed to provide adequate flow resistance to prevent the RHR design flow from being exceeded. We find this acceptable.
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- 4. The existing core deluge manual valve SI-V-873 will be replaced with a M0V. This provides a redundant, remote means to isolate the core deluge from the ECCS in the event of a core deluge line break. This is necessary to prevent RHR pump runout during long term recirculation. Presently FCV-796 is throttled to prevent excessive RHR flow and resultant RHR pump damage. At the time the new MOV is placed in service, following the Cycle 15 outage, CYAPC0 stated that FCV-796 will be fully opened to assure adequate net positive suction head for proper HPSI pump performance. The fully open position of FCV-796 during long term recirculation has raised staff concern with regard to excessive RHR pump flow. CYAPC0 advised that in this mode of operation one of the redundant core deluge paths would be blocked closed and the other path throttlet by remote operation of a gate valve. Throttling with a gate valve is not a recommended industrial practice and the staff questions the acceptability of long term operation in this mode. The staff considers this an open issue related to accepta-bility of the permanent modification.
- 5. Remote operation from the control room of redunuant isolation. valves in the HPSI pump minimum flow line will be provided. The concept is
. acceptable to the staff. However, finalized details have not been provided. The HPSI pump minimum flow final design remains an open item, subject to staff review and approval.
CYAPC0 performed a simplified failure modes and effects analysis to assure complianca with the single failure criteria for the ECCS. The staff reviewed the'results and is in general agreement with them. Sone specific concerns are addressed below.
- 1. Addition of the cross-tie interconnect for RHR/HPSI raises the potential for the Low Pressure Safety Injection (LPSI) system to discharge to the suction of the HPSI pumps during HPSI operation and recirculation from the containment sump. The licensee's letter of April 1, 1987 states that the MOVs (MOV 901 and M0V 902) on the HPSI/RHR cross-tie will be interlocked to prevent their inadvertent opening while the HPSI pump breakers are
5 i closed to prevent overpressurization of the HPSI suction line. .The staff ,
also expressed concern with regard to the potential for HPSI overpressurization resulting from a LPSI start during HPSI operation in the recirculation mode. CYAPCO, by letter dated July 20, 1987, stated that prior to HPSI operation during recirculation, the LPSI pumps are to be j breakered out. Thus, the potential for overpressurization in that mode is reduced. We find this acceptable.
- 2. The licensee's single failure analysis did not consider the potential for three injection flow paths with HPSI during recirculation (two injection paths plus single failure). The staff expressed concern that this condition could cause RHR design flow to be exceeded. By letter dated July 20, 1987, and subsequent discussions, CYAPC0 addressed this concern.
They stated that: during recirculation if a single failure opens an additional M0V, then three HPSI injection paths are open and can result in excessive RHR flow. However, procedures require that no more than two
.of the four HPSI injection paths be open for coolant flow to the reactor.
Valve position lights, which are powered from emergency buses would give indication to the control room operator that more than two paths (MOVs) are open and the operator would then take appropriate action to close one M0V. With two remaining MOVs then open, the resulting flow resistance seen by the RHR pump prevents its runout. This mitigates the concern of j exceeding the design capability and subsequent RHR pump or motor damage.
Further, adequate core cooling is assured with only one injection line should the break be in one of the two flow paths. We find thic acceptable.
CYAPC0 also provided the results of a LOCA analyses associated with the permanent modifications to the ECCS to demonstrate adequate core cooling for the injection and recirculation phases. The licensee stated that the bases for the acceptability of ECCS flows during the injection phase are the previously approved Westinghouse analyses which demonstrate acceptable ECCS performance in accordance with the Interim Acceptance Criteria for the full spectrum of breaks.
6 For the recirculation phase of the LOCA, the licensee presented data which illustrated that the ECCS delivery is larger than the RCS boil-off rate. Thus, no additional analyses is required since ECCS long term cooling is assured following a LOCA. We find this acceptable.
1 2.2 ECCS Modifications - Stress Analysis By letter dated September 30, 1986, CYAPC0 submitted a request for extension of single failure exemption for Haddam Neck Plant's modification of the emergency core cooling system (ECCS) until the end of the cycle 15 outage. Subsequent information with regard to the core deluge systems' piping stress analysis, i was provided by letters April 1, 1987 June 9, 1987, July 20, 1987, and August 12, 1987, per requirement of NRR's Safety Evaluation Report dated December 24, 1986, " Supporting Amendment No. 88 to Facility Operating Licensee .
No. DPR-61."
The stress analysis is based on the provisions of ANSI B.31.1 Power Piping Code, 1973 Edition, Summer 1973 Addenda and approved design criteria by the )
NRC per D. M. Crutchfield letter to W. G. Counsil, "SEP Topic Ill-6 Seismic Design Considerations Haddam Neck Plant," dated February 25, 1983. j The stress analysis review of the core deluge system consisted of:
(1) comparison of a sample of calculated maximum stress valves to specified allowable code limits, (2) implementation of approved codes, (3) verification that the 8 inch cross-tie piping and new valve masses were considered in the analysis.
In each case, the staff found the calculated stress values were within the !
specified allowable limits and ANSI 8.31.1 Power Piping Code, 1973 Edition, Summer 1973 Addenda was used for the analysis. In addition, the licensee confirmed by letters dated July 20, 1987 and August 12, 1987, that the 8 inch cross-tie piping and new valve masses were included in the analyris.
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l 2.3 New Modification Effects On Present ECCS Configuration and TS Changes The newly installed MOVs, with the exception of SI-MOV 873, will not be electrically connected following the Cycle 14 outage. CYAPC0 has proposed TS changes to fix positions of the new MOVs and thus assure that the present ECCS configuration for all modes of operation will be unaffected.. The proposed changes also require the four three inch throttle valves installed in the HPSI injection lines to be locked ir, their preset position. The changes to assure proper ECCS configuration are discussed below.
- 1. SI-MOV-854A AND B. These HPSI pump suction isolation valves are replacing manual valves which are normally open during operation. The proposed change TS requires verification that these valves are in the locked open position once per twelve hours. We find this acceptable.
- 2. SI-M0V-901 AND 902. These valves isolate the new cross-tie line and are required to be closed to assure the present ECCS flow configuration. The j proposed TS change requires verification that these valves are to in the j locked closed position once every twelve hours. We find this acceptable.
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- 3. SI-M0V-873. This valve is located in the core deluge line and will serve as a redundant means of isolating the core deluge line when the permanent modifications are completed and approved. It replaces a manual valve j which is open during operation. The proposed TS change requires )
verification that this valve is locked in the open position prior to startup from cold shutdown and also electrically deenergized. We find ]
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- 4. SI-V-905,906,907, and 908. These are manual throttle valves which are set I to balance flow in the four HPSI injection lines. The valves are also set !
to prevent HPSI flow from exceeding RHR design flow during HPSI recirculation. The correct positions will be established by test. The j i
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1 i proposed TS change requires verification that these valves are locked in the throttled position prior to start up from cold shutdown. Correct i position verification is also to be required within four hours following maintenance on these valves. We find this acceptable.
- 5. RH-FCV-796. The proposed TS change requires verification of the correct position of this. valve within four hours after stroking or maintenance.
We find this acceptable, i
M, CYAPC0 has also proposed a TS change f or a flow b'alance test, which is t be 'I performed during Mode 5 or 6 following completion of modifications to the ECCS subsystems that alter flow characteristics. This TS change would become
. effective during the Cycle 14 outage. This would verify that HPSI pump injection lines with a single pump running and two lines isolated would have a flow rate through each line of 1000 + or - 100 gpm. We find this acceptable.
A RHR pump flow test was also proposed. This test is to assure that with a :
single pump running, the RHR pump flow is equal to 1500 + or - 280 gpm. We j find this acceptable, however, the means of throttling to assure proper pump flow remains an open item.
I 2.4 Extension of Exemption to GDC 35 CYAPC0 has attempted to complete modifications required to assure compliance ]
of the ECCS with GDC 35. Construction of a building that would house safety-related switchgear for the ECCS is not to be completed before Cycle 15 operation. Because CYAPC0 has made a good faith effort to resolve the single failure problem, the staff considers their request for an extension to the q previously granted exemption as reasonable. Our review of the modifications !
indicates that operation of the ECCS without the electrical power for the j newly added MOVs will be no different that that of Cycle 14 which was found acceptable by [[letter::B11409, Responds to IE Bulletin 80-06, ESF Reset Control. Trip Signal to Containment Air Activity Pump & Containment Sump Pump Provided.Removal of Safety Injection Actuation Signals from RHR Valves Being Evaluated|letter dated April 28, 1986]]. We find extension of the exemption to GDC 35 acceptable for Cycle 15. j i
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SUMMARY
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The licensee has proposed interim fixes to mitigate the possibility of
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inadequate core cooling'resulting from small and intermediate LOCAs. The staff q
. has previously reviewed-the interim fixes and found them to be acceptable. l The licensee has proposed long term solutions to provide adequate core cooling l resulting from the above LOCAs. These require permanent modifications to the ECCS, some of which cannot be completed during the Cycle'14 outage. Thus j CYAPC0 requires an extension to the previously granted exemption. We find the 4 proposed modifications will not adversely affect the ECCS operation during 'l Cycle 15 and it is therefore acceptable to extend the temporary exemption of April 28, 1986 until the completion of Cycle 15.
.The staff finds that the proposed TS changes assure that the present ECCS configuration remains unchanged and are therefore acceptable.
Based upon our review, we find the proposed changes for long term resolution to be acceptable provided the open items of the throttling requirements for the RHR pump and the finalized design for the HPSI minimum flow line discussed j above is resolved prior to start up of Cycle 16. ]
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4.0 CONCLUSION
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i We have reviewed the information provided by CYAPC0 relative to their request j for extension of the single failure exemption to GDC 35 for Cycle 15. The staff has concluded, based on the considerations discussed in previous 1 3
sections, that: (1) there is reasonable assurance that the health and safety 4 of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Commission's ]
regulation, erd the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public. ):
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5.0 ACKNOWLEDGEMENTS i
l Principal Contributors: D. Katze, SRXB and T. McLellan, EMEB, NRR l
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