ML20082M381
| ML20082M381 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 08/30/1991 |
| From: | Fay C WISCONSIN ELECTRIC POWER CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| CON-NRC-91-090, CON-NRC-91-90 VPNPD-91-296, NUDOCS 9109050168 | |
| Download: ML20082M381 (3) | |
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n hVisconsin Electnc POWER COMNwY i
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231 w Mcntert no 90,2043 Muaun o. wi 5320s tai 4)2252345 i
VPNPD-91-296
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August 30, 1991 l
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I U.
S.
NUCLEAR REGULATORY COMMISSION
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Document Control Desk i
Mail Station P1-137
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Washington, DC 20555 i
i DQCXRT 50-266 QYERPEREJURE MITIGATLH9_EYETIN OPEBATIQH l
EqlNT BEACH _NUCLEAB,ELANT, UNIT 1
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I On May 10, 1988, an ovent occurred at Point Beach. Nuclear Plant which resulted in the operation of the Overpressuro Mitigation System (OMS).
At that timo, Point Beach Nuclear Plant Technical Specification 15.6.9.2 stated that if the overpressure mitigation system operated to relievo a pressure transient which, by
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licensoe's ovaluation, could have resulted in an overpressure incident had the system not been operable, a special report shall I
be submitted to the Commission within 30 days.
The purpose of this lotter is to provido the details of the subject event.
Additionally, wo have described corrective actions that will ensure that special reports are submitted, as necessary, for tho OMS actuations that have occurred sinco tho spocial reports have i
boon required.
i On May 10, 1988, Point Beach Nuclear plant Unit I was in cold i
shutdown modo.
The roactor coolant system (RCS) was at a temperature of 164*F and a pressure of 332 psig.
The RCS was
" solid" and both reactor coolant pumps were secured.
At 1723 on May 10, 1988, the "B"
reactor coolant pump (RCP) was started.
i The ensuing plant heatup, which resulted because the secondary sido of the "B" steam generator was warmer than the primary i
coolant, increased the primary system pressure.
At 1724, when i
the RCS had reached its maximum pressure of 420 psig, the low i
temperature overprossure protection (UTOP) system circuit j
momentarily opened a proscurizer power-operated relief valvo, RC-l 430, to reduce the RCS pressure.
By 1729 the transient had l
terminated; the RCS temperature stabilized at 173*F, and the RCS j
pressure stabilized ut 330 psig.
1 In May 1988, a calculation was performed to determine whether or f
not the reactor coolant system would have been pressuri.ed in excess of the current 10 CFR 50 Appendix G criteria, 11 the OMS
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had failed to function during the May 10, 1988 event.
This t
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9109050168 910830 V
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A subsam dllimum Dm nentkw
4 NRC Document Control Desk August 30, 3991 Page 2 evaluation determined that, even if the pressurizer power operated relief valves (PORVs) had failed to operate in the OMS mode, the residual heat removal (RHR) relief valves, with a setpoint of 500 psig, would have operated to mitigate the pressure transient and to prevent the reactor coolant system from exceeding the 10 CFR 50 Appendix G critoria.
Because the RHR roller valves were not installed as part of the OMS upgrade, it was not recognized at that time that the RHR relief valves should be considered a subsystem of the OMS and that the RHR relief valves should be considered inoperable in our evaluation of the event.
At the time of the original evaluation, we did not recognize that the NRC's Safety Evaluation Report (SER) dated May 20, 1980 directed that the special report be submitted not only for PORV Low Temperature Overpressure Protection (LTOP) operation, but also for actuation of the residual heat removal (RHR) system relief valves, if such actuation would have mitigated an overpressurization incident.
Thus, the original analysis took credit for a portion of the OMS when it should not have, and a special report was not submitted.
The reportablity of the May 1988 event came to light in July 1991 while responding to an internal audit of Point Deach Technical Specifications.
The event was reevaluated, and a now calculation was performed in which the RHR relief valves were considered inoperable.
The results of the new evaluation indicated that the 10 CFR 50 Appendix G criteria would have been exceeded if both the pressurizer PORVs and the RHR relief valves failed to operate during the May 10, 1988 ovent.
By letter dated February 9, 1989, we notified you of a separate event which occurred on November 11, 1987, in which our evaluation of an OMS operation erroneously considered the RHR system operable and we subsequently failed to submit the required special report within the required 30 days.
In our February 9, 1989 letter, we recognized that the RHR system should be considered a part of the OMS system and that future evaluations of those types of events should consider the RHR relief valves inoperable when determining whether or not the 10 CFR 50 Appendix G criteria could have been exceeded.
As part of our corrective action for the November 11, 1987 event, we submitted a Technical Specification Change Rcquest to clarify that the OMS includes both the pressurizer PORV8s in the LTOP mode and the RHR relief valves.
This change to Technical Specification 15.6.9.2 was approved by the NRC on August 28, 1989.
NRC Document Control Desk August 30, 1991 Page 3 Corrective actions, however, did not include the reevaluation of other similar events.
Therefore, in addition to the May 10, 1988 ovent, we are reviewing other OMS actions that have occurred since 1980 when the special report ' quirements were added to the Point Beach Technical Specificatier We will submit additional special reports as required, if suo mnt evaluations determine that the 1.) CFR 50 Appendix G criter.
'ould have been exceeded during an OMS actuation if not only th.
PORVs but also RilR relief valves had failed to operate.
If your have any questions concerning this event, please contact us.
Very tru14 yours, Cf'i f;a -
Y W.
Fay Vice President Nuclear Pober Copics to NRC Regional Administrator, Region III NRC Resident Inspector l
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