ML20039E846
| ML20039E846 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 12/30/1981 |
| From: | Widner W GEORGIA POWER CO. |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.K.3.28, TASK-TM TAC-48277, TAC-48278, NUDOCS 8201110541 | |
| Download: ML20039E846 (3) | |
Text
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W. A. Widner
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EDWIN I. HATCH N'JCLEAR PLANT UNITS 1, 2 NUREG-0737, ITEM II.K.3.28 QUALIFICATION OF ADS ACCUMULATORS Gentlemen:
NUREG-0737, Item II.K.3.28 required that BWR licensees verify the qualification of accumulators on Automatic Depressurization System (ADS) valves.
The purpose of this letter is to justify the accumulator sizing basis and describe the provisions for long-term safety / relief valve (S/RV) operability at Plant Hatch.
SHORT-TERM ADS OPERABILITY Short term is defined for this discussion to be the time required to depressurize the reactor to the residual heat removal (RHR) shutdown cooling pressure permissive setpoint, stabilize the reactor water level, and place l
the reactor in the shutdown cooling mode.
Each ADS accumulator is presently sized to provide two ADS S/RV l
actuations at 70% of drywell design pressure.
Analysis has shown that this is equivalent to 4-5 actuations of the ADS S/RVs at atmospheric pressure in the drywell, and is in agreement with the Final Safety Analysis Reports (FSAR).
The ADS valves are designed to operate at 70% of drywell design pressure because that is the maximum pressure for which rapid reactor depressurization through the ADS valves is required (greater drywell pressures are associated only with the short duration primary system blowdown in the drywell immediately following a large pipe break).
For large breaks which result in higher drywell pressurc., sufficient reactor depressurization occurs due to the break to preclude the need for ADS.
One ADS actuation at 70% of drywell design pressure is sufficient to depressurize the reactor and allow inventory makeup by the low pressure ECC systems.
However, for conservatism, the ADS accumulators are sized to allow 2 ADS actuations at 70% of drywell design pressure.
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-Page Two This. design supplies sufficient -compressed gas to the ADS valves to permit.depressurization until the RHR shutdown ' cooling mode can be initiated.
In order to ensure-that the required number of ADS valve actuations can be performed, the existing hard seat check valves at the inlets to the ADS accumulators at Plant Hatch will be replaced with soft seat check valves to limit leakage. As. discussed in our. letter of November 4, 1981, these valves are on order with_ an earliest delivery date of February 1982.
They will be installed during the first outage of sufficient duration after they are received'on site as discussed in our November 4, 1981 letter.
LONG-TERM ADS CAPABILITY The requirement for long-term operability of ADS valves does not appear-in NUREG-0737 Item II.K.3.28 nor was this an original _ design basis as defined in the FSARs for the Hatch units.
However, the BWR Owners Grcup Emergency' Procedures Guidelines required by NUREG-0737 Item I.C.1 have identified.a contingency need for the long-term capability to hold an S/RV open. This would provide an alternate shutdown cooling path for the reactor in the event that one of the RHR shutdown cooling valves were to fail in the closed position The present plant arrangement utilizes one of two non-safety grade compressed gas systems, either the Drywell Pneumatic System or the Instrument Air System, to supply the S/RVs and other pneumatically operated components in the drywell.
Should this supply become inoperable, such as would occur following a ' loss of off-site power, a safety grade non-single-failure proof backup -system, the Nitrogen System, will be tied in automatically to provide a continued supply of compressed gas.
The nitrogen source for this system is a 11guld nitrogen storage tank located outside the reactor building. (The Unit 2 nitrogen tank is presently empty; however,
'following the January, 1982 refueling outage the Unit 2 drywell will be inerted and this' tank will have a nitrogen supply.
In the interim, a manual valve can ~be opened to tie in the Unit I nitrogen tank should the need arise).
This tank is accessible following a loss of coolant accident and could.be refilled _to ensure S/RV operability for 100 days.
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- GeorgiaPower A Director of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission December 30, 1981 Page Three-This submittal completes our response to NUREG-0737 Item II.K.3.28.
If you have any questions please contact this office.
W. A. Widner states that he is Vice President of Georgia Power Company and is authorized to execute this oath on behalf of Georgia Power Company, and that to the best of his knowledge and belief the facts set forth in this letter are true.
GEORGIA POWER COMPANY By: h Y l/k k es/
W. A. Widner Sworntoandsubscribedbe(orgmethis30thdayofDecember,1981.
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