ML20126A348
| ML20126A348 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 06/07/1985 |
| From: | Fiedler P GENERAL PUBLIC UTILITIES CORP. |
| To: | Zwolinski J Office of Nuclear Reactor Regulation |
| References | |
| TASK-03-04.A, TASK-3-4.A, TASK-RR NUDOCS 8506130314 | |
| Download: ML20126A348 (4) | |
Text
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GPU Nuclear Corporation Nuclear
=== 388 Forked River, New Jersey 08731-0388 609 971-4000 Writer's Direct Dial Number:
June 7, 1985 Mr. John A. Zwolinski, Chief Operating Reactors Branch No. 5 Division of Licensing U.S. Nuclear Regulatory Commission Washington, D.C.
20555
Dear Mr. Zwolinski:
Subject:
Oyster Creek Nuclear Generating Station Docket No. 50-219 SEP Topic No. III-4.A, Tornado Missiles The purpose of this letter is to respond to the questions raised by your staff -
during our telephone conversation in February of this year concerning the subject SEP topic.
The staff identified several components (e.g., motor control centers, control rod drive hydraulic filters, isolation condenser fill piping and containment spray valves) in the vicinity of the aechanical equipment access opening of the reactor building that are potential targets for missiles penetrating the access doors. While the previously submitted report by GPUN addressed the probability of a missile striking the access door, the staff stated that the probability range given in the report (1.1x10-b to 6.1x10-6 per year) is not acceptably low. The staff stated that the probability must be below lx10-7 per year for the staff to conclude that the probability of potential damage to the components is sufficiently low and thus an additional investigation is not necessary. The staff requested GPUN to further evaluate the potential for and consequences of tornado-missile impact on components in this area and provide protection, if necessary.
In our tornado missile simulations, no missiles penetrated the inner airlock door if it was closed. Thus if the door is kept closed when it is not in use, the frequency of missiles entering the building decreases. With the plant in operation, it is estimated that both the inner and outer doors are closed approximately 80% of the time. Based on this estimate, the new range of missile entrance probabilities is approximately 2.2x10-7 to 1.2x10-0 per year.
The consequences of tornado missile damage to certain safety related components in the vicinity of the access door was also evaluated.
The intent of this evaluation was to show that even with loss of certain components near the access door, unaffected paths exist to achieve and maintain safe shutdown.
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O GPU Nuclear Corporation is a subsidiary of the General Public Utilities Corporation
-.The equipment of most concern is that located in the area shown on General Arrangement drawing 2060-4 (Plan Elev. 23' - 6") between column lines R1-R4 and RA-RD,'outside of the drywell wall.
This includes the following equipment:
1.
Containment Spray System II heat exchangers, piping and valves.
2.
Control Rod Drive Hydraulic System piping, valves, filters, and drive modules.
3.
Isolation Condenser (IC) fill piping.
4.
MCC DC-1, which provides power to the following equipment:
a.
Shutdown Cooling System Valves V-17-1, 2, 3, 55, 56, and 57.
b.
Cleanup System Valves V-16-2 and 14.
c.
Main Steam Line Drain Valves V-1-Il0 and 111.
d.
Emergency Condenser Valves V-14-31 (A Steam isolation), 33 (B Steam isolation), and 34 (A Condensate return).
5.
MCCIA218, which provides power to the following equipment:
a.
CRD Hydraulic System Valves NC-18 and NC-40.
b.
Containment Spray System I Valves V-21-7, 9, 11, 17, and 18.
c.
Emergency Service Water Valve V-3-88 (System I).
d.
Cleanup System Valves V-16-13, 32, 49, 50, 57, 59, and 60.
e.
Core Spray Recirculation Valve V-20-27 (System I).
Equipment located outside of this area (between column lines RD-RF) is much less likely to be impacted.
This area includes core spray booster pumps (System II) and valves, and MCCIA21A.
A worst case tornado scenario would be one in which all of the following was assumed to occur:
-3_
Loss of offsite power (causes reactor and turbine trip, loss of'feedwater)-
Failure of Condensate Storage Tank-(source of IC makeup and CRD makeup to Reactor Pressure Vessel (RPV))
Failure of Demineralized Water Storage Tank (source of IC makeup)
Failure of all pumps at the intake structure (service water, emergency service water, circulating water)
Failure of all fire pumps and storage tank (alternate source of IC and RPV makeup).
Failure of all equipment on 23' elevation of Reactor Building (RB) listed in 1 through 5 above.
Considering the low frequency of tornados and of tornado missiles, the failure of all'of this equipment due to a single event is incredible. However even in this incredible scenario, safe shutdown can be achieved and maintained as described below.
The following successful actions are expected to occur since they are unaffected by the failures listed above:
Reactor scram (the failure in 2 above does not negate the scram function)
Reactor vessel isolation Isolation Condenser B initiation (the failure in 3 above does not drain the IC shell side water inventory, due to check valves on the RB 95 foot elevation)
The operable B Isolation Condenser can remove decay heat for approximately 45 minutes before the shell side level starts to drop below the top of the tube bundles (decay heat can still be removed for some undetermined period of time after-the start of tube uncovery). An additional 55 minutes (100 minutes total) is available if the operator manually initiates the A isolation condenser (by opening the DC condensate return valve, V-14 34, using its hand wheel).
t t
Makeup to the isolation condenser shells can be provided from the torus ushng a modification to be installed (SEP IPSAR Section 4.6.4).
This modificati$i would allow one of two core spray pumps to supply water. via temporary hosev, with permanent hose connections to be installed on a core spray relief valve discharge and the isolation condenser shell overflow line. The torus water used in this manner provides a large heat sink, sufficient to maintain the reactor in a safe shutdown condition for several days.
Should makeup to the
. reactor vessel be required (due to leakage, which is expected to be within Technical Specification limits, and volumetric shrinkage due to cooldown) it can be provided by the core spray system. An isolation condenser has the.
ability to depressurize the reactor coolant system to the core spray injection permissive while the core is still covered by a two-phase mixture in this scenario.
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m While an isolation condenser was in use to remove decay heat, and the core spray system used intermittently to provide reactor coolant makeup, if needed, repairs would be under way.
In particular, offsite power restoration would have a high priority and could be expected to be accomplished within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> (no historical loss of offsite power at a nuclear power plant has exceeded 9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br />). Other items of high priority would be the plant electrical distribution system (MCCs in the reactor building) and the pumps at the intake structure.
As described above, even given the extraordinary magnitude of tornado damage postulated in the above scenario, safe shutdown can be achieved and maintained. A plant modification necessary to provide isolation condenser makeup from the torus, will be accomplished during the next fuel cycle (cycle 11).
Very truly yours, t=, 2:"fi~edler Vice President & Director Oyster Creek Ir/1836f cc: Administrator Region I U.S. Nuclear Regulatory Commission 631 Park Avenue King of Prussia, Pa.
19406 NRC Resident Inspector Oyster Creek Nuclear Generating Station Forked River, N. J.
08731
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