ML20072B389
| ML20072B389 | |
| Person / Time | |
|---|---|
| Site: | Hatch  |
| Issue date: | 02/22/1983 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20072B392 | List: |
| References | |
| TAC-49705, NUDOCS 8303040241 | |
| Download: ML20072B389 (2) | |
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SAFETY EVALUATI0f1 BY THE 0FFICE OF llVCLEAR REACTOR REGULATI0f1 FACILITY OPERATIllG LICEllSE fl0. DPR-57 GEORGIA POWER COMPAllY OGLETHORPE POWER CORPORATION MUllICIPAL ELECTRIC AUTHORITY OF GEORGIA CITY OF DALT0ll, GEORGIA EDWIll I. HATCH flVCLEAR PLAtlT, UllIT 1 DOCKET fl0. 50-321 Introduction Technical Specification 3.7.A.5.b requires "within the 24-hour period subsequent to placing the reactor in the RU!1 mode following a shutdown, the containment atmosphere oxygen concentration shall be reduced to less than 4% by volume and maintained in this condition". However, during the return to operation of February 22, 1983, it has become apparent that this Limiting Condition for Operation (LC0) cannot be met.
Inability to meet the 24-hour LCO is due to time limits imposed.on the use of the 18-inch containment purge and vent valves. This necessitates the use of 2-inch lines (bypass lines for the 18-inch valves) for containment purge and vent functions.
These 2-inch linos do not permit timely inerting of the containment.
flo other lines are available for containment purge and vent functions.
Inerting commenced at about 7:00 p.m. (CST) on February 20, 1983, following last personnel entry into primary containment.
The licensee, therefore, has requested a one-time extension of the 24-hour LC0 to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />.
The 24-hour LCO interval began at about 9:00 a.m. (CST) on February 22, 1983.
Eval uation The basis for the present 24-hour requirement on attaining a 4%
oxygen concentration following entry into the RUf1 mode is to minimize the possibility of hydrogen combustion following'shed, as stated in the bases for a loss-of-coolant accident (LOCA).
The 24-hour period was estab1i Specification 3.7. A.5, as being sufficient to perform necessary drywell inspections and establish the required oxygen concentration.
The control' is administrative and supplements the Containnent Atmosphere Dilution (CAD) system, which can be used to control oxygen concentrations.
The CAD system provides the basis for assuring containinent integrity post LOCA.
At the time Unit 1 was licensed, the CAD systen was installed to meet the applicable regulations addressing hydrogen evolution.
Because the 24-hour limit is an administrative control, as opposed to providing a safety function, margins of safety, as defined in the Technical Specifications, are not reduced by allowing a longer period of time to complete drywell inerting.
The safety margin is provided by the CAD system.
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-i Additionally, due to plant factors, maximum thermal power itill not exceed fifty percent (50%) while oxygen concentrations exceed 4%.
-l Extension of the drywell inerting LCO also necessitates an extension of the LCO for Technical Specification 3.7.A.7.(1), Drywell-Suppression Charber Differential Pressure, for a like time period.
Required differential pressure cannot be established until inerting is completed as 'the contain-ment vents are open during inerting.
l Hatch Unit I has previously used the 18" purge. and vent lines for inerting purposes while starting up.
Due to the NRC's requirements to limit operation of larp purp systsa.s with unqualified purge vahes to 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> a year, Hatch Unit 1 is nu attempting to inert by using the qualified 2" l
purge bypass valve, which does not have a time restriction.
This is the first plant startup using only the smaller purge line.
Currently contain-
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ment atmospheric, monitors measure the oxygen concentration at appmximately 6%.
The licensee has determined that permanent Technical Specification changes are necessary because 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> do not allow sufficient time for inerting.
This is because the licensee has decided not to use the 18" purge system for the purpose of inerting, thus preserving the 90 hours0.00104 days <br />0.025 hours <br />1.488095e-4 weeks <br />3.4245e-5 months <br /> of use for other situations. We will pursue permanent Technical Specification changes with the licensee in the future.
However, for the present plant startup situation, we will address the licensee's proposed one-time only change.
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We believe that a basis exists to permit acceptance of the proposed changes.
They are as follows:
1.
The' containment atmosphere is presently at 6% oxygen concentration.
This in itself greatly reduces the pmbability of hydrogen combustion in the event of a postulated LOCA and subsequent hydrogen generation.
2.
The maximum thermal power will not exceed 50% during the 72-hour interval.
This will limit fjssion product and decay heat buildup. Thus, the worst case scenario will be less than the design basis event.
3.
There is a very low likelihood of an accident involving large amounts of hydrogen generation in the 72-hour interval.
Conclusion We conclude, based on the reasons given above, that an extension of 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> in the LCO of Technical Specification 3.7.A.5.b and 3.7.A.7(1) does not pose an unacceptable risk to the health and safety of the public.
Dated: February 22, 1983
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The following NRC personnel have contributed to this SER:
D. Pickett and G. Rivenbark.
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