ML20083H776

Forwards Addl Info Re Requesting Substitution of Longer Values for Scram Discharge Vol Vent & Drain Valve Closure Times.Closure Times Proposed in Do Not Meet Acceptance Criteria in SER

ML20083H776
Person / Time
Site:	Hatch
Issue date:	12/22/1983
From:	Gucwa L GEORGIA POWER CO.
To:	Stolz J Office of Nuclear Reactor Regulation
References
NED-83-629, TAC-53327, TAC-53328, NUDOCS 8401130346
Download: ML20083H776 (3)

Text

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Georg.a Power Company 333 Pe1mont Avenue

-0 Attanta. Georgia 30308 Telephone 404 5266526 MaAng Address Post oft ce Ocs 4545 Atlanta. Georgia 30302 Georgia Power L T. Gucwa tN sour %vo eetnc sys'em Manager Nuclear Eng.neenng and Chief Nuclear Eng nee' NED 83-629 December 22, 1983 Director of Nuclear Reactor Regulation Attention: Mr. John F. Stolz, Chief Operating Reactors Branch No. 4 Division of Licensirg U. S. Nuclear Regulatory Cm mission Washirgton, D. C.

20555 NRC DOCKET 50-321 OPERATI!G LICENSE DPR-57 EININ I. HA'ICH NUCIEAR PLANP UNIT 1 SCRAM DISCHAIGE VOLtNE VENP AND DRAIN VALVE CIOSURE TIMES Gentlemen:

Enclosed is additional information in regard to our letter of December 14, 1983, which requested substitution of lorger values for Scram Discharge Volume vent and drain valve closure times.

Closure times for these valves were originally specified in proposed Technical Specification changes dated September 19, 1983.

It has cince been determined that the orfginally proposed closure time values cannot be met without further modifications to the scram discharge system.

%e closure times proposed in the December 14, 1983 letter do not meet acceptance criteria contained in the NDC's Generic Safety Evaluation Report (SER) on the BWR Scram Discharge System, dated Decenter 1,1980.

The enclosed qualitative analysis performed by our Architect /Ergineer considers possible mechanisms resulting in hydrodynamic forces in the scram system, and their relation to vent and drain valve closure times, as discussed in the SER. It is the conclusion of the analysis that there is no evidence that the hydredynamic forces which may be present for valve closure at 120 seconds will be significantly different than those forces which may be present at 30 seconds.

It is noted that the NBC SER contained requirements that any deviation from stated criteria be aubnitted to the NRC for advance approval. Wrough an oversight, the required subnittal was not made.

If the enclosed qualitative analysis is not sufficient justification for demonstrating acceptable deviation from the SER, we request a delay in implemental; ion pertaining to valve closure times.

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~g GeorgiaPbwer A Director of Nuclear Reactor Regulation U. S. Nuclear Regulatory Comnission December 22, 1983 Page 2 Tenporary operation with the lorger valve closing times will not result in any threat to public health or safety.

All remaining scram discharge system modifications on Unit 1 are functional.

Inboard vent and drain valves will continue to operate with the same closure times as in the past.

Operation with these closure times for several years has not resulted in damage to the SW or its supports (see attachment).

Only the newly installed outboard valves will be subject to longer closing times, and the only purpose of these valves is to isolate the SW following the unlikely failure of the inboard valves. 'Iherefore, ue believe it would be reasonable to allow continued operation with the longer closure times pendirg resolution of this concern.

Your expeditious resolution of this concern would be appreciated in order to prevent shutdown of the unit.

Please contact this office if further information is desired.

Very truly yours, M* SM L. T. Gucwa REB /

Enclosure xc:

J. T. Beckham, Jr.

H. C. Nix, Jr Senior Resident Inspector, Plant Hatch J. P. O'Reilly (NBC-Region II) 700775

o Attachment to Letter dated Deconber 22, 1983 (Scr a Discharge Volune Vent and Drain Valve Closure Times

%e mechanisms discussed by the NIC by which hydrodynmic forces could be generated in the SW due to delayed valve closure (Ref. Dec.1.1980 NIC SER Para 1.3.3) have been reviewed:.

It has to be noted that the primary concern of the hydrodynmic loads was possible damage to the float level switches which was observed in certain plants where the float taps were connected directly to the vent or drair$ lines.

At Hatch, the piping arrangenent was modified such that the float taps connect directly to the 8 inch dimeter SW.

nis design precludes the possibility of creating a high differential pressure or flow through the float switch during a scrm or scre reset which might otherwise danage the float.

We NRC describes two possible mechanisms specifically related to valve closure which could result in water hamer in the SW.

%e first mechanism involves high flow rates through the vent and drain lines followed by valve closure.

%e second mechanism involves hot water entering the SW and in part flashing to stem followed by valve closure.

The NRC indicates that upon valve closure the SW will pressurize causing collapse of the stean and possible water hamer.

Another likely cause for stean collapse is the mi,xing of steam with relatively cold water in the SW resulting from the initial rod insertion. This may possibly result in sme chugging within the SW.

%e apparent effect that delayed valve closure has on both mechanisns is that it allows hot water to enter the SW.

Flashing of this hot water will tend to pressurize the SW prior to isolation and could cause high flow through the vent and drain line or result in the stean bubble collapse described above.

Hot water could enter the SW, due to CRD seal leakage, before 30 seconds following a scrm as well as after.

The initial scran takes approximately 6 seconds and will discharge mostly cold water into the SW. Depending on the actual quantity of discharge, the SW will be half to mostly full (SW Volume Hatch Unit 1 = 482 gal.).

Thereafter, hot reactor coolant driven by reactor pressure will leak by the CRD seals at up to 41/2 GPWrod (617 GPM total) and will enter the SW.

(Refer to NUREG-0803).

Since the gravity drain rate of the SW is on the order of 12 GPM, the SW will tend to pressurize due to this CRD seal leakage.

This pressurization will occur before the water initially discharged into the SW has a chance to drain out of the SW.

It should be noted that the Hatch units have not experienced any SW danage due to the hydrodynanic loads.

As part of I&E Bulletin 79-14 walkdown, a support for the vent discharge line in the vicinity of the hub was found bent--that danage was attributed to an installation error.

Since the mechanisms identified by the NRC as causing water hatraur in the SW can occur prior to 30 seconds, as well as after, the longer valve closure times ~ should not introduce any additional hydrodynanic forces.

We conclude, therefore, that the acceptance criteria for valve closure provided (60 seconds for inboard valves, 120 seconds for outboard valves) are satisfactory.