ML20098G640

Responds to IE Bulletin 84-03 Re Potential for Refueling Cavity Water Seal.Gross Seal Failure Considered Extremely Low Probability Due to Sys Design

ML20098G640
Person / Time
Site:	Davis Besse
Issue date:	09/27/1984
From:	Crouse R TOLEDO EDISON CO.
To:	James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
1-466, IEB-84-03, IEB-84-3, L-466, NUDOCS 8410050265
Download: ML20098G640 (10)

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Docket No.'50-346 W1LEDO License No. NPF-3 Serial No. 1-466 I,1 N "

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September 27, 1984 i

Mr. James G. Keppler, Regional Administrator k- Region III United States Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137

Dear Mr. Keppler:

This is in response to your August 24, 1984 letter, IE Bulletin 84-03 (Log No. 1-1021), concerning Refueling Cavity Water Seal. Specifically, Toledo

-Edison has evaluated the potential for, and consequences of, a refueling cavity water seal failure at the Davis-Besse Nuclear Power Station and this letter provides a summary of that evaluation.

The seal ring arrangement at Davis-Besse is a passive system. There are ne' active components, such as pressurized seals, involved in the design.

A cross sectional sketch of the seal ring configuration is provided in Figure 1.

g The seal ting is a continuous ring of stainless steel plate wide enough to

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span the gap between and overlap the reactor vessel flange and the refueling L- canal floor. The seal ring sits in a depression on the vessel flange and the canal floor. A rubber gasket is placed between the seal ring and a groove in each seating surface. The rubber gasket is designed to accommo-date any difference in elevation between the vessel flange and canal floor.

The seal plate is held in place by 36 adjustable clamps, which ora torqued 4 'in a specified sequence to apply a downward pressure on the seal ring. An additional seal is provided by applying a commercial sealant to the inner and outer edges of the seal ring after the holddown clamps have been ad-justed. Toledo Edison considers a gross seal-failure of this arrangement to be an extremely low probability event.

Figures 2 and 3 illustrate the configuration of the Davis-Besse Fuel Hand-ling equipment and the areas flooded during fuel handling activities. The refueling canal inside containment is connected to the Auxiliary Building by two fuel transfer tubes. At either end of the transfer tubes are the upender mechanists for the fuel transfer system. These devices rotate fuel assemblies between the vertical and horizontal positions necessary for fuel handling or fuel transfer between buildings.

8410050265 PDR ADOCK 840927 G 05000346 PDR THE TOLEDO EDISON COMPANY EDISON PLAZA 300 MADISON AVENUE TOLEDO, OHIO 43652 ISEP'9 8 1@#

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In containment, the upender mechanisms are located i'n th'e lowered section

'of the refueling canal, such that the top of a fuel assembly located in an upender mechanism'in the vertical-position will be approximately level with~the vessel. flange and main refueling canal floor.

- The upender mechanisms in'the Auxiliary Building are located in a separate pool area which can~be isolated from the spent fuel storage area by a movable gate. Additional isolation between the containment and Auxiliary

Building 'can be provided by large gate valves on the Auxiliary Building end'of the fuel ~ transfer tubes. The gate valves are manually actuated from the top of the pool.

M .During refueling operations, the refueling canal, spent fuel storage area, an,d the fuel transfer pool in the Auxiliary Building are all inter-connected and flooded-to within about two. feet of the top of the refueling canal.

There are no active components,_such as pressurized seals, in this configur-ation..

If'a' gross' seal' ring failure is assumed during refueling activities and no

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operator action is taken, the refueling canal. spent fuel storage pool, and fuel transfer pool water level would drain to the level of the riactor ves-sel flange. Fuel assemblies located in the reactor vessel would continue to be cooled by the' decay heat removal system.

-Any fuel-assemblies located-in the. fuel handling mast of any'of the three fuel handling bridges would.be completely uncovere'd and could not be. cooled.

~In such.a condition, an' estimate of the time to cladding failure, from the time the assembly'is exposed, is approximately 30 minutes.

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- Any- fuel assemblies _ located . in the spent fuel stornay nu, its any. of the -

upender mechanisme3 cr in MA t W .j hvioing racks located in the deep-end of the refueling canal along side the upender mechanisms (not shown on

~ drawings),- would be immersed in water to a depth of approximately three inches over the topfof the fuel pins. Cooling of these assemblies would

-be limited.to heat transfer to the surrounding water.

While Toledo-Edison does not believe that gross seal ring-failures are a

.realiscic; concern, the fuel handling bridge. operators have'been given in-

.structions'to deal with a decreasing refueling canal level. The objective of the instructions is to maximize the level of water over any spent fuel asscably. The instructions' include:

Fuel assemblies'in the masts of fuel bridges inside containment are to be placed11n an upender mechanism or in the. reactor vessel.

Fuel assemblies located in the upender mechanisms are to be placed in cthe horizontal position.-

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Fuel assemblies-located in-the temporary racks in the refueling canal are to be moved lto the reactor vessel or~to the upender mechanism.

. Fuel assemblies 'in the mast of. the fuel transfer bridge in the spent fuel area are to be lowered into the spent fuel storage area rack.

lThe gate between the spent fuel storage area and the adjoining pool in-the. auxiliary building is to be'put in place.

If time permits, the cables which drive the transfer mechanisms are to be ~ removed to allow complete closure of the' gate valves on the

' Auxiliary Building end of the transfer tubes. In any case, the gate valves' are to be closed as tightly as possible.

JAt those times during a refueling outage when the refueling canal is filled but no' fuel handling activities are in progress, operator instruc-

tions exist to minimize the risks associated with a loss of water level rand no operator action.- These instructions include:

Fuel assemblies are not to be left in the fuel handling masts of an unattended . fuel handling bridge'.

-Fuel assemblies are not'be be left unatten0=u in an upender mechanism 11n the vertical position.

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= Tf _ ftal handling activities aracto' be suspended . for a period in ex-

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cess of 24' hours, the gate between the spent fuel storage area and

. the adjacent pool is to be installed and the gate valves on the transfer tubes.are to be closed as far as possible without damaging the transfer: equipment cable.

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, Additional protection against the unattended drop in refueling canal level is provided by1the spent fuel pool level annunciator in the control room, which falarms on decreasing spent fuel: pool' level with a set point approximately half-g a foot below normal refueling level.

In the' event of a decreasing' water level in the refueling canal, make up E s water.can be_ injected from the borated water storage tank. Technical-j Specifications require a minimum of 70,700. gallons of water to be main-t rained in the borated water storage tank. This water can be injected into

.the' refueling canal through the. reactor vessel via the decay heat _ pumps at

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la rate 1offmore than 3,000 gym.

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Duiing the 1984 refueling outage the reactor vessel internals will be re-moved for modification. Prior to their-removal, the entire core will be transferred to the spent fuel pool. storage racks. Once the internals are removed, each reactor coolant system cold leg will be plugged with an inflatable. seal. This _will allow the internals modification work to pro-ceed underwater while the reactor coolant system cold legs can be drained to perform reactor coolant pump work.

The failure of one of the inflated seals could lead to the draining of the refueling canal. However, since no refueling activities will be in pro-gress, the gate between the spent fuel pool and the adjoining pool in the Auxiliary Building will'be in place and the gate valves on the transfer tubes will be closed as far as possible.- Toledo Edison believes that these precautions will provide adequate protection of the spent fuel in the spent fuel pool.

Very truly yours, RPC:JRL:SGW:nif/bc encl.

cc: DB-1 NRC Resident Inspector l

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.. .a ATOMIC ENERGY ACT OF 1954-SECTION 182a SUBMITTAL IN RESPONSE FOR THE DAVIS-BESSE NUCLEAR POWER STATION UNIT NO. 1 FACILITY OPERATING LICENSE NO. NPF-3 This letter is' submitted in conformance with Atomic Energy Act of 1954,

-Section 182a, in' response to IE Bulletin 84-03 (Log No. 1-1021). This deals with the potential for and consequences of a refueling cavity water seal-failure at the Davis-Besse Nuclear Power Station, Unit No. 1.

p By R. P. Crouse Vice President, Nuclear Sworn to and subscribed before me this 27thday of Sept. , 1984.

, %w Notary- PubMc, State of Ohio

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NORA LYNN FLOOD Notary Public, State of Ohio My Commission Expires Sept.1,1987

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