ML20155J087

Forwards Supplemental Info for NRC Review Re TS Change 208 Request on Sf Pool Cooling Sys

ML20155J087
Person / Time
Site:	Maine Yankee
Issue date:	11/05/1998
From:	Zinke G Maine Yankee
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GAZ-98-59, MN-98-70, NUDOCS 9811120020
Download: ML20155J087 (4)

Text

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.s. 4 MaineYankee P.O. BOX 408 + WISCASSET, MAINE 04578 a (207) 882-6321 November 5, 1998 MN-98-70 GAZ-98-59 Proposed Change No. 208 Supplement No. 1 UNITED STATES NUCLEAR REGULATORY COMMISSION Attention: Document Control Desk Washington DC 20555

Reference:

(a) License No. DPR-36 (Docket No. 50-309)

(b) Letter: M. J. Meisner to USNRC: Proposed Technical Specification Change No. 208 - Fuel Storage Pool Water Level: MN-98-25. dated ,

April 13. 1998 ~ J

Subject:

Proposed Technical Specification Change No. 208 - Fuel Storage Pool Water Level: Supplement No. 1 Gentlemen:  !

In Reference.(b). Maine Yankee submitted a proposed change to the Technical Specifications to base the Limiting Condition for Operation for the Fuel Storage Pool Water Level on the revised analysis for the Fuel Handling Accident and on a new  ;

analysi's for radiological shielding during movement of irradiated fuel. The purpose of this letter is to supplement that submittal with additional information to support NRC's review. This additional information which is provided in Attachment .

A includes a description of the need for the Technical Specification and an  !

evaluation of the effect of the requested Technical Specification change on the i Spent Fuel Pool Cooling system.

-This supplementary information does not affect the Significant Hazards Evaluation presented in Attachment I of Reference (b). If you have any questions, please contact us.

Very truly yours, f\

. ,7 George A. Zinke-, i ctor f Nuclear Safety & Regulatory Affairs o\

,"1 - st o 3v' Attachments. ,

ci Mr.(HubertMiller

'Mr.~ Michael Webb-Mr. Mike'Masnik' Mr. Mark' Roberts ~

Mr. Clough Toppan Mr. Patrick J. Dostie

.Mr. Uldis Vanags 9811120020 991105 "

PDR ADOCK 05000309 V W PDR h

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e ATTACHMENT A Page 1 of 3 PROPOSED CHANGE NO. 208 ,

SUPPLEMENT N0. 1-In response to a verbal request from the NRC. Maine Yankee is providing the following additional information supporting the need for the proposed Technical Specification change and its effect on the spent fuel pool cooling system.

DESCRIPTION OF NEED l

Maine Yankee's current Technical Specifications require the fuel storage pool water l- level to be greater than or equal to 23 feet over the top of irradiated fuel l

! assemblies seated in the storage racks during movement of irradiated fuel assemblies o -in the fuel storage pool. This minimal level approximately corresponds to the normal water level of the fuel storage pool. In February 1998. Maine Yankee

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completed a spent fuel pool elevation study. According to this study, the minimum fuel storage pool level required by Technical Specifications, when applicable, is 0.184 feet (2.208 inches) above the normal water level of the fuel storage pool.

l Accordingly, a change to the Technical Specification basis was processed in accordance with Technical Specification 5.C.4 " Technical Specification (TS) Bases Control Program" This basis change indicated that the minimum fuel storage pool

. level required by Technical Specifications, when applicable, is at the 44.2 foot elevation, which corresponds to 0.2 feet (2.4 inches) above the normal water level (rounded up for operator convenience). .

While it is possible to maintain the fuel storage pool water level at the minimum required by the ' existing Technical Specification, when applicable, it does not provide the operators with the desired operating margin for compliance without L increasing the water level to undesirable elevations. Raising the water level too l

high interferes with the ability of the skimmers to function and floods certain electrical connections. Therefore, in order to provide the operators with  !

additional operating margin for compliance with the Technical Specifications. Maine  !

Yankee has requested a change to the Technical Specification lowering the level by i two feet-(i.e. at the 42.2 foot elevation). I EFFECT OF THE LEVEL CHANGE ON THE SPENT FUEL P0OL COOLING SYSTEM The purpose of the Spent Fuel Pool (SFP) Cooling. System is to remove decay heat from pool water to maintain SFP water temperature within a normal range. The system also provides for_ SFP filtering and skimming functions. The system is composed of two

-spent fuel pool cooling pumps (primary side), a heat exchanger, two decay heat removal pumps (secondary side), six fan coolers each containing three fans, piping, valves and other associated equipment. This system does not perform a safety related function. Analyses demonstrate that the fuel, the storage racks and the '

l fuel pool structural components are capable of sustaining boiling as a service

condition. For operational considerations pool temperatures are normally

-maintained below 120 F. . The system is designed to prevent a siphoning event below

'the 40 foot elevation which would provide almost 19 feet of water above the top of fuel assemblies seated in the spent fuel storage racks. In addition, adequate time is available to the operators to identify and remedy a low pool water level condition or loss of cooling incident.

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l I l ATTACHMENT A Page 2 of 3 )

PROPOSED CHANGE N0. 208 SUPPLEMENT NO, 1 I

Even though the spent fuel pool cooling system does not provide a safety related l function, it is prudent to evaluate the effect of the proposed fuel storage pool water level change on the normal operating function of the spent fuel pool cooling l system. When the level decreases below 6 inches from the normal water level, the skimming function of the spent fuel pool purification system, if in operation, will be interrupted. The loss of the skimming function does not impact the ability of the spent fuel pool cooling system to remove decay heat.

The other impact the proposed fuel storage pool water level change will have on the l

spent fuel pool cooling 'ystem is associated with the two spent fuel pool cooling pumps (primary side). The effect on the pumps is related to (1) net positive suction head of the pumps and (2) the increased possibility of vortexing at the siphon protection piping (located at about 40 foot, 11 inches) and the consequential introduction of air into the pumes. Calculations were performed to determine these effects. The results of these caiculations indicated that two spent fuel pool l cooling pumps may be operated at fuel storage pool Water levels corresponding to 43 foot elevation or above without impacting the minimum net positive suction head and without vortex-induced-air-entrainment. At fuel storage pool levels below that corresponding to the 43 foot elevation, spent fuel pool cooling pump operations need to be limited to one pump to prevent vortex-induced-air-entrainment. Both situations require some throttling of flow at extreme fuel storage pool temperatures (eg. above 200 F). However, at these extreme temperatures, the heat removal capability of the throttled flow is enough to reduce the fuel storage pool temperature to a point at which the flow may be unthrottled. These restrictions will be maintained by administrative controls.

These effects are acceptable because the spent fuel pool cooling system is not required to protect the integrity of the fuel, the storage racks or the fuel storage pool structure itself. Analyses demonstrate that these structures and components are capable of sustaining boiling as a service condition. However, a normal range .

of spent fuel pool temperatures has been established for operational considerations. 1 One spent fuel pool cooling pump provides sufficient heat removal capability to maintain the spent fuel pool temperature in the normal operating range under most conditions and in the acceptable range under all conditions. During extreme summer l temperatures, operations would operate two pumps to maintain the spent fuel pool I temperature in the normal operating range, at which time the fuel storage pool water level would be maintained at or above the 43 foot elevation. Since fuel storage ,

pool water level and temperature transients occur over a long period of time (eg. l l days), there is ample time to recover level, if necessary, should it be lower than I l normal. Furthermore, an analysis of the fuel storage pool shows that a loss of the spent fuel pool cooling system can be sustained indefinitely as long as adequate makeup is supplied to replace fuel storage pool water that is lost due to evaporation. Fuel storage pool water makeup is available from multiple sources independent of the spent fuel pool cooling pumps.

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l ATTACHMENT A Page 3 of 3 PROPOSED CHANGE N0. 208 SUPPLEMENT NO. 1 l

l Notwithstanding Maine Yankee's request to decrease the minimum fuel storage pool water level by two feet. Maine Yankee does not intend to operate the pool at this

level. Maine Yankee intends to operate the fuel storage pool at the normal water ,

l level This level preserves the function of the fuel storage pool skimmmers and  !

will provide a large margin for compliance with the proposed Technical Specification l

minimum fuel storage pool water level, i 1

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