ML20247R682

LAR 97-07 to License NPF-86,revising Refueling Water Storage Tank low-low Level Setpoint

ML20247R682
Person / Time
Site:	Seabrook
Issue date:	05/20/1998
From:	Feigenbaum T NORTH ATLANTIC ENERGY SERVICE CORP. (NAESCO)
To:
Shared Package
ML20247R662	List: ML20247R656 ML20247R682 ML20247R702
References
NUDOCS 9805290198
Download: ML20247R682 (4)

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This License Amendment Request is submitted by North Atlantic Energy Service Corporation i pursuant to 10CFR50.90. The following information is enclosed in support of this License Amendment Request:

. Section 1 - Introduction and Safety Assessment for Proposed Change

. Section 11 - Markup of Proposed Change

. Section lli - Retype of Proposed Change

. Section IV -

Determination of Significant Hazards for Proposed Change

. Section V - Proposed Schedule for License Amendment issuance and Effectiveness

. Section VI - Enviroamentalimpact Assessment Sworn and Subscribed before me this

2n Wday of [h(L ' .1998 ,.

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1. n ;t%d fed C. Felgeni.aun[

() Notaiy Public Executive Vice President and Chief Nuclear Officer 9805290190 990520 J PDR ADOCK 0500044a P PDR ,

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5 Section i Introduction and Safety Assessment for the Proposed Change i

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L INTRODUCTION AND SAFETY ASSESSMENT OF TIIE PROPOSED CHANGE A. Introduction License Amendment Request (LAR) 97-07 proposes a change to the Seabrook Station Technical Specifications (TS), Engineered Safety Features Actuation System Instrumentation Trip Setpoints, Table 3.3-4, Functional Unit 8.b, RWST Level--Low-Low, and associated Bases Section 3/4.3.2. The proposed change will revise the Refueling Water Storage Tank (RWST) setpoint associated with Automatic Switchover to the Containment Sump. The proposed setpoint is the result of a revised setpoint calculation which increases design margin and enhances the setpoint by providing both an upper and lower allowable value to more closely satisfy design basis requirements.

Currently, TS Table 3.3-4, Functional Unit 8.b, specifies the RWST Level Low-Low setpoint as 122,5.26 gallons with an Allowable Value of 2121,609 gallons. The proposed new setpoint will be 120,478 gallov with an Allowable Value band of 2119,435 to $ 121,521 gallons. Also revised is the Total Allowance (TA) and Sensor Error (S). The proposed changes are enhancements to account for the design bases of the setpoint and a revised drift value to accommodate a 24-month fuel cycle surveillance interval extension.

H. Safety Assessment of the Proposed Change The design bases for the RWST Level Low-Low setpoint, which initiates automatic ECCS transfer switchover, is to ensure that the minimum volume of water to support the assumptions made in the safety analysis is injected prior to switchover; and that there is adequate time available for the operators to complete the manual actions necessary to complete the switchover to the recirculation mode prior to reaching the level in the RWST where the onset of vortexing is of concern. Switchover from the RWST l to the containment recirculation sumps must occur before the RWST empties to prevent damage to the ECCS pumps and a loss of core cooling capability. For similar reasons, switchover must not occur before there is sufficient water in the containment sump to provide sufficient net positive suction head (NPSil) to support ECCS pump operation. Furthermore, early switchover must not occur to ensure that sufficient borated water is injected from the RWe~. This ensures the reactor remains shut down in the recirculation mode.

The RWST is a dual function component. For normal operation it is used to fill the refueling pool and canal for refueling operations, and to provide makeup to the spent fuel pool. For accident ec'iditions it is the source of borated water for the Emergency Core Cooling System (ECCS) pumps during the injection phase. When the water level in the RWST reaches the Low-Low setpoint, automatic ECCS transfer from the injection mode to the recirculation mode is initiated, i.e., the containment sump isolation valves are opened automatically and alarms are provided to alert 9 operators to begin the manual actions necessary to complete the transfer to the recirculation mode. Should full transfer (automatic and manual) i not be completed in sufficient time an RWST EMPTY alarm is provided to alert the operators to provide l adequate time to secure the ECCS pumps taking suction from the RWST prior to potential vortexing

j. conditions occurring.

To satisfy the aforementioned requirements, the RWST Level Low-Low Allowable Value/ Trip Setpoint has both upper and lower limits. The engineering calculation that derived the RWST Level Low-Low Allowable Valueffrip Setpoint established an upper safety analysis limit (USAL) and a lower safety analysis limit (LSAL). The USAL is set at the minimum volume of borated water in the RWST that Page 2

6 must be injected into the reactor coolant system (RCS) during the injection phase to satisfy desigt basis requirements prior to initiation of automatic switchover to the containment building recirculation sumps.

The USAL is based on the TS limit alarm setpoint, minus instrument uncertainty and minimum injection allowance volume. The LSAL is set at the minimum volume of water in the RWST at which initiation of automatic switchover must occur in order to afford sufGeient time for the manual portion of switchover to the recirculation phase prior to reaching the level in the RWST where the onset of vortexing is of concern. The LSAL is based on the vortexing level plus an allocated transfer allowance volume to account for the manual transfer to the recirculauon mode, plus an allocated ECCS pump shutoff allowance volunie to account for securing the ECCS pumps after receipt of the RWST EMPTY alarm,

and the instrument uncertainty band for the RWST EMPTY bistable. The LSAL includes the instrument uncertainty band for the RWST EMPTY bistable since the design basis for the lower limit is to provide adequate time to complete the switchover to the recirculation mode prior to receipt of the RWST

, EMPTY alarm. The proposed RWST Level Low-Low setpoint accounts for instrument uncertainty and l was selected to fall between the USAL and LSAL.

In addition, the new setpoint takes into account a revised drift value to accommodate a 24-month fuel cycle surveillance interval extension. The instrument uncertainty calculations used to support determination of the RWST Level Low-Low setpoint are based on the on-going Westinghouse effort in support of the surveillance interval extension to 24 months. Westinghouse speci0 cations for the current RWST level transmitters associated with the RWST Level Low-Low setpoint specify a value of 1% as the limit for drift over a 12-month interval. The 1% value, originally for a 12-month interval, is currently applied to the instrument uncertainty calculation for an 18-month interval. For the 24-month surveillance interval, a value of 2% is used. The Westinghouse drift analysis for these transmitters indicates a bias of 0.2% with a random uncertainty of 1.2%. Therefore, the 2% drift value used is conservative as compared with the Westinghouse analysis. Furthermore, the quarterly Trip Actuating Device Operational Test (TADOT) surveillance test will check for drift of the transmitter "Zero." This will provide additional assurance the transmitters are performing as expected.

Since the design bases place limits on the RWST Level Low-Low setpoint in both the upward and downward direction two Total Allowance and two Allowable Values were derived for TS Table 3.3-4.

These values reDect the USAL and LSAL. One Allowable Value places a limit on the setpoint in the upward direction and the other Allowable Value places a limit on the setpoint in the downward direction.

Correspondingly, TS Table 3.3-4 was also revised to reflect a new sensor error.

Overall, the proposed new RWST Level Low-Low setpoint increases the potential total volume of water injected from the RWST into the reactor coolant system (RCS) and/or containment by approximately 2000 gallons. It has been determined that the containment Hood level assumptions following a LOCA will not be adversely affected by the revised setpoint. The effect on sump pil and containment spray pH for accident conditions were evaluated with the conclusion that the change in pH is negligible. Therefore, there is no impact on Containment Building Spray (CBS) System performance or the parameters used for Environmental Qualification of electrical equipment.

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