ML20204E346
| ML20204E346 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 03/12/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20204E343 | List: |
| References | |
| NUDOCS 9903250006 | |
| Download: ML20204E346 (4) | |
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UNITED STATES e*
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NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 2055 5 0001 g
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1 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 60 TO FACILITY OPERATING LICENSE NO. NPF-86 NORTH ATLANTIC ENERGY SERVICE CORPORATION SEABROOK STATION. UNIT NO,1 DOCKET NO. 50-443 i
1.0 INTRODUCTION
By letter dated May 20,1998, as supplemented by a letter containing clarifying information dated January 28,1999, the North Atlantic Energy Service Corporation (NAESCO) submitted a request for changes to the Seabrook Station, Technical Specifications (TS). The requested changes would revise the low-low level setpoint of the Refueling Water Storage Tank (RWST) that initiates automatic switchover of the source of borated water for the Emergency Core j
Cooling System (ECCS) from the RWST to the containment sumps. The January 28,1999, 4
letter did not change the initial proposed no significant hazards consideration determination.
I 2.0 EVALUATION 2.1 Backaround The RWST is the initial source of borated water for the ECCS pumps following certain accidents. When the water level in the RWST decreases to the low-low setpoint during accident mitigation, the source of borated water for the ECCS pumps is switched to the containment sumps. The RWST low-low level sotpoint automatically initiates the transfer and provides an alarm to alert the operators to manually complete the transfer. If the transfer is not completed in sufficient time, an RWST EMPTY alarm alerts the operators to secure the ECCS pumps taking suction from the RWST prior to potential vortexing conditions that could result in ECCS pump damage and subsequent loss of core cooling capability.
Therefore, the design basis for the RWST low-low level setpoint is to ensure that: (1) The transfer does not occur before t"ere is sufficient water in the containment sump to provide the required net positive suction head (NPSH) to support ECCS pump operation, (2) the transfer does not occur before sufficient borated water is injected from the RWST to ensure the reactor remains shut down in the recirculation mode, and (3) the initiation of the transfer occurs while there is still sufficient time for the operators to complete the manual actions necessary to comp lete the transfer prior to reaching the level in the RWST where vortexing could occur.
Consequently, the transfer must occur during the time period after certain events, but also prior to certain other events, thereby requiring the RWST low-low level setpoint to actuate within a given range bounded by upper and lower Allowable Values.
9903250006 990312 PDR ADOCK 05000443 P
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l-2.2 Setooint Determination Currently, Seabrook's RWST low-low level setpoint has an Allowable Value associated only with the lower limit. On May 20,1998, NAESCO submitted License Amendment Request 97-07 that proposed a change to the RWST low-low setpoint and added an upper Allowable Value limit.
This request would require a change to the Seabrook Station 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.
l Currently, TS Table 3.3-4, Functional Unit 8.b, specifies the RWST low-low level setpoint as l-122,525 gallons with an Allowable Value of 2121,609 gallons. The proposed new setpoint would be 120,478 gallons with an Allowable Value band of 2119,435 to s 121,521 gallons.
The upper Allowable Value is set at the minimum volume of borated water in the RWST that must be injected into the reactor coolant system (RCS) during the injection phase to satisfy design basis requirements prior to initiation of automatic switchover to the containment building recirculation sumps. The upper Allowable Value is based on the TS limit alarm setpoint, minus instrument uncertainty and minimum injection allowance volume. The lower Allowable Value is l
set at the minimum volume of water in the RWST at which initiation of automatic switchover must occur in order to afford sufficient time for the manual portion of switchover to the l
recirculation phase prior to reaching the level in the RWST where vortexing could occur. The f
lower Allowable Value is based on the vortexing level plus an allocated transfer allowance volume to account for the manual transfer to the recirculation mode, plus an allocated ECCS pump shutoff allowance volume to account for securing the ECCS pumps after receipt of the l
RWST. EMPTY alarm, and the instrument uncertainty band for the RWST EMPTY bistable.
The lower Allowable Value 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 l
switchover to the recirculation mode prior to receipt of the RWST EMPTY alarm. The proposed i
RWST low-low level setpoint accounts for instrument uncertainty and was selected as the mid-i point between the upper and lower Allowable Values.
t in addition, the new setpoint, along with the associated Total Allowance and Sensor Error were also revised to include a more conservative drift value that would account for drift periods up to 24 months. According to the licensee, Westinghouse specifications for the current RWST level transmitters associated with the RWST low-low level 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. The new value includes a drift value based on a 24-month drift period. 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.
Oection 7.1.2.1.1. of the Seabrook Updated Final Safety Analysis Report (UFSAR) states that j
.the methodology used to determine the bistable setpoints complies with the methodology j
outlined in Regulatory Guide 1.105 (Rev.1), as supplemented by the information presented in l
lSA Standard S67.04, Draft F. Based on the information provided, the method used to select the new RWST low-low level bistable setpoint is acceptable.
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2.3 Increased iniection Volume The proposed new RWST low-low level setpoint increases the potential total volume of water injected from the RWST into the reactor coolant system (RCS) and/or containment by J
approximately 2000 gallons. The licensee determined that the containment flood level assumptions following a LOCA will not be adversely affected by the revised setpoint and that the effect on sump pH 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. The increased injection volume that could occur as a result of the proposed change is, therefore, acceptable.
2.4 NPSH Chanoes NAESCO's 90-day response to Generic Letter (GL) 97-04 dated January 5,1998, states that the most limiting pump alignment 9garding available NPSH for the Safety Injection (SI) and Charging (CS) pumps occurs privr to switchover to ECCS recirculation operation when the pumps are taking suction from the RWST. The proposed change lowers the RWST low-low level setpoint by 1.5 inches which corresponds to an equivalent reduction of NPSH available to the ECCS pumps prior to switchover. However, though this may be the most limiting case, the available NPSH for both the SI and CS pumps is significantly greater than the required NPSH.
Per the 90-day response to the Generic Letter, the available NPSH for the SI pumps is 40.5 feet and the required NPSH is only 16 feet. The available NPSH for the CS pumps is 40 feet and the required NPSH is only 28 feet. Therefore, a reduction of 1.5 inches is insignificant. In addition, the supplemental information provided by NAESCO on January 28,1999, states that a review of the hydraulic calculations confirms that sufficient NPSH continues to remain available for the most limiting pump alignments during the ECCS operational phases and that the assurance of sufficient NPSH for the ECCS pumps provided in NAESCO's 90-day response to GL 97-04 dated January 5,1998, is still valid. The change to the RWST low-low level setpoint with regard to the available NPSH prior to switchover is, therefore, acceptable.
The most limiting pump alignment regarding available NPSH for the CBS and Residual Heat Removal (RPR) pumps was identified by NAESCO as occurring during ECCS recirculation.
However, since the proposed change would lower the RWST low-low level setpoint, a greater inventory would potentially be delivered to the containment sumps which would increase the NPSH available to the CBS and RHR pumps during the recirculation phase. The change to the RWST low-low level setpoint with regard to the available NPSH during recirculation is, therefore, acceptable.
2.5 Ooerator Action Response Times The amount of time available to the operator to complete the manual portion of the ECCS transfer from the RWST to the containment sumps is based on the volume of water in the RWST designated as the " Transfer Allowance" along with the flow rate. The amount of time available to the operator to secure the ECCS pumps upon receipt of the RWST EMPTY alarm is based on the volume of water in the RWST designated as the " Shutoff (Single Failure)
Allowance" along with the worst case flow rate. During the derivation of the new RWST low-low
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, level setpoint, the volume of water attributed to the Transfer Allowance and the Shutoff (Single
- Failure) Allowance were not changed. Since the design basis flow rates from the RWST were also not changed, the operator action response times would not be affected by the proposed RWST low-low level setpoint change and, therefore, are acceptable.
3 2.6 Summary Based on the above evaluation, the proposed changes to the RWST low-low level setpoint are acceptable. Appropriate changes have been made to TS Table 3.3-4 to depict the new setpoint
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and its associated parameters. TS Table 3.3-4 Table Notations were also revised to add notations to ac count for the new range of acceptable values. In addition, appropriate changes were made to the Bases to explain the necessity of adding an upper Allowable Value.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the New Hampshire and Massachusetts State officials were notified of the proposed issuance of the amendment. The State officials had no comments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20. The NRC staff has determined that the amendment involves no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendment involves no significant hazards consideration, and there has been no pub!ic comment on such finding (63 FR 43205). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
5.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, thct: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with_the
- Commission's regulations, and (3) the issuance of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: John Harrison Date:
March 12, 1999