ML20206C890
| ML20206C890 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 04/26/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20206C884 | List: |
| References | |
| NUDOCS 9905030239 | |
| Download: ML20206C890 (5) | |
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UNITED STATES y-s j
NUCLEAR REGULATORY COMMISSION
- 2 WASHINGTON. D.C. 20566 0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.170 TO FACILITY OPERATING LICENSE NO. DPR-28 VERMONT YANKEE NUCLEAR POWER CORPORATION VERMONT YANKEE NUCLEAR POWER STATION DOCKET NO. 50-271
1.0 INTRODUCTION
o The Vermont Yankee Nuclear Power Station is a boiling water reactor (BWR), model BWR-4, with a Mark I containment. By letter dated November 2,1998, the Vermont Yankee Nuclear Power Corporation, the licensee for the Vermont Yankee Nuclear Power Station, submitted for Nuclear Regulatory Commission (NRC) staff review a proposed change to the Technical Specifications (TSs). The licensee proposed changes to the TSs to more clearly describe the emergency core cooling system (ECCS) actuation instrumentation for the core spray (CS) system and low pressure coolant injection (LPCI) system or residual heat removal (RHR) system. The proposed changes to TS Table 3.2.1 involve the time delay relays for LPCI and CS pumps. These time delays are used to ensure, by load sequencing, that the emergency diesel generators (EDGs) are not overloaded when required to power pumps following an ECCS actuation and ensure that the loss-of-coolant accident (LOCA) safety analysis assumptions are met by providing flow within the time frames assumed in the LOCA analysis.
2.0 EVALUATION 2.1 Proposed Chance to TS Table 3.2.1 for Time Delav (10A K51 A&B)
The licensee proposed to change the Vermont Yankee, TS Table 3.2.1 by deleting trip function
" time delay (10A-K51 A&B)" and all other associated information for this function. The licensee stated that the start sequence for the RHR pumps in response to an accidqnt signal depends upon the availability of power to the emerg'ancy buses. If normal power is dvailable, all RHR pumps start immediately and directly from the accident signal. If normal power is not available, the four RHR pumps will automatically start in a predetermined sequence after the associated EDG has powered the associated emergency bus. Two pumps will start immediately and two l
pumps approximately 5 seconds later. The timed starting sequence is provided to prevent overloading of the EDGs. Additional equipment is similarly sequenced cn the emergency buses to ensure that the EDGs are not overloaded.
4 The relays that were used in the original plant design to accomplish the predetermined loading sequence for all four RHR pumps used time delay contacts with an adjustable range of 0.2 to i
180 seconds (minimum setting of 200 milliseconds). Because of an inherent drift, these relays were subsequently replaced with General Electric (GE) specified replacement relays 9905030239 990426 DR ADOCK 05000271 p
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These relays have since been replaced with " instantaneous" logic sequence relays and the time delay function is no longer applicable. The instantaneous logic sequence relay will function to initiate RHR Pump A/D start within 35 milliseconds of reenergization of the associated emergency bus. The installation of the " instantaneous" logic sequence relays is consistent with the intent of the 0-second time delay which existed in the plant TS.
The RHR pump A/D start time is within the assumptions of the LCLA safety analysis of record.
In the most limiting LOCA failure, two LPCI pumps are initiated at 28.1 seconds after the start of the LOCA accident (see Table 6.5.3 of the FSAR). Therefore, the licensee did not take credit for the iritiation of the first set of pumps (LPCI A & D) for the most limiting failure. The second set of pump's start time of 5 seconds is covered by the time delay relay (10A-K50A & B) given in the ECCS system actuation table. Therefore, the actuation of the second set of pumps is within the design basis accident analysis and the proposed change is acceptable.
The deletion of the 0-second time delay trip function is consistent with the methodology existing in the TS for " instantaneous" logic sequence relays. A separate trip function is not listed for instantaneous relays, and these relays are functionally tested once per operating cycle under the trip system logic trip function. The only change is that a calibration will not be required for an instantaneous logic sequence relay.
The staff finds that calibration of this instantaneous relay is not necessary and this enange is an improvement over the previous 500-millisecond time delay. The proposed change is acceptable since EDG loading requirements and LOCA safety analysis assumptions will continue to be met with the proposed change.
2.2 Proposed Chance to TS Table 3.2.1 for Time Delav (10A-K50A&B)
The licensee proposed changing the Vermont Yankee TS Table 3.2.1 by adding a lower limit to the " trip level setting" for trip function " time delay (10A-K50A&B)." The licensee proposed revision of the trip level setting from "s5 seconds" to "3s t s 5 seconds." W;thout a lower limit, the trip level setting of s5 seconds could allow the time delay to be set too l$w. As a result, the second two RHR pumps could start before the first two pumps have fully started and before EDG voltage and frequency have recovered. Therefore, a lower limit of 3 seconds is being proposed for the trip level setting. This proposed trip level setting of 3 s t s 5 seconds has been evaluated in accordance with the Vermont Yankee instrument setpoint and uncertainty program and validated through testing performed during integrated ECCS testing.
The licensee stated that the addition of 3-second lower limits to the second RHR pump start time delay (10A-K50A/B) trip level setting is a more restrictive change that ensures a minimum time lapse between the instantaneous start of the first RHR pump and the sequential start of the second RHR pump on the associated 4-kV emergency bus (powered by the EDG).
The proposed change ensures that the EDG has sufficient time to recover from the loading of the first RHR Pump set (A/D) before the loading of the second RHR Pump set (B/C).
Surveillance testing during the integrated ECCS test demonstrates that the EDG output voltage I
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. recovers to the rated voltage within 3 seconds following the start of each load group. The proposed minimum 3-second delay is bypassed when normal power is available.
On the basis of its review, the staff finds that this change is acceptable since specification of a lower limit for this time delay ensures that the EDG will be not be overloaded by these pumps and the lower limit does not affect the LOCA safety analysis.
2.3' Proposed Chanae to TS Table 3.2.1 for Time Delav (14A-K16A&B)
The licensee proposed changing the Vermont Yankee TS Table 3.2.1 by adding a lower limit to the " trip level setting" for trip function " time delay (14A-K16A&B)." The licensee proposed 3
revision of the trip level setting from "s10 seconds" to "8s t s 10 seconds." Without a lower i
limit, the trip level setting of s10 seconds could allow the time delay to be set too low. As a result, the core spray pumps could start before the second set of RHR pumps have fully started and before EDG voltage and frequency have recovered. Therefore, a lower limit of 8 seconds is being proposed for the trip level setting. This proposed trip level setting of 8 s t s 10 seconds has been evaluated in accordance with the Vermont Yankee instrument setpoint and uncertainty program and validated through testing performed during integrated ECCS testing.
The licensee stated that the addition of the 8-second lower limits to the core spray pump start time delay (14A-K16A/B) trip level setting is a more restrictive change which ensures a minimum time lapse between the B and C RHR pump start and the sequential start of the CS j
pump on the associated 4-kV emergency bus (powered by the EDG). Surveillance testing i
during the integrated ECCS test demonstrates that the EDG output voltage recovers to the rated voltage within 3 seconds following the start of each load group. The proposed minimum 8-second delay is bypassed when normal power is available.
On the basis of its review, the staff finds that this change is acceptable since specification of a the lower limit for this time delay ensures that the EDG will be not be overloaded by these pumps and the lower limit does not affect the LOCA safety analysis.
2.4 Prooosed Chance to TS 3.2 Bases 5
The licensee proposed modification of TS Bases 3.2 to include the following.
Upon receipt of a LOCA initiation signal, if normal ac power is available, all RHR pumps and both CS pumps start simultaneously with no intentional time delay, if normal ac power is not available, RHR Pumps A and D start immediately upon restoration of power, RHR Pumps B and C start within 3 to 5 seconds of restoration of power and both CS pumps start within 8 to 10 seconds of restoration of power. The purpose of theJe time delays is to stagger the start of the i
RHR and CS pumps on the associated Division 1 and Division 2 buses, thus limiting the starting transients on the 4.16-kV emergency buses. The time delay functions are only necessary when power is being supplied from the standby power sources (the EDGs). The time delays remain in the pump start logic at all times as the time delay relay contact is in parallel with the auxiliary power monitor relay contact. Either contact closure will initiate pump starts. Thus, the time delays do not affect low-pressure ECCS pump operation with normal ac power available. With normal ac power not available, the pump start relays that would have started the B and C RHR l
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, pumps and both CS pumps are blocked by the auxiliary power monitor contacts and the pump start time delay relays become the controlling devices.
On the basis of its review, the staff finds that the licensee has revised the bases to adequately reflect the proposed changes to TS Table 3.2.1 previously discussed. The staff does not object to the proposed bases change.
2.5 Summarv in summary, the staff concludes that the proposed revisions to the TSs to: (1) eliminate the RHR Pump A and D time delay function (trip level setting - O second); (2) provide a lower limit of 3 seconds to the existing s5 second trip level setting for the RHR Pumps B and C start time delay function; (3) provide a lower limit of 8 seconds to the existing s10 second trip level setting for the CS pump start time delay function; and (4) modify the bases of TS Section 3.2 to include a discussion of the RHR Pumps A through D and CS Pumps A and B LOCA start sequences are acceptable since the changes ensure that EDG loading requirements and the LOCA safety analysis will continue to be met.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Vermont State official was notified of the proposed issuance of the amendment. The State official 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 and changes surveillance requirements. The NRC staff has determined that the amendment involves no i
significant increase in the amounts, and no significant change in the types of any effluents that i
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 hszards consideration, and there has been no public comment on such finding (64 FR 6714). 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 assessmentIneed be prepared in connection with the issuance of the amendment.
5.0 CONCLUS!QN The Commission has concluded, based on the considerations discussed above, that: (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 ir6uarce of the amendment will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributors: Z. Abdullahi A. Pal Date: April 26,1999
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DATED: April 26,1999 AMENDMENT NO. 2 TO FACILITY OPERATING LICENSE NO. DPR-28 VERMONT YANKEE NUCLEAR POWER STATION plSTRIBUTION gwmx PUBLIC J. Zwolinski/S. Black J. Clifford R. Croteau PDI-2 r/f T. Clark A. Pal Z. Abdullahl OGC-G. Hill (2)
W. Beckner ACRS C. Norsworthy (E-mail)
C. Anderson, RI i
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