ML20077K254
| ML20077K254 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 01/05/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20077K226 | List: |
| References | |
| NUDOCS 9501100255 | |
| Download: ML20077K254 (5) | |
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1 UNITED STATES g
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NUCLEAR REGULATORY COMMISSION 2
WASHINGTON. D.C. 30e06 0001
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NOS.113 AND 106 TO FACILITY OPERATING LICENSE NOS. DPR-42 AND DPR-60 NORTHERN STATES POWER COMPANY l
PRAIRIE ISLAND NUCLEAR GENERATING PLANT. UNIT NOS. 1 AND 2 DOCKET NOS. 50-282 AND 50-306
1.0 INTRODUCTION
By letters dated October 3, 1994, and November 30, 1994, Northern States Power Company (the licensee) submitted a request for change to the Technical Specifications (TS) for the Prairie Island Nuclear Generating Plant, Unit Nos. I and 2, specifically, TS Section 4.6 " Periodic Testing of Emergency Power System." The TS change was submitted to provide a more flexible test band during the 24-hour load test of an emergency diesel generator (EDG), and to rephrase various EDG test requirements.
2.0 EVALUATION 2.1 Backaround Each EDG at the Prairie Island Nuclear Generating Station, as a backup to the normal standby a-c power supply, is capable of sequentially starting and supplying power to one complete set of Engineered Safety Features equipment for one reactor unit, while providing sufficierit power to allow the second unit to be placed in a safe shutdown condition.
The Unit 1 EDGs consist of two Fairbanks Horse units each rated at 2750 kiiowatts (kW) continuous (8750-hour basis), 0.8 power factor, 900 rpm, 4160-volt, 3-phase, 60 Hertz.
The 2000-hour rating of each Unit 1 EDG is 3000 kW.
In addition, the EDG manufacturer's design limits include a required special inspection to verify that the EDG has not been damaged if the time of operation between 3000 and 3250 kW exceeds 30 minutes.
The TS require a 24-hour load test at least once every 18 months.
The load test verifies that the EDGs can start and run continuously at full load for an interval of not less than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The test requires that the EDGs be run at a load equivalent to 110 percent of the continuous duty rating for at least 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />, and at a load equivalent to the continuous duty rating for the remainder of the 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The licensee proposes to revise the 24-hour load test to avoid exceeding the 30-minute rating during the test.
The licensee is concerned that the present 2-hour testing band, as stated in the TS, of 105-110 percent of the continuous rating of the EDG, could cause the 30-minute rating of 3000 kW (109.1 percent) to be exceeded when instrument error is considered.
9501100255 950105 PDR ADOCK 05000282 P
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,. 2.2 Evaluation Amendment to the 24-Hour load Test On October 3, 1994, the licensee submitted a license amendment request to provide a more flexible test band during the 24-hour EDG load test which is performed every 18 months. The primary concern addressed by the licensee's amendment request is the potential overloading of the Unit 1 EDGs.
Prairie Island's Unit 1 EDGs have a 30-minute rating between a range of 3000 and 3250 kW (109.1 and 118.2 percent). The current TS require that each EDG be operated once each 18 months for at least 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> while loaded to 2887.5 to 3025 kW (105 to 110 percent).
Considering a potential instrument error of i 2 percent, an EDG could be operated above the 3000 kW design limit during the load test. As a result, the licensee desires to maintain the load at 107.1 percent during the 2-hour run of the 24-hour test to avoid exceeding the 30-minute rating set by the manufacturer. However, operating at 107.1 percent indicated load creates the possibility of exceeding the low end of the test band, currently defined in the TS as 105 percent, considering instrument error. Therefore, the licensee is proposing to change the recuired test band from 105-110 percent to 103-110 percent, which would allow the licensee to run the 24-hour load test without exceeding the manufacturer's 30-minute rating of 3000 kW (109.1 percent).
In Generic Letter 88-15, " Electric Power Systems - Inadequate Control Over Design Processes," dated September 12, 1988, the NRC discussed the hazards of testing EDGs at a load greater than the design rating specified by the manufacturer. The NRC's concern is that repeated testing beyond the manufacturer's design load limit could, over time, jeopardize the diesel generator's capacity to reliably perform its intended safety function during an event involving a loss of offsite power.
The highest anticipated event loads at Prairie Island are 2510 kW and 3813 kW for Unit I and Unit 2, respectively.
For the EDGs,103 percent of the continuous rating represents a significantly greater load on the EDGs than the highest anticipated event load for either unit.
Unit 1, 103 percent of 2750 kW (continuous rating) = 2832.5 kW (represents 112.8 percent of the highest anticipated event load)
Unit 2, 103 percent of 5400 kW (continuous rating) - 5562 kW (represents 145.9 percent of the highest anticipated event load)
A test load of 103 percent is significantly greater than the load required for each unit during accident conditions. Since the surveillance test would continue to demonstrate an adequate level of electrical load carrying capacity to ensure that each EDG is capable of performing its accident-mitigating function, the NRC staff finds the proposed change of the 24-hour test band from 105-110 percent to 103-110 percent, to be acceptable.
Rechrasina of Various EmeroencY Generator Test Reauirements Proposed changes:
(A) Change the first sentence of Technical Specification 4.6.A.l.e from
" Verify the diesel generator can start and gradually accelerate to synchronous speed with generator voltage and frequency at 4160 i 420 volts and 60 i 1.2 Hz" to " Verify the diesel generators can start and gradually accelerate. Verify the generator voltage and frequency can be adjusted to 4160 1 420 and 60 i 1.2 Hz."
The reason for the change is that TS 4.6.A.I.e had been previously modified to allow monthly " slow starts."
It was the intent of this change to allow the diesel to accelerate to operating speed prior to field flashing the generator.
Field flashing the generator prior to achieving operating speed is harmful to the generator and would partially defeat the purpose of conducting " slow starts." The subject TS change is intended to clarify the test requirement.
(B) 1. Change the words in the sentence contained in TS 4.6. A.I.e from "should be conducted in accordance with the manufacturer's recommendations...." to "should be conducted in consideration of the manufacturer's recommendations...."
- 2. Change the words in the sentence contained in TS 4.6. A.d from "should be conducted in accordance with the manufacturer's recommendations...." to "should be conducted from standby conditions in consideration of the manufacturer's recommendations...."
The reason for the changes is to clarify the intentions of the original TS Section 4.6.A.1.e.
The licensee believes that it was not the intention that all of the manufacturer's recommendations be incorporated into the procedures without the use of good judgment and operational and maintenance experience by the licensee.
The new wording would provide the necessary latitude to balance all of the inputs to the procedures development process and would provide for prudent decision-making.
(C) Relocate existing TS 4.6.A.3.e. "During this test operation of the emergency lighting system shall be ascertained", to become new TS 4.6.A.3.b.3.
TS 4.6.A.3.e states: "During this test...."
However, "this test" refers to the test specified in TS 4.6.A.3.b.
The purpose of this proposed change is merely to place the specification in its logical location.
(D) Combine existing TS 4.6.A.2.a. " Verify the diesel generator starts and accelerates to at least synchronous speed in less than or equal to 10 seconds," and 4.6.A.2.b, " Verify the generator voltage and frequency to be 4160 i 420 volts and 60 t 1.2 Hz within 10 seconds after the start signal," to the following new specification 4.6.A.2.a.
" Verify the diesel generator starts and achieves generator voltage and frequency of 4160 i 420 volts and 60 1.2 Hz within 10 seconds after the start signal."
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, The purpose behind combining TS 4.6.A.2.a and 4.6.A.2.b is to remove the words
" accelerates to at least synchronous speed." The test is intended to verify that the c;tesel is ready to accept load within 10 seconds of a start signal.
The licensee does not have an instrumented method of verifying that the diesel has achieved synchronous speed, and verification of this does not provide any necessary information.
(E) Relocate existing TS 4.6.A.3.b.4, " Verify that the diesel generater system trips, except those for engine overspeed, ground fault, and generator differential current (Unit 2:
except those for engine overspeed and generator differential current), are automatically bypassed.", to become new TS 4.6.A.3.e, "For each unit, simulate a safety injection signal and verify that the diesel generator system trips, except those for engine overspeed, ground fault, and generator differential current (Unit 2: except those for engine overspeed and generator differential current), are automatically bypassed."
There are two purposes associated with the relocation of existing TS 4.6.A.3 b.4 to 4.6.A.3.e.
The first is to de-couple this test from the
" Integrated Safety Injection Test" required by TS 4.6.A.3.b.
It is unnecessary to perform these two tests simultaneously, and the subject change will clarify the recuirement to verify the bypass of selected diesel generator system trips.
The other purpose is to remove the requirement to simulate a loss-of-offsite powcr and a safety injection signal in order to verify that the diesel generator trips are automatically bypassed.
Simulation of a safety injection signal is sufficient to automatically bypass the system trips.
(F) Delete the existing TS 4.6.A.3.b.3, " Verify that the auto-connected loads do not exceed 3000 kW (Unit 2: 5100 kW)."
The licensee's purpose for deleting the requirement to " Verify that the auto-connected loads do not exceed 3000 kW (Unit 2: 5100 kW)", is that this requirement is not appropriate for a surveillance test, but rather is a configuration management issue. During the performance of the integrated safety injection test per TS 4.6.A.3.b, the licensee observes and records the loads on the EDGs, and ver fies that the loads do not exceed 3000 kW (5100 kW for Unit 2). However, thi; provides no meaningful information since the loads during the test are signflicantly less than those during an actual event, due to differences in plant unditions.
2.3 Conclusion The staff concludes that changing the 24-hour test band for the EDGs at Prairie Island from 105-110 percent to 103-110 percent does not affect the EDG's ability to carry required loads, and thus perform their accident mitigation function, since the EDGs have significantly greater load carrying capacity than that required during a worse case accident condition.
Additionally, the proposed changes in A, B, C, D, E, F are intended to clarify the meaning of the existing specifications without changing the requirements. These changes to the TS will not change the manner in which the plant is operated or maintained.
Iherefore, the changes are considered acceptable by the staff.
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3.0 STATE CONSULTATION
In accordance with the Ccmission's regulations, the Minnesota State official was notified of the proposed issuance of the amendments. The State official had no coments.
4.0 ENVIRONMENTAL CONSIDERATION
The amendments change surveillance requirements. The NRC staff has determined I
that the amendments involve 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 Comission has previously issued a j
proposed finding that the amendments involve no significant hazards consideration and there has been no public comment on such finding (59 FR 55877). Accordingly, the amendments meet 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 shtement or environmental assessment need be prepared in connection with the issuance of the amendments.
5.0 CONCLUSION
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 issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
M. Pratt Date:
January 5, 1995 h
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