ML20056E478
| ML20056E478 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 08/04/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20056E476 | List: |
| References | |
| NUDOCS 9308240115 | |
| Download: ML20056E478 (5) | |
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E UNITED STATES 7A NUCLEAR REGULATORY COMMISSION
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WASHINGTON, D C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REL ATED TO AMENDMENT NOS.171 AND 151 TO FACILITY OPERATING LICENSE NOS. NPF-4 AND NPF-7 VIRGINIA ELECTRIC AND POWER COMPANY OLD DOMINION ELECTRIC COOPERATIVE NORTH ANNA POWER STATION. UNITS NO. 1 AND NO. 2 DOCKET NOS. 50-338 AND 50-339
1.0 INTRODUCTION
By letter dated March 10, 1993, as supplemented by letter dated July 28, 1993, the Virginia Electric and Power Company (the licensee) proposed a change to the Technical Specifications (TS) for the North Anna Power Station, Units No.
l 1 and No. 2 (NA-l&2). The proposed changes would revise the NA-l&2 TS requirements pertaining to the High Head Safety Injection System (HHSI) flow i
balance tests.
TS 4.5.2.h requires that the HHSI flow balance tests be performed following the completion of modifications to the Emergency Core Cooling System (ECCS) subsystems that alter the subsystem flow charateristics.
1 The successful completion of the HHSI flow balance testing is ensured by two surveillance requirements.
These surveillance requirements are for the sum of the flows through the two lowest flow branch lines, and a total HHS1 pump flow requirement.
These requirements provide a specified acceptance range for HHSI flow balancing of only 4%, which is too narrow to consistently be met during the tests.
This is due to the sensitivity of throttle valve positioning and the uncertainty of flow measurements caused by instrument inaccuracies.
l The flow rates currently specified for the sum of the flows through the two lowest flow branch lines and the total HHSI pump flow are conservative with respect to the existing NA-l&2 safety analysis values.
The flow rates would be revised to remove any instrument inaccuracies.
Normal instrument inaccuracies would be factored into the acceptance criteria of the periodic surveillance tests which perform the flow balance testing.
The proposed changes would decrease the sum of the flows through the two I
lowest flow branch lines from 2 384 gallons per minute (gpm) to 2 359 gpm, and increase the total HHSI pump flow from s 650 gpm to s 660 gpm.
This expanded acceptance range would ensure that the system performance remains bounded by l
the existing NA-l&2 safety analysis and would make test failures due to instrument inaccuracies less likely.
In addition, a surveillance requirement would be added to define a value of 2 J
48.3 gpm to be used for simulated reactor coolant pump (RCP) seal injection
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9308240115 930804 PDR ADOCK 05000333 P
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2 flow during cold leg injection balancing. A siraulated RCP seal injection flow has been taken into account during actual surveillance tests.
It is added for completeness of the surveillance requirements, but does not change the way the surveillance test is currently being performed.
l The July 28, 1993 letter provided additional information requested by the i
staff. This additional information did not alter the proposed action or affect the staff's determination of no significant hazards consideration as noticed in the Federal Reaister on April 14, 1993 (58 FR 19491).
2.0 DISCUSSION j
The function of the ECCS is to provide core cooling and negative reactivity to ensure that the reactor core is protected after any of the following accidents:
Loss of Coolant Accident (LOCA), Rod Ejection Accident, Loss of Secondary Coolant Accident, and Steam Generator Tube Rupture (SGTR).
During i
the initial phase of these accidents, HHSI flow enters the Reactor Coolant System (RCS) via the cold leg injection to the three RCS loops and the reactor coolant pump seal supply. The following existing TS ensure that HHSI flow is available as required by the current safety analysis:
o TS 4.5.2.h.1.a requires the sum of the two lowest branch line flows l
to be 2 384 gpm with the RCS depressurized (this means the third branch line flow must be 2192 gpm and total flow of the three l
branch lines must be 2 576 gpm).
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TS 4.5.2.h.l.b requires total HHSI pump flow rate to be s 650 gpm with the RCS depressurized.
o TS 3.4.6.2.e and TS 4.4.6.2.1 requi e RCP seal injection to be throttled to s 30 gpm and controlled leakage measured once every 31 l
days with the RCS at 2235 20 psig (this ensures that seal injection will be less than or equal to the 48.3 gpm value assumed in the safety analysis if the RCS suddenly depressurizes).
Based on the TS requirements above, total HHSI pump flow must be 2 624.3 gpm (576 gpm + 48.3 gpm) and s 650 gpm during cold leg injection.
These l
requirements provide a specified acceptance range of only 4%, which is too narrow to consistently be niet during the tests. This is due to the sensitivity of throttle valve positioning and the uncertainty of flow measurements caused by instrument inaccuracies.
These instances have been reported in Licensee Event Reports (LERs).
LER 90-008-00, for NA-2, and 91-001-00, for NA-1, documented that the flows obtained during recent surveillance testing were outside the TS limits.
Part of the " Actions to Prevent Reoccurrence" in LER 91-001-00 was to determine if tne safety analysis would support TS changes.
A review of the existing NA-1&2 safety analysis has determined that the HHSI system performance will remain bounded if the summation of the indicated flows of the two lowest flow branch lines is 2 359 gpm with no measurement
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uncertainty. This would allow the adjustment of test values depending on the accuracy of the test equipment used.
l The small break LOCA analysis was performed using the NOTRUMP evaluation model (Reference 1), assuming HHSI flow rates from the two minimum flow branch lines which are equal to those contained in the proposed TS 4.5.2.h.
The analysis was implemented as the analysis of record via a station 10 CFR 50.59 safety evaluation (Reference 2), per the provisions of TS 6.9.1.7, which specifies allowable LOCA analysis methodologies for establishing operating limits for key core parameters. The results of the revised small break LOCA analysis were reported to NRC in Reference (3), which provided the required notification of change in the peak clad temperature (PCT) results for this transient.
The PCT for limiting casa small break transient is 1873*F The manufacturer for the HHSI pumps was contacted to obtain the maximum flow l
rate allowed for these pumps.
The manufacturer stated that the maximum flow rate for these pumps was 675 gpm. An engineering study was performed to determine the required net positive suction head (NPSH) for the HHSI pumps at the manufacturer's maximum flow rate.
The study determined that under all l
circumstances the NPSH available exceeds the NPSH required. However, to prevent HHSI flow from exceeding 675 gpm during the safety injection recirculation mode of operation, the study recommended the maximum flow of the HHRI pump be s 660 gpm when flowing from the refueling water storage tank to the RCS. The effect of this change on low head safety injection (LHSI) flow and NPSH during the safety injection recirculation mode was also evaluated and found to be acceptable.
The total HHSI pump flow rate is limited to 660 gpm in proposed TS 4.5.2.h.
In the existing analysis of record for the mass addition transient, 705 gpm was assumed as the HHSI pump runout flow rate.
This analysis, submitted by letter dated December 27, 1991, was approved via Reference (4).
Although not specifically delineated in TS 4.5.2.h.1, during the HHSI cold leg injection flow balancing performed to meet this specification, a simulated RCP seal injection flow has been accounted for to support the basis of TS 3.4.6.2.e.
This is part of the original design basis and has been taken into account during actual surveillance tests.
It is added for completeness of the surveillance requirements. A simulated RCP seal injection flow is not required for hot leg injection flow balancing due to the system configuration at the time of switchover to hot leg injection.
The flow rates currently specified in TS 4.5.2.h.1.a and b are conservative with respect to the existing safety analysis values. The revised flow rates would not incorporate any instrument inaccuracies. Normal instrument inaccuracies will be factored into the acceptance criteria of the periodic surveillance tests which perform the flow balance testing. This expanded i
acceptance range will ensure the system performance remains bounded by the existing safety analysis and will make test failures due to instrument inaccuracies less likely.
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4 The proposed TS changes would continue to ensure that the three RCS loops and the reactor coolant pump seal supply are throttled to meet the following constraints-i o
When one RCS loop is faulted (i.e., doubled ended cold leg break),
sufficient flow is delivered to the two intact RCS loops.
o The HHSI pump flow does not exceed runout flow with the RCS completely depressurized.
o With the LHSI pump supplying the HHSI pump, total LHSI flow does not decrease HHSI NPSH available below the NPSH required.
3.0 TECHNICAL SPECIFICATION CHANGES TS 4.5.2.h.1.a would be modified by decreasing the allowable sum of the flows through the two lowest flow branches lines, with a single HHSI pump running, from 2 384 gpm to 1 359 gpm.
TS 4.5.2.h.l.b would be modified by increasing the allowable total flow of the f
i HHSI pump, with a single HHSI pump running, from s 650 gpm to s 660 gpm.
TS 4.5.2.h.1.c would be added to define the value of 2 48.3 gpm used for simulated RCP seal injection flow during HHSI cold leg injection flow balance measurements.
j In addition, minor editorial changes have been made to these TS sections to improve the readability.
4.0 EVALUATION A safety evaluation has been performed for the proposed changes using NRC approved methodologies. The safety evaluation results show that a peak l
cladding temperature of 1873*F for the limiting core small break transient l
complies with the 10 CFR 50.46, Appendix K criteria.
The proposed changes l
will not affect the capability of the ECCS to perform its design functions and i
system performance remains bounded by the NA-l&2 safety analysis.
I Finally, HHSI pump runout is not increased because the limiting HHSI pump flow of 660 gpm is bounded by the manufacturer maximum flow allowable of 675 gpm.
Therefore, based on all of the above, the staff finds the proposed changes to be acceptable.
5.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Virginia State official was notified of the proposed issuance of the amendment.
The State official had no comment.
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6.0 ENVIRONMENTAL CONSIDERATION
j These amendments change 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 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 Commission has previously issued a proposed finding that these amendments involve no significant hazards consideration and there has been rm public comment on such finding (58 FR 19491). Accordingly, these 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 statement or environmental assessment need be prepared in connection with the issuance of the amendments.
7.0 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 3
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 j
defense and security or to the health and safety of the public.
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Principal Contributor:
Leon B. Engle Date: August 4, 1993 l
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References:
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i (1) WCAP-10054-P-A, " Westinghouse Small Break ECCS Evaluation Model Using the NOTRUMP Code," dated August 1985 (Westinghouse Proprietary).
(2) " North Anna Power Station Units 1 and 2 - Implementation of Extended SGTP Small Break LOCA Analysis," 10 CFR 50.59 Safety Evaluation 92-SE-0T-005, j
dated January 21, 199?.
(3) Letter from W. L. Stewart to USNRC, " Virginia Electric and Power Company
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- North Anna Power Station Units 1 and 2 Report of Errors / Changes in Application of ECCS Evaluation Models Per Requirements of 10 CFR 50.46,"
j Serial No.92-091, dated February 10, 1992.
l (4) Letter from Leon B. Engle (NRC) to W. L. Stewart, " North Anna Units 1 and
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2 1ssuance of Amendments Re:
Pressure / Temperature Operating Limits and l
Low Temperature /0verpressure Protection System Setpoints (TAC Nos. M83154
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and M83155)," dated March 25, 1993.