ML20078H458
| ML20078H458 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 01/31/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20078H440 | List: |
| References | |
| IEIN-94-060, IEIN-94-60, NUDOCS 9502060215 | |
| Download: ML20078H458 (3) | |
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UNITED STATES g
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NUCLEAR REGULATORY COMMISSION 4
WASHINGTON, D.C. 20656 4001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 102 TO FACILITY OPERATING LICENSE NO. NPF-49 NORTHEAST NUCLEAR ENERGY COMPANY. ET AL.
MILLSTONE NUCLEAR POWER STATION. UNIT NO. 3 DOCKET NO. 50-423
1.0 INTRODUCTION
By letter dated July 22, 1994, the Northeast Nuclear Energy Company (the licensee), submitted a request for changes to the Millstone Nuclear Power Station, Unit No. 3 Technical Specifications (TS). The requested c!.anges revise the Technical Specifications to incorporate a different setpoint and transient methodology for determining the maximum allowable power range neutron flux setpoint. These changes allow Millstone Unit 3 to operate with a reduced number of main steam-line safety valves at a reduced power level, u determined by the high flux setpoint.
2.0 BACKGROUND
On August 22, 1994, the U.S. Nuclear Regulatory Commission (NRC) issued an information notice (IN 94-60) to alert all holders of operating licenses or construction permits for pressurized water reactors. The notice cautioned the addressees about a potential for overpressurizing the main steam system during periods when one or more main steam safety valves (MSSV) are inoperable. All recipients were expected to review the information for applicability to their facilities and to consider actions to avoid such problems.
Westinghouse Nuclear Safety Advisory Letter NSAL-94-001, " Operation at Reduced Power Levels With Inoperable MSSVs," January 20, 1994, describes a deficiency in the basis for Standard Technical Specifications (STS) Table 3.7.1,
" Operable Main Steam Safety Valves Versus Applicable Power in Percent of Rated Power." The basis assumes that the maximum allowable initial power level is a linear function of mein steam safety valve flow capacity. Westinghouse has determined that this assumption is not correct and notes that, when operating at low power in accordance with STS Table 3.7.1, with one or more safety valves inoperable, a loss-of-load / turbine trip (LOL/TT) transient concurrent wit 1 the loss of feedwater could result in overpressurization of the main steam system.
9502060215 950131 PDR ADOCK 05000423 P
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, The equation used in the original Westinghouse bases for Table 3.7.1 reduces the power range neutron flux trip setpoint linearly with the assumed reduction in safety valve flow capacity.
Therefore the potential for overpressurization of the main steam system exists. NSAL 94-001 recommends the use of a more conservative equation to calculate the power range high neutron flux trip setpoint. The new equation is linear with respect to the power level rather than with respect to safety valve flow.
3.0 EVALUATION The licensee proposed changes that would revise the TS Table 3.7-1 and associated Bases by changing the maximum allowable power range neutron flux high setpoint when one or more MSSVs are inoperable. New values for TS Table 3.7.1 were submitted and the corrected methodology was provided to the NRC staff for review. The licensee calculated the new neutron flux high setpoints using the Westinghouse revised algorithm.
The principal reason for this change is that in calculating allowed power levels, transient response based on less than full power operating conditions was not accounted for properly. When the Millstone Unit 3 plant is operating at reduced power levels, a high pressurizer pressure or overtemperature AI trip will be delayed or may not occur following a LOL/TT with concurrent loss of main feedwater which is the design basis transient for determining the MSSV capacity. Under those conditions, the reactor trip may be initiated by a signal from low steam generator water level at a later time into the transient which may cause the secondary system pressure to exceed 110% of the design pressure.
The NRC staff has evaluated the proposed method and agrees that the allowable power level calculated by this conservative method would bound the design basis transient initiated at all power levels and would not lead to overpressurization in the secondary system. The new setpoints are more conservative than the previous setpoints. Based on the above information, the NRC staff approves the proposed changes to TS Table 3.7-1 and has no objection to changes made in Bases 3/4.7.1.1.
4.0 STATE CONSULTATION
In accordance with the Comm!asion's regulations, the Connecticut State official was notified of the proposed issuance of the amendment. The State official had no comments.
5.0 ENVIRONMENTAL CONSIDERATION
The amendment changes a requirement with respect to installation or use of a facility component located within the restrictted area as defined in 10 CFR Part 20.
The NRC staff has determined that the amendment involves no
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! significant increase in the amounts, and no significant change in the types, of any eff18 ants that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously irsued a proposed finding that the amendment involves no significant hazards consideration, and there has been no public comment on such finding (59 FR 47171). Accordingly, the amendment meets the eligibility criteria for categorical exc1csion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environcental impact statement or environmental assessment need be prepared in connection with the issuance of the amendment.
6.0 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 amendment will not be inimical to the common defense and security or to the health and safety of the public.
i Principal Contributor: Maudette Griggs Date:
January 31, 1995 P
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