ML20080F926
| ML20080F926 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 01/25/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20080F920 | List: |
| References | |
| NUDOCS 9501310427 | |
| Download: ML20080F926 (4) | |
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i UNITED STATES 0
j NUCLEAR REGULATORY COMMISSION 2
WASHINGTON, D.C. 30666 4 001
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.166 TO FACILITY OPERATING LICENSE NO. DPR-46 NEBRASKA PUBLIC POWER DISTRICT COOPER NUCLEAR STATICS DOCKET NO. 50-298
1.0 INTRODUCTION
By letter dated September 26, 1994, Nebraska Public Power District (the licensee) requested a change to the Cooper Nuclear Station (CNS) technical specifications (TSs). The proposed changes would revise CNS TS limiting condition for operation 3,5.C.1 and 3.5.C.4 to increase the minimum pressure at which the high pressure coolant injection (HPCI) system is required to be operable from 113 psig to 150 psig.
From a systems viewpoint, the staff considered the impact of the proposed changes on the outcome of design-basis events and the ability of the emergency core cooling systems (ECCS) to provide sufficient core cooling over the range of system pressures associated with design basis events.
In particular, the ECCS response to both the large break and small break loss of coolant accident (LOCA) was evaluated. These events have been analyzed in both the Cooper updated safety analysis report (USAR) and vendor reports. Other ECCS components were evaluated on an individual basis to determine the impact of the proposed modifications.
2.0 TECHNICAL SPECIFICATION CHANGES The Cooper TS changes resulting from the proposal are as follows:
(1) TS 3.5.C.1:
The low pressure limit above which HPCI is required to be operable is changed from 113 psig to 150 psig.
]
(2) TS 3.5.C.4:
If TS 3.5.C.1 cannot be met, reactor system pressure must be reduced in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to 113 psig or less.
This limit is changed to 150 psig.
1 3.0 EVALUATION The purpose of the HPCI system is to maintain reactor vessel water inventory after a small LOCA which does not depressurize the reactor vessel. The HPCI system is descriced in Section IV-4-1 of the Cooper USAR. HPCI consists of a 9501310427 950125 PDR ADOCK 05000298 P
PDR l
- single 4250 gpm turbine-driven constant flow pump assembly and system piping, valves, controls, and instrumentation.
The design basis of the HPCI system i
includes coolant injection into the core at 4250 gpm between 150 to 1120 psig
)
(Reference 1).
The HPCI system is a component of the ECCS, which also includes the automatic depressuriza "on system (ADS), low pressure coolant injection (LPCI), and core spray (Cs,.
The other components of the ECCS add redundancy and diversity in satisfying high pressure and low pressure core 1
cooling requirements.
If HPCI becomes inoperable at pressures near normal operating values or if the leak rate is greater than HPCI capacity, ADS is designed to reduce the nuclear system pressure so that CS and LPCI can provide flow to the reactor. The ADS uses six of the eight nuclear system pressure relief valves to relieve high pressure steam to the suppression pool. The valves open upon coincident signals of low level and discharge pressure of either LPCI or core spray. The LPCI system is initiated upon a low vessel water level or high containment drywell pressure signal (Reference 2). CS is initiated on the same signals.
During reactor startup, the HPCI low steam supply isolation pressure switch setpoint is established above the required TS minimum pressure of 100 psig and below the HPCI TS operability limit of 113 psig. The pressure switches are i
used to ensure HPCI is not isolated for system pressures greater than 113 l
psig.
However, the licensee submittal states that surveillance data has j
indicated the pressure switches would not reset within an allowable range to ensure HPCI operability at the TS limit.
Furthermore, switches able to meet the TS limit could not be obtained.
Problems with the HPCI pressure switches have also been identified in Cooper licensee event report (LER)94-012, dated August 8, 1994.
Increasing the TS limit to 150 psig will provide greater margin for the pressure switches. The greater margin will allow switch tolerances and instrument inaccuracies to be taken into account when determining switch setpoints.
The small break LOCA event has been analyzed in the Cooper USAR and in accident analyses provided by General Electric in NED0-21662-2, " Loss-of-Coolant Accident Report" (Reference 3).
For a small break in the coolant pressure boundary where the vessel remains pressurized, the proposed modifications will not affect the operability status of the HPCI system.
Normal operating pressure is near 1000 psig, which is well above the existing and proposed minimum pressure for HPCI operability.
The ECCS system also provides redundancy and diversity for the HPCI function.
If the HPCI system is inoperable for other reasons, the ADS system and LPCI are designed to provide adequate coolant injection for all break sizes normally covend by HPCI. Consequently, the HPCI system, taken together with the redundant LPCI/ ADS systems, should provide sufficient protection against inventory loss events occurring with the vessel remaining pressurized.
The large break LOCA event is analyzed in the Cooper USAR and in accident analyses provided by General Electric in NED0-24045, " Loss-of-Coolant Accident Analysis Report" (Reference 4).
In order to ensure adequate core cooling for i
the LOCA event with the incorporation of the proposed modifications, it is necessary to evaluate the importance of high pressure injection as opposed to low pressure injection and core spray.
The analysis performed for the large
i break LOCA event does not take credit for HPCI availability at pressures below 150 psig. Therefore, the new range of Inoperability for HPCI from 113 to 150 psig should not affect the outcome of the large break LOCA event.
Design information from the USAR also states that the range of pressures over which HPCI is required to deliver rated flow of 4250 gpm is 150-1120 psig.
During a LOCA event leading to depressurization, effective injection flow from LPCI begins when system pressure has decreased below approximately 290 psig (Reference 5). Therefore, overlap of HPCI and LPCI should exist between 290 psig and 150 psig, which is the low pressure cutoff setpoint for the HPCI turbine (Reference 6).
When the HPCI system becomes incperable at 150 psig, LPCI is operating and is rated for a flow rate greater than the HPCI capacity of 4250 gpm for an injection pressure of 150 psig (Reference 7). The LPCI and core spray systems are designed to provide cooling for break areas ranging from approximately 0.2 square feet up to and including the double-ended recirculation line break without availability of the high pressure emergency core cooling systems (Reference 8). Operation of both LPCI and CS should not be impacted by the proposed changes.
Therefore, the LOCA analysis previously submitted by the licensee bounds the effects of the proposed changes.
The proposed changes to CNS TSs have been reviewed at the systems-level.
Analyses of design-basis events submitted by the licensee and General Electric, particularly loss of coolant events, have been reviewed by the staff.
The entire range of break sizes for the most limiting location in the coolant pressure boundary have been considered.
For small breaks during normal operations, the reactor system pressure will remain near 1000 psig, and the HPCI system will not be affected by the proposed changes.
For larger break sizes outside the capacity of HPCI, the LPCI and ADS systems will provide adequate cooling.
The operability of LPCI and ADS should not be affected by the proposed modifications. Analysis of these events therefore bounds the effects of the proposed changes. On these bases, the staff finds the proposed changes acceptable.
REFERENCES 1.
Cooper Nuclear Station Updated Safety Analysis Report, page VI-3-2.
2.
Cooper Nuclear Station Updated Safety Analysis Report, page VI-4-8.
3.
NED0-21662-2, " Loss of Coolani Accident Report", General Electric, July 1977.
4.
NED0-24045, " Loss of Coolant Accident Report", General Electric, August 1977.
5.
Cooper Nuclear Station Updated Safety Analysis Report, page VI-5-2.
6.
Cooper Nuclear Station Updated Safety Analysis Report, page VI-5-10.
7.
Cooper Nuclear Station Licensee Event Report 94-012, August 8, 1994.
8.
Cooper Nuclear Station Technical Specifications, page 124.
3.0 STATE CONSULTATION
l In accordance with the Commission's regulations, the Nebraska State official I
was notified of the proposed issuance of the amendment.
The State official had no comment.
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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 ti.iding that the 7,
amendment involves no significant hazards consideration and there has been no public comment on such finding (59 FR 53841). Accordingly, the amendment meets the eligibility criteria for categorical exclusion set forth in 10 CFR Section 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, 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.
Principal Contributors:
G. Golub T. Kim Date:
January 25, 1995 k