ML20125C928
| ML20125C928 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 12/08/1992 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20125C924 | List: |
| References | |
| NUDOCS 9212140158 | |
| Download: ML20125C928 (5) | |
Text
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UNITED STATES 9
8">y, *j NUCLEAR REGULATORY COMMISSION g
WASHINGTON, D. C. 2055!.
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ENCLOSURE 3 SAFETY EVALUATION BY THE OFFICE OF NVCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.165 TO FAClllTY OPERATING LICENSE N0. DPR-77 AND AMENDMENT N0.155 TO FACILITY OPERATING LICENSE NO. DPR-7]!
TENNESSEE VALLEY AUTHORITY SE0V0YAH NUCLEAR PLANT. UNITS 1 AND 2 DOCKET NOS. 50-327 FND 50-328 i
1.0 JhlflQEUCi10N By application dated November 9, 1992, the Tennessee Valley Authority (the licensee) pro;)osed amendments to the Technical Specifications (TS) for Sequoyah Nuclear Plant (SQN) Units 1 and 2..
The requested changes would provide an alternate method for satisfyino the response time Nguirements of the engineered safety features actuation system (ESFAS) for the feedwater instrumentation channels when the feedwater line is isolated.
This would be accomplished by adding the following to TS Table 3.3-5, Notation 2:
"The ESFAS instrumentation channel RESPONSE TIME requirement for specific feedwater air operated valve (s) can also be met when the associated air-operated valve is either closed with air supply (s) isolated, isolated by a closed manual valve, or isolated by a closed feedwater isolation valve wit'.i power removed. When using one of these provisions for satisfying the air-operated valve response time, the closed or isolated conditior, described above will be verified at least once per 7 days."
The TS for SQN requires that tha response time for feedwater line isolation be maintained within the limits assumed in the accident analysis. As a result of the need to perform maintenance on the air-operated feedwater valves, it was discovered that a literal interpretation of the TS provides no alternative means to meet the response f.ime requirements when the feedwater line is isolated (i.e., the res ponte time requirements are in effect even if the valve is already in its isolutica position). Therefore, the requirement would remain in effec; for al iaoperable feedwater isolation valve, even if the safety function was being provided by other means. Therefore, the licensee i
submitted the 1S chant.e to address requirements that would allow maintenance of the feedwater valvo', while, at the same time, maintaining the safety function of the feedw'.ter isolation system.
9212140158 921208 PDR ADOCK 05000327 p
_a 4 2.0 EVALUATION The engineered safety features portion of the feedwater system includes the auxiliary feedwater system, feedwater check valves, feedwater motor operated gate valves, feedwater air-operated flow control valves, feedwater valve air-operated bypass valves, manual feedwater isolation valves, and associated ESFAS instrumentation.
The ESFAS instrumentation is designed to limit the core energy released as a result of a steamline break, to limit the magnitude of the reactor coolant system cooldown, and to prevent or mitigate the effect of excessive cooldown, by shutting the feedwater air and motor-operated valves when a feedwater isolation signal is generated.
According to the TS Bases, operability of the ESFAS instrumentation systems ensures that (1) the associated action will be initiated when the parameter monitored reaches its setpoint, (2) the specified coincidence logic is maintained, (3) sufficient redundancy is maintained to permit a channel to be out of service for testing or maintenance, and (4) sufficient system functional capability is available from diverse parameters.
Since the instrumentation itself would not be affected by the proposed TS change, these concerns would not be affected.
The feedwater isolation signal is generated by the reactor protection system and causes all of the feedwater regulator valves, bypass valves, and motor-operated isolation valves to shut upon receipt of any of the following isolation signals:
a.
High-high steam generator water level in any steam generator, b.
Safety injection signal (containment pressure high, pressurizer pressure low, steam line pressure low), or Reactor trip coincident with low reactor coolant Taeg c.
Upon receipt of an isolation signal, the feedwater regulating valves close in a nominal 6.5 seconds, and the motor-operated isolation valves close within 7.5 seconds.
The air-operated feedwater regulating valves are the primary-mechanism for feedwater isolation assumed in the loss of coolant accident (LOCA) and non-LOCA analysis. Closure of the motor-operated feedwater isolation valves is considered a backup mechanism in the analysis, in conjunction with tripping of the feedwater pumps. The proposed TS change will not affect the ability of the trip system to generate a trip signal.
The feedwater isolation response time specified in the TS, which includes the valve closure time and the inherent electronic time delays for sensor and circuitry actuation, is required to be less than or equal to 8 seconds for the safety injection signals trip, and less than or equal to 11 seconds for the high-high steam generator level signal trip. The assumptions used to determine the appropriate response time for accident analysis purposes are the following:
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. a.
SQN is an ice condenser plant that by design reduces peak pressure in the containment, both in magnitude and duration; b.
The unisolatable volume of the feedwater system between the regulating valves and the steam generators is no more than 104 cubic feet, which is less than the maximum volume of 150 cubic feet recommended by Westinghouse Electric Corporation; and c.
The main feedwater pumps are tripped on a feedwater isolation signal.
These considerations are unaffected by the proposed TS change. However, inclusion of the valve closure time in the response time limits specified in the TS, with no alternative provisions, has resulted in the inability to meet the specification when a feedwater regulator valve is inoperable.
Implementation of the proposed change would allow the isolation of a feedwater flow path to serve as the alternative and, thereby, satisfy the ESFAS instrumentation response time requirement for feedwater valve closure. With the flow path isolated, the safety function provided by the feedwater valves and the isolation signal have already been achieved, since the response time for feedwater line isolation is reduced to zero. However, if an isolation signal is generated by the instrumentation, it will continue to shut the remaining feedwater valves.
The licensee has pro)osed three methods that would, by isolating-the feedwater flow path, satisfy tie TS requirements for a specific feedwater ESFAS instrument channel.
The first alternative, isolation of the air supply (s),
ensures that the referenced valve is deactivated to prevent inadvertent operation, since they fail closed by spring pressure on loss of air.
For the second alternative, use of a closed manual isolation valve, the same isolation of feedwater flow is provided that is assumed by closure of the air-operated feedwater valve with no time delay.
For the third alternative, closure of the motor-operated feedwater valve with power removed, feedwater flow is again isolated from the main and bypass air-operated valves.
In addition, removal of power prevents inadvertent operation of the valvo.
The licensee also proposed verification every 7 days that the isolated condition is in effect to ensure that no changes are made to the status of the isolation.
Staff review of the proposed TS change has determined that the safety requirements of the ESFAS instrument channels would continue to be satisfied by implementing any of the alternatives allowed by the proposed change, since the safety function would be in effect (the feedwater line would be isolated) when the response time requirement could not be satisfied.
In addition, the verification interval is consistent with similar system status checks and the Standard Technical Specifications.
Therefore, the staff has determined that the proposed change is acceptable.
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3.0 STATE CONSULTATION
t In accordance with the Commission's regulations, the Tennessee State official was notified of the proposed issuance of the amendments. The State official had no comments.
4.0 EXIGENT CIRCUMSTANCES
The staff has reviewed the licensee's proposed amendments and finds (1) that exigent circumstances exist, as provided for in 10 CFR 50.91(a)(6),
in that the licensee and the Commission must act quickly and that time does not permit the Commission to publish a Federal Reoister notico allowing 30 days for prior-public comment, and (2) that the licensee has not failed to use its best efforts to make a timely application and avoid creating the exigent circumstance._-The Commission noticed the licensee's November 9, 1992 application for amendments in the Federal Register on November 20, 1992 (57 FR 54865), at which time the Commission made a proposed finding that the amendments involved no significant hazards condition and there has been no-public comment in response-to the notice.
5.0 FINAL NO SIGNIFICANT HAZARDS CONSIDERATION
DETERMINATION The Commission's regulations in 10 CFR 50.92 provide that the Commission may make a final determination that a license amendment involves no significant '
hazards considerations if operation of the facility in accordance with the -
amendment would not:
a.
Involve a significant increase in the probability or consequences of an accident previously evaluated.
The proposed TS change fully maintains the feedwater isolation (FWI) functions assumed in the accident analysis.
In addition, no component functions will be affected by utilizing the alternate methods to ensure completion of the FWI function for accident mitigation.
Since maintaining the conditions to provide FWI is not postulated to create an-accident, there is no increase in-the probability of an accident.
By maintaining isolation of the feedwater flow path when the response time for automatic actuation of the air-operated FWI valve is considered inoperable, all safety functions assumed in the accident analysis for FWI are met to mitigate accident conditions. Therefore, there is no increase in the consequences of an accident-because the safety functions for accident mitigation are maintained by the alternate isolation methods, which are more conservative than the normal time-delayed valve actuation.
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-5 b.
Create the possibility of a new or different kind of accident from any previously analyzed.
The isolation of feedwater flow is not considered the source of an accident although inadvertent isolation may initiate automatic unit shutdown that is an analyzed event. This change will not alter any plant design or operating parameters such that conditions could be created that would create new accident potentials.
The isolation methods are the same as or equivalent to the closing of the air-operated valves and will not create any additional safety concern or plant operating impact.
c.
Involve a significant reduction in a margin of safety.
This change provides alternate FWI methods that are more conservative than the delayed isolation assumed in the accident _ analysis.
By placing the flow path in an isolated condition, the safety function is already achieved without the need for the valve actuation and the associated response time.
Therefore, the use of these alternate FWI methods to s&tisfy TS response time requirements will actually result in an increase in the margin of safety when compared with normal plant operation.
Based on the above, the Commission has made a final determination that the proposed amendments involve no significant hazards consideration.
6.0 ENVIRONMENTAL CONSIDERATION
The 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 the amendments involve no significant hazards consideration, and there has been no public comment on such finding (57 FR 54865). Also, the staff has made a final no significant hazards consideration determination. Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9).
Pursuant to 10 CFR Sl.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 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:
D. LaBarge Date: December 8, 1992
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