ML20034H199
| ML20034H199 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 03/11/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20034H198 | List: |
| References | |
| NUDOCS 9303160158 | |
| Download: ML20034H199 (4) | |
Text
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UNITED STATES NUCLEAR REGULATORY COMMISSION o-j
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WASHINGTON. D. C. 20555
- q SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO. 159 TO FACILITY OPERATING LICENSE'NO-DPR-46 NEBRASKA PUBLIC POWER DISTRICT COOPER NUCLEAR STATION DOCKET NO. 50-298'
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1.0 INTRODUCTION
By letter dated January 5, 1993, the Nebraska'Public Power District (the.
l licensee) submitted a request for changes to the. Cooper Nuclear. Station (CNS)
Technical Specifications (TS). The requested changes modify the-TS to delete-the Limiting Conditions for' 0peration 'and Surveillance Requirements for-1 Residual Heat Removal- (RHR) and Core Spray (CS) low voltage. auxiliary relays Di 27X3 1A/1B. Deletion of these relays'from the TS reflects a design change to
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install a new Emergency Transformer. This change, which will re:; ult in the' 1
27X3 1A/IB relays being removed from the plant, is schedul_ed to be implemented during the spring 1993 refueling outage.
The specific changes made to the TS are as follows:
A.
On TS Page 53, Table 3.2.B (Page 1), " Aux. Bus Low Voltage Relay 27X3 -
IA & IB" is removed.
i B.
On TS Page 55, Table 3.2.B (Page 3), " Bus I A low Voltage Aux. Relay 27 X-q 3/1A", and " Bus IB Low Voltage Aux. Relay 27 X 3/IB" are removed.
C.
On TS Page 70, Table 4.2.B (Page.1), " Aux. Bus Low Voltage Relay 27X3 -
lA & IB" is removed.
j D.
On TS Page 71 Table 4.2.B (Page 2), " Low Voltage Relays 27 X 3/1A", and
" Low Voltage' Relays 27 X 3/1B" are removed.
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2.0 EVALUATION l
i The Cooper Nuclear Station.has two levels of. undervoltage protection for each i
of the two 4160 Vac emergency buses, F and G.
The first level is an -
- l instantaneous undervoltage scheme that was' installed during plant -
q construction. The first level undervoltage relays ~ {27/lF and 27/1G) are required by the_TS to have a setpoint of 2300 V i 5% with a time delay between
^l 0.0,and 5.0 seconds..The'second level of. undervoltage. protection is a sustained undervoltage. scheme that was installed in' 1978'in response to a 4
June 3, 1977 letter from the NRC staff.concerning susceptibility of-onsite electrical equipment to sustained degraded grid. voltage. The second level of j
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undervoltage protection for each electrical division includes two sets of undervoltage relays having contacts in series with a separate timer (relays 27/lF-1, 27/lFA-1, 27/1G-1, 27/1GB-1, and timers 27X7/lF and 27X7/1G). The undervoltage relays also incorporate integral timers. These undervoltage relays are required by the TS to have a setpoint of 3880 V 152 V and_ have a time delay set at 7.5 seconds i 0.8 setnnds. The TS require the separate timers in series with the relay contacts to be set at;5 i 0.5 seconds. These relays and timers perform the main undervoltage protection functions for emergency buses F and G.
The RHR and CS relays 27X31A/lB are auxiliary relays in the first-level (loss of voltage) undervoltage protection scheme for the normal-service buses IA and
- 18. The relays are presently listed in TS Tables 3.2.B and 4.2.B.
Emergency buses IF and 1G normally receive power from the Normal Station Service Transformer (NSST) or the Startup Station Service Transformer (SSST) via buses IA and IB respectively, with backup power directly provided by either the Emergency Station Service Transformer (ESST) or the Emergency Diesel Generator (EDG).
In its January 5, 1993, letter, the licenseu stated that when the RHR and CS 27X3 1A/IB relays were originally included in the CNS design, their function was to initiate a block start signal of tne Emergency Core Cooling System (ECCS) pumps onto the SSST when voltage was available on buses IA and IB and i
the tie breakers between buses-1A and IF and IB and IG were closed during a design basis Loss of Coolant Accident (LOCA). However, the licensee, in 1988, removed the block start loading of the SSST and incorporated sequential loading of the ECCS pumps from this power source.
Since that time, the RHR and CS 27X31A/IB relays have functioned to detect whether power is available i
to buses IA and IB from the SSST and to bypass the sequential loading timers for the ECCS pumps during a design basis LOCA.
However, with the existing bus IF and IG first-level undervoltage systems and the second-level undervoltage system as modified in 1988, the RHR and CS 27X3 -
1A/IB relays are redundant. The bus IF and IG first-level undervoltage relay system will ensure an immediate transfer of power sources on loss of voltage-to buses IF and IG when powered from the SSST or ESST and initiate the sequential loading timer. The second-level undervoltage relay system logic will ensure that buses IF and 1G are powered either from offsite sources with adequate voltage or the EDGs. As noted above, the first-and the second-level undervoltage relays are currently controlled by the CNS TS with attendant setpoints and surveillance frequencies to ensure they are operable.
During the upcoming spring 1993 refueling outage, the licensee plans to replace the existing ESST with a new Emergency Transformer.
Included as part of the installation of the new Emergency Transformer will be overvoltage protective relays in the control logic for the 4160 volt switchgear breakers IFS and IGS which connect the new Emergency Transformer to the 4160 F and G buses. This transformer replacement will require the use of the 52a contacts from breakers IFS and IGS in the new overvoltage relay protection scheme.
Thus, by removing the redundant RHR and CS power monitoring logic, the 52a
contacts from breakers IFS / LGS will be available for use with the new Emergency Transformer.
The licensee states in its January 5,1993 submittal, that removal of the RHR and CS 27X31A/IB relays and the RHR and CS relay logic modifications will not change the operation, duration,' or timing of the sequential loading logic for the ECCS loads. The RHR and CS emergency core cooling systems will still perform their intended safety function under LOCA conditions as described in the Updated Safety Analysis Report (USAR). By maintaining the safety function of these ECCS systems, CNS will continue to meet the criteria prescribed in the 10 CFR 50.45 and Appendix K unalysis assuring that the ECCS are capable of meeting their design bases and licensing requirements. The removal of the RHR and CS 27X31A/lB relays will sittplify the RHR and CS pump start circuitry while providing the same safety function.
In summary, the licensee states.
that the proposed design and TS changes will not change the performance or safety function of the RHR or CS systems.
f In its review of the proposed changes, the NRC staff has reviewed the licensee's submittal of January 5,1993, as well as the previously issued amendments related to the affected systems, and has discussed the proposed change with the licensee in telephone calls. Based on its review, the staff finds acceptable the proposed deletion of relays RHR and CS UX31A/lB from the CNS TS, because the licensee will use a revised undervoltage protection scheme that fulfills the same function as the previous system, without use of these relays.
3.0 STATE CONSULTATION
In accordance with the Commission's regulations,-the Nebraska State official 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 and changes in surveillance requirements. 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 i
occupational radiation exposure. The Commission has previously issued a pro-j posed finding that the amendment involves no significant hazards consideration and there has been no public comment on such finding (58 FR 7001).
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.
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5.0 CONCLUSION
'I The Commission has concluded, based on the considerations discussed above,
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(1) there is reasoriable 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,'
I 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, l
l Principal Contributor:
H. Rood o
l Date:
March 11, 1993 l
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