ML20149L184
| ML20149L184 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 07/30/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20149L179 | List: |
| References | |
| NUDOCS 9707310176 | |
| Download: ML20149L184 (3) | |
Text
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UNITED STATES g
j NUCLEAR REGULATORY COMMISSION o
WASHINGTON. D.C. 20666 4 001 Q4..... /
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDHENT NOS. 206 AND 187 TO FACILITY OPERATING LICENSE NOS. NPF-4 AND NPF-7 VIRGINIA ELECTRIC AND POWER COMPANY NORTH ANNA POWER STATION. UNITS NO. 1 AND NO. 2 DOCKET NOS. 50-338 AND 50-339
1.0 INTRODUCTION
By letter dated February 4. 1997. Virginia Electric and Power Company (VEPCO) proposed changes to the setpoint and the allowable value of the intermediate range (IR) trip for the North Anna Units 1 and 2 Technical Specifications (TS). The same changes had been proposed previously in a letter dated November 9. 1987, and supplemented March 31. 1988, and June 8. 1992.
VEPC0 resubmitted the proposed changes on February 4. 1997, in order to take into account changes to the TS that had been made in the interim.
The proposed changes are as follows:
The trip setpoint specified in TS Table 2.2-1 would be changed from s25% to s35% of rated thermal
)ower (RTP) and the allowable value would be changed from s30% to s40% of RT). TS 3.10.3 and 3.10.4 would similarly be revised.
In addition a footnote would be added for Mode 1 in the Applicable Modes column of TS Table 3.3-1 and to the Modes in Which Surveillance Required column of TS Table 4.3-1 to limit applicability to power levels below the P-10 (low setpoint power range neutron flux interlock) setpoint.
2.0 EVALUATION Presently, an IR trip is generated based on one-out-of-two channels exceeding a detector current equivalent to 25% of RTP.
The channels can be manually by)assed when permissive P-10 (2 of 4 power range channels greater than 10% of RT)) is active. Therefore, the channels are not required to be operable for power levels above 10% of RTP where the power range neutron flux-high setpoint trip and the power range neutron flux-high positive rate trip provide core protection for a rod withdrawal transient. The power range trips are required to be operable during Modes 1 and 2.
In Modes 3. 4. or 5. the source range flux trias must be operable whenever the control rods are energized and capable of wit 1drawal. As a result. there is no operating condition under which the IR trip provides sole overpower protection. Therefore, the IR nuclear flux trips merely provide backup reactor core protection during reactor startup and no credit is taken for their operation in the safety analyses.
Therefore. the increase in the IR setpoint from a nominal value of 9707310176 970730 PDR ADOCK 05000338 P
.-/.- 25% of RTP to 35% of RTP is acce margin between the nominal (35%)ptable.In addition, retention of the 5%
and allowable (40%) setpoint reflects the effects of instrument drift between surveillance tests and is acceptable.
With the IR setpoint at 25% of RTP. the variability in IR channel response with control rod position was such that in some conditions there was very little operating space between the P-10 permissive level, which allows the operator to block the IR tri) function, and the power level at which the IR trip occurs. As a result. t1ere was a potential for unneeded unit trips due to inadequate response time available to the operator for blocking the trip during power ascension.
By raising the setpoint to 35% of RTP. the minimum amount of operating space between the interlock and a potential trip is increased thereby allowing for more time to block the trip when normal power ascension is occurring and its protective function is not required.
The proposed footnotes to TS Tables 3.3-1 and 4.3-1 state the operability and surveillance requirements for the IR trips for those conditions where the IR trias perform a backup function to the power range low setpoint trips, i.e..
in iodes 1 and 2 below the P-10 interlock.
The requirement for the shutdown modes (with the trip breakers closed) involves monthly verification (via permissive checks) that the power range low setpoint and source range trips cannot be blocked below the appropriate power levels.
Therefore, their ranges of protection are properly overlapped and the proposed footnotes are acceptable.
3.0
SUMMARY
Based on the above evaluation, the staff concludes that the proposed TS tnan9 s to the IR flux trip setpoint and allowable value for North Anna Units 0
1 and 2 are acceptable.
4.0 STATE CONSULTATION
In accordance with the Commission's regulations, the Virginia State official was notified of the proposed issuance of the amendments.
The State official had no comment.
5.0 ENVIRONMENTAL CONSIDERATION
i 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 no public comment on such finding (62 FR 33136). 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.
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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 i
- activities will be conducted in compliance with the Commission's regulations, 1
and (3) the issuance of the 6,Jendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
L. Kopp Date: July 30,1997 t
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