ML19269D971
| ML19269D971 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 03/30/1979 |
| From: | Ippolito T Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19269D969 | List: |
| References | |
| NUDOCS 7906210349 | |
| Download: ML19269D971 (5) | |
Text
UNITED STATES j
NUCLEAR REGULATORY COMMISSION p"
g
,j WASHINGTON, D. C. 20566 e
\\.... /
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 52 TO FACILITY OPERATING LICENSE NO. OPR-28 VERMONT YANKEE NUCLEAR POWER CORPORATION VERMONT YANKEE NUCLEAR POWER STATION DOCKET NO. 50-271 Introduction By letter dated March 5,1979, Vermont Yankee Nuclear Power Corporation (the licensee) requested changes to the Technical Specifications (Appendix A) appended to Facility Operating License No. DPR-28 for the Vermont Yankee Nuclear Power Station (VY). The proposed changes provide min-imum critical power ratio (MCPR) limits applicalle to the exposure interval from 2 gigawatt day / ton before the end of the present fuel cycle (E0C-2 GWD/T) on to end of cycle (EOC).
The transient analyses performed in support of Cycle 6 operation of VY included analyses of control rod withdrawal, loss of 100 F of feedwater heating, and feedwater controller failure (References 1 and 2). The transient decreases in MCPR obtained in these analyses for 7x7, 8x8 and 8x8R fuel were accepted as limiting by the staff for the exposure range up to 2 GWD/T before the end of Cycle 6 (Reference 3), and the current VY Technical Specifications are based on these results.
The transient normally anticipated to be limiting near the end of cycle, turbine trip without operation of bypass valves (TT w/o BP) and load rejection without operation of bypass valves (LR w/o BP), were not analyzed for the previous submittal. The staff understood that the licensee intended to provide such analyses, based on measured rather than Technical Specification scram times, prior to reaching 2 GWD/T before end of Cyc'e 6.
Because of the unavailability of the analyses using measured scrar. +.imes the licensee has submitted in Reference 4 results of analyses of the TT w/o BP and LR w/o BP transients for the exposure range from E0C-2 GWD/T to EOC, based on Technical Specification scram times. These results have been incorporated into proposed MCPR limits for the remainder of Cycle 6.
The licensee has proposed.the following MCPR limits:
2264 187 7906210 3 %
. 7x7 8x8 8x8R BOC to E0C - 1 GWD/T 1.23 1.22 1.24 (1.22)*
E0C - 1G WD/T E0C 1.23 1.27 1.27
- l.24 is to be used when the rod block set point is 1.06 and 1.22 when the set point is 1.05.
Our evaluation of these limits is given in the following section.
Evaluation As stated in References 1 and 4 the transient analyses performed to deter-mine the MCPR limits for all portions of VY Cycle 6 were based on methods described in the GE " Generic Reload Fuel Application" (Reference 5).
These methods have been accepted by the staff as adequate for such analyses (Reference 6). On this basis we conclude that the licensee has used acceptable methods to determine the Cycle 6 MPCR limits.
The input data used for the analyses included plant specific data presented in Reference 5 and accepted by the staff in Reference 6.
Additional cycle dependent input data presented in Reference 1 have been reviewed and found to meet the criteria for such data stated in the staff SER on the " Generic Reload Fuel Application" (Reference 6). We therefore conclude that the transient analysis input data used to arrive at the proposed VY Cycle MCPR limits are acceptable throughout Cycle 6.
Reference 4 includes results of the TT w/o BP and LR w/o BP analyses for the last 2 GWD/T of full power operation during Cycle 6.
References 1 and 2 originally included analyses of rod withdrawal errors, loss of 100 F of feedwater heating, and feedwater controller failure events valid for all of Cycle 6.
Based on discussions of the scope of the transients to be included in reload cycle anlayses in References 5 and 6 we conclude that a sufficiently complete set of transient analyses has been performed to identify the limiting transient ACPR for each fuel type.
Bat 1 on transients initiated from rated power and flow conditions the 7x7 MCPR limits could be as low as 1.21.
However, in accordance with the require-ments of Section 6.4 of Reference 6, an operating limit MCPR below 1.23 is not allowed for 7x7 fuel until acceptable Kr factors for operatioa in the manual flow have been provided. Consequencly the VY Cycle 6 7x7 MCPR will be 1.23 rather than 1.21.
2264 188
. In Reference 3 the staff concluded that it will not be necessary to adjust VY Cycle 6 MCPR limits based on consideration of postulated fuel loading errors unless off-gas activities indicative of fuel failures due to fuel misloadings are observed. The MCPR adjustments required in the event off-gas activities exceed 0.236 Ci/sec at the steam jet air ejector are dis-cussed in Reference 3, and have been incorporated into the VY Technical Specifications.
Although fuel failures have been observed at VY during Cycle 6 they 1 ave not resulted in off-gas activities above the Technical Specification limit.
Preliminary assessment of the failures indicates that specific fuel rod lots dispersed over a number of fuel bundles are failing. This is in contrast to the expected failure pattern for postulated bundle misloadings, i.e., failures localized in the misplaced or mis-oriented bundle. The VY fuel is being thoroughly inspected to confirm the preliminary findings and to assure that all leakers will be removed. Tests are also being conducted by GE to determine the cause of the failures. The staff is following the investigation closely.
We believe that the current VY Technical Specifications with the fuel loading error related off-gas activity limits provide adequate assurance that fuel failures due to misplaced or mis-oriented fuel bundles will not result in unacceptable fuel damage. We, therefore, conclude that the VY MCPR operating limits may be determined on the basis of anticipated transients alone.
In summary, based cn our evaluation we conclude that the licensee has used acceptable input data and methods to perform the VY Cycle 6 transient analyses, and that the transients involving the most severe CPR reductions have been considered. Furthermore, the proposed MCPR limits are in com-pliance with the staff safety evaluation report (Reference 6) on the GE
" Generic Reload Fuel Application" (Reference 5) with regard to operation in the manual flow control mode.
For these reasons we conclude that the proposed MCPR limits provide adequate assurance that anticipated transients will not result in violation of fuel thermal limits.
Because we have also concluded that MCPR adjustments based on high off-gas activities associated with postulated fuel misloadings are already ade-quately included in the VY Technical Specifications, we believe that operating limit MCPRs may be based on consideration of anticipated transients only.
Therefore, we find the proposed VY MCPR limits for the remainder of Cycle 6 to be acceptable.
2264 189
. Environmental Considerations We have determined that the amendment does not authorize a change in effluent types or total amounts nor an increase in power level and will not result in any significant environmental impact. Having made this determination, we have further concluded that the amendment involves an action which is insignificant from the standpoint of environmental impact, and pursuant to 10 CFR 951.5(d)(4) that an environmental impact statement, or negative declaration and environmental impact appraisal need not be prepared in connection with the issuance of the amendment.
Conclusion We have concluded, based on the considerations discussed above, that:
(1) because the amendment does not involve a significant increase in the probability or consequences of accidents previously considered and does not involve a significant decrease in a safety margin, the amendment does not involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (3) su " activities will be con-ducted in compliance with the Commission's regui tions and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.
Dated: March 30, 1979 2264 190
Re fe rences_
l.
Letter from D. E.
Vandenburgh of Vermont Yankee Nuclear Power Corporation (VYNPC) to NRC, dated June 21, 1978.
20, 1978.
Letter from D. E. Vandenburgh of VYNPC to NRC, dated September 2.
Amendment No. 47 to License No. DPR-28 Docket No. 50-271, October 10, 3.
1978.
Letter from D. E. Vandenburgh of VYNPC to NRC, dated March 5,1979.
4 General Electric Boiling Water Reactor Generic Reload Fuel Application.
5.
NEDE-240ll-P May 1977.
NRC Safety Evaluation of the GE Generic Reload Fuel Application 6.
(NEDE-240ll-P) April 1978.
f