ML20023C888
| ML20023C888 | |
| Person / Time | |
|---|---|
| Site: | Pilgrim |
| Issue date: | 05/03/1983 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20023C884 | List: |
| References | |
| NUDOCS 8305180216 | |
| Download: ML20023C888 (1) | |
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o 0oo00 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO.70 TO FACILITY LICENSE NO. DPR-35 BOSTON EDISON COMPANY PILGRIM NUCLEAR POWER STATION DOCKET NO. 50-293 1.0 Introduction By letter dated April 5,1983, Boston Edison Company (BECo, licensee) requested changes to the Pilgrim Nuclear Power Station (PNPS) Technical Specifications (TSs) for the latter portion (after approximately 6000 MWD /ST burnup) of Cycle 6.
This change is required to accommodate the spectral shift mode of operation which is being employed during Cycle 6 operation.
2.0 Evaluation In the spectral shift mode of operation the power distributicii is shifted toward the bottom of the core (with respect to the Haling distribution) during the first part of the cycle with the result that excess burnup occurs at the bottom.
During the latter part of the cycle the rods are withdrawn and the power distribution shifts to9ard the top of the core and the accumulated plutonium is burned out. However', the initial scram insertion reactivity is degraded during the latter portion of the cycle due to the low power in the bottom of the core. As a result of operation in the spectral shift mode, the MCPR Ifmits must be increased for operation during the latter portion of the present cycl e.
The licensee's proposed TSs reflect this change to the MCPR values.
The licensee has submitted reanalyses of the limiting pressurization events to account for the changed scram function. The analyses used burnup distributions obtained by the BWR simulator code using the planned Cycle 6 rod patterns. The licensee has asserted (Telecon on April 21,1983) that any deviation from the l
planned pattern will be such as to make the resulting burnup distribution con-servative with respect to that used in the analysis.
In addition the axial power distribution is still conservative with respect to that assumed for the GETAB analysis. The loss of feedwater heating event (which is analyzed by the REDY code) was not redone but this is a very mild event in which scram does not occur so the changed scram shape would have no effect.
3.0 Summary The licensee's proposed changes reflect the necessary revisions to the table of operating limit MCPR values required for the spectral shift mode of operations.
Based on this and on the fact that an approved method (0DYN Code) was used to-perform the analysis, that the input parameters will not be nonconservative, and that the GETAB analysis is still valid for the changed power shape, we conclude that the changes to the Technical Specifications proposed by the licensee are acceptable.
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