ML20206N249
| ML20206N249 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 06/24/1986 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20206N246 | List: |
| References | |
| NUDOCS 8607010414 | |
| Download: ML20206N249 (3) | |
Text
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7 g rarg#o UNITED STATES NUCLEAR REGULATORY COMMISSION o
h WASHINGTON, D. C. 20555
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SAFETY EVALUATION BY YHE OFFICE 0F NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT ii0. ol TO FACILITY OPERATING LICENSE NO. DPR-28 VERMONT YANKEE NUCLEAR POWER CORPORATION VERMONT YANKEE NUCLEAR POWER STATION DOCKET NO. 50-271
1.0 INTRODUCTION AND BACKGROUND
By letter dated May 10, 1985, Vermont Yankee Nuclear Power Corporation proposed that the Yemont Yankee Nuclear Power Station Technical Specification pressure and temperature limit curves be changed.
The proposed change would revise the Technical Specifications to accommodate the change in toughness properties for the reactor vessel materials that were induced by radiation effects.
Periodic review and, if necessary, adjustment of the pressure and temperature limit curves to account for the effects of increased neutron exposure are required by 10 CFR Part 50, Appendices G and H.
This change adjusts the reactor vessel pressure and temperature limitations to compensate for the effects of incrcased neutron gxposure to pemit operation to a cumulative energy output of 1.790x10 MWh(t). This adjustmentisnecessarygecausetheexistingcurvesarelimitedtoan energy output of 1.33x10 MWh(t),avaluewhichisexpectedtobereached during 1986. This change also adjusts the fluence factor and fluence vs.
thermal energy curves to incorporate revised fast neutron fluence calculations. The licensee submitted clarifying information by letter dated November 21, 1985.
The new curves incorporate results from the surveillance capsule removed in March 1983 and new tests performed on unirradiated specimens for archival base, weld, and heat affected zone materials.
l 2.0 EVALUATION The purpose of the reactor vessel surveillance program is to monitor the effect that neutron irradiation and the thermal environment will have on the beltline materials' reference nil-ductility temperature (RTNDT). The method recomended by the staff for predicting the effect of neutron irradiation and the thermal environment on beltline materials' RTNOT is documented in Regulatory Guide 1.99 " Effects of Residual Elements on Predicted Radiation Damage to Reactor Vessel Naterials." In revision 1 to this regulatory guide, the estimate of the increase in RTNDT is based i
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upon the amount of copper, phosphorus and the neutron fluence. In proposed revision 2, dated February 1986, the increase in RT is based upon the amount of copper, nickel and the neutron fluence.
bposedrevision2 was prepared from the analysis of commercial reactor vessel material surveillance data generated during the staff's review of the issue of
" Pressurized Thermal Shock" and has been issued for public comment.
In order to develop revised curves, several material parameters needed to be re-established or revised for the Vermont Yankee reactor vessel limiting materi'l.
Changes were needed to reflect the results of impact tests a
performed on surveillance capsule material which was removed from the reactor vessel in March 1983. In addition, new tests were performed on unirradiated archival base, weld, and heat affected zone specimens to more clearly establish initial nil-ductility transition temperatures.
The base metal for the Vermont Yankee reactor pressure vessel is A533 Grade B, Class 1 steel.
Charpy V-notch and tensile specimens were prepared from an actual beltline plate (No. 2 shell and piece marked 1-14).
The specimens were prepared from A533 steci plate (Heat No. C3017-2) provided by Lukens Steal Corporation in 1969.
Only two plates lie in the vessel belt line, pieces 1-14 and 1-15.
The limiting plate has been established as piece 1-14 which is the surveillance plate.
An initial RT
= 40 F was established for this plate.
Frog 6the Battelletests,thesNtinRT was 19 F at a fluence of 4.3 x 10 n/cm,
2 UtilizingthecalculationalprobureoftheproposedRegulatoryGuide1.99, Revision 2, a shift of only 4.7*F results at this fluence.
The Chemistry Factor (CF) for piece 1-14 is 76, representing a copper content of 0.11 weight percent and a nickel content of 0.68 weight percent.
The measured shift is within one standard deviation of that calculated (Regulatory Guide 1.99, Revision 2 assumes la = 17 for base metal).
However, because the calculational procedures of the Regulatory Guide results in a less conservative prediction of shift, a modified Regulatory Guide fluence factor curve was developed. The modified curve utilizes the same curve shape and damage prediction as Regulatory Guide 1.99, Revision 2, but passes through the Vermont Yankee surveillance capsule data point.
In effect, the fluence factor parameter in the. Regulatory Guide 1.99 reference temperature shift equation is multiplied by a factor of 4.17 to duplicate the measured RT shiftatVermontYankee.Futureshiftvalupscanthenbedeterminedfro$DT this curve until the next surveillance specimen is removed.
i Regulatory Guide 1.99, Revision 2 proposes that surveillance test results can be used after two capsules have been tested with reliable results.
However, we consider the' described method of using one data point from one capsule to be very conservative in this case and therefore acceptable.
The results of this procedure are also conservative with respect to Revision 1 of the Guide.
v In the future, a revised shift in RT of the vessel material will be establishedperiodicallyduringoper$kIonbyremovinganoevaluating,in accordance with ASTM E185-82, reactor vessel material irradiation surveillance specimens installe'd near the inside wall of the reactor vessel.in the core area.
Because the neutron spectra at the irradiation samples and vessel inside radius are essentially identical, the measured transition shift for a sample can be applied with confidence to the adjacent section of the reactor vessel.
We have reviewed the calculations which form the basis for the proposed change and find them acceptable.
The proposed changes to the Technical Specifications relating to the pressure and temperature limits for hydrostatic and leak tests, subcritical/ critical heat up and cool down, and operation meet the requirements of 10 CFR 50, Appendix G, Regulatory Guide 1.99, Revisions 1 and 2 and Appendix G,Section III of the ASME Code.
The proposed changes are acceptable for incorporation into the Technical Specifications.
3.0 ENVIRONMENTAL CONSIDERATION
S This 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. The 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 the cumulative occupational radiation exposure.
The Commission has previously issued a proposed finding that this amendment involves no significant hazards consideration and there has been no public comment on such finding.
Accordingly, this amendment meets 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 this amendment.
4.0 CONCLUSION
We have 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, and (2) such activities will be conducted in compliance with the Commission's regulations, 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.
Principal Contributor:
H. Conrad Dated:
June 24, 1986 l
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