ML19224D448
| ML19224D448 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 06/01/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19224D442 | List: |
| References | |
| TASK-05-04, TASK-05-06, TASK-5-4, TASK-5-6, TASK-RR NUDOCS 7907120188 | |
| Download: ML19224D448 (3) | |
Text
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UNITED STATES j
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 62 TO PROVISIONAL OPERATING LICENSE NO. DP NORTHEAST NUCLEAR ENERGY COMPANY, ET AL MILLSTONE NUCLEAR POWER STATION, UNIT NO.1
_DO_C._K. ET N O. 50-24 5 Introduction By letter dated June 8,19 76, as supplemented by letter dated July 1,1977, Northeast Nuclear Energy Co apany (NNECO) submitted an application for an amendment to the Appendix A Technical Specifications appended to Facility Operating License DPR-21 for Millstone, Unit 1.
The requested changes would modify the reactor coolant system pressure-temperature limits to account for increases in the reactor vassel metal reference nil-ductility temperature (RTNDT) due to irradiation.
Discussion 10 CFR Part 50, Appendix G, " Fracture Toughness Requirements," requires that pressure-temperature limits be established for reactor coolant system heatup and cooldown operations, inservice leck and hydrostatic tests, and reactor core operation. These limits are required to ensure that the stresses in the reactor vessel remain within acceptable limits.
They are intended to provide adequate margins of safety during any conditior, of normal operation, including anticipated operational occurrences.
The pressure-temperature limits depend upon the metallurgical properties of the reactor vessel materials. The properties of materials in the vessel beltline region vary over the lifetime of the vessel because of the effects of neutron irradiation.
One principle effect of the neutron irradiation is to increase with time. The pressure-temperature that it causes RTNDT operating limits must be modified periodically to account for this radiation by increasing the temperature required for a given induced increase in RTNDT The.perating limits for a particular operating period are based pressure.
on the material properties at the end of the operating perico.
By periodically revising the pressure-temperature limits to account for radiation damage, the stresses and stress intensities in the reactor vessel can be held within At the beginning of life, material other than that in acceptable limits.
the beltline region may be the limiting material because it is subjected to high stresses and stress intensities.
However, since material outside the beltline region is not subjected to high level irratiation, its RTNOT will not change as the beltline region will and at some period of life, the beltline materials will become limiting.
F 6 1217 9 0712 0 / N' is proportional to the neutron fluence to The magnitude of the shift in RTNDT which the materials are exposed.
The shift in RTNDT can be predicted from the results of tests on material surveillance specimens-or from the guidance contained in Regulatory Guide 1.99.
Evaluation The revised operating limits are based on the calculational methods contained i-ASME Code,Section III and Appendix G to 10 CFR Part 50.
The operating limits are proposed for operation through 9.0 X 106 MWDth at which time the neutron fluenge at the 1/4T* location in the reactor vessel wall will be about 7 X 1017 n/cm. The amount of radiation damage is predicted from the results of tests conducted by General Electric on similar materials.
Section IV. A.2.b of Appendix G, requires that pressure-temperature limits include margins of safety for high stressed regions near discontinuities comparable to those required for shell areas remote from discontinuities.
For the propased period of operation the feedwater nozzle material is limiting because of the high stress intensity in this area.
We have reviewed the proposed changes to the operating limits for Millstone Unit 1 and have performed independent calculations to verify compliance with Appendix G.
We conclude that at 9 X 106 MWD h the fluence at the 1/4T location t
will be about 7 X 1017 n/cm.
This fluence will result in an increase in 2
RTNDT of the limiting beltline material of about 500F which is based on the guidance contained in Regulatory Guide 1.99, Revision 1.
This 50cF increase in RTr,497 causes the vessel beltline weld material to become the limiting material.
We have modified the Technical Specification changes proposed by NNECO letter dated 6/8/76 for the purpose of making them consistent with information proviced in a later NNECO letter dated 7/1/77, and also for including some relatively minor editorial changes.
All of these modificatioi.s have been discussed with and agreed to by NNECO.
We conclude that the proposed pressure-temperature operating limits would be in conformance with Appendix G to 10 CFR Part 50 for operation through The conformance would ensure adequate safety margins during 9 X 106 MWDth.
operation, testing, maintenance and postulated accident conditions and would constitute an acceptable basis for satisfying tne requj renents of NRC General Design Criterion 31, Appendix A,10 CFR Part 50.
On this basis, we find the proposed changes acceptable.
- 1/4 I is one-tourth the thickness of the vessel wall, me asured from the inside.
326 130
- Environmental Consideration 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 detennination, 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 this amendment.
Conclusion We have conclu,ded, 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) 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.
Date:
June 1,1979 326 1j;
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