ML18024B145
| ML18024B145 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 11/14/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML18024B144 | List: |
| References | |
| NUDOCS 7911290116 | |
| Download: ML18024B145 (6) | |
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+w*e+'NITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO.
55 TO FACILITY OPERATING LICENSE NO.
DPR-33 AMENDMENT NO.
50 TO-FACILITY OPERATING LICENSE NO.
DPR-52 AMENDMENT NO'.
27 TO FACILITY OPERATING LICENSE NO.
DPR-68 TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT UNIT NOS.
1 2
AND 3 DOCKET NOS.
50-259 50-260 AND 50-296 1.0 Introduction.
By letter dated August 6, 1979,. the Tennessee VAlley Authority (the li.censee or TVA) requested changes to the Technical Specifications (Appendix A) appended to 'Facility Operating Licenses Nos.
DPR-33, DPR-52 and DPR-68 for the Browns Ferry Nuclear Plant, Units Nos.
1, 2 and 3.
The proposed amendments and revised Technical Specifications would allow partial tensioning of the reactor vessel head bolts, at 70'F rather than the 100'F requi rec"'by the, present Technical 'Specifications.
There would be no'hange in the requirement that the temperature of the pressure vessel head flange, be at least 100'F. for full tension boltup.
2.0 Discussion 10 CFR Part 50, Appendix G "Fracture Toughness Requi rements",
requires that pressure-temperature limits be established for reactor coolant system heatup and cooldown operations, inservice leak 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 condition 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 belt-line region vary over the lifetime of the vessel because of the e'ffects of neutron irradiation.
One principle effect of the neutron irradiation is that V911290 ) /Q
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it causes the vessel material nil-ductility temperature (RTl]DT) to increase with time.
The pressure-temperature operating limits must be modified periodica11y to account for this radi'ation induced increase in RTNpT by increasing the temperature required for a given pressure.
The operating limits for a particular operating period are based on the material properties at the end of the operating period.
By periodically revising the pressure-temperature limits to account for radiation
- damage, the stresses and stress intensities in the reactor vessel are maintained within acceptable limits.
10 CFR Part 50, Appendix G also requires that for nozzles, flanges and shell regions near discontinuities, operating limits provide the same margin of safety as specified in ASt1E Code,Section III, Appendix G.
ASHE Code Appendix G (1977 Edition) states that when the flange and adjacent shell region are stressed by the full intended bolt preload and by pressure not exceeding 20K of the preoperational system hydrostatic test pressure, minimum metal temperature in the stressed region should be at least the initial RTgpT temperature for the material in the stressed regions plus any effects of irradiation at the stressed regions.
3.0 Evaluation Tennessee Valley Authority proposed that the reactor vessel head bolting studs may be partially tensioned (four sequences of the seating pass).orovided the studs and flange materials are above 79'F.
Before loading the
~ langes any more, the vessel flange and head flange must be greater than 100'F, and must remain above 100'F while under full tension.
The present Technical Specifica-tion requires that studs shall not be under tension unless the temperature of the vessel head flange is greater than 100'F.
The General Electric Company (GE) has determined that the closure flanges may be preloaded by partial bolt tensioning (either eight bolts under full tension or a greater number of bolts under partial tension to give equivalent loading) in order to seat and seal the 0-rings at a temperature of 70'F.
Because of the sequence of the boltup procedure, the head seating passes will result in loading the bolts and flanges to meet the above restriction.
We have reviewed the proposed change to the operating limits and have performed independent calculations to verify conformance with Appendix G, 10 CFR Part 50.
The maximum RTNpT of materials in the reactor vessels of Units 2 and 3 is 40'F.
In the Unit 1 vessel the shell to flange weld may be an atypical (off-chemistry) weld metal.
The atypical material has an RTN0T of 90 F.
The radi ation levels in the flanqe region of the reactor vessels are very low, so no increase in the RTN0T values is anticipated throughout service life.
Therefore, we conclude that the prooosed boltup limits for Browns Ferry 2
and 3 are acceptable.
For Unit 1 partial tensioning will produce maximum stresses in the flange of about 1400 psi, which is less than 10% of the stress at final tensioning.
Since the stresses at partial boltup are very 1ow, the proposed boltup limit for Browns Ferry 1 is acceptable.
O~
No changes were proposed for the operating limits during heatup and cooldown,
.leak testing and for core critical operation.
However, these specifications were reviewed and found to be in conformance with Appendix G, 10 CFR Part 50.
4.0 Environmental Consideration We have determined that these amendments do 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 these amendments involve an action which is insignificant from the standpoi'nt of environmental
- impact, and pursuant to 10 CFR Section 51.5(d)(4)'hat an environmental impact statement; or negative declaration and environmental impact appraisal need not be prepared in connection with the issuance of these
-amendments.
5.0 Conclusion We have concluded that:
(1) because the amendments do not involve a significant increase in the probability or consequences, of accidents previously considered and do not involve a significant decrease in a safety margin, the amendments do 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 cvmpliance with the Commission's regulations and the issuance of these amendments will not be inimical to the common defense and security or to the health and safety of the public.
Dated:
November 14, 1979
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