ML19319E187
| ML19319E187 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 08/13/1976 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19319E176 | List: |
| References | |
| NUDOCS 8003310703 | |
| Download: ML19319E187 (4) | |
Text
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UidfTED STATrS t.
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' SAFETY EVALUATIO!T BY THE~ OFFICE OF NUCLEAR REACTOR REGITLATION-SUPPORTING AMEEDITE*iT NO. 7 TO FACILITY LICENSE NO. DPR-54 SACRAME!'TO MimICIPAL UTILITY DTSTRICT RANCHO SECO NUCLEAR GENEPATIliO STATION DOCKET NO. 50-312 Introduction By letter dated April 8, 1976, the Sacramento Municipal Utility District (the licensee)_ requested an exemption from the requirements of 10 CFR Part 50, Appendix H.Section II.C.2 te permit the operation of the Rancho Seco Nuclear Generating Station (the facility) for the remainder of Cycle 1 (approximately 280 days) with the reactor vessel surveillance capsules removed fron the reactor vessel. The licensee requested corresponding changes to the Technical Specifications appended to Facility Operating License No. DPR-54 for the facility. These changes would reflect the removal of the reactor vessel surveillance capsules for the re=ainder of Cycle 1.
By letter of May 21, 1976, the licensee notified the Coccaission that the capsule holder tubes would be removed from the reactor before the facility returned to operation.
Discussion ~
The Rancho Seco design includes three reactor vessel surveillance capsule holder tubes located adjacent to the reactor vessel inside wall. Each holder tube contains two surveillance capsules which held specimens to be irradiated in accordance with the requirements of the reactor vessel material surveillance program as described in Appendix H to 10 CFR Part
- 50. The purpose of the surveillance program is to monitor changes in the fracture toughnts' properties of ferritic materials in the reactor v.essel beltline region resulting from their exposure to neutron irradiation and the thermal environment.
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- The licensee has -been recently notified by the NSSS vendor (Babcock-
.& Wilcox)' that other _B&W reactors had experienced damage to the reactor vessel material' surveillance holder tubes.. Subsequent-inspection
-at Rancho'Seco revealed evidence of wear on the internal surface of all three holder tubes;at;each of~the push rod spacer axial locations, at the location of the holddown spring _and at the surveillance capsule rings.. The wear indications were all very' shallow with the exception of soma: deep wear at the location of the ' spring cartridge on the upper ends of all three tubes"and at the fourth spacer, location of one tube.- The damage.was attributed to contact and relative motion of the holddown spring, spacers, and surveillance capsules.at their respective locations. There was also~ evidence of.some external tube wall thinning over a portion of the circumference;in' the journal bearing area. There were no loose parts generated as a result of this damage.-
To preclude the possibility-of unacceptable wear during tihe remainder of Cycle 1 the surveillance. capsules and holder tubes were removed. Engineer-ing of new holder tube aad push-rod assembly design modifications and
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anterial precurement will be completed during the. remainder of Cycle 1 to allow in'stallation of the revised holder tubes prior to the start of Cycle 2.1 Rancho Seco is one of several' facilities with nuclear steam supp'ly systems j
vent valves to prevent vapor lock in the reactor vessel in the event of a supplied by Babcock & Wilcox (L&W) that are equipped with reactor internals reactor coolant cold leg leak. The licensee confirms the closure of internal vent valves during reactor operation by monitoring reactor vent valve thermocouples.: In' August-1975, B&W submitted to the NRC a generic
. report entitled,; "BiW Operating Experience of ' Reactor Internals Vent Valves."
Based on'our review of this report, we have concluded.that sufficient evidence has been presented co assure that the reactor internals vent valves on-B&W. plants will remain closed during normal operation. By letter dated
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-March 10, 1976, we informed the licensee of-this conclusion and of our
. surveillance requirement if he is to take credit for vent valves remaining closed.
Because-the surveillance capsula equipment removal involved internal vent 4
valve thermocouple removal,.in his letter of April 8, 1976, the licensee
. proposed surveillance _ Technical Specifications to' confirm that no internal
. vent valves are stuck open. -
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' Evaluation-
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.-As' required by. Paragraph II.C.2 of Appendix H to 10 CFR Part 50, the surveillance capsules of Rancho Seco are positioned during reacter operation so.that the neutron-flux received by the specimens is at
. least as -high but not more than.three times as high as that received by!the reactor vessel inner wan. A recent calculatio'n by Babeack &
1Wilcox indicates that the neutron flux is 2.4 times greater at the
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' specimen location-than at the reactor vessel van at 1/4 wall thickness (1/4 t).
Cycle 1 and cycle'2 are planned to last 450 EFPD (effective-ifull power days) and 264 EFPD respectively. The current shutdown occurred
-after the reactor had been operating for 169 EFPD. Therefore, the specimens
-have been exposed.to the equivalent of 400 EFPD of neutron irradiation relative to 1/4 e or to approximately 90 per cent of the exposure that is
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projected for the vessel van during the entire Cycle 1.
By removing the specimens at this. time and reinstan ing them at the end of Cycle 1, the equivalent exposure at the end of Cycle 2 would be 714
.EFPD for the reactor vessel wall and 1039 EFPD for the specimens. The irradiation effects' accumulated during the first 169 days of Cycle 1 will not be altered in those specimens that are-stored outside the reactor
,during the remainder of Cycle 1.
Data accumulated from other B&W plants h
with similar. vessels and vessel material surveillance programs may be used 3
to: adjust the operating pressure and temperature limitations in the Technical Specifications in'accordance with Appendix G of 10 CFR Part 50
~for Cycle 2' operation,~ if necessary. Subsequent adjustments can be based
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on the results of the specimen testing program performed-on specimens removed from Rancho Seco after Cycle 2.
The licensee should also review the adequacy of.its'withdrawa1' schedule.at'the end of Cycle 2.
'In view'of-the above, we consider.it acceptable to allow the licensee to remove the surveillance specimen capsules and holder tubes during the
-remainder of Cycle,1 for Rancho Seco. The specimens shan be stored until
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the beginning of Cycle 2'to permit reinstan ation after redesign of the
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~. specimen capsula holders..
The addition of a. surveillance requirement.for the~ internal check valves.
to assure that the valves are closed and are free to operate adds a restriction to the' Technical Specifications that did not previously exist.
11a our letter'to the licensee dated March 10, 1975, we. included our evaluation-
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of B&W internal vent valve test results and operating experience. We concluded that " sufficient-assurance exists that reactor internal vent valves are not opening -in operating reactors and that' the possibility of a stuck open vent valve is acceptably low.
To further minimize the probability of'such an occurrenei we specified~the surveillance testing included in this Technical
- Specifice an change. This surveillance testing requirement replaces the'use of thermocouples -(which have now been: removed) to-confirm the closure of the internal' vent valves. JOther B&W reactors do not have internal vent valve thermocouples; nor do we, require.them'now for newly licensed plants. We conclude that the : assurance thae the internal vent valves will remair closed during' reactor i.
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4-operation is not significantly decreased by the substitution of the new surveillance Because the assurance
.requirecents'for internal vent valve thermocouple monitoring.
that the internal vent valves will remain closed during reactor operation is not significantly decreased, there is no significant increase in'the probability or Based on consequence of an accident or significant decrease in the safety margin.
~the above,'there is no significant hazards consideration.
We have also eliminated the surveillance capsule removal schedule
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from section'3.1.2.7 of the Technical Specifications, because the same schedule appears as Teble 4.2-1.
This. change-merely removes redundancy.
We have determined that this 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 impa,ct. Having made this determination, we have further concluded that this amendment involves an.
action which is insignificant from the standpoint of environmental impact and pursuant to 10 CFR 851.5(d)(4) that an environmental statement, negative declaration, or environmental impact appraisal need not be prepared in connection with the issuance of this amenduent.
CONCLUSION We have concluded, based on the considerations discussed above, that:
(1) because the change 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 change does not involve a significant hazards consideration, (2) there is reasonabic assurance that the health and safety of the public will not be endangered by operation in the proposed manner, and (3) s.uch activities will be conducted'in compliance with the Cecmission's regulations and the issuance of this amendment will not be inimical to the common defense and security o,r to the health and safety of the public.
Dated: August 13, i976 l
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