ML19322B387
| ML19322B387 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 03/26/1976 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19322B374 | List: |
| References | |
| NUDOCS 7912020235 | |
| Download: ML19322B387 (4) | |
Text
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UNITO STATES t
NUCLEAR REGULATORY COMMISSION WASHINGTON. D. C. 20SS5 f'.FETYEVALUATIONBhTHEOFFICEOFNUCLEARREAC'IDRREGULATION SUPPORTING AMENDMENT NO. 21 "!D FACILITY LICENSE. NO. DPR-38 SUPPORTING AMENDMENT NO. 21 TO FACILITY LICENSE NO. DPR-47 SUPPORTING AMENDMENT NO. 18 TO FACILITY LICENSE NO. DPR-SS DUKE POWER COMPANY
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OCONEE NUCLEAR STATION, UNITS 1, 2, AND 3
_ DOCKET NOS. S0-269, 50'270, AND 50-287 Introduction By letter dated March 16, 1976, Duke Power Company (the licensee) requested an exemption from the requirements of 10 CFR Part 50, Appendix H.Section II.C.2 to permit the operation of Oconee Unit 1, Cycle 3 with the reactor vessel surve'.11ance capsules removed from the reactor vessel.
The licensee requested corresponding changes to the Technical Specifications appended to Facility Operating Licenses No. DPR-38, DPR-47, and DFR-5S for the Oconee Nuclear Station, Units 1, 2, and 3.
These changes would reflect the removal of the reactor vessel surveillance capsules for Cycle 3 operation and would require the submittal of a revised surveillance capsule withdrawal schedule prior to Cycle 4 operation.
Discussion -
The Oconee Unit I design includes three reactor vessel surveillance capsule holder tubes located adjacent to the reactor vessel inside wall. Each j
i holder tube contains two surveillance capsules which hold the 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 parpose of the surveillance program is to monitor changes in the fracture toughness properties of ferritic materials in the reactor vessel beltline region resulting from.their exposure to neutron irradiation and the thermal environment.
In a recent inspection of the surveillance capsule holder tubes, conducted during the current refueling outage, evidence of wear was observed at several locations witnin the holder tubes. The damage was evidently caused by flow-induced relative motion between the holder tubes and various L
y components of the surveillance capsule train which positions and holds the 1
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surveillance capsules in place during reactor operation. Although there are indications of significant wear, all three holder tubes are intact and the licensee has indicated that the structural integrity has been retained.
To preclude the possibility of additional wear during Cycle 3, the licinsee is proposing' that:
1.
The surveillance capsules and push rod assemblies be removed during Cycle 3 operation, and 2.
The holder tubes be secured from motion by a spring-loaded retaining device, similar to the existing holddown device, which would be loaded into the upper end of each holder tube.
The licensee has indicated that the above propo::ed action would allow time for the engineering of modifications to the holder tube and push rod assembly design and the procurement of material prior to the resumption of the surveillance capsule irradiation program.in Cycle 4.
Evaluation As required by Paragraph II.C.2 of Appendix H to 10 CFR Part 50, the surveillance capsules of Oconee Unit I are positioned during reactor i
operation such 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 vessel inner surface. More specifically, as reported in Babcock and Wilcox Topical Report BAW-10100A. February 1975, the, specimen capsule locations in th'e Unit I reactor vessel provide a neutron flux 2.4 times greater than the inside 1/4 wall thickness (1/4 t) location of,the reactor vessel beltline. The lead factor between the center of the specimens and the 1/4 t vessel wall location is considered when determining the relative fracture toughness properties of the beltline region materials. Cycles 1 and 2 have accumulated 1.64 effective full power years (EFPY) of actual' exposure for an equivalent capsule irradiation of 3.94 EFPY. Cycle 3 operation is planned for 292 EFPD (0.S EFPY) of operation, and therefore of 3.94 EFPY a margin will exist between the present capsule irradiation and the reactor vessel irradiation at the end of Cycle 3 of 2.4 EFPY. The irradiation effects accumulated by the specimens during Cycles 1 and 2 will not be altered and appropriate allowances can be made to revise the capsule withdrawal schedule and thus insure that the required data is obtained.
Based on the above we conclude that the licensee's proposed action to remove the reactor vessel surveillance capsules during Cycle 3 operation will not adversely affect the Unit I surveillance program.
In addition, sufficient data presently exists from the irradiation of specimens during Cycles 1 and 2 to establish a revised withdrawal schedule which will take into account the removal of the specimens during Cycle 3 operation and which will meet the requirement: of 10 CFR Part 50, Appendi,x H.
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_3 tives from Duke Power 23, 1976, with representaf ty implications involved In a meeting held on MarchCompany and Babcock 6 Wilcox, w Of major concern.was the mechanical-in the core after removal with the licensee's proposed action. integrity of the holder tu i
As discussed earlier d assemblies.
internal surfaces of the of the surveillance capsules and push ro b
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areas of significant wear were observed on t eThe wear does pe i
two three tubes at three of four spacer locat ons holder' tubes.
The worst wear involves the loss of material o rod assemblies.circumferencial lengths of approximatelyThe two worn throu We reviewed the stress loadings circumference of about 11".
an undamaged ligament of material.during the Unit 1 Hot Functional Tests A comparison allowable loads.
incurred by the holder tubes h
agree that they are very low compared to t eReport BAW-10039, April 19 of these loads is provided in BAW Topicalwas also performed by the lic i
the as-l ces A fatigue evaluationmeasured strains and included appropriate al owan wear sites on notch effect associated with the d agree We reviewed the results of this evaluation anIcVels cross-sectional area and the holder tubes.
for.the material involved.
that the noximum alternating stresswell below i
d by flow-induced motion between The data presented by BSW and th9 wear incurred on the holder tubes was causeBy removing the surveillanceof wear the holder tubes and push rod assemblies.
the source capsules and push rod assemblies, we agree th h
The spring-loaded retaining device proposed by t eld ~be compressed hield. The spring onto the upper end of each holder tube wou flange as the plenum is lowered into the core support sibration du force would thus prevent holder tube movement or v operation.
fail at one or more of In the unlikely event that the holder. tubes mighti g system would de i
the wear locations, the loose parts mon tor nresultan be taken.
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llow the holder tubes to In view of the above, we consider it acceptable to aCycle 3 operatio remain in the Unit I reactor vessel during removed and the spring-holder tube restraint.
i survelliance capsules and push rod assembl esloa l
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We have determined that these amendments do not authorize a change d will effluent types or total amounts nor an increase in power level anHaving made not rev:lt in any significant environmental impact. determinat l impact action which is insignificant from the standpoint of -environmeta ative and pursuant to 10 CFR ~B51.5(d)(4) that an environmental statement, n declaration, or environmental impact appraisal need not be prepared in connection with the issuance of these amendments.
Conclusion We have concluded, based on the considerations discussed does probability or consequences of accidents previously considered and (1) because the change does not involve a significant decrease in a safety margin, d
d assurance that the health and safety of the public will not be en angered by operation in the proposed manner, and (3) such activities wi in compliance with the Commission's regulations and the issuance of i
to amendments will not be inimical to the common defense and secur ty or the health and safety of the' public.
1 March 26, 1976 Date:
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