ML20072J919
| ML20072J919 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 03/16/1983 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20072J908 | List: |
| References | |
| TAC-49905, NUDOCS 8303300261 | |
| Download: ML20072J919 (7) | |
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UNITED STATES
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NUCLEAR REGUL,ATORY COMMISSION 8
ti r E WASHINGTON. D. C. 20565
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACT _0_R REGULATION SUPPORTING AMENDMENT NO. 83 TO FACILITY OPERATING LICENSE NO. DPR-65 NORTHEAST NUCLEAR ENERGY COMPANY, ET AL.
MILLSTONE NUCLEAR POWER STATION, UNIT NO. 2 DOCKET NO. 50-336 Introduction By letter dated March 14, 1983, Northeast Nuclear Energy Company (NNECO or the licensee) proposed a change to the Technical Specifications (TS) to allow for a one time postponement of the steam generator inspection requirements of Technical Specification 4.4.5.1.3.C.1 regarding unscheduled inspections due to tube leaks until the 1983 refueling outage scheduled for late May 1983.
Dicussion Since April 1982 Millstone Unit 2 steam generators had been operating with slowly increasing primary to secondary leakege which was at 0.286 gpm at the end of February 1983.
On March 1,1983 NNECO initiated a shutdown of Millstone Unit 2 in accordance with Technical Specifi-cation Action Statement 3.4.6.2.b due to unidentified reactor coolant system (RCS) leakage exceeding the Technical Specification limit of 1.0 gpm.
NNECO proceeded with investigations wit.hin the containment to identify and quantify leakage from two valves which, from past inspections, were known to be leaking.
The results of these 4,
investigations, however, were not completely successful as the 88 Lg unidentified portion of the total RCS leakage could not be reduced to within the limits of Technical Specification 3.4.6.2.b.
It was 00 8
decided that an inspection of S.' G. No. I would be conducted to OEQh better quantify the primary to secondary leakage from the steam generators.
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"pon inspection of S. G. No. I with the use of a secondary-to primary side hydrostatic test, leakage from an unplugged steam generator tube was identified. This leakage was quantified to be 0.21 gpm at a differential pressure of 200 psi.
With this information, NNECO per-formed evaluations to determine the amount of primary-to-secondary leakage which would have existed at normal plant operating conditions.
These evaluations were complicated due to the differences which exist between normal plant operating temperatures, pressures and stresses and those which existed at the time of the hydrostatic leak test.
The evaluation is further complicated by the lack of a definitiv charactei-ization of the defect.
Using conservative assumptions regarding the type of defect (i.e., to maximize primary-to-secondary leakage), it has been concluded, that at the time the plant was shut down, the primary-l to-secondary leakage rate in S. G. No.1 exceeded the limits of Technical Specification 3.4.6.2.c (0.5 gpm, in any one steam generator).
The leaking tube was located at Column 120, Row 94 adjacent to a stay 1
rod on the hot leg side of S. G. No. 1 The eddy current inspection l
results for this tube obtained during last year's inspection have been rereviewed and it has been concluded that a defectin excess of the plugging limit existed but was overlooked.
The rereview has quantified the depth of the defect to be approximately 83% through wall.
The defect has been located at the top of the tube sheet, within the limits of eddy l
current accuracy, and coincides with various interferences from the com-l bination of deposits, denting, and tube sheet entry.
. NNECO has performed eddy-current examinations on the tubes adjacent to the defective tube as well as tubes located around another stay rod on the hot leg side of S. G. No. 1.
No other defective tubes have been identified in these inspections.
One potentially degraded tube has been identified (Column 121, Row 93) with an indication of 34%,
although the indict. Lion could also be characterized as coppfr related interference.
NNECO has reviewed last year's eddy-current examination results for those tubes located around all stay rods in the hot leg of S. G. No.1 and has not identified any degraded tubes.
NNECO has also reviewed the eddy-current examination results for randomly selected tubes in the hot leg of S.
G~. No. 1, some of which exhibited a tube sheet dent signal, to ensure that additional defective tubes were not overlooked last year.
The results of this review have not revealed any additional degraded tubes.
Based on the eddy-current and visual inspections conducted on the defective tube, in combination with the destructive and nondestructive examination results obtained during the 1981/1982 refueling outage, the failure mechanism responsible for the leaking tube (120, 94) is most probably due to pitting corrosion.
A boro-scopic examination of the inside 11ameter of the leaking tube revealed that the defect appeared to be two pits joined by a crack.
. NNECO has staked and plugged the defective tube and plugged the tube with the 34% indication.
An inspection of S. G. No. 2 was not performed based on the fact that the reviews of last year's information for S. G. No. 1 has not revealed any additional oversights regarding degraded tubes.
The primary,to-s'econdary leakage rate in S. G. No. 2 corrected to reflect the data obtained from S. G. No. 1;as discussed above, remains well within the Technical Specification limits.
These factors provide substantial assurance that the integrity of S. G. No. 2 will not become unacceptably degraded during the remaining 9 weeks of operation.
NNECO currently intends to undertake several extensive projects related to the stc3m generators at Millstone Unit No. 2 during the upcoming refueling outage.
These projects include decontamination of the primary side of the steam generators, extensive eddy-current and profilometer examinations in both steam generators and an extensive tube sleeving program.
Based on the information obtained to date and presented herein, an eddy-current examination of the steam generators at this time is not considered to be necessary, particu-1 larly when a more extensive program of inspections is planned to i
commence in approximately 9 weeks with the Cycle 6 refueling outage.
Personnel exposures to perform such an examination will be reduced during the outage by the steam generator channel head decontamination program.
Current radiation fields in S. G. No. 1 are on the order of 17 rem / hour.
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Concerning the capability'to measure primary-to-secondary leakage rates in the future, NNECO is' investigating the use of the condenser steam jet air ejector radiation monitors together with revised empirical relationships for the secondary side gross activity measurement tech-1 nique.
The discrepancy between the, primary-to-secondary leakage measurements obtained during operation and'that calculated from actual leak rate measurements obtained during the current outage can be attributed to the difficulty of obtaining a representative secondary side sample of steam generator bull. chemistry to be used for gross activity determinations.
It is NNECO's intention to administratively include an appropriate scaling factor in the primary-to-secondary leak rate' calculation to reflect the data obtained during the current outage and subsequent startup.
These actions will result in more accura,te absolute primary-to-secondary leakage ra',e determinations.
I Evaluation l
l Northeast Nuclear Energy Company's program of hydrostatic leakage r
testing, eddy current and bo oscopic examinations, rereview of eddy l
current inspection tapes from~the last inspection, and tube plugging 1
has provided sufficient verifica ion of the source of the observed leakage and the corrective measures undertaken provide assurabee r
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. against excessive leakage during the proposed 9 additional weeks of operation prior to a full inservice inspection of the steam generators.
However, for future assurance of steam generator tube integrity, the strength of tubes with linkage of individual pits via a crack network shou.; be examined eitiier analytically or experimentally.
t' Conclusion We have concluded that operation of the Millstone 2 steam generators for approximately 9 weeks prior to performing a c'heduled inservice inspection does not represent an undue risk to public health and safety.
Due to uncertainties inherent in primary-to-secondary leak rate measurements, we recommend that the technical specification leak rate limit be decreased from 0.50 gpm to 0.35 gpm per steam generator.
We also find it necessary to de kept informed of the minimum reasonable increase in primary-to-secondary leakage.
To accomplish this, the licensee shall continue per T.S. Table 4.7-2 to I
report within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> any increase of 0.05 gpm or more over the base-line leakage followed by a written report within 14 working day.
The written report will contain the licensee's evaluation of the increased leakage and justification for continued operation. The staff may, after review of these increased leakage reports, take action' as necessary, including o'rdering a reactor shutdown to protect the primary system integri ty.
In addition, the licensee should submit a complete inspection plan for the May 1983 refueling outage 30 days in advance of the outage.
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_7 Enviromental Consideration We have determined that the a..endment does not authorize a changc in effluent types or total amounts nor an increase in power level and will not resuit in any significant environmental impact. Having made this determination, we have further concluded that the amendment involves an action which is insignificant from the standpoint of environmental impact and, pursuant to 10 CFR 551.5(d)(4), that an envh anmental impact statement or negative declaration and environ-mental impact apprr.' al need not be prepared in connection with the issuance of this amendment.
Conclusion We have concluded, based on the considerations discussed above, that:
(1) because the amenunt does not involve a significant increase in the probability or consequences of an accident previously evaluated, does not create the possibility of an accident of a type different from any evaluated previously, and does not involve a cignificant reduction in a margin of safety, 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 c'ompliance 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 an'd i
safety of the public.
I Date: March 16, 1983 Principal Contributors:
Louis Frank Herbert Conrad l