ML19323G163
| ML19323G163 | |
| Person / Time | |
|---|---|
| Site: | Pilgrim |
| Issue date: | 05/20/1980 |
| From: | Prior J FRANKLIN INSTITUTE |
| To: | |
| Shared Package | |
| ML19323G158 | List: |
| References | |
| CON-NRC-03-79-118, CON-NRC-3-79-118 TER-C5257-088, TER-C5257-88, NUDOCS 8005300481 | |
| Download: ML19323G163 (4) | |
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.l REPORT OF TECHNICAL EVALUATION MISCELLANE0US N0ZZLE CRACKING:
PILGRIM STATION, UNIT 1 NRC TAC No. 07064 FRC Task No. 88
- i Prepared by:
J. E. Prior Performing Organization Franklin Research Center
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The Parkway at Twentieth Street FRC Project No.
l Philadelphia, PA 19130 C5257 i
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i Sponsoring Agency Nuclear Regulatory Commission NRC Contract No.
J Washington, D.C.
20555 NRC-03-79-118 i
This report was prepared as an account of work sponsored by an agency of the United States a
Government. Neither the United States Govern-ment not any agency thereof, or any of their employees, makes any warranty, expressed or implied, i
j or assumes any legal liability or responsibility for any third party's use, or the results of such use, of any information, apparatus, product or prn ;ss disclosed in this report, or represents I
that its use by such third party would not infringe privately owned rights.
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REPORT OF TECHNICAL EVALUATION i
UNIT: PILGRIM STATION, UNIT 1 LICENSEE: BOSTON EDISON COMPANY
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DOCKET NO. 50-293 TAC NO. 07064 1.
SUMMARY
As a result of ultrasonic testing (UT) in 1974, reportable cracks were detected in Nozzles N2B and N4A of the reactor vessel at Pilgrim Station, Unit 1.
These defects were monitored by UT in 1976 and again in 1977. Based upon an g
evaluation of these data, it is, concluded that Nozzles H2B and N4A are acceptable for continued operation and that:
.j e Nozzle N2B should be monitored by UT at subsequent refueling
- I outages to ensure that crack growth has not occurred.
4 4 e Nozzle N4A may be returned to a normal In-Service Inspection (ISI) schedule.
2.
INTRODUCTION The results of the 1977 UT ernmination of the N2B recirculation inlet nozzle-to-shell weld and the N4A feedwater-nozzle-to-shell weld in the Pilgrim Station i
i Unit 1 reactor pressure vessel were submitted to the NRC for review. The object of this FRC Technical Evaluation is to assess the adequacy of these welds with respect to their continued use and return to the normal ISI schedule. The review is confined to the issue of the pressure-boundary integrity as influenced by nozzle-weld cracking.
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BACKGROUND Experience has shown that cracks have occasionally been detected in nozzle welds in boiling water reactor (BWR) pressure vessels.
In 1974 and 1976, UT inspection revealed indications in nozzle-to-shell welds in Nozzles N2B and N4A at Pilgrim Station, Unit 1.
Due to changes in inspection requirements, a cali-bration block, fabricated from a prolongation of the actual pressure-vessel plate, was used in 1976 to ensure more accurate and reliable UT results. The i
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4 calibration block used in 1974 wa's made 6f a material of similar class but not i
of actual vessel material. A review by an independent consultant of the UT
'f, data taken in 1974 and 1976 concluded that:
.l The change in calibration blocks reduces the gain setting I
of the ultrasonic instruments substantially. This results in a reduction of the reported size of the flaw due to the reporting procedure required by the applicable ASME Codes.
The reported apparent size of the flaw at a single location would be about four times less than the 1.5 inches if the lower instrument gain were used.
Because of the instrument recalibration, indications of flaws found,in Nozzle N4A were so reduced in size in the 1976 inspection that they were charac-r I
terized as not reportable. The flaw in the Nozzle N2B weld was found to be of
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- l reportable size in the 1976 inspection; however, it was deternined that no flaw l
growth had occurred. A review by an independent consultant also concurred that
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no growth was evident in the flav of the Nozzle N2B weldment between 1974 and i :l 1976.
Unfortunately, the dedicated transducers used in the 1976' inspection could not be located and, therefore, were not usea in the 1977 incoection. Transducers i
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with similar. characteristics were utilized.
Calibration Block PIL-5A, used in 1976, was available and was used in the 1977 inspection.
4.
TECHNICAL EVALUATION 4.1 RECIRCULATION INLET N0ZZLE N2B l
UT inspection of the N2B nozzle-to-shell weld was conducted by Southwest Research Institute (SWRI) during the August to November refueling outage in 1977.
!j It was concluded that no significant flaw growth had occurred in the weldment between the 1976 and 1977 examination of Nozzle N23. A review of the data by an H
independent consultant (Sandia Laboratories) concurred that no change in flaw size had occurred.
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In 1976,it was established through fracture-mechanics analysis that a con-servative, maximum, acceptable through-wall dimension at the flaw location would j
be 2.5 inches.
Since the maxinem flaw size measured by UT examination was 1.5 inches in through-wall dimension--considerably less than the calculated acceptable s
size--Nozzle N2B was acceptable for continued operation at that time.
Therefore, I t l
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o since no crack growth occurred between 1976 and 1977, Nozzle N2B is still acceptable for continued operation.
4.2 FEEDWATER N0ZZLE N4A-i A review of tae results of the 1976 inspection of N4A feedwater-nozzle-to-shell weld shows that some indications were detected but no reportable flaw indications were found.
It ahould be noted that no flaw indication of any kind was locat'ed in 1977.
It is apparent that some of the confusion arising during the 1974 and 1976 inspections of tnis weldment was caused by inadequate baseline data and a change in calibration blocks.
Since no reportable indications were l
found in the weld in 1976 and no flaw indication whatever was located in 1977, Nozzle N4A can be returned to the normal ISI schedule.
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5.
CONCLUSION It is concluded that the Recirculation Inlet Nozzle N2B is acceptable for continued operation,since no indication of crack growth was found between the 1976 and 1977 inspections. UT examination should be conducted on the Nozzle N2B weld during the next refueling outage using the results of the 1976 inspection as baseline data. Monitoring the weld cracking will ensure that crack dimensions remain within the limits of the allowable flaw size established by Section XI of l
the ASME code.
Should crack growth be indicated in the Nozzle N2B weld during
.l the next scheduled inspection, justification must be submitted before continued j
operation is approved.
This UT examination of the 'weldment is not intended to j
supplant the regularly scheduled ISI program. Additionally, the licensee should
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submit for approval, a continuing inspection program to monitor Nozzle N23.
i No evidence of flaw indications was noted during the examination of Feed-water Nozzle N4A in 1977.
It is, therefore, concluded that this nozzle is adequate for continued service and that it may be returned to the normal ISI schedule.
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