ML20084N257
| ML20084N257 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Nine Mile Point |
| Issue date: | 05/26/1983 |
| From: | Knight J Office of Nuclear Reactor Regulation |
| To: | Lainas G Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20083L677 | List: |
| References | |
| FOIA-84-14 TAC-51434, NUDOCS 8306030079 | |
| Download: ML20084N257 (3) | |
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ATTACHMENT INTRODUCTION As a result of cracks found in the reactor nozzle safe ends and the recirculation system piping at Nine Mile Point Unit 1 (NMP1), the licensee has repaired and replaced all safe ends and recirculation piping.
As part of the restart requirements, a stress analysis of the recirculation system piping has been cortpleted by the licensee. The nozzle safe ends and attached elbows were removed and replaced by the Newport News Industrial Corporation (NNI). The stresses in the recirculation system piping were reanalyzed by the Teledyne Engineering Services (TES).
Niagara Mohawk Power Corporation submitted reports from both contractors on April 22, 1983.
DESCRIPTION AND DISCUSSION The purpose of the stress reanalysis was to show that the NMP1 repaired reactor recirculation system piping satisfies the requirements of the 1977 ASME B&PV Code, Section 111, Subsection NC with all addenda through Winter 1979.
This plant was originally designed to the B31.1 Code.
The recirculation system consists of five loops numbered 11 through 15 and similar in all respects except for the branch piping arrangements.
Of the five, loop 12 has no significant branch piping, and loop If has the largest dianeter branch piping.
For stress analysis purposes, these two loops were selected to represent bounding cases for all five loops.
Branch lines were modeled as part of the loop and were analyzed up to the first respective anchor points.
Thermal loads, deadweight, preesure, seismic and cold spring during irstallation were all accounted for in the analysis.
The resulting stresses in both loops were within the allowable design and limits. ASME SA358 Grade 316, " Nuclear Grade",
meeting the special requirements of SA655 piping with 0.02*. maximum a
carbon content and 0.10 maximum nitrogen content, was used for the replacement. A low carbon content (
0.0357) also prevents the occurrance of intergranular stress corrosion c-acking.
An output of the piping system analysis is support loading and component nozzle loading.
Using these loads, stresses at supports were also analyzed. When the j
loads changed significantly from the oriqinal analysis, they were reevaluated. When the loads were essentially the same, no additional analysis was performed.
For all reevaluations, analyses results were all within the allowable (cde stross design limits and the displacement design limits.
The repair and replacement work perforr'ed by NN! was in accordance with the requirec;ents of ASf'E MPV Cod. rection l'!.
The work was done according to an approved procedure by a qualified weld method, followed (l
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2 by a post weld heat treatment, and then restored to the before r?poir dimensional condition. Thermal stress analysis indicated that stress levels never exceeded allowabie limits during the repair.
Radiographic inspection (RT) performed on the repaired area revealed no rejectable defects.
Following the completion of the reinstallation, TES perforned an as-built w61kdown of the recirculation system and its attached pipine No significant discrepancies were noted.
CONCLUSION The techr.ical reports prepared by NNI and TES verified that the construction of the NMP1 reactor recirculation system piping was according to the 1977 ASME B&PV Ccde 'ection III, Subsection NC and addenda through 1979.
Since all stress levels were within design limits and PT did not reveal any rejectable defects, the staff concludes that the repair has been satisfactorily completed and reconmends that the restart of NMP1 power operation be pernitted.
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