ML20058D688
| ML20058D688 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 11/23/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20058D693 | List: |
| References | |
| NUDOCS 9312030268 | |
| Download: ML20058D688 (3) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RE0 VEST FOR AUTHORIZATION TO USE ASME CODE CASE N-516 FOR USE IN UNDERWATER WELDING CLINTON POWER STATION. UNIT I DOCKET NO. 50-461
1.0 BACKGROUND
During the current refueling outage, and while investigating the results obtained from an inspection recently performed on piping supports associated with the "A" and "B" loops of the Residual Heat Removal (RHR) system, a design deficiency in the piping supports was identified. These supports are for the RHR full flow test return lines and are physically located inside containment in the suppression pool.
It has been determined by the licensee that the support design is deficient due to a misapplied structural section modulus equation such that the actual stresses in the support structure would be higher than originally predicted.
The proposed modification to reduce these stresses would require welding of steel support plates to the existing piping support structures.
Repair of components within the scope of the American Society of Mechanical Engineers (ASME),Section XI, must be performed in accordance with Section XI Article IWA-4000.
Per Article IWA-4300, welding must be performed in accordance with the requirements of ASME,Section IX, and the additional requirements of Sections III and XI. However,Section IX does not address underwater welding.
The licensee considered several options to lower the suppression pool level in order to expose the piping supports.
The suppression pool level would have to be reduced approximately four feet which would correspond to 250,000 gallons of water. The first option considered was to drain the suppression pool and temporarily store the water.
Storage was not considered feasible due to limited available storage facilities and the resulting impact on ongoing work ass 0ciated with the refueling outage. The second option considered was to discharge the water to the environment and process new water.
This option would involve an unnecessary release to the environment and would require a lengthy evolution that would adversely impact the outage schedule. The third option involved constructing a coffer dam to displace water immediately around t'
pipe support structure. This nption was rejected due to the time net.essary to design and install t % dam, difficulties anticipated in overcoming pool buoyant forces, attaching the dam, and working within limited clearances. The final option was to perform underwater welding.
9312030268 931123 PDR ADOCK 05000461 p
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i ASME,Section XI, Code Case N-516, specifically addresses underwater welding to facilitate repairs of P-8 materials (of which the RHR supports are constructed) and was approved by the ASME Code Case Committee on August 9, 1993. While the Code Case has been approved by the ASME, it does not appear i
in the most recent listing of NRC approved Code Cases in Regulatory Guide l.85, " Materials Code Case Acceptability - ASME Section III Division 1,"
l Revision 29.
The licensee's letter of November 4, 1993, requested authorization, pursuant to 10 CFR 50.55a(a)(3), to use ASME,Section XI, Code Case N-516. While the licensee's letter focused on the RHR piping supports described above, the 1
licensee stated that their investigation was ongoing and requested t
authorization to apply the Code Case to other supports located in the t
suppression pool if it is determined that the design deficiency exists and underwater repairs are required for those supports as well.
2.0 EVALUATION The Code Case addresses controls (in addition to ASME Section IX) for welding procedure qualifications and welder performance qualifications. During discussions with the licensee, the staff has been informed that the welders will be qualified to plate positions 1G, 2G, 3G, and 4G in order to perform i
the fillet welds as specified by Table 2.1-2 of the Code Case.
The Code Case also requires each filler metal heat, lot, waterproof coating type, and r
supplementary coating type to be tested and a confirmatory weld to be done in the same or similar underwater conditions to confirm the ability to achieve the proper weld quality.
Further, the Code case provides alternative examination procedures for those instances in which the procedures required by Section XI would be impractical. The staff has reviewed the Code Case and concludes that the controls stated above, particular1; the requirement to i
perform a confirmatory weld, provides adequate assurance of welds performed under water and provides an acceptable level of quality and safety.
l The staff has reviewed the Code Case and finds it acceptable for this specific application. The staff has inspected welds performed underwater and concludes that satisfactory results can be attained using Code Case N-516.
3.0 CONCLUSION
The staff has determined that use of Code Case N-516 is acceptable for use by the Clinton Power Station for this specific refueling outage.
Relief is authorized pursuant to 10 CFR 50.55a(a)(3)(1), as the proposed alternative provides an acceptable level of quality and safety. The Code Case use is provided for the RHR system modifications and may be extended to other piping supports of this type located in the suppression pool.
Use of this Code Case is restricted to piping support applications described in the licensee's letter of November 4, 1993.
Principle Contributor:
D. Pickett Date: November 13, 1993 i
i f
-Mr. Richard F. Phares November 23, 1993 r
other supports of this type located in the suppression pool, and (3) l authorization is limited to piping supports as described in your letter and may not be extended to other applications.
A copy of our Safety Evaluation is enclosed.
j i
Original signed by I
George F. Dick for-James E. Dyer, Director Project Directorate III-2 Division of Reactor Projects III/IV/V-Office of Nuclear Reactor Regulation
Enclosure:
Safety Evaluation cc w/ enclosure:
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DISTRIBUTION Docket File NRC & Local PDRs PDIII-2 r/f TMurley/FMiraglia LJCallan
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