ML17158B788
| ML17158B788 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 09/06/1996 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML17158B787 | List: |
| References | |
| NUDOCS 9609120199 | |
| Download: ML17158B788 (2) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 RE VEST TO USE ALTERNATIVE MAT RIALS IN THE CONTROL ROD DRIVE HYDRAULIC SYSTEM PENNSYLVANIA POWER AND LIGHT COMPANY SUS UEHANNA STEAM ELECTRIC STATION UNITS 1
AND 2 DOCKET NOS. 50-387 AND 50-388 O $
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION
- 1. 0 INTRODUCTION By letter dated April 29,
- 1996, Pennsylvania Power and Light Company, the
- licensee, requested approval under the provisions of 10 CFR 50.55a(a)(3) to use American Society of Mechanical Engineers Pressure Vessel Code (ASME Code),
Section III, Code Case N-71-16 for the Control Rod Drive Hydraulic System (CRDHS) at the Susquehanna Steam Electric Station, Units 1 and 2.
The CRDHS for Susquehanna was constructed in accordance with ASME Section III 1974 Edition with Addenda through Winter 1975.
The later requirements of Subarticle NF-2610 from the 1977 Edition with Addenda through Winter 1977 and Code Case 1644-8 apply to piping system supports.
The piping supports for the insert and withdrawal lines in,the plant utilize Unistrut 'channel aTId pipe straps.
Code Case N-71-16 is proposed to be used to procure Unistrut pipe straps made from American Society for Testing and Materials (ASTM) A 570 Grade 33 material.
Grade 33 material 'is now the manufacturer's current standard material for the pipe straps.
In the past, Uniskruk used Grade 36 as the standard strap material.
Until recently, the licensee had been able to procure Grade 36 material straps from stock, but they are no longer able to do so.
Without the use of the Code Case N-71-16, the straps would have to be specially procured and fabricated using Grade 36 material.
2.0 DISCUSSION The original design of the system utilized ASTM A 570 Grade C material for pipe straps, as permitted by ASME Code Case 1644-8, which was approved by the NRC.
A minimum Yield Strength of 33 ksi and an Ultimate Tensile Strength of 52 ksi was specified.
In the 1978 version of ASTM A 570, the letter grades were changed to number grades;
- however, Grade 33 material was not included.
The ASTM Specification was written so as to permit the use of Grade 36 material as a replacement for Grade C material.
The following year, A 570 was again revised and this time Grade 33 material was included.
However, the ASME Code Case was not changed to reflect this until the N-71-16 version.
9609120199
'M0906 PDR ADCICK 05000387 P
A 570 Grade 33 material-is identical to A 570 Grade C material from the earlier editions of the ASTM.specification, except for the specified manganese and sulfur content.
Grade C material had manganese specified at 0.25X to 0.60X and maximum sulfur specified at 0.04X, while the proposed alternate Grade 33 material is specified to have a maximum content of 0.90X for manganese and 0.05X for sulfur.
Both Grade C material and Grade 33 material are specified to have 33 ksi minimum Yield Strength and 52 ksi minimum Ultimate Tensile Strength.
The use of Grade 33 Material meets the original design basis of the piping supports.
The increase in the maximum permitted manganese content from 0.60X to 0.90X could only be beneficial.
The staff has evaluated the change in the increased maximum limit on sulfur from 0.04X to 0.05X and finds that any metallurgical effect of the change on weldability would be acceptable because the Code Case restricts welding to materials containing a maximum of 0.35X carbon, requires weld procedure qualifications, and welder qualification in accordance with Subsubarticle NF-4320 of the Code.
The additional requirements of the Code Case will apply to the use of this material and ensure that the material will not be used without all applicable Code requirements.
3.0 CONCLUSION
The staff concludes that based upon the available technical
- evidence, the use of Grade 33 material in this application is an acceptable substitute for Grade 36 material on the basis that such use does not adversely effect the safe operation of the CRDHS.
Additionally, the staff finds that the Code Case appropriately identifies and classifies the material with respect to the original design basis for the pipe straps for the CRDHS for Susquehanna Steam Electric Station.
The use of Code Case N-71-16, would thereby eliminate any hardship or unusual difficulty that might be imposed on the licensee by the requirement for special procurement of Grade 36 material under the previously
.authorized Code Case.
The staff further finds that the requirement to use the Grade 36 material would not result in any compensating increase in quality or safety.
The staff has reviewed the request and supporting information and concludes that the use of the subject Code Case as an alternative to ASME Code requirements provides an acceptable level of quality and safety and is, therefore, authorized under the provisions of 10 CFR 50.55a(a)(3)(i).
Principal Contributor: H.'. Conrad Date:
September 6, 1996
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