ML19257B038
| ML19257B038 | |
| Person / Time | |
|---|---|
| Issue date: | 09/20/1978 |
| From: | Ippolito T Office of Nuclear Reactor Regulation |
| To: | Sherwood G GENERAL ELECTRIC CO. |
| Shared Package | |
| ML19257B035 | List: |
| References | |
| REF-GTECI-B-48, REF-GTECI-CR, TASK-B-48, TASK-OR NUDOCS 8001150135 | |
| Download: ML19257B038 (2) | |
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Appendix C I
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UNITED STATES NUCLEAR REGULATORY COMMISslON y
, j,,j WASHINGTON. D. C. 20555 l.
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$EPTEMBER 2 0 9 I
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l General Electric Company i
ATTN: Dr. G. G. Sherwood, Manager Safety & Licensing 175 Curtner Avenue
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San Jose, California 95114 Gentlemen:
REFERENCES:
1.
Letter, R. L. Gridley to L. C. Shao, dated May 8,1978 2.
Letter, H. T. Watanabe to G. Lear, dated June 2,1978
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" Collet Retainer Tube Design Modification Development",
General Electric Report NEDE-24004 (Proprietary),
June 1977 i;
4.
"XH-19 Materials Qualification", General Electric Report NEDE-21653 (Proprietary), July 1977
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- 5. ' CRD Components program", General Electric Report NEDO-21809 (Hon-proprietary), March 1978 j
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In Refirences 1 and 2, the General Electric Company (GE) has requested that'NRC review the reports listed in References 3, 4 and 5.
These l
reports describe the design modification development program for the The modification upgrading of Control Rod Drive ~ (CRD) components.
development program is being perfomed by GE to resolve the cracking problem of CRD components such as the collet retainer tube (CRT).
1 GE further requested that NRC send a letter notifying GE of NRC agree-ment with the GE program to resolve the control rod drive collet retainer I
tube, index tube, and piston tube materials degradation problems.
The program description includes (a) reports of investigations to determine the causes of the observed cracking, (b) a desription of the design and function of the CRT, (c) a failure consequence analysis of the CRT, (d) descriptions of component design modifications, (3) supporting materials and process qualification programs, and (f) the qualification testing performed to support the modifications.
GE concluded that the cracking which occurred in components of the CR0 fabricated from wrought Type 304 stainless steel with nitrided surfaces was due to the susceptibility of the material to intergranular stress corrosion cracking (IGSCC) in crevice areas.
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General Electric Company GE further concluded that ASTM A-351CF-3 and XM-19 alloys are more suitable materials for use in the CRT, index tube, and piston' tubes of GE CRD mechanisms.
The Engineering Branch, DOR and the Materials Engineering Branch, DSS with their consultants have reviewed the reports listed as References 3, 4 and 5.
We. agree that the development and test data submitted by GE supports the conclusion that the use of these alloys will be an improve-We agree that ment over the use of unstabilized austenitic Type 304 SS.
the use of these materials is appropriate for the CRD modification in the BWR 4, 5 and 6 designs. The data indicate that the A-351CF-3 modified CRT has a greater resistance to crevice corrosion and can withstand service conditions which caused SCC failures in the 304 SS. The XM-19 --
alloy has higher strength combined with greater resistance to sensitization and IGSCC than 304 SS.
We find that the data supporting the GE conclusion provides reasonable I,
assurance that cracking in the modified CRD mechanism components will not.
We further find that' the continuing peridic surveillance program occur.
proposed by GE in order to cetect failed parts will provide assurance of 2the continuing integrity of the CRD mechanism components such as the CRT, index tube, and piston tube.
On the basis of the foregoing considerations, NRC will accept the development data and program reports as supporting documentation for the l
licensing of plants and continued operation of plants with modified CRDs.
tl A Licensing Topical Report (LTR) is not necessary for a generic NRC gl approval.
I Should you have any questions regarding this matter, please contact us.
Sincerely, bl
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&.Ippolito, Chief f
Thomas Operating Reactors Branch #3 Division of Operating Reactors l
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