ML20237D078
| ML20237D078 | |
| Person / Time | |
|---|---|
| Issue date: | 08/04/1987 |
| From: | Stello V NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | Kerr W Advisory Committee on Reactor Safeguards |
| Shared Package | |
| ML20235V501 | List: |
| References | |
| ACRS-GENERAL, NUDOCS 8712230034 | |
| Download: ML20237D078 (5) | |
Text
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EDo 0 0 A35 C
AUG 0 4 W MEMORANDUM FOR:
Dr. William Kerr, Chairman Advisory Committee on Reactor Safeguards FROM:
Victor Stello, Jr.
Executive Director for Operations
SUBJECT:
ACRS COMMENTS ON THE EMBRITTLEMENT OF STRUCTURAL STEEL Your letter of July 15 on low temperature low-dose-rate irradiation of reactor structural steels correctly focused on the important issue emanating from the HFIR study that applies to. operating comercial LWRs.
That issue is whether the appearance of a dose rate effect for low temperature irradiation translates to a possible unexpected increase in the embrittlement of reactor vessel support structures (RVSS) that could pose a problem for safe continued operation of LWRs.
We have therefore initiated actions to assemble information and make such analyses as necessary to make this assessment.
The
. essential elements of the effort are shown in the enclosure.
We have assigned the Heavy Section Steel Technology Program staff at Oak Ridge overall responsibility for the work, with important contributions to be provided by Argonne National Laboratory in the determination of. mechanical properties of
.the Shippingport reactor neutron shield tank.
Within NRC, the Office of Nuclear Regulatory Research will manage the effort.
Oak Ridge believes that they can provide us with an initial response on the analysis portion of the work by September 4, with a more complete response by the end of September.
We are proceeding to obtain material from the Shippingport reactor shield tank for validation as. rapidly as the operations schedules at the reactor site will allow.
Presently, we believe that it will require several additional months to gain access to the reactor and retrieve the material for machining and testing.
Thus, the validation part of the effort could be delayed until the end of the year.
In summary all the issues raised in your letter will be considered in the conduct of this safety assessment.
I will be in direct communication with you concerning the results of the work.
Your letter helps to focus some assessments currently being made by the staff on embrittlement characteristics of those materials for aging and for extended service life. While we have been aware for many years of the higher embrittle-ment for steels irradiated at lower temperatures as was the HFIR vessel, it is only more recently that we have also begun to observe higher rates of embrittlement for vessel steels irradiated for longer times at lower dose rates.
For example, only power reactor surveillance data are now being proposed as the basis for trend curves in Regulatory Guide 1.99, Revision 2 " Radiation Embrittlement of Reactor Vessel Materials" because they are a distinct body of data separate from test reactor data, and because they show more embrittlement than the test reactor data.
Also, data obtained to date from the cooperative 1
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Dr. William Kerr l.
i program with the - MPA-Stuttgart in the Federal Republic of Germany on the Gundremmingen reactor vessel material also show somewhat more embrittlement than would be expected for the fluence received.
As you well know, the staff is actively engaged in preparing for evaluation of L
applications for significant extension of operating life beyond the original 40 year license period.
One of the most important aspects of that evaluation is radiation embrittlement of the reactor vessel and other components subject to neutron flux during service.
Because of the recent information suggesting the low-flux-induced dose-rate effect, this' will be studied much more intent?y and incorporated into aging and extended plant life evaluations.
I Original signed by yictpIStello Victor Stello, Jr.
Executive Director for Operations DISTRIBUTION:
(KerrLtr)
RES Circ /Chron MEB r/f, s/f ED0 003025 JMTaylor TARehm HLThompson
.TEMurley ELJordan ESBeckjord DFRoss GAArlotto RJBosnak CZSerpan RES-87-0525 i
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RES:MEB RES:DD/DE CZSerpan:h RJBosnak rlotto DFRoss ESBeckjord 7/24/87 7/ /87 87 7/ /87 7/3l/87 7/
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RADIATION EFFECTS ON REACTOR VESSEL SUPPORT STRUCTURES (RVSS) i Objective:
To make a rapid assessment if there is a safety problem with RVSS subject to neutron radiation in consideration of a dose rate effect and low temperature irradiation.
Technical Issues:
Flux and fluence in RVSS areas currently and at E0L Materials and mechanical properties of RVSS Embrittlement trends of RVSS materialc Estimated dose rate effect and application to RVSS embrittlement trend.
Stresses and loadings on RVSS in normal operation and accidents Consequence to safety and safe shutdown of brittle failure of RVSS Experimental Validation:
i Measure embrittlement of Shippingport shield tank material Absolute NDT temperature Transition temperature increase (using exterior tank material for reference)
Identify material composition and detailed chemistry Determine fluence, flux and exposure history Assure irradiation temperature Iritegration and Assessment:
Combine material embrittlement trends with accident loadings to predict possible fracture of RVSS, and determine if such failure has an impact i
on safety and safe shutdown. Validate calculations and predictions using Shippingport material and data.
Initial Technical Assessment - ORNL September 4, 1987 Final Technical Assessment September 30, 1987 ANL December 31, 1987 Shippingport Validation Data 1
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EDO PRINCIPAL CORRESPONDENCE CONTROL FROM DUE:
EDO CONTROL: 003025 DOC DT: 07/15/87 5
WILLIAM KERR FINAL REPLY:
ACRS TO:
STELLO l
FOR SIGNATURE OF OREEN SECY NO:
EXECUTIVE DIRECTOR DESC:
ROUTING:
ACRS COMMENTS ON THE EMBRITTLEMENT OF STRUCTURAL STELLO STEEL TAYLOR REHM DATE: 07/17/87 THOMPSON ASSIGNED TO: RES CONTACT: BECKJORD MURLEY JORDAN CFILES SPECIAL INSTRUCTIONS OR REMARKS:
FOR APPROPRIATE ACTION b
OFFICE OF THE SECRETARY CORRESPONDENCE CONTROL TICKET
-C PAPER NUMBER:
CRC-87-0842 LOGGING DATE: Jul 16 87 u
ACTION OFFICE:
EDO AUTHOR:
W. Kerr AFFILIATION:
ACRS (ADVISORY COMMITTEE ON REACTOR SAFEGUARDS)
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LETTER DATE:
Jul 15 87 FILE CODE: O&M-7 ACRS
SUBJECT:
ACRS comments on the embrittlement of structural steel ACTION:
Appropriate DISTRIBUTION:
RF SPECIAL HANDLING: None NOTES:
DATE DUE:
SIGNATURE:
DATE SIGNED:
AFFILIATION:
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