ML19257B069
| ML19257B069 | |
| Person / Time | |
|---|---|
| Issue date: | 09/14/1978 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19257B062 | List: |
| References | |
| REF-GTECI-B-48, REF-GTECI-CR, TASK-B-48, TASK-OR NUDOCS 8001150185 | |
| Download: ML19257B069 (4) | |
Text
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CATEGORY B TECHNICAL ACTIVITY
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TASK ACTION PLAN
Title:
BWR Control Rod Drive Mechanical Failures (B 48)
Lead Responsibility:
Division of Operating Reactors Lead Branch Chief:
L. C. Shao, Chief Engineering Branch, D0R Task Manager:
Kahtan N. Jabbour, DDR John J. Zudans 1.
Problem Description Surface cracks were discovered,in some control rod drive internal parts, at some of General Electric's BWR plants.
The cracking, although only observed to be local at present, could eventually cause a failure of the control rod drive to function.
The internal parts where cracking was identified were the collit retaining tube (CRT), the piston tube, and the index tube.
The cracking in the collet retaining tube were located near a change in tube thickness approximately six inches down the tube.
The cracks appear to have initiated on the outer tube surface and extend circumferentially in the areas between the flow holes of the tube.
The cracking in the index and piston tubes occur in the creviced, sensitized and non-nitrided threaded areas of these tubes.
The extent of the cracking, observed at the G.E. plants at the present time, is not sufficient to impair the ability of the control rod drives to operate in their required capacity.
However, further investigation of the cracking phenomenon and an evaluation of the proposed CRD modifications are necessary to insure safe operation of y
all the affected plants.
2.
Plan for problem Resciution G.E.'s analysis and :esting, at present, indicates that the probable causes of the cracking phenomenon are high thermally induced cyclic 1750 048 s 0 011 s o Jg5~~~
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' stresses in parts that are sensitized by nitriding and exposed to an environment which is conducivc to intergranular stress corrosion.
A report submitted by G.E. which discusses this mechanism for cracking and presents some test results is currently under review by the staff.
G.E. is currently investigating a new design O r the CRT. This new design includes elimination of the change in tube thickness section by redesigning the tube into two parts, consideration of new materials and, by handfacing the interior surface, using Colmonoy instead of nitriting. Testing of this new design is presently in work.
G.E. is investigating the use of NHRONIC-50 (xm-19), which is a stabilited austenitic stainle:,s steel, as an alternative material in portions of the index and piston tubes.
Improved water quality and reduced stress levels at critical areas are also being considered as alternatives or supplements.
The tasks that are needed to be completed for the resolution of this generic issue are:
2.1 Operating Plant Related Problem 2.1.a Inservice Surveillance and Test Requirements - review the current inservice surveillance and testing requirements, and determine the extent to which they are adequate in revealing the existence of cracking.
2.1. b Test and Analysis - perform confirmatory tests and analytical investigation of cracking due to thermally induced stresses on existing design and/or proposec modifications.
Evaluate the influence of water quality in, arresting crack growth.
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2.1.c Material Suitability - evaluate the suitability of proposed metals, and processes for hardening and treating of free surfaces in arresting crack growth.
2.1.d Recommended Staff Position - evaluate proposed modifications of CRD mechanism for operating plants, and recomend the staff position.
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2.2 New Plants Test and Analysis - perform confirmatory tests and analytical 2.2.a investigation of cracking due to thermally induced stresses on proposed new deign.
Evaluate the influence of water quality in preventing cracks.
Material Suitability - evaluate the suitability of proposed metal 2.2.b and processes for hardening and treating of free surfaces in-preventing cracks.
Recommended Staff Position - develop criteria for the staff review T 2.c and acceptance of CRD mechanism for new plants.
2.3 Staff Position on BWR CRD Hechanism Combine and coordinate the end products of tasks 2.1.d and 2.2.c into the recommended staff positions.
3.
NRR Technical Oraanizations Involved Engineering Branch, Division of Operating Reactors, has the A.
overall lead responsibility in the replacement or modifications of the CRD's in operating plants. The immediate safety impact of this problem is in operating plants, but a coordination effort with DSS is required to reflect the design changes in all C.P.
and 0.L. applications.
Manpower Estimates:
.1 manyears FY 77
.1 manyears FY 78
.1 manyears FY 79 Materials Engineering Branch, Mettallurgy Section will coordinate B.
with the Engineering Branch in order to maintain current status s
with the program objectives.
Manpower Estimates:
.1 manyears FY 77
.1 manyears FY 78
.1 manyears FY 79 Technical Assistance Requirements Technical assistance may be needed to help in the review of the analysis prepared and submitted by G.E.
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. 1. Contractor: Has not been selected.
Funds Required
$50k FY 78-79 5.
Interaction with Outside Oraanizations Interaction is required with General Electric Company.
6.
Assistance Requirements from Other NRR Offices Norie required.
7.
Schedule for Problem Resolution Task Completion 2.1. a June,1978 2.1.b December,1978 2.1.c November,1978
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2.1.d January,1979 2.2.a February,1979 2.2.b March,1979 2.2.c April,1979 2.3 July,1979 Potential Problems The progress of this task is very much dependent on cooperation from General Electric Company.
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