ML20002C740
| ML20002C740 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 04/19/1972 |
| From: | Sewell R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Morris P US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 8101100807 | |
| Download: ML20002C740 (3) | |
Text
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-/i f Dr. Peter A. Morris, Director Re: Docket 50-155 fpgdi$
Division of Reactor Licensing License No DPR-6 United States Atomic Energy 6;
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Dear Dr. Morris:
\\,'y Two auxiliary neutron sources were instalied in the Big Rock Point Plant reactor in February 1971. These neutron sources are a homogeneous 50-50 mixture of antimor.;-beryllium first en-capsulated in a stainless stm tube then secondarily encapsulated in a zirconium-alloy tube.
During the cur: ent refueling outage, a visual inspection of these two auxiliary neutron sources was conductcd. This inspec-tion revealed that the outer zirconium-alloy encapsulation was failed in the area of the lower end-cap weld on both neutron sources.
The failed area had the appearance characteristic of typical hydride attack.
The lower end cap of the outer zircalloy tube was removed from one of the auxiliary neutron sources and the inner stainless steel encapsulation was visually examined. No abnormalities were detected. The inner encapsulation of the second neutron source also will be visually inspected prior to reencapsulation (as described later in this letter).
The outer encapsulation of tilese neutron sources was per-formed by the fabricator of our cobalt target rods. Approlimately h0 percent of the cobalt target rods were visually examined. No deterioration was observed. On the basis of this examination, it was concluded that a generic welding problem does not exist.
It was concluded that the cause of the failure was due to internal contam-ination. Investigation is continuing to determine the source of the contamination.
A new outer encapsulation is being provided for the two auxiliary neutron sources. Zircalloy tubes with the upper end caps velded to the tubing have been obtained. The stainless steel en-capsulated neutron sources will be placed 'n this tubing and a lower b.
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2 Dr. Peter A. Morris
';z.x Docket 50-155, Licensa No DPR-6 April 19, 1972 end cap inserted. Mechanical forces will be utilized to crimp the tubing to the lower end cap.
Because of the radioactivity of the neutron sources, it is impossible to perform this repair in an environment that allows tight moisture control and have the neutron sources available for plant start-up following the current refueling outage. Flow holes are being provided at the top and the bottom of the sheathing to permit flow of water and steam in the annulus between the inner stainless steel encapsulation and the outer zircalloy tubing. The flow holes are provided to eliminate the effects of hr.ving moisture trapped inside the zircalloy tubing. With the exception of the flow holes and the crimping of zircalloy tubing at the lower end cap, the two auxiliary neutron sources will be identical to those originally installed in 1971.
These auxiliary neutron sources are being reinstalled in the reactor for use during the next two operating cycles.
Because of flow holes in the outer zircalloy encapsulation, particular emphasis will be placed on monitoring for antimony in the plant reactor water chemistry program to detect any abnormal changes.
l Yours very truly, f'
Afk-
'u.a RBS/dmb Ralph B. Sewell Nuclear Licensing Administrator CC:
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