ML20198F783
| ML20198F783 | |
| Person / Time | |
|---|---|
| Issue date: | 11/10/1998 |
| From: | Penny R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | Jankovich J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| Shared Package | |
| ML20198F790 | List: |
| References | |
| SSD, NUDOCS 9812280213 | |
| Download: ML20198F783 (3) | |
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U.S. NUCLEAR REGULATORY COMMISSION Region IV 611 Ryan Plaza Drive. Suite 400 Arlington. Texas 76011 DIVISION OF NUCLEAR MATERIALS SAFETY
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98y22p13981110 SSD PDR 8818098 '0N XVd Al B OBN El:60 3fli 86-01-A0N p pggJ0)g
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STEWS-DATTS-OP 2 OCT 96 l
MEMORANDUM FOR STEWS-DES-R, George Wenz t
SUBJECT:
Operational Changes implemented at Gamma Range Facility (GRF)
- 1. Following identification of a failure in the source encapsulation of GRF sources #5
_' and #8, preemptive steps have been taken by this organization to reduce the risk of l
similar damage to the new sources now in use. We have implemented these immediate interim measures to minimize the possibility of similar damage to the present source inventory. Additionally, we have initiated a comprehensive engineering study of
.the GRF system to define more precisely the cause of the failure and to identify those i
L changes, both operational and design, necessary to affect a permanent solution.
These steps are described more fully below.
Background
- 2. The GRF has been in continuous service since 1974 for operations supporting / tmy test programs. During this 22 year period, a total of three source related problems have i
arisen - all involved our medium size sources.
The first problem occurred in 1975 with the failure of the carrier window for one medium source and the bulging of the windows on 3 other medium sources. Source encapsulation was not compromised and no leakage occurred. Fchwing this j
i-occurrence, changes were made to the carrier design to stren$nen the carrier windows.
The new design was verified in 1976 using 2000 test transfers.
in 19821983 extemal contamination was discovered on medium sources #5 and e8 attn'butable to leaking. As a result of this, the transfer air pressure system was modified to allow for a timed blow duration (thereby moderating and giving greater control over the transfer velocity) and full circumference welding of the source carrier end caps was implemented.
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From 1983 to 1994 there were no further source related problems. The present J
problems with medium sources #8 and #5 were noted in 1994 and 1996 respectively when we identified a failure in the interior encapsulation of these sources.
S. All failures have occurred in medium size sources and appear to be related to the mechanical stresses associated with transfer of the sources between the lead storage vault and the exposure head. These stresses are highest when the sources are brought to a sudden stop at the exposure head.
immediate Steps 4.~ The following operational procedure changes have been implemented:
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Restricted use of all medium sources. The medium sourcas will net be use in 4
routine facility operations. The facility technical engineering specialist, l
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l Mr. Richard Wilitms, will be cont:cted prior to the transi:r of cny medium I
source to discuss the technical reasons for its use. If use of the source is justified, Mr. Williams will approved a test plan that specifically states the limited conditions of its use for that single experiment. Before operations personnel support a GRF test using any medium source they must have a signed copy of a test plan showing that me61um source uso is authorized and the rostrictions that pertain to its use.
Meolum source transfer velocity reduction. The object of this change was to reduce the arrival velocity of the source at the exposure head and to reduce the subsequent mechanical stresses on the source. The reduced transfer velocity is accomplished by shortening tt.e duration of the air pressure pulse applied to tho transfer tube during a console SEND operation. The air pressure duration has been reduced by over 60% from a previous value of 0.8 seconds to the current value of 0.8 seconds.
Increased surveillance of source Integrity. Each source position on the exposure head will be surveyed at least once a week whenever any source has been transferred. The survey instrument used for this measurement will be s
capable of detecting a 0.05 mrem per hour difference from the established background. The readings for each position on the head will be recorded and compared to historical records to establish trends or noticeable changes Long-term Solution
- 0. The above procedural changes have been taken as interim steps only. A comprehensive engineering study has been initiated which will examine the complete source transfer and handling process. The scope of the study will not be limited to any one area but will include examination of operational parameters and procedures, exposure head design, source carrier design, and source encapsulation. The goal of this study is to a) understand the process and mechanism by which encapsulation failure occurred, b) to identify and evaluate corrective options which address the causes of failure, and c) to select, test, and assess specific corrective changes for recommendation to the NRC. Initial results of this study are expected in approximately 6 months,
- 6. We will continue to keep your office advised of all progress in this area. Please do not hesitate to call me for further clarification or to discuss of any of those actions. I can be reached at 678-4161.
ROLAND L PENNY Chief, Operations and Support Division TOTR. P.03 E0 'd 88!8098 'ON XW Al E DEN pl:60 301 86-01-A0N