ML20212E992
| ML20212E992 | |
| Person / Time | |
|---|---|
| Site: | 07000754 |
| Issue date: | 10/30/1997 |
| From: | Bassett C GENERAL ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9711040141 | |
| Download: ML20212E992 (3) | |
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GENuclear Energy cemaieax cmw Varecucs fixlev Center r o ea a wxacaca Plewton, CA 34%6 October 30,1997 q'{
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l U. S. Nuclear Reguistory Commission Document Control Desk Washington, D.C.
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Subject:
30-Day Report Regarding the Observed Failure of the Radioactive Materials Laboratory g
(RML) Criticality Detector Gentlemen:
The following repe : is submitted pursuant to the requirements of 10CFR70.50(b)(2)(i) for a written g?
follow-up report within 30 days of an initial report. He following incident was reported by telephone to d
the NRC Operations Center on October 2,1997, t
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During the routine monthly source check of the Radioactive Materials Lab (RML) criticality detector L -
system on 10/1/97 and 10/2/97, the alarm failed to nound when the AmBe neutron check source was placed next to the detector. This test normally produces an alarm condition. The accidental criticality detector system in the RML, at that time, consisted of a single lithium iodide (Lil) neutron detector with
- a battery-powered photomultiplier tube which sends a signal current to a remote readout and alarm circuit, The alarm is triggered by a Beede microammeter which semes the current from the detector.
The alarm condition sounds a local klaxon horn and actuater, an alare: condition in the central Security building. In addition to the local horn sounding, an announcement is broadcast over the site ali-call system of the criticality alarm. Since the time of the reported failure, a new commercially manufactured gamma detection criticality system hss been installed in both of the monitored areas at the Vallecitos site, in addition to the RML facility, criticality monitoring is conducted at the Hillside Storage Facility.
- At the time of the til system test failure, the following obserntions were made of the 0-10 microcmp alarm initiating meter:
- 1. All fuel movement in the RML is prohibited during the testing and repair.
- 2. The dark current (background) before the test was normal at 0.6 microamps.
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- 3. The alarm point was set at 3.1 microamps.
- 4. Normally, the meter will read 4.5 micreamps with the check source at the detector.
Si The meter read 1.5 microamps with the check sourr at the detector during the test, l
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- 6. After the source was removed the meter returned 10 0.6 microamps.
- 7. He detector and battery pack were replaced and the test was repeated. The meter went to 6 microamps this time, and the alarm sounded.
- 8. When the source was removed, the meter only returned to 1.2 microamps instead of 0.6 microamps.
- 9. The de ector was disconnected, and the meter went to 0.9 microamps and wouldn't mechanically zero (0.2 microamps was the lowest it would go). A sticking meter needle, whose movement past a set point triggers the alarm, was assumed to be ths nroblem.
- 10. The removed detector and battery paak were shop to 'ed on another meter and responded properly.
- 11. He RML meter was removed and replaced with a spare, which functioned properly.
- 12. The faulty meter was transported to the Instrument Shop and, when tested with the old detector, was found to operate normally.
- 13. It is assumed that the handling during temoval and transport to the shop caused the apparent sticking meter to self-correct.
- 14. The suspected faulty meter was replaced in the chassis and tested in the Instrument Shep.
- 15. The replacement meter continued to function properly, and no subsequent failures have been obsen ed.
The total quantity of fissile material, in the form ofirradiated UO, in the RML at the time of the 'c. sting 2
was approximately 1,756 grams, distributed throughout several physically separated Ciitdity Limit Areas (CLA) in the facility. The maximum amount of fissile mt.erial allo ved in any CLA is typically limited to 500 grams or less. Approximt'ely 14 fuel moves were made during the one-mon'h period since the prior criticality detector source check. The maximum amount of fissile materin m t.ny one move was approximately 162 grams. There are several alarming area radiation monitors in continuous operation in addition to the criticality detector. No unusual radiation levels were detected during the month. No unusual personne! radiation exposures have been detected on workers' self-reading dosimeters or processed vendor dosimeters.
The malfunction was reported to C. A. Ilocker, Walnut Creek Office, Region IV, NRC at approximatcly 11:20 a.m.,10/2/97, and to the USNRC Operations Center by telephons,(201) 816-5100 at 12:44 p.m.,
10/2/97.~
USh'RC October 30,1997 He recurrencc of this problem should be reduced significantly by the installation and use of the new, modern gamma detection accidental criticality system at the Vallecitos site. The new system uses three detectors in each of the two monitored areas. A two-out-of-three coinciden:c alarm condition is necessary to actuate an alarm, and alann actuation doesn't require a mechanical meter response. The new detector system is fully operational at the Ilillside Storage Facility, and the old til system is out of service. Iloth of the systems are currently in operation at the RML facility in 13uilding l'12, and the til system will be taken out of service aft;r November 5,1997, if you have any questions or concerns regarding this report, please call me at (510) 852-4469.
Very truly yours,
.- 4 C. W. Bassett, Manager Regulatory Compliance cc:
USNRC Region IV Field Oflice 1450 Maria Lane, Suite 210 Walnut Creek,CA 94596 ll
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