ML19309G404
| ML19309G404 | |
| Person / Time | |
|---|---|
| Site: | 05000142 |
| Issue date: | 12/26/1979 |
| From: | Ostrander N, Zane A CALIFORNIA, UNIV. OF, LOS ANGELES, CA |
| To: | |
| References | |
| NUDOCS 8005060257 | |
| Download: ML19309G404 (3) | |
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. .arter own inma u>s acetsi . minuos . nu oirco . in rawcaco sim 4m 4 . i m c cz 2567 Boelter Hall SCHOOLOF ENGINEERING AND APPUED$CIENCE LLS ANCELES, CAUFORNIA 90014 26 December 1979 Mr. Robert W. Reid, Chief Operator Reactors Branch #4/NRR U.S. Nuclear Regulatory Comission Washington, D.C. 20555 Docket No: 50-142 License R-71 l
Dear Mr. Reid:
An abnormal occurrence at the UCLA nuclear reactor took place on 19 December l 1979 at 16:30 hours. A telephone report to the NRC Region V on the following day !
described the incident as "an uncontrolled or unanticipated reactivity change" (UCLA Technical Specifications, Section L.2.b). The occurrence lead to a high flux scram, all safety systems operated correctly.
This preliminary report describes the event, the staff analysis of the occurrence, the actions that have been taken to reduce the likelihood of reoccurrence, and invites comments and/or suggestions from the Radiation Use Comittee and the UCLA Office of Environmental Health and Safety. Because the required 10 day reporting period overlaps the UCLA inter-quarter vacation period j it is not possible to assemble that committee to review and critique the contents of this statement within the required reporting period. A final report will be submitted not later than January 15, 1980. ;
The Event 1
During the course of a routine operation, involving the use of the pneumatic j sample transfer system, two strip chart recorders simultaneously ceased inking. 1 The reactor was nominally on automatic control at 10 kw. The operator proceeded to refill the inkwells. A high flux scram occurred before the refilling operation was completed. All operations were suspended pending an analysis of the cause of the event.
l Preliminary Analysis The logarithmic power (Log N) recorder had been re-inked and recorded the i power history immediately prior to the scram. The absence of prompt-jump excluded .
l the possibility of excessive reactivity insertion via a pneumatically inserted I l sample. The chart was more typical of a ramp insertion of reactivity and l l suggested failure of a rod drive mechanism. Checks of the individual drives j) indicated nonnal operation. /70M S f
//6 Nt' CLEAR ENERGY LABORATORY IVAN CATTON, DIRECTOR l
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- Sa n2CISCO SAW B4RSARA * $A G CRUZ Chief Reid, page two SCHOO!,OF ENGINEERlNC AND APPUED 5CIENCE ws ANcEtzs, CaurORN A we 26 December 1979 Debriefing revealed that the operator had t:irned off the linear recorder while refilling the inkwell. Concentrating upon restoring that recorder trace, and perhaps distracted by questions from an interested :tudent, he failed to see the behavior of Log N recorder. More important, he overit,cked the fact that the linear recceder, via a self-balancing potentiometer, provides the error signal that drives the automatic rod control system. By turning off the chart drive, he disabled the self-balanding potentiometer. Halted in a position demanding more reactivity and unable to self-position, the constant (erroneous) error signal continued to demand more reactivity. Full scram occurred at 125 kw.
This preliminary analysis attributes the scram to two principal causes:
- 1) operator error, possibly due to a training deficiency, and 2) an instrument-related inadequacy. The two are somewhat related.
The instrument is of a kind widely used in industry and is highly reliable.
No event of this kind is known to have occurred in the prior history of the reactor. However, it is usually called a recorder-controller to emphasize its dual function. The abbreviated name, linear recorder, used in operator training at UCLA fails to reflect / emphasize the dual function.
The instrument itself did not fail; the controller function was disabled by 1 operator intervention. Clearly the disabling switch could be interlocked with I scram or inhibit circuits, the latter preventing rod withdrawal (increasing reactivi ty) .
Immediate Actions Operator debriefing commenced on the afternoon following the scram, and the cause detennined that evening. On the following morning, supervisory personnel decided to convene a meeting of reactor operators to review the event, describe the causes, discuss the importance of the controller function, and stipulate the following procedural instructions:
- 1. Recorder inkwells to be checked and replenished prior to each start-up;
- 2. In the event of ink flow failure, the operator is to call !
for assistance; and l
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- 3. No instruments are to be turned off during operation.
In addition, the obligation and authority of the reactor operator to reject or i eliminate distractions was reaffirmed.
Nt' CLEAR ENERGY LABORATORY IV uN CAlTON, DIRECTOR
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y Chief Reid, page three scnootor ENciNEERiNc AND APPUED $CIENCE LOS ANGELES, CAUFORNIA 90024 26 December 1979 Recommendations to the Radiation Use Committee Aside from seeking comittee approval of the previous procedural instructions, no specific recommendations are imediately offered. General recommendations will be to:
a) strengthen the operator training program; and b) review interlock-inhibit-scram options for improving the safety of the automatic power controller and possibly other instruments.
The full import of these options, their implementation, and their interaction with other system circuitry is yet to be analyzed.
This is a preliminary report, subject to review by the Radiation Use Comittee and the UCLA Office of Environmental Health and Safety. That comittee and EH&S are invited to review this report and to prepare questions and/or coments for a meeting to be held on January 9,1980. A confirmed report will be submitted to the NRC on or before January 15, 1980.
Sincerely, A. Zane, Reactor Superviosr 1
Ilidd ( OSbhX.
N. C. Ostrander, Manager Nuclear Energy Laboratory AZ/N0/jb cc: Radiation Use Comittee I. Catton V. Dhir J. Hornor G. Pomraning A. Zane Environmental Health & Safety W. Wegst Robert H. Engleken, USNRC - Region V J. Hobson, Vice Chancellor (for information only)
NL' CLEAR ENERCY LABORATORY IVAN CATTON, DIRECTOR l
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