ML20236K725

RO 33732:on 980217,manual Scram Failure Occurred.Caused by Spring Return Key Switch Failing to Return Completely to Operate Position & Wiring Change Difference.Removed & Cleaned Switch & Performed Encl 10CFR50.59 Evaluation

ML20236K725
Person / Time
Site:	Oregon State University
Issue date:	02/20/1998
From:	Dodd B Oregon State University, CORVALLIS, OR
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20236K728	List: ML20236K725 ML20236K730
References
NUDOCS 9807100056
Download: ML20236K725 (2)

Text

, 02/20/98 14:29 0 541 737 0480 RADIATION CENTER @ 002 RADIA110N CElfTER Onecos SrrreUmvenstry 100 Radiation Cantar, corvallis, oregon 97331-5903 Tele;&me 541737.2341 rax 541-737-0480 February 20,1998 U.S. Nuclear Regulatory Commission Document Contro. Desk Washington, D.C. 20555

Reference:

Oregon State Univcersity TRIGA Reactor (OSTR)

Docket No. 50-243, License No. R-106

Subject:

Scram Failure on February 17,1998 - Event No. 33732 Gentlemen:

This letter is in response to our commitment to confer with you regrrding the subject event prior to restarting the reactor.

Let me describe again the basic event. A reactor operator trainee under the direction of a licensed reactor operator started up the reactor and performed the daily core excess measurement at 15 watts as usual. The operator instructed the trainee to manually scram the reactor once this had been done.

When the trainee attempted to comply by pushing the manual scram button, the reactor failed to scram. The reactor operator immediately attempted to scram the reactor himself. When the scram button failed again, the operator checked the key switch and felt it click from a position a little to the right of the OPERATE position (between the OPERATE and RESET position) back to the OPERATE position. He then pushed the manual scram button again which resulted in a proper scram. The operator secured the keys and notified the Reactor Supervisor of the event. From the first attempted scram to the actual scram, the time period was approximately 2-3 seconds.

The occurrence has two causes. The first is a result of the spring return key switch failing to return /,

completely to the OPERATE position after being turned to reset the scrams. Logical analysis concludes that it must have continued to touch contacts A4 and B4. (See figures included with the j attached 10 CFR 50.59 safety evaluation.) The root cause for its failure to completely return to the OPERATE position appears to have been a long term build-up of dirt. Since being removed and cleaned, the switch shows no tendency at all of being sticky or not fully returning. 7 The second cause is a wiring change that makes the OSTR circuit different from that in the original General Atomics (GA) Instrument Maintenance Manual. Figure 1 shows the relevant portion of circuitry from the GA manual. It can be seen that if the key switch is turned to the OPERATE position, magnet current is supplied from TB1-4 through TBl-9, then TB2-3, A3, Al and the console power switch. However, when the key is turned to RESET this circuit is opened and there is no 9007100056 980220 PDR ADOCK 05000243 s PDR

+ O2/20/98 14:29 @541 737 0480- ' RADIATION CENTER @ 003

' U.S. Nuclear Regulatory Commission Page 2

- February 20,1998 j

. magnet current, thereby causing the rods to drop in if they were up, or disabling their withdrawal if they were down.

A careful examination of the actual OSTR consolc circuitry showed that it was different from that illustrated in the GA manual. The difference can be seen in Figure 2 where it is shown that thejumper between TB1-9 and TB2-3. is in fact between TB2-3 and TB10-10. The impact ofthis change is that control rod magnets have power whenever the key switch is in either the OPERATE or the RESET

. position. When the key switch did not fully return to the OPERATE position, the scrams and the control rod magnets were both energized. Therefore, when the manual scram button was pushed the relay did not close and the reactor did not scram.

Investigations of OSTR documentation have so far indicated that thejumper was wired in this manner sometime during the initial installation of the reactor console. The reasons for this thinking will be detailed in the required 14 day letter, liowever, it is very clear that there is very good documentation of all facility changes made since the first one performed under the provisions of 10 CFR 50.59 in March of1968. j The attached 10 CFR 50.59 safety evaluation outlines the corrective actions which are being completed. As discussed in our telephone conversation, the Reactor Operations Committee has met this morning and approved reactor restart no sooner than Febmary 24,1998 pending satisfactory completion of the actions described in the 10 CFR 50.59 safety evaluation. It is our conclusion that these actions provide good assurance that such an event as this cannot happen again and there are no other deviations from the facility as approved.

On a related, but separate matter, I would also like to provide this written confirmation of the verbal notification I made this morning that we will be implementing Section 8.2 of our Physical Security Plan this afternoon at 5:00 p.m. PST.

Should there be any questions regarding the information in this cover letter or should you require 3

more information, please let me know.

Y ours sin , ely, is i f l' rf Brian Dodd, PhD Director c: Oregon' Department of Energy,625 Marion Street, NE, Salem, Oregon 97310, Atta: Mary Lou Blazek L

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