ML20236K730

Osu Triga Reactor (OSTR) Changes,Tests & Experiments Evaluated Under Provisions of 10CFR50.59

ML20236K730
Person / Time
Site:	Oregon State University
Issue date:	02/20/1998
From:	Binney S, Crail S, Dodd B Oregon State University, CORVALLIS, OR
To:
Shared Package
ML20236K728	List: ML20236K725 ML20236K730
References
NUDOCS 9807100057
Download: ML20236K730 (7)

Text

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03/30/98 14:30 @s41 737 0480 RADIATioM CENTER @ 004

.o OSU TRIGA Reactor (OSTR)

Changes, Tests and Experiments Evaluated Under the Provisions of 10 CFR 50.59 NUMBER: 98-2 DATE: February 20,1998 TITLE: Modification to the Scram Circuit System DESCRIPTION On Febmary 17,1998 at 0855, the reactor failed to scram when the manual scram button was depressed. The reactor had been operating for 14 minutes at a power level of 15 W. Reactor shutdown was achieved within two seconds by the operator checking the key switch and finding that it clicked from the reset into the operate position. He then retried the manual scram button and it operated properly. Subsequent investigation discovered that the TB2-3 to TB1-9 jumper shown on the attached figure 1 is not present. The metual circuit found is shown in figure 2. At sometime in the past, a connection has been made between TB1-9 and TB10-10 which was further connected to the B deck of the console key switch. This in turn was connected to the AC(neutral) at TB10-4.

(The investigation is continuing to discover when and under what conditions this modification occurred). The consequence was that an alternate path was created to supply power to the control rod magnets. When the key switch is in the reset position, the scram bus is disabled, so instead of the magnet power being dismpted, the altemate power source kept the magnets energized resulting in the failure to scram.

It is prol>0 sed that the facility be modified:

1) to remove the connection between TB1-9 and TB10-10 and

2) to reinstall the jumper between TB2-3 and TB1-9.

The proposed changes are shown in the simplified schematic of figure 3.

In addition, the Scientific Instrument Technician will electronically check the rest of the

[ scram loop circuitry to provide assurance that the as-built condition matches the circuitry shown in the facility doctunentation. The semi-annual S&M 15.11, Console Checklist, will also be conducted prior to restart of the facility. l I

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, 02/20/98 14:30 @541 737 0480 RADIATIO % CENTER @ 005 l

'It is further proposed that a modification be made to the startup procedure, OSTROP 2, to add a scram test which would confirm that the control rod magnetic power is de-energized v, hen the console key switch is in the reset position.

SAFETY EVALUATION The proposed facility change will return the operate permissive circuitry to its original, as designed, configuration and hence remove the possibility that the scram bus could be rendered inoperative by positioning the console key switch in the reset position. The procedural change will provide operational verification before each startup that indeed the magnetic power is de-energized when the console key switch is in the reset position.

Additional testing of the remainder of the scram circuitry pmvided assurance that there were no further deviations from the as-designed circuit of figure 1 other than the change identified in figure 2.

These proposed changes will permit compliance with the requirement in the Technical l Specifications that scrams identified in Table I of section 3.5.3 be operable when the reactor is unsecured. These changes correct an identified malfunction of equipment which was evaluated in the safety analysis report. They do not introduce a possibility for a different type of malfunction and clearly the overall margin of safety is increased by ensuring that the scrams are operable during all phases ofoperation.

The changes described above were reviewed and approved by the Reactor Operations Committee (ROC) prior to being implemented. ROC approval included a review of this evaluation and the Committee's conclusion that the changes did not require a change in the OSTR Technical Specifications and did not constitute an unreviewed safety question as defmed in 10 CFR 50.59(a)(2). This evaluation also included a review of applicable radiation protection aspects and was found to be consistent with the Radiation Center's commitment to ALARA.

CONFORMING PROCEDURAL CIIANGES l 1

OSTROP 2, page IV.2.13 add an item e (4) which reads " Repeat steps e (1) - e(3). I Add the following section after section e.

f. Key Switch Reset Position (1) Tum key to Reset Position and hold.

(2) Observe that the scram test sequence has occurred.

(3) Reset the circuit.

On page IV.2.12 section 2.8.a.2 change the sentence " .. circuit and then release." to ". . circuit and then return to operate position."

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i l  : 02/30/98 14:31 '8 541 737 0480 RADIATION CENTER @ 006 l

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'On page IV.2.12 change 2.8.b.1 from "... position and release." to "... position and then return to j operate position."

1 On the OSU TRIGA REACTOR STARTUP CHECKLIST add under item 2.8 the line:

KEY SWITCH RESET (TRANS. ROD) . .

Extracted from 10 CFR 50.59 (a)(2)

A proposed change, test, or experiment shall be deemed to involve an unreviewed safety question:

(i) if the probability of occurrence or the consequence of an accident or malf'.:nction of equipment important to safety previously evaluated in the safety analysis report may be increased; or l (ii) if a possibility for an accident or malfunction of a different type than any evaluated I previously in the safety analysis report may be created; or (iii) if the margin of safety as defined in the basis for any technical specification is reduced.

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02/20/98 14:31 C541 737 0480 RADIATION CENTER @ 007 l.

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'APPRUVALS The changes described above were reviewed and approved by the Reactor Operations Committee (ROC) prior to being implemented. ROC approval included a review of this evaluation and the Committee's conclusion that the changes do not require a change in the OSTR Technical Specifications and does not constitute an unreviewed safety question as defined in 10 CFR 50.59(a)(2). This evaluation also included a review of applicable radiation protection aspects and was found to be consistent with the Radiation Center's commitment to ALARA.

The following signatures indicate review and approval by the Reactor Operations Committee and review by licensed operators. If any ROC member does not completely concur with or understand the proposed change then that member should hold this form unsigned and notify the ROC Chairman. The matter will then be discussed at the next meeting of the Committee. If any individual ROC member is unable to sign the sheet due to absence or illness this will be so noted.

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