ML20086G263

Ro:Unscheduled Reactor Trip Occurred While Measuring Temp Coefficient of Reactivity.Caused by Secondary Cooling Water Dropping Below 8 Gpm Min Required by Limiting Safety Sys Setting.Cooling Water Logic Placed in City Water Mode

ML20086G263
Person / Time
Site:	05000083
Issue date:	11/27/1991
From:	Vernetson W FLORIDA, UNIV. OF, GAINESVILLE, FL
To:	Ebneter S NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20086G266	List: ML20086G263 ML20086G268
References
NUDOCS 9112050004
Download: ML20086G263 (3)

Text

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NUCLEAR ENGINEERING SCIENCES DEPARTMENT Nuclear Reactor Facility Un!versity of Florida WT,. Veme* son. Demotor '

November 27,1991 . .-

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Unscheduled Reactor Trip on Loss of Secondary Flow Fint.1 14 - Day Report Nuclear Regulatory Commission Suite 2900 101 Marietta Street, N.W.

Atlanta, Georgia 30323 Attention: Mr. Stewart Ebneter Regional Administrator Region 11 Re: University of Florida Training Reactor Facility License: R-56, Docket No. 50-83 Gentlemen:

Pursuant to the reporting requirements of paragraph 6.6.2(g) of the UFTR Technical Speci6 cations, a description of an unscheduled reactor trip was reported by telephone /

telecopy(Attachment I) on 18/19 November 1991 and a final 14-day written report is submitted with this letter to include occurrence scenario, NRC notification, evaluadon of consequences, corrective action and current status. This event was evaluated as not being a reportable occurrence; nevertheless, the commitment was made internally to make a prompt report on the occurrence.

Scenario After a startup begun at 1210 hours0.014 days <br />0.336 hours <br />0.002 weeks <br />4.60405e-4 months <br /> intended to measure the temperature coefficient of reactivity (A-1, Surveillance), an unscheduled reactor trip occurred at 1234 hours0.0143 days <br />0.343 hours <br />0.00204 weeks <br />4.69537e-4 months <br /> due to the secondary cooling water flow dropping below the 8 gpm minimum as required by the Limiting Safety System Setting (LSSS). Previously the secondary city water had been valved back to assure higher temperatures for the A-1 surveillance. A daily checkout had been completed with both the well water and the city water supplying the secondary cooling water. The secondary oling water logic had beer, placed in the city water mode of operation and had been tested

.isfactorily, signifying city water now was about 8 gpm. The well water warning light and the fisw scram light were on as normal in city water mode operation. When reactor power was brought above one kilowatt (where the secondary water LSSS protective function implements),

the reactor tripped automatically. The cause was evui.ated te be that the city water flow rate s had dropped below the 8 gpm setpoint and had caused a trip on low flow.

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lt was decided to report his event to NRC Region 11 in the same way as for a potential Tech Spec violation although the evaluation of the UFTR Staff and Reactor Safety Review Subcommittec Executive Committee was that it is not an occurrence requiring prompt notification.

NRC Notifical19n NRC Region 11 was notified of this event per a telephone conversation 'on 18 November 1991 with Mr. Joe Troup. The occurrence was confirmed in a following telecopy on 19 November 1991 (Attachment I). After being briefed, Mr. Troup agreed with our evaluation and the decision to make a prompt report on the occurrences. On this basis and since the RSRS Executive Committee had evaluated the event as not promptly reportable and with no violation involved, the requisite preoperational checks were performed and the UFTR was approved for restart on 18 November 1991.

Evaluation / Corrective Action in normal city water secondary cooling operation, the only indications of flow are the 60 gpm light (well water FLOW SCRAM) and the SEC PRESS scram light. When flow is 8-60 gpm, there is currently no indication of the correct flow - only yes or no on 8 gpm. The actual flow could have been slightiy above the trip setpoint and subsequently fell below with a slight variation in city watcr pressure.

All safety and control systems functioned properly and all procedures were followed prior to this event. The trip review and evaluation indicates there are no safety or radiological problems associated with this event. The cause of the trip lies in the lack of gooct variable flow determination in the city water system as well as expected fluctuations in water pressure from the local utilities.

In order to avoid this trip occurrence in the future, two recommendations have been made and aproved by the RSRS Executive Committee. The firit is to install a flow meter on the city water line on the secondary piping system. This device would allow for an accurate determination and indication of actaal flow. The second recommendation is to install a throttle or globe valve on the line. Currently there is a gate valve, which is used for isolation but does not give gocxl throttling characteristics. These two adjustments would allow for more accurate f'ow rate informatica for operation in the city water mode and assure better vahi:.g of the flow rate. Use of this city water cooling mode for reactor protection is committed to be discontinued until these or equivalent changes are implemented. Since it is very mfrequently used, this restriction is not a problem; as a result, the requirement that city water flow be used for the A-3 surveillance has been removed from SOP-E.7 per approval of the RSRS Executive Committee at its meeting on 25 November 1991. Craig Bassett of Region II was apprised of this change in an unrelated telephone call on 26 November 1991.

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Qttrint Status /Coltsecuences The Reactor Safety Review Subcommittee (RSRS) Executive Committee met on November 18, 1991 to review this event. The Committee essentially agreed with actions to that point and with the staff evaluation that the event is not promptly reportable. The Executive Committee also agreed that the event codd be promptly reported as was donc and approved the return of the UFTR to normal operat.'ons. Reactor Management and the RSRS Executive Committee agreed there has been no compomise to reactor safety in the occurrence, nor to the health and safety of the public. Other than making the improvements to the city water cooling system to allow better flow <ontrol and flow monitoring as well as committing not to use the system for reactor protection until improvements are made and then considering the event in the next regular RSRS meeting, this occurrence is now considered closed.

If further information is needed, please advise.

Sincetely, p  % '

William G. Vernetson Director of Nuclear Facilities n Nh 1. , Iljn%L IQotary Publi'c , , Date

,. . a cc: R. Pibi'uilo Reactor Safety Review Si.bcommittee Document Control Desk Attachment I e

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