ML20099H764
| ML20099H764 | |
| Person / Time | |
|---|---|
| Site: | 05000083 |
| Issue date: | 08/10/1992 |
| From: | Vernetson W FLORIDA, UNIV. OF, GAINESVILLE, FL |
| To: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| Shared Package | |
| ML20099H767 | List: |
| References | |
| NUDOCS 9208190189 | |
| Download: ML20099H764 (4) | |
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4 NUCLEAR ENGINEERING SCIENCES DEPARTMENT Nuclear Reactor Facility University of Florida esv
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August 10,1991 14 Day Report:
Failure of Fuu 90x Outlet Thermocouple Nuclear Regulatory Commission Suite 2900 101 Marietta Street, N.W.
Atlanta, GA 30323 i
Attent on:
Regional Administrator, Region II Re:
University of Floride. 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 Specifications, a description of a potential violation of the Technical Specifications was reported by telephone /telecopy(Attachment I) on 28 July 1992 and a 14-day written report is submitted with this letim to include occurrence scenario, NRC notification, evaluation of consequences, corrective action and current status. The potentially promptly reportable occurrence involved the failure of the thermocoup'a circuit on fuel box #2 outlet line.
Scenario On 27 July 1992 following a full power run for 10 mint anc dter the second startup of the day was ber 9.t 1505 and at 1609 after 35 minuter
' opes.tm at 100 kW full power, temperature -
aer mi t #7 was noted to be reading i inscale indicating a failura in the circuit monn-g the water temperature - at the exit of the south canter f~uel box #2.
Because of..e fa9ure, an unscheduled reactor shutdawn was commenc~1 at 1609 hours0.0186 days <br />0.447 hours <br />0.00266 weeks <br />6.122245e-4 months <br /> with the reactor shutdown.nt' secured at 1610 hours0.0186 days <br />0.447 hours <br />0.00266 weeks <br />6.12605e-4 months <br />. With the exception of the temperature recorder Paint #2, al' 3, sems were r.oted to respond tormally during the shutdown for which two(2) SROs were present.
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1 Nuclear Regulatory Commission Safety Channel #2 Circuit Failure Page 2 August 10,1992 After completion of the unscheduled shutdown, Maintenance Leg Page #92-24 was opened and circuit continuity was checked and verified from the temperature recorder in the control room back to the equipment pit from which point the circuit leads to the thermocouple in the fuel box #2 outlet line which is not normally accessible beneath the biological shield.
A careful check of the temperature recorder showed that temperature recorder point #2 had failed downscale about 7-8 minutes prior to completion of the first rur. at 100 kW for which the reactor was shutdown and secured at 1430 hours0.0166 days <br />0.397 hours <br />0.00236 weeks <br />5.44115e-4 months <br />. Subsequently, the failure downseale was not noted due to the downscale failure point printing on the thickly inked sdge of the recorder paper with all the other points printing in a bunched area as expected.
The SRO was the same for both runs but he had been rel:e"ed by a second SRO for eight minutes for sample insertion during the second run at the 1 watt power level prior to running up to 100 kW and neither noted the failure until the first SRO did so after about 30 minutes at full power.
Primarily because of the delay in noting the failure (understandable per the explanation above), this event was reported to a special Reactor Safety Review Subcommittee Executive Committee - meeting on 28 July !992. The unscheduled shutdown performed on July 27, 1992 was reviewed with agreers Mt the failure downscale of the thermocouple for fuel box #2 was not a violauon of ne
- ' ' cal specifications. Tech Spec items considered here were the Design Features itt ws ' 6.1listi% all the thermocouples as well as Table 1 in Section 3.2.3in the Limiti.. @ ' on for y cration(LCO) which only specify six(6) of the eight(8) thermocouples ot N pm ary side. This LCO consideration was the key one applicable versus Specification @ m W Limiting Safety System Settings as the water would not exceed 155*F for any conditions considered normal. Indeed normal maximum operating temperatures for the fuel box outlet water are in the range of 120*F.
Dr. Vernetson indicated he would report the occurrence to Region II and follow any instructions they might have. There was considerable discussion about whether blockage of fuel box #2 could be detected in this case with indications in the negative reactivity effects of boiling, probable rupture disk breakage if any steam would be generated, flow changes due to increasing pressure differences and variations of the other temperature indications all giving the operator _ evidence of a flow blockage should such occur. The flow changes in other fuel boxes would occur long before any buling could occur even in a cartially blocked fuel box.
On this basis the committee approved. rief restarts with one failed thermocouple to complete several experiments provided the NRC would concur in this evaluation. One of the reasons for this consideration was that fuel inspection (B-2 Surveillance) requiring biological shield unstacking was already scheduled for mid-August; therefore, it was planned that both the repairs to the thermocouple system and the fuelinspection could be performed with one unstacking in the interest of ALARA and overall safety. The RSRS Executive Committee was also, be notified prior to such a restart with running limited to no more than three hours at power for the two experiments.
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7, Nuclear Regulatory Commission Safety Channel #2 Circuit Failure -
Page 3 August 10,1992 NRC Notification
- After the RSRS Executive Committee meeting NRC Region II was informed of this event per a telephor.
conversation on 28 July 1992 with Mr. Craig Bassett relative to the loss of the temperature indication from fuel box #2. The situation was confirmed in a following telecopy (Attachment I). At this time the failure was described, the by Tech Spec sections were reviewed especially the fact that there is no limiting condition for operation preventing startup provided 6 of the 3 primary temperature monitoring points are operable and the fact that the maximum normal fuel box outlet temperature is only about 120*F. There was agreement on a request by the Region II Inspector to treat the event as reportable.
In a subsequent conversation with Craig Bassett of Region II and NRC Project Manager Ted Michaels(Rockville), it was agreed that the UFTR could be restarted for the two experiments to be completed subject to special vigilance by the operators involved; one run would be at 100 kW for one hour, the other at 10 kW for one hour.
Current Status -
This information on NRC permission to restart briefly war communicated to RSRS Executive Committee members and the two runs were completed uneventfully on July 30(100 kW) and July 31 (10 kW) respectively with the reactor then shutdown and secured awaiting fuelinspection and whatever repairs would be needed for the tkrmocouple system.
As of this date(August-10), no further information _can be provided until the core region can l
be accessed and inspected.
Plans are to unstack the core shielding and proceed to inspect the fuel and repair the thermocouple-system in a timely fashion. Plans are to inspect the fuel first allowing further ' decay of the activated materials around the thermocouple where most of the dose for these two projects is expected to be committed.
This inspection effort is expected to begin on August 11,1992 with unstacking of the core biological shielding with fuel inspection occuring on August 12, 1992 and thermocouple sy: tem repairs to commence after fuelinspection is complete. Following completion of all checks and necessary surveillances the UFTR will be restarted to full power performed in steps to assure shielding replacement is adequate. After performing the requisite radiation
-surveys, the UFTR will then be returned to normal operations.
Evaluation Corrective Actlan I=
_ This event is evaluated not to have involved a violation of UFTR technical specifications.
The planned maintenance will be used to conect the problem. Considering the difficulty l
of noting this failure, the reactor was shut down and secured in a responsive interval.
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Nuclear Regulatory Commission Safety Channel #2 Circuit Failure Page 4-August 10,1992 Current Status / Consequences As indicated the Reactor _ Safety Review Subcommittee (RSRS) Executive Committee met on July 28,1992 to review this event and the members were notified prior to the brief restans. The committee essentially agreed with actions taken and with the staff evaluation that the occurrence did not represent a violation of the UFTR Technical Specifications.
The Executive Committee will be consulted for approval of restart of the UFTR and subsequent return to normal operations after the corrective action has been implemented, Reactor Manage mnt - and the RSRS Executive Committee agree there has been no significant comprc'.dse to reactor safety in the occurrence and no impact on the health and safety of the public. Other than considering the event in the next regular RSRS meeting, this occurrence is now considered closed, though NRC Region II will be notified prior to restart for the radiation surveys needed before return to normal-operations.
If further information is needed, please advis3 Sincerely, b
William G. Vernetson Director Nuclear Facilities
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Reactor Safety Review Subcommittee USNRC - Document Control Desk
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