ML20055D595

Technical Review Rept AEOD/T90-09, Inadvertent Partial Draining of Condensate Storage Tank

ML20055D595
Person / Time
Site:	Browns Ferry
Issue date:	06/27/1990
From:	Cintula T NRC OFFICE FOR ANALYSIS & EVALUATION OF OPERATIONAL DATA (AEOD)
To:
Shared Package
ML20055D593	List: ML20055D592 ML20055D595
References
TASK-AE, TASK-T90-09, TASK-T90-9 AEOD-T90-09, AEOD-T90-9, NUDOCS 9007090151
Download: ML20055D595 (3)

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AEOD TECHNICAL REVIEW REPORT UNIT:- Browns Ferry Unit 1- TR Report No.: 'AEOD/T 90-09

' DOCKET NO.: 50-259 DATE: June 27, 1990 LICENSEE: ' Tennessee Valley Authority EVALUATOR / CONTACT: T. Cintula NSSS/AE: Utility / Utility

SUBJECT:

-INADVERTENT PARTIAL DRAINING OF CONDENSATE STORAGE TANK

SUMMARY

A- decrease in water, level in the condensate storage tank at Browns Ferry Unit I was originally thought to be a level instrumentation problem due-to cold weather, not an actual loss of water inventory from the condensate storage tank. -Investigation determined that the heat trace for interfacing instru-

! mentation on the condensate head tank had failed and indicated the condensate head tank needed replenishment. Accordingly, approximately 192,000 gallons of water reserved for non-safety applications was transferred from the condensate storage tank to the condensate head tank. The water overflowed the head tank and was released unmonitored'into the environment. We searched for other events of unanticipated draining of the condensate storage tank.

Eight other events were found. From our review, it appeared that the draindown at Browns Ferry was merely another event in a recurring pattern of

~ inadvertent condensate storage tank inventory reductions at BWRs. In every case, the-inadvertent draindown could not affect condensate-storage tank inventory needed for safeguard operation, or the condensate storage tank was not a safety-related component at the plant.

DISCUSSION

1. Partial Draining of Condensate Storage Tank On February 9,1989, between 0400 and 0800 hours0.00926 days <br />0.222 hours <br />0.00132 weeks <br />3.044e-4 months <br /> at the Browns Ferry Nuclear Plant, the level in the number 1 condensate storage tank (CST) for Unit I deceased from 26.7 feet to 10.1 feet. The control room was aware of the rapid level decrease in the CST beyond normal usage. But, because no suction pumps were running at the time of observation, together with the combination of 20 freezing degrees Fw)eather conditions and a troublesome (the with history outside air temperature the CST was approximately level instrumentation, it was predetermined by the operators that the CST level instrumentation was malfunctioning, and an actual loss of CST inventory had not occurred.

Later,, investigation determined that the condensate head tank heat trace had fai' led; this allowed the condensate head tank level instrumentation to freete, giving an erroneous low condensate head tank water level. The CST level instrumentation was found to be indicating correctly and the true CST level was approximately 10.1 feet.

9007090151 900627 9 DR ADOCK 0500

The low level : egnal from the condensate head tank automatically started the condensate transfer pumps. The pumps ran continuously, transferring water from the CST to the condensate head tank. The transfer of 16.6 feet from the CST-is equivalent to 192,000 gallons of water. This amount of water was transferred to the condensate head tank, overflowing'the tank. The overflow then flowed through the reactor building roof ~ drains (which are not monitored for radioactivity and was discharged to the river through.the yard drainage system. The licensee concluded the activity of the released water did not exceed 10 CFR limits.

The piping configuration of the CST (availability of water reserved for safety-relatedapplicationsisguaranteedbyastandpipeintheCST)issuch that water needed for safety systems cannot be inadvertently discharged to non-safety systems, i.e., the condensate head tank. However, all of the non-safety inventory may have_ been transferred to.the condensate head tank.

In; this case, the non-safety condensate transfer pumps may have been operating for an extensive _ time without a supply of water to the pump's suction. The pumps and pump seals were checked for damage; no damage or leakage was observed.

2. Purpose of Investigation In this case, the licensee originally thought the reduction in CST water level was a. CST in:trumentation problem due to cold weather or other problems with

'the -level indication system, not an actual inventory loss from the CST. In reality, sensing lines that were not a part of the CST, but interface with the CST led to the inadvertent draining of the CST. Due to the large volume of water transferred from the station control area, it seemed appropriate to seek other events of inadvertent CST drainage to determine how frequently these events occur, their safety consequences, and a desirable course of action to prevent recurrence.

3. Search Technique The Nuclear Document Control System (NUDOCS) and the Sequence Coding and Search System (SCSS) were used to search for other events of inadvertent or unrecognized CST draining.

FINDINGS The event searches found an additional eight events of inadvertent CST inven-tory reductions. The amount of inventory loss varied significantly. Each event was caused by a human factors deficiency that resulted in an incorrect valve line-up or equipment failure.

In reviewing the data, events of CST inventory losses greater than the Browns Ferry event were attributable to equipment failure that subsequently resulted in a complete loss of CST inventory (LER 410/87-025; 450,000 gallons from a large crack near the bottom of the CST and LER 341/86-045; 275,000 gallons from an overpressurization failure of piping below the CST). The greatest

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3-loss of CST inventory due to a human f actor deficiency was 37,000 gallons (LER 278/85-008). Most of the LERs of CST depletion ttributable to a human factor deficiency were inconclusive to the time duration for corrective response, 50 it could not be determined if the 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> draindown at Browns Ferry was an unusual lengthy period for corrective action to occur.

None of the events caused adverse safety consequences. Availability of analyzed inventory was guaranteed by either standpipes, or level control valves that close when the quantity of CST inventory dross to a preset value, or by tapping non safety suction piping on the side of tie CST at a height that ensures minimum safeguard inventory. In other events, the CST water inventory was not safety-related and emergency equipment was capable of drawing water from an alternate source, e.g., the safety-related suppression pool at boiling water reactors.

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CONCLUSION Events of significant loss of CST inventory have occurred in the past and although the event at Browns Ferry initially seemed significant both Irom the large reduction in inventory and untimely corrective response, the event merely falls into a previously established pattern of inadvertent CST draindowns at BWRs. The review of the Browns Ferry and other CST draindown events indicates that these operating events did not affect plant safety.

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