05000344/LER-1982-009, Forwards LER 82-009/03L-0.Detailed Event Analysis Encl

Forwards LER 82-009/03L-0.Detailed Event Analysis Encl

ML20058D877
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	06/28/1982
From:	Steele R, Yundt C PORTLAND GENERAL ELECTRIC CO.
To:	Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V)
Shared Package
ML20058D882	List: 05000344/LER-1982-009, Forwards LER 82-009/03L-0.Detailed Event Analysis Encl 05000344/LER-1982-009-03, /03L-0:on 820528,chemical & Vol Control Sys B Hut Partially Collapsed When Pumped to Spent Fuel Pit.Caused by Water Buildup in Sys,Allowing Partial Vacuum to Be Drawn on Tank.Hut Repaired
References
CPY-497-82, NUDOCS 8207270427
Download: ML20058D877 (4)

LER-1982-009, Forwards LER 82-009/03L-0.Detailed Event Analysis Encl

Event date:
Report date:
3441982009R00 - NRC Website

text

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Y;d ~y 's June 28, 1982 Portland General Electric Company

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CPY-497-82 Trojan Nuclear Plant P.O. Box 439 Rainier, Oregon 97048 p,g'-

(503) 556-3713 Mr. R. H. Engelken Regional Administrator US Nuclear Regulatory Commission 1450 Maria Lane - Suite 210 Walnut Creek, California 94596-5368

Dear Sir:

In accordance with the Trojan Plant Operating License, Appendix A, USNRC Technical Specifications 6.9.1.9.d, attached is Licensee Event Report No.

82-09 concerning the partial collapse of a chemical and volume control system holdup tank.

Sincerely,

$.h ml Jo C. P. Yundt

/

General Manager

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/

R. L.3Steele, Manager Nuclear Projects Engineering Attachments c:

LER Distribution File 93.24a(Q) 8207270427 020628 PDR ADOCK 05000344 S

PDR [97c//

REPORTABLE OCCURRENCE 1.

Report No:

82-09 2.

Report Date:

June 28, 1982-3.

Occurrence Date:

May 27, 1982 4.

Facility: Trojan Nuclear Plant, PO Box 439, Rainier, Oregon 97048 5.

Identification of Occurrence:

On May 27, 1982 the

'B' CVCS holdup tank was partially collapsed when it was inadvertently subject to a slightly negative pressure.

6.

Conditions Prior to Occurrence:

The plant was shut down and in a defueled condition at the time of this occurrence.

7.

Description of Occurrence:

The CVCS holdup tanks (HUTS) are used as a reservoir for. letdown coolant, coolant drains, coolant leakoffs, fluid from the spent fuel cooling system and several other effluent flow paths.

Each tank is

' kept under a cover gas at approximately 2 psig which is supplied either from the waste gas decay tanks (WGDT)- or from the nitrogen supply system. The contents of each HUT may be processed via the boric acid evaporators or recirculated to its source.

On May 27 provisions were made to transfer the contents of the

'B' HUT to the spent fuel pool using a gas stripper feed pump.

Prior to this some problems had been experienced maintaining the HUT cover gas pressure.

In addition it was assumed the backup nitrogen cover gas supply was not operational due to several problems that had been experienced with its pressure control regulator. When the transfer of the

'B' HUT was initiated the HUT pressure indicator read 2 psig and the

'D' WGDT was supplying cover gas.

It should be noted that I

the HUT pressure indicator (PI-192) is actually a common indication l

of cover gas pressure for all three HUTS.

As the contents of the

'B' HUT were being transferred, the pressure indication decreased to 1.0 psig. At this point the transfer of the

'B' HUT was stopped and an investigation was initiated to determine the cause of the cover gas pressure drop. The HUT cover gas pressure regulator (PCV-4348) was found closed and was subsequently stroked fully open in an attempt to recover the HUT pressure. By this time the HUT pressure had decreased to.5 psig and PCV-4348 was stroked fully open a second time. The pressure in the

'D' WGDT had dropped from 36 psig to 8 psig so the

'C' WGDT was placed on cover gas service. PCV-4348 was fully open at this time and the

'A' WGDT was placed on cover gas service to facilitate raising the HUT pressure which was by this time.8 psig and rising. Transfer of the

'B' HUT was restarted and the ' A' WGDT was left on cover gas service. At this thne the WGDT drains were opened and the tanks were blown down.

At approximately the same time

1 Reportable Occurrence Page Two the Auxiliary Building radiation monitor, PERM-2C, alarmed when the count rate increased frvm 20 cpm to 300 cpm.

An investigation was begun to locate the source of the gas release; simultaneously the HUT pressure decreased again to.75 psig. As a result of not finding an apparent gas release and the stable high radiation count rate it was thought and subsequently verified the leak was from one of the HUTS.

At this time all the HUTS were isolated.

Further investigation re-vealed damage in the upper third of the

'B' HUT.

8.

Designation of Apparent Cause of Occurrence:

The cause of this event is attributed to the design of the cover gas system. The cover gas is normally supplied from the waste gas system with a backup from the plant's nitrogen system. The input to the waste gas system comes from many sources including the boric acid and radio-active waste evaporators.

The gas discharged from these systems con-tains large amounts of water vapor which collects in the gas decay tanks. As a result gas taken from the tanks for cover gas may contain large quantities of water.

The cover gas piping between the decay tanks and HUTS contains many vertical sections where water can accumu-late.

Under normal circumstances this is controlled by periodic draining of the line; however, prior to this event the gas decay system contained an excessive volume of water due to extensive use of the evaporators. Normal draining was not sufficient and a water seal was developed between PCV-4348 and the holdup tank.

This prevented an adequate supply of cover gas from reaching the HUT.

In addition water accumulation affected the ability of the nitrogen regulator to open to provide a backup cover gas supply. The pressure indicator for the tanks was similarly affected periodically giving erroneous readings of HUT pressure. Without a cover gas supply a vacuum was drawn in the

'B' HUT as it was being pumped to the spent fuel pool.

This vacuum was sufficient to cause the tank to collapse.

9.

Significance of Occurrence:

This event had no effect on either plant or public safety. Two other holdup tanks were available to process water as required.

Radioactive releases associated with this event were within allowable limits.

10.

Corrective Action

Immediate corrective action was taken to stop processing the

'B' HUT and place the system in a lineup to minimize the release of gas to the Auxiliary Building.

Special instructions were issued to Operations personnel detailing the design of the cover gas system describing the potential for water buildup and giving specific actions that should be taken when proces-sing the HUTS to avoid similar situations. The design of the cover

e%

Reportable Occurrence Page Three gas system is being reviewed and permanent changes to eliminate this problem will be made. A design change request will be initiated by July 5, 1982.

Repairs to the collapsed tank are underway and should be completed by July 5, 1982.

It is expected that the tank will be fully restored.