ML20058K724

Ue 263/74-03:on 740715,excess Water Collected in Drain Line for 6-inch Off Gas Piping Between Compressed Gas Storage Bldg & Stack.Failed Off Gas Stack Filters Replaced & Tested for Satisfactory Efficiency

ML20058K724
Person / Time
Site:	Monticello
Issue date:	08/14/1974
From:	Mayer L NORTHERN STATES POWER CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
References
UE-263-74-03, UE-263-74-3, NUDOCS 9102130538
Download: ML20058K724 (2)

Text

NORTHERN OTATES POWER COMPANY i

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from #12 filter cell had no apparent damage. The #11 stack filter tested at 07. efficiency. The plant was returned to power operation with #12 filter in service.

The following morning, July 16, 1974, the stack drain line again became plugged as evidenced by oscillation in stack filter differential pressure (up to the alarm point), higher than normal air ejector discharge pressure, and constant water level in the drain collecting tank for the stack. La ter that evening, the stack drain line was unplugged by applying a backpressure at the drain tank and the water was drained from the off gas piping.

On July 17,1974, the #11 stack filter was replaced with a spare which tested at 99.707. efficiency. The #12 stack filter was tested at 0% efficiency.

This indicated that moisture had again reached the filter. Plant operation was continued with #11 filter in service.

On July 30, 1974, the ftlter cartridge removed from filter cell #12 on July 15, 1974, was re-installed after being allowed to dry out for about 10 days. This filter tested at 97% efficiency.

7. Designation of Apparent Cause of the Event:

Equipment Malfunction - The stack filters became wet as a result of flooding of the line between the compressed gas storage building and the stack building after the line to the drain tank plugged.

8. Analysis of the Occurrence:

Although the stack filters were wet and were not effective particulate filters, the total stack release rate remained within the technical specification release Ibnits.

9. Corrective Action:

The off gas stack 3 filters which failed the filter efficiency test were replaced with spare units and tested for satisfactory efficiency. The level in the stack drain tank is being more closely monitored by operating personnel to detect evidence of plugging as soon as it occurs. Techniques for unplugging the drain line have been developed. Additionally, modifications to lessen the probability of plugging the drain line are being investigated-

, 10. Failure Data:

This series of stack off gas filter failures is the first such event at Monticello Nuclear Generating Plant. The filter cartridges are a special design manufactured by Mine Safety Appliance Company for the Monticello plant.

9 9102130538 740914 CF ADOCK 05000263 a h70A[kar :/1P L 0 Mayer, PE 4 #

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Director of NMlear Support Services cc: J G Keppier

._ G Charnoff Minnesota Polle' ion Controi Agency - Attn. EA zina

MSRB NORTHERN STATES POWER COMPANY

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-,~~..~,.G..,~~..m....,RE ULATORY DOCIGTEELE COPY.

Mr. J F O' Leary, Director -(f ,

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Directorate of Licensing Office of Regulation 77 a(Mi U S Atomic Energy Com:nission [ .

Washington, DC 20545 p "@, , 3a * * ;g].) ,

f UNUSUAL EVENT REPORT TO THE AEC Off Gas Hugh Efficiency Particulate Filter Failures s , . -

1. Report Number: UE 263/74-03 2A. Report Date: August 14, 1974 2B. Event Date: July 15, 1974  ;

3. Facility: Monticello Nuclear Generating Plant (DPR-22)

Monticello, Minnesota 55362 b -

4.

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Identification of Event: -

• ].

• This report concerns two off gas stack filters which tested at 07.

efficiency on July 15, 1974 and July 17, 1974.

5. Conditions Prior to the Event:

Steady State Power - The plant was operating at 887. of rated power. ,

6. Description of the Event:

On July 15, 1974, demineralized water was added to the loop seals at the off gas stack. Due to a plugged drain line for the 6" off gas piping

• between the compressed gas storage building anC the stack, excess water collected in the line. This created a backpressure sufficient to cause unstable air ejector operation and resulted in moisture reaching the stack off gas filter, as indicated by a stack filter high pressure differential alarm. The standby filter (#11) was then placed in service and the operating filter (#12) was isolated. A loss of condenser vacuum caused by unstable air ejector operation resulted in instability of the condenser hotwell water level. While operating personnel were attempting to manually control hotwell level the hotwell makeup and reject valves were inadvertently opened simultaneously. This resulted in a low suction pressure trip of the reactor feed pumps and a reactor scram from low water level. Later that after-noon, the stack drain line unplugged itself, and the drain collecting tank was emptied three times, i

During the evening of July 15,1/12 stack filter was replaced with a spare which l tested at 99.967. efficiency. Other than being wet, the filter cartridge removed  ;

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