ML20084R184

Ao:On 730703,gamma Scan of 730702 Reactor Bldg Ventilation Stack Sample Cartridge Indicated Limit Release Rate for I-131 & Particulates Exceeded.Caused by Combination of Drywell Atmosphere Leakage & Steam Leaks

ML20084R184
Person / Time
Site:	Quad Cities
Issue date:	07/20/1973
From:	Stephenson B COMMONWEALTH EDISON CO.
To:	Oleary J US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20084R187	List: ML20084R184 ML20084R190 ML20084R198 ML20084R206 ML20084R259
References
BBS-73-151, NUDOCS 8306140822
Download: ML20084R184 (4)

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John F. O' Leary 9;. 'd

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U. S. Atomic Energy Commission V % . -[p (VU Washington, D. C. 20545 N~ d L _

Subject:

Quad-Citics Nuclear Power Station, Units 1 & 2 Docket Numbers 50-254 and 50-265 DPR-29 and 30, Appendix A Sections 1.0.A.2, 3.8.B.3.A, and 6.6.B

Dear Mr. O' Leary:

On July 8, 1973, the gamma scan of the July 7, 1973 reactor building ventilation stack sample cartridge indicated that the limit for release rate for Iodine-131 and particulates with half-lives greater than 8 days had boon excceded. On July 9, 1973, the gamma scan of the July 8, 1973 sampic showed similar results. This abnormal occurrence was previously reported by telegram on July 9, 1973. Gamma scans of samples from the reactor building ventilation stack on the 9th and the lith also showed that the limit had been exceeded. This extension of the abnormal occurrence was previously reported by telegram on July 12, 1973. Mr. J. Fishbaugher indicated via telephone conversation that the 10 day letter should be written with reference to the July 12 reporting date.

PROBLEM AND INVESTIGATION ,

On July 7, 1973,'the unit one reactor was in the cold shutdown mode to facilitato repair of a leak in the drywell. The main-tenance required supplied air because of the high airborno activity due to the Icak. The area was inaccessible with MSA air packs, so supplied air lines were run through the drywell air lock doors to the work location. Having the air lock doors open allowed some drywell atmosphere to leak into the 595' elevation of the unit one reactor building, even though the drywell uas being purged to standby gas treatment. When this condition was discovered the purge inlet valves were closed and the drywell was purged with air coming in through the air lock doors. Airborne Iodine-131 concentrations on the 595' r (

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F~ l O O John P. O' Leary . July 20, 1973 elevation were initially 2.1 x 10-9 uci/cc at 1750 on July 7, ~

1973. At 0300 on Jul 8, 1973, the Iodine-131 concentration was down to 2.0 x 10-y0 uci/cc. This leakage from the drywell was believed to be the cause for exceeding the limit on July 7 and 8 as reported to the AEC on July 9. On July 10, 1973 re-sults of the July 9 sample shoucd initially that we were at 4.25 times our release limit. At 0645 the standby gas treat s mont system was initiated and the reactor building ventilation s_,

was isolated. The source of Iodine for exceeding the limit on July 9 and 10 was now believed to have come from steam leaks occurring from the startup of the reactor at 4:45 a.m. on July 8, 1973. Leaks were found by maintenance personnel in the unit one regenerative, non-regenerative clean-up heat exchanger room. Operators went into the room and stopped the leaks.

The standby gas treatment system was turned off at 1915 on July 10, 1973, and reactor building exhaust fans lA and 1B were started. The Iodine-131 value for the reactor building ventilation stack for July 10, 1973 was initially 58% of the limit. Since some leaks had been found and isolated, the source of Iodine-131 was thought to have been climinated. However, on July 12, 1973, the results of the July 11 sample showed an increase of Iodine such that the limit was again exceeded, this time by 52.7%. At 0755, July 12, 1973, the standby gas treatment system was again initiated and the unit one reactor building ventilation system isolated. Resumed scarches for steam leaks found leaks in the unit one main steam isolation valve room and in the regenerative, non-regenerative heat ex-changer room. Air samples showed the MSIV room to be the major contributor of the Iodine-131. The main steam leaks were significantly reduced by the afternoon of July 13. An estimate be turned of release back was nade to see if the ventilation could on. Calculations showed that the inventory of Iodine-131 in the MSIV room would cause the limit to be exceeded again. Plastic shecting was placed over the inlet suction of the air supply to the MSIV room to keep the flow through the area down to an absolute minimum. At 0001 on July 14, 1973, the reactor building ventilation was returned to normal. Analysis of the July 14 sample shoucd Iodine-131 to be at 84.4% of the limit. Late on July 15, 1973 a portion of the plastic was removed from the inlet suction duct allowing some flow through the MSIV room area. By July 18, 1973, the plastic was completely removed. The percentage of limits for the 15, 16, 17, and 18 were 50.1, 56.5, 37.31 and 20.3 respec-tively. It can be concluded then that a combination of drywell atmosphere leakage and steam leaks caused the limits to be excccded.

O 0 John F. O' Leary ,

July 20, 1973 SAFETY EVALUATION The Iodine release rate for the reactor building ventilation stack is considered as a ground level release and no credit is allowed for building wake. Also a reconcentration factor of 700 is assumed for the grass to milk path. These assump-tions make the release limit so low that for a release rate of less than 2% 11PCa of Iodine-131 (9 x 10-9 uci/cc) for a 40 hour4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> / week occupational exposure, and with normal ventilation flow, (96,000 cfm/ unit) the limit is exceeded. This means that in-plant air sampling may detect no problem at all, even though we are over the limit. The off-site environmental sampling frequency has been increased to determine the impact on the environment.

An additional problem is that the sample for Iodine-131 is taken over a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period and counted several hours after removal.

The analysis will show that the limit for the previous 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period was exceeded and will not give any indication of where the current 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> period's results will fall.

CORRECTIVE ACTION Procedure revisions, referred to in the June 10, 1973 violation, are being expanded to include all types of primary system leaks.

Maintenance procedures will be revised to address the problem of potential release paths of airborne contamination.

Further corrective action will be a refueling outage, already scheduled for September 15, 1973, to remove failed fuel which is the source of the Iodine.

We are considering several alternatives to prevent a repetition of this occurrence. The first is to re-route the reactor buiJding ventilation to the main chimney. Because of plume heig'.7.t , a dilution factor is used and'for a similar release rste no limit vill,be exceeded.

The second alternative is to modify the iodine monitoring system so it can indicate any trends more precisely by utilizing a detector for the iodine cartridge alone. Possibly the output of the detector could be run to the process computer and hourly estimates of release could be made.

These alternatives are in progress as modifications requiring g engineering evaluation. Therefore we request about 30 days to make a commitment.

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John F. O' Leary ,

July 20, 1973 CUMULATIVE EXPERIENCE A similar release, occurring on June 10, 1973, indicates that thi's is a recurring problem which requires remedial action.

Very truly yours, COMMONWEALT!! EDISON COMPANY Quad-Cities Nuclear ower Station j

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