ML19309A411
| ML19309A411 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 09/03/1974 |
| From: | SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | |
| Shared Package | |
| ML19309A408 | List: |
| References | |
| NUDOCS 8003270857 | |
| Download: ML19309A411 (2) | |
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W UNUSUAL OCCURRE!!CE REPORT Number Docket.50-312-74-1 Report Date:
September 3,1974 Time Unknown Occt-ence Date:
Approximately 8-23-74 Facility:
Rancho Seco Muclear Generating Station, Unit No.1 Clay Station, California Identification of Occurrence:
Leakage of hypochlorite into plant effluent Conditions Prior to Occurrence: The plant was at refueling shutdown conditions and jus't completing initial fuel loading.
Description of Occurrence:
The Nuclear Service Raft Mater System is treated with sodium hypochlorite to control pH and inhibit algae growth.
There are two independent NSRH systecs, each of which have a 500-gallon hypochlorite feed tank. On Augus t 22. 1974, a tank truck arrived to fill each of these tanks.
Durine the filling of the west hypochlorite feed tank, no leakage of hypochlorite was observed.
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h On August 23, 1974 the plant effluent sample showed a total chlorine level of.3 ppa which is 1-1/2 times the naximum allowed by the operatino license. Additional dilution was initiated, however, periodic samples of the site effluent for the period of August 23, 1974 through August 28, 1974 continued to show chlorine levels of from.26 to.7.opm total chlorine.
Chlorination of the circulating water system was secured uhile attemotinn to determine the cause.
A check of the west hypochlorite tank found that that tank was empty.
Further testing of the tank proved that the drain valve had failed, thus providing a path for the hypochlorite solution to leak'out into a storm drain which drains into the plant discharge.
Samples taken on August 29, 1974 showed that the total chlorine level had decreased to less than.02 pom indicating that all of the hypochlorite had been washed out of the drain piping and the chlorine level was controllable to a value less than the operating license requirement.
Corrective Action Taken:
The brass drain valve on the west hypochlorite tank was replaced with a poly vinyl chlorida cap which is resistant to attack by hypochlorite solution.
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Desianation of Annarent Cause:
Component Failure Analysis of Occurrence:
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The hypochlorite chemical tank drain valve was made of brass. The U
stored sodium hypochlorite solution produced an accelerated corrosion of the D
s o os 270
Unusual ~0ccurrenus Pcport 74-1 September 3, 1974
~s of the valve causing it to fail.
The failed valve allowed the hypochlorite solution to leak out onto the ground and into a storm drain. The periodic backwash of the Muclear Service cooling water filter _ discharges water into the same storm drain. Over the period of August 23, 1974 to August 28, 1974, this periodic backwash washed out the sodium hypochlorite solution lying in the storm drain and by August 29, 1974 the last of the solution was discharged.
Equipment I.D. :
The valves are brass, size one (1) inch, manufactured by the Crane Company, Catalog No. 424 with 400fW0G; inlet and outlet are threaded connections.
I Failure Data:
1 1
The drain valve on the east hypochlorite tank was observed to be leaking and was replaced on August 22, 1974 hypochlorite tank.
prior to filling the east Action Required to Prevent P.coccurrence:
Replace both the brass drain valves on each hypochlorite tank with valves manufactured from poly vinyl chlorida material.
Valves have been ordered and will be installed upon receipt.
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