ML19309A361
| ML19309A361 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 11/27/1974 |
| From: | SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | |
| Shared Package | |
| ML19309A356 | List: |
| References | |
| NUDOCS 8003270817 | |
| Download: ML19309A361 (2) | |
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UNUSUAL OCCURRENCE REPORT til DOCKET NO. 50-312-74-4 Reporting Date:
November 26, 1974 Occurrence Date:
November 8, 1974 Time: 1615
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Facility:
Rancho Seco Nuclear 1
Generating Station Unit No. 1
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Clay Station, California j
Identification of Occurrence:
High chlorine in Plant Effluent.
Condition Prior to Occurrence:
The reactor was at cold shutdown conditions to perform minor maintenance on the turbine throttle valves.
Description of Occurrence:
On November 8, 1974, the daily sample of the plant effluent showed a tott,1 ch'.orine residual level o~f 0.32 ppm with 9000 GPM dilution flow.
The maximum level permitted in the Technical Specifications, Appendix B, section 2.2, is 0.2 ppm. A check was undertaken immediately to determire the source of the chlorine.
Due to knowledge gained from a previous Unusual occurrence on September 11, 1974, a sample was taken from the discharge from the sewage treatment system at 1630. The sample indicated 20 ppm chlorine, much higher than normally measured at the sample point.
Corrective Action Taken or Which Should be Taken:
Oper,ations personnel were informed of the problem at 1700 and they decreased the chlorine injection pump stroke from the preset 100% to 25%.
To be further conservative the chlorine injection pump was totally secured one-half.^
hour later. At 1910, the chlorine residual had decreased to 0.08 ppm at the effluent discharge.
Designation of Apparent Cause: Design.
Analy' sis of Occurrence:
This occurrence is due to a continuing effort to correct the problem stated in Unusual Occurrence Report 74-2.
A design review of the sewage treatment system by the ".ngineering Group i'ndicated that a more uniform flow could
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be obtained by throttling the discharge valve between the sump pump and the sewage treatment tank. The excess flow recirculates back to the sump. Originally the valve was 100% open with full flow to the tank. Since the design flow of the sewage treatment system is 20 GPM, the engineer had the valve throttled to obtain the required flow to the tank. The valve was left in a position approximately 90% closed. However, unknown to the engineer, the chlorine injection pump operates concurrent with the sump pump. The sump pump had to operate approximately five times longer to pump the sump down to the low level shutoff and at the same time the chlorine injection pump operated five times longer than required. This condition over chlorinated the contact tank and resulted in higher than normal chlorine discharge in the site effluent.
j Equipment I.D.:
The sewage treatment system is manufactured by CLOU Company, Waste Treatment Division, Model Aer-0-Flow S-90-33-3.
j Action Required to Prevent Reoccurrence:
~ l The site Plant Review Committee met on November 25, 1974 to discuss the continuing problem stated in Unusual Occurrence 74-2 and to review this occurrence. As stated in the September 21 report the surges caused by high sewage use at specific times and the sump pump operating intervals were causing overflow of the contact tank. The pumping interval of the sewage treatment sump i
has been reduced as required during the previous occurrence. A further investigation l
indicates that the Auxiliary Building Sump is also operating at a three foot sump interval and this in turn pumps to the sewage treatment sump which operates.over a three inch interval. This sequence causes surges greater than the operating capacity of the sewage system. The Auxiliary Building sump pumping interval will be changed,1'l to operate over a range of approximately three (3) inches rather 'than three (3)' feet./
This is similar 'AEC"on Septembdrto. Unusual occurjr nce 74-Failure Data:.
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repor'ted to'th'e 21, 1974.
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