05000312/LER-1981-026, Forwards LER 81-026/01T-0 & Submits Detailed Event Analysis

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Forwards LER 81-026/01T-0 & Submits Detailed Event Analysis
ML19346A266
Person / Time
Site: Rancho Seco
Issue date: 05/29/1981
From: Mattimoe J
SACRAMENTO MUNICIPAL UTILITY DISTRICT
To: Engelken R
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19346A267 List:
References
NUDOCS 8106050523
Download: ML19346A266 (2)
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LER-1981-026, Forwards LER 81-026/01T-0 & Submits Detailed Event Analysis
Event date:
Report date:
3121981026R00 - NRC Website
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' S?!]UD SACRAMENTO MUNICIPAL UTILITY DISTh'tCT C 6201 S Street, Box 15830, Sacramento, Califomia 95813; (916) 452 3211 May 29, 1981

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9'Uf h R$h R. H. ENGELKEN, DIRECTOR REGION V 0FFICE OF INSPECTION & ENFORCEMENT AN041993;5g d(Qj %ru D 0.3. tco U. S. NUCLEAR REGULATORY COMMISSION m

1990 N CAL!FORNIA BLVD

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WALNUT CREEK PLAZA, SUITE 202 WALNUT CREEK CA 94596 to OPERATING LICENSE DPR-54 00CKET NO. 50-312 REPORTABLE OCCURRENCE 81-26 in accordance with Technical Specifications for Rancho Seco Nuclear Generating Station, Section 6.9.4.1(c) and Regulatory Guide 1.16, Revision 4, Section C.2.a(3), the Sacramento Municipal Utility District is hereby submitting a follow-up report to Reportable Occurrence 81-26 which was initially reported to the Duty Officer at Bethesda, Maryland on May 16, 1981 and by a confirmation letter to your office of May 18, 1981.

On May 16, 1981, the Rancho Seco Plant was operating at approximately 98% full power.

At 2200 an alert indication on the gondenser air ejector radiation monitor was received. This was followed by a high alarm on the same monitor 25 minutes later.

Subsequently both the gland steam radiation monitor and the "B" loop main steam line radiation monitors also gave indication of activity.

Personnel were sent into the area to verify the indications, and a primary system leak calculation was performed.

Verification of the alarm indications, a calculated leak rate of 1.7 gpm, and an independent leak rate calculation using the change in tritium concentration in the condenser all indicated the existence of a small primary to secondary leak.

After acknowledging the existence of a small primary to secondary leak and identifying the "B" OTSG as the source, a reduction is reactor power was initiated. The reactor was runback in a controlled manner 9 $106 050 %

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&D ft R fM T R B @. 8 Y S T E M S E RVIN G MORE THAN 600.000 IN THE HEART OF C A LI F O R N I A

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R. H. Engelken 'May 29, 1981' d

q to a:suberitical-condition. lThe. controlled. runback.and control of-the turbine bypass valves during the subsequent' cooldown prevented i

the main steam safety valves from opening 1during the transient. 1The-RCS'was sufficiently cooled down and depressurized so.that by 0514-on May 17, 1981, the RCS cooling _was maintained by the. decay heat' 4

removal ~ system.

inservice inspection personnel f rom' Babcock and Wilcox,. the NSSS

. vendor, were brought on site to perform.an ' eddy current-: inspection of the "B" OTSG.

Both a visual inspection ~ ( i.' e'., f i l l i ng t he'.

primary ~ side and observing 'the secondary side tube sheet =for leakage)'

and subsequent eddy current inspection identified oneLtube, No.'77-17, j

as.the source of the leakage.- Subsequent fiber optic-examination of the tube ~ Indicated a 360 through-wail crack Latthe. upper end of the, 15th tube support plate.

j SincetubeNo.77-17isa.lanerowtube',all-ofthelane[rowtubes, three rows out from the lane row and from the 13th tube suppo'rt plate I

' up, were inspected. Additionally, all tubes which had.known indications' from previous inspections were given a full-length Inspection. This inspection encompassed 400 plus tubes.

Besides the leaking tube, three additiona.1' tubes in the lane region i

had Indications wbich were determined to warrant. plugging. These tubes:are identified as tube No.s 75-18,-75-19 and 75-27.. All fo'ur tubes were stabilized and plugged.

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j Presently a program for processing the secondary-system water which :

was contaminated as a result of this occurrence Is in progress. Power-l

- operation wil; be resumed upon satisfactory processing of.the water i

and secondary system cleanup.

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hsALN A John J. Mattimoe l-Assistant General Manager and Chief Engineer cc:

ISE Washington (30) p MIPC (3) ~

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