05000267/LER-1979-046, Forwards LER 79-046/03L-0

Forwards LER 79-046/03L-0

ML19254F894
Person / Time
Site:	Fort Saint Vrain
Issue date:	11/09/1979
From:	Warembourg D PUBLIC SERVICE CO. OF COLORADO
To:	Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML19254F895	List: 05000267/LER-1979-046, Forwards LER 79-046/03L-0 05000267/LER-1979-046-03, /03L-0:on 791011,noted That Sequence of Manual Switching of Primary Coolant Low Level Dew Point Moisture Monitors Can Result in Degraded Mode of Limiting Conditions for Operation.Sys Operating Procedure Revised
References
P-79267, NUDOCS 7911190367
Download: ML19254F894 (5)

LER-1979-046, Forwards LER 79-046/03L-0

Event date:
Report date:
2671979046R00 - NRC Website

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November 9,1979 Fort St. Vrain Unit No. 1 P-79267 Mr. Karl V. Seyfrit, Director Nuclear Regulatory Comission Region IV Office of Inspection and Enforcement 611 Ryan Plaza Drive Suite 1000 Arlington, Texas 76012 REF: Facility Operating License No. DPR-34 Docket No. 50-267

Dear Mr. Jeyfrit:

Enclosed please find a copy of Reportable Occurrence Report No. 50-267/79-46/03-L-0, Final, submitted per the requirements of Technical Specification AC 7.5.2(b)3.

Also, please find enclosed one copy of the Licensee Event Report for Reportable Occurrence Report No. 50-26 7/ 79-46 /03-L-0.

Very truly yours, D~ 4)-%/n Don Wareebourg Manager, Nuclear Production DW/alk cc:

Director, MIPC 1343 182 YK\\

791119036 7

' REPORT DATE:

November 9,1979 REPORTABLE OCCURRENCE 79-46 ISSUE O OCCURRENCE DATE:

October 11, 1979 Page 1 of 4 FORT ST. VRAIN NUCLEAR GENERATING STATION PUBLIC SERVICE COMPANY OF COLORADO 16805 WELD COUNTY ROAD 19 1/2 PLATTEVILLE, COLORADO 80651 REPORT No. 50-267/ 79-46/03-L-0 Final IDENTIFICATION OF OCCURRENCE :

On October 11, 1979, it was determined that due to procedural inadequacies, a particular sequence of manual switching of the primary coolant low level dew point moisture monitors could have resulted in a degraded mode of LCO 4.4.1.

This is reportable per Fort St. Vrain Technical Specification AC

7. 5. 2 (b) 3.

EVENT

DESCRIPTION

On October 11, 1979, with the plant operating at 60% thermal power and 190 MW electrical power, plant instrumentation personnel determined that it was pos-sible to inhibit moisture monitor trip actions without putting the inoperable channels in a tripped condition. This had inadvertantly been done while using the primary coolant moisture monitors to indicate primary coolant moisture levels.

See Figure 1.

The normal operation of a moisture monitor on high moisture in the primary coolant would be a low reflected light level at the moisture trans-mitter

07), (l'), which would transmit a trip ignal to the moisture monitor (HM),

, m 1sture indicating switch (MIS),

3

, and the moistuve switch high (

),

4 This trip signal then goes to "and" circuits, 5

, where if no i ibits are present the signal passes to the first in with ockout cir-cuit, 6

, which will allow the first trip signal to pass, but locks out any subseq uent trip signals from the other loop instrumentation. This circuit pre-vents both loops from tripping on high moi ure in the primary coolant. The trip signal then passes t rough an "or",

, circuit and ir.to the "two out of three" trip circuit, 8

If two out o three signals r.re present the trip signal is transmitted to t e "and", 9, circuit where a cwo out of three low level moisture monitor trip and a hi level moisture monitor trip is required to transmit a trip signal to the XCR's for a loop shutdown.

When using the moisture monitors to indicate the primary coolant moisture levels, the usual method was to trip the moisture monitor, normally MM-1118 and/or MM-1122, by going to light ground on the light control circuit, which simulated a low reficeted light level and tripped the instrument channel by the above action. This locked out the complementary moisture monitor (the complementary monitors are those which share the same first in with lockout circuit). With one moisture monitor in the other loop locked out it would now require two of the remaining two moisture monitors to trip for a protective action to occur.

This is not acceptable as LCO 4.4.1 requires a minimum degree of redundancy of one for these moisture monitor trips.

1343 183

REPORTABLE OCCURRENCE 79-46 ISSUE O Page 2 of 4 EVENT DESCRIPTION (continued):

This situation did occur during power operation because of problems experienced with analytical moisture monitors, MM-9306 and MM-9307, which did require the other moisture monitors to be used to follow primary coolant moisture levels.

During this period there were no moisture ingresses that required the operation of the moisture monitor protective circuits.

CAUSE

DESCRIPTION:

An approved change (Field Change Notice 3738B) made the automatic trip upon moisture monitor system failure a manual action and revised the logic to per-mit individual manual trip of the associated moisture monitor (as opposed to disabling by pairs). This change added a switch to the system failure and test module which in the Plant Protective System trip position, (1), (see Figure 1) would place an inhibit on the " firs in with lockout" circuit, 5

, and a trip into the 2 out of 3 trip circuit, 8 This would prevent the complimentary monitor from being locked out when monitor was in the tripped condition.

However, with the revised circuit configuration, if the monitor was tripped before the sys tem failure and test switch was placed in the Plant Protective Sys tem trip position, the complimentary monitor would be locked out.

CORRECTIVE ACTION :

To correct this problem the system operating procedure was revised to show the correct switching sequence to trip the moisture monitor and prevent the first in with lockout circuit from locking out the other loop's instrument.

See Figure 1.

The system failure switch, C1, for whichever moisture monitor is to be tripped, is put in the Pla e Protective System trip position which puts an in-hibit on the "and" gate, 5

, preventing the trip signal from locking ut the co=plimentary monitor whi e putting a trip signal into the "or" gate, 7, and then into the 2/3 trip circuit.

No other corrective action is anticipated or required.

1343 184

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REPORTABLE OCCURRENCE 79-46 ISSUE O Page 4 of 4 Prepared by:

4d4 Asa B. Reed Technical Services Technician Reviewed by:

. W. Gahm Technical Services Supervisor Reviewed by:

Frank M. Mathie Operations Manager Approved by:

• )v b

Don Warembourg N/

Manager, Nuclear Production 1343 186