05000338/LER-1978-133-03, /03L-0 on 781226:Loop a Steam Flow Indicator (FI-1474)indicated High W/Re to Its Redundant Indicator. Caused by Reference Leg Flashing Due to Steam Leak on Root Isolation Valve 1-MS-4

/03L-0 on 781226:Loop a Steam Flow Indicator (FI-1474)indicated High W/Re to Its Redundant Indicator. Caused by Reference Leg Flashing Due to Steam Leak on Root Isolation Valve 1-MS-4

ML19289C602
Person / Time
Site:	North Anna
Issue date:	01/16/1979
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19289C595	List: 05000338/LER-1978-130, Forwards LER 78-130/03L-0,78-133/03L-0 & 78-135/03L-0 05000338/LER-1978-130-03, /03L-0 on 781220:during incore-excore Detector Cross Calibr,Axial Flux Deviated Contrary to Tech Specs. Caused by Personnel Error 05000338/LER-1978-133-03, /03L-0 on 781226:Loop a Steam Flow Indicator (FI-1474)indicated High W/Re to Its Redundant Indicator. Caused by Reference Leg Flashing Due to Steam Leak on Root Isolation Valve 1-MS-4 05000338/LER-1978-135-03, /03L-0 on 781226:axial Flux Difference Deviated Beyond Tech Spec Limit Due to Power Reduction Caused by Steam Leak in Drain Line of D Moisture Separator
References
LER-78-133-03L, LER-78-133-3L, NUDOCS 7901190111
Download: ML19289C602 (2)

LER-1978-133, /03L-0 on 781226:Loop a Steam Flow Indicator (FI-1474)indicated High W/Re to Its Redundant Indicator. Caused by Reference Leg Flashing Due to Steam Leak on Root Isolation Valve 1-MS-4

Event date:
Report date:
3381978133R03 - NRC Website

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Virginia Electric and Power Company North Anna Power Station, Unit fio.1

Attachment:

Page 1 of 1 Docket flo. 50-338 Report No. LLR 78-133/03L-0 Description of Fvent:

On 12-26-78, during normal mode 1 operation, loop A steam flow indication FI-1474 was noted to be abnormally high uith respect to the redundant steam flow indication on FI-1475.

This occurred immediately after a power transient.

Further investigation revealed the cause to be flashing of the reference leg due to a leaking root isolation valve 1-MS-4 for the steam flow transmitter.

The affected instrument was declared inoperable and the appropriate bistables were tripped.

After a period of time, the affected indication returned to normal as the reference leg refilled itself.

The instrument was then returned to operation and the tripped bistables were reset.

Normal operation was resumed.

Probable Consecuences of Occurrence:

The Engineered Safety Feature Actuation System required by T.S. 3.3.2.1 is provided to initiate automatic protective actions in the event of an accident.

In this case, the steam flow transmitters are used to monitor steam flow and generate a signal used to provide the protection described by Tech. Spec. Table 3.3-4 part "d" of section 4 " Steam Line Isolation".

By placing the affected instrument out of service and placing its appro-priate bistable in the tripped position, only one additional trip from either of the other steam flow instrument loops would be required to initiate a protective action.

This is more conservative than the normal 2 out of 3 coincidences required to generate a protective action and thus there was no danger to the health and safety of operating personnel or the general public.

Cause

The cause for the abnormal indication from FI-1474 is believed to be due to reference leg flashing caused by steam leakage from the root isolation valve 1-MS-4.

Inmediate Corrective Action:

Placed instrument in tripped condition until normal indication returned as per action 14 of T.S. 3.3.2.1.

Scheduled Corrective Action:

Inspect the transmitter and repair steam leak on 1-MS-4 if required as soon as conditions permit.

Due to the valve being unisoluble, mode 5 operation is required to repair it.

Action Taken to Prevent Recurrence:

No action required.