05000338/LER-1980-028-01, /01T-0:on 800223,actuation of ECCS Occurred Due to High Streamline Differential Pressure.Caused by Valve NRV-MS101C Being Opened While NRV-MS101A & B Remained Closed & Steam Flow Existed

/01T-0:on 800223,actuation of ECCS Occurred Due to High Streamline Differential Pressure.Caused by Valve NRV-MS101C Being Opened While NRV-MS101A & B Remained Closed & Steam Flow Existed

ML19290E384
Person / Time
Site:	North Anna
Issue date:	03/07/1980
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19290E380	List: 05000338/LER-1980-028, Forwards LER 80-028/01T-0 05000338/LER-1980-028-01, /01T-0:on 800223,actuation of ECCS Occurred Due to High Streamline Differential Pressure.Caused by Valve NRV-MS101C Being Opened While NRV-MS101A & B Remained Closed & Steam Flow Existed
References
LER-80-028-01T, LER-80-28-1T, NUDOCS 8003110056
Download: ML19290E384 (4)

LER-1980-028, /01T-0:on 800223,actuation of ECCS Occurred Due to High Streamline Differential Pressure.Caused by Valve NRV-MS101C Being Opened While NRV-MS101A & B Remained Closed & Steam Flow Existed

Event date:
Report date:
3381980028R01 - NRC Website

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NRC FORM 366 U. S. NUCLEAR REGULATORY COMMISSION (7-77)

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2 lAt 1912 on February 23, 1980, an actuation of the Enerponey Core Cooline Sys te

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North Anna Power Station, Unit #1

Attachment:

Page 1 of 3 Doc ke t No. 50-338 Report No. LER 80-28/01T-0

Description of Event

At 1912 on February 23, 1980, a Safety Injection occurred due to a high steamline dif ferential pressure.

Prior to this event, metal impact noises indicating possible loose parts in the steam generators we e detected.

In an attempt to link the noises with loose parts in the plant secondary side, non return valve NRV-MS101C was opened to allow noise data to be obtained by Westinghouse.

Because non return valves NRV-MS101 A and 101B remained closed when NRV-MS101C was opened with steam flow occurring, a high steamline diffe-rential between the steam generators resulted,which in turn caused the automatic actuation of the Emergency Core Cooling System.

The Safety Injection lasted approximately 15 minutes and cacsed pressurizer level to increase from 16% at the start of the transient to 59% at the end.

The greatest temperature drop occurred in Loop B cold leg and was determined to be 41.2*F.

As a result of the safety injection, the contents of the Baron Injection Tank were flushed to the Reactor Coolant System which caused the concentration of the BIT to fall below the Tech. Spec. limit of 20,000 ppm borated water.

Although the T.S. Limiting Condition for operation was not met, the BIT did perform its intended function.

As a result of the safety injection, the Emergency Condensate Storage Tank (ECST) went below the value given in T.S. 3.7.1.3 This is an expected event following an ECCS actuation since the auxiliary feedwater pumps which take suction from this tank start on a SI signal.

The ECST performed its intended function.

As a result of the safety injection, the control room pressurization system air bottle depressurized to pressurize the control room.

During the event the air bank pressure dropped below the value given in T.S. 4.7.7.2.a.

This is an expected event following ECCS actuation and the air bottles performed their intended function.

During the safety injection, the following unexpected events occurred which are contrary to Technical Specifications:

Upon receiving a Phase A isolation signal from the SI, seal leakof f isolation valve MOV-1380 failed to close as required by T.S. 3.6.3.1.

Also, upon receiving the safety injection signal, emergency diesel generator 1H automatically started as designed,however, tripped shortly thereafter on overspeed.

The trip was reset and the diesel was successfully restarted.

The ECCS actuation is reportable per T.S. 3.5.2 and 6.9.2.

However, Regulatory Guide 1.16 states that ECCS actuations are reportable under Unit 1 T.S. 6.9.1.8.1 which requires a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> notice and written followup.

This report is intended to meet the additional requirements of the 90 day report for T.S. 6.9. 2.

The other events included in this discussion are reportable as 30 day items by T.S. 6.9.1.9.b.

Page 2 of 3 This is the fourth ECCS actuation reportable under T.S. 6.9. 2.

Probable Consequences of Occurrence The purpose of the Emergency Core Cooling System is to ensure adequate cooling of the reactor in the event of a loss of coolant accident.

Although the safety injection system performed its intended function to inject borated water into the Reactor Coolant System and because the B.I.T.,

ECST, and control room pressurization system performed as required and the transient was not severe, there was no requirement for the S. I. and the health and safety of the general public were not af fected.

There are no generic implications associated with this event.

Cause of Event

The cause of the safety injection was a high steamline differential pressure which resulted when non return valve NRV-MS101C was opened while NRV-MS101A and 101B were both closed and steam flow to the condenser through the steam dump valve system existed.

The low level of the ECST, the underboration of the BIT, and the under-pressurization of the control room air bottles are all normal results of a safety injection and are expected to occur.

Seal leakoff isolation valve MOV-1380 failed to close upon receipt of t.e Phase A isolation signal because of a chemical buildup under the valve's torque switch which prevented the motor from closing the valve completely.

It is suspected that the IH diesel generator tripped on overspeed because the starting air remained engaged too long allowing the speed of the governor to reach the trip setpoint.

Immediate Corrective Action

At 1915 SI was reset and one of the two high head safety injection pumps was secured.

Using the applicable emergency procedure, normal charging and letdown were established and the operators returned the plant to stable conditions.

The operators refilled the ECST, reborated the BIT, and repressurized the control room bottled air system as required by the appropriate Tech.

Spec. ACTION statements.

The torque switch lug on MOV-1380 was thoroughly cleaned and the valve was successfully stroked several times to ensure proper operation.

Scheduled Corrective Action Actions to correct the diesel overspeed trip problem are pending further information from the governor manufacturer.

As ca-r ua die vendor bulletin is received, the app ropriate ren. 2; or aojustments will be initiated.

A similar problem with the lH Emergency Diesel Generator occurred on March 2, 1980.

Further investigation is continuing and will be discussed in a LER (LER/R0 80-032/03L-0), for March 2,1980 occurrence.

t Page 3 of 3 Actions Taken To Prevent Recurrence No further actions are required.