05000338/LER-1979-024-43, /43X-1:on 790228,radwaste Release Occurred Unexpectedly During Pumping of Unit 2 Containment Sump Via Temporary Pump to Storm Drain Sys.Caused by Pressure Relief Valve Leaks in Units 1 & 2 Purge Headers

/43X-1:on 790228,radwaste Release Occurred Unexpectedly During Pumping of Unit 2 Containment Sump Via Temporary Pump to Storm Drain Sys.Caused by Pressure Relief Valve Leaks in Units 1 & 2 Purge Headers

ML19209B962
Person / Time
Site:	North Anna
Issue date:	10/09/1979
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19209B960	List: 05000338/LER-1979-024, Forwards LER 79-024/43X-1 05000338/LER-1979-024-43, /43X-1:on 790228,radwaste Release Occurred Unexpectedly During Pumping of Unit 2 Containment Sump Via Temporary Pump to Storm Drain Sys.Caused by Pressure Relief Valve Leaks in Units 1 & 2 Purge Headers
References
LER-79-024-43X, LER-79-24-43X, NUDOCS 7910110294
Download: ML19209B962 (4)

LER-1979-024, /43X-1:on 790228,radwaste Release Occurred Unexpectedly During Pumping of Unit 2 Containment Sump Via Temporary Pump to Storm Drain Sys.Caused by Pressure Relief Valve Leaks in Units 1 & 2 Purge Headers

Event date:
Report date:
3381979024R43 - NRC Website

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LVENT DATE 14 75 REPORT DATE 80 E 2NT DESCRIPTION AND PROBABLE CONSEQUENCES h l An uncontrolled and unplanned release of radioactive waste occurred by oumaina the 1

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I Unit II containment sump, via a temporary pump, to the stonn drain system. Samples I

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4 lshowed no detectable radioactivity. The health and safety of the general public were l o

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40 41 42 43 44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS I A pressure relief valve on Unit 1 sampling purge header leaked via tressure relief I

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l i 171 l System 4 Implemented EPIP 1 and 2, isolated source and decontaminatad linit ? cvcen-c l

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NAVE OF PREPARER PHONE:

Update Report - Previous Report Date 3-27-79 Virginia Electric and Power Company florth Anna Power Station, Unit flo.1

Attachment:

Page 1 of 3 Docket flo:

50-338 Report tio:

LER/R0 79-024/43X-1 Descript'on Of Event On February 28, 1979, during preoperational tests on Unit 2, an uncontrolled and unplanned release of radioactive wasta occurred.

The Unit 2 sump had become contaminated. Without knowledge of this contamination, a temporary pump was used to pump out the sump into the storm drain system.

Probable Consequences of Event The estimated total activity released to the Unit #2 Reactor containment was 7.42 E4 pCi.

Estimated total activity released to the Sta'ica Storm Drain System is 3.11 E3 pCi. The estimated release to the discharge cer.al exceeded the maximum permissible concentration (MPC) for the mixture by a factor of 20 to 1.

Based on a sump pump capacity of 400 gpm and a main circulating water flow of 9.52 E5 gpm, the estimated release rate at the site boundary was 0.00845 times MPC for the mixture.

Samples taken from the storm drain discharge and the discharge canal concur with these calculated values. That is, all samples showed no detectable con-tamination. Also, all radiation surveys conducted on Unit 2 containment detected no direct radiation greater than imRem/ hour and all swipes taken were less than 1000 dpm/100Ca2

Cause

When a sample is taken from the Unit 1 primary coolant system, the sample line is purged to the Hydrogenated Contaminated Liquid Purge Header. This purge header empties into the Unit 1 Volume Control Tank (VCT). Off of this purge header is a pressure relief valve with a pressure relief line that dumps into the High Level Waste Drain Tank via a four inch inlet line.

This tank and inlet line is shared with Unit 2 via a pressure relief line and a pressure relief valve off of the Unit 2 purge header.

During nomal sampling operations on Unit 1, the relief valve on the Unit 1 purge header leaked. The Unit 2 purge header relief valve leaked also, causing contamination to get into the Unit 2 purge header. This contamination then spread to the Unit 2 Volume Control Tank (VCT).

The Unit 2 VCT was act used for some period of time until the Charging System was put on recirculation via an abnormal path for 2-PO-36.3.

This patn went through the VCT rather than coming in just downstream of the VCT outlet as does the nomal recirculation flow. The contamination was spread in this manner throughout the Chemical and Volume Control System all the way to the inlet valve on the Boron Injection Tank and to the main flow control valve for Safety Injection.

Some leakage occurred past the inlet valve to the Boron Injection Tank, through the boron injection line and into the vessel via "A" Loop Cold Leg.

The major flow of the contaminated water occurred, however, through the main flow control valve for the Safety Injection System into the vessel via the "B" Loop Charging Line.

This valve maintains a small flow at all times to provide for 1131 224 thermal balance. This water was then pumped into the Unit 2 sump ;y a temporary constructicn cump and then into the Unit 2 storm drain system.

In this v.anner, the unplanned and uncontrolled release of radioactive contamination occurred.

Immediate Corrective Action

Irmediately upon discovery of the contaminated water in the Unit 2 reactor vessel and sumpwthe applicable Emergency Plan Implementing Procedures were put into action. These actions included the evacuation of Unit 2 containment, collection of air samples and smears, and the sampling of various tanks and systems to determine the source and extent of the contamination.

Also, all known conta-minated systems and all possible contaminated systems were isolated and tagged out.

Next, a system by system search was begun to determine the source and the pathway that the contamination took to go from Unit 1 to Unit 2.

This search revealed that the Unit 1 sampling system was leaking reactor coolant through the relief valves on the Unit 1 Hydrogenated Contaminated Liquid Purge Header to the Unit 2 VCT via the Unit 2 Hydrogenated Contaminated Liquid Purge Header. This system was left isolated pending the installation of new relief valves.

The contaminated water that remained on the Unit 2 sump and vessel was then pumped to the High Level Liquid Waste System in the Auxiliary Building. These systems and associated piping were then flushed with water to the High Level Liquid Waste System until radioactivity levels were below MPC. Also, all the soil around a hose leak, which was contaminated, was picked up and put in 55 gallon 17 H drums.

Finally, the area around the storm drain input, which had minor contamination, was decontaminated.

Schedulp Corrective Action The relief valves on the Unit 1 purge header and the Unit 2 purge header have been isolated pending arrival of replacement valves. As scon as the new relief valves arrive, they will be installed.

Action to Prevent Recurrence Currently, the Unit 1 Hydrogenated Contaminated Liquid Purge Header is isolated from the Unit 2 VCT. This isolation will remain in effect until the Unit 2 Sampling System and Hydrogenated Contaminated Liquid Purge Header are operational. At that time, Unit 2 containment will be a controlled area and the Unit 2 VCT, a contaminated system.

To insure that an uncontrolled and unplanned release does not recur, approval from Fealth Physics is required prior to operation of the Unit 2 containment temporary sump pump.

Supplemental Information Initial samples obtained from Unit 2 systems indicated possible trace amounts of XE-133 in the component cooling as early as December 14, 1978 and a definite presence of XE-133 in the RCS during hot functional testing in January 1979. The presence of XE-133 in the RCS appeared to result from a single incident as the activity levels decreased corresponding to the decay half life for XE-133 and no additional nuclides were found in the RCS. This incident was suspected to be an 1131 225

overpressurization of the sample purge header while obtaining a Unit 1 primary coolant sample.

The radioactivity levels detected in the Unit 2 RCS were well below the E.T.S. limit of 4 x 10-5 Ci/ml for noble gases released in liquids to unrestricted areas and had diminished to below minimum detectable limits by the completion of hot functionals on February 1,1979. Samples taken from the Unit 2 containment sump during hot functionals did not indicate radioactive contamination present.

The Unit 2 RCS was drained to mid-loop level on February 4th via the RHR system to the Boron Recovery System. Draining of the RCS was continued to the Baron Recovery System on February 6th :.nd completed on February 7th. The Unit 2 reactor vessel was drained to the containment sump via the transfer canal on February 12th and 13th. No additional activities involving the transfer of water within the primary systems in Unit E containment are recnrded in the Unit 2 control room operation's log until t:e charging system was placed on recirculation for 2-P0-36.3 on February 27th.

The Unit 2 VCT was #illd to 40% on February 8th and 47% on February 17th.

The VCT level had decreased to 21% on February 17th before refilling and to 21%

on February 26th. A review o. the control room operators surveillance sheets for the period indicates the VCT level was dropping by approximately 2-3% per day. No entries in the control room operators' log on use of the charging pumps during this period were fcund. The decrease in volume may have resulted from cooling of the VCT liquid after hot functionals.

In conclusion, the date of the initial unplanned release of radioactivity reported under LER 79-024/43L-0 was February 28, t 79 as previously reported.

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