ML19257A521

Responds to IE Circular 79-21, Prevention of Unplanned Releases of Radioactivity. Identifies Potential Pathways for Unplanned Release of Radioactivity & Corrective Action to Prevent Unplanned Release

ML19257A521
Person / Time
Site:	Peach Bottom
Issue date:	12/31/1979
From:	Daltroff S PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	Eisenhut D Office of Nuclear Reactor Regulation
References
IEC-79-21, NUDOCS 8001040549
Download: ML19257A521 (5)

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PHILADELPHIA ELECTRIC COMPANY 2301 M ARKET STREET P.O. BOX 8699 PHILADELPHI A. PA.19101 SHIELDS L. DALTROFF ELECYasc Pn D CTioM December 31, 1979 Re: Docket Nos. 50-277 50-278 Mr. Darrell G. Eisenhut Acting Director Division of Operating Reactors US Nuclear Regulatory Commission Washington, DC 20555

SUBJECT:

Prcvention of Unplanned Releases of Radior.ctivity

References:

1) Letter dated October 17, 1979 from D. G. Eisenhut to All Operating Nuclear Power Plants, titled " Radioactive Release at North Anna Unit 1 and Lessons Learned.

2) Nuclear Regulatory Commission's IE Circular 79-21 dated October 19, 1979.

We have completed a study that identifies potential pathways for an unplanned release of radioactivity and the necessary corrective action to p revent or mitigate en unplanned release. The p otential pathways identified are described in Attachment A to this letter. Attachment B summarizes the results of corrective action p reviously taken and corrective action in progress as a result of this study. Should you have any y

questions regarding this matter, please do not hesitate to A _ ,n contact us. M

.5 Very truly y ours , lll , ,y ,

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December 31, 1979 Response D ocket Nos. 50-277 50-278 ATTACHMENT A Potential Radioactivity Release Pathways at Peach Bottom

1. The scram discharge volume in the reactor building drains to the waste collector tank in the radwaste building f ollowing reset of a scram. This tank is vented to the Radwasta Vent System.

2. Drywell sump discharges to the waste collector tank and floor drain collector tank in the radwaste ouilding.

3. The Reactor Water Cleanup System demineralizer backwash discharges to the Backwash Receiving Tank in the reactor building. From here, the backwash resin is transferred to the phase separator in the radwaste building. The phase separator is vented to the building.

4. The mechanical vacuum pump discharges directly to the main stack f ollowing plant shutdown.

5. The main condenser vacuum breakers, when opened following shutdown, connect the condenser to the turbine building.

6. Offgas system leaks to the turbine building or recombiner building.

7. Emergency Core Cooling System leaks outside primary containment will collect in the reactor building sumps which discharge to the waste collector or floor drain collector tanks in the radwaste building.

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December 31 Docket1979Resbonse Nos. S -277 50-278 ATTACHMENT B Evaluation of Potential Release of Radioactivity Pathways SOURCE PROCEDURAL CONSTRUCTION DESIGN EQUIPMENT DEFICIENCIES DEFICIENCIES DEFICIENCES DEGRADATION

1. Scram Yes (1) No Under No Discharge Review (1)

Volume

2. D rywell No No Yes (2) No Sumps

3. RWCU Yes (3) No No No Backwash

4. Mech. Yes (4) No No No Vacuum Pump Discharge

5. Main Yes (5) No No No Condenser vacuum Breakers

6. Offgas No No Yes (6) Yes (6)

System

7. ECCS No No No Yes (7)

Systems Leakage Note: Numbeys in parenthesis correspond to the notes below.

Notes:

(1) Scram Discharge Volume Drains Operating procedures are being revised to p reclude immediate operator action to reopen scram discharge volume isolation valves after a transient which could have resulted in fuel damage. Design of the scram discharge volume isolation valve logic will be reviewed with the General Electric Company to determine if improvements are necessary.

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December 31, 1979 Response Docket Nos. 50-277 50-278 (2) Drywell Sump Discharge The isolation logic for the dryvell sump discharge valves has been modified on Unit 3 and will be modified on Unit 2 during the next outage, which is scheduled to begin on or before December 31, 1979, so that f ollowing an is olation the valves will not reopen upon reset of the isolation signal.

(3) Reactor Water Cleanup (RWCU) Backwash Discharge The RWCU system valves receive containment isolation signals.

Use of this system during p os t-accident conditions would

• require a conscious decision, thus resultant release of radioactivity would be planned. Through offgas release activity measurements and analysis of coolant samples, the operator is aware of fuel leaks. The use of the RWCU backwash during the condition of fuel leaks is a conscious decision; thus, the release would be planned. The procedures are being revised to ensure that sufficient guidance is provided to prevent an unplanned release.

(4) Mechanical Vacuum Pump Discharge Operating procedures for unit startup and shutdown have been revised s o that the release rate is maintained below Technical Specification allowable limits. This is not a post-accident concern since the condenser will be isolated following a LOCA.

(5) Main Condenser vacuum Breakers Operating p rocedures for unit startup and shutdown will be revised to start the mechanical vacuum pump prior to opening the vacuum breakers. This will p revent back flow (dif f usion) of offgas to the turbine building. This is not a p os t-accident concern since the condenser will be isolated following a LOCA.

(6) Offgas System Leaks 1685 088 The design of the offgas system has previously been reviewed, resulting in modifications. Modifications have als o been made to the offgas system in order to replace degraded equipment. This is not a post-accident concern since the condenser will be is olated f ollowing a LOCA. The status of corrective actions for the offgas system are as follows.

a) Perforations have occurred in one elbow in the Unit 2 SJAE discharge. The elbows were removed and metallurgically examined. The conclusion from this examination was that the perf orations were probably due to erosion-corrosion of the pipe wall caused by

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December 31, 1979 Response Docket Nos. 50-277 50-278 impingement of water droplets in the saturated gas assisted by the oxygen in the gas stream. The elbows were replaced with a flanged, cast stainless steel albow. The cast stainless steel was used to provide better resistance to the erosion-corrosion phenomenon.

The flanged elbow was used to minimize personnel exposure during installation. The potential f or leakage from the flanges is minimal due to the low pressure (0-1 psig) in the system.

b) Offgas system loop seals in the turbine building have occassionally vented during offgas system transients or ,

trips. These loop seals are self sealing by design and, therefore, releases due to pressure transients are of limited magnitude and duration. The frequency of pressure transients should be substantially reduced following completion of several modifications to the recombiner system. These modifications involve additional water removal equipment and changes in piping configuration.

c) Valve packing leaks have occassionally caused releases.

System valves downstream of the first stage of the mechanical compressors have been replaced with packless valves.

d) Mechanical comp ress or p ressure pulsation dampener drain lines have occassionally experienced through-valve leakage which resulted in gaseous releases to the building sumps. A second shutoff valve was added to the 3B suction dampener drain line. Releases via this pathway have not been rep orted since.

e) Leaks have occurred at the offgas '7drogen analyzers due to metal bellows pump failures and loosened compression fittings. Replacement of the metal bellows pumps is being implemented. The new pumps will be capable of handling condensation f rom the sample line and will be mounted to minimize vibration.

(7) Emergency Core Cooling System (ECCS) Leakage The ECCS leakage outside primary containment will be identified and reduced by the leakage inspection p rogram that is being developed under NUREG 0578, Section 2 1.6.A.

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