ML20086S578

AO-S1-74-11:on 740820,during Depressurization Procedure, Alarm Indicated High Surge Tank Pressure Received in Control Room.Cause Not Listed.Overhead Gas Compressor Stopped & Pressure within Gas Stripper Surge Tank Reduced

ML20086S578
Person / Time
Site:	Surry
Issue date:	09/26/1974
From:	Stallings C VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	Moseley N NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
References
AO-S1-74-11, NUDOCS 8403020448
Download: ML20086S578 (7)

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) O j Vinot$sA Ex.ncrnic Asp Powen Com Paxd j It ac t Ft O N D. YI H OI N t A 23361 September 26, 1974 Mr. Norman C. Moseley, Director Serial No. 288 Directorate of Pegulatory Operations P0&M/JTB:clu United States Atomic Energy Commission ..

Region 11 - Suite 818 h Docket No. 50-280 230 Peachtree Street, Northwest License No. DPR-32 Atlanta, Georgia 30303

Dear Mr. Moseley:

Pursuant to Surry Power Station Technical Specification 6.6.B.1, the Virginia Electric and Power Company hereby submits forty (40) copies of Abnormal Occurrence Report No. A0-SI-74-11.

The substance of this report has been reviewed by the Station Nucicar '

Safety and Operating Committee and uill be placed on the agenda for the next meeting of the System Nucicar Safety and Operating Committee.

Very truly yours,

, f. PAObic-C. M. Stallings Vice President-Power Supply and Production Operations Enclosures '3 '4 ,

V 40 copies of A0-S1-74'-11 .g t-pgCliv[ 0 ,.\

cc: Mr. K. R. Goller, Assistant Director _

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ABN0RMAL OCCURRENCE REPORT REPORT NO. A0-SI-74-11 GASEOUS RELEASE FROM CAS STRIPPER SURGE TANK AUGUST 29, 1974

_ DOCKET NO. 50-280 LICENSE NO. DPR-32 SURRY POWER STATION VIRGINIA ELECTRIC AND POWER COMPAhT l

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l'b (~b V V I, INTRODUCTION In accordance with Technical Specification 6.6.B.1 for Surry Power Station, Operating License No. DPR-32, this report describes an abnormal occurrence which was identified on August 20, 1974. The Directorate of Regulatory Operations, Region II, was notified on August 21, 1974.

The occurrence reported herein is classified as an abnormal occurrence pursuant to Technical Specification 1.0.I.3 which states that "An abnormal occurrence is defined as: "Any uncontrolled or unplanned release of radio-activity from the site."

The occurrence described herein resulted in an insignificant, unplanned gaseous release from the station.

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II.

SUMMARY

OF OCCURRENCE On August 20, 1974, Unit No. I was operating at approximately 99 per cent of rated power and 805 MWe generator output. Unit No. 2 was at cold shutdown conditions for maintenance of a pressurizer spray valve. Three (3) freeze seals were being used to isolate the pressurizer spray volume from the reactor coolant system. To ensure the freeze seal intergrity, it was necessary to depressurize the reactor coolant system below 450 psig.

During the depressurization (letdown) procedure, an alarm indicating a high surge tank (overhead gas compressor discharge) pressure was received and acknowledged in the control room. However, simultaneous station evolutions prevented immediate corrective action by the boren recovery panel operator.

Upon his subsequent return to the boron recovery panel, the opetatuc discovered a release was in progress and immediately terminated it.

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, III. ANALYSIS OF OCCURRENCE The maintenance on the pressurizer spray valve required the establishment of freeze seals to isolate the pressurizer spray volume. In accordance with HMP-S-021, Special Maintenance Procedure for Freeze Seals of Stainless Steel Piping, the reactor coolant system was being depressurized from 450 psig to 150 psig, minimizing the differential pressure across the seals. The letdown was directed to the primary drain tank (PDT), increasing the PDT level and reducing the gas space in the tank. The displaced gases of the PDT were transferred to the vent gas system.

The gases which are transferred to the vent gas system are compressed by the overhead gas system compressors which take suction from the vent gas system and are stored in the stripper surge tank. When the stripper surge tank pressure exceeds approximately 120 psig, the gas is automatically transferred to the hydrogen catalytic recombiner system or to the waste gas system directly via two (2) pressure regulator valves in series, PCV-BR-132A at approximately 120 psig and PCV-GW-107 at approximately 7 psig. A relief valve (RV-BR-120) set at approximately 150 psig protects the gas stripper surge tank from over-pressurization. The relief path is to the process vent header and then to the atmosphere. In addition, there is a high/ low pressure alarm on the gas stripper surge tank, set to alarm on a high pressure signal of 140 psig.

At the time of the occurrence, the hydrogen recombiner system was not in operation. The direct flow to the waste gas system was isolated by valve 1-BR-79, because the waste gas decay tank in service was at its upper operating pressure.

During the depressurization of the reactor coolant system, one of the

-overhead gas compressors was being run in the manual mode. An operator was monitoring the PDT level and gas stripper surge tank pressure (overhead I

o o gas compressor discharge pressure). Due to the occurrence of a number of simultaneous station evolutions, observation of these parameters was curtailed.

The pressure in the surge tank increased to 140 psig, an alarm was received and acknowledged, but no immediate corrective action was taken. A continuing increase in pressure resulted in the eventual lifting of RV-BR-120, releasing the gases of the surge tank to the process vent system and activating the process vent gaseous monitor alert, RI-GW-102, (set at 8 x 10* cpm). The operator, upon noting the condition, took immediate steps to terminate the release.

IV. CORRECTIVE ACTION TO PREVENT RECURRENCE The immediate action taken by the operator following the detection of the release was to stop the overhead gas compressor. Pressure within the gas stripper surge tank was reduced by opening pressure control valve -

PCV-BR-130A. This diverted the contents of the overhead gas tank to the gas stripper overhead system, reducing the pressure of the gas stripper surge tank to approximately 130 psig. At no time did the pressure in the gas stripper surge tank exceed 150 psig. The Health Physics Department was notified and a representative sample was obtained from the gas stripper surge tank for analysis.

Following the return to normal, a check was made of the alarm setpoints.

It was found that the setpoint on the high pressure alarm, which had been-changed to 140 psig from 180 psig '(abnormal occurrence report, A0-S1-7'3-14, dated November 15, 1973) still alarmed at 140 psig. The setpoint was lowered,_

however to 130 psig, to ensure sufficient time for an operator to take-corrective action in' event of future alarms._ Both high~and low pressure alarms on the over-i headagas compressor discharge-were tested and found.to be operating properly, f

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.. .. . g Tha licensW is precently investigating the casibility of installing a high pressure cutout switch to operate in conjunction with the overhead gas compresaor's high pressure alarm.

V. ANALYSIS AND EVALUATION OF SAFETY IMPLICATION OF TilP. OCCURRENCE An estimated twenty-five (25) cubic feet of radioactive gas was discharged to the process vent system via relief valve RV-LR-120 and released to the atmosphere. The release lasted approximately ten (10) minutes with the 5

maximum reading on the process vent gaseous radiation monitor of 2 x 10 cpm (5.04 x 10-7 pCi/cc).

Based on a representative sample taken from the gas stripper tank immediately following the occurrence, the total activity released was approximately 5.91 curies, including Xel33 = 5.87 Ci; Xel33 (metastable) L O.04 Ci; 1131 = 0.546 x 10-6 Ci; 1133 = 0.220 x 10-6 Ci; Gross By = 0.560 x 10-9 Ci.

The rate of release was well below the allowable controlled release rate as delineated in Section 3.11.B.1 of the Technical Specifications. The specified maximum release rate for gaseous and airborne particulate waste limit is as follows:

5 3 IQ1/(MPC)g $2.0 x 10 m /sec where:

Q1 = controlled release rate (curies per second of-any radioisotope 1)

(MPC)1 = defined in Column I, Table 11 of Appendix B to 10 CFR 20 (microcuries per cubic centimeter)

For the release reported herein; 4 3 IQg/(MPC)g = 3.98 x 10 m /sec 4 /sec The release rate of 3.98 x 10 m 3 was approximately 19.9 per cent of that permitted by the Technical Specifications for norma'l. controlled-

T O O releases.

It is evident from the release rate calculated above that the radio-activity discharged to the environment was insignificant and did not adversely affect the health and safety of the general public or station employees. Upon failure of operator or instrumentation to prevent overpressurization, the appropriate system safety equipment (RV-BR-120) functioned as designed and the release was terminated immediately af ter detection.

VI. CONCLUSIONS The licensee concludes that:

1. Simultaneous station evolutions prevented the control room operator from adequately monitoring the overhead gas compressor discharge pressure and rr.sulted in the subsequent lifting of relief valve RV-BR-120.

2. t.n insignificant amount of radioactivity was released to the environment.

3. The occurrence described herein did not affect the safe operation of the station.

4. Tr.c occurrence described herein did not adversely affect the health or safety of the general public.

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