ML20077K768

Selected Operating Reactors Issues Program Ii,Rcs Vents (NUREG-0737,Item II.B.1), Final Technical Evaluation Rept

ML20077K768
Person / Time
Site:	Three Mile Island
Issue date:	04/06/1983
From:	Held J ENERGY, INC.
To:	Alberthal G Office of Nuclear Reactor Regulation
Shared Package
ML20077K772	List: ML20077K768
References
CON-FIN-A-0250, CON-FIN-A-250, TASK-2.B.1, TASK-TM TAC-44411, TF-386-0823A, TF-386-823A, NUDOCS 8306020536
Download: ML20077K768 (6)

Text

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- LAWRENCE LIVERMORE LABORATO3Y lC 7 # '

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ENCLOSURE 2

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Selected Operating Reactor Issues Program II ,

Reactor Coolant System Vents (NUREG-00737 Item II.B.l.)

NRC FIN A0250 - Project 9 FINAL TECHNICAL EVALUATION REPORT FOR THREE MILE ^ ISLAND 1

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T-Docket Number 50-289 NRC TAC Number 44411 Prepared by.J. T. Held of Energy Incorporated Seattle (Subcontract 4324401) for Lawrence Livermore National Laboratory under contract to the NRC Office of Nuclear Reactor Regulation, Division of Licensing.

NRC Lead Engineer - Gus Alberthal' NOTICE

! "This report was prepared as an acccunt of work sponsored by the United .

l - States Government. Neither the United States nor the United. States Department of Energy, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any infonnation, apparatus, product or process disclosed, or represents that its use would not infringe privately-owned rights." -

, TF-386/0823a ,

April 6, 1983 De@$D /

S Copy Hos Been'sent*stDj Unleursity o: California P.O. Sus 808 L errnore, Calilornia 94550 3 Telephone (415)4221100 Q Twx 910 386 8339 UCLL LVMR

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,w s wes .w-s.us NRC T.AC Number 444 il i

, TECHNICAL EVALUATION REPORT ON REACTOR COOLANT SYSTEM VENTS i FOR THREE MILE ISLAbD I d

INTRODUCTION ,

The requirernents for reactor coolont system high point vents are stated in paragraph

. (cX3Xiii) of.10 CFR.a50.44'; " Standards for Combustible Gas Control System in Light

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Water Cooled Power Reoc= ors," and ore further described in Standard Review Plan (SRP)

Section E4.12, "Reoctor Coolont System High Point Vents," and item II.B.I of NUREG-0737," Clarification of TMI Action Plan Requirements." In response to these and previous reauirements, Metropolitan Edison Cormony has submitted information in References I and 2 in support of the vent system at Unit I of the Three Mile Island

Nuclear Generating Station. . .

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+ EVALUATION The function of the high point vent system is to vent noncondensible gases from the high -

points of the reactor coolont system (RCS) to assure that core cooling.during natural circulation will not be inhibited. The Three Mile Island I high point vent system provides venting copobility from high points of the~ rcoctor vessel head, the pressurizer, and both RCS hot legs. The noncondensible gases, steam, and/or liquids vented from the re octor vessel head are piped and discharged directly to the containment atmospher4.

Discharges from the pressurizer and the hot legs are normally directed to the reactor coolant drain tonk (RCDT) and may be vented to the containment atmosphere through a new RCDT vent. The hot leg vent paths may also discharge directly to the contoinment atmosphere vio o rupture disc. The high point vent system is designed to be copoble of venting a volume of noncondensible gas equivalent to one half of the RCS volume in one hour. However, the reactor vessel head and hot leg vent line sizes have been selected to

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ensure that the flow from o pipe rupture or from inadvertent octuotion of the vent system would be limited to less than the copobility of the reoctor coolont makeup system. The pressurizer high point vent piping is connected to previously existing pressurizer piping, and therefore the flow from o pipe rupture or inadvertent actuation of

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i the pressurizer high point vent would be equal to or less than that from previously 1

I onalyzed pipe ruptures. Hence,, the licensees complionce with 10 CFR 50.46,

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"Acceptonce Criterio for Emergency Core Cooling Systems for Light Water Power .

Reactors," has not been offected by the oddition of the high point vent system.

i The vent paths from the reactor vessel head, the pressurizer, and the RCS hot, leg high points each contain two volves in series which are remotely controlled from the main control room. Positive indiention of volve position is also provided in the main control room. The licensee has stoted that this positive volve position indication is derived from stem operated limit switches or comparable means to provide octual volve position for

'J.; . oil new vent volves,,, but the power supply and the method . . .- of positive volve position i indicotion for the existing motor-operated volve RC-V28 in the pressurizer vent line have

~ not been described. Thiiis aMfirmatory item. A degree of redondoney has been provided by powering each hot leg vent path from o different Class IE emergency bus to eruure that RCS venting copobility from at least one hot leg high point is maintained.

Flow elements in each vent path with associated indication in the main control room may be used to detect volve seat leokoge from the reoctor.coolont system through the vent system isolation volves.

The portion of each high point vent path up to and including the second normally closed .

j volve forms o part of the reactor coolant pressure boundary, and th'us must meet reoctor i coolont pressure boundary requirements. The licensee has stoted that the high point vent system is designated Seismic Category I in compliance with Regulatory Guide 1.29. The licensee hos also classified the new piping and volves up to and including the second normally closed volve os Nuclear Class 2 in occordonce with the original plant design.

The vent system is designed for pressures and temperatures corresponding to the RCS design pressure and fernperature, in oddition, the vent system materials are compatible with the reactor coolant chemistry and will be fabricated and tested in occordonce with

, existing plant requirements and/or the ASME Boiler and Pressure Vessel Code. The vent system is also occeptably protected from missiles and the dynamic effects of pos'tulated piping ruptures. We therefore conclude that the design and construction of the portion of the high point vent system up to and including the second norrnally closed volve conforms to all reoctor coolont pressure bou'ndary requirements, including 10 CFR 50.55o ond the opplicable portions of General Design Criteria 1, 2, 4,14, 30, and 31. The licensee hos further oscertained that the essential operation of other safety-related systems will not be impoired by postulated failures of vent system components.

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e # e We have reviewed the licensee's high point vent system design to assure on o' cceptably ,

low probability exists for inadvertent or irreversible octuation of the. vent system. The reactor vessel head and hot leg high point vent paths each have two Torget Rock

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solenoid-operated volves in series, and the pressurizer high point vent path hos one solenoid- and one motor-operated volve in series. Eoch volve has on individual

key-locked control switch, which is administratively controlled, and positive position indication in the main control room. The volves oil receive emergency Class IE power and the solenoid-operated volves foil to the closed position in the event of loss of power. Also, on uform in fl,ic main controf mom is octivated if both volves in a vent path

'. . ore in the open position, and each vent path hes a flow /no-flow indicolor in the main control room. Furthermore, the licensee has stated that all displays and controis located in the moln control room due to oddition of the high point vent system have been considered in the human factors analysis required by it! REG-0737 Item 1.D.1, " Control- .

Room Design Reviews," in order to reduce the potential for operator error. _However, _.

.the Three Mile Island I high poin't vent system design may be susceptible to common mode failure because operation of an upstream solenoid-operated volve may cause the

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downstream solenoid-operated volve to open temporarily, lhe licensee will he required to evoluote this potential problem and present, their conclusions including ony alesign changes necessary to rninimi/c flie prohthility of on inadvertent vent systern oc t uat ion. We therefore find th'ot no single active component failure or human error should result in inodvertent cpening or irreversible operation (i.e., failure to close offer intentional opening) of the high point vent system, confirigent on satisfoctory resolution of the obove identified potential solenoid-operated volve problem.

We have also examined the locations where the vent system normally discharges to the containment atmosphere. Based on o description provided by the licensee, these locations are in orcos that will provide good mixing with the containment atmosphere to prevent the occumulation or pocketing of high concentrations of ihdrogen in compliance with 10 CFR 50.44. " Standards for Combustible Gas Control System in Light Water

, Cooled Power Reac tors." Additionally, these locations are such that operation of safety-related systems would not be impacted by the discharge of the anticipated mixtures of stearn, liquids, and noncondensible gases.

The licensee hos made provisions for operability testing of the high point vent system in occordance with subsection IWV of Section XI of the ASME Code for Colegory B volves and hos stated that the vent volves will be exercised during refueling.

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. . . o CONCl.t JSION ,

We conclude that the Three Mile Island I high point vent system design is sufficient to effectively vent noncondensible gases from the reoctor coolant system without leading to on unocceptable increase in the probability of a LOC.A or o challenge to containment integrity, meets the design requirements of NUREG-0737 Item II.B.1, and conforms to the requirements of paragraph (cX3Xiii) of 10 CFR 50.44. We therefore recommend that the Three Mile Island I high point vent system design be found acceptable with the following two confirmatory items. The' power source and the rnethod of volve position

.g . indication for motoq-op,erated volve,RC-y28,must be described in sufficient detail for ,

NRC'~to det..er..m..i.n..e. that they are acceptoble, and the potential common mode failure problem noted above conceming, solenoid-operated volves must be satisfactorily re5cived. In addition, it should be noted that the following items were excluded from the scope of our review: seismic and environmental qualification of the high point vent system, operating guidelines and procedures for the high point vent system, and requi:ed modifications to the plant technical specifications and in-service-inspection program for the high point vent system.

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F' REFERENCES  !

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I. Letter, H.D. Hukill (Metropoliton Edison Cornpany) to J.F. Stolz (NRC), "Three Mile Island Nuclear Station, Unit 'l (TMI-1), Operating License No. DPR-50, Docket No. 50-289, RCS High Point Vents (LM-21 )," dated September 3,1981, and referenced documents.

2. Letter, H.D. Hokill (CPU Nucleor) to J.F. Stolz (NRC), "Three Mile Island Nuclear Station, Unit I (TMI-l), Operating License No. DPR-50, Docket No.50-289, RCS Vents (NUREG 0737 !!.B.1)," dated August 23,1982.

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