ML20077K773

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

ML20077K773
Person / Time
Site:	Prairie Island
Issue date:	02/23/1983
From:	Held J ENERGY, INC.
To:	Alberthal G NRC
Shared Package
ML20077K776	List: ML20077K773
References
CON-FIN-A-0250, CON-FIN-A-250, RTR-NUREG-0737, RTR-NUREG-737, TASK-2.B.1, TASK-TM TAC-44398, TAC-44399, NUDOCS 8306030415
Download: ML20077K773 (6)

Text

g Lawrence Livermore National Laboratory 2 .

L ENCLOSURE 2 4

Selected Operating Reactor Issues Program II Reactor Coolant System Vents (NUREG-00737 Item II.B.l.)

NRC FIN A0250 - Project 9 l

FINAL TECHNICAL EVALUATION REPORT FOR PRAIRIE ISLAND 1 AND 2 Docket Numbers 50-282 and 50-306 NRC TAC Numbers 44398 and 44399 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 Regula, tion, Division of Licensing.

NFC Lead E tgineer - Gus Alberthal FoTICE

~

"This ryc.t was prepared as an arxount of work i spnareri b the U sted Sates oov:rne: cat.

bcitter t1.2 nat4 Siatn not the Unit 2 Sutw --

Ocrartment of Entrn.nor any cf their employees, not a..y c.f tae r ccatractors, suxontractors, or their employees, makes any warranty. express or implied or assumes any legalliabilit or respon-sibility for the accuracy. com iences or  !

usefulness of an information, apparatus product )

[

cr process di osed. or represents that its use 1 l

would not infringe privately-own.ed rights." ,, , _ ,

l XA Copy Has Been Sent to PDR l TF-342/0809a February 23, 1983 m

e 300o=50'l l s' 41Expa!CWstr yEnctbv vimesnyof Calkma

• RO BarBOB LMymom.CalkrruMSS0

• ery v ~ , .1,22 "^^ "::: :auJ39 UCLLL LVMR

1

. ' Docket Numbers 50-282 and S0-306 NRC TAC Numbers 44398 and h4359 .

TECHNICAL EVALUATION REPORT ON REACTOR COOLANT SYSTEM VENTS FOR PRAIRIE ISLAND I AND 2 INTRODUCTION The requirements for reactor coolant system high point vents are stated in paragrcph ,.

(cX3Xiii) of 10 CFR S0.44, " Standards for Combustible Gas Control System in Light '

Water Cooled Power Reactors," and are further described in Standard Reiiew Plan (SRP)

Section 5.4.12, "Raoctor Coolant System ,High Point Vents," and item II.B.I of NUREG-0737,"Cicrification of Ti31 Action Plan Requirements." In response to these and previous requirements, the Northern States Power Company has submitted informati$n'in

~

References I through 3 in support of the" vent system pt Units { ond 2 of the Prairie Island Nuclear Generating Plant.

EVALUATION .,

The function of the reactor coolont system (RCS) vent system is to vent rencondensible goses from the high points of the RCS to assure that core cooling during natural circulation will r9t be *nhibited. The Prairie Island I and 2 RCS vent system provides venting c'opobility from high peints of the pressurizer. steam space and the reactor vessel head. The nonconds.sible gases, stecra, cc.d/or iiquids vented from dther tis pressu?iler or the reactor vessel head are piped and discharged to one of two locations, the pressurizer relief tank (PRT) or directly to the containment. Each RCS vent path is designed to vent a volume of gas approximotely equal to one half of the RCS volu.me in one hour. A flow restriction orifice in each RCS vent ~ path, however, limifs the flow from o pipe rupture or from inadvertent actuation of the vent system to less than the capability of the reactor coolont makeup system. Hence, the licensee's cornpliance with 10 CFR S0.46, " Acceptance Criterio for Emergency Core Cooling Systems for Light Water Nuclear Pow [er Reactors,"is not offected by the addition of the RCS vent system.

The vent path from the reactor vessel head and the vent path from the pressurizer each contain two independently powered solenoid-operated volves in parallel and connect to o I Iy/TER-P-21 Enelara 3

I l

~

common header that discharges either to the containment atmosphere or to the PRT.

The lines to the containment atmosphere and the PRT each contain on isolation valve a

powered from independent power sources. Thus, o degree of redundancy has been provided by powering RCS vent valves from different emergency power supplies, to 1 ensure that RCS venting capability from both the reactor vessel head and the pressurizer is maintained. Valve control switches and indication of volve position are provided in the main control room. RCS vent volve seat leakoge is detected by pressure instrumentation with associated alarms in the main control room.

The portion of each RCS veht path up to and including the second normally closed valve forms a pan o'f the reactor coolant pressure boundary and thus must meet reactor s

coolant pressure boundary requirements. The licensee has stated that this portion of the 1 vent system is designated Safety Class 2 (Safety Class I upstream of the flow restriction orifices) and Seismic Category'I in compliance with 10 CFR 50.5,5a and Regulatory Guides 1.26 and 1.29. The RCS vents are designed for pressures and temperatures corresponding to the RCS design pressure and temperature. In add.ition, the vent system materials. ore compatible with the reactor coolant chemistry, and the reactor vessel. head vent and the press'urizer vent are occeptably separated and protected from missiles and the dynamic effects of postulated piping ruptures. However, the licensee hos not

.. ;!emenstrated that the vent system will be fabricated or.d tested in occordance with ' '

cceeptabla requirmnents (e.g., SF Section 5.2.3). We therefore conclude that the design of the portions of the RCS vent system up to and including the second normally closed volve conforms to o!! reoctor coolant pressure boundary requirements, including 10 CFR 5'h5So and the applicable portions of General Design Criterio I,2,4,14,30, and 31, contingent on verification by the licensee that the vent system will'he fabricated and

^

9ested in occordance with SRP Section 5.2.3 or other occeptable requirements. The licensee has further ascertained the essential operation of other safety-related systems will not be impaired by postulatcd failures of RCS vent system components.

We have reviewed the licensee's RCS vent system design to assure on acceptably low probability exists for inadvertent or irreversible octuation of the vent system. Eoch vent path has two solenoid-operated valves in series and each volve has on individual control switch.

Power will'be normally removed from the valves at the power supply panel, l minimizing the probability of isolation failure due to hot shorts and at the some time minimizing the probability of inodvertent operation of the vent system. After the need to vent has been determined and administrative approval to energize power to the valves i

l

l ly/TER-P-21

- --- - - - - -- ~ ~ Enclosure 3_ __ . _ J

has been given, the volves will then be repowered by reptocing the fuses at the panel.

l The volves are designed to fait closed upon loss of electrical power and will remain leak l tight in a deenergized state. The licensee has otso stated that the controls and displays added to the main control room will be considered in a human factors analysis during the Detailed Control Room Design Review to be conducted at a later date in accordance with NUREG-0700. However, the Prairie Island I and 2 RCS vent system design includes Target Rock solenoid-operated volves, which may be susceptible to o common mode failure because operation of one volve may cause other volves in the system to open temporarily 6,ee Refe.rence 4). The licensee will be required to evoluote this problem

~

and present their conclusions including a1y design changes necessary to minimize the probability of an inadvertent vent system Etuation. We therefore find that no single octive component failure' or human error}.should result in~ inadvertent opening or irreversible operation (i.e., failure to close offer"intentiono!'ipening)'of the RCS vent system, contingent on s'atisfoctory resolution of the problem with Torget Rock solenoid .

operated volves. HowSer, RCS vent volve position indicot. ion is dependent on control i power, and therefore ' removing c,3ontrol power os described above will result in loss of positive volve position Indication during normal plant ' operation Until on acceptable '

alternate method of minimizing the probability of inadvertent operation or ensuring continuous position indication is provided, this is on open item.

m We hak also examined the locations where the vent system discharges to the containment atmosphere, either directly or vio the FRT rupture disc. Based on a description provided by the licensee (Reference 3), these locations are in arcos that assure good mixing with the containment atmosphere to prevent the occurrrAotion or pocketing of high concentrations of hydrogen in complicnce with 10 CFR 50.44,

" Standards for Combustible Gas Control System in Light Water Cooled Power Reoctors." Additionally, these locations are such that the operation of safety-related systems would not be adversely offected by the discharge of the anticipated mixtures of steem, liquids, and noncondensible gases. -

The design provides for individual test and open/ closed indication of each volve, and the licensee has stated that operability testing will be performed in accordance with subsection IWV of6ection XI of the ASME Code for Colegory B volves during refueling.

I ly/TER-P-21 Enclosure 3 t Pagt3 of 5

1 CONCLUSION -

We conclude that the Prairie Island I and 2 RCS vent system design is sufficient to effectively vent noncondensible gases from the reactor coolant system without leading to j on unocceptable increase in the probability of a LOCA or a challenge to containment Integrity, meets the design requirements of NUREG-0737 Item li.B.I, and conforms to the requirements of paragraph (cX3Xiii) of 10 CFR S0.44 with one exception concerning positive valve position indication as noted above. We therefore recommend following resolution of this open item that the Prairie Island I and 2 RCS vent system design be found acceptable with the following two confirmatory items. Th6 Target Rock solenoid-operated volve problem noted above must be satisfactorily resolved, and the fabrication and testing of the portion of the vent system that forms part of the reactor coolant pressure boundary must be determined to be occeptable (e.g., in occordance with SRP Section S.2.3). In addition, it should be noted that the following items were excluded from the scope of our review: seismic and environmental qualification of the RCS vent

! system, RCS vent system operating guidelines and procedures, and required modifications to the plant technical specifications and in-service inspection program for the RCS vent system. -

l I

j l

e l

I ly/TER-P-21 Enclosure 3 Page 4 of S

REFERENCES

l. Letter, L.O. Mayer (Northern States Power Company) to Director of Nuclear Reactor Regulation (NRC), " Lessons Learned Implementction," . doted December 31,1979

2. Letter, LO. Mayer (Northern States Power Co.mpany) to Director of Nuclear Reoctor Regulation (NRC), "Information Submitted in Response to TMI Action Plan 11 ems 11.B.1 and ll.D.1," dated July 6,1981 ..

3. Cetter, L.O. Mayer (Northern States

• Power Company) to Director, Office of Nuclear Reactor Regulation (NRC), " Response to Request for ~ Additional Information Concerning Reoctor Coolant System Vents," dated April 26,1982

~

4. NRC Memorandum, T.P. Speis (Division of Systems Integration) to T.M. Novak (Division of Licensing), " Unintentional Lifting of Solenoid Operated Pilot Volves in RCS Vent System," dated Mor:h 9,1982 ,

l t

t I ly/TER-P-21 Enclosure 3

_ _ _ _ _ _ . nasa