ML19331E431
| ML19331E431 | |
| Person / Time | |
|---|---|
| Issue date: | 05/30/1980 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-1724, NUDOCS 8009100160 | |
| Download: ML19331E431 (9) | |
Text
DATE ISSUED: 30 May 80 pgna g N l.
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1 f p fjSJBCOMMITTEE MEETING MINUTES g
} [ [g L ATURAL CIRCULATION HEAT REMOVAL q l:(lTe MARCH 26 1980 s
TheACRSSubcommitteeonNaturalCirculationHeatRemohalmetonMarch26, 1980 in Room 1046 at 1717 H Street, N. W., Washington, D. C.
The purpose of themeetingwastorehiewthepresentstateofknowledgeonvariousmodesof naturalcirculationheatremohalinPWR'swhichmightbeimportanttodecay heat removal during accident or transient conditions. Notice of the meeting was published in the Federal Register on March 10 and March 19, 1980 (Appendix A). Dr. Andrew Bates was the Designated Federal Employee for the meeting. A list of meeting attendees is attached as Appendix B.
No written statements orrequestsfortimetomakeoralstatementswerereceihedfromthepublic.
NRC STAFF PRESENTATION ON CURRENT REQUIREMENTS FOR AND KNOWLEDGE OF NATURAL CIRCULATION IN COMMERCIAL PLANTS Mr. W. Hodges indicated that Regulatory Guide 1.68 required testing for natural i
circulation (water solid) during the start up phase of each reactor unless tests at a similar reactor could be shown to be equivalent. The major problem in running the tests is in merarement of the natural circulation. Flow is too low to be detected so herification is dependent upon establishment ofAT values across the core and steam generator as well as a system heat balance.
Verification of natural circulation is dependent upon examination of the sys-l temtemperatures,herificationofstablehotandcoldlegtemperatureswith l
a AT across the core and steam removal from the steam generators. All of the l
current requirements relate to natural circulation under water solid condi-l tions (bubble in pressurizer); there are no requirements for any tests under two-phase conditions and such testing would be avoided as possibly damaging to the reactor fuel. Testshahebeenrunundersteadystateconditionsand transient conditions from high power. The startup tests are initiated at about 5% power with a reactor trip and a coolant pump trip. A number of events hahealsobeeninitiatedatnearfullpowerduetolossofpowertothereactor coolantpumpsorothertransientehentsleadingtopumptrip. In either case naturalcirculationhasbeenprohentofunction.
In response to questions
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theStaffindicatedthatthetestshahebeeninitiatedfromRCPcoastdown conditionsandtherehaYenotbeentestsoftheselfstartingcapabilityof natural circulation. The Staff indicated that they did not see any potential
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Nat'lCirHeatRemohal March 26, 1980 7's probleminEandCEdesignssincetheSteamGeneratorElehationwassuffi-ciently above the core, on B&W reactors the secondary side water level would hahetobehighenoughtoinitiatethenaturalcirculationflow.
Dr. B. Sheron indicated that the NRR Staff had a number of unanswered questions with regard to two-phase natural circulation. Certain small break LOCAs require heat removal by the steam generators. Calculations indicate that two-phaseloopflowandr'e'fluxboilingshouldtakeplace;howeher,noexperimental data is available. NRR has asked Research to experimentally verify that two-phase natural circulation will take place. At the present time significant problems are not foreseen; however, the capability of natural circulation to remohedecayheatwhenlargeenoughquantitiesofnon-condensablegasesare introduced into the primary system is still of concern. The Staff indicated that gas may arise from accumulator nitrogen, dissolved gases, core oxidation, or failure of th,e UHI cut off valves. For very small breaks where the steam generators are required to remove decay heat the pressure does not decrease to the accumulator set point, for breaks which do turn on the accumulator the RCS pressure must fall to about 150 psia before significant quantities of N2 enter the system. At this pressure the LPIS and RHR system can provide adequate core cooling. The Staff does not believe that there is a significant problem with non-condensables, unless there is significant core oxidation or failure of the UHI valves which should block N2 injection.
(SeealsoypresentationonUHI to ECCS Subcommittee on March 25,1980).
The Staff also reviewed the guidelines given to the plant operators for veri-fying natural circulation. The guidelines require verification of reactor trip, start of the diesels if offsite power is lost, verification of natural circulation for core AT values, verification of steam dump setpoint, starting of auxiliary feedwater pumps.,and actions to prevent a too rapid cooldown of of the primary system. Instrumentation available to the operatcr includes T hot, T cold, pressurizer level, pressure, incore thermocouples, secondary steam pressure, and steam generator level. The procedure also contains corrective actions to establish natural circulation if the verification procedures fail to indicate natural circulation.
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Nat'l Cir Heat Removal March 26, 1980
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Mr. R. Baer outlined the special low power tests to be performed at the Sequoyah plant during start up. At the time of the meeting the Staff indi-cated that they still did not have detailed information on the procedures to
,be used in conducting the tests or a detailed safety analysis for the tests.
The proposed tests include:
(1) Natural circulation under normal conditions (2) Natural circulation (N/C) with simulated loss of offsite AC (3) N/C with loss of pressurizer heaters (4) Effect of steam generator isolation on N/C (5) N/C at reduced pressure (6) Cooldown capability of charging / letdown system (7) Simulated loss of all AC (8) Establishment of N/C from stagnant conditions (9.afForcedcirculationcooldown (9.b) Boron mixing and cooldown in N/C.
The criteria in choosing the tests to be performed include:
(1) The tests should provide meaningful information (2) The tests should provide supplemental operator training (3) The tests should not pose undue risk to the public (4) The risk of plant damage should be low, and (5) The post test radiation levels should not preclude implementation of the future TMI-2 requirements.
The Staff noted that none of the tests is expected to enter a region of two-phase fluid flow. In response to questions Mr. Baer indicated that TVA would be adding some supplemental instrumentation for the tests but not a lot. The con-sultants and Subcomittee members expressed concern over the adequacy of instru-mentation and the value of any data (or lack of data) that might be obtained from the tests. The consultants also questioned how meaningful the tests would be-if they did not include two-phase flow. Mr.BaerindicatedthattheStaffhiewed the tests more as a method of operator training than as needed experimental data.
i Mr.BaerrehiewedtheNRCStaff'spresentpositionswithregardtofeedand I
bleedheatremohal. The B&O Task Forc concluded that the capability of plants with low head HPI pumps to depressurize with the PORVs to initiate HPI in time to preclude core damage is highly uncertain and that a diverse decay heat removal path independent of the steam generators was desirable. They recom-
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Nat'lCirHeatRemohal May 29, 1980
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mendedconsiderationbegihentoincreasedPORVcapacity, high head HPI pumps, or high pressure residual heat removal systems.
At the present time there are no NRC requirements for plants to have a feed and bleed capability. There are a number of different opinions within the NRCStaffastowhetheritisbettertohahefeedandbleedcapability,a high pressure RHR system, or increase the reliability of the auxiliary feed-water system.
Mr. J. Ebersole indicated that the reliability of natural circulation would limittheextenttowhichimprohementsinthesecondarysidewouldbeuseful.
The Staff indicated that for cases where there were no non-condensable gases they did not forsee any interruption of natural circulation.
In the case of UHI injection you would not be injecting N2 until the system pressure was below about 600 psia. At that point the steam generator would be acting as a heat source rather than a heat sink. W has also submitted a calculation that the Staff is reviewing (See ECCS meeting March 25,1960) which indicates that even with the UHI gas there is sufficient area and volume in the steam gene-rator tubes to maintain the heat transfer process. The Staff is still review-ing this submittal and the Subcomittee consultants indicated that they have some questions with regard to the degradation of the heat transfer cuafficient.
The Staff stated that there could be a number of problems with feed ar ed even in reactors with high head HPI pumps; these include lack of safety tcade controlstoPORVs,reliabilityofthehalhesundertwophaseorliquidflow, and the dumping c: large amounts of water into the containment.
(Thereis currently an NRC research program which is following tests which are planned byEPRIonPORVand.safetyhalhedischarges. These tests should address some of the unanswered questions on flow rates under different conditions of the
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fluid).
Dr. S. Fabic reviewed the present status with regard to the ability to calculate natural circulation under water solid two-phase loop flow, and reflux condi-tions. He also discussed the experimental data needs for assessment of the codes calculational ability. Experimental knowledge of hot and cold leg flow
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Nat'l Cir Heat Removal March 25, 1980
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rates, stratification, fluid densities, liquid and vapor velocities, froth lehels,andfluidtemperaturesinboththeprimarysideandsecondarysideare important. Some data is available from LOFT Tests L3-1 and L3-2 for compari-son to the calculations. Rehiewofthedatashowstheneedtotakeinto account stratified flow, counter-current flow, and fluid conditions upstream of the break orifice. Knowledge is needed on the flow regimes which will occur in the steam geoerator tubes and in the hot leg in order to properly model the flow. Present codes (RELAP 4) are basically homogeneous flow, more advanced codes (TRAC and RELAP 5) should be able to eventually handle the two-fluid flow involved with counter current conditions, stratification, and refluxing. TRAC will also eventually include a non-condensable gas field.
Dr. Fabic indicated he felt that with the recent experimental uncertainties and lack of needed measurements he could not say whether the codes were doing a good job or a bad job in calculating two-phase natural circulation.
In response to a question from Dr. Theofanous, Dr. Fabic indicated that the presenthendorehaluationmodelswhichdonotincludetwo-fluidmodels were probably inadequate for calculation of some of the small break LOCA sequences. He indicated that Research was using both advanced codes and codes which were similar in model (but best estimate) to the vendors codes in order to gain knowledge as to,the important phenomena that need to be modeled.
Dr.Cattonrecommendedthatconsiderationbegihentodoingasimpleexperi-ment to determine the effect of ncn-condensables on reflux boiling. He indi-cated that such a test could be done as a gross basis to determine when enough gas had been injected to shut off the refluxing, this could be done using a heat balance without need to measure where the gas vent or other param-
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eters that might be of interest to the advanced code development people. The j
details could be worked out in the longer term.
Dr. Fabic pointed out a number of modeling problems with the codes. These include the need to model stratified flow in pipes, counter-current steam-liquid flow in steam generator tubes and the hot leg, ECC mixing at the injection nozzle, and system leakage flows and bypass flows. All of these items have been shown to be important in LOFT tests.
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Nat'l Cir Heat Removal March 26, 1980
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The Subcomittee consultants and members generally agreed that decisions were going to have to be made as to the level of detail necessary in the code, otherwise, with a purely microscopic appro6ch the experimental program would neheryieldsufficientdatatoaccuratelycalculatethedesiredtransients.
Dr.H.Su11than,NRCResearch,rehiewedanumberofprogramsintheSystems Engineering Branch that will be looking at natural circulation. In response to a question he indicated that some tests would be conducted from stagnant conditions to verify that natural circulation would start by itself without any forced flow. Dr.Sullihanindicatedthatp;9;entcalculationswithRELAP 4/ MOD 7, and RELAP 5 have indicated that natural circulation under water solid conditions is not a problem. The codes also predict that the reactors can enter into a two-phase natural circulation.
The Research program will be conducting a number of tests in experimental facilities to study natural circulation under various conditions. This will include single phase, two-phase - one component, and two-phase - 2 component (non-condensable and water) tests. Test results will be used to study the adequacy of the calculational methods. The goal is to obtain codes in which we have adequate confidence so that the NRC Can use them to perdict the behahioroflargePWRs.
InrepsonsetoquestionsDr.Sullihanindicatedthatstudieswerebeingcon-ducted to determine how much non-condensable gas might be injected or produced in a reactor system. This would then be used as a basis for running tests in Semiscale or other facilities to determine whether or not it can casue problems ininterruptingheatremohalthroughtherefluxingprocess. Dr. Sullivan also indicated that they have not planned any tests on feed aM bleed since NRR has not requested them. They do have the capability of doing some tests if requested.
(NRR subsequently asked for some tests on loss of AC and DC power and core boil off of water, A preliminary test has been conducted in Semiscale.) Tests will be canducted to look at the heat transfer in the core and steam generator, phase separation, transitions between phases, mass injection and removal, imbalance between steam generators, two-phase mixture levels, and counter-current flow effects. A number of tests will be conducted in various facilities including LOFT, Semiscale, Flecht-Seaset, PKL, CCTF, THTF, TLTA, and in various univer-sity programs. A number of the facilities are scaled to be full height and
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Nat'lCirHeatRemohal March 26, 1980 t
theyarearecapableofrunningataharietyoftest pressures. The univeristy program involves looking at steam generator U tube behavior using transparent U-tubes for flow visualization.
One major problem that Research is working on with each of the experimental facilities is the adequacy of the instrumentation.
In many cases improvements are needed for the phenomena that need to be measured, i.e.; low flow, counter-current flow, and two-phase flow.
The Subcomittee members and consultants expressed their opinions on a number of items that they thought should be investigated furhter. Mr. Bender indicated thatthecapabilitytodepressurizetheprimarysystemwouldsolhemanyofthe problems associated with needing natural circulation or feed and bleed. Dr.
Lienhard indicated that he felt more could be done with proper use of dimension-less groups in scaling of flow between the small experiments and larger systems.
The meeting adjourned at 5:30 pm.
Additionalinformationisahailablefromthemeetingtranscriptahailablein the NRC Public Document Room, at 1717 H Street, N. W., Washington, D. C.
A complete copy of the slides presented is on file at the ACRS office with the reocrd copy of the minutes.
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ATTENDEES LIST ACRS MEMBERS M. Carbon M. Plesset H. Etherington J. Ebersole I
M. Bender ACRS CONSULTANTS J. Lienhard V. Schrock Z. Zudans I. Catton T. Theofanous ACRS STAFF A. Bates, Designated Federal Employee E. Abbott, ACRS Fellow
-G. Young, ACRS Fellow NRC STAFF W. Hodges, RSS B. Sheron, RSB H. Ornstein, AEOD T. Speis, RSB P. Norian, AB R. Baer, DPM R. Auluck, STD H. Sullivan R. Landry Z. Rosztoczy, NRR C. Graves, NRR Others R. Turk, GE J. Gloudermans, B&W D. Lambert, TVA R. Olson, Balt Gas & Elec l
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Federal Raist:r / W1. 45. Nr. 55 / Wedn;sday. MErch 19. 1980 / N;tices
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'... rAneticipot;d Transidents WithoutScrom review
- user needs"in structural May241990-Agendoissen,
(A TWSI. March 26,1980. Washmatou. DC engineering rad the w:y in which these The Subcornmittee will meet with needs have been met.
fune 5-7.1980-Agendo to be om..,
representauves of the NRC St.ff to
- ReortorRodeologico/Erfects. April 23.1980.
Datei March 14.1980.
L continue escussion of the proposed Washington, DC The Subcommittee wiu lohn C HO)le.
resolu!!nn of ATWS. Netae of this rneeting eeview the raiological protection AdvisoryCommitteeMonocemeny.
was pubhr.hed March 11.
programs at nuclear power plants.
- Three Mde Island Unit 2 Accident Action
- Noturo! Circulation andFeedandBleed I"***"*****'******I Flons. Aprill-2.1990. WashinFton. DC An NeotRemoval. Apri!24.1f,J0. An Ad Hoc auseo cooe nos.4w Ad Hoc Subconi:nittee wtB review Draft 3 Subcommittee will continte its review of of NRC NUREG-0000. " Action Plans information presently available on natural Deseloped as a Result cf The TMI-2 drculation and feed and bleed heat Advisory Committee on Reactor Accident." Notice of this meeting was removal systems. Also aresa where Safeguards, Subcommittee c.i published March 17.
inadequa te information is available will be Emergency Core Cooling System '
'Bobcock & Wilcox WaterReactors. April 8, examined, and planned NRC (or other)
Change of Date 19so, Washington. DC.The Subcommittee tuts that will be run to obtain needed wiU complete its review of the NRC Staff information wiU be stu6ed and the The March 26.1980 meetm.g of it.-
study to determine whether constructica possible need for other tests will be ACRS Subcommittee on Emerynry should be halted on certain B a W plants explorei Core Cochng Systems has been because of sensitivig of the once.thtonsh-steam generator (CTISG) to feedwater
.Meto/ Components. Apr0 24-25.1980. Oak rescheduled to be held on Mari.h -- 5.:!
Ridge.TN.The Subcommittee wiu meet items pertaining to this meetin;; r. -
, transimts.
with representatives of the NRC anu ORNL the same as announced in the Fedce..I
.t
" ' Section Steel ice ons Ap 9.90, as ing*on.
Register March 11.1980 (45 FR 15?m T
ogy sm DC An Ad Hoc Subcommit'ee wiu discuss Implications of the TMI-2 Accident as they
.ReactorFuel. Apn! 29.1980. Washington.
Dated March 14.1980.
DC. The Subcocimittee williscuss the John C Ho}!e.
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cuo e am). Wa shington. DC The Subcommittee in c mmerdal LWRs. including particular p1one, so. ens ra.d us am aos el e
mal evnta that occurnd will review regulatory pides and reWons
,p$s gaAamo coce neo.e w to exts'ing replatnry gddes; also it may discuss pertinent methities which arTect the
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current Lcensing process and/or reactor 30.
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C Advisory Committee on Reacter operat on.
e Deed t d a
eafety Safeguards, Ad Hoc Subcommittee on f
g,,,d,e el0p qu Natural Circulation Heat Removal;
'PowercridElectrice/ Systems. April 9.1980 (240 pcG. Wa sh.'ng*on. DC The Subcommittee wiH coesicer the ncclear consideration of the actual form these goals Change of Date data hnk [NDL). presently being developed may take and whct they should De March 25.1980 meeting of the by NRC as part of the TMI-2 Accident
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a
.s of Class ccidents. May e.
ACRS A,d Hoc Subcommittee on Ntural Acens Mans.
,RecctarSafetyResearch Aptd 9.1980. [4.00 1980. Washington. DC The Subcommittee Circulation Heat Removal has been pm). Wa shin; ton. DC The Subcommittee will discun consideration oflow rescheduled to be held on March 26.
probability. high consequence accidents 1980. Notice of this meeting was g a or Re ea h o s to (inc!cding core meh) as part of the announced in the Federal Register roccamendations to Coneress on NRC licensing process. The Integrated Fuel Melt March 10.19G0 (45 FR 1534/).
research (NUPIG-0657)dtso, the FY-42 Research Program win alsa be discusu&
In addition, the title of this Ad floc budset tesiew and prepar=*aon of the ACRS Full t%-nittee Meetings Subcommittee has been changed to j
ACRS report to NRC wiu he d: set.ssed.
A O*I2' "
"ACRS Ad Hoc Subcommittee on
'Cenem!Electr c TestReactor(CETR). Apr11 P
Natural Circulation and Feed and IVced
%-19. :900. Sanc! CA. De Subcommittee A.
- Floating Nuclear Plant-Core ladle Heat Removal."
wiU continue its review of the geologic and conceptual design.
seismolegic aspects of the GrrR plant site.
B. 'Sequoyah Nuclear Power Plant. Unit t-All otheritems regarding 6 meeW.
j Also, other matters related to the NRC Augmented low-power test program.
remain the same as announced m, cited Order to Show Cause may be discutsed.
C ' Anticipated Transients Without Scram notice.
Notice of this meeting was pubhshed (ATWS)-Proposed plant modifications.
Dated March 14,1980.
February 22.
D.
- Pressurized Water Reactors with Once
'l.icensee Event Report (IER/. April 72.1980.
nrough-Steam Cenerators (OTSG)--
}ohn C Hoyle.
I (8.30 str). Washington. DC The Dynamic response to transients.
Advisory Com. nitsee Monesement Oficer.
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Subcommittee will review p!ans of the new E. 'NRC Action Plans to Implement lessons pn poc. so ane rJed Ms.am Hs aml NRC Omce of Analys:s and Evaluation of 14amed from the 311-2 Accident-saleco coot rses.es-se Operations! Data, ard NRC action in Preposed implementa tion oflong term response to the ACRS L R Report.
Items.
j r
(NUFIO-05?2).
F. ' Cods of Federal Regulations (10 CFR. Part Advisory Committee on Reactor
' Site Evol.otion. April 22.1960. (1.00 pm)
- 50. Appendix K.ECCa Evaluatina Safeguards, Subcommittee on Washington. D*. The Subcomcuttee v.iu Models)-Proposed chariges in techniques review the proposed Frcergency Planning to calculate clad.ba!!ooning.
Concrete and Concrete Strectures; Rule (10 CFR. Part 50), published in the C. ' Proposed Rep!ies to NRC Co nmissioner Chan9e of Date Federal Re:;fster December to.19 3 na.d V. Cilinsky re ACRS Re port dated Dec.11.
He meeting of the ACES NUREG 0054. "Cn:eria for Prepar.uion and 1979 on the pause in licensing and Subcommittee en Concrete and Eva!aauon of Radioleg! cal Emeritency proposed use of the nuclear data link Concrete Structures announced in the
. Response P!ans and Preparedness tr.
(NDL).
Federal ReE ster March 10.1930 (45 FR i
Support of Nuc! car Power riants " Nctics H.
- Meeting with NRC Chairman J. Aheame of this meeting was pubished Februirv 22.
and other NRC Comrrissioners who may be 15340) has been rescheduled from M.irch i
- Concret, cadConcrrreStmchtres. Arn!22-present re ACRS actisities as en NRC 25-28. to April 22-2't. I'.MO. All othc r l
23.1980-Reschernited frnra March 25-24 adviscry commit:ee. including ACRS items regarding this meeting roamin the Washinron.DC ne S.bcomclittee will comrnents on the NRC Action Pl. ins.
same as announced in the cited notice.
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