ML17309A352

Forwards Evaluation & Guidance Re Proposed Westinghouse & Exxon Models for Large Break LOCA Analysis for Upper Plenum Injection Plants,To Aid Licensee Development of Acceptable ECCS Evaluation Model Per App K & 10CFR50.46

ML17309A352
Person / Time
Site:	Ginna
Issue date:	02/12/1985
From:	Zwolinski J Office of Nuclear Reactor Regulation
To:	Kober R ROCHESTER GAS & ELECTRIC CORP.
References
NUDOCS 8502140121
Download: ML17309A352 (34)

Text

I REGULATORY

'ORMATION DISTRIBUTION SYS.

M (RIDS)

ACCESSION NBR:8502140121 OOCeDATEt 85/02/12 NOTARIZED:

NO DOCKET FACIL:50-244 Robert Emmet Ginna Nuclear Planti Unit 1i Rochester G

05000244 AUTH,NAME AUTHOR AF F ILIAT'ION ZHOLINSKIzJ,A ~

Operating Reactors Branch 5

RECIP ~ NAME RECIPIENT AFFILIATION KOBERpR AN, Rochester Gas ln Electric Corp-,

SUBJECT:

Forwards evaluation 8, guidance re proposed Nestinghouse Exxon models for large break LOCA analysis for upper plenum injection plantsito aid licensee development of acceptable ECCS evaluation model per App K L 10CFR50

~ l6e DISTRIBUTION CODE:

SE01D COPIES RECEIVED!LTR '

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TITLE:

NRR Correspondence re SEP Topics NOTES:NRR/DL/SEP icy, OL:09/19/69 05000244 RECIPIENT ID CODE/NAME MILLERi C INTERNAL'CRS ELD/HDS4 IE/DQASIP/ORP 8 NRR/DL/SEPB RF EXTERNAL; DIST EX(2 e-

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UNITED STATES NUCLEAR REGULATORY COMMISSION

'LVASHINGTON,D. C. 20555 February 12, 1985 Docket h'o. 50-244 Mr. Roger W. Kober, Vice President Electric and Steam Production Rochester Gas 8 Electric.Corporation 89 East Avenue Rochester, New York 14649 Re:

SUBJECT:

DEVELOPMENT OF AN ACCEPTABLE ECCS. EVALUATION MODEL WHICH INCLUDES

'THE EFFECT OF UPPER PLENUM INJECTION R.

E. Ginna Nuclear Power Plant This letter i's sent to you as the licensee of one of six operating Westinghouse two-loop plants which uses upper plenum injection (UPI) in their emergency core cool.ing systems (ECCSs).

Ginna is operating under 10 CFR 50.46(a)(2)(v) using Westingbouse and Exxon evaluation models that were accepted by the staff on an interim basis in 1978 staff Safety Evaluation Reports.

Continued plant operation was accepted on the basis that "the long term effort to produce an acceptable ECCS evaluation model for treating Upper Plenum Injection should continue unless the two-loop plant owners propose to modify the ECCS har'dware to eliminate Upper Plenum Injection."

The staff met with representatives of Rochester Gas 8 Electric Corporation (RGSE), the other UPI licensees, and Westinghouse on July 24, 1984 to discuss current evaluation models (EM) submitted to demonstrate compliance with 10 CFR 50.46 and 10 CFR Part 50, Appendix K.

The staff has completed its evaluation of current EMs submitted by Westinghouse and Exxon.

The current EM submittals continue to have deficiencies similar to those identified by the staff in our 1978 SERs.

Briefly, there are problems with inadequate documentation, absence of sensitivity studies, absence of physically meaningful models addressing upper plenum phenomena, the effects of UPI on refill, reflood, and heat and mass transfer, an absence of comparison of EM predictions with experiments, e.g.,

experimental data from Semiscale and the Cylindrical Core Test Facility, and lack of consideration of the differences between UPI and'non-UPI plants.'he staff'valuation of the deficiencies in the current EM submittals is enclosed.

Consequently, there is disagreement between your efforts and the staff regarding the degree of compliance which currently exists to meet the requirements of 10 CFR 50.46 and Appendix K.

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Nr. Roger M. Kober February 12, 1985 Utilizing the enclosed

guidance, provide a response regarding each of the areas in question to include plans, schedules and efforts to'e expended regarding each area identified as a staff concern.

<To the-extent practical y'ou should address each area'nd document the technical basis (by reference where possible) you rely upon to assure compliance, with 10 CFR 50.46 and Appendix K.

Your response should be submitted witfiin 60 days from receipt.

of this letter.

The reporting and/or recordkeeping requirements of this letter affect fewer tha'n ten respondents; therefore, ONB clearance is not required under.P.L..

96-.511.

Sincer y,

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Enclosure:

Evaluation

'John

. Zwolinski, Chief Operat'ng Reactors Branch ¹5 Division of Licensing cc w/eiic1osure:

See next page

Mr. Roge'r W. Kober February 12, 1985 CC Harry H. Voigt, Esquire.

LeBoeuf; Lamb,. Leiby and MacRae 1333 New Hampshire Avenue',.N.W.

Suite 1100 Washington, D.C.

20036 Ezra Bialik Assistant Attorney General Environmental Protection: Bureau New York State Department of Law 2 World Trade Center New York, Hew York 10047 Resident Inspector.

R.E.

Ginna Plant c/o U.S.

NRC 1503 Lake Road

Ontario, New York 14519 Stanley B. Klieberg, Esquire General. Counsel New York State Energy Office Agency Building 2 Empire State Plaza

Albany, New York 12223 Dr. Thomas E. Murley Regional Administrator Nuclear Regulatory Commission Region I Off'ice 631 Par k Avenue King of Prussia, Pennsylvania 19406 Supervisor of the Town of Ontario 1850 Ridge Road

Ontario, New York 14519 Jay Dunkleberger Division of Policy Analysis E Planning New York State Energy Office Agency Building 2 Empire State Plaza

Albany, Hew York 12223 U. S. Environmental Protection Agencv Region II Office ATTN:

Regional Radiation Representative 26 Federal Plaza New York, New York 10007

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Enclosure 1

EVALUATION AND GUIDANCE REGARDING PROPOSED WESTINGHOUSE AND EXXON MODELS FOR

'ARGE-BREAK LOCA ANALYSIS FOR UPI PLANTS On July 24, 1984, during a meeting at the NRC Offices, the licensees requested detai.led guidance on what should be included in any future evaluation model (EH) submittals for Westinghouse two-loop plants that use upper plenum injec-

. tion (UPI) during emergency core cooling (ECC).

That guidance is given here relative to the Westinghouse EN submittals and the Exxon EH submittals The

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.-.,guidance is similar because the Westinghouse and Exxon submittals suffer from similar deficiencies.

The guidance ends with comments on plant-specific accept-

.ance criteria for an ECC system (ECCS).

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A.

INTRODUCTION The staff, Safety Evaluation Reports (SERs) of 3/78 and 9/78 allowed for con-tinued plant operation [per 10 CFR 50.46(a)(2)(v)j'but they stated that the then-existing EM submittals for UPI plants were in need of improvemeht.

In particular, the SERs cited the need for revised EM submittals which would con-sider the thermal and hydraulic characteristics of the core and of the reactor

system, and the.need.for better documentation and.sensitivity studies.

The current Et< submittals continue to have deficiencies similar, to those identified

.- by the staff in our 1978 SERs.

UPI GUIDANCE

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There are two parts of 10 CFR 50 Appendix K that are particularly relevant to the perceived deficiencies in the current EM submittals for UPI plants.

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first is part I.D., "Post Blowdown Phenomena; Heat Removal by the ECCS."

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first five paragraphs of that part relate to PMRs, and our curr'ent understand-ing of UPI plants indicates'that'compliance with those paragraphs requires in-terpretation and analysis quite different f'rom that for non-UPI plants.

The second part of Appendix K that is particularly relevant is part II, paragraphs 3, 4 and 5 which (1) require sensitivity studies to address assumed phenomena, (2) require predictions of appropriate data by EMs, and (3) require the EMs to account for reactor differences such as UPI.

Section B of this evaluation and guidance document focuses on some of the de-ficiencies in the-current EM submittals and how the deficiencies are related to

- 'the Apphndix K paragraphs cited above.-

Sections C and D address the changes made by Mestinghouse and Exxon to their standard non-UPI EMs in order to account for UPI and elaborate some of the concerns raised in section B.

Section E is a.

summary of all prior sections; section

.F addresses plant-specific acceptance criteria for an ECCS.

There are additional compliance or compliance documentation issues related to other portions of Appendix K.

These become apparent upon a line-by-line ex-r amination of Appendix K.

However, they are not included here, either because (like Appendix K part I.B) they are not obviously significant in the context of the current EM submittals or because (like Appendix K part I.A) they would be better addressed when the staff is assured that a more appropriate EM exists for UPI plants. UPI GUIDANCE

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DEFICIENCIES IN THE CURRENT EN SUBNITTALS The conservativeness or appropriateness of th'e relationships among percent of v

the upper core plate covered by water in the: upper plenum,. top down quench,

~,core.heat'.transfer,'upper plenum heat:transfer, and UPI water penetration has not been'emonstrated.

The current EM submittals do not account for pooling of UPI water in the upper plenum; they assume that UPI water falls quickly into the core.

Semiscale

data, Cylindrical Core Test Facility (CCTF) data and TRAC analyses indicate that sig-nificant upper plenum pooling occurs for a range of UPI conditions.

There are several effects of pooling.

First, it calls into serious question the correla-tions used for vertical and horizontal entrainment of UPI water by steam flow.

-. These correlations did"not consider the existence of pooling or frothing.

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Second, pooling adds a hydrostatic head which is not accounted for in the cur-rent EN submittals.

'Third, a pool or froth of any significant depth (as shown

" -in the current data and analyses) clearly indicates virtually 100K of the upper-plenum is covered-by UPI water within a. very short time of the beginning of reflood, negating the physics of the EM submittals.

The pooling must be ac-counted for or the licensees must provide experimental data showing a different phenomenon exists in a UPI plant under UPI conditions.

During core reflood, the CCTF data and TRAC calculations show that flows at the cor e entrance plane are downward for UPI.

Hot rod heat transfer'-and carryover.

rate fraction correlations, which'are key ingredients in classical non-UPI EM reflood analysis, are derived from refined experiments with forced ~award flow.

The current EN submittals for UPI plants use reflood correlations based on w3w UPI GUIDANCE

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~u ward flow, but no basis has been provided showing that this data can e

be related to UPI plants.

A basis must be provided or some parameter other than flooding rate '(such as quen'ch height) needs to:be used along with a mass inventory procedure. that more nearly describes the mass:flow behavior in a UPI I

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system.

Alternatively, a more'echanistic model could be developed.

I The current EM submittals assume refill is similar to that for non-UPI plants; the differences in hydraulics and heat transfer during refill are not addressed.

Injection of UPI water into the upper plenum during refill may cause steam I

binding and delay water accumulation in the lower plenum and core, and this is not considered.

C.

THE RECENT WESTINGHOUSE EM SUBMITTALS Westinghouse proposed to determine the-effects of UPI by making ten modifica-tions to the WREFLOOD code (which is one part of the 1981 Westinghouse EM).

Evaluation and guidance comments are provided.for each of the ten modifications as follows, uss'ng the modification sequence and titles selected by Westinghouse.

1.

Metal Heat Transfer to UPI Water.

Heat transfer from upper plenum metal to UPI water is calculated by a lumped thermal capacitance model; It is necessary to show that either (a) the coeffi-cients used in the model are correct, (b) sensitivity studies show that results are insensitive to the values chosen for the coefficients, or (c) the coeffi-cients selected are.conservative for all cases and conditions of interest.

UPI GUIOANCE

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U er Plenum In ection Flow Distribution Westinghouse (W) assumes that safety injection (SI) forces ECC water into the upper plenum and this water covers only part'. of the core.

The percent core

~ coverage. is important because the W UPI EM uses different analyses for the t

covered and uncovered core regions.

Ci Acceptance of the partial core coverage concept would require explanation of experimental data from the Semiscale and CCTF test facilities which indicate upper plenum pooling occurs in the test facilities and hence may occur in UPI plants.

It would also require determination and analysis of worst case cover-age conditions and consideration of steam-water interactions.

3.

Deca Heat and Stored Ener

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This section of the Westinghouse EM submittal

says, in full, that "The decay heat calculation uses ANS plus 20 percent.

The initial stored energy at the beginning of reflood is based on the 'stored energy at the end of blowdown plus a calculation that adds the decay heat generated through the refill period to the core stored energy."

In evaluating the significance of this portion of the proposed model, the staff notes that the docketed EM submittals indicate that the refill period includes 14.45 seconds of pumped UPI before bottom of core recovery (BOCREC).

The. pro-posed Westinghouse EM ignores this UPI water during refill, which should be I

conservative relative to vessel inventory.

However, it is necessary to address the effect of this 14.45 seconds of pumped UPI on (a) steam generation and steam flow or steam, binding, (b) changes in fuel and metal wall stored energy prior to BOCREC, and (c) reflood, this being done with (d).1 and 2 trains of SI UPI GUIDANCE

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'Alternately,

('e) it is necessary to show that the proposed treatment is conservative and that injection of UPI water before BOCREC will not cause steam binding and delay BOCREC.

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Fuel Rod with To'ench F'ront j

I Operation of an SI train injec'ts ECCS water'nto the upper.pl'enum.

The M model assumes that this UPI water covers a fixed percentage part of the core, and that it will flow downward into that part of the core and cause a top-down quench.

- Mestinghouse assumed that the time required. for the top-down quench to reach

• the midplane of a fuel bundle was a specific linear function of the UPI mass flow rate per fuel assembly.

Adequate technical justification of the function describing the top down quench would require (a) much more specific identifi-cation of the experimental data used to develop the quench-time function, (b) a showing that the data applies to the UPI situation, and (c) a showing that the flow per assemb~ly is a valid correlation parameter.

Mestinghouse stated that it used a quench-time function which is a "bound to the [experimental data] since more rapid quenching increases heat transfer to UPI water and results in more steam generation."

This more rapid steam genera-tion is presumably detrimental because it will impede reflood.

However, to justify use of this'bounding quench function, it would be necessary to show that an over-estimate of top down quench speed (and/or of UPI flow per assem-bly) will riot cause an underestimate of peak cladding temperature (PCT).

UPI GUIDANCE

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Core Heat Transfer Model P

The Mestinghouse non-UPI EM uses very simple'heat generation and heat transfer models to determine core.exit fluid conditiohs.

Mestinghouse has made what

~ appears to be relagiyely simple.modifications to its non-UPI EM to account for r

heat,transfer'n the top down quench region.

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given for using this simplified model under UPI co'nditions.

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6.

Core Steam Generation It is necessary. to clarify the location of the UPI water, and whether part of it is held up in a pool in the upper plenum; and it is necessary to demonstrate l

'hat the correlation for carryover from core to upper plenum is applicable to two-loop UPI plants.

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The staff notes that water can be injected into the upper plenum at a rate which may be more than 10 times as large as the rate at which water can be I

= -injected into the intact cold leg, and that these flows determine the peak cladding temperature after the accumulators are empty.

The licensees must submit a reflood and refill model which considers these flows and -relevant thermal and hydraulic ch'aracteristics.

The licensee must specifically show how and why the water injected into the intact cold leg is or is not bypassed throughout the transient.

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Condensation The licensee must explain and justify (a) what happens if the falling subcooled UPI water can condense all the rising steam in the covered:region, and (b) the the equations and.assumptions coupling the covered and uncovered regions.

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UPI GUIDANCE.

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Vertical. Entrainment Steam may be generated by the UPI watter falling through the core.

This steam tt

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is assumed to entrain and carry part of the UPI water upward.

Mestinghouse has I

J not shown that the experimental, data on entrainment was;applicable to the con-It t

I'itions in a UPI pla'nt, or that there exists a reasonable technical basis, for g I 1

extrapolating the correlation butside the data base.

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Horizontal Entrainment Mestinghouse assumed that 1.67'f the ECCS water which is injected into the upper plenum is entrained by horizontally moving steam which carries this 1.67K

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The Mestinghouse entrainment model hasn't been

.proven valid because the model is based on (a) entrainment test data which has tt

..not been demonstrated to be applicable to the conditions in the upper plenum of

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'. a UPI plant, and. on (b) air flow tests which have not been documented enough to be reviewed.

Any new submittal will have to address the data from the CCTF experiments which imply that a frothy mixture exists up to.the hot leg nozzle.

10.

. Total Steam Addition Due to UPI

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No theoretical justification has been given for assuming that there is no inter-action of the steam-water mixture rising vertically from'the bottom quench front and the steam-water mixture rising vertically f'rom the falling UPI liquid.

Further,.the quality of each steam-water mixture is calculated by a different

method, and there has been no discussion of the effects of different flow rates t

even though the two.flow rates may be vastly different.

UPI GUIDANCE

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D.

TOTAL EXXON SUBMITTALS Ex'xon Nuclear Company (ENC) proposed to deter'mine the effects of UPI by use of a model called'"REFLEX/UPI," created by making four modifications to the refill and reflood portions of the'xisting non-UPI EM.

Evaluation and guidance com-ments are provided for each of the four modification as follows, using the modi-

'ication sequence selected by ENC.

1.

REFLEX/UPI:

Refill Model No attempt.has been made to consider the effects of UPI on pressure in the upper plenum and in the reactor core.

[These pressures can affect refill.

They must be given consideration as part of the consideration of the thermal and hydraulic characteristics of the core and of the reactor system required by Appendix K part I.D.3 (K.I.D.3)j.

,2.

REFLEX/UPI:

Ener Release Model Com onents ENC uses the term "energy release" to mean "heat transfer [to ECCS fluidsj."

Energy releasexis discussed separately for the core and upper plenum regions.

a.

Core ener release model com onent The ENC model assumes that water does not build up above any part of the

core, so one analysis method is used.for all parts of the core..

This as-sumption is not acceptable because it conflicts with experimental data from Semiscale and the CCTF and from analytical data from Sandia TRAC cal-culations.

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UPI GUIDANCE

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'.U'r lenum str'ucture ener release com onent

,It is 'necessary to document and justify choices for dimensions and pro-perties and demonstrate. tha't a conduction-limited solution is applicable.

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REFLEX/UPI:

S stem E uations Durin Reflood j

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3.1 Physically, ENC assumes that water injected into the upp'er plenum will I

flow into the core or will be entrained by steam and carried into the steam generators, but will in no case contribute to any liquid pool buildup in the upper plenum.

The staff will not,accept this assumption in the absence of ex-perimental data which not only confirms this assumption, but overrides the results on pool buildup now available from experiments and TRAC calculations.

,3.2 Given the above assumption, ENC assumes that the subcooled water injected into the upper plenum mixes with the steam rising from the core and that the mixture comes to thermodynamic equilibrium instantaneously.

The use of UPI water to condense steam rising from the core has the effect of decreasing the possibility of steam.binding, and the assumption of thermodynamic equilibrium mixing will cause the greatest possible decrease in such steam binding.

ENC must demonstrate the acceptability of this assumption.

3.3 The reactor system is modeled as a system of nodes, junctions and loops.

The equations used for the REFLEX/UPI EM are stated to differ in only three cases from the equations used for the REFLEX model.

"10-UPI GUIDANCE

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ENC assumes th'at the pressure drops due to friction and area change are balanced by the gravitational l.evels in the downcomer and core.

It should be shown that (a)..the core loop equation can allow reverse flow from the core to the downcomer to the break, (b) the frictional data used is rele-1 vant and applicable for the complex flow expected in the UPI plant, and (c) terms have not been improperly omitted from the momentum equation (per K:I~ C.3).

b.

Core.exit unction The ENC core exit junction equation makes tractable the set of equations covering the. entire reactor system because it allows ENC to compute the steam flow rate M's proportional to a linear combination of ener'gy re-'

leases.

The equation for M is not acceptable until ENC demonstrates that g

(a) there is no liquid pooling in the upper plenum, (b) the various energy release terms are insensitive to changes in the assumed parameters'governing them, (c) the assumption of all energy releases occurring at the upper plenum does not violate the thermal hydraulics of the real

system, and (d) super heated steam can never exist in the upper plenum, even at the start of UPI.

c.

U er lenum exit unction e uation Saturated water accompanies the saturated steam flowing from the upper plenum into the hot legs.

The assumption of 1.6X horizontal entrainment must be better justified, and (b) the ENC model does not address carryover of fluid from core inlet to core.exit plane,'ontrary to the requirement of K. I. D. 3.

UPI. GUIDANCE.

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REFL'EX/UPI: 'Qut ut ENC indicated that the "principal output of REFLEX/UPI is the core reflood rate and fluid conditions as a function of time dunng reflood... for...

subse-quent hot rod heatup.analyses."'he equation for the reflood cate uses a carry-I i

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'ver rate fraction (CRF) term;.'NC must document (a) the validity of using the CRF concept for UPI plants, (b) the actual ENC procedure for,using the CRF, (c) a the validity of the correlation at the very high reflood rates (over 5 inches

'I per second) shown in ENC's Figure 4.2, and (d) the availability of water to provide these reflood rates.

E.

SUMMARY

Section A identifjed Appendix K parts I.D and II.3, 4, 5.as being particularly

, relevant to the perceived deficiencies in the current EM submittals.

Section B

then documented the ways in which the EM submittals did not meet the require-ments of Appendix K.

Sections C and D examined, on a component-by-component

basis, the ways in which the Westinghouse and Exxon EM submittals did not meet

'he requirements of Appendix K.

The staff's main concerns were over inadequate documentation, absence of.sensi-tivity studies, absence of a physically meaningful model'addressing upper plenum phenomena, the effects of UPI on refill,'eflood, and heat and mass

transfer, an absence of comparison of EM predictions with experiments, lack of consideration of the differences between,UPI and non-.UPI plants, and non-compliance with various required features of Appendix K.

These concerns were documented for both the Westinghouse and Exxon EM submittals. UPI GUIDANCE

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The best general guidance we can give is that an EM must account for all rele-vant phenomena or the licensees must obtain and submit relevant and applicable experimental data and analysis which justifies use of a simpler:EM.

The EM

. must'meet,the standards, of acceptability specified in Appendix K Part II.5, JF including a demonstration of a level of safety and margin of conservatism com-.

parable to the acceptable EMs.

The licensees must responsively address the guidance provided here before the staff can find that the EM submittals meet the requirements of 10 CFR 50 Appendix K.

F.

10 CFR 50.46.AND GDC 35 PLANT-SPECIFIC ACCEPTANCE CRITERIA FOR ECCSs After an EM has been found acceptable as a calculational framework, it"is necessary to determine whether the ECCS of an individual UPI plant is accept" able.

This is done by testing the ECCS against 10 CFR 50.46 and against General

~Design Criterion 35 (GDC 35).

Licensees can facilitate reviews by documenting conformance to all. parts of Appendix K and 10 CFR 50.46 and GDC 35 on an item-by-item basis, by providsng the material called for in Regulatory Guide 1.70, and by ensuring the avail-ability of the materials needed by the 'staff in using the Standard Review Plan (especially sections 6.3 and 15.6.5).

The staff review of EH submittals'does take into account significant differ-ences in the reactors to which the EMs apply.

This was shown in the safety evaluation report.(SER) on plants equipped with upper head injection "13-UPI. GUIDANCE.

(NUREG-0297,'age 1-3). This flexibilityis inherent in. the procedures normally e

used by the staff to ensure acceptability of an EM and of any ECCS described by that EM'as demonstrated in the individual sections'of the "Standard Review Plan"

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6.3 and 15.6.5) and-.in Regulatory Guide 1.70].

However,,'where there were I

'arge uncertainties in phenome'na or in experimental data, the'taff has re-bl dth ~hti b'

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h relations used in an EM.

Currently, the staff is willing to accept an alter-nate approach in which an EM would conservatively bound only the overall uncer-

~taint in the phenomena and experimental data, provided of course that the EN conforms to all required features of Appendix K.

This willingness is documented in NRC Information Report SECY-83-472, "Emergency Core Cooling System Analysis Methods," 11-17-83.

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