ML20140H797

Summary of 970415 Meeting W/Listed Attendees in Rockville,Md Re Issues Associated W/Lower Head Integrity Under in-vessel Steam Explosion Loads for AP600

ML20140H797
Person / Time
Site:	05200003
Issue date:	05/09/1997
From:	Joseph Sebrosky NRC (Affiliation Not Assigned)
To:	NRC (Affiliation Not Assigned)
References
NUDOCS 9705130282
Download: ML20140H797 (9)

Text

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i o n M3 y  % UNITED STATES j

/ s NUCLEAR REGULATORY COMMISSION  !

j $ 't WASHINGTON, D.C. 20666-0001 l

% .o May 9, 1997 APPLICANT: Westinghouse Electric Corporation

! FACILITY: AP600 i

SUBJECT:

SUP94ARY OF APRIL 15, 1997, MEETING WITH WESTINGHOUSE TO DISCUSS ISSUES j

ASSOCIATED WITH THE LOWER HEAD INTEGRITY UNDER IN-VESSEL STEAM EXPLO-SION LOADS FOR THE AP600 I

l The subject meeting was held on April 15, 1997, in the Rockville, Maryland, offices of the Nuclear Regulatory Commission (NRC) between representatives of t

Westinghouse, and the NRC staff. Attachment 1 is a list of meeting attendees.

i The purpose of the meeting was to discuss comments that were sent to Westing-i

" house from the staff in a March 25, 1997, letter concerning a report entitled

" Lower Head Integrity Under In-Vessel Steam Explosion Loads," (D0E/ID-10541).

i i Prior to the meeting Westinghouse provided Attachment 2 to the staff detailing the questions that they believed needed to be addressed as a result of the j comments that were sent to Westinghouse. The staff agreed with Westinghouse i

i that the questions in Attachment 2 captured all of the questions that were imbedded in the comments sent to Westinghouse in the March 25, 1997, letter.

2 However, the staff did not agree with Westinghouse's assignment of the categories for the disposition of the questions. During the meeting the disposition of the questions was discussed. Therefore, the questions in

Attachment 2 served as the agenda for the meeting and attachment 3 provides the disposition for the questions. The staff requests that Westinghouse enter the nine questions in attachment 2 into the Open Item Tracking System.

At the end of the meeting there was a brief discussion about the status of the peer review comments for the DOE report. Westinghouse stated that the peer j i review comments without the responses would be provided to the staff in the 1

1 near term and that responses to the comments would be provided to the staff by '

! the end of May. The staff stated that they were still in the process of j reviewing the reports (D0E/ID-10489, DOE /ID-10503, and DOE /ID-10504) which i-  !

form the basis of and/or supplement the findings in the main report. The i j

j staff further stated that any additional comments that it may have concerning the peer review comments and the additional reports would be provided to /y '

b '

9705130282 970509 ADOCK 0520 3 gDR g (hh

May 9, 1997 Westinghouse by the end of May. A draft of this meeting summary was provided to Westinghouse to allow them the opportunity to ensure that the representa-tions of their comments and discussions were correct.

original signed by:

Joseph M. Sebrosky, Project Manager Standardization Project Directorate Division of Reactor Program Management Office of Nuclear Reactor Regulation Docket No.52-003

' Attachments: As stated cc w/ attachments:

See next page

)ISTRIBUTION w/ attachment:

0)ocket;F.11e, ~

PDST R/F TKenyon PUBLIC WHuffman DJackson JSebrosky SBasu, T-10 K8 CTinkler, T-10 K8 MSnodderly, 0-8 H7 DISTRIBUTION: w/o attachment:

SCollins/FMiraglia, 0-12 G18 RZimmerman,.0-12 G18 AThadani, 0-12 G18 TMartin MSlosson TQuay JMoore, 0-15 818 WDean, 0-17 G21 ACRS (11)

DOCUMENT NAME: A:IVSE. SUM (6F AP600 DISK)

TD seceive e copy of this deewnent,indcote in the ben: *C* = Copy wkhout e techment/enclogure a *E* = Copy whh attachment / enclosure *N* = No copy 0FFICE PM:PDST:DRPM ISCSB:DSSA tr RES:DSTTAE8. D:PDST:DRPM NAME JSebrosky:sq-fA7 MSnodderly N2 5 CTinkleiV((.O i TQuay T/4 DATE 04/zq/97 (/ 04/21/97 04/1o/97 gl4/97 0FFICIAL RECORD COPY

\

Westinghouse Electric Corporation Docket No.52-003 5

cc: Mr. Nicholas J. Liparulo, Manager Mr. Frank A. Ross Nuclear Safety and Regulatory Analysis U.S. Department of Energy, NE-42 l

Nuclear and Advanced Technology Division Office of LWR Safety and Technology  !

Westinghouse Electric Corporation 19901 Germantown Road P.O. Box 355 Germantown, MD 20874

Pittsburgh, PA 15230

Mr. Ronald Simard, Director Mr. B. A. McIntyre Advanced Reactor Program Advanced Plant Safety & Licensing Nuclear Energy Institute

Westinghouse Electric Corporation 1776 Eye Street, N.W. i Energy Systems Business Unit Suite 300

Box 355 Washington, DC 20006-3706 Pittsburgh, PA 15230

Ms. Lynn Connor i

! Ms. Cindy L. Haag Doc-Search Associates i

! Advanced Plant Safety & Licensing Post Office Box 34 l Westinghouse Electric Corporation Cabin John, MD 20818 l i Energy Systems Business Unit j Box 355 Mr. James E. Quinn, Projects Manager  ;

i Pittsburgh, PA 15230 LMR and SBWR Programs GE Nuclear Energy

. Mr. M. D. Beaumont 175 Curtner Avenue, M/C 165 Nuclear and Advanced Technology Division San Jose, CA 95125 3 Westinghouse Electric Corporation One Montrose Metro Mr. Robert H. Buchholz l 11921 Rockville Pike GE Nuclear Energy i

^

Suite 350 175 Curtner Avenue, MC-781 Rockville, MD 20852 San Jose, CA 95125 Mr. Sterling Franks Barton Z. Cowan, Esq.

U.S. Department of Energy Eckert Seamans Cherin & Mellott NE-50 600 Grant Street 42nd Floor 19901 Germantown Road Pittsburgh, PA 15219 Germantown, MD 20874 Mr. Ed Rodwell, Manager Mr. S. M. Modro PWR Design Certification Nuclear Systems Analysis Technologies Electric Power Research Institute Lockheed Idaho Technologies Company 3412 Hillview Avenue Post Office Box 1625 Palo Alto, CA 94303 Idaho Falls, ID 83415 Mr. Charles Thompson, Nuclear Engineer AP600 Certification NE-50 19901 Germantown Road Germantown, MD 20874

a WESTINGHOUSE AP600 IN-VESSEL STEAM EXPLOSION LOADS MEETING ATTENDEES April 15, 1997 H6ME ORGANIZATION CINDY HAAG WESTINGHOUSE JIM SCOBEL WESTINGHOUSE BRIAN MCINTYRE (PART TIME)

WESTINGHOUSE 1 CHARLES THOMAS DEPARTMENT OF ENERGY

THE0 THEOFAN005

' UNIVERSITY OF CALIFORNIA, SANTA BARBARA SUDHAMMAY BASU NRC/RES CHARLES TINKLER NRC/RES s

MICHAEL SN0DDERLY NRC/NRR/DSSA/SCSB J0E SEBROSKY NRC/NRR/DRPM/PDST i

Attachment I

g  :

I J

Westinehouse comments nrovided to the staff orior to the meetina l

T 4

Here is a summary of the potential RAIs that we have harvested from the NRC review of the In-Vessel Steam Explosion Report. Please Confirm with the NRC that this list covers all the topics that they wish to discuss at the 2 pm meeting on April 15. We have placed the comments into two categories:

(A) comments for which we believe they should supply a written questions so we 1 can supply a written response, and (B) comments we believe can be resolved

with discussion in the meeting.

j 1. Provide the values or set of values used for the crust growth constant, A

used in the freezing time calculation for the lower core blockage. (A)

2. Provide assessment of the effect of uncertainties in conductivity of the

blockage material and the power density in the crust on the heat flux used to calculate the water contact time for the lower core blockage. (A) j 3. Provide evidence to support the claim that the range of sizes of the 4

sideward failure in the reflector represents a reasonable range for the

calculation of the melt release rate. (B)

! 4. Provide an extre:ne parametric case to investigate the bounding melt i release rate that can produce lower head failure. (B)

! 5. Provide the basis for the 20 m melt length scale used in the analysis. <

j (B)

6. Discuss how the results of [NRC Review Letter] Table 2 relate to the i conclusion that the impulses do not depend strongly on the size of the i mixing zone. (B) l 7. What value of the melt participation factor was used in the ROAAM

! calculations? (B) l

8. It is recommended that the report discuss how the case of intersecting j

load and fragility curves would be treated within the R0AAM framework.

(B) i 9. Why is the 11 percent plastic strain criterion not used in the case of j the reflood FCI? (A) i i

I Attachment 2 7

d j

, i Disposition of Comments on the In-vessel Steam Explosion Report i

l

1. Provide the values or set of values used for the crust growth constant, A '

used in the freezing time calculation for the lower core blockage. (A)

Disposition: Westinghouse will provide a written response to this ques- l tion.

2. Provide assessment of the effect of uncertainties in conductivity of the blockage material and the power density in the crust on the heat flux used to calculate the water contact time for the lower core blockage.

Disposition: During the discussion of this question, Westinghouse stated that the downward heat flux would remain the same even if the blockage thermal conductivity and/or power density was varied. As a result, the water evaporation time would not i change. Consequently, it would be more appropriate to I assess the effect of uncertainties in the conductivity and j the power density of the blockage crust thickness. There- '

fore, at the meeting it was decided that Westinghouse would provide a written response to Item 2 in terms of the effect on the blockage crust thickness instead of in terms of the 4 effect on water contact time for the lower core blockage. 1 Subsequent to the meeting, the staff further evaluated the  ;

issues and has concluded that unless there is an extreme change in crust thickness as a result of the parametric  :

studies, the result is not likely to shed additional light  !

into the melt relocation scenario considered in the report. 1 In fact, the staff is of the view that it is necessary rather to document the basis for the Westinghouse position that downward heat flux would not change as a result of parametric variation. Therefore, the staff wishes to reformulate the question and ask Westinghouse to demon-strate that the downward heat flux will remain the same as will the relative partitioning of downward, upward and sideward heat fluxes.

Attachment 3

l 1  :

i-

.2 j 3. Provide evidence to_ support the claim that the range of sizes of the l sideward failure in the reflector represents a reasonable range for the 1

i calculation of the melt release rate.-

Disposition:. See item 4 below.

l l 4. Provide an extreme parametric case to investigate the bounding melt j . release rate that can produce lower head failure.

1

! Disoosition: During'the discussion of questions 3'and 4 Westinghouse j

provided additional background information. Specifically, i

Westinghouse stated that the release rate is an intangible i parameter that was difficult to bound. In addition to the release rate, Westinghouse considered the trigger time and breakup size to be intangible parameters. Westinghouse believed that they used conservative numbers for these l parameters and that with the conservative treatment of i these parameters there was still sufficient margin in. the

[ calculations to demonstrate that the reactor vessel would j not fail.

The staff noted that the peak impulse loads calculated in i the DOE report were close, at least in one case, to the

fragility limit. Consequently, the staff was concerned

about the implication of higher melt release rates than the

ones considered in the report on the-likelihood of lower

head failure. Westinghouse responded that the peak impulse i

loads should not be considered by themselves, instead they i

! should be combined with the effect of the area reduction

factor. The staff agreed to reassess questions number 3 ,

.and 4 based on the information on area reduction factor in  !

the report. (See question #6 for a related discussion)  !

i The staff has since reviewed Chapter 3 of the report with  :

g particular focus on the area reduction factor argument, t

The argument, simply, is that when the load is localized, ,

part of it is transformed into bending energy. Consequent-j~ ly,.the effective impulse corresponding to a localized load

is smaller than the impulse corresponding to a uniform l '

load. Likewise, the effective plastic strain for a local-ized load is smaller than that for a uniform load. The

report assumes that the fractional impulse, I l ed in bending is directly proportional to the,/I, dissipat-total im-i pulse, I, and inversely proportional to the fractional area loaded - the latter meaning, the smaller the area loaded i the higher the bending energy dissipated and vice versa.

The proportionality constant, 8, in equation (3.8) is identified as a material and geometric constant implying l' that the value of 8 depends on the lower head material and the geometry. Even though no value is specified in the

report, an examination of equivalent plastic strain plots

i .

~

l _3- l 4

in Figure 3.9 leads us to conclude that a value of 0.2 is j i chosen for 6. Westinghouse needs to confirm the value of 8 and provide justification for the chosen value.

4 l With B-0.2 assumed, calculations were carried out to deter-

mine the effect of load localization on effective impulse, i I, (- I-I rat'e inclu8)d),

e e, andThe on equivalent results indicate plastic strain that (with strain for the threeloadingpatYe.rns considered in the report (see Table 3.2), the local plastic strain is 23 percent for an impulse <

load of 300 kPa-s with least load localization. In fact, the plastic strain .is limited to 40 percent or less for impulse loads up to 400 kPa-s with least load localization.

Note that this impulse load is 2 times the maximum impulse

(~ 200 kPa-s) calculated in the report for a parametric run with 400 kg/s melt release rate. Assuming that the impulse is proportional to the release rate, it means that a 800 kg/s release rate-is'likely to produce 400 kPa-s impulse and equivalently, 40 percent plastic strain when the load is-least localized. Therefore, Westinghouse's assertion of ,

the area reduction factor argument has a basis; however, it is contingent upon the assumed value of 8.

In the staff review, two cases were found when the plastic strain exceeded 40 percent (see Figure 3.8 of the report).

The cases are 450 kPa-s (corresponding strain of 52 per-  ;

cent) and 570 kPa-s (corresponding strain of 87 perr.ent) '

impulse loads, the first one with least load localization and the second with intermediate load localization. Fol-lowing the proportionality assumption _between the melt release rate and the impulse as above, these cases corre-spond to melt release rates of 900 kg/s and 1150 kg/s, respectively. Westinghouse should demonstrate, based on geometry and other arguments, why these cases are not ,

considered in the framework of ROAAM.

1 In its previous review, the staff noted that the melt release rates (100, 200, and 400 kg/s) considered in the subject report are comparable to the TMI-2 scenario (~ 160 kg/s). However, the hole sizes (10 cm x 10 cm, 10 cm x 20' cm, and 10 cm x 40 cm, respectively, corresponding to the three release rates) are much smaller than the TMI-2 hole size (60 cm x 150 cm). The implication is that if the TMI-2 hole size is considered, the release rate will be much larger and the steam explosion load will likely be much larger. This concern formed the basis of the staff comment (see item 3 in Attachment 1) dealing with the reasonable-ness of the hole sizes considered in the report.

For its part Westinghouse agreed to address why the hole size seen at TMI-2 which was much larger (60 cm x 150 cm) than the hole sizes used in the DOE report was not consid-

ered. (The reference to the TMI-2 hole size can be found l in the comments of the March 25, 1997, letter.) Westing-house agreed to provide this assessment in a revision to i the DOE report.  ;

5. Provide the basis for the 20 mm melt length scale used in the analysis.

Disposition: Westinghouse will revise the DOE report to provide a dis- l cussion as to why consideration of a larger value of ini-tial melt length scale does not affect the conclusions of the report.

6. Discuss how the results of [NRC Review Letter] Table 2 relate to the conclusion that the impulses do not depend strongly on the size of the mixing zone.

Disposition: See disposition of item 4 above for a related discussion.

Westinghouse agreed with the staff that there were calcu-lated values of the peak local impulses on the lower f.ead that should be reinvestigated. Specifically, Westinghouse referred to Table 6.1 of the DOE report for the C2 casa where beta equaled 20 and the trigger time was 0.120. This case resulted in a peak pressure of about 1000 MPa. llest-inghouse stated that they were concerned about this case because it exceeded 800 HPa. Westinghouse stated that it would reinvestigate this calculation.

7. What value of the melt participation factor was used in the R0AAM7 Disposition: Westinghouse stated that I was used as the melt participa- l tion factor. The staff agreed with Westinghouse that this was a conservative treatment of this parameter. Therefore, the staff considers this question resolved.

8. It is recommended that the report discuss how the case of intersecting load and fragility curves would be treated within the ROAAM framework.

Disposition: Westinghouse will revise the DOE report to address this issue.

9. Why is the 11 percent plastic strain criterion not used in the case of the reflood FCI?

Disposition: Westinghouse will revise the DOE report to provide an explanation for why 20 percent was chosen for the plastic strain criteria in the reflood case instead of 11 percent as in the baseline case.