ML20150C563
| ML20150C563 | |
| Person / Time | |
|---|---|
| Issue date: | 04/25/1988 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-2570A, NUDOCS 8807120539 | |
| Download: ML20150C563 (34) | |
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- 5 t tro Advisory Connittee on Reactor Safeguards Thermal Hydraulic Phenomena Subcommittee Meeting Minutes April 20-21, 1988 Idaho Falls, ID PURPOSE: The purpose of the meeting was to: (1) review the final version of the proposed revision to the ECCS Rule (10 CFR 50.46 and Appendix K); and (2) hold a working level session to develop a draft letter on the NRC T/H research program for consideration by the ACRS.
ATTENDEES:
ACRS NRC-RES
- 0. Ward, Chairman L. Shotkin W. Kerr, Member N. Laubin C. Wylie, Member N. Zuber I. Catton, Consultant t
M. Plesset, Consultant l
Y. Schrock, Consultant P. Boehnert, Staff (DF0) l MEETING E HIGHLIGHTS, AGREEMENTS, AND REQUESTS
- 1. L. Shotkin (RES) reviewed the long-range direction planned for RES T/H research programs. He noted that he would discuss a on-going l
reorganization of RES and a prioritization of research programs.
Dr. Shotkin noted that the prioritization effort has T/H research l "falling-out" as the lowest priority item at this time.
RES showed a slide of the current and planned T/H research programs l (Figure 1). RES plans to phase out most T/H research by 1991. Mr.
l Ward noted a proposal to extend leak-before-break to aspects of the ECC systems. He asked if RES will be involved with this. Dr.
Shotkin said he only sees a small role for his Branch here.
8807120539 080425' DESIC!'ATED ORIGINAL PDR ACRS l
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T/H Phenomena Mtg Minutes April 20-21, 1988 The Applications area of T/H research will continue at some modest funding level. In this area, the following new projects are underway: (1) containment issues request from NRR, (2) generic issues requests from RES, SGTR, and reactor trip without turbine trip, (3) LaSalle analysis for AE00, (4) NPA at the technical training center, and (4) in-vessel accident management plan. Most of these projects have short turn-around times. In response to Dr.
Kerr, Dr. Shotkin indicated that applications research will be characterized by such short-range projects as noted above; the traditional T/H research projects are being phased out.
Mr. Schrock questioned the underlying logic of Item (5) above if it is to involve understanding of pre-core melt phenomena. Dr.
Shotkin indicated that NRC has yet to address the phase of an accident between the beginning of core melt and the breach of the containment; he said that's where the accident management research will focus.
RES has established a RES/NRR/AEOD Task Group on future needs for "traditional" T/H research. The "ground-rules" for the Group's activities are given on Figures 2-4. Positions advanced by RES include the following: the Technical Support Center will be continued, to assure an on-going base program; all major T/H test facilities will be closed by 1991-42 (Figure 4); a code maintenance plan is proposed for RELAP-5 and TRAC-PWR (Figure 4), with the remaining codes put "on the shelf" for use as needed (TRAC-B, RAMONA, COBRA-NC,etc.). In response to Dr. Catton, Dr. Shotkin said there would not t.. a QA manual for the shelved codes, but input decks and user manuals would be included with these codes.
The Task Group will meet in early May to thrash out the above proposals. In response to Dr. Kerr, Dr. Shotkin said the above proposals originated from his Branch with concurrence from senior
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r T/H Phenomena Mtg Minutes April 20-21, 1988 RES office management. Dr. Kerr asked if the NAS recommendations for NRC research were factored into the above recommendations. Dr.
Shotkin said they did not impact the research areas addressed by the above recommendations.
Dr. Shotkin showed proposed budget figures for FY 88-92 (Figure 5).
The proposed budget shows declining emphasis on T/H research and increasing support for accident management.
In response to Mr. Ward, Dr. Shotkin discussed the pending reorga-nization. He indicted that severe accident research will receive more emphasis as severe accidents receive more attention. The Deputy Directors' missions have also been clarified.
- 2. L. Shotkin introduced discussion of the final version of the proposed ECCS Rule revision. Points noted by RES included:
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- Rule package was signed off by RES Office Director l
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- Key NRR staff have been briefed on-the final version
- Draft comments received from NRC-ARM (rules and records) and incorporated l
Rule scheduled for issuance in August 1988
- Rule remains unchanged after the public comment period 1
- The Regulatory Guide has explicit incorporation of language
! about non-use of statistical confidence limit
- Other minor changes made.
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T/H Phenomena Mtg Minutes April 20-21, 1988 Regarding the statistical confidence limit, RES said they are not requiring a demonstration of a confidence level for the uncertainty analysis acccmpanying the BE LOCA model.
Rcgarding ACRS coments on the proposed rule, Dr. Shotkin noted that:
- Provision for grandfathering the existing ECCS Rale will be maintained (10 CFR 50.46 and Appendix K)
- 2200'F PCT limit has been clarified per recent experimental research data
- SGTR (GI-141 - concurrent LOCA with SGTR) issue will be prioritized; issue probably will be dropped due to expected low priority (DROP or LOW).
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- CSAU demonstration of reflood peak scheduled to be complete by l
8/88. CSAU schedule is not being tied to Rule issuance.
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In response to Mr. Ward, Dr. Shotkin said RES fully expects the
! CSAU effort to be successfully concluded. He also expects that the industry will be able to demonstrate the necessary uncertainty analysis for use of a best-estimate LOCA model.
- 3. N. Laubin provided detailed discussion on the final version of the l proposed ECCS rule package. Key points noted by Mr. Laubin included:
- The development history and current ECCS rule provisions were noted. Because of the rule's conservatisms, many plants are l
calculating PCTs at or near the 2200'F limit. Some vendor l designs are limiting plant operations because of the tightened rule requirements.
T/H Phenomena Mtg Minutes April 20-21, 1988
- Over $1 billion has been spent on ECCS research. NRC proposed revision of the rule in 1978, this was subsequently delayed by the THI-2 accident. In response to a request from GE, NRC, in 1983, allowed use of a best-estimate (BE) LOCA model, except for the incorporation of the required features of Appendix K.
In addition, an uncertainty evaluation was also required to show that required Appendix K conservatism was sufficient to cover the uncertainty in the best estimate calculations.
Activity related to current rulemaking has shown a large (4-1000'F PCT) conservatism in the EM's; the major conservatism is in the decay heat (3-400*F). Most Appendix K conservatism is during reflood. Once the time of PCT is shifted to the blowdown phase, ems may not have sufficient conservatism to cover the uncertainty in the calculation. Thus, the need for an-uncertainty evaluation with the new rule.
- The proposed rule and regulatory guide have been subjected to
( public coment. Key features of the proposed rule are:
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- The rule is general and requires "realistic" calculations of ECCS performance with consideration of uncertainty such that there is a "High Level of Probability" that criteria would not be exceeded. The required criteria (e.g., 2200*F PCT) remain unchanged.
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- Alternatively, present Appendix K features remain acceptable as an optimal method not requiring an uncertainty evaluation (grandfathering existing ems and allowing future use of revised Appendix K, if desired).
- All error corrections and changes to be reported annually andallerrorsandchangesorcumulative(absolutevalue) l
T/H Phenomena Mtg Minutes April 20-21, 1988 errors resulting in greater than 50*F PCT change to be reported within 30 days. No further action required beyond reporting. Staff may take action consistent with safety significance. Errors or changes resulting in exceedingcriteria(e.g.,2200'FPCT)areimmediately reportable (within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />) and immediate steps to assure compliance must be proposed.
- Evaluation models approved prior to the rule revision that make use of Dougall-Rohsenow would continue to be acceptable, as long as the current level of overall conservatism in the EM is not significantly changed (
50 F change).
Mr. Ward asked if the SECY-83-472 method will be acceptable under the new rule. RES replied in the affirmative. Mr. Ward asked if the SECY-83-472 uncertainty evaluation will be reviewed consistent with the uncertainty evaluation requirement per the new rule. Mr.
Laubin said they would be reasonably consistent but not identical-as the CSAU is on-going and not all the vendors have had the benefit of evaluating CSAU. In response to Mr. Schrock, RES l indicated that the Staff will use CSAU to assure discipline of the vendors individual uncertainty submittals.
Dr. Kerr urged the Staff to assure they are even-handed in their dealing with the licensee, particularly regarding the "tradition" (conservatisms) that will arise with use of the new rule. Dr.
Zuber urged the Subcommittee to assure the Staff holds to high, consistent standards vis-a-vis NRCs review of the vendors BE LOCA ,
submittals.
Dr. Kerr took exception with the requirement that a licensee take "immediate steps" to bring the plant into compliance, if the 2200*F l
T/H Phenomena Mtg Minutes April 20-21, 1988 limit is violated. He felt the licensee should be given some time to deveiop a response. Mr. Ward felt that the 4-hour reporting re-quirement is unnecessary and probably unfair.
- The provisions of the regulatory guide include:
- Defines the high level of probability stated in the rule as 95% probability.
- Provides general features expected in a best estimate calculation and the uncertainty evaluation, but does not specify or prescribe any specific methods.
- Lists a limited number of acceptable best estimate models (e.g., 1979 ANS/ ANSI decay heat, Cathcart-Pawel metal-waterreactionrate),andinsomecases,dataappropriate to model assessment is provided.
Dr. Kerr questioned the wording in the regulatory guide regarding l
probability limits versus confidence levels. Specifically, he questioned how one can do a probability level determination in the face of a set of uncertainties some of which are undefined. Mr.
Lauben said that the NRC statistician indicated that given the methods suggested in the Guide, it is not necessary to consider confidence limits. Dr. Kerr indicated he was skeptical of this reply.
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- The draft Compendium will include another Volume (Volume 2) l which will detail the results of the CSAU effort.
- Discussing the details of the final rule package, the follow-l ing highlights were noted:
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T/H Phenomena Mtg Minutes April 20-21, 1988
- The public comments on the rule were sumarized (Figures 6-7). In general, the coments supported the rule change and grandfathering of the current rule.
- The ACRS question on indefinite grandfathering of the Rule was discussed. The Subcomittee noted that the concern was with the word indefinite. Dr. Kerr asked if the Staff did a systematic analysis to determine if plants operated under the new rule pose additional risk.
Mr. Lauben indicated that no systematic analysis was done, rather the Staff beliavas the risk is little changed based on the low probability of a LB LOCA. Dr.
Kerr noted that the new rule does decrease conservatism and since there will be a change in plant operations, we really don't know what the impact of the new rule will be vis-a-vis plant risk.
- Mr. Schrock noted that going to a BE analysis gives the ber.efit of grounding the LOCA model more firmly on engineering judgment and scientific fact, Mr. Ward agreed and said this point was the thrust behind the ACRS coment on grandfathering.
In response to Mr. Ward, Mr. Lauben noted that the final rule version deletes reference to any safety benefit of the prop, sed rule.
- The coments received and changes made to the regulatory guide were discussed. Dr. Catton suggested that the regulatory guide be made more specific regarding the steps required to perfonn the uncertainty analysis. Dr. Catton also asked if the TRAC and RElAP-5 "QA Reports" will be referenced in the guide as well, RES indicated that they will consider this suggestion.
T/H Pnenomena Mtg Minutes April 20-21, 1988
- The probahility vs confidence level issue was again discussed.
Mr. Schrock urged RES to give a forthright discussion of the engineering approach normally applied to uncertainty analyses for such situations as we are faced with here.
- Enclosures I and J of the rule package were discussed (Figure 8).
- 4. N. Zuber discussed the status of the CSAU methodology development effort. Key points noted by Dr. Zuber were:
- The response of the Technical Program Group (TPG - the Group that is developing CSAU) to the Peer Review of CSAU was noted.
The TPG will provide detailed response to the Peer Group's criticisms. As part of its review, the Group responded to two questions posed by NRC, i.e.: (1) Is the methodology syste-matic, logical and practical?, and (2) Has the methodology been demonstrated? For (1), the Group said the method is systematic, logical, and practical. For (2), the Group saw no insunnountable difficulties, but conditioned their approval on completion of the entire CSAU method. TPG is optimistic that the methodology will be effective for other accident scena-rios. Infact, NRC intends to extend and apply the CSAU methodology to a severe accident initiated by a SBLOCA.
Dr. Zuber noted that the Peer Group provided an excellent defini-tion of the CSAU method, i.e., "A formal method for combining quantitative analysis and expert opinion in a controlled way to minimize the subjectivity of the experts in arriving at computed values of uncertainty."
In response to Dr. Kerr, Dr. Zuber said he is confident that CSAU can be successfully applied to the severe accident issue. He l
T/H Phenomena Mtg Minutes April 20-21, 1988 believes it will provide a coherent approach by integrating both the analytical and experimental efforts.
Figures 9-11 detail the Peer Groups general coments on their review of CSAU. The Peer Groups concerns with CSAU centered on:
the fact that the scale effects were not sufficiently characterized and that nodilization and uncertainty effects have not been adequately addressed. Figures 12-15 detail the actions planned by the TPG to address these concerns. Other concerns noted by the Peer Group, and the NRC response, are detailed on Figures 16-17.
I The above additional action items have resulted in a slip in the completion of the CSAV effort of three months to September 1988 (Figure 18).
- 5. G. Wilson detailed the status of the on-going effort to respond to the above Peer Group action items. The topics addressed incisded:
(1) inclusion of additional data not used in code develop .snt end
! assessment, (2) the effects of additional hydrodynamic cross products, and (3) the effects of hot channel thermal-hydraulics on l
i PCT. Key points noted were:
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- The effect of adding additional "virgin" data was negligible (PCT changed by n 1% with an ~ 16% increase in data). With 301 test data points, the variability in blowdown PCT is 350*F (Figure 19). The preliminary data for reflood were also shown I
(Figure 20).
- For Item (2) above, the TPG has determined that the use of additional hydrodynamic cross products resulted in a lower blowdown PCT at 95% probability; the change was small (16*F,"
1%). Figure 21 shows the results.
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T/H Phenomena Mtg Minutes April 20-21, 1988
- Item 3 above has been evaluated by the TPG. The preliminary results indicate that a bias (penalty) of 68'F may be suffi-cient to account for the hot pin effect on the hot channel model (Figure 22).
- 6. Mr. Ward proposed that the rule be brought to the ACRS in May.
The Subcomittae had no objection to bringing the rule to the ACRS for its review.
Mr. Ward recommended a 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> presentation on the rule, including the status of the CSAU effort.
- 7. The Subcommittee made the following comments on the RELAP-5 MC report discussed on April 19, 1988.
I. Catton - RELAP-5 has problems similar to TRAC. The "QA" docu-ment needs to be augmented. Both reports need discussion on the code's respective numerics. Discussion on reflood for RELAP-5 is needed. Also, the impact of use of a constant Webber Number should beaddressed(forTRACaswell). Both codes should receive some sort of peer review. The documents should be published as NUREG's ASAP. Tha issue of appling RELAP-5 to the LBLOCA should be cleared up - the code should not be limited to modeling of SB LOCA and transients.
t M. Plesset - Prefers RELAP-5 to TRAC. RELAP-5 has kept the needs of the user in mind. He supports completion of MOD-3. He recom-mends shelving some codes (like TRAC).
V. Schrock - Concerned with the missing elements in the QA report, l
as is Dr. Catton, Believes the QA reports should be consistent from code-to-code. The flooding models need to be completely defined in the report, as does the stratification model. The
T/H Phenomena Mtg Minutes April 20-21, 1988 practice of "modifying" correlations to be used in the code should notbedone(bothINELandLANLaredoingthis). If it is done, the modification should be reported in the Literature in order to subject it to peer review.
C. Wylie - INEL needs to specifically identify what work is re-quired to convert RELAP-5 into a LB LOCA code.
- 8. The meeting recessed at 3:10 p.m. and reconvened to go into an open working group session to discuss a draft letter on the NRC-RES T/H research program.
- 9. The Subcomittee developed a draft letter for ACRS consideration on NRC research related to the thermal hydraulic perfonnance of nuclear pcwer plants. This letter will be introduced to the Comittee at its May 1987 meeting. It was also decided to request a presentation from Dr. L. Shotkin (NRC-RES) at the May full Cmmittee meeting on the current and future plans of RES regarding T/H research.
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- 10. The meeting was adjourned at 11:25 a.m., April 21, 1988.
f NOTE: Additional meeting details can be obtained from a transcript of this meeting available in the NRC Public Docunent Room, 1717 H Street, N.W., Washington, D.C., or can be purchased j
from Heritage Reporting Corporation, 1220 L Street, N.W.,
Washington, D.C. 20555,(202)628-4888.
,. 1, PLANT PERFORMANCE
PLANS RESEARCH AND APPLICATIONS
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- 3. Background and Charter for RES/NRR/AEOD Task Group on Future T/H Thermal Hydraulic Research I. BACKGROUND A. Declining Emphasis on T/H Research All major thermal-hydraulic research programs are planned to be completed by the end of CY 1991. There will be a long-term declining emphasis and resources on T/H code development and assessment. A solid base program effort will be maintained in this .
area to: make necessary code improvements based on new information; retain a cadre of er,perts; and address new issues as necessary. A T/H Technical Support Center (TSC) has been formed to efficiently accomplish both immediate and long-term goals.
This solid base program will include codes, basic studies, the T/H TSC, the Nucle 6r Plant Analyzer, and a significant applications effort addressing priority issues. The Task group is being asked to I
help fomulate the "codes" portion of this base program.
B. T/H Codes and Their Uses Within NRC l The Task Group should consider future agency needs for the following T/H Codes: TRAC-PWR, TRAC-BWR,RELAP5, COBRA-NC(whichincludes l
COBRA-TF and COBRA / TRAC) and RAMONA-3B, y/4.3
These codes have been used to analyze both generic and specific transients and accidents that have occurred in light water reactors (LWR's). These include loss-ef-Coolant Accidents (both small-break and large-break LOCA's), ATWS and a full complement of operational transients. Enclosure 1 provides a reasonably complete list of these analyses perfomed under NRC funding with TRAC and RELAP.
The codes ability to calculate LWR transients has been comprehensively assessed against data from several scaled experimental facilities specifically designed to address the accident scenarios being analyzed.
Finally, these codes are used as the "front-end" of mechanistic severe accident codes (RELAP/SCDAP and TRAC-MELPROG) and also provide the boundary conditions for fuel codes such as FRAP.
C. RES Close-out Plans for T/H Codes and Their Major Capabilities YEAR FOR CODE FINAL VERSION MAJOR CAPABILITIES l
RELAP5 1989 1-0 PWR Accidents i TRAC-PWR 1989 3-D PWR Accidents j?.ydb- TRAC-BWR - 1988 3-D BWR Accidents COBRA-NC- M t 1987 Containment (Also,sub-channel)
RAMONA-3B M E 1987 BWR Accidents with Neutronics f
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D. RES Close-out Plans for T/H Test Facilities and Their Major Capabilities TEST YEAR FOR FACILITIES FINAL VERSION MAJOR CAPABILITIES LOFT 1987 PWR Accidents with Nuclear Fuel SEMISCALE 1986 PWR Accidents FIST 1985 BWR Accidents MIST 1988 B&W Accidents 2D/3D 1989 PWR LOCA (rull Scale)
ROSA-IV 1992 PWRAccidents(largescale)
ICAP(BETHSY, LOBI, GEST-GEN) 1991 PWR Accidents E. RES Current Maintenance Plans for T/H Codes MAINTENANCE CODE PLAN REASONS RELAPS 2-3 MY/Y Widely used TRAC-PWR 0-3 MY/Y As use dictates TRAC-BWR Put on Shelf Little used COBRA-NC Put on Shelf Used Occasionally RAMONA-3B Put on Shelf Used Occasionally Note that user conveniences will still be provided for RELAPS through its use on the Nuclear Plant Analyzer.
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- 4. FY90 BUDCET EXERCISE (M$)
s PROJECT FY88 E M 91 E T/H RESEARCH ROSA-IV 0.4 0,5 0,5 0.5 0.5 2D/3D 2.0 1.3 1,2 - --
B&W TESTING 1,6 3.6 1,0 0.5 --
ICAP 0.7 0,7 0.8 0.5 --
T/H COCES 1.8 1,7 2.0 2.0 2.0 CSAU 1,4 1,0 0,3 0.2 0.2 BASICSTUDIES M Q.4 M M 1,0 '
T/H RESEARCH TOTAL 8.9 9.6 6.8 4,7 3.7 FECULATCRY APPLICATIONS TECH SUPPCRT CENTER 0,8 1.5 2.0 2.0 2,0 CONTAltfENT 0,2 0,7 0,8 0.5 0.5 NPA/DB/SitULATORS 1.0 0,9 1,0 1.0 0.8 ADVANCED LWR'S 0.2 1.5 1.0 M REGULATORY APPL, TOTAL M 3,J 5,3 4.5 4,3 TOTAL T/H RES 8 REG, APPLICATION 10.9 12.9 11.3 8.4 7,2 IN-VESSEL ACC, t%NAESTNT 0,7- 1.4 1.6 1,8 1,8
! ENCLOSURE D l
SUMMARY
OF PUBLIC COMMENTS .
l GENERALLY SUF#ORTED NEW ECCS EVALUATION APPROACH l
i SUPPORTED GRANDFATHERING OF CONSERVATIVE APPENDIX K METHOD (ACRS QUESTION)
L DID NOT FEEL THAT EXPLICIT DEGREE OF CONSERVATISM NEED BE SPECl-FIED ( ASSELSTINE QUESTION)
OID NOT NEGATE COMMISSION'S CONTENTION THAT INCREASED FISSION PRODUCTS WITH POWER OPERATING IS NEGLIGIBLE WHEN COMPARED TO UNCERTAINTY OF FISSION PRGDUCT RELEASE (ASSELSTINE QUESTION)
INDEPENDENT REVIEW OF TECHNICAL BASIS SHOULD BE BY ACRS (ASSELSTINE QUESTION)
GRANDFATHERING OF DOUGALL-ROHSENOW GENERALLY SUPPORTED SUPPORTED USE OF UNCERTAINITY EVALUATION MANY COMMENTS ON REPORTING REQUIREMENTS
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SUMMARY
OF PUBLI_C CRMMENTS (c_ONT'D1 ,
- SUPPORTED MAINTENANCE OF EXISTING ACCEPTANCE CRITERIA
- SUGGESTED BROADENING OF RULE TO INCLUDE ZIRCONIUM-BASED ALLOYS
- BROADENING OF RULE SCOPE SGTR CONSEQUENT TO LBLOCA LONG TERM DECAY HEAT REMOVAL SHOULD BE ADDRESSED
- RULE IS NOT LEGAL BECAUSE IT BASED SOLELY ON COST-SAVINGS CONSIDERATIONS s
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- EXPERIMENTAL BASIS FOR RULE IS -INADEQUATE BECAUSE FULL SCALE ECCS BYPASS DATA IS NOT YET AVAILABLE S
Y
ENCLOSURE H - ENVIRONMENTAL ASSESSMENT
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NO CHANGES ENCLOSURE I - REGULATORY ANALYSIS CHANGE SINCE 12-87 P. 6 DELETED DISCUSSION OF 400 F MARGIN. NOTE THAT '
EFFECT ON PUBLIC SAFETY IS DEEMED NEGLIGIBLE ENCLOSURE J - 2200 F INHERENT MARGIN 1
NEW ENCLOSURE DISCUSSES RECENT INFORMATIN REGARDING FUEL, CLADDING, CONTROL ROD BEHAVIOR IN THE 2200*F RANGE.. CONCLUDES THAT MARGIN ABOVE 2200*F NOT SIGNIFICANT TO RULE I
1 J
l 1.2 PRG's General Comments l (Cont'd) b Recommendations and Benefits
! = "The peer review strongly encourages work on the development and demonstration of the methodology"
! * "The pursuit of such a program on comprehensive utilization of research results, not only has potential benefits for operating reactors, but J
offers a focus for planners and researchers in the conduct of future investigations" 4
'. * "The benefits also include the comprehensive documentation of computational codes and data
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I l 1.2 PRG's General Comments (Cont'd) i i
1 j NRC Comments:
! o NRC intends to apply the CSAU methodology to in-vessel severe
! accident manage:nent activities 1
I . The overall objectives of such a program will 'oe to:
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); 1. Bring within the CSAU framework, the research (experimental and analytical) conducted to date on in-vessel severe accident l processes and phenomena.
- 2. Provide a basis for integrating experimental and code
! development activities.
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- 3. Provide a basis for comprehensive and quantitative evaluation (in contrast to a fragmented, piecemeal and qualitative approach) of the present status and future research (experimental and
- analytical) needs concerned with in-vessel severe accident n i
N phenomena, processes and issues. [
W i NSLOO933
1.2 PRG's General Comments (Cont'd)
- 4. Conduct a "first pass" evaluation of code uncertainties to calculate parameters of interest to in-vessel accident management.
- 5. Identify and specify on a cost-effective basis, what kind of code improvements would be needed ;
to reduce code uncertainties.
- 6. Provide NRC with an auditable, traceable, and quantifiable methodology for in-vessel accident management. ,
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j 1.3 PRG's Concern (Cont'd) i
- The objective is to:
Develop a method which can be used to quantify the l effects of distortions and/or to provide a measure (index)
! of applicability of available correlations to conditions of interest to NRC applications.
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- The results are needed to:
- 1. Assess the applicability of a code to the accident scenario and to evaluate its scale-up and modeling capabilities.
- 2. Identify, specify and prioritize future experiments if needed. ,
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g 3. Quantify the effect of scale distortion.
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1 1.3 PRG's Concerns (Cont'd) .
PRG's Concern: :
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Some members of PRG were concerned that the effects of nodalization on uncertainty were not adequately addressed TPG's Response: ,
This question will be examined in detail at the next meeting of TPG [
NSLOO939
1.3 PRG's Concerns (Cont'd)
PRG's Concern:
The methodology concentrates on the uncertainty of the primary safety criteria (PCT for LBLOCA). The uncertainty of other parameters is not considered.
TPG's Response:
o TPG believes that it is sufficient and cost effective to oetermine the uncertainty only for the primary safety criteria used in licensing / regulation decisions.
NSLOO940
t 1.3 PRG's Concerns (Cont'd) o TPG recognizes that the defensibility of an uncertainty quantification depends to a large extent on demonstrations that the code simulates other important parameters adequately.
Such demonstrations are (or should be) provided in code assessment reports.
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PRG Response Items Resulting in Delayed Completion of CSAU Project
- 1. Items already addressed and to be presented at the Ary:i r ACRS meeting:
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- a. Hot channel investigation 2.:id results. .
- b. Evaluation of the effect of double hydraulic cross products.
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- c. Inclusion of additional "independent" experimental l
LHGR.
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PRG Response items Resulting in Delayed Completion of SCAU Project
- 2. Items that are being or will be addressed:
- a. Development of success / sufficiency criteria for the steps in the i i
methodology.
l b. Additional support for the standard NPP nodalization strategy.
- c. Additional support for the suf ficiency of the scaling evaluation.
- d. Additional support for the sufficiency of quantifying uncertainty for primary safety criteria (PCTJ only
- e. Expanded final documentation covering new topics.
- f. Additional PKL experimental data included in the scaling . study Dx '
NSt.00949
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e CSAU Milestones
_O LD_ NEW o Complete transient calculations MAR 88 JUN 88 for blowdown dominate uncertainties o Complete transient calculations APR 88 JUL 88 for refill /reflood dominate uncertainties o Complete determination of total MAY88 AUG 88 uncertainties ,
o Complete NUREG draft JUN 88 SEP 88 i s
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THE CHANGE IN THE TOTAL BLOWDOWN PCT UNCERTAINTY BETWEEN THE DATA BASES CONTAINING SINGLE AND DOUBLE HYDRODYNAMIC VARIATIONS IS SHOWN BELOW (VALUES IN OF)
OLD NEW PARAMETER VALUE VALUE CHANGE MEAN PCT 1107 1102 -5 STANDARD 172 149 -23 DEVIATION T05 1379 1363 -16 OLD VALUE = DATA BASE CONTAINING ONLY SINGLE HYDRODYNAMIC VARIATIONS NEW VALUE = DATA BASE CONTAINING SINGLE & DOUBLE HYDRODYNAMIC VARIATIONS N
it
ON A COMBINED UNCERTAINTY BASIS (PDF) THE HOT CHANNEL .
EFFECT ON PCT IS 68 0F, FOR THE ANALYSIS PERFORMED TO DATE TEMPERATURE (OF)
HOT HOT PDF ORIGINAL CHANNEL CHANNEL PARAMETER MODEL MODEL EFFECT -
MEAN PCT 1093 1176 83 STANDARD 218 193 -25 DEVIATION PCT AT 95% 1511 1579 68 PROBABILITY PDF's WERE GENERATED FROM FULL 2ND ORDER RESPONSE SURFACES CONSTRUCTED FROM THE NOMINAL AND CRITICAL FLOW 1 SIGMA NPP RUNS
.