ML20052C827
| ML20052C827 | |
| Person / Time | |
|---|---|
| Issue date: | 02/08/1982 |
| From: | Wu T Advisory Committee on Reactor Safeguards |
| To: | Plesset M Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-CT-1417, NUDOCS 8205050597 | |
| Download: ML20052C827 (4) | |
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Fr.bruary 8,1982 Aae ygn
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V== /WY Dr. M. S. Plesset, Chairman ECCS Subcommittee k
Memo to:
T. Y. Wu, ACRS Consultant From:
Scientific report on ACRS Subcommittee Meeting da ECCS
Subject:
December 2-3, 1981 The subject meeting was held on December 2-3, 1981, in I.cs Alamos, NM, to review selected portions of the RES Program o
- and ECCS for In this t
wou e to the Committee's annual report to Congrecs.
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provide some comments and recommendations on th opics covered s't-e
' ' $S np meeting.
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1.
RES Code Development Program
~a5Dgg Being developed from RELA technologyp ihes in RELAP-5 objective of RELAP-5 program is to provide an econo c7advancedWD BE Currently the MOD-2 version of REI:AP ~5nu W ' being s
(best estimate) code.
developed by EGLG INEL based on an improved two-phase model, using a Its MOD-1 fast numerical scheme and designed to suit user's convenience.
version, released in December 1980, has been furnished with configuration control for system applications to provide prediction of SB (small break)
In addition, it has been LOCA transients in Semiscale and' LOFT operations.
applied to train users in an NRR Workshop and an International Workshop.
Judging from the results of RELAP-5 LOFT ATWS (Anticipated Transient without Scram) simulations with particular reference to pre-and J
post-tests of separate effects as well as of integral system performance, RELAP-5 Program may be regarded as having accomplished very satisfacto-It seems to have even become an all-rily what it was expected to achieve.
capable code to some people. In regard to user o.pendence, sentiments ran from one extreme that some users are ignorant of the code's capabilities and limitations to the other that RELAP was the winner in the workshops held, primarily owing to user's great familiarity with the details of the code.
These superficially inconsistent reports relating to users status, if both true They might experiences, could be valuable and should be further explored.
substantiate the view that a well designed users training course can be effective and users support should deserve a high priority.
I would like to support the position that MOD-2 be the final major development effort for RELAP-5. It is desirable to have a severe core damage fuel model added and to have the capability of real time mode for EGN ORIGN'
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simulator functions.
I would like to recommend that as the code is going into maintenance mode, its improvement and enhancement be continued, especially on issues requiring better physical understanding such as that on the constitutive properties knd heat transfer package involving phase-change and noncondensible effects on two-phase fluids.
TRAC-P Highlights of the TRAC-P code, developed under the responsibility of LASL, include the following aspects of improvement and plans for enhece-(1) Reflood modeling - The earlier TRAC-PIA reflood modeling has ment.
been greatly improved in the TRAC-PD2 and -PF1 by adding a detailed heat-transfer analysis for both the reactor vessel and the loop components.
(2)
Mass conservation - the rather inadequate situation in TRAC-PIA enforce-ment of mass conservation (apparently due to its geometry-dependent sensitivity and its loose iteration convergence) has been claimed to be nearly all corrected.
(3 ) CPU time - greatly shortened by using the SETS (stabilizing equation two-step) numerics and is no longer a problem.
(4)
SB-LOCA modeling - TRAC-PFI, an improvement over PD2, uses a full two-fluid model for computing one-dimensional and three-dimensional j
r.ountercurrents.
The two-step numerics in the 1-D components affords rapid calculation of slow transients.
(5) Constitutive relationships - continuous improvement in this area includes adoption of Dukler's model of pool entrain-ment, stratified flow and interfacial shear. Also being improved in a continuing process are on the heat transfer package and jet condensation.
It appears highly desirable that in the work on -PFI/ MOD-1 for j
operational transient use and in the subsequent major work on -PD3, high priority be assigned to continuing development on flow-regime-dependent constitutive relationships based on sound physics modeling and to further improvement of heat transfer models and numerics, especially for the cases of reflood model, stratified flow model and choking flow model. In addition, I also wish to support Dr. Catton's suggestion to have the energy conservation checked by LASL on an overall level of the TRAC code in comparison with the relatively coarser error currently allowed for mass conservation.
TRAC BD-1 Development of effective code for modeling large-and small-break LOCA and ATWS transients in BWR operations should be given proportionately
3 equal attention as for PWR's. As an improvement over the TRAC-BDI, which has been well documented and released for applications, the BDl/
MOD-1 version undertaken by EG8:G will extend its modeling capability for LOCA, ATWS and operational transients. While this worthy task is under-way, and while a follow-on work on a BD2-version may eventually commence, I feel strongly in support of the on-going thoughts that attempts be made to use RELAP-5, with necessary modifications and further efforts, for BWR transient calculations.
The successful results of RELAP-5 (being primarily a one-dimensional code) produced under various circumstances seem to infer that two-and three-dimensional thermo-hydraulic processes can indeed be averaged out, Li appropriately done, to provide a one-dinensional repre-sentation. With this possibility viewed together with cost-effectiveness and time-benefit, the idea of adapting RELAP-5 to BWR applications appears attractive.
2.
RES Code Aspssment Program Crudely speaking, I seem to have the impression that the RES codes in current use nearly all can pass the mark of satisfaction if the margin off their respective design state is sufficiently small. When that margin is no longer small, say less than the magnitude of a large break LOCA, then often is the case that no certainty can be said for the results on transient calculations.
It thus seems meritorious to first establish, for the purpose of code assess-ment, a primary " mission-oriented" operation versus which the subject code is considered to be optimally suited for application and is accordingly evalua-ted for its capability and performance under that specific premise.
The new concept of identifying main missions or giving classification to scenarios is appealing. Without taking this first step, there would be lack of firm basis for testing the basic thermo-hydraulics and heat-transfer package of a code against (1 ) separate physical effects and (2) the integral system performance. I would like to share the strong ciews in favor of establishing acceptance criteria in connection with assessment of the BE System codes.
It may greatly facilitate the assessment work if the criteria are based on
'l separate and different missions, in each of which case the code is required to predict the results. When so classified, the varying ranks of the system codes in different categories of applications may help focus the need of the users.
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Experimental Facilities Continued support should be kept for planned use of the SS (semiscale for PWR) and the FIST (Full integral simulating tests for BWR) facilities, for they will be the principal facilities the RES work can turn to, after the phasing-down of LOFT, in addition to the access to the overseas information through joint programs with Germany and Japan. In this connection, I think it may serve our purpose handsomely by keeping close observation for NRC to participate actively in the programs of high interest to NRC and to avoid commitments to sharing costs of those programs of little interest.
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