ML20154J014
| ML20154J014 | |
| Person / Time | |
|---|---|
| Issue date: | 02/02/1986 |
| From: | Catton I Advisory Committee on Reactor Safeguards |
| To: | Boehnert P Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-CT-1832, NUDOCS 8603100434 | |
| Download: ML20154J014 (4) | |
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TD R 03bs6 o us,k UNITED STATES NUCLEAR REGULATORY COMMISSION o
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U ADVISORY COMMITTEE ON REACTOR SAFEGUARDS g'*o j,,#[g WASHINGTON, D. C. 20666 o
February 2, 1986
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MEMORANDUM T0:
Paul Boehnert, Senior Staff Engineer gh FROM:
. Catton, ACRS Consultant 4
SUBJECT:
ECCS SUBCOMMITTEE MEETING - IST' PROGRAM, PALO ALTO, CALIFORNIA, JANUARY 23-24, 1986 During the two days we met, we heard about six experimental programs, two code programs, a scaling study and how they all will be integrat-ed.
In all respects, the IST Program is the best of its type. Three integral test facilities of differing characteristics will yield the most complete set of data we have. The separate effects experiments complement the integral experiments very well. The program managers should be complimented for a job well done. Although the data' set will be very near complete, there are some questions remaining.
In particular, we must not loose sight of the fact that the codes must still extrapolate a long way when predictions are made of the behav-for of full size LWRs.
The following paragraphs contain detailed comments about each of the experimental programs as well as the codes and the integration effort.
SRI Facility The SRI facility seems to be close to being operational. The kinds of problems they are having are typical shake down troubles for a facility of its type. The facility should yield some valuable data.
In particular, the downcomer and vent valves should allow us to gain insight into behavior not observable at any other facility. The vent valve chatter, however, deserves more attention. We need to estab-lish whether or not it is real and if it is not, how to stop it in the facility. A damper may help and a simple spring mass ty)e d
analysis would be enlightning. The hot leg sight glass is a)out to be removed because it has broken twice. The present glass being used is pyrex. There are a number of other types of glass that are much better. Before loosing the ability to see into the hot leg, other types of glass should be evaluated. The type of information one can gain from visual observation cannot be overvalued.
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ECCS 1/23-24/86 Meeting February 2, 1986 MIST Status I am always impressed with the very competent way Randy Carter carries out his charter.
To within the bounds atypicalities of the MIST facility will place on the value of the data, the program is progressing very well. The plans for system characterization will help characterize MIST. They will even allow us to distinguish between what we think should happen and what MIST does. There are obvious shortcomings to the planned approach.
The cost of Feed and Bleed experiments will be close to $100,000.
It seems to me that characterization of the flow characteristics of PORVs is needed more than a MIST Feed and Bleed experiment.
If we cannot calculate flow through plant PORVs with reasonable accuracy, then the MIST test serves little purpose. Further, it is not clear that the pressurizer diffuser plate is properly characterized. This, with the tall skinny nature of the pressurizer, could lead to an entirely different en-vironment for the MIST PORV.
The need for PORV characterization is an argument for a general hydraulic laboratory. The MIST steam generator blowdown rate is limited in such a way that a full MSLB cannot be studied.
Hence questions about MSLB/SGTR can only be partially answered by MIST.
Considering its other atypicalities, extrapolation by the codes or use of the other two facilities may(be more appropriate.
The MIST follow-on program may be premature I think it is).
A number of reasons why a follow-on program should be sought were given by Bill Beckner.
I don't agree with his arguments for several reasons:
(1) the system atypicalities may degrade the value of further data; (2) SRI-2 and UMCP may supply enough additional infor-mation for many of the transients to be conducted during the proposed follow on; (3) AFW SG data may well be flawed; (4) normal o SG heat transfer data is better obtained elsewhere; and (5)peration in a period where budgets are being reduced, one ought to look closely at where the money is being spent.
I think there are other places more deserving than a MIST follow-on. The MIST follow on will involve a major commitment of funds and needs serious consideration before a decision is made.
University of Maryland Facility Y.Y. Hsu reported some interesting but rather unsurprising results.
The type of work being done is relatively low cost and in my view allows v,ery large variations in parameters. This should yield a great deal of data for code assessment. University of Maryland code development, no matter how minimal, does not help us develop faith in the codes used by NRR to assess the safety of full scale LWRs.
ECCS 1/23-24/86 Meeting February 2, 1986 ANL Candy' Cane Studies The studies being carried out at ANL are primarily experimental. A very nice pyrex simulation of the hot leg and U bend have been built based on the scaling study study Ishii did some time ago. Two size hot legs are being studied; 2" and 4".
The work may not be applica-ble to a full size system because the pipe diameter is rather small.
It should yield models that will allow MIST and other small scale systems to yield data that is meaningful. The models can be used in codes like TRAC allowing interpretation of other aspects of the experiments.
The question of permanent flow interruption is noted to be governed by void fraction distribution in the hot leg and the thermal center location in the steam generator. You should recall that whether or not it occurs results in a difference of five orders of magnitude in vessel conditional failure probability. This points to the need for the codes to be able to determine what the proper flow regime is.
Coordination of Support Projects The approach being taken by the IST program is unique. This is the first NRC major research program that has integrated several facil-ities of different scales and separate effects in a sensible way.
From an experimental point of view, the issues seem to be covered.
I would now like to see a shift in emphasis from explaining individu-al system atypicalities to demonstrating understanding of the differ-ences using our computational tools.
It would be of value to see what MIST-type atypicalities would do to estimated plant behavior using TRAC and RELAp-5. This would be of more value than the tests outlined in the report on the subject. With the analysis in hand, one could probably eliminate those tests that will yield meaningless plant behavior and replace them with more meaningful tests. The tall skinny steam generator may be too tall and skinny to act like a full size steam generator. The aux feed heat transfer process is probably multi-dimensional at the tube sheets. The single T/C per tube sheet will not yield enough data about the multi-dimensionality to be worthwhile. The instrumentation in the steam generator should be augmented to deal with such questions as code modeling of steam generators is inadequate except in the crudest sense. The SRI-2 and UMCP are scaled a bit differently. Even so, they are still too tall and skinny to avoid a host of atypicalities. They will, however, be very helpful in verifying the codes.
What does not come across clearly in the report is how the different systems will be used to demonstrate that our advanced codes can predict the behavior of a full-scale PWR.
For example, one needs to lay out a plan for demonstrating that all behavior in all three HLUBs
1 ECCS 1/23-24/86 Meeting February 2,19R) 1 l
is predicted well enough. A series of tests could be selected from the three systems' test matrices. One would have to be sure that the tests have the proper detail for the code analyst to test his predic-tive capability. Tests run in the three facilities at the same pressure could be used to test the codes' ability to model geometric effects.
Varying pressure in regions of overlap will give us confi-dence in our ability to reproduce certain thermodynamic processes. A serious effort is needed to select an appropriate minimum set of tests for such a study. Scaling data from each facility up to a full size plant implies knowledge we may not have.
I think it wculd be better to model each facility and then analyze differences between data and calculations.
In doing the analysis one might develop scaling principles for certain parts of the system that will be of value. The IST program presents us with the opportunity to do it right. We should try to do so.
Scaling Report Status The report is an interesting exercise. The results should help us pick a set of meaningful tests for the three facilities. At present, however, I think the author is trying too hard to find the ideal set i of conditions that will yield exact similitude. None of the facil-ities are idealy scaled and exact similitude is impossible under any cor**tions. Some scaling questions I would like to see addressed are t;m following: (1) impact of downcomer scaling (SRI-2 and UMCP are di fferent); (?.) impact of non-ideal upper plenum internals and aspect ratio; (3) L/D of the horizontal section of the hot leg (Ishii says it is not important); and, (4) will slugging take place in the scaled hot legs and if it does what is the impact on the value of the test.
TRAC /RELAp5 Differences The hedt transfer packages are essentially the same in both codes.
The steam generator modeling is somewhat different but neither is very good. There are a number of examples where the modeling is just wrong. To compound one's frustration, the incorrect models are used even when it is known they are wrong, and data as well as correct models are readily available. Wetted tube heat transfer in the steam generator is based on Chen's nucleate boiling correlation. The wetted tube heat transfer estimation requires that one use a film evaporation model. Why one cannot change the model to the correct one escapes me. Arguments about " frozen codes" are nonsense. The nodalization used by the code analyst is not frozen. By changing the nodalization and time stepping, one can change the answers to match the available data. This can lead to answers that look good with incorrect physics. How can we be expected to believe full size plant predictions when such monkey business is under way. Nodalization studies make no sense when the physics are incorrect.
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