ML19260C059
| ML19260C059 | |
| Person / Time | |
|---|---|
| Issue date: | 10/09/1979 |
| From: | Catton I Advisory Committee on Reactor Safeguards |
| To: | Bates A Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-CT-1177, NUDOCS 7912180294 | |
| Download: ML19260C059 (3) | |
Text
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October 9,1979 gg8;9$tMi lyt'21
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. TO:
Or. Andrew BatesY FROM:
I, van Catton 4g R
SUBJECT:
ECCS Subcomittee Meeting - 27, 28 August 1979, Idaho Fal%
COPY TO: Professor M. S. Plesset Sumary Both the Semiscale and LOFT programs are to see an emphasis on engineering analysis. The result should be an increased understanding of the processes being studied.
It is hoped that this emohasis will carry over to other NRC experimental programs as well. The area of scaling needs more attention.
It is presently not possible to scale all Semiscale results to LOFT and therefore scaling LOFT to a full scale PWR is not without reservation.
The code programs are being redirected towards the small break.
In that the small break is a quasi-steady process, aserfes of steady states.
At present, more attention should be given to the Michelson type analysis.
it seems that a great deal of expensive code running and' comoaring is being conducted without taking advantage of the small break q'uas'i-steady aehavior.
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General Discussion Dr. L. S. Tong's criteria for a meaningful program for studies of small breaks look very good.
The emohasis on understanding and engineering analysis is a shift that will improve the productivity of the program.
Dr. Tong stated that there would be a shift in emphasis to give more Semiscale is not similar to LOFT nor is it similar to a importance to analysis.
Scaling with non-similar geometry is in violation of a cardinal rule PWR.
Under such circumstances one must vary the non-similarities of similitude.
to detemine the sansitivity of the deviations from similitude.
It is not clear that sensitivity studies will be carried out.
If not, encouragement to do so should be given.
A great deal of data has been collected during the semiscale program as well as during the GE blowdown heat transfer program and the A part of the emphasis on understanding ORNL blowdown heat transfer program.
should be fuller utilization of data from past experimental programs as well Collection of data without full understanding and as planning new programs.
The CREARE ECC bypass data seems to interpretation is a waste of money.
also fall in the category of unexplained infomation.
The restructuring of the LOFT program, as described by Dr. Kaufman, This should make to give engineering analysis more emphasis is long overdue.
the LOFT program more effective. Use of LOFT to study scuil breaks may not yield as much infomation as planned because of resistance to endangering the facility. Certain regimes of core voiding are important to our understanding of small breaks yet may not be palatable to LOFT engineers.
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page two October 9,1979 Risk increases as one approaches the regimes of interest.
In scaling the LOFT results to full scale, one must consider whether there are any anomalies introduced by combining the intact loops.
It was noted by Dr. J. H. Lineberoer that LOFT test L2-2 resulted in stagnation flow in-core whereas L2-3 resulted in stagnation flow above the core. This phenomenon does not seem to be procerly addressed. We need to ask why the stagnation point moves as a function of heating. Variation of parameters in the experiments must be carried out if LOFT is to be scaled to a full size PWR.
It appears-as if the important parameters are hot leg' flow resistance, pump flow characteristics and core flow resistance. All will play a role and their individual contributions must be sorted out.
A very infomative study was described by Dr. Nelson. By comparing predictions with LOFT exoerimental results and trying to explain differences, he was lead to assess the data base. This lead him to conclude that there was almost no data in the region of interest.--This clearly points out an area for further :eparate effects experiments. More such studies are needed and the shift in emphasis from data collection to
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engineering analysis should ensure that they result.
There is still some concern about the effect of external themocouples on the quench behavior in the LOF7 core. The exoerimental results presented by Professor Dhir clearly show oremature quenching.
Dhir's results are corroborated by Chen (Lehigh) and Hewitt (Hamell) as well as Geman and Jaoanese work. Dr. rotula of EG&G demonstrated that external themocouples measurs am ly the same temperature as internal themocouples. This has never been in question. Rather, the external themocouoles act as fins and encourage premature quenching of the entire fuel pin. At very low flooding rates (-2cm/sec) the effect is small but at higher values (-30cm/sec) the effect is quite pronounced. At a high enough value precursor cooling will dominate and the fin effect of the external themoccuoles will be second order. The problem is that we don't know what the fin effect is at any given flooding rate or core flow velocity.
Use of the Iloeje correlation to simulate the effect of external themoccuoles does not help us predict the behavior of a full scale PWR without external themocouples. A number of experimental programs that are to answer the above concerns were described. The results must be analyzed with care as effects of external themocouples extend beyond the fuel pin they are attached to. Faster quenching of adjacent pins has been measured. As a result single oin and even four pin experiments may be of no use.
It was interesting to see that RELAP5 runs at almost twice real time whereas RELAP4/M007 runs at over ten times real time on a CDC 7600.
It is my belief that RELAPS deserves more attention as a result of its The RELAP5 simulation of Marviken III looks quite reasonable.
success.
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page three i
, October 9, 1979 The presentation on Semiscale scaling was not too enlightening.
Volume scaling with similar heights to maintain unity scaling of velocities and times is not trivial. This leads to a loss of geometric similitude and some concern as to the meaning of results obtained. Further, the electricall.y heated rods introduce a different time scaling than actual fuel rods. A great deal more study of scalino is needed. The present aoproach is not being carried out in a way that 15dicates what is being compromised.
It would be infonnative to see.a scaling analysis carried out that starts with the governing equations. For example, the steam generator tubes are presently smaller in diameter than full scale. This leads to inconsistencies because if surface area and primary side heat transfer coefficient are scaled properly then the primary side will be cooled too fast. The result is scaling length and making relative elevations non-prototypica The Beacon code does not seem to have prooressed very much.
It does, however, seem to be in better hands. The fact that it cannot handle an irreversible loss seems strange. The numerical diffusion problems described by Dr. Broadus are not surprising.
The NRC has requested that Semiscale experiments be examined critically. Experiments on UHI may be unduly penalizing because of the Semiscale 1-0 character.
It is not clear why Semiscale was not scaled differently for UHI experimentsr. Small break LOCA studies that lead to concern-about geysering are not in themselves a concern. Rather, one wonders why a one-dimensional apparatus yields behavior that cannot be predicted with a one-dimensional code.
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