ML19296B092
| ML19296B092 | |
| Person / Time | |
|---|---|
| Issue date: | 10/29/1979 |
| From: | Catton I Advisory Committee on Reactor Safeguards |
| To: | Boehnert P Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-CT-1185, NUDOCS 8002200051 | |
| Download: ML19296B092 (3) | |
Text
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- 2) October 1979 TO:
Paul Boehnert g
Ivan Catton fk DISTRiiiUTED TO ACRS MEMBERS FROM:
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SUBJECT:
Review of Proposed DOE /WR In-Pile Safety Testing and Research Program, 8 Oc+wber 1979, Salt Lake City, Utah ENCLOSURE: " Experiment Requirements to Determine and Relate Fuel Damage Limits to Core-Wide Conditiens In Pressurized Water Reactors",
EGG-TFBF-50ll, September 1979 An experimental program is being proposed to study DNBR under realistic conditions using a 201 fuel rod assembly that is three feet long.
The goals are to better define fuel rod damage criteria and to obtain a rule change that will allow greater flexibility in plant operations. This program is thought to be a natural follow up to the single fuel rod power-cooling-mismatch experiments now being conducted at INEL as part of the Thermal Fuels Behavior Program in the Power Burst Facility. Work done to date indicates that the fuel rod in PBF can operate in film boiling and incur significant damage before failure actually occurs. The conclusion reached as a result of the experiments is that exceeding the DNBR limits as now stated does not mean fuel failure. The purpose of the meeting was to try and establish whether or not the proposed program would confim the conclusion reached and yield sufficient information to justify a change in the present rules governing DNBR.
The benefits resulting are mainly economic. Studies now underway db at B & W and CE, funded by EPRI, are attempting to establish the benefits of reducing the margin, power uprating, better core design, enhanced plant
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maneuverability, elimination of down time and faster licensing. Preliminary results show tnat a program such as the one suggested is easily cost effective for PWRs. When future involvement with the program was discussed GE indicated no interest and W refused. With the benefits of an experimental program established, the question becomes one of deciding whethar or not the proposed program will be adequate.
The e~xperiment was proposed by fuels resea chers and the review group heavily populated with experts on thermal hydetulics. The result was a great deal of concern being expressed about the lack of instrumentation in the bundle and the shortness of the powered portion. The bundle will have a power of 55kw/M at steady state with 75kw/M transient cacability. Pressure transients from 2250 pisa to 2740 psia will be possible. Before discussing the problems associated with the experiment as described, a brief summary of the vendor and EPRI opinions will be given.
Tom Patten, EXXON. Present licensing methods cannot accurately predict location of DNB and underpredict time to its occurance. This leads to present. methods be 39 conservative. The margins for a BWR are larger than for a PWR and as a result more gains are to be made with BWR fuels (note that this is in contradiction to the GE position). Clearly, identifying and quantifying conservatisms would go a long way in helping the industry.
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H. Chelemer, Westinghouse. The phoposed experiment was thought to be a noble effort and was ooviously a lot of work. A consensus of the Westinghouse position is contained in the following corments.
- 1. 5% power increase capability based on experiments can already be obtained based on existing DNB margin. Problems will be encountered with pellet clad interaction and LOCA margins Mfore achieving the 5%.
- 2. Not sure results of the proposed program would convince NRC to change the rule.
- 3. Establishing failure limit carameter correlations for control room use if probably unattainable. The program would be better if failure limits were tied to local thermal hydraulics.
- 4. The program objectives should be to relate fuel perfomance under condition I and II transients to local themal hydraulics and leave the vendors to pursue margin changes.
- 5. Measurements of local themal hydraulics must be made. A much more extensive measurement program must be established.
- 6. Westinghouse supports the program but does not agree with the cost benefit arguments as presented by EG&G.
R. Stout, Babcock & Wilcox. EPRI is funding a study to determine whether or not enanges in fuel design limits are worthwhile. They have been given the following tasks:
- 1. Identify what post DNB data is available;
- 2. What phenomena governs (separate effects);
- 3. Generate a fuel design limit;
- 4. Detemine benefitrt; and
- 5. Establish what future research is needed.
At this point they have concluded that post DNS heat transfer and rewetting data are desperately needed. Critical needs regarding clad are: about deformation, short tem annealing of zircaloy and rod bowing. Preliminary 0
thoughts on criteria are 1) no change in geometry, 2) 1250 F for 10 seconds and 3) limits on clad temperature versus differential pressure. Any program initiated should address these needs with bench mark data for codes being an important objective.
J. Church, Combustion Engineering. Rod bos is an important factor in plant operation as it costs 2% for the first cycle, 4% for the second cycle and tne asymptotes slightly higher. CE wou,ld like to replace the present 95/95 non-exceedance of the DNBR limit with a time at temperature condition.
To make the proposed program acceptable, the following concerns need attention:
- 1. Need better quantification of payoff;
- 2. Need out-of-pile tests to establish length effects;
- 3. Need knowledge of core wide themal hydraulics; and
- 4. Would like to see 60,000 MWD / Ton burn-ups looked at.
With the above concerns addressed, CE endorses the program.
n M. Merrilo. EPRI. Allowing brief excursions past DNB would yield gains in operating maneuverability. To obtain the information needed to confim that the excurtions should be allowed experiments such as 'those proposed are needed. Concerns expressed about the present program are as follows.
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- 1. With prototypicality being impossible, there is a hign risk of the results not being acceptable. The program must be integrated with other programs.
- 2. The proposed fuel bundle needs a great deal more ins trumentation.
- 3. There is an acparent lack of analysis. Bundle length severly compromises any results that might be obtained.
It was suggested that out-of-pile experirrents using 3, 6 and 12 foot lengths be run.
If the three lengths cannot be related (scaled) then the entire program should be teminated.
The length of the proposed experiment, 3 feet, is the largest drawback to its success. When one considers the problems associated with LOFT and semiscale (6 foot cores), a three foot core will create discussions that will be around for years and a rule change will be a low probability event. The suggestion by EPRI seems to be a reasonable route. For circumstances where the flow is single phase and turbulent, the three foot core would be satisfactory. Unfortunately, typical heat fluxes are on the 2
order of 400,000 Bto/ft hr and DNB will only occur at quality. The question becomes whether one can mimic the proper inlet conditions.
It seems to be the opinion of most that you cannot eliminate slugging when trying to obtain a quality flow at the inlet. To compound tha snort core problem, Westinghouse data shows that not only does DNB increase as the core is shortened but the effect gets very strong for very short ::res. The flat power profile will lead to trouble in assessing DNS proca;i ":r-Another drawback is the rate of increase in the heat flux near the
- teing far greater than in a twelve foot core and its effect on DNS. Als.
- DN3 heat transfer will be mocified by the shortness of the core.
An interesting discussion took place between the vendors.
If a standard fuel of some design, not necessarily that of a given vendor, is tested and the results are gecd, all vendors will argue that the fuel is similar to their own.
If, however, the results are bad, the differences will be pointed out.
A well thought out out-of-oile program needs te be underey before an in-pile "ogram is initiated. Large scale s:2-c-alone i -cile programs do not have a history of being cost e"ecF ve.
'e are:csed aragram lacks front end analysis and.has many aspects --=
++: : rengtnering.
M it were suitably backed up by an out-of-pile pregm
+ re::crendations of the review group (particularly EPRI) were incor -
could be a worthwhile effort.
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