ML20028G356
| ML20028G356 | |
| Person / Time | |
|---|---|
| Issue date: | 12/07/1982 |
| From: | Theofanous T Advisory Committee on Reactor Safeguards, PURDUE UNIV., WEST LAFAYETTE, IN |
| To: | Boehnert P Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-CT-1538, NUDOCS 8302080475 | |
| Download: ML20028G356 (2) | |
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SCHOOL OF Ruct*AR {NGg{tlNG December 7, 1982 c.
A. Paul Bochnert 1717 H. St. N.W., 10th Floor Washington, D.C.
20006 RE: ECCS Subcommittee Meeting, 12/2-3/82, San Jose, California
Dear Paul:
I think GE is getting close to having a good story to tell.
In fact, I believe that the story is already there. Now we have to get GE to do a much better job in telling it. Perhaps cur next and " detailed" meeting could be the appropriate forum for that.
The goal is an important and timely one. The overall approach is sound.
General Electric's initiative in this effort is admirable. The technical achievements both in the experimental and analytical fronts are of high quality. And the results are most significant.
I would like to say a few words about each one of those items.
Since the creation of Appendia K there have been major improvements in technology. The time is ripe for factoring these improvements in our licensing process as well as into our safety design and procedures.
It is easy in retrospect to knock Appendix K, as some newcomers do, however, I believe that this rule was the best that could be done at the time.
Some judgments had to be made and significant margins had to be incorporated to protect the health and safety of the public. Now we know much bette:-
what is really going on, and therefore, as in the case at h:nd, we can visualize the large margins that we have imposed on ourselves. This provides no reason to ridicule Appendix K.
We should rather credit cur regulation process for t job well done. Now the time has come, in fact in my opinion it is somewhat overdue, for change.
In several previous attempts to modify Appendix K I advised the ACRS against a piecemeal revision.
I am happy that GE takes an integrated approach to such a revision.
I agree also with the elements of this approach. A sim-plified code (EM) th'at is not cumbersome (and expensive) to use (SAFER, GESTR) is crucial to developing an adequate understanding of system response e
West Lafayette, Indiana 47907 8302080475 821207 DESIGNATID CRIGIl?AL PDR ACRS
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Mr. Paul Boehnert December 7, 1982 Page 2 under a wide range of transient and accident conditions. The use of a wide range of fundamental and integral experiments together with advanced code technology (TRAC) to guide these codes to realistic behavior (EE) through better understanding of the phenomena is also ell conceived. The idea to evaluate safety margins through a best estimar result and an uncertainty estimate is also good. The evalustion of the t.ncertainty can be in principle a somewhat sticky problem but in this case the safety margins appear to be so great that I do not expect it to present in practice a serious obstccle.
The technical effort is based on an appropriate range of separate effects and integral facilities. The analytical techniques (both BE and E!!) are highly successful. One will always find areas that can be improved but we should not forget to judge the significance of these improvements against the i
total perspective of system response on the one hand and the safety evaluation l
goals on the other.
I believe that GE could have done a better job in explain-ing the key technical elements of their proposals.
The way I see it mechanisms appear to exist whereby the presence of water within fuel bundles is promoted.
Key mechanisms here include (a) slowing down of bundle draining due to counter-current flow limitations (CCFL) at the bundle bottom (core support area), (b) formation of a liquid pool in the upper plenum and radial temperature stratification following the sub-mergence of spray nozzles, (c) CCFL breakdown due to this local subcooling and liquid pool damping i u.o the peripheral bypass region, (d) leakage of this water into fuel bundles and (e) CCFL at the bottom of fuel bundles in-hibiting the rapid drainage of this leakage water into the lower plenum thus yielding improved cooling before complete reflooding of the core. These pro-cesses are driven by relatively small p(flashing, metal heat), sinks (conden-ressure differentials and can be dractically affected by vapor sources sation) and leakage (relief paths such as jet pumps, bundles, etc).
I wculd like to see a detailed accounting of these vapor flows and associated pressure differentials (experimental vs. reactor conditions) as the starting point of a detailed discussion of the key physical processes enumerated above. Addi-tional items I would recommend for discussion include pool-wide comparisons of predicted vs. measured temperatures and details of geometry, data, and correlations for CCFL st all important locations, and details of geometry of the bypass regions and communication between the peripheral locations of CCFL breakdown and more central areas of the core (and the modeling of these regions).
In conclusion I believe that the meeting was very useful in setting the stage i
for a more technical detailed discussion which I will have to see prior to l
offering a final judgment on the quantitative aspects of the effort.
Sincerely,
> C>
T. G. Theofanous Professor TGT:wb l
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