ML19331C342
| ML19331C342 | |
| Person / Time | |
|---|---|
| Issue date: | 05/10/1980 |
| From: | Catton I Advisory Committee on Reactor Safeguards |
| To: | Quittschreiber Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-CT-1255, NUDOCS 8008140581 | |
| Download: ML19331C342 (3) | |
Text
H E C '~ ' ' ! E D C T' - /Mr S I.RC.
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.ay 1980 AM 7,,g T0:
G. Quittschreiber f
FROM:
I. Catton Class 9 Subcomittee Meeting, Chicago, 9 May 1980
SUBJECT:
During the opening executive session of the subcorraittee meeting Dr. Kerr' raised questions about "what should be done" and "how one decides what to do" I have a few ideas and would for Z/IP, near tem Ols, and future designs.
My thoughts are based on the like to take this opportunity to express them.
assumption that a core melt must be accomodated independent c' the probability Risk studies should be pursued independently.
of its occurrence.
Decisions have to be made too soon to be based on any new infoma-Two aspects of a core melt need to be addressed in a best estimate Z/IP.
tion.
engineering judgment sense.following vessel failure needs to receive a more detailed Second, a best of-rise of pressure impacts directly on mitigation systems.
estimate of whether or not an ex-vessel debris bed will dry out A number of conceptual studies of passive made.
should receive serious attention.
Some may be useful for Z/IP and should and active core catchers have been made.For example the type under consideration for receive consideration.
Third, the benefit of increasing the reliability could be retrofit to Z/IP.
of the containment spray system should be considered as it could mitigate both the pressure spike, the long term pressure rise and the possibility of a hydrogen This The benefits will only accrue if the sprays are properly located.
burn.
aspect needs to be detemined.
Near term OLs still have the flexibility to make minor Near Tem OLs.
In detemining whether or not design changes should be made, the The results changes.
results of Z/IP class 9 considerations can be brought to bear.
from the SANDIA fragmentation studies (molten fuel debris in water) can be used to improve our estimates of the pressure spike characteristics as well Further core catcher as better define the debris bed for dry out estimates.
design efforts can be completed and, if necessary, retrofit in t cavi ty.
Studies of quenching of hydrogen burning to optimize their effectiveness.
A detailed with sprays could be completed within a year (if initiated pr l
of different raaterials.
Studies now underway in Germany to detemine how a core melts can be incorporated into a MARCH type analysis so that initial conditions Future Desicns.
Debris beds resulting from core for containment threat are better defined.
melt down will be defined well enough that dryout can be ruled cut or accepted Conceptual designs of both passive and active as a problem to be dealt with.
core catcher schemes should be developed and tested as a parallel effort that they can be used if needed.
will answer many of the questions needing resolutuion for future designs.
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As noted by Dr.' J. Meyer, NRR staff, mitigation devices presently under c'onsideration are FVCS, core retention devices and hydrogen control methods.
FVCS design depends strongly on how fast steam is generated during the period immediately following vessel failure.
This steam spike is the result of a calculation by the. MARCH code.
It is not clear that it is the subject of the Integrated Fuel Melt Research Program e2 cept for the fragmentation studies.
A redirection to give the steam spike attention seems in order. With Z/IP being the center of attention, it is not clear why the IREP has its attention elsewhere.
Dr. Kelber's four year plan will not be very helpful to Z/IP cr near 'tenn OLs.
For example the hydrogen problem will be the subject of rule making in the near future and a lot of decisions need to be made.
If core catchers are I'
to be used, some early attention to materials other than Mg0 is needed. As mentioned above, to answer the steam spike questions requires information about i
heat transfer, fragmentation and how well water can get to the hot material.
Dr. Kelber should be encouraged to re-direct his efforts towards obtaining answers to questions raised by Z/IP. His early study in this regard was very good but needs further refinement in light of the May 7-8 meetint etween the staff and the utilities.
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Debris bed coolability studies planned at SANDIA are probably not necessary.
In that UCLA, ANL, SANDIA and others are in essential agreement about cool-
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ability in a given debris bed, attention needs to be focussed mainly on what debris bed to expect.
It is clear that in-pile debris bed dry out experiments with water as the coolant are not needed.
Fragmentation of core debris in water will yield the needed infonnation about debris beds.
Knowledge about how much of the core need be considered will not be obtained in time to be of any use for Z/IP or near term OLs.
There are presently no core retention device studies underway other than the FNP core ladle. NRR will get little help for materials other than Mg0.
j Scoping experiments with other materials should be initiated irm:ediately even
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if it means stopping the Mg0 study.
In particular actively cooled depleted 00 and Th0 beds should be studied.
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i Dr. Kelber should be encouraged to incorporate a study of sprays and contain-i ment cooling into his research program. The question to be answered is how to control the core-water interaction steam by condensation and thereby control i
containment pressure rise.
Sprays could also control or eliminate the potential for hydrogen burn if properly placed.
Hydrogen control research seems to be devoted to studies of its production j
combustion and deformation limits.
This is a well studied area.
The Germaus are doing work in this area under reactor containment conditions.- It seems l
as if questions about where the hydrogen will be, trapping in tne top of rooms, where to put detectors and where to put intakes to re-combiners are not a part j
of anybcdies research program. All past work seems to be based on the notion that the hydrogen will be unifonnly mixed throughout the containment.
Two ongoing programs in Germany are addressing the possibility of hydrogen dis-tribution. This aspect needs more attention as does the use of sprays to quench combustion.
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Subjects for consideration at future Class 9 Subcommittee meetings should include the following:
1.
A review of past conceptual designs of core catchers and their applicability to LWRs (GE LMFBR concepts, FFTF, CRBR, SNR-300 and others).
2.
A state-of-the-art summary of' hydrogen control and problems by somebody from NASA or NBS (I can find names of people if you wish).
3.
Results of a cost-benefit study of the Integrated Fuel Melt Research Pro' gram and how it will be used to re-direct the present program.
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4.
A description of the KESS system of codes being developed in Germany for use in analyzing Class 9 accidents for comparison with the MARCH / CORRAL package developed in the US.
5.
A summary of mitigation devices or systems in existing plants (sprays, etc.).
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