ML20138C406
| ML20138C406 | |
| Person / Time | |
|---|---|
| Site: | 05200003 |
| Issue date: | 09/26/1996 |
| From: | Matt Young SANDIA NATIONAL LABORATORIES |
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| ML20138C152 | List: |
| References | |
| NUDOCS 9704300108 | |
| Download: ML20138C406 (6) | |
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M/27/96 FRI 10142,FAI..t 630 352 4780 A>L-C!E **5 .wtuu. o w P5 E 2 FAX:5058453117 7 hg h .56 13:53 ID:G N L ORG 6423 I
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Review of 1.ower Head intestrity Under in-Vessel Steam Explosion I.nads, by T. G. t
)
Theofanous et al.,1X)E/lD-10541.
Reviewed by Michael F. Young, Sandia National Laboratories, Org. 6421.
This is a manive piece of work which includes,in addition to steam explosion loads, '
some arcan with which I am not panicularly familiar, such as probability methodolog
' and plugging behavior of molten materials. I will therefore comment mostly on the explosion loading.
'!he approach taken in this report to determinc steam explosion loads is essent one that has been recommended by most if not all steam explosion researchers: us computational models validated against experiments to determine bounding reactor accident scenarios. Prof. Theofanous has taken an additional l step here in j
4taa. I 4 simplifying the pmbabilistic framework with his RO l believe that the work described in this report has suu.essfully accomplished the cnveloping the steam explosion loading. The usefulacas of the results in rulema howsver, therefore depends on the confidence placed in the initial conditions of the accident scenario and in the analytic tools used.
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in regard to the initial conditions, it is very important to the conclusions real report that the melt be introduced throughi the side o l
expertisc, so 1 will not comment further other than to point out again that co i
the initial conditionx la very important, In regard to the analytic tools used for calculating steam i explosion f t in loads,I ha l commenix concerning possible gaps in the cases considered and in verificat on o cer l
parameters used in the modela.
First, I see that trigger timing was varied parametrically butll not trigger locati ;
i that the cases were triggered near the bonom of the mixture region h next to the l
although ! suspect that this is probably the most severe case, I am won consequences of other trigger locations.
Second, in EPROSE.m. therc are three parameters that must be set from e entrainment factor, a fragmentation constant, and a thermal l k f dataenhanceme l'
appears to be some dependence on the melt material for thane factors, with reactor materials to set these parameters concems me. I believe this w pointed out by 'theofanous et al. in the " Concluding Rernarks" s verification report, in regard to expanding the microinteractions dat= hee to rea i
materials. 11sa of parameters that had been set fnwn s'apariments would enhance confidence in this aspect of the calculation. In regard to the f 9704300108 970415 PDR ADOCK 05200003 A PM l ,
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microinteraction model itself, I believe that this model is sufficiently close to reality t experimental results can be extrapolated in reactor scale.
Third, the lack of a atratified mixina case bothers me, or rather, the lack of data to properly model this case. I do not doubt that what the authors say is correct: if EPROSE.m werc run with a stratified case, it would pmhably produce a very nonenergetic steam explosion for the reasons stated. However,if memory servea, a i
l stratified explosion in a foundry involving water dripping into a" car" containing m iron produced an explosion strong enough to take out some of the walls of incident seems in contrast to what would be prodlcted with EPROSE.m. although th 1
mcit is different (iron versus reactor material) and the water was undoubtedly su The incident mentioned probably involves mixing of the stratified material caused j
initial interaction; how well docs EPROS!!.m deal with such an effect? Or is this the ,
province of PM.AI.PIIA? Maybe the authors could comment on this, or ma l indicates the need for some stratified experiments.
l l Fousth, on page 6-4 there is a conclusion that the sire of the impulse do l strongly on the siza of the mixture region. I think that this is in contrast to first 4
i principles, which would suggest that it would he directly proportional, ig effects like the varying void fraction, and to the results in Table 6.1, which indicate ,
strong variation, ignoring the timing, between cases C1l and C2: 90 vs.12 and 120 vs. 200 for p - 20. Or did I misread the sentence? Also, how do the resu comparc in magnitude to the impulse of the initial trigger itself?
F Fifth, in the section on stratified layer of molten steel and reflood, Chapter g i
appears to be one piece missing to make the casc that the bl scenario is l
thickness of the crust is not mentioned. Specifically,is this a" thick" crust that or is it a " thin" skin that could be broken?
All in all, this appears to be a very complete piece of work.
Following are minor points and typos, l
- 1. In the discussion of the AIAAQUS model of the lower head, it is referr f model; this is somewhat confusing at first, as shell models are normall meaning t_hin shells, i.e., no bending moments are supported. 'lhis l by calling the model a thick shell, for instance.
l l 2. On p.4-4, there is a commant about approximately 25% of the fuel re '
l uncovered. la there a reference for this?
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- 3. On pp. 5-6 through 5-9 it is hard to compare the graphs chosen axis scales and varying times for the plotted lines. l'or instance, the Cl nh
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.>9/26 '96 13:54 at 0,4 s whereas the RCl-nb plots end at 0.12 s. I see that there are other plots with overlapping tirnes in the Appendix, so maybc one of these would be better.
- 4. On p.5-10, it says "only a very small fraction of the coolant is found to coexist with the water"; should this be melt?
' 5. In the graph for C2-10 ca on p.B2-7, the last time is given as 215 s instand cro.215 s.
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,m . u. ,,.,,3, u, 09/ 27/ fed FHf 20:40 FA1 1 oJU 454 4730 l
1 ARGONNE NATIONAL LABORATORY j
- 9700 South Cass Avenue, Argonne, Illinois 60439 Phone: (630) 252-4595 '
~
' Fax: (630) 252-4780 4
September 25,19% M; e . C t . I V i. . u IEACTOR ENGINEER't?3 CC::Cid
-D!PICTCR'S CITM.: -
A Dr. L. W. Deitrich j Reactor Engineering Division SEP 261996
] Argonne National Laboratory Acran: .__ . Af.4 t 4 9700 South Cass Avenue p.r m fen:
Argonne, Illinois 60439 t_ g - ~ T Q - ~ ~ ,
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Dear Walt:
1 In response to the request made in your letter of June 17, 1996, I have reviewed the report
" Lower Head Integrity Under In-vessel Steam Explosion I.oads" by T. G. Theofanous et al. You i
indicated that this report and a companion dement together " intend to demonstrate the effectiveness of *in-vessel retention' as a severe accident management concept for a reactor like the AP600". You further indicated that "the purpose of this review is to assess whether this inten has been achieved to a sufficient degree for the results to be of use in the regulatory / licensing l
area". Based on my review of the report, I find that additional supporting work would be needed if the conclusions of the report were to be used in the regulatory / licensing area.
1 l
On page 9-1, the authors state that " Methodologically, the asmsment involved only a s scenario depandance, principally on the permanance of the blockages preventing direct l i through the lower core support plate, relocation", and that "thus the ==mement is of Gr in the ROAAM scale". I think the scenario dependence is more than slight, so the assessment 4
may be more of Grade C than Grade B in the ROAAM scale. Suppose aThe steam expl l
i take place in the downcomer region or in the lower plenum, as desenbed in the report.
r explosion may not be strong enough to fall the lower head, but it may be energetic en mechanically disrupt the blockages formed at the lower end of the core. Further, the explos would likely expel some water from the lower plenum so that the lower core support plate may i
no longer be in contact with water (i.e., the ability to cool the core support plate would Thus, the initial explosion, while not faihng the lower head, could severely weaken the block mechanic 211y as well as thermally. It would seem possible that a relatively small initia
- would be followed by a massive downward ralar*rian of core snelt through the core suppor setting the stage for a secondary explosion probably involving a much larger melt ma l
lower head may weil survive such a secondary explosion, but a separate assessment possibility would definitely be needed.
Based on the code calculations performed, the report concludes that the samrated coola in the lower plenum leads to highly voided premixtures that have a damaaaing effect l
resulting explosion energetics. While I am not judging the validity of the calculations difficult to reconcile this conclusion with available experunental evidence. Experience tells c
triggering of a steam explosion would be more difficult with saturated water than w l- subcooled water. H g;.ever, once triggered, the explosion energetics does not seem to depe
,_ _ 09eJre90 rdi Au:41 e tt i oJu 4 4 4 4750 .0L-64 - s. su rutc.u. .wva l 2
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L. W. Deitrich 2 September 25,19% 1 the coolant temperature that much. Consider, for example, the results of the KROTOS tests Nos. ,
] i 28,29, and 30 [H. Hohmann et al., "FCI Experunents in the Alummum Oxide / Water System,"
Nucl. Eng. Design 155 (1995) 391-403). In these tests, approximately 1.5 kg qu2nri% of Al203
= melt at 2300-2400*C were poured into a column of water and steam explosions took place. In KROTOS 28, the water was nearly saturated at 87'C while in KROTOS 29 and 30, the water was l
highly subcooled at 20*C, The energy conversion ratio was estimated to be 1.3%,0.8%, and ,
1.25 %, respectively, for KROTOS 28,29, and 30. It thus appears that the explosion with the nearly saturated water was at least as energetic as those with the highly subcooled water. Similar findings regarding the effect of water temperature on the explosion energetics were also made in our recent ZREX experunents. Such experimental evidence would need to be considered when
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i discussing the explosion energetics. Perhaps additional parametric calculations in terms of the
- breakup and trigger ummgs might Se useful.
In all supporting calculations, the water was considered to be saturated with the pnmary system completely depressunzed to 1 bar. Even in a large-break LOCA, the containment back pressure would remain in the range of 2-4 bars for a long period of time. It would appear that a system l
- pressure somewhat higher than 1 bar (e.g., 3 bars) would have been more realistic for the supporting calculations.
Reflood FCIs were discussed in Chapter 8. I suspect that reflood FCIs in stratified configurations would be of secondary importance compared to the premixed explosions addressed in the rest of l
the report. Nevenheless, reflood FCIs need to be considered for completeness, panicularly in view of the potential for vessel wall thinning due to chemical attack by the metallic melt. The l authors should be commended for making an effort here. I would have to say that this effort j represents a best-estimate assessment based on engineering judgment. At present, there is no adequate database or computational tool for large-scale stratified explosions. .
l On pag; 7-1, the authors state that "Also in this chapter, we would normally present a series of arbitrary parametric and sensitivity calculations, to illustrate, for cases where the base results
- happen to be benign, the margins to failure" and claim that "This, in effect, has already been done, too, by the breakup and triggering calculations, in the course of bounding the behavior".
I believe additional work would be needed to make this claim fully valid, and I am confident that the authors will succeed in doing that.
i Finally, the authors are to be commended for conducting such a detailed evaluation of a very complex issue.
Sincerely, l
1
-/b .~
D. H. Cho i Reactor Engineering Division i l
/at
M1.-RE - 5, sua C 3,/J,2 / 06 THC 03: AF FM & 630 2s2 4790 NORTHWESTERN UNIVERSITY 2145 5HERIDAN ROAD 1 EV AN1 TON. ILLINots 60208 3120 Ll$A l
4 TPMPHONE. (8471 491 5267 FAX: (847) 491 3728 5 CEORCE BANKoFF E Meil(gbankoffecastAaens sew edu)
WALTER P. ML'RPHY PROPE3soR EMERrTL*s CHEMICAL ENGINEERLNG DEPARTMENT
., August 23,1996 4
Dr. L. W. Deitrich, Director Reactor Engineering Division -
Argonne National Laboratory 9700 South Cass Avenue ,
Argonne,IL 60439 4
Dear Walt:
I enclose herewith my review of DOE /ID-10541. I had to read the suppo documents as well in order to get the necessary perspective. In the pro hours, which convinced me that in-vessel retention is a valid concept fo .
With kind regards, W
S. G. Bankoff ,
4 SGB:hke Encl.
4 RECEIVED REACTOR ENGINEERING DIVISION -
-DIRECTOR'S OFFICE-i AUG 2 91996 :
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