ML20138C177
| ML20138C177 | |
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| Site: | 05200003 |
| Issue date: | 06/30/1996 |
| From: | Maureen Burger GERMANY, FEDERAL REPUBLIC OF |
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Text
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10/16/96 FRI 13:gg FAI-1 630 252 4780 nt,q ~~~ S. Sunbc.LL yn3 i
Review of the report L d"
,, Lower Head Integrity under In-Vessel Steam Explosion oa s l
by T. G. Theofanous et al., DOE /ID-10541, June 1996 i l
Manfred Burger i Institut fur Kemenergetik und Energiesysteme, Universitat Stuttgan Pfaffenwaldring 31, D-70569 Stuttgart, Germany f
Tel. +49-711-685 2368, Fax +49-711-685 2010. E-mail buerger @i T
L Purpose, Procedure and Main Conclusions of the Study I
The purpose of the work is to show that the lower head of a r load of steam explosions. According to the ROAAM ll pHlosoph i
paths that could lead to failure have to be investigated. The d 4
centralareasof analysis:
l
- 1. Since pressures in the kilobar range have been obtained f il in (although not yet with corium and in one dunension), ki it a direct cannot be done. Thus, detailed calculations of possiblef explosion 3D l a
account the specific s *E4iy with respect to venting effects. This is don version of ESPROSE.m.
l
- 2. The possible spectrum of melt / coolant mixtures i developing f PM-assumed core melting must be determined. This is done by use of a 3 ALPHA.
l
- 3. Possible timings and strengths of triggers have to be consid
' envelopping approach is pursued here, conceming the timing a 4.
Since close to the wall pressures in the kilobar range are o investigations on failure criteria are required. This is don 9704300060 970415 I PDR ADOCK 05200003' A PDR L
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10/isf 90 ygg '13:19 FM i 630 252 Uso mg -
.,3, 30 %
1 means of the ABAQUS code. Considerations on the possible interac are also required.
l
- 5. Considerations on the melting and relocation process in the core a plenum have been considered as necessary for restricting the p mixtures. This is done by separate estimates.
i The main arguments in the report are:
It is assumed that a pool of ceramic melt surroundedl by dcrusts fo 4
r cooling capabilities of remaining water in the lower plenum (at
~
f the be ons with level at ~25% of active core height) and the large heat capacity fuel bundle with lower Zr plugs and the lowermost spacer grid. The downward relocadon path of melt through the core support location plate is id d
' through of reflector and core barrel is assumed ~. yielding finally a s ewar s 4
through the downcomer.
4 This sidewards relocation is restricted in extent assuming' failu based on the analysis of heat transfer from the pool and assumin Further, it is argued that only one failure location is available withi l
mixing of the relocated melt in the water and triggering. 3D-PM-Strong under the expected conditions of saturated water is expected and ca 1
- ALPriA. Thus, only small amounts of melt in the ii lower tens of kg f h lower tentially explosive. This is taken to direcdy exclude large break possi head. Various calculations with ESPROSE.m d assuming by comparison suffic j
tionally taken to exclude also local threats to the RPV. 'Ihis h is finally on b bili-with failure criteria for the RPV wall yielding directly (without applica 4
' stic framework) the conclusion that failure is physically unreasonable.
i
' Further, reflood scenarios are evaluated to even mitigate the p lt in the pool is not h
threats, due to cooling and preventing melt outflow. Mixing with t e me fl considered as effective (small yield of stratified explosions). i In a by reflood would also mean to exclude mixing of melt w 2
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10/13/90 FRI 15:20 FAI 1 G30 252 4780 D L.- RE i d J
considered as the only case with a potential to challenge the lower head due '
penetration depths without excessive voids.
i Cases with thermally weakened RPV walls are restricted to later phase Then the water and mixtures are already assumed as strongly i voided. R j
sidered in the report in stratified configuration,i.e. waterf above i a meta excluded due to rapid spontaneous interactions with the subcooled wat of the metal surface before a thick water layer establishes which cou 1 straint for strong pressure buildup.
Based on these considerations, the major conclusion of the study
~ induced lower head failure in an AP600-like reactor is ,, physically un
- 2. General Comments .
The procedure as well as the general arguments are convinciag.
l d ith
. The argument that a strong cold trap at the corel support t the upperplate, Wa
" water, can prevent the downwards release path to occur before sidewar region of the melt pool. This yields a significant hreduction b tt m is in m f especially to a possible downwards release in multiple d streams. I strong enough, no downwards release will occur until all melt is !
co:,tinous failure progression.
high voids, since
- Then, the saturated coolant condition prevents larger premixtures without larger premixtures could only develop within longer times. T l
4 flow through the downcomer also favors this.
l ible.
- The strong voiding of mixtures calculated with PM-ALPHA is thus p aus h b ve
- With the small mixtures (small melt masses) of not extensivearvoid pl(
statements, the ESPROSE results are also plausible (the obtained
' astonishingly high - probably due to the restricted venting).
3 1
, - - - - . w , ~
- S. SORRELL l 10/15/98 FRI 13:20 F.C 1 630 252 4780 QL-RE @ 006,
! I f
e Dus, also the conclusions on the threats are plausible.
i f The high number of calculations with PM-ALPHA and ESPROSE conditions can also be taken as supporting.
J i :
In spite of thi~s agreement in principle, thereb remain problems i firm the s
and performance of the analysis. Improvements may be performed discussed as follows statements and conclusions as a basis for use in licensing actions. This t itical ,
in some detail. Since, in my opinion, the statements on i i g the and relocatio point I firstly concentrate on this, theni considering i hi h appear to be the wellsubsequ I
explosion. I will not consider the aspects of structural failure cr ter a established. I will only give fe5 arguments on possible further scenar I, reflood.
l
. 1 4
3.
Conunents on Melting and Relocation fi i Firstly, it is shown by estimating plugging times from a free heat conduction that the plugging l takes place in a range flow is not taken into account temperamres 0.6 s with Zr and 2.4 s with UO ). However, 3
i distance. the me E.g., t in these considerations. His means, that the fuezing zone may exten i al velocity from CORA experiments. Higher 1
-0.6 m would result for i s with 0.6 m/s as a typ c f mation should require lk velocities would result with thicker melt films. Thus, the final i btooc age or a crust some more time and datance (need of additional melting and melt
- by remelting and relocation of upper partshhof ald partly traps at bloc yield local incoherencies of the crust fh formation,i.e. also w the bottom give certainly a unifying trend. Thus, in order to urt erl i ld blockage formation calculations with a corei llmelt h heatup code of wou a more detailed perspective on related (subsequent) important que the cold trap regions and the water level development.
Secondly, assuming an existing blockage with an ove 00 K for metallic steady state with a stable crust below rnelting point (-2800 K 4
- - - w - t--
10/tS/98 FRI 13:31 FAI 1 630 252 4780 D1.- RE *** S. SURRELL ggon7 l ih a material respeenvely) can exist. Metallic and ceranue crusts are considered ,
heat flux from the molten ceramic pool above of 5; 0.02 MW/m', a volum f
MW/m' in the ceramic crust and cooling from below via radiation. Here, i me why the fraction of fuel volume is only taken as ~30% (p. 4-6). This l intact structures. However, if the metallic parts are all relocated during ceramic crust, then this may consist essentially of UO/ZrO, (-80/20 wt r factor should also not be decisive due to the crustUO/Z ' formadon 0, from l
up of decay heat of 300 W per kg fuel (p. 4-18) this would yield -2 MW per m !
crust.
For the downward heat flux from the molten corium pool above, a m MW/m' (fully developed) is assumed. This is derived from Eq. (4.14)
Reinecke correlations for a rectangular geometry (typing dii s error in (4 of 0.049). However, this correladon is only confirmed ' for Ra' < 510". For considered here, I obtain a value of Ra' ~ 10", assuming H $= 1.8 m and Q The correladon is also derived for non-isothermallateral li boundary present assumptions. The influence of the lateral boundary con however. For a case with vertical cylinder and melting point wwsu THEKAR calculations (1) also yield a rather similar correladon (N Ra' numbers below 10'.
l But, the main question is to me whether - in viewdmion of theand above argu cooling potential - the assumpdon of a rectangular pool geometry is a d Such geometrical other geometries closer to hemispherical shapes can b really d y The be exclude .
variations would yield significant variations in the heat transfer to the lowe i i fl oce versus stable influence of the lateral boundary would increase (natural lconvect on n uc shape) stratification). For a hemisphere (certainly an rmreme b under the given fl d ry accoming,to even a mean heat flux of 1.05 MW/m' would fresult at the curved IVR. With (5.28) from the IVR report and at the center ' still 0.1 lyMW/m' 3 cm of according, a thermal load from the melt pool of 0.1 MW/m' and Q ='b2MW/m t5cm. in the crus stable ceramic crust would result from equations (4.3) and (4.4), with 0 5
10/16/96 FMI 15:23 FAI 1 630 353 4780 - S. SORRELL 4,008
_ _ OL-RE Further, the first blockage should be metallic and l ab ttom ceramic crust sh combined system of ceramic and metallic cmsts should be considered.l His y ld become even thinner.
temperature, thus lower radiative heat removal. Therefore, the crusts shou I If, due to heatup of the lower strucmres, the lower region ion, of the me relocates, this yields a further decrease of downwards heat removal from th thus inducing forther remelting.
l Finally, the downwards relocation path appears lnot heat yet as sure l
mentioned here that local melt streams intot inties theofmelt the processpool of could strong l transfer to the bottom crust as shown in [1]. nus, together b with thelocal timates, uncer a cmst formation considered above and the smaller hb mcrust thickne inhomogeneities of the crust may become important and may induce '
However, the basic idea that significant cooling potential is provi P h s somefurthercalculations the lower head and the massive core support plate is promising. t onsideration for er ap ,
d related to the above objections could yield further support But, the stea y sta lopment of melting and d
the crust may not be sufficient in general. Calculadons i on the time- eve crust development with available codes may be necessary for bener confirma s ible The main statement is that sidewanis melt-through occurs f significa downwards relocation, within the dme of - 100 minutes during wh i h t sidewards remaining water above the core support plate is available. h t take The the basic state cooling is much less effective than downwards cooling. This appears Deto evaluadons sidewards boundary condition as adiabatic, i.e. no lateral k it heat remov I
be a too strong restriction. On one hand, heat removal by the pmd h barrel and outside account. On the other hand, heamp of the RPV wall byf 500 radiation K over from t e vessel cooling by floodmg should be considered.f Taking the calculations a temperature d i
the barrel and reflector and an outer barrel temperanus of- di d1000 to the K as g ven r (Figs. 4.8 - 4.12) nearly half of the heat flux through barrel and r !
RPV wall (if taken at saturation).
i The calculations on core heatup and rnelting essentially f t yield the
(- 42 57 minutes from core uncovery to 20%) to be related t 6
10/18/96 FRI 15:22 FAI 1 630 253 4780 ,
O L-RE ~ S. SURRELL @ 009
[
h h atupof the above the lower core support plate and for heamp of reflector ll as andbarrel.The the ceramic pool and the overlying metallic melt layer resuhing from reflector hearup and melting of reflector and barrel f is calculated lar pool shape).
by mea which (4.14) has been questioned above (questioning the assumption a rectang With the lateral heat flux in the ceramic pool an additional i li g time of 3 reflector melting. This is taken to verify lateral melt release at a time from below (water above lower core plate). But,lditbehas radiated to be rem removal is neglected. At melting temperature, at hleast half of the lateral h atup and melting of F h to the RPV wall (if this is not taken to be superheated sufficiently). urt er, e the sidewards ceramic crust as well as of the barrel is not consi The considerations on the overlying metal layer resulting hfh from the yield important effects with respect to the final limelttially release. A ,
reflector can be expected in this range, this onlyf rneans t ialthatmustthe reflec relocated into the gaps between the reflector and the barrel.b Butl then, th 5
melt again to get break through. Certainly, freezmgi uthal heats up th material. But, the material and energy redistribution by these h process homogenization. Thus, the assumption of a local azimuthal f il fai l
considerations on geometrical inhomogenities in the report. In gen locations and size are problematic, although hthe lbounding ion of a i
my view, the main objections could be, on one hand, those of ab downwards failure, and, on the other hand, the exclusion of se >
certainly short time frame. i d
The laner point indicates a further deficit: the fl further f the whole course sufficiently. Even with an outflow rate of 400 kg/s (seeatbelow) ld occur multiple the ti corium melt pool would last some minutes. During this time, failure d cou locations, overlapping in time. Further, local meh/ coolant i by such interactions aisc larger failures. A question is whether failures of theiybosom of early of the f
can be excluded. On the other hand, the strong voiding E hanced with the r evaporation triggering to get explosions restricts the possibilities for coinciding ev -
of the water pool also acts in this direction.
7
t0/13,J6 FR1 15:23 F.LI 1 630 253 4780 m.g -
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i- =
i Scenarios of ex-vessel reflood are considered with respect to th He considerations conceming the establishment of effective lateral coolingidas nly discussed the above on vessel flooding before or jutt about the time of reflector bil nt duemelt-through to co cooling aspects and thennal effects of focusing by thinespecially Further, meal layers. Bu ;
rapid quenching may favor failure of the pool surroundings at any ll i lt release.
i entrapment explosions in the gaps may yield such failures and thus mo I' 4. Comments on Breskup and Pr*m*g From the assumed failure location and size, melt f the coreflow ratesj yielding ~5m/s entrance velocity into the saturated Ii water d that pool atl i
support plate. Den, the next main point is in myi view voidingthe frag ~
adequately bounding the effect of various degrees of'i breakup lea f l developing rapidly in all cases. This voiding of premixtures 0 is PM-ALPHA. De melt stream is assumed to be broken aredto up ihit f ("large enough value to represent a minimallyf broken-up
! f factor 8.4 melt s a coherent stream of -11cm diameter (with 400 kg/s and Sm/s), ld this higher and correspondingly a higherhb heat kuptransfer may then not be and stea 1 j
thus yield significantly less steam production. On the other f l hand, ith t e rel sufficient for explosive premixtures. A factor ofThus, 6 still results fo mixtures l
correspondingly smaller diameters which faciliates breakup again to d assuming several jets with smaller l
' 'with smaller void may result from transient breakup an i diameters. On the other hand there remains certainly a limita consuming process of breakup.
l In my opinion, these contrary effects with respecti toh gettin breakup or too strong voiding with stronger breakup,t shou inherent limitations to explosive mixtures. Although theA,state l be plausible, it may not be possible to demonstrate h bove it for smaller window for explosive mixtures may become plausible t :
8 f
l
10/19/96 FRI'13:34 FA.I 1 830 232 4780 M -RE -- s. soxxEu 01A
. t i h weaker voiding.
effects of time requirement for breakup and too coarse breakup combined w Perhaps, some additional variations with PM-ALPHA k l th could b ,
considering plausible time laws for breakup cf coherent jets together scales.
f Indeed, the THIRMAL calculations give some perspective on this, s little stripping of small fragments for a thick jet (7.3in cm diam i ly cases
,i smaller jets (2.9 cm and 1.8 cm) due to long wave instabilities. f Howe between these extremes of breakup behaviour should h i ificantbe conside
' jet breakup modeling cannot be taken as verified. This i is also differences between results based on Kelvin Helmholtz instab
[2].
account velocity profiles (Miles) which have been obtained with IKEJE d i h the Since multiple jets may occur from one hole by some i D,p.separatio failure mode) or from several failure locations, the restrictiqn f D-6 for the case with thinner jets appears not to be justified. PHA A
' 5-12 "that both length scales and voidf fractions i dica *ad are with the well, en calculations" appears to me as too rough, in' view of the variations l h o ca THIRMAL calculations and considered above. i t On ted water theand other l
' expectation of strong voiding based on the ii situation may evert better considere with the necessity of breakup for explosive mixtures. Furtherbvar atons demonstrate this, as indicated above. I think, this could also failures of the melt pool, excluded in the report. 'Ihe excl f h l wer spacer grid and the Zr plugs J
considering additionally the cold trap properties o t e o i t this region quantitatively for conditions after boil-off in this hregion i i g of and w l
before latent melting of reflector and barrel occurs (or; impro the events, with respect to the above discussions).
l i
I 4
9 i
10.lb ge FRA 15:24 FAI t 630 2s2 4780 D L- RE *** s. s0RRELL 4012' Comments on Explosion, together with Premixing 5.
if A trigger of sufficient strength is applied to the mixtures l dons as inin ESPRO explosions. The chosen trigger appears d withto be sufficiently respect to possible trigger strong to p the KROTOS experiments, but its strength is not assesse i ay no longer strengths. I agree that with a sufficiently strong trigger the escalation d depend on the trigger strength (if overdriven cases are ex d for funher variation. In view the numerical tests may indicate such a limiting strength and id no d asnee strong of the effects in the KROTOS experiments, the chosen f bounding thetrigger effect of can also i
enough to yield major effects. Looking at di (
early rather than later t mes trigger timing appears also appropriate in view of the strong voi ng exc of melt release as discussed in the previous chapters).
h The results given in the repon show significant differences lt in th maximum impulses as well as loaded areashigher andmelt times flow a of' load mass flow, the breakup behaviour and the time of triggeting. f 5 m' 'results E.g., wil 100 120 kPa s 'and maximum area o maximum pressure > 5000 bar, impulse i 0.05 s (case C2-10(0.05)), as f choosing
= 10 for fragmentation and an instant of trigger ng at 012 s (case C2-20(0.12)).
compared to nearly 10' bar,150-200 kPa s and 3.5 m' forCl- p = 20 an On the other hand, there seem also to be similarities 10 (0.05),or bound ;
1 10(0.05) with the lower melt flow, But S small
= 10shifts and 0.05 s, the resu in trigger time give with somewhat smaller impulses and areas in Cl-10(0.05). 0 The same is valid also strong differences, e.g. pages C.3-16 to C.3-20 in the 16).report f for the companson of C2-10 and C2 20 with similar i trigger This is certainly due to the relation between f timein getting n inties developm optimum mixture configurations at different times. This is one ca I
explosive events or not (together with iriggering time).
Conceming this problem of sensitivity, the large number i I They yield maximum events but in a limited range and n for premixing breakup and perhaps the still have with this respect concerns the choice of 10
10/18/96 FRI ts:3s FAI 1 630 2s3 47s0 .Bl.- RE s .
e i l ads appear to be underlying time law of breaicup (not given in the irepon). ing to jumpSince to the rc=
l f obtained with case C2-20(0.12) as compared to the lower $, it is not qu i ld further variations.This f
j I
nb and not to consider cases between. Other time dependences ll h melt flows. may y e '
concems the questioning of above concerning the premixing process ito l j.
J Conceming the latter point, it is to ibe remarked that the main loaded by the explosion (perhaps j i the water - if taken as saturated - would be that a larger be possible, reg on thisscould be l also some funher escalations in more extended premixtures mayill be fun checked by ESPROSE calculations) and that thus the venting f nher confirm w the pressure relief in the vessel wall will hkh then be limited.
o'mcidence effects. Thus, it is t
exclusionof such multipleevents(smallwindowsforthis!)ortoc ec t ec l f PM-ALPHA It remains to formulate some general questioning conceming thl I
and ESPROSE. Although a lot of work has been performed on th ,
remain. Even if numerical aspects may be considered as well esta These are e.g.:
l i 1 there remain open areas concerning the physical formulat ons.
llvolume pans of l
- Checks with MAOICO were - to my knowledge - restricted to relat '
v spheres.
l in and need further
! . In general, correlations for exchange processes in three phase !
i clarification. ;
e The uncenainties on jet breakup have already been mentioned abo '
l l detonation l~
The microinteractions formulation fordrop hydrodynamic a well as finally for drop fragmen l .
waves needs further clarification and development, for single i l ffect experiments as assemblica. This concems the conclusions based on theory and o !
'. well as on KROTOS experiments.
i d s have ;
l With respect to FARO and KROTOS i analyses, differenj I
shown the capabilities to calculate the expr.s.watal behav our. vincing formulations and thus the physical interpretations h differences especially differin st, I
comprehensive understanding has up to now been gained on t e kis necessary to l premixing behavior between UO,/ZrO, and Al,0, in KROT !
11 l'
r
-- +
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10/18/98 FRI 13+26 FAX 1 630 2s2 4730 .0L-RE --- -
444 s, sogggtt 014, 1 d be more convincing get approved understandmg models and codes. In general, ding the if supported also by other codes based on a common physica
' fonnulations.
' 6. Comments on Reflood Scenarios l
l b t ken into As already remarked under 3. of my comments, ii the exsvessel the conclusions on r l
account with respect to the considerations l on the cooling as l
i the relocation path. In the context of vessel reflood a so t ed I hould thennat stresses favouring failure should be considere l d water . t iss avoided or not conditions larger melt release and in this case contact with subcoo threatening. Entrapment explosions, e.g. In the gaps between re ec addressed conceming a possible increase in failure and melt release. .
t of rapid Conceming the interaction of reflood water with melt pools, I a small scale interactions, rapid soEmation andf ixing in gineral due to the smawater explosions. However, it should be addressed whether kf elled relevant impact and due to small-scale interactions dii f still existing (also taking melt / water f
water) can be excluded. The situation of reflood l ols in the under c i mixtures in the lower head may be even more important f h r melt tha .
- lower head, if the reflood water could enhance mixing aga l d ttled melt, i.e. thermal release by the above prewenet, and this under the conditions of a r load at the bottom.
' 7.
Some Comments for Formal knprovements d il d checking),
Some typing errors of relevance are given below (I had no together with some need for detailed descriptions:
N lture.
- Ra' in Nomenclatuit: factor g is missing, g also missing in omenc a 3
12
__________m__.____._____._._____ _ _ _ . , - _ _ _ _ _ _ - m _-. .., - , e-, - --
10/18/96: FR1 13:36 FAI 1 630 333 4780 .M -RE -
~ s. soRREu 4 015 P. 4-6, second line from below: 0.2 MW/m' instead of m'.
i lin contrast to P. 4-18: effective power density of 0.26 W/g. does this mean ,
fuel?
- P. 4-21, eq. (4.14): Ra'"".
- P. 5-2: giving the breakup law would be helpful. uld be helpful, e.g.
P. 5-4: some further informations on this and on the other co length scales, quantities of melt volume fraction.
P. 5-5: z directed to top, but in subsequent results inversely.
P. 5-10,13th line from above: ,, melt" instead ,, coolant".
tobebecer characterizedby pours
- P. 5-10, second line from below: ,,two slower poun" - seem with smaller diameter. ,
d t of the I ,, propagation intensity is basicany indepen en
- P. 6-1, second line from below: '
i eant, e.g. with ,, propagation 7
magnitude of the trigger." - It is not quite clear to me what s m intensity".
996a)?.
- P. 6-1, end of second paragraph: (Iheofanous et a!,1
- P. 6-4: 6th line frombelow:0.1 m' cales
- Fig. 6.2: should be bener chanctenzed: length scales, presau
- Fig. 6.4: locations att identified in Fig. 6.27 4 i 6 41
'
- Fig.6.5: location of peakloading: where?,notincluded
- P. B.1-1 etc.: color characterization is not quite clear to me:
jet.
- Appendix C: color pictures: case? charactenzations? ning micro-interactions?
l l
- choice of pararneters in the ESPROSE calculations, espec l 1
- P. C.313 etc.: locations? f I
- P. D-4,6th line from above: R,,,instead R*,,,,5 R, ;
w 13
A0'I8'88 ERI 13:27 FAI 1 830 232 4780 .u t,_ g *
- 3. su u .t:.ta, ,g_
I References
[11 Mayinger, F. et al.: ,,Untersuchung thermodynarnischer Vo j
in der Kernschmelze. Teil I: 29eammenfas July 1975
[2] Blirger, M., Cho, S.H., v. Borg, E., Schat ,
' (1995) 215-251 i
l I
l Stuttgart, September 30,1996 4
Manf:edBurger i
14 ,
. ~ . __ __ . . _ . _ . _ __ . . . _ . . _ . _ _. _ _.._. - _
D L-RE ... S'. 50RAELL 4 o03 {
G3/26/97 WED AS:3s FAI 1 830 3s3 4780
"%"ucasT KUNGITEKNISKAH6GsxcxAN RoyalInstitute of Technology w . 1997 02 26 ;
Div. ofNuclear Power Safety. Dr. Walter Deitrich ,
Prof. B A Sehgal Director, Reactor Engineering Tel: 46 8 790 654i Argonne National Laboratory Fax: 46 8-790 7678 Arsonne, IL 60439
- crnail: sehgal@nc.kth.se USA t
Subject:
Review of the Reports DOE /ID-10541, DOE /ID-10503 and DOE /ID-10504
Dear Walt,
! ' I have enclosed reviews of the three subject reports in the =*-h==t. The particulars of the
- three reports are
4
- 1) T.G. Theoufanous et.al, " Lower Head Integrity under In-Vessel Steam Explosion Loads", !
. DOE /ID 10541, ARSAP Program (June 1996) {
- 2) T.O. Theofanous et.al, "Propogation of Steam Explosions: ESPROSE-m in Veri 5 cation Studies" DOE /ID-10503, ARSAP Program (August 1996)
- 3) T.G. 'Iheofanous et.al, "Pr-ivine of Steam Explosions PM ALPHA Verification Studies", l DOE /ID-10504, ARS AP Program (September 1996)
I have structured the reviews in the following order:
?
l a) Overall approach, b) PM-ALPHA verification report DOE /1D 10504 '
c) ESPROSE-M veriEcation report DOE /ID-10503 i d) Assessment of the lower head steam explosion loads DOE /ID-10541
< c) Concluding remarks I believe the above order follows the scenario of a steam explosion, as well as considers the method verification before the method application.
Thanks for providing me the opportunity to review thns repons. I enjoyed reading them. I am sorry, it took so long to accomplish these reviews. I hope that you and Prof. Theofanous are
. happy with them. ' ~ " ~ "
' ~ ~
RcC!V
"" C C- ,
With best regards, . REETOP. ENGINEERING D".';.:C:J 7 l
- -NN NC- , j sincerely yours, 1
. 'o MAP.101997
- *C N - ..._....._
BalRaj ehgal
-- i Professor inmune.s: -r; w . A:~jr -
- * *~9
- q. g . .
10o 44 570CKHOLM SWEOf,N +46 8 790 60 00 3
- __. _ I
4 ASL-RE 4.* 5. s0RRELL 4 003 03/26/97 WED 18:36 FA.I.1 630 252 4750
) ' Review of the Reports DOE /ID-10504, DOE /ID.10503 AND DOE /ID-10541 (June - September 1996) by L Professor T. Theofamous and Co-Workers
- L Review of the Overall Approach i
This is the fourth time I have had the opportunity to review a body of work that Professor Theofanous and co-workers have produced for the resolution of a specific safety issue, or a specific concern. I believe, this is the most complex of all the issues (or concerns) so far and I l
- believe, Professors Theofanous, Yuen and co-workers have done their Snest work so far. This '
body of work is of greater, and of more lasting, value, than earlier efforts, since a major part of this work is the development and verification of the methodology to describe the steam i
explosion phenomena, and to predict the loads imposed by the poWad occurrence of a -
steam explosion. This methodology, and the codes developed, could be applied to other accident scenarios, than the one considered in the present application.
I believe, some comments are in order on the overall approach followed in these three reports, .
- l complemented, of course, with the ROAAM method, and the previous work that Pr'ofessor ,
Theofanous and his teams have performed, (e.g., for the Alpha mode failure of an LWR containment during a severe accident). l
'- Professor Theofanous and co-workers, with their accumulated experience in steam explosion j modeling and applications, have developed a very well-focussed overall approach in the body of work presented in the three reports. It is clear that an in-house experunental program was i,
structured to provide the key observations, for the ideas needed, to advance the steam explosion modeling to the point where some meaningful predictions can be made. The
- innovative experiments performed in the MAGICO facility provided the germane ideas on L steam depletion, and on the difficulty of obtaining pre-mixtures, which could lead to very e
large steam explosions. Likewise, the experiments performed on the SIGMA facility provided the basis for the micro-interactions concept for the steam explosion itself, i.e., the concept and i treatment of the m fluid. I believe, the expertmental underpinning of the ideas and concepts employed, and the further verification of the methods used in the codes against the integral experiments, has provided great strength to the overall approach.
The overall approach followed, in the application report, conforms to the ROAAM method and employs the PM-ALPHA and the ESPROSE-m methodology. The extremely high values j for the fragility curve made the task much simpler than the earlier applications of the
- ROAAM methodology, but it is well justified and credible, Perhaps, the two points of possible short coming in the overall approach, which have also been admitted by the authors, should be stated:
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2 First, is the question of maturity. Clearly, there is not enough separate-effect and integral-effect data to provide sufficient validation of the steam explosion methodology developed.
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This methodology employs many many correlation and submodels, whose individual i verification is a monumental task. Nevertheless, an experimental verification matrix should be developed, with priorization ofimportant effects, and executed, to provide greater
- verification of the methodology, thereby providing it greater matur.'ty.
1 1
Second, e u=nanistic treatment of the initial phase of the steam exphsion scenario, i.e., the 4
break- op of the meltjet, and its sequential fragmentation, has not beat included in the
' methodology developed so far. The authors claim that this phase of the saam explosion
- process can be conservatively-bounded parameterically. Perhaps, the authors have done that successfully in this study, however, a more general treatment of the break-up phase, and its linking with the pre-mixture phase, should be pursued to provide greater assurance that all the initial-condition-effects have been taken into account.
a ne above two points, in no way, diminish the value of the overall approach, and the results achieved. The above two are outlines of further work to solidify the validity of the overall 4
approach followed here, as, I believe, the authors have themselves identified. The present treatment of the physics is the ' State of Art'. I believe, rapid advances in understanding and modeling will follow the germ ofideas that the authors have provided here. Some of those advances will surely be accomplished by Professors Theofanous, Yuan and co-workers.
i II. Review of the Report doe /ID-10504 (Sept.1996) " PREMIXING OF STEAM
- EXPLOSIONS: PM-ALPHA VERIFICATION STUDIES" by T.G. Theofamous, l W.W. Yuen, S. Angelini This report is the verification document for the Code PM-ALPHA, which treats the pre-l mixing phase of the steam explosion scenario. He report has two importset appendices: (a) which describes the PM- ALPHA models and (b), which describes a wt of experiments in the L MAGICO-2000 facility, in which several kilograms of high temperature partic!cs of a i specific material, and of specific diameter, are dropped into water to obtain observations and
' data on the pre-mixing geometries and void fractions. He front parts of the report provide the comparisons of the predictions with the PM-ALPHA code against the data from selected
! experiments. In the following paragraphs, I will provide comments on the main sections of this report.
il 1 Avvendix B: " MIXING OF PARTICLE CLOUDS PLUNGLVG INTO WATER "
I am very impressed with the MAGICO facility. I believe the authors have performed outstanding expenments using quite high temperatures and respectable masses of the hot l
panicles. The video pictures are outstanding. I am a bit disappointed with the quantitative data that could be obtained. 'nte X-ray pictures (in reproductions) do not communicate any information and the void fruction data shown in Figures B.23, B.25 and B.27 is rather meager as a validation standard.
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' 3 The comparisons of the PM-ALPHA predictions to the measured data, shown in Appendix B, for the cold runs, show substantial differences in the advancement of the particle front. It j appears that a central part of the particle cloud tunnels through the water. His is not predicted
- well by the code. For the hot runs, it appears from Figures B.26, that the calculations predict that the dense particle cloud also leaves the steam region behind, if a slight subcooling (3' C) is present. There are no comparisons shown for the hot runs, as shown for the cold runs in the _,
Figs. B14 and B.15.
The concluding remarks state that the hot tests quantified local voiding in the mixing zone and global voiding through the level swell. Figures B.25 and B.26 indicate that the voiding .
front is coincident with the particle front, only, for the zero subcooling case. The particle front is substantially ahead of the voiding front for a slight (3* C) subcooling of the coolant. ;
The extensive steam generation, indicated by the axial void prodic also may increase the local i
subcooling by pressurization. I wish there was some quantitative data for the particle volume j fractions, to compare in Figures B.25 and B.26. Was it not possible to obtain quantification of the spatial particle volume fractions from the X-ray pictures? l In this context, if the PM ALPHA predictions for the advancement of the particle front lagged behind the measurements in the cold runs (cf. Figs. B.14 and B.15), would they not do the same for the hot runs, since same modeling is employed for both hot and cold runs. I do expect that the steam generation, caused by the radiative heat flux on the coolant from the particle cloud, will retard the advancement of the particles. I believe, this effect is represen j
in the code, since a radiation heat flux model is employed, however, I can not quantify its l
effect, on the differences in the particle cloud distribution between the hot and the cold runs.
l ne subcooled coolant is important. The only data shown for the 18' C subcooling case is the l
lack of measured level swell. I would be interested in the axial void fraction and the particle volume fraction profiles, to understand if there are signi5 cant phenomenological differences between the saturated and the subcooled cases, and if these differences can be predicted by I the PM- ALPHA Code.
All in all, I believe the MAGICO experiments are relevant for the ideas, and data, on the mixing zone and the pramiving conditions. I would like to connect the meltjet particulation to the particle cloud water interaction. Als may be in the next phase of authors' experimen
- investigations.
H.2 Accendix A: "PM-ALPHA: A COMPUTER CODE FOR ADDRESSENG THE PREMIXLVG OFSTEAMEXPLOS10NS" PM ALPHA is a three (melt, coolant and vapour) field code employing separate mass, momentum and energy equations for each field. Thus, it is a very detailed code - more
' detailed than the codes RELAP-5 and TRAC. It also employs two and three dimensional geometry. Thus, it has capabilities beyond those of the conventional CFD codes, which, 2 generally, employ only a single field. PM-ALPHA is a very advanced and detailed computer
' code, indeed. There are other codes, currently in development, in Europe, e.g. IVA (Siemens, Germany) and MC 3 D (CEA, France), which are also incorporanng similar capability, in order to treat the very complex, and very dynamic, physics of melt-water interaction and steam explosions.
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4 It is a general rule that more detailed the formulation for the description of a process, more
', . detailed the information required to bring closure to the formulation; and more intuitively intelligent approximations have to be made to obtain credible solutions from the formulation.
This is quite apparent for PM-ALPHA, when a whole page (A-20) is needed, to show the i dimensional groups that appear in the constitutive laws for the fuel to coolant heat transfer.
This can not be avoided, however, the collective constitutive laws may provide reasonably-J correct predictions for a particular set of pre-moung circumstances, and not for another set I i believe, that veri 5 cation on an even less integral level than the MAGICO experiments should be considered by thinking through, and devising, a set of separate-effect experiments. They i
should be prioritised, so that the most important are performed first.
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In the following paragraphs,I will provide some detailed comments.
II.2.1 PM-ALPHA Formulation 3
i The modeling approach is logical and well-thought. The authors admit that the formulation so i far, emphasizes the multifield aspects of pre-mixing. The melt jet and particle break-up are treated parameterically.
4 Two length scales are employed for the fuel field: one large, encompassing the original fuel drops, or fuel-melt jet, which may break-up but still are considered as fuel; and the other small enough to be called a debris, which mixes with water and gets quenched. The decisions
- about the amount of the ' fuel' and the 'debtis' are made with a correlation for the fragmentation rate.
The debris particles assume the same temperature, and velocity, as the coolant,instantly.
They are not allowed to sediment down with gravity, as they would normally do. This assumption is justified for the time interval considered, if the particles are of micron size.
The large length-scale fuel particles are assumed to have uniform temperature. There is no treatment of the heat conduction from the fuel particle to the coolant. For the prototypic l
- binary-oxide mixture melt, it is important to determine the solidification front growth into the particle, since it may either prevent fragmentation, or reduce the rate of fragmentation, thereby changing the heat source to the coolant.
Another factor in the treatment of the fuel particles, is the change in physical properties that '
l occurs, as the fbal particles cool down from above-liquidus to below-solidus temperature. The i
increase in viscosity and surface tension affect the fragmentation characteristics, which in turn affect the terms in the debris mass equation, and in the liquid and debris momentum and l
energy equations. A paper submitted by Okkonen and Sehgalin the forthcoming FCI me in Japan discuss the two factors mentioned above for the behaviour of the fuel drops.
l Recently, we at Royal Institute of Technology (RIT), have performed some experiments 3 on l the interaction of relatively low temperature cerrobend (an alloy with density of = 9 000 kg/m
) jets with subcooled water. We have found that the jet breaks-up into small particles '
a distribution to the particle size or mass, however, there were no particles oflength- scale comparable to the jet diameter. In these experiments the jet breaks-up completely. The FA i
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- 38 FA.I 1 630 2s3 4780 5 expenments show a melt ' cake' at the bottom, however, it is not clear whether it is the unbroken jet or an agglomeration of melt droplets belonging to some size distribution, which, perhaps, does not contain length-scales approaching the meltjet diameters.
Summanzmg the above discussion I believe, the treatment of fuel as having two length i
scales in the PM ALPHA formulation is valid. However, the source terms in the equations should be reviewed again. The variation of properties of the fuel drops, with temperature, should also be taken into account; and the change in the temperature of the fuel drop should
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be calculated employing conduction equations. Meltjet, or drop, interactions with subcooled coolant may produce atomization, with no large particles of size similar to that of the meltjet.
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l II.2.2 Interfacial Momentum Trmfer in PM.ALPMA i
7 The drag correlation used in PM ALPHA for fuel-coolant interface distinguishes between th i
dispersed and the dense fuel regimes. The latter is taken as that for flow of gas through a !
densely-packed bed. His correlation, perhaps, should be chW since predicted '
! penetration of the fuel cloud in the MAGICO expenments is less than the measurements.
Also, comparisons could be made with the isothermal tests in the BILLEAU and the QUE facilities. The logic diagrams on pages A 16 and A-17 were helpful.
IL 2.3 Interfacial Heat Transfer in PM-ALPMA
' There are many regimes of convective heat transfer and many correlations. The authors use the best that they can find . Then, there is the large effect of radiation heat transfer, which was found to be important for the comparisons to the QUEOS test data. neir synergism, j.
and effects of one regime on another, may need further exploration. For example, radiatio l
absorption will produce vapour which will change the convective flow patterns of the coolant, and, perhaps, change the heat transfer regime. Some separate- effect tests c designed to test the synergism and the effect of different convective regimes on order to test the heat transfer correlations package employed.
i IL 2.4 Fuel Break Un and Fran=tation Mohline in PM ALPHA I have referred to this earlier in the comments on the PM-ALPHA form area equation (3.73) assumes spherical particles on break-up and fragmentation. Th be appropriate. Perhaps, data from FARO or other fragmentation-break-up experi be employed to develop a more prototypic interfacial area representation. In some o experiments with cerrobend in subcooled water, we do not find spherical particles.
in saturated water, with large flows of steam, the particle shapes may be spherical.
I The model for fragmentation of fuel drops is based on the Bond number. I believe, data on hydrodynamic and thermal fragmentation of large-size melt droplets may be availab future. The model could be checked against such data, when available.
The model forjet and large fuel-drop-break up is parametric with an input -specified parameter Q, whose value is varied in analysis. This approach is, perhaps, adequa present. However, it will be desirable to have a phenomenological/ mechanistic mo l
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03/26/9* oED AsiJd r4 a 030 dso'Mou 6 The authors distinguish between fragmentation and break-up as two separate processes. In i some of our meltjet-water interaction experiments, we were not able to separate the two
- processes. The jet breaks-up (or fragments) into particles having a size distribution ranging ,
from submillimeter to 3-4 millimetres. The process appears to be concurrent and not
- sequential, as assumed in the parametric models described here. ,
l
- 11. 3 VERIFICATIONOFthe PM-ALPHA CODE .
The front part of the report doe /ID-10504 describes the verification pursued for the PM-ALPHA code by performing analytical tests, and by comparing with the data meuured in l
several experiments. This was a very large effort, and I believe, it has largely achieved its purpose. I will comment on a few comparisons of the data with the code predictions. ,
- 11.3.1 OUEOS Exneriment nese experiments are similar to the MAGICO expenments. The comparisons shown in
' Figures 4 to 13 are remarkably good for such a dynamic process. The comparisons appear to be better than those for the MAGICO tests.
4 It is not clear to me what the experimental image actually implies, in terms of the s
distribution of hot particles, and of void. The pictures in Fig. 7 at 0.3 and 0.4 seconds seem to show that the experimental hot particle image may be not as advanced as the calculated contour. This also appears to be the case in Fig 6. at 0.3 and 0.4 seconds. The graphs in Fig.
! 8, however, show very good agreement between measured and calculated front-advance i locations versus time.
II.3.2 MIXA Exoeriments i
Re MIXA experimcats employ a Uranium-Molybdenum thermite melt of several kilograms, at 3600K, poured into near saturated water pools, ne meltjet was broken into 6 mm diameter droplets. The MIXA 6, snalysed here, used 3 kg melt pour into very nearly (51 K difference) saturated water. This, thus, is a prototypic experiment, albeit with small mass.
The compansons are very good. I am somewhat concerned about the sensitivity of the resu to the break up-cut-off- void-fraction and particle size. The authors recognise this, still, a change of only 5 % (85 % to 80 %), with the particle size of 1 mm, decreases the calcula pressure rise from = 0.4 bars to = 0.2 bars. Increasing the particle size from 1 mm to 1.2 mm at the 85 % cut-offlevel decreases the pressure rise from = 0.4 to = 0.28 bars. Thus, the break-up and fragmentation models appear to be very influential in the very high temperature, prototypic material expedments.
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II.3.2 FARO Exneriments i nese are. perhaps, the most imponant experiments, since they use substantial quantities (2100 kg) of prototypic materials; and there are several experiments already performed and more are underway.
The comparisons shown are very good indeed. Unfonunately, FARO does not produce any
< data on the rnixing region, thus the colour figures, presented, show only calculations and no data.
. I did not understand why the initial panicle size is chosen as 4 cm for ajet diameter of 10 cm.
d The p value chosen is 50, while for the MIXA test it was chosen as 20. He mmimum particle size chosen is 1 mm, while in the MIXA test is was chosen as 1.2 mm.
One experimental result, which FARO produces is the fraction of thejet material deposited as 3
a ' cake' on the bottom plate. His is not provided by the authors from their analysis with the PM-ALPHA code.
1 H4 Numerical Aspects The authors do not provide a discussion on this topic. I believe, this is an important topic.
The ICE technique is known to have significant numerical diffusion. It !s not clear whether 1
any advanced space time discretization scheme was employed. Node sizes of several I centimetres are generally not fine enough. The authors, perhaps, by now, have investigated the numerical aspects further, and I would welcome a greater discussion of this topic.
l 1 i i
i HI. Review of the Report: Propagation of Steam Explosions: ESPROSE.m Verification Studies by T.G. Theofanous, W.W. Yuen, K. Freeman and X. Chen
)
This report deals with the next phase in the steam explosion process, after the pre-mixtng has been achieved. He report, therefore, deals with the explosion process and develops a methodology to describe the process, and evaluate the energetics, which are then employed to assess the damage potential of the explosion on structures, which surround the explosion. A trigger is assumed, which starts the explosion process, in which intimate contact of the fuel
- and the coolant leads to production oflarge amounts of vapour, and the supercritical
! explosion.
The report consists of the front part, where the results of the verification calculations are compared to the observations, and data, obtained in the SIGMA facility at U.C. Santa 4
Barbara. The report also contains four iniportant appendices in which the code models, a 1-D characteristics model, constitutive laws for micro-interactions and thermal-detonations are
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discussed.
In the following paragraphs, I will comment on each of the major sections of this report.
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111.1 Appendix A: THE ESPROSE. m MODEI.S l The overall approach of the model development is brilliant. Recognising that the dynamics of a pressure wave, generated by a trigger, coupled with fuel fragmentation, micro (or local) ,
mixmg and heat transfer result in energetic steam explosions, the authors have concentrated l J
on those aspects. Perhaps, the SIGMA experiments provided the key observations towards the ,
development of the micro-interaction concept and the m fluid, where the fuel coolant heat l
j transfer occurs. The energy transferred is then employed in the multifluid treatment to calculate the pressure fields as a function of time and space (2 D/ 3D). The damage potential 4
< is, then, evaluated with the calculated dynamic loading imposed in terms of kilo Pascal seconds.
l The modeling approach is similar in most respects to that employed for the PM-ALPHA l
4 code, i.e., solution of a set of multifield conservation equations, with specified constitutive l
i relations. The fields chosen this time are fuel, liquid and the m fluid. There is an additional
- mass conservation equation for the debris, i.e. the fragmented material. He m fluid equations contain source and sink terms, which are based on a picture ofliquid entratiment and phase
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i change. Fuel fragmentation is included, which contributes to the increase in interfacial areas.
The heat transfer across the fields is included in the energy equations. The system of l i
equations appears to be complete. He constitutive relations between the 3 fields for interfacial drag, beat transfer and phase change, again involve many correlations and dimensionless numbers.
I believe the comments that I had made regarding the complexity of the constitutive relations for the PM-ALPHA code also apply here, and the possibility of checking the synergisms between the momentum and heat transfer processes through separate effect experiments, should be explored. New data may have to be obtained and some prioritisation should be performed. The fuel fragmentation is treated as in the PM-ALPHA code and is controlled parameterically through p , nere is another parameter which enhances the fragmentation for thermal effects. Both of these parameters are user-specified. The entrainment ofliquid in the m fluid is controlled through the parameter E, which is taken as a function of the fragmentation rate.
I believe, the parametric treatment is very intuitive, and the authors admit that it is an
- important component of the micro-interactions concept with somewhat speculative j
constitutive laws. Since, the m fluid interactions are the basis of ESPROSE m ,I hope that the authors have already obtained additional data from the SIOMA facility to provide greater support for the experimental basis of the parametric treatment.
- 111.2 Appendix C
- Constitutive Laws ofMicro-interactions j This appendix describes the experiments performed in the SIGMA-2000 facility with gallium l and molten tin, subjected to high pressure waves, in order to derive the constitutive laws for l j
the micro-interactions, needed for the m fluid.
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- The expenments are described. by are really very difficult, but precise experiments. Some ,
results are shown as movie, X-ray and SEM images for the change in pre-mixing volume, as
. a function of time.
4 i
A The results of experiments are used to derive the values for e, y : and f. , the entrainment factor. For example, Fig. C-13 shows fe7,8 and 12 give best fits, respectively, for three isothermal Gallium tests i.e., G/204/45, G/68/45 and G/272/45. The more conservative value f.=7 is then used te detennine the value of e9. The value ofy i is derived from Fig C-10, j while keeping f.=7, md Qe9. It appears that y varies from 1.4 at 68 bar pressure to 4.2 at j 204 bar pressure.
The above is a logical but highly empirical determination of 3 parameters from a small
- number of tests. Perhaps, more data has been obtained from SIGMA to confirm the choices
' made for these key parameters. Obviously, more data is needed from SIGMA or another shock tube. I believe, different materials should also be tested, in particular, melt drops of binary oxides. Their fragmentation behaviour maybe different, due to changes in properties
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they experience with a chang in temperature.
111. 3 Appendix D. On the ibistence of Thermal Detonations This is a very interesting re-evamination of the Board-Hall model for steam explosions. The micro interaction model and the concept of the m fluid is employed to show that supercritical steam explosions can be obtained with lean mixtures in highly voided regions; conditions for which the Board-Hall model will predict only very weak explosions. j i j My understanding of the micro-interactions concept, introduced by the authors, is that they take place in the m fluid in a limited volume. I believe, this results from the observations
facility. The previous concept was that the pressure wave will fragment a melt drop into fInc I
droplets, which will mix with the whole coolant volume. & SIGMA expenments showed that this does not occur in the time frame of the pressure-wave-melt drop interaction. The heat l J
l transfer to the m fluid's coolant, in the limited volume occupied by the m fluid, generates very high pressures. b shock wave then travels into the non-participating fluid around the
] j 2 m fluid, increasing its pressure to sustain the propagation. This makes possibic the supercritical swam explosion with a fuel coolant mixture, which is lean on an overall- l j j volume basis, but is not so lean on the m fluid volume basis. (Cc Figures D-8 and D-9, where high pressures are obtained for the coolant to debris mass ratio fel in the case of tin at '
1500*C and for fe2 to 8 for the case of UO2 at 3300*C)
I believe, the authors have provided a very logical explanation and frame work. I am, however, a bit concerned about the value for fe, which was chosen as 7 in Appendix C, based on the data from the gallium experunents in the SIGMA facility. In Fig D-8, a value of f.=7 will not produce a supercritical steam explosion. Thus, the value of fe may be material dependent, and more information is needed to choose an appropriate value.
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' to 111. 4 VERIFICATIONSTUDIES The front part of the ESPROSE. m report describes the analytical tests, the SIGMA experiments, explosion coupling, integral aspects, numerical aspects, and finally, a comparison with the KROTOS tests. I will comment on these, briefly, individually.
1
- 111.4.1. Analvtical Tests These are very valuable exercises and show that the modeling in ESPROSE-m can predict pressure wave propagation. Here are many 6gures. I wish there were more explanations j e.g., Figures 17 and 18, both show very good comparison between the analytical and the ESPROS-m pressure distributions for early times, but deviate at later times. Is there an
- explanation? Similarly, there is a crater in the middle of the pressure wave in Fig 19. Is there a physical explanation for that? This section may be improved by the authors, through some ,
explanatory text. It is very valuable, otherwise.
J
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i III.4.2 SIOMA Merimem ,
i These experiments, specially conducted in the SIGMA shock tube provide data for verification of the ESPROSE-m models for pressure wave propagation. The comparisons are excellent. There are some differences for the inhomogeneous cases, which, perhaps, are difficult to fix. All in all, it is a splendid performance for the code for these separate-effect l
tests.
i I III. 4.3 Comearisons with KROTOS Exneriments KROTOS experiments pmtide the most appropriate data for the veri 5 cation of the ESPROSE m models. N KROTOS facility has performed steam explosion e.xperiments by
- triggering the pre-mixtures of water with several different marnial melts. He initial conditions, e.g. melt mass, melt temperature, melt superheat, pressure, water subcooling have i been varied to provide a reasonably extensive data base. The cest program is continuing, and could provide the data base needed for the ESPROSE m validation. Unfortunately, as in most of these melt-water interaction integral experimenta, the data obtained is integral and the premixing and the steam explosion processes are not delineated. Thus, detailed verification i
and validation of the ESPROSE m (or any other steam explosion code) may not be possible. ;
i The document provided on the analysis of the KROTOS tests speculates that the melt break-up and quick freezing may be a reasonable explanation for the non-explosivity of the Uranium oxide tests. We reached similar conclusions, and also, evaluated the effects of the change in the surface tension and viscosity of the binary-oxide melt, as it cools down below the liquidus temperature. Dis has been reported in the 1995 ICONE meeting, and additional l work will be reported in the forthcoming FCI meeting.
Coming back to the comparisons of ESPROSE-m (using PM ALPHA pre-mixtures) predictions against the measured data, the authors admit difEculties of representing particle l freezing correctly in the PM-ALPHA formulation. The fuel- participation factor chosen affects the result greatly. The pressure wave shapes versus time appear to be reasonable but j i
- . .- . . , - - - - . - ._ _ - . .. ~ ---. -- . - .
- LD Ls: u i.a L m m o >< .m - u.
ou2 sat 11 there are differences e.g. for K5 there appears to be an earlier venting of pressure wave. I believe, revision of the PM-ALPHA numerical scheme and/or modeling of the heat conduction in the fuel particles (as was mentioned earlier in the comments on PM-ALPHA modeling) may resolve this difficulty. He sensitivity to fuel participation factor is very large, indeed.
III.4.4 Numerical Asnects I have similar comments as I had for this topic in the PM-ALPHA document. The authors
> should provide more discussion and, perhaps, comparisons of the use of the ICE technique for similar problems. The numerical diffusion inue is quite important when, tracking pressure waves and/or interfaces. Recently, special numerical schemes have been devised to reduce or eliminate numerical diffusion. The ICE technique does not, compare well to such l schemes, in term of its performance, and with respect to numerical diffusion. Perhaps, the authors have implemented another scheme in developing the ESPROSE-m-3D code.
IV. Review of the Report: Lower Head Integrity Under In-Vessel Steam Explosion, DOE /ID.10541
' by TG Theofanous, W.W. Yuen, S. Angelini, J.J. Sienicki, K. Freeman, X. Chen and T. Salmassi 1
i This report is concemed with answering the question: "Will the lower head of the advanced l
passive reactor AP-600 fail, under the dynamic loading imposed by an in-vessel steam !
explosion, ifit were to occur?" This is an important issue for the accident management l
strategy chosen for the AP 600, i.e. retention of the core melt in the lower head, by employing extemal cooling of the vessel, l l l I The methodology used to resolve this issue is the ROAAM method developed by Prof. l l
Theofanous, employed most recently to respond to the companion question "Is it possible to '
retain the molten core of the AP-600 reactor,in the lower head by cooling the vessel 4
extemally?" This question was answered in the affirmative by employing the ROAAM
! method. He ROAAM method has been extended and further clarified by Prof. Theofanous l i
- in a recent publication, attached as Appendix A in this report.
Besides the ROAAM philosophy and procedures described in Appendix A, the detailed pre-mixing and explosion teruits are described in Appendices B and C respectively. Appendix D provides additional pre mixing perspectives from the THIRMAL code, prepared by Drs. Chu and Sienicki of Agronne National Laboratory. De important chapters, in the main body of the report, are concerned with structural failure criteria, melt relocation characteristics, l quantification of pre-mixtures and explosion loads and finally the assessment of the integrity of the lower head of AP-600.
I d
-t , ,r . ,
ANL-RE .. 4 .wnw.- .m E 03'26/97 FED 15:42 FAI 1 830 252 4760 12 In the following paragraphs, I have provided cornmente on the appendices, chapters and conclusions of the report in the order:
- Chapter 3: Structural failure criteria l
- Chapter 4: Melt relocation characteristics
. - Chapter 5: Quantification of pre-mixtures
- - Appendix B
- Detailed pre-rmxing results
- Appendix D: Additional pre-mixing perspectives from the THIRMAL code 4 - Chapter 6: Quantification of explosion loads
! - Appendix C: Detailed explosion results i - Chapter 8: Consideration of reflood FCIs
- Chapters 7 and 9: Integration, assessment and conclusions i
W.1 Chapter 3: Structural Failure Criteria i This is an important chapter, since it establishes the fragility curve, giving the probability of 1 the lower head failure for dynamic loads ofincreasing magmtudes. The impulse loading, of interest, is in the range of 100 to 300 kilo ' Pascal seconds.
1 The authors have employed a commercial structural-analysis code, whose results they have l
compared with a simple analytical solution. ABAQUS is a 3-D finite element code, able to l
model the hemispherical lower head and the dynamic IHiaan imposed. The code provides the strain as a fhnction of time.for the assumed loading. These calculated results are, then, j converted to a fragility curve, assuming probabilities oflower head failure, when strains of greater than 11 % are reached over certain fractions of the lower head wall thickness.
! The ABAQUS calculations are performed for various loading patterns on the lower head. The non-uniformity ofloading was found to decrease the stram for a specific impulse. The colour i
pictures provide very nice strain morphologies.
.t This chapter provides clear and transparent results. The ABAQUS results are confirmed against a simple model for uniform loading. The fragility curve makes good sense. !
I am a bit concerned about the very local non-homogeneous lWin== of the type predicted, l l later, in the report. Perhaps, a few ABAQUS calculations could be performed to establish the '
fragility curve for such a local loadmg pattem.
$ j W. 2 Chaprer 4. Melt Relocation Characteristics i )
This chapter provides the initia1 conditions for the scenario of melt water interaction in the lower head. The chapter, therefore, deals with the melt pool formation in the original core j
boundaries and, later, relocation of the melt from the in-core location of the lower head. The
' quantities needed are the rate of melt addition to the water in the lower head, the jet geometry l
(diameter, velocity and location in the vessel), the melt composition and superheat and, fmally, the timing of this event relative to the other events in the core nelt-progression process.
~. . - -. _. ._ -. .. - . _ -- . - - - . - ._ _ . - _
02/26/97 WED 19:43 FA.I t 630 as3 6780 A>L-RE *os 2. 3 W.c. W 13 The authors, first point out the differences in the AP-600 core configuration from that of the conventional PWR. He AP-600 has some features which are quite favourable in terms of the melt releases conditions. These are the massive 36 cm thick core support plate, the core reflector, the gap between the core barrel and the reflector on the flat sides of the reflector; and the long unheated section in the fuel elements at the bottom.
The authors have developed a credible scenario of melt pool formation, melt attack on the reflector and the core barrel. It is supported by enveloping models of appropriate complexity, which provide physical insight and transparency. The authors are wise not to use one of the i
myriad codes, which provide user-motivated results. The analysis is brilliant and quite
- comprehensive. The melt release conditions of 200 to 400 kg/sec should be bounding values.
- 'Ihe melt superheat of 180 K r.lso should be a good bounding value. The location of the release, near the top of the core in the vessel downcomer, may also be credible. The jet velocity of few meters /second also appears to be sound. I, however, would like the authors to consider the following cautionary points
(i) The timing of the melt release 76 to 91 minutes is much too close to the timing of = 100 3
minutes for evaporation of water in the bottom 25 % of the core height by the radiative heat
- flux imposed.
' (ii) The core plate is massive but it is also loaded heavily. If the core plate temperatures go y
beyond 700*C, the yield strength will deteriorate.
(iii) The melt pool with =40 to 60 % unoxidized zirconium and some stainless steel, will I' l
probably form a primarily metal layer on the top. His layer is thin and will focus the heat flux to the sides. Recent work at RIT has evaluated the heat transfer from the metal layer to the vessel (which is of a thickness similar to that of the reGector) with a two-dimensional code, and found that the highest heat flux is still at the comer of the oxide pooljust below the metallic layer. Thus, the failure could be below the metal layer.
(iv) While, I agree with the authors that the flat part of the reflector being closest to the core centre is most likely to be attacked first by the pool. The oxide pool however may not be axially symmetric and there may be azimuthal regions in the core, where fresh fuel and high power are dominant. Evaluation of a possible attack on the non Gat parts of the reflector j
- should be considered.
l (v) The draining and freezing of the metallic layer into the well between the flat part of the reflector and the core barrel, without participation in any melt water interaction, is vety likely, but sounds too convenient. Additionally, in the absence of water above the core plate in the well, the thermal loading imposed by the superheated metallic melt on the core plate, or on
' the core barrel region directly above the core plate should be evaluated.
4 Summartsing, I believe, the authors' estimates for the range of melt-release-characteristics is y l i
credible, however, additional evaluations may help to put these estimates on a more solid l footing.
J
ru:. --a. m- ..a O.426e97 4ED 18:4.3 FA.I 1 630 232 47o0 .
IV. 3 Chapter 3. Quantipcation ofPre mixtures :
Appendix.B: DetailedPre-mixingResuhs he chapter 5 develops the rationale for the pre mixmg that results from the release of the UO2 - ZrO2 melt from near the top of the core, through the downcomer, into the water pool of the lower head. The water level is assumed to be a few centimetres above the top of the core
- support plate. Melt release rates of 200 and 400 kg/sec, reaching the velocity of 5 m/sec at entry into water are considered. He melt superheat is assumed as 180K.
The oxide melt jet is distributed over an effective radial width of 10 cm in the downcomer, with an initial melt volume fraction of = 25 % at water impact. His would translate to a melt
' stream of dimensions = 10 cm x 16 cm for the release rate of 200 kg/sec and = 10 cm x 32 cm for the release rate of 400 kg/sec. j 1
The expanded melt jet is then allowed to traverse 20 mm in water, before break-up ensues. !
- The break-up rates are parameterized from no break up to very rapid break-up (forming 2 mm size particles within 10 cm of travel in water.)
1 De above initial conditions were employed in the PM ALPHA code to provide results on pre-mixture characteristics i.e. the melt and the void volume fractions and the fuel length i 1
scale, as a function of time, and position. The integral quantity ofinterest is the number of kilogram of melt mixed with coolant, before the triggering and explosion.
l The Appendix B presents a number of colour pictures and many graphs giving detailed I
~;
results. The graphs of fuel length scale, fuel volume and void fractions are presented for more p values and for times upto = 1 sec. These pictures and graphs provide good back- up for the results, and arguments, presented in chaptar 5.
l I believe the authors have presented a clear method of evaluation and the results are credible. I do have the following comments.
(i) ne melt through failure of the reflector and core barrel are assumed to be near the top of
- the melt pool in the original core boundary. If the failure is lower, the starting velocity for
- the melt jet would be higher, and so will be the velocity at water impact. This may be 1 beneficial for break up.
(ii) The initial impact area on the water surface is quite large. The jet going through the 2 meter steam region should not break up, to that extant. l 1
(iii) Both the very fast and the no-break up cases show (Cf. Figs. 5.4 (a) and 5.4 (b)) that for !
i the initial =0.1 see the fuel &ont is more advanced than the void & action front. This was also observed in the PM-ALPHA verification report. Later on, the void fraction front seems to catch up with the fuel front. For the C 1-10 case at = 0.4 seconds (Page B.3-3) a large fraction of fuel seems to be hung up in tne voided zone. He same is true for C 1 - nb case (Page B.3- l 5). In the Cl-10 case, there would be a large steam flux rising, which could retard the l
descent of the fuel particles. For the C 1 - nb case the steam flux should be smaller, and the fuel particles of 2 cm should be ahead of the void fraction front.
03-36/07 *ED AS:44 FAI A 630 asa 6780 O L-RE --- a. mm.4. e, a ts Summarising, I believe the break-up assumptions, both, in the steam during descent from
< the original core boundary, and during water interaction, play a crucial role and, perhaps, this part of the pre-mixing analysis could be strengthened. The no-break-up case appears to produce approximately the same results as the high break-up cue. This has been reco'gnised, i also, by the authors (Page 5-10). Perhaps a physical explanation of why these cases produce such similar results may be provided by the authors.
I
[M AppendixD: AdditionalPremixing Perspectivesfrom the THIRhfAL Code
_In this appendix, the THIRMAL code has been used by C.C. Chu and U. Sienicke of
' Argonne National Laboratory to provide a perspective on premixing. The code had to be modified to describe the meltjet-water interaction in the confined geometry of the down i
j comer. The calculations were performed for melt release rates of 14 to 220 kg/sec, with corresponding jet diameters of 18 mm to 73 mm. The 220 kg/sec case resulted in median droplet size of 2.75 mm, with a mixing zone radius and void fraction at pool surface of 160 mm and 74 %, respectively.
1
- These results are not too different from what were obtained from the PM ALPHA Code, although the jet entry conditions are different. THIRMAL calculates jet entry diameter of 6 cm (i.e., no break-up in the down comer steam zone). Models for break-up in THIRMAL l must be quite different from the parametric model employed in the PM-ALPHA Code.
IV.S Chapter 6. Quantifcation ofExplosion Loadr.
- Appendix C: Detailed Explosion Results l
The chapter 6 and Appendix C present the results of explosion-propagation calculations l
I performed with the ESPROSE m code, using, as initial conditions, the pre mixture configurations calculated with the PM-ALPHA code. The trigger time is chosen as very short, l l! since dunng the early time the void fractions of the coolant around the fuel particles are - I relatively low. Later, the void & actions increase substantially, and would inhibit fuel break up and triggerability, i The results are presented for the C-1 and C-2 scenarios with three values of p and a set of
! trigger times. For the no break-up case these times vary from 0.05 see to 1.0 sec, while for the break-up cases, they vary from 0.04 to upto 0.19 seconds.
The results on pressure, impulse and effective area are shown for various locations in the lower head. Peak loadings histories are also shown as a function of trigger times. The extreme sensitivity to trigger time is evident from Table 6.1. If the trigger is delayed by 0.06 seconds for the Cl-10 and C2-10 cases, there is only a very weak explosion. For the Cl-20 and C2 20 cases, there appears to be a time interval of only 15-30 msec for the trigger to generate a supercritical explosion. Thus, triggering time appears to be the deciding factor. A physical explanation for this extreme sensitivity should be provided by the authors.
The Appendix C gives very nice pictures of the pressure wave traversing through the lower head. The pressure signals at various points in the lower head are shown, and the peak
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, 03136/97 WED 18:44 FAI A 630.8s3 47S0 16 j
pressures and impulse loadings are shown as graphs versus thne. Reses pictures and graphs were very helpful in the review of Chapter 6. .
i Summarising, I can say that the authors have performed logical analyses of the loadings !
imposed by a steam explosion, and have provided very nice results. I have not understood the reasons for tu extreme sensitivity of the calculated results to the trigger time. The peak loadings, shown in 'able 6.1 are, in general, modest. The highest loading is found to be 1 =200 k. Pa. 5. Is it possible that for p = 30, a higher value than 200 k. Pa. s. is calculated?
4 l
IV.6 Chapter 8. Consideration ofthe reflood FCL's 1 I
This chapter deals briefly with the stratified steam explosions that may result, if the reflood is effective, and a layer of water is brought on top of the melt pool, which has a metallic layer, at top.
)
.It was found that the stable water layer may not exceed 10 cms, due to the low reflood rate 4
and the time to freeze the upper metal layer. Any stradfied explosion will be easily vented.
) I believe, the authors have a good argument. Certainly the peak pressures in such an explosion i
should be low and reflood FC1's may not be a problem.
IV.7 Chapter 7: Integration, Assessment j
- s Chapter 9: Conclusions These chapters combine the results achieved in the previous chapters and appendices to provide an overall nunament. This work was already practically done by the results achieved, since the maximum impulse loading was below the minimum of the fragility curve.
This was also confirmed by performing AB AQUS calculations for the peak loading for the l actual cases and finding that the lower head strains were very low.
The authors conclude that for the saturated water case, the lower head integrity can not be compromised by a steam explosion. Having highly subcooled water is the only possible to, potentially, involve a larger mass of melt, and produce a more energetic explosion. Th
! authors conclude that obtaining highly-subcooled water, even in reflood scenarios for the AP-i 600 is not credible.
i 1
V. Concluding Remarks in this section. I would like to provide a few concluding remarks after the review of the three j
reports, I must congratulate the authors for producing such a fine and comprehensive body of wo treating the tricky and controversial area of steam explosions. While, most of the resea the authors have leaped ahead in this area are still trying to understand the M==*e=1 .
with new concepts, advanced codes and considered judgements to provide a reasonably
' robust estimation of the damage potential of a steam explosion. They have combined *.his
1 0',/26/99 WED 18:4s FAI a 630 as2 4750 ANL-RE .. S. SORRELL 20A9 17 I
with structural analysis to show that AP-600 tower head can withstand the dynamic loads imposed.
4 The authors have, also, noted the peculiarities of the AP-600 configuration and employed the advantages and disadvantages they confer on the analyses. Some of these peculiarities I
(differences) provide great advantages e.g. in the core melt progression and the melt release l
characteristics. These sound a little bit too convenient and, perhaps, should be re-visited.
4 The authors have modelled the fuel break up and fragmentation process only parametrically. .
)
This may be a weak point in the whole development; since those processes provide the initial
- l conditions for both the pre mixing and the propagation phases of the steam explosion.
Perhaps, the analyses am well-bounded for these processes; however, the sensitidty of the l l l results to the break up and the fragmentation modeling is very large.
Then, there is the questica of maturity and of validation versus verification. I believe the methodology and the data presented, robust as they are, are still very new. The compuisons I
presented against tort data are not extensive, and I think, the authors recognising this, have wisely titled the reports as verification reports. Further experience with this methodology and (
ibrther comparisons with separate-effect (e.g. SIGMA, MAGICO, BILLEAU and QUEOS) l
- l data and integral-effect (e.g. FARO and KROTOS) data would provide validation and maturity to this methodology. In particular, the constitutive relations, being so many for such l complicated phenomena, need greater experimental back-up. I believe, the authors are already l busy in achieving such experiments in the MAGICO and SIGMA facilities.
g Lastly, I must say that I have enjoyed reading the reports and leamed much from them. I think, I now understand the concept of micro-interactions and the m fluid. I have made constructive (hopefully) critical comments at places, to provide input to authors towards improvement of the reports. I believe, they have largely achieved the objective they had set I
out to achieve.
a i
l 1
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oA/t/97 RT 18:00 FA21 G20 233 4780 1-16-87 ; 16:48 : FAI - No. SHORE- 1 630 352 47eu;e D 4 se.7 Gy:
Feesake 4 Asemmisees, hue.
January 14, 1997 Dr. L. W. Daiuich Dimeter, Reactor Engineering Division Argonne National Laboraanry 9700 South Cass Avenus Argonne, Illinois 40439
Dear Dr. Datnch:
Subjec Eaview af,,,,tm,ar
- **4 InL dtv Ud In V=' h== NWm 7 wn" by T a w ' - : .e at As aquested in your laser dated June 17,19#, the following comments are offered the arena of Meltdown /matm% Phenomenology and Steam EEpioSion Imds.
Maladown/Ealamatlon Phensmenolosr - We seras compisenty that a downward r*1=% path of the maldag cars material through the cars suppost someture (and res large fuel pour rates) is "physir. ally unmassnabas". Further nore, the predicted relo to the side and from a fully developed malt pont landing m a moltan fuel pour suas inen reactor vessel plasma of about 200 kg/s, is consistant with the Brus nails Island Unit 2 C Raiocation as described by Epsesin and Faushs (Nuclear Tashmology Vol. 89, p.10 Densmber 1989). Pust pour stans of this magnitude tby themasives As illustratedcliminate by concer to global vossal failures, aves if an ansrgeticidl samara espl
, that can be found in transit within the lower planum to values at least an order of magn tu than that requimd int incipisnt lower head dhilus (3 to 5 tons). Quoting Epstein and (1989) " A immy aspect of the relocados is, then, that is, significaat parbaps, thequandfies most of coriu l
- not mized with water at one tims. The sisw melt miocation -=figura7 pronunendy
- in important piens of la8a-anan galaad from ThG 2 medias and sh planum fhilure due to fust debris overheating." His is cisarty the case in the cur pnmdad by Th nrama er al Saana Empleslam ie - Having eliminnend the poenneal for global vessel failure Theofanous at al. prossed to evalusta the potential for localland damass, by cons shock loading, with peak amplitudes in the Khar range, as a result of a suam exp occurnacs. Again, the conclusion is that failurs is " physically unrussonable". His c
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is funhar supported by nodng the following observations.
"Ihs above loadings are produced by subjecdag the m= Mag prenustures at atmospheric Quodng the authors, "our pressure to triggers resuldng from relsmaing Wamm at 100 bar. -
triggers are chosen sufHcient to initiate capiosions, and they have no relation to what might aria
" We agram with this observados, and in fact belisve that the spontaneously during a pour.
occurrones of spontaneous snesa emplosions with the moltan carium-naturated water system The at atmospheric pressure considered by 2'!henfamous at aL is 'phyhally ure=dla".
snormous film boiling heat flux (~ 3 Mw/m ) and corresponding 8
vapor flux resulting with this system (asveral times the critical heat Gux of - 1 Mw/rs ) promosas separation and prevents physical contact between the moltan corium and waaer, a prerequisits for rtamm saplosio a fuel-water pre mixture. Temperatures (- 2000*C) which are well below the melting t-y siere of cursum (- 2700*C), would be required in order in reduos the vapor flux in connection with film bailing to fall below the fluidization vapor flux. The above consideradons ,
are consistant with the noted absence of "caplosivity" for the carium-water system (I. Huhtiniemi er al., *FCI Experiments in the Corium/ Water System" NUREG/CP-0142,1712-1727,1996).
This is in sharp contrast to the noted *eaplosivicy* with the often used 2 3 moltan slumina (A t 0 ) -
2 waamr syntam. Here the estimated film baling vapor Sun (~ 0.5 Mw/m ) is well below the fluidization vapor fhas allowing physical contact whda the alumina is still molten. While the '
noted ef!5ciencias aru quits low, the super critical pressures abaarved with the alumina-water .p
..F tases in the KROTOS fasdity (Hohmann, H. D. et al., Nuclear Eng. A Design, 155, 391-403,-
1995), apparently encouraged 'Ihanismous at at to model such events and apply them to the LWR system.
We also reviewed the approach tahan to assess the steam explosion created impulsive loads. Cartainly the effests performedby the authors areimpressive in the number of analyses performed and the desailed graphical presentation of the results. W ~W~is Our are based on the nuarointeractions model which appears to be applied in a self-consistant manner.
question is whether this is the only way that the raisvant asperimecal information can interpreesd. N underlying supposition in such models are that dynamic firagmentation \ an insurmining of msk and warar can occur on an explosive timescals. Cartainly However, we' are notthe available J
infbrmation shows that fragmentaden an occur dunas an sapiosion.
convinced that the elements med=w with fragmentation and intermiains on such a rapidgv wt have been demaastrated. In particular, the SIGMA taats performed with molten 1 4' ;l alununum indicais virtually no fragmentation for melt osmperatures where numerous Y lar studies have obearved explosive events.
Pur$armana, the dasonation concept is compared to me EROTOS molten da-water and motien *-w = oxide.wmaar rases won ibe agrasmans nom ibis comparison, rh. authors, in a provmus nost report (postro-losas), w* that law void freedan geomeaw can produce highly supercritical, energetic dasonadons." Our analyses show that thars is
- pi=a eiaa es the xmoros experiments that requires no mek fragmentaden. If his is the cas the comparison of the microinteractions model with the KROTOS asperimmats indica mars than that ESPROSE approach is consissent with tbs experimental observations. It does no prwide justification far the micrainteractions physical concept.
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o./21/97 TH 19 : 01 F.L1 1 630 253 47 80 1-14-97 ; 16:45 ; FAI - w, SHogg 'l OYMa nova hT SEVT SY.: 1 1
4 i
' nereform, we are of the opinion thas 'hyp r.A taken in this docernent is conservative in that it overstatas the possible loads that could be createrl as a rusult of thermal explosions.
If a design evaluadon uses this model and concludes that the W 7 would not be challcaged, we believe that the mnelusion is sound. However, if the modeltag approach is used and the .
i resulting loads exceed the capabilities of the structures, we do not believe that this represents
!- an actual challenge to the system integrity.
Befott such a fragmentation approssit can be reconunended for ramlimirally assessing the structure lands, it should be proven that a raladvely small pressure increase would be l sufHcient to self-trigger a coarsely fragramased and laterinized system. In particular, it sh i
be demonstrated that a coarsely misad system could assalass from a small triggering eve an event like that characterned in these svaluations. Assuming that a single grid is filled wit momm at 100 bars as a triggering mashanism, it is far too coarns to provids such a dennitive
..,.==*.
lir In summary, we belisve the rawing of fust rolocation and getina of premixtures to be rummonable and aandmaat with experimental abservanons including the TMI-2 incide j
On the other hand, the asaamament of steam explosion loads appent to be very conssiva corium-saturated waaer system is not 11kaly a exhiint "szplosivity'. Dersfare, a very strong cans can and has been made for the ef!!setiveness af "in-vessel rutan j management emicapt for a reactor like the APtl00.
Y a.k.Y $ E K. Pauska Robert E. Henry senior vice President
(
President 1
HEF: lab I
i I
A.4-R.E 3 av % w l 01/3A'97 RI A8:-03 FA.I A 630 2S2 6750 W: 'lb o
% u.
! Los Alamos Date : January 8.1997
%r to : ssA sA:s7.oos J4 National Laboratory ELA_
! Los Alamos, New Mexico 87545 i
sn,n nno se;.nc.. a Anne.en. 4 ESA.EA, Engc.oring Analysis. MS P946 i l
4 Dr. L W. Deitrich Argonne National Laboratory i 9700 S. Cass Ave.. Bldg. 208 Atgonne,IL 60439
- 1
Dear Dr.Dokich:
1 The purpose of this letter is to clarify the applicability of comments that I made in the att I
~
previous letter to you dated December 1996, regarding review of the report en integnty Under in-Vessel Stream Explosion Loads " by T. G. Theofanous, et al.
The comments made on that attachmert were limited toThe Chapter 3 of the subject repo fragility curves are consequently, affect the fragility curves developed in that chapter.
subsequently referred to in reaching conclusions in Chapters 6 and 7 of the report. t maice clear, however, that the fragility curves in question do not have major effect on l' reached in those chapters. The loads developed in Chapter 6 and applied in Chapter 7 enough that the vessel response is definitely below the lowest probability level us curves (10).
i I should also point out that I concur that the probability levels used in developing the fragi consentative. The association of these levels with strain magnitudes through the ves acceptable. However, the calculated strain levels used to develop the deta level may not be conservative, if the curves are ever used for evaluetmg higher lo
' reevaluated based on the review comments that I previously subtrMed. Irnplement information in these comments w$ affect the shape of the curves and could shift the levels of impulse load (to the left in figure 3.11 of the subject report).
1 if I can be, of further heh please do not besstate to contact me.
Sincerely, Thomas A. Butler, PE l Fi5 C E l V E .-i TAB:rbh s r- --'
, REACTOR ENGINEER!IM :L
! ~DIRErTOTS O.:
Cy: T. G. Theofanous ,
I W. M. Walsh JAN 131997 CIC-10. MS A150 .
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