ML20138C210
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| Issue date: | 11/18/1996 |
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OL-RE .. 3 3ma 4 1D06 96 FRI 16:50 FAI 1 c30 232 4 50 Review of DOE /ID-10541
" Lower Head Integrity Under In-Vessel Steam Explosion Loads" by T.G. Theofanous, W.W. Yuen, S. Angelini, J.J. Sienicki, K. Freeman, X. Chen and T. Salmassi Reviewer: D.F. Fletcher, Department of Chemical Engineering, University of Sydney, NSW 2006, Australia.
November 18,1996 Summary This review covers the study of lower head integrity under steam explosions performed at t'CSB by Theofanous and co. workers, together with the code validation reports for PM ALPHA and ESPROSE.m. The study and validation reports contain a massive amount o very high quality work.The depth of the study and extremes to which the authors have to use validated tools is second to none world. wide. For example, no one else is performin 3D premixing and propagation calculations.
The work is of very high quality and in my view the conclusion that steam explosion indure lower head failure is unphysical is completely justified. The technical arguments support thi with a high degree of redundancy.
1 Introduction Firstly. I believe it is important to comment on both the quantity and quality of the docu-mentation supplied for this review.The very complete verification manuals for PM-ALPH and ESPROSE.m are unique. A minor semantic point but they are much more than veri-fication (which implies that the code does what it shoulo) manuals but are also validation manuals as they examine how well the code represents real experiments.
Secondly. I wish to record that I wasimpressed by the scope, depth and quality of th It provides a very comprehensive basis for rejection of steam explosion-induced f the lower head.
The remainder of this document presents spxific comments on the Study and the two validation repoits.
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This section dea!s with the main document of the study (DOE /ID 10541) and pays part
- attention to the steam explosion part of the study.
2.1 Introduction This section gives a brief summary of earlier work on lower head failure. It discusse earlier studies by Bohl et al, Theofanous et al and Turland et al, all of which highlight ,
the need for mechanistic pressure loading calculations before the lower head issu addressed adequately. This is the first such study in which this approach has been 2.2 Problem Definition and Overall Approach This section sets out the methodology to be used. Essentially, the now establishe procedure is used in which the overall event is split up into well-denned ) The physic that can be modelled, combined with intangible parameters (such as triggering time .
proposed sequence of events and the split betwes.n physical processes th using a entidated model and those which must be treated in a parametric manner s correct to me. In particular, I believe that the flow chart shown in Figure 2.3 gives a cor and well judged progression of events. Details of the modelling will be discusse ever, it is important to empha. size that the identification of a sound methodology important and I believe that the authors have done a good job at this stage o process transparent.
2.3 Structural Failure Criteria This section deals with quantification of the likelihood of vessel failure for a transi localized load. The material in presented in a clear manner and there is a step-by-s progression from an axisymmetric model to the examination oflocalized lo presented in equation (3.10) and Figure 3.3 provides a neat means of d l loca!ized loading and the performance of equation (3.10)in correlating the datais Also I believe that the failure criteria given in Table 3.3 are sensible and fit th database.
This chapter is important in that it sets up the ba.wis for the determination of w particular explosion loading will or will not fail the lower head.h There wo signi6 cant conservatism in the analysis, as noted on page 3-1 and from Fi high imput.<e end. and therefore it provides the required function for this stud .
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Quantification of the Melt Relocation Characteristics -
J 2.4 1
This section presents an analysis of the melt relocation characteristics. It is important to note that the analysia does not use a system code but instead a numbor of highly s models have been developed to address the physical processes deemed to 1.e was the approach followed in the Sizewell B study and seem to me to be tt.e corre l
proceed. Based on my participation in the Sizewell B study I believe that th used and the conclusions drawn are correct.
i :
- The melt flow rates and release conditions are consistent with t study. In particular, I believe that musive pours of many tonnes per second out on the correct physical basis.
In the section on reflooding the authors do not consider the posibility that a stea may occur as the water refloods the molten pool. It is covered in a later sec perhaps be wise to have given a forward reference here.
2.5 Quantification of the Premixture '
This section addresses the determination of the premixture configuration. Fir ,
portant to note that the highly 3D nature of the pour hu been 2D, taken into extension of the PM-ALPHA code to 3D. Thus the localized, ratherldthan smeared characteristics of the melt water interaction process can be simulated. Secondly, it be noted that melt breakup has been taken into account in a parametric manne i
sight this may seem like a weaknem, a many prop breakup be addremed in a parametric manner. As pointed out in ii the report,in t that the melt enters the water pool and runs along the vemel wall, there will be less m than calculated here and therefore the explosion energetics will be reduced.
Based on my experience of premix!ng experimenta and modelling I have no d believing that only tens of kilogrammen of melt are likely to be mixed in the uration. Clearly the high voiding rate is a consequence of the 6 water ding pool bein was left wondering whether in the event that the melt pour occurred during the re oo processes whether there would be sufficient subco which would still result in small mixture zones. .
i t 2.6 Quantification of Explosion Loads This section deals with the determination of the magnitude of the possible!
[ could be generated from the premixtures calculated using PM-ALPHA. It is imp t
' note that these calculations, performed using ESPROSE.m are fully 3D and c; account properly for explosion venting.The validation of the mmlelis disensned in
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$4/06/96 FRI t? 00 FA.I 1 G30 252 6780 section. It is sufficient here to note that the code has been subjected to a very validation effort which I believe shows that it is ' fit for purpose'.
i Specifically, triggering at different I agree with the approach adopted regarding trigger ng. ddition, the effect of the times and looking for the maximum load is clearly conservative. In a premixing breakup parameter J is consistent with experimental i r observ the fact that the uncertainties in breakup can be takeninto account in a parametr c m Given the premixture configurations determined using PEALPHA [ am not the prised that none of the explosions challenges the integrity of the lower head 2.7 Integration and Assessment This very brief section explains that as a consequ between explosion loads calculated and those required for failure. In orde QUS calculations this is not an artifact of the approximate structural treatment, full ABA showed there to be no problem.
I agree the.t the only way to obtain a significant explosion ll is to hav requires highly subcooled water. I believe the arguments against this if one keeps in mind that the enormous amount of heat which would be s core support' structure would be available to remove subcooling.
2.8 Consideration of Reficod FCIs .
This is an important section, as the above analysis has clearly shown th sions cannot cause failure of the lower head. I agree withate the a view take very substantial overlying water pool f tos film ht provide su water addition rates, the ease with which the melt surface freezes and the act t a a boiling occurs the overlying pool will develop voids reducing ld fail the its abilit analysis rules out to my satisfaction the possibility that stratified explosions co !
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' 2.9 Conclusions The conclusions contain a summary of the results presented in the e presents a concise summary of the important physical li features mechanisms which lead to the conclusion that failure of the lower head by a is unphysical. I really appreciated this carefully presented summary.
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3 PM-ALPHA Verification Studies (DOE /ID-10504)
This section presents a review of the PM ALPHA verification studies report. It is importani to note up-front that PM ALPHA has been the subject of continuous development and review (at conferences) over an 8-10 year period. It is therefore a mature piece of so 4 3.1 Introduction The main point of interest in this section is Figure 1 which lays out the verificat validation approach. This is very comprehensive and covers numerical aspects, c with other codes and analytical solutions and with experimental data. l can suggest no improvements to this validation matrix. It is also worth noting that this sectio the new feature of PM-ALPHA, namely extension to 3D which is clearly needed in Study. This clearly represents a massive amount of work but the new lasights g definitely worth the effort.
3.2 Multifield Aspects This section deals with the testing of the multiphase constitutive relations l andj elling for the sedimentation of particles or clouds of particles. PM ALPHA cl results are compared with experimental data and analytical models (based onj
' approximation) for the sedimentation of single particles and clouds. In all casl is excellent. A novel feature of this presentation is that the trajectory of the soluI drift flux volume fraction phase space is presented. These resulta show that thel approached in a variety of ways and helps to explain why multiphase numeric be so complex. These results confirm that the code can reproduce the correc speed, an important feature the steam explosion study.
' Numerous refereed papers have been presented showing that PM-ALPHA MAGICO tests, where in most cases there is also phase transformation. These also show good agreement with localdata on mixture composition and void
"- important as PM-ALPHA must predict the correct mixture composition if the of explosion propagation are to be reliable.
Comparisons of PM ALPHA simulations with data from the QUEOS tests good. There is evidence of numerical diffusion in, for example. Figure 6 bu
- are aware of this and are planning runs on finer grids. In the hot cases I agre 4
authors that both the relatively low melt temperature (making radiation absorp phenomenon) and the gravity induced subcooling are important. If the e l dilference in steam produerion advanced in the text is correct (namely the '
!ayer of water during the fall stase)it means that interpretation hof experime where there is relatively little steam production, will always be very complicated.
short time available to the authors to analyze this data and the experimental u I feel that PM ALPHA performed as well as could be expected. l I
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3.3 Integral Aspects The code comparisons with CHn!ES and between the 2D d and and that 3D versiora o a high degree of confidence that the buic numerical algorithm is correcti) code the 2D and 3D approaches are consistent.
The comparison with data from the MIXA06 experiment is at least u good by the experimenters using the CHYMES code. The lack of melt spread is very similar to that found using CHYMES. The level h swell his testand is steam prod well reproduced given the experimental uncertainties. Again i i it isrding fair to say t at t well simulated given that there are several important experimental uncerta nt es rega particle breakup and the steam flow rate.
- The comparisons of code calculations with data from the L-14 l FARO ex good. In this experiment there is no local h l cal data an to match these data seems very reuonable. I found the figures illustrating h t e non-o absorption of radiation interesting and these clearly illustrated the importa nomenon for high temperature melts. To my knowledge these are the first c include this feature, which is clearly of importance in high temperature mel 3.4 Breakup Aspects I completely agree with the chonen approach to breakup. As more tests be possible to increase the degree of confidence in the chor,en values for t Clearly, given that the melt surface area transport equation is already co simple matter to include a mechanistic model, shou'Id l adivalidated i s break available. However, the analysis presented in the study shows f d that il dthe overal pr of loading are insensitive to the choice of these parameters. Therefore the lack model does not in any way effect the conclusions of this study.
3.5 Numerical Aspects i
The authors are clearly aware of the need to avoid numerical differencin presented calculations show that they are taking care to addrass this probl 3.6 Concluding Remarks Ihave think made thismore section identifies of the fact that this the is thecorrect areas for future most comprehensive validat and that the code has performed extremely well.
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12/06/96 'FRI 17:02 F.d L 630 252 4780 .0 L.- 6 --- s . sue.u. w 3.7 Appendices i l
Appendix A provides a comprehensive description of the constitutive laws and A !
provides a detailed paper on the MAGICO tests.The reviewer is familiar with In the Appendices and this has not been reviewed in detail.
4 4 ESPROSE.m Validation Studies (DOE /ID-10503)
Firstly, it is important to tackle head on the ESPROSE.m formulation, which fair to say has not been widely accepted. I find it hard to understand why this is th Euentially, the novel feature in ESPROSE.m is the inclusion of an additional Auld Huid) which representa the fragments and the 8uid in intimate contact wi l being heated. The need for such an approach seems beyond doubt to me foll careful experimental analysis of Baines [1] and my own attempta data to analyze K tests using CULDESAC (2]. The authors have provided comprehensive experim for appropriate pressure loadings to show the finite mixing rate. They ide for an enlarged database but it should be recognized that the ESPROSE.m fo conservative in the sense that by mizing the fingments with onlyh a fraction of they gencrute high local prenure . This point should be kept in mind when exa use of ESPROSE.m results.
1 The remainder of this section contains detailed comments on the various chap verincation report.
4.1 Introduction The main feature of this chapter is Figure 1 which give the validationi strategy. Thi .
extensive and to my knowledge is the first model to be subjected toI specific l wave d and explosion coupling verification studies against analytical and experimenta covers the two main experimental programmes KROTOS and ALPHA.
4.2 Wave Dynamics The ID solutions for the shock speed and particle velocity (important in relative fragmentation) are excellent. The same applies to wall re6ection studie d agreement and the effect of non condensable gu. The venting calculations also show goo with 'the CHAT results. I was curious to know why the calculations were perf a pressure step of 40 bars over a bue pressure of 100 bars and over a of only 1.4 cm. I would have preferred to see venting on the 0.1 m scale (wi mesh) and a pressure difference of say 10 bars venting to atmosphere. '
the ESPROSE.m results only exhibit dispersion at the first few time steps an numerical diffusion in modest. .
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The 2D comparisons are impressive and show that ESPROSE.m captures the very well. The only point that this section raim for me is why in the type B b ESPROSE.m results have a spike at the origin (as expected l i i i from n? the source d the analytic solution does not (see Figures 7,13 and 19). Is this simply a p ott ng om s The experimental comparisons with data from the hSIGMA tfacility ns- are interes that ESPROSE.m is capturing the average wave behaviour well. Clearly. t e pressure r ducers are picking up many local reflection events which are due dto the inhomog
' nature of the ' mixture' and cannot be modelled via a continuum ti dif- approach. I a that ESPROSE.m has done so well for this system with the only apparent systema ference is the tendency for a ~1 ms time lag. -
This section provides very solid verification for the code algorithm and the parameters.
4.3 Explosion Coupling This section contains test cases in which energy is input linto i the gas pha relationship in which the energy input into the gas hphase iisinput proportional to e
to the power 1.5. This is done to represent the fact that in ESPROSE.m t e ene in the m-fluid. Results for calculations for both cases l considered' ines the are in exc with the CHAT simulations. Figure 5, for simulations on a larger hit space fesca e. exam effect of grid size. The comparisons are good with differences being confined region.
4.4 Integral Aspects The analytical tests show that ESPROSE.m ca 6 of the fragmentation rate and entrainment factor these are real rather than numerical. Could the authors comment?
The confirmation that the 2D and 3D models give similar results is thor i agree with the authors that the KROTOS tests h are too lidation case.poorly ch validation studies and therefore I do not think this section is central t The point about melt freezing is verySurface interestin is asumed to be at a uniform temperature, where UO2 in KROTOS.
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4.5 Numerical Aspects I agree with the conclusions drawn. The presented calculations clearly show that the authorsi are aware of the need for adequate spatial and temporal resolution. In addition, the results l
show a good compromise between diffusive and dispersive errors.
l 4.6 Concluding Remarks This is a very important section and I believe the authors have judged the current situation very well. I agree entirely with the conclusions they have drawn from the very comprehen sets of calculations performed to date. There is a clear need for the high temperature SIGMA data and I am aware that plans to obtain this are well advanced.
I personally doubt that it will every be possible to characterize the KROTOS experiments much better and my experience with the MIXA testa tells me that there will always be something left to be measured. Therefore I agree that this in a lower priority. The comments on secondary pressure waves are interesting and clearly of a very fundamental nature. I d not believe that such effects could be addressed easily within the continuum model but I would certainly encourage their investigation.
Finally, I agree com pletely with the closing paragraph: moving to large-scale, multi 4
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I experiments will only add confusion.
4.7 Appendix A f
I have no specific comments here. I am generally familiar with the modelling approac; and I believe appropriate modelling choices have been made from the available database l of constitutive laws. It should be recognised that it is in the formulation stage that the ;
ESPROSE.m model differs fundamentally from othersin that it is 3D and uses the microin!
teraction concept to allow for thermal disequilibrium within the coolant.
4.8 Appendix B 1 j
This section contains a description of the CHAT code used'to provide analytteal solution!
code comparisons. The model in formulated for the case of homogeneous flow of li coolant (no slip but different temperatures). Thus the system has only real characte and therefore can be solved in an elegant and accurate manner. It provides an excellent means of testing ESPROSE.m. 1 l
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'2/06/96 FRI 17:04 F.u 1 630 253 6780 4.9 Appendix C This appendix is a reprint of a conference paper which describes the microinteraction data and its implementation into ESPROSE.m. I am familiar with thia work (from the paper and visiting the facility) and believe it to be both unique and of a high quality. Whilst at present results from low temperature melts have to be extrapolated to the reactor case, plans are well advanced to produce the required data.
4.10 Appendix D ,
This appendix also contains a reprint of a conference paper which discusses the manner in which the 'real world' differs from the Board-Hall model. It is very interesting as it shows how the inclusion of mictointeraction physica produces p'ropagation behaviour'which is very different from the Board-Hall model and other propagation models which do not allow for micro mixing. Essentially, it allows propagation in systems which are melt lean because the energy from the melt is transferred to only a fraction of the water present. It provides an interesting perspective on which to end the ESPROSE.m validation report and clearly illustrates what a significant advance the mictointeraction concept has been in propagation modelling.
References
[1] Baines, M. (1984). Preliminary measurements of steam explosion work yields in a strained system. Irwt. Chem. Eng. Symp. Series. 86.97-10A.
j
[2] Fletcher, D. F. (1991). An improved mathematical model of melt / water detonatio II. A study of escalation. Int. J # cal Mass Tmns/ce,34,2449-2459.
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$8, M "8 " 2 ARGONNE, Illinois 60439 5&T- ,
'__ m. c' ra.n u so u FAA 4 M 50 3e November 20,1996 t
Dear Doctor Deitrich,
Lower Head Please find enclosed my review concerning the document
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Integrity under In vessel Steam Explosien Loads a by T.G. Theofanous et I must confess that it took me more time than the allocated 24 ho I am also sending an invoice corresponding to a 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> work to the University of California to M. Vaughn Boyle.
Sincerely, 3
5 G. Berthoud
- Chef du Laboratoire d' Etudes Fondamentales Service de'Itermohydraulique pour les Applications Industrielles RECEIVED
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