UNCLASSIFIED We 1 21, 111 WY X TA 1 . . INT . Who MVC ., .. WAST 238 Lobbra, ORAL-P-238 DOES 116-571-12- VY THEORY OF FISSION PRODUCT FRACTIONATION IN REACTOR FUEL EXPERIMENTS, REACTOR ACCIDENTS, AND WEAPONS FALLOUT* C. E. Miller, Jr., W. E. Browning, Jr., B. F. Roberts, and R. P. Shields Reactor Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee Chicago ACS Meeting, August 30-September 4, 1964 Radiochemical analyses of the components of experiments at ORNL in which fission products are released by melting miniature stainless steel-clad vo, fuel elements in the Oak Ridge Research Reactor have shown that fission products appear in varying proportions in various locations, and sample compositions are in general different from those predicted for normal f1sbion yields. This fractionation occurs because differences in the physical and chemical characteristics of individual fission products result in differences in their behavior in release, transport, or deposition processes. - Slide I shows the in-pile facility in which these experiments are carried out in . - .. . ... . . . . ..- - -- -- the core of the reactor. Slide 2 shows the detail of the reactor furnace in which the. *Research sponsored by the U. 8. Atomic Energy Commission under contract with the Union Carbide Corporation. - LEGAL NOTICE --- This report na propered as an account of Goreniment sponsored work. Neither the United Raw, the Commuten, nor My porno ita lian Count : A. 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Manager We are interested in the amounts of f1ssion products contained in transported materials and in any information we can extract as to the mechanisms of their release, transport, and deposition. We have developed a model which predicts fission product fractionation and which gives satisfactory agreement with data from these experiments. 811de 5 shows the basis for this model. At thu surface of the puddle of molten von crownou in writt 1. R encanto QUINTURAS munon ming, . menu MES 1. condemna ami.. -MO . и • Тема. there exists vaporization equilibrium between the lission products dissolved in the melt and the vapor. The gas is diluted by a ratio r after which the partial pressure of any one fission product is rxk 'p where x is the mole fraction in the melt, k' is the modified Henry's law coefficient fc. the vaporizing fission product, and pº is the vapor pressure of the pure fission product substance at the temperature of the melt. We assume that k' 16 Independent of temperature and that x changes negligibly. The gas mixture having this partial pressure of fission product passes out of the high temperature zone eud deposition occurs at locations which depend indirectly upon the vaporization temperature. During the course of an experiment, the temperature 18 . 2 want humanitatis . . . - -. . - varied over a range. Slide 6 shows the equations which describe the behavior of Perxck po :. .:: T-a + bt .. røk'xP'dT :.: - BRT std 2rok'x pim pºdt bRTd Iti' fission products in this model. P is the partial pressure of fission product after dilution of the gas mixture. The temperature excursion is represented by a linear expressica. The number of moles of f'ission product vaporized while the temperature changes over the increment dT is given by dn, where Ø 18 the flow rate of the gas, o is the rate of temperature change, R is the gas constant, and Tsta 18 the standard temperature at which gas flow 18 measured. Integrating this expression over the range of temperatures gives the total amount of fission product vaporized, ng. The constant k' is difficult to evaluate theoretically or by reference to the literature so we make use of information from the experiment about the total amount of fission product vaporized to determine a value of k', and substitute it into the expression for da. In slide 7 we have done this and expressed on as a fraction of the total Wodne, a post [pºst "* 2. Speut aspect 120.9.PESPOT 0P:SP;GT po.donWRT -5- inventory of the Pission product. We may obtain a similar expression for a different Pission product, and by taking the ratio between them we can eliminate at, the temperature range over which the fission products in the particular sample were vaporized. pº 18 a function of temperature, as shown in the third line, and substituting we obtain an expression for the ratio of the fractions of two f18sion products occurring in a single sample. We may obtain another expression like this for the ratio of a third fission proäuct and, between the two, eliminate the value T, the temperature at which vaporization produced the sanple in question. Performing this operation we obtain the results shown in Slide 8. This expression is simplified in the bottom line to show that data should yield a straight line on a log-log plot .6 - - - .. and the slope of the straight line will be a simple function of the heats of vaporization of the fission products, (AH1 - A)/(A4, - A8). The heat of vaporization of a fission product depends upon the chemical form in which it is vaporized. Thus, the slope of the line on the log-log plot reveals the chemical forms in which fibbion products are vaporized in these experiments. In this expression temperature is an implicit parameter and different samples found in -6- different places are regarded as having been vaporized at different effective temperatures. Slide 9 shows a plot of data from one of the experiments in which • (INWENTAL DATA IM MCOKICO I Wan INAKSANATION incor rom SOSION moouci OOS. mnoo porn mo samo FOI Imcom WTO meier.. .. SIKIO MALOmIUmOjamas INIO TOT I MILANO Freellemento a ww Flooten Moaklo owing month Moting at 10, (Common o) stainless steel-clad vo, was melted in He. The ordinate is the log of the ratio of barium to zirconium in each sample and the abscissa is tie similar quantity for strontium to zirconium. Individual points represent individual samples found at different places in the experimental assembly. The samples differ in composition because they were vaporized at different temperatures. The two lines show the predicted plots based on the two assumptions that these three fission products vaporized as the elements in one case and as the oxides in the other. No parameters have been adjusted; both the slope and the intercept are predicted by the theory. It is clear that the fission products vaporized in the elemental form. The agreement with the data appears to validate the assumptions of the model and to identify the mechanism of fractionation as being a simple vapor transpiration process. Since the method seems to work for this particular fission product release experiment, we decided to attempt to fit similar data from other types of release experiments. An experiment has been reported by English workers on deposition of fission products from a flowing gas stream. This involved post-irradiation heating of Vo, at approximately 20001°c. The result of the fractionation analyses for five of an -7- these experinento 18 shown iu slide 10. 8 ORIOL un monton : come un . : che : : DO 19 .-1.0 as 0 0. nachoon Movement mume we come a word Iratmethen there, Iron Ouring on them witoon moet as thetty freno moving in Mrven (NCMCM1110) These five lines are not predicted by the theory but were fitted to the experimental points. There was not sufficient information given in the paper for calculation of the intercepts. A comparison of slopes predicted by the theory for element and oxide vaporization is shown in the top portion of the slide. You can **** see that three of these experiments appear to involve elementa). release of fission products and two experiments involve oxide release. The result of the application of this theory to ancther type of experiment are shown in Slide 11. This experiment, reported by N. M. Meyers during the Aircraft Muclear Propulsion Program, described the plate-out of fission products in lines sampling the effluents from various engine test reactors. Again only the slope was been predicted and corresponds to elemental release of f'ission products. MAR . Muur ( -7). -80 Carrying this analysis to the extreme, we decided to look at tall-out data. The model described thus far considers the fractionation step to be the vaporization of fission products from the fuel. This, of course, would not be the case in the vaporization of f18sion products from an atomic weapon. The condensation step should be the fractionation step, and an alteration in the model 18 required. In the early development of the transpiration model, condensation was considered as the fractionating step and the model was called the co-condensation model. Both models predicted the same slope for log-log piots, but different intercepts. We tested the data of E. C. Freiling from his article "Radionuclide Fractionation in Bomb Debris" printed in Science 133, 1991-9 (June 1961) and we find that the slopes can be predicted using only the heats of vaporization of the species cordensing. The species condensing was estimated to be that precursor in the chain present ten minutes after the bomb shot. Slide 12 shows a comparison of Freiling's slopes determined by least squares See page 10 and our slopes determined from the heat of vaporization of the elemental form of the condensing species. -G- We feel that this application of thermodynamics has provided a general method for predicting fractionation of materials. We are continuing in the development of both the vapor transpiration and co-condensation models to predict quantities of material being released and the mechanisms of their transport. esign D Isotope Analyzed Fallout Fractionation Least Square Slopes and 95% confidence Limits of Logarithmic Fractionation Correlations* 90 gr 132 99M0 1 329e 1370& . 140, 144ce Coral surface bursts .24 + .12 1.10 + .11 .40 + .21 Submegaton Deep water surface burst .52 4.40 .89 1.08 .12 .13 -.42 1.51 Deep water surface 2.02 1 .22 2.02 + .91 '.09 .901 .48 + 1.26 -56 - .411.21 .60 1 .23 .37 1.86 .52 1.82 .62 .55 + .62 .437.09 .55 7.50 .92 1.12 .941.09 .70 7.4 1.06 1 .19 .941.06 ourst Shallow water surface burst +1 .38 .18 Cumulative slopes for .32 1.08 1.32 1.34 .60 1.23 1.11: .9 .601 .14 -.04 + .70 ..06 .31 1.04 + .10 1.05 high field surface bursts 8lopes Calculated from Co-condensation Theory goar 99 No 13286. Isotope Calculated 13/xe - 140 Be 144ce 2370 239 0.24 1.85 0.52 -0.19 0.21 0.89 1.32 1.32 *E. C. Freiling, Radionuclide Fractionation in Bomo Debris, Science 133, 1991-98 (1961). -.'. -10- : . ! . . Min TE . - - 1 . DATE FILMED 11/23/164 = Time N E . 4 . .. į K 2. . a î 24 ; Y - LEGAL NOTICE " This roport was preparod as an account of Government sponsored work. Neither tho Unitod Statos, nor the Commission, nor any person acting on behall of the Commission: A. Makes any warranty or representation, expressed or implied, with respect to the accu- racy, complotoness, or usofulnous of tho information contained in this roport, or that the uso of any information, apparatus, monod, or process disclosod in this roport may not Infringe privately ownod rights; or B. Assumes any liabilities wild respect to the use of, or for damages resulting from the use of any information, apparatus, molhod, or process disclosed in this report. 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