This paper addresses known methods used to purify regenerated uranium in single and double cascades. A new method for separating regenerated uranium has been developed that enables a significant reduction of the concentration of 232,234U in the additional product flow. Matched abundance ratio cascades (M∗-cascades) with different key components and additional product flow are used in the new method. Main product flow of the M∗-cascade contains low enriched regenerated uranium. It can be used for reactor fuel production. Purified product can be enriched in the ordinary cascade in compliance with the requirements of ASTM C 996-10 set for isotopes 232,234U in low enriched commercial uranium, which is usually produced from the natural one. Computer experiment based on the new method has been performed. The experiment shows that the best cascade with the maximum flow of the enriched purified product is M∗-cascade with key components 232,236U. © Published under licence by IOP Publishing Ltd

Maslyukov, E. V.

Palkin, V. A.

Journal of Physics Conference Series

English

E V Maslyukov

V A Palkin

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Regenerated Uranium Separation in Matched Abundance Ratio Cascade with Additional Product Flow

Institutional repository of Ural Federal University named after the first President of Russia B.N.Yeltsin

Journal of Physics: Conference SeriesPAPER • OPEN ACCESSRegenerated Uranium Separation in MatchedAbundance Ratio Cascade with Additional ProductFlowTo cite this article: E V Maslyukov and V A Palkin 2016 J. Phys.: Conf. Ser. 751 012002 View the article online for updates and enhancements.Related contentMass separation experiment with apartially ionized rotating plasmaO Kaneko, S Sasaki and N Kawashima-Laser isotope separationNikolai V Karlov and A M Prokhorov-This content was downloaded from IP address 213.142.35.54 on 20/07/2019 at 08:54Regenerated Uranium Separation in Matched Abundance Ratio Cascade with Additional Product Flow E V Maslyukov and V A Palkin Ural Federal University named after the first President of Russia B.N. Yeltsin, Institute of Physics and Technology, 19 Mira Street, Yekaterinburg, Russian Federation E-mail: eugene_v_m@mail.ru Abstract. This paper addresses known methods used to purify regenerated uranium in single and double cascades. A new method for separating regenerated uranium has been developed that enables a significant reduction of the concentration of 232, 234U in the additional product flow. Matched abundance ratio cascades (M*-cascades) with different key components and additional product flow are used in the new method. Main product flow of the M*-cascade contains low enriched regenerated uranium. It can be used for reactor fuel production. Purified product can be enriched in the ordinary cascade in compliance with the requirements of ASTM C 996–10 set for isotopes 232, 234U in low enriched commercial uranium, which is usually produced from the natural one. Computer experiment based on the new method has been performed. The experiment shows that the best cascade with the maximum flow of the enriched purified product is M*-cascade with key components 232,236U. 1. IntroductionRegenerated uranium is produced from irradiated nuclear reactors fuel. It plays an important role in the nuclear fuel cycle. It contains isotope 235U, which has a concentration higher than that in the natural uranium. However, there are significant amounts of impurity isotopes 232, 234, 236U in the regenerated uranium. It is impossible to separate them chemically. The impurity isotopes cause the main difficulties for using regenerated uranium in the production of reactor fuel [1]. The most significant problem is the presence of the isotopes 232U and 234U because of their high radioactivity. The isotope 236U captures neutrons in a nuclear reactor. Its presence leads to an increase of the concentration of the fissile isotope 235U in the fuel. This problem affects the economic indicators of a nuclear reactor. To minimize radiation hazards and improve fuel quality it is necessary to reduce the concentration of 232, 234, 236U. For this purpose cascade separation technique of the uranium hexafluoride (UF6) and dilution operations can be used. There are different ways of regenerated uranium enrichment with the reduction of 232, 234, 236U concentration in a separate cascade. One of these is its enrichment to a concentration of the 235U up to 10–90% in the ordinary cascade and subsequent dilution down to 2–7% [2]. Despite the good quality of the product obtained, this method has significant drawbacks: 235U isotope with a concentration over 5% is formed as an intermediate product of the purification process. Moreover, this method involves using natural uranium. International Workshop on Physical and Chemical Processes in Atomic Systems IOP PublishingJournal of Physics: Conference Series 751 (2016) 012002 doi:10.1088/1742-6596/751/1/012002Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributionof this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Published under licence by IOP Publishing Ltd 1Also, there are methods of regenerated uranium purification in double cascades [3–5]. The first ordinary cascade enriches the uranium hexafluoride up to 20% and above for 235U. The product flow of this cascade is fed the second cascade, where 232, 234U are removed from the waste flow. The purified wasted uranium hexafluoride of the second cascade is diluted to obtain the desired concentration of 235U. When the additional carrier gas [5] is used in the second cascade feed flow the content of 232U is reduced down to 3×10-8 – 4×10-9 % without using special diluents. The only disadvantage of the double cascades [3–5] is obtaining a highly enriched uranium with 235U concentration more than 20% at some stages of separation. Another method uses additional feed flow with natural uranium in the cascade [6]. When using this method, the regenerated uranium is enriched to a concentration less than 5% 235U while the content of 232, 234, 236U is decreased. The consumption of natural uranium can be efficiently reduced by utilizing one more feed flow with depleted waste uranium [7]. However, this leads to an increase in the expenses for separation work. Another method involves using a cascade with an additional product flow and two feed flows with regenerated and with natural uranium [8]. In this case, additional expenses for separation work are practically nonexistent. However, with a significant reduction in the concentration of 232, 234, 236U in the intermediate product flow, their content increases in the final commercial product flow of the low enriched uranium. The alternative is a double cascade, where 235U concentration is limited and the pattern is changed so as to remove 232, 234U in the first ordinary cascade. Thus, the feeding point is significantly shifted toward the product flow. Its purified depleted stream is fed to the second ordinary cascade, where the desired commercial product of low enriched uranium is generated in the product flow [9]. Studies have shown that reducing the concentration of 232U to (3-4)×10-9 % in the final product is possible with 235U enrichment to 5 % in the cascades [10]. However, this method features high expenses for separation work and does not provide for significant removal of 234, 236U isotopes. More efficient removal of 234U is possible using the method described in [11]. This paper deals with the purification of the regenerated uranium in the additional product flow of the matched abundance ratio cascade (M*-cascade) [12] and subsequent enrichment of the purified product in the ordinary cascade. Calculations are based on the methodology [13] for the M*-cascades for various key components. 2. CalculationsThe scheme consisting of two cascades is shown in Figure 1. Figure 1. Double cascade scheme Let F, W, and P denote feed, waste, and primary product flows of the first cascade, respectively; let Pk denote additional product flow, and СiF, СiW, СiP, СikP denote corresponding concentrations (massfractions) of the i-th component. Additional flow Pk is taken from the waste flow of stage k of the first cascade. W2, P2 are waste and product flows of the second cascade; and СiW2, СiP2 are thecorresponding concentrations of the i-th component. Matched abundance ratio cascades with one additional product flow were calculated for various key components. Feed flow F was 10 g/s and consisted of a mixture of isotopes: 232U – 1.5×10-7 %, 234U – 1.6×10-2 %, 235U – 0.85 %, 236U – 0.35 %. PkCikP FCiFW, CiWW2 CiW2P2 CiP2P,CiPInternational Workshop on Physical and Chemical Processes in Atomic Systems IOP PublishingJournal of Physics: Conference Series 751 (2016) 012002 doi:10.1088/1742-6596/751/1/0120022The selected concentrations of feed correspond to the characteristic isotopic composition of regenerated uranium [14]. The cascades consisted of 51 stages with the feed in the stage number 45. This configuration has been chosen based on the given separation factors and the need to achieve a concentration of the 235U not exceeding 5% in the primary product flow and 0.04 – 0.3% in the waste. Under these conditions, the primary product flow meets the requirements of ASTM C 996–10 for low enriched regenerated uranium and can be used to produce the corresponding reactor fuel. The number of the additional product flow stage k varied from 2 to 45, its flow quantity Pk ranged from 1 g/s to 5 g/s in steps of 0.1 g/s. The separation factor per unit mass difference was assumed to be 1.091. For each calculation, the additional product flow of the M*-cascade fed the ordinary cascade. The parameters of the latter were assessed by analytical formulas [15]. The concentration of the 235U at this cascade was set equal to 0.3% for the waste and 4.4% for the product. The concentration of the 235U in the product flow of the ordinary cascade was taken on the basis of its required content of 3.2 – 3.6% in the fuel without regard for the parasitic neutron capture by 236U isotope. The compensation factor in the product was 0.2 – 0.3. The content of the impurity isotopes in the product was limited to 1×10-8 % for the 232U and 4.8×10-2 % for the 234U. These concentrations of impurity isotopes meet the ASTM C 996-10 specification for low enriched uranium with a concentration of commercial 235U equal to 4.4%. 3. ResultsIt was found that the concentration of the components 232-236U decreases with the increase of the additional product flow (Table 1). Table 1. Concentration of components in function of additional product flow for stage No. 14 (k = 14) of M*-cascade with key components 232, 236U. Pk(g/s) CikP(%)232U 234U 235U 236U 1.7 6.45×10-10 7.03×10-3 0.8498 0.4057 2.0 6.32×10-10 6.70×10-3 0.8193 0.3978 2.5 6.12×10-10 6.21×10-3 0.7731 0.3853 3.0 5.94×10-10 5.79×10-3 0.7318 0.3736 3.5 5.76×10-10 5.42×10-3 0.6946 0.3626 4.0 5.60×10-10 5.09×10-3 0.6610 0.3521 4.4 5.47×10-10 4.86×10-3 0.6364 0.3442 As the additional product stage number increases, the 232-236U concentrations increase too (Table 2). It follows from these that an optimal stage number exists for each selected value of the additional product flow Pk in the matched abundance ratio cascade. The product flow of the ordinary cascade P2 will be maximal for this stage number taking into account the limits assumed. Table 2. Concentration of components in function of additional product flow stage number of M*-cascade with key components 232,236U when Pk=2.7 g/s. k CikP(%)232U 234U 235U 236U 2 5.58×10-11 2.66×10-3 0.469 0.287 5 1.07×10-10 3.54×10-3 0.568 0.324 10 2.87×10-10 4.96×10-3 0.691 0.364 14 6.05×10-10 6.03×10-3 0.756 0.381 It should be noted that when the restrictions on the concentration of 232,234U are met the 236U content in the product flow of the ordinary cascade increases as Pk grows (Figure 2). International Workshop on Physical and Chemical Processes in Atomic Systems IOP PublishingJournal of Physics: Conference Series 751 (2016) 012002 doi:10.1088/1742-6596/751/1/0120023Figure 2. Concentration of the 236U in product flow of ordinary cascade in function of additional product flow of M*-cascade: 1 – key components 232,236U; 2 – key components 232,238U; 3 – key components 234,235U; 4 – key components 235,236U. Thus, it is possible to reduce the product flow of the ordinary cascade to decrease the 236U concentration. For example, a decrease of the flow by 4 % from the optimal value for the matched abundance ratio cascade with key components 232,238U leads to a decrease of the 236U concentration by more than 16 % (Table 3). Table 3.Variation of 236U concentration in product flow of ordinary cascade K Pk(g/s) CikP(%)P2 (g/s) C2iP(%)232U 234U 235U 236U 232U 234U 236U 30 1.8 2.26×10-9 4.40×10-3 0.654 0.390 0.156 9.93×10-9 3.76×10-2 4.10 29 2.7 1.74×10-9 3.50×10-3 0.523 0.340 0.162 8.98×10-9 3.96×10-2 5.10 When the Pk flow increases the feed flow of the ordinary cascade also increases. At the same time, the 235U concentration in the feed flow decreases. These two factors have opposite effects on generation of the product flow P2 at the given concentrations for the product and waste of the ordinary cascade. The first of them results in the increase of P2 and the second one leads to its decrease. As a result, the maximum P2 is observed at certain optimum value of Pk (Figure 3). Table 4 presents examples of additional product flows of the M*-cascades that correspond to the maximal values of P2 with the restrictions set for 232,234U met. Table 4. Parameters of additional product flows of M*-cascades and ordinary cascades with maximal product flows P2. MARC k Pk (g/s) ΣL (g/s) CikP (%) CiP235(%) P2 (g/s) C2iP (%)232U 234U 235U 236U 232U 234U 232U 232,236U 14 4.4 2357 5.5×10-10 4.9×10-3 0.64 0.344 4.95 0.36 2.5×10-9 4.3×10-2 3.78 232,238U 29 3.0 2821 1.7×10-9 3.5×10-3 0.52 0.339 3.94 0.16 9.0×10-9 4.0×10-2 5.10 234,235U 26 3.2 2576 2.0×10-9 5.2×10-3 0.66 0.362 4.50 0.28 8.8×10-9 4.4×10-2 3.80 235,236U 32 1.4 3094 1.8×10-9 2.9×10-3 0.49 0.368 3.41 0.06 9.9×10-9 3.5×10-2 6.29 These examples show that the best matched abundance ratio cascade is a cascade with key components 232,236U. Moreover, the product flow of the ordinary cascade contains the minimal quantity of the impurity component 236U. The total flow ΣL in this M*-cascade is significantly lower as compared to other cases. 0246810121 1.5 2 2.5 3 3.5 4 4.5 5C2iP (236U) (%) Pk (g/s) 1 3 4 2 International Workshop on Physical and Chemical Processes in Atomic Systems IOP PublishingJournal of Physics: Conference Series 751 (2016) 012002 doi:10.1088/1742-6596/751/1/0120024Table 5 shows the isotopic compositions of primary product flows of the matched abundance ratio cascades, which are the best in terms of the flow P2. The parameters specified meet the ASTM C 996–10 requirements set for the low enriched uranium. Figure 3. Product flow of ordinary cascade in function of additional product flow of M*-cascade: 1 – key components 232,236U; 2 – key components 232,238U; 3 – key components 234,235U; 4 – key components 235,236U. Table 5. Parameters of the primary product flows of M*-cascades with maximal product flows P2. MARC CiP(%)P(g/s) P2 (g/s) 232U 234U 235U 236U 232,236U 1.65×10-6 0.91 0.36 1.128 1.65×10-6 0.146 232,238U 9.04×10-7 1.65 0.16 1.068 9.04×10-7 0.090 234,235U 1.22×10-6 1.23 0.28 1.109 1.22×10-6 0.115 235,236U 6.73×10-7 2.22 0.06 1.034 6.73×10-7 0.070 4. ConclusionThe method developed allows purifying the regenerated uranium to remove the impurity isotopes 232, 234U from the additional product flow of the matched abundance ratio cascade with a concentration of the 235U in the product flow up to 5 %. The purified product can be then enriched in another cascade while meeting the requirements of ASTM C 996–10 set for these isotopes in the low enriched commercial uranium. As for achieving the maximum flow of the enriched and purified uranium, the best cascade is the M*-cascade with key components 232,236U. References [1] Nikipelov B V and Nikipelov V B 2002 At. Energy Bull. 9 34[2] Vlasov A A et al 2004 Russian Pat. 2236053 Method of the isotopic restoration of regenerated [3] uranium Vlasov A A et al 2004 Russian Pat. 2242812 Method of the isotopic restoration of regenerated [4] uranium Vodolazskih V V et al 2006 Russian Pat. 2282904 Method of the isotopic restoration of [5] regenerated uranium Prusakov V N, Sazykin A A, Sosnin L Yu, Utrobin D V and Chel’tsov A N 2008  0.000.050.100.150.200.250.300.350.401 1.5 2 2.5 3 3.5 4 4.5 5P2 (g/s) Pk (g/s) 1 3 4 2 International Workshop on Physical and Chemical Processes in Atomic Systems IOP PublishingJournal of Physics: Conference Series 751 (2016) 012002 doi:10.1088/1742-6596/751/1/0120025J. Atomic Energy 105 194  [6] Sulaberidze G A et al 2006 Theor. Found. of Chem. Eng. 40 5 [7] Smirnov A Yu and Sulaberidze G A 2014 J. Atomic Energy 117 44 [8] Palkin V A 2010  Perspektivnye materialy 8 11 [9] Sulaberidze G A, Borisevich V D and Xie Quanxin 2004 Proc. of IX Russian sci. conf.  “Fiziko-himicheskie processy pri selekcii atomov i molekul” (Zvenigorod) p 78 [10] Palkin V A 2013 J. Atomic Energy 115 32 [11] Palkin V A 2015 J. Atomic Energy 118 130 [12] A De La Garza, G A Garrett and J E Murphy 1961 Cascades J. Chem. Eng. Sci. 15 188 [13] Palkin V A and Maslyukov E V 2012  J. Atomic Energy 112 389 [14] Zhurin V A at al 2010 Russian Pat. 2399971 Method of the isotopic restoration of   regenerated uranium [15] Palkin V A and Maslyukov E V 2012 Proc. of 12th Int. Workshop on Separation Phenomena   in Liquids and Gases p 21 International Workshop on Physical and Chemical Processes in Atomic Systems IOP PublishingJournal of Physics: Conference Series 751 (2016) 012002 doi:10.1088/1742-6596/751/1/0120026

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Regenerated Uranium Separation in Matched Abundance Ratio Cascade with Additional Product Flow

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Institutional repository of Ural Federal University named after the first President of Russia B.N.Yeltsin