Study on high conversion type core of innovative water reactor for flexible fuel cycle (FLWR) for minor actinide (MA) recycling

In order to ensure sustainable energy supplies in the future based on the well-established light water reactor (LWR) technologies, conceptual design studies have been performed on the innovative water reactor for flexible fuel cycle (FLWR) with the high conversion ratio core. For early introduction of FLWR without a serious technical gap from the LWR technologies, the conceptual design of the high conversion type one (HC-FLWR) was constructed to recycle reprocessed plutonium. Furthermore, an investigation of minor actinide (MA) recycling based on the HC-FLWR core concept has been performed and is presented in this paper. Because HC-FLWR is a near-term technology, it would be a good option in the future if HC-FLWR can recycle MAs. In order to recycle MAs in HC-FLWR, it has been found that the core design should be changed, because the loaded MA makes the void reactivity coefficient worse and decreases the discharge burn-up. To find a promising core design specification, the investigation on the core characteristics were performed using the results from parameter surveys with core burn-up calculations. The final core designs were established by coupled three dimensional neutronics and thermal–hydraulics core calculations. The major core specifications are as follows. The plutonium fissile (Puf) content is 13 wt%. The discharge burn-up is about 55 GWd/t. Around 2 wt% of Np or Am can be recycled. The MA conversion ratios are around unity. In particular, it has been found that loaded Np can be transmuted effectively in this core concept. Therefore, these concepts would be a good option to reduce environmental burdens.     

Kinetics of the carbothermic reduction of a ThO2 + UO2 + C mixture to prepare (Th,U)C

Carbothermic reduction of mechanically mixed ThO₂ + UO₂2 + C compact to (Th, U)C has been studied in the temperature range between 1743 and 2043 K with emphasis on reaction kinetics. The rate-limiting step of this reaction was attributed to the diffusion of CO gas in the outermost layer of the reaction products. By X-ray diffraction, ThO₂ and UO₂ were found to react with graphite respectively to produce two nearly separate dicarbide phases, both of which then reacted with residual ThO₂ to form a monocarbide phase. An apparent activation energy of about 320 kJ mol⁻¹ was obtained for this carbothermic reduction. Such a high activation energy can be explained by the CO gas diffusion through micropores in that product layer, by taking into account the standard enthalpy changes of the related reactions to produce CO gas.     

LD泵浦的Nd:YLF激光放大技术

从理论模拟和实验两方面对环形 LD 泵浦的 Nd:YLF 激光放大系统进行了研究。激光放大系统采用离轴双程放大结构。实验结果表明:系统在注入能量为 150 μJ,放大输出为 109 mJ 时,系统净增益为 1115;采用环形 LD 紧密泵浦的 Nd:YLF 激光放大器,有效地提高了二极管的转换效率,在 1053 nm 处,获得了 1.01 J 的振荡输出。     

Precipitation of Thorium or Uranium(VI) Complex Ion with Cobalt(III) or Chromium(III) Complex Cation, (III)

Chloride ion (foreign ion) effect on the precipitation of thorium or uranium (VI) sulfato, carbonato and oxalato complex ions has been studied. The results are in correlation with the chemical species present in the solution.

The precipitation of highly-charged complex ions is affected by chloride ion and the precipitation yield decreases with chloride salt concentration. The precipitation of sulfato complex ion shows only slight dependency on the chloride salt concentration because of the absence of highly-charged sulfato complex ion under the experimental conditions.     

Separation of Nd metal by using disproportionation reaction of Nd(II) in molten chlorides

In order to separate neodymium (Nd) from lanthanides in chloride melts, the electrochemical characteristics Nd ions in molten LiCl-CaCl₂ eutectic were studied. The formal redox potentials of the Nd³⁺|Nd²⁺ and Nd²⁺|Nd couples in molten LiCl-CaCl₂ eutectic at 823 K were determined to be −2.745 ± 0.005 and −3.081 ± 0.005 V vs. Cl₂|Cl⁻. Under the controlled potential electrolysis by applying negative potential to form Nd²⁺, Nd²⁺ was disproportionated to Nd³⁺ and metallic Nd fog according to the reaction; 3Nd²⁺ ? 2Nd³⁺ + Nd. When a quartz glass was immersed in the melt during the electrolysis, Nd was coated on the quartz surface. The chemical composition of the recovered Nd was analyzed to be Nd metal and Nd₂O₃ by scanning electron microscopy, X-ray diffractometry, and electron probe microanalysis. The same electrolytic method was carried out under the coexistence of Nd³⁺ and lanthanum ion (La³⁺). Nd³⁺ was separated from La³⁺ and recovered to be Nd₂O₃.     

A Nuclear Magnetic Resonance Study on Ligand Exchange Reactions in La(III), Nd(III), and U(VI) Nitrato Complexes with n-Octyl(pheny1)-N,N-Diisobutylcarbamoylmethylphosphine Oxide in Non-aqueous Solvents

The exchange reactions of n-octyl(pheny1)-N, N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in La(III), Nd(III), and U(VI) nitrate complexes with CMPO (La(III)-, Nd(III)-, and U(VI)-CMPO complexes) have been studied in CD₃COCD₃ by means of ³¹P NMR method. The number of CMPO coordinated to the first coordination sphere of La(III) ion was directly determined to be 3 by the area integrations of ³¹P NMR signals of free and coordinated CMPO molecules. The same coordination number of 3 was also obtained for the U(VI)-CMPO complex. The coordination number was not determined for the Nd(III)-CMPO complex, because of its paramagnetic behavior. The exchange rate constants of CMPO in La(III)- and U(VI)- CMPO complexes were obtained by the two-site exchange model. Paramagnetic line broadening was observed in the Nd(III)-CMPO complex and the rate constant for the exchange of CMPO was determined by the line-broadening method. The exchange rates of CMPO in La(III)- and Nd(III)-CMPO complexes depend on the free CMPO concentration ([CMPO]), while that in U(VI)-CMPO complex is independent of [CMPO]. The dissociative (D) and dissociative interchange (I_d ) mechanisms were proposed for the exchange reactions in the La(III)- and Nd(III)-CMPO complexes, and dissociative (D) or I_d mechanism was proposed for the U(VI)-CMPO complex. The dissociative rate constants (s^?1) at 25°C and activation parameters ΔH^# (kJ·mol^?1) and ΔS^# (J·K^?1·mol^?1) are 4.76x10³, 28.7±0.1, ?78.4±0.2 for La(III)-CMPO complex, 4.72x10³, 42.6±0.4, ?31.7±1.3 for Nd(III)-CMPO complex, and 3.20x10³, 46.9±0.6, ?20.5±2.2 for U(VI)-CMPO complex, respectively.     

Economic Scale of Utilization of Radiation (III): Medicine

Our previous study revealed that the use of radiological technology in medicine was spreading in Japan. For example, in 1991, the economic scale was about 10b$ (billion dollars, 1$=121¥) corresponding to 4% of the national health expenditures (240b$) or 0.24% of the nominal GDP (gross domestic products, 4,231b$). This time, the economic scale was compared between Japan and the U.S.A. within limited parameters. (1) For the TDHE (total domestic health expenditures) base, it was 981b$ in the U.S.A. and 219b$ in Japan, implying that the American people spent rather much money for their health. (2) For the economic scale estimated by studying parameters (ESP), approximately 49b$ for the U.S.A. and 12b$ for Japan. ESP in the former is large in magnitude by a factor of 4, implying that U.S.A. people do not hesitate to use radiological technologies for curing their diseases. This tendency was clearly observed by the expenditures on prostate cancer and the FDG-PET and so on. (3) The ratio between ESP and GDP within the scope of this study was 0.6% for the U.S.A. and 0.3% for Japan. The use of medical radiology may be enlarged in the future due to its high quality of life (QOL).     

Applicability of dynamic programming to the accelerator-driven system (ADS) fuel cycle shuffling scheme for minor actinide (MA) transmutation

The accelerator-driven system (ADS) is under development in several countries to reduce the burden for conditioning and disposal of the high-level radioactive waste (HLW) by transmuting minor actinide (MA). It is expected that the fuel shuffling can make the power distribution flat and transmute MA effectively by using only one kind of fuel composition. But the total number of calculation cases becomes huge for finding the globally optimum case. In order to find the best shuffling scheme for MA transmutation by ADS, we attempt to develop a calculation code within an acceptable time by employing dynamic programming. It is used successfully for a cylindrical core with three fuel regions with 20 times of fuel shuffling.     

Precipitation of Thorium or Uranium(VI) Complex Ion with Cobalt(III) or Chromium(III) Complex Cation, (I)

The precipitation of uranium(VI) peroxo complex ion with both tris (ethylenediamine) cobalt (III) and tris(trimethylenediamine) cobalt(III) salts has been studied.

The precipitates obtained immediately are, respectively, [Co(en)₃]₄ [(UO₂)₂ (O₂)₄]₃nH₂O and [Co(tn) ₃]₄ [(UO₂)₂ (O₂)₃]₃nH₂O, which change to [CO(en) ₃]₄ [(UO₂)₂ (O₂)₂ (OH) ₄]₃nH₂O and [CO(tn) ₃]₄ [(UO₃)₂ (O₂)₂ (OH) ₄]₃nH₂O with time.

Carbonate ion affects the precipitation reactions by forming stable outer-sphere complex ion with cobalt (III) complex cation.     

Precipitation of Thorium or Uranium(VI) Complex Ion with Cobalt(III) or Chromium(III) Complex Cation, (II)

The precipitations of thorium and uranium(VI) sulfito complex ions with hexammine cobalt(III) chloride as the precipitant have been studied.

The orange-colored uranium(VI) precipitate obtained is [Co(NH₃)₆]₄[UO₂(SO₃)₃]₃22H₂O, which is in the form of square bipyramid, about 4 μm across in a cubic symmetry of the diamond type with a=10.40Å It decomposes to an oxide mixture of Co₃O₄ and U₃O₈ above 850°C in the air through a sulfate mixture of CoSo₄ and UO₂SO₄.

Composition of the thorium precipitate varies with the precipitation conditions. Therefore, it is considered that the thorium precipitate contains thorium hydroxide and basic thorium sulfite.     

Separation of Americium(III) and Europium(III) by thermal-swing extraction using thermosensitive polymer gel

Extraction separation of Am(III) and Eu(III) was examined by the thermal-swing extraction technique using a thermosensitive gel, poly-N-isopropylacrylamide (NIPA) crosslinked with a TPEN derivative, N,N,N′,N′-tetrakis(4-propenyl-oxy-2-pyridylmethyl)ethylenediamine (TPPEN). The separation of Am(III) from Eu(III) was observed in the swelling state of gel (5 °C) and the separation factor of Am(III) was evaluated as about 18 at pH 5.2. The distribution ratio of Am(III) was reduced to about 1/8 by the volume phase transition from the swelling state (5 °C) to the shrinking one (40 °C). These results suggest that Am(III) can be separated and recovered effectively from Eu(III) in nitrate aqueous solution by the thermal-swing extraction technique using TPPEN–NIPA gel. This technique is applicable to the MA partitioning process, which is one of the important chemical processes in the P&T technology.     

Radiolytic reduction of Am (VI) and Am (V)

We obtained the rate constants of the radiolytic reduction of Am O ₂ ²⁺ in perchloric, sulfuric, and nitric acids by determining the radiation yield of the reducing products. These values, combined with data on hydrogen peroxide yield, make it possible to evaluate the consumption of hydrogen radicals in the over-all reduction reaction. A mechanism is proposed for the radiolytic reduction of Am O ₂ ²⁺ and AmO ₂ ⁺ . The expression for the rate of Am O ₂ ⁺ reduction makes it possible to calculate the yields of hydrogen peroxide and hydrogen radicals in the solutions investigated.     

Electrochemical and thermodynamic properties of europium(III), samarium(III) and cerium(III) in 1-butyl-3-methylimidazolium chloride ionic liquid

Electrochemical behavior of trivalent lanthanides such as europium(III), samarium(III) and cerium(III) in 1-butyl-3-methylimidazolium chloride (bmimCl) was investigated by cyclic voltammetry and chronopotentiometry at platinum working electrode in the temperature range of 343-373 K. The cyclic voltammograms of these metal ions in bmimCl at Pt electrode consisted of quasi-reversible waves occurring at a cathodic peak potential of −0.769 V, −0.547 V and −0.558 V (vs. Pd, 373 K) were attributed to the reduction of Eu(III), Sm(III) and Ce(III) to their respective divalent states. A prewave observed in the cyclic voltammogram of Eu(III) represents the reduction of Eu(III) to Eu(II) adsorbed on Pt electrode. The diffusion coefficients of these trivalents in bmimCl were determined to be of the order of ∼10⁻⁸ cm² s⁻¹ by cyclic voltammetry and chronopotentiometry and the charge transfer rate constants (k_s) were determined to be of the order of ∼10⁻⁵ cm s⁻¹ by Nicholson method. The apparent standard potentials, E^0* (vs. Cl₂/Cl⁻), and some thermodynamic properties of reaction of LnCl₃ from LnCl₂ were determined and the results are reported in this paper.     

Investigations of neutronics of some (D,T)-driven experimental thorium hybrid blankets with actinide multipliers

An experimental fusion-fission hybrid research facility, known as LOTUS and located at the Swiss Federal Institute of Technology (EPFL), is nearing completion. The first series of experiments are likely to commence in early 1984. A whole series of neutronic investigations are already underway to assess the feasibility of experimentally testing various blanket concepts. The following analysis centers around the use of actinide wastes as multiplier for blankets with thorium oxide fuel. The multipliers considered are UO₂, AmO₂, and CmO₂. The limited size of the experimental cavity coupled with the bulky, sealed 14 MeV (D, T)-neutron generator recommends the setting up of blankets in slab geometry. The analysis encompasses the corresponding confinement geometry configurations also for the sake of perspective. It is found that the neutronic performance of thorium oxide hybrid blankets improves radically both from the standpoint of fissile fuel production and energy multiplication in the presence of transplutonium actinides. It is also reported that the specific activities of tritium and²³³Pa are adequate for good counting statistics.     

Synergistic extraction and separation of Am(III) and Ln(III) with HBMPPT-sulfoxide-HNO3-toluene system

1 INTRODUCTIONAmericiuxn is a typical transuredum element. The Chemical properties of Am(lll)are similar to that Of trivalent lanthanides, Ln(lll). The separation of Am(lll) froman(lll) represents one of the most difficult and twortant ploblems in the separationscien..[1-7]. Actinides (ill) overlap in size with Ln(lll) and thus two groups have sedlaxcharge-to-radius ratios. Choppin[61 considered that Am(lll) and Ln(lll) both ethbit"hard acid" Character and their interaction in solutio…     

Basic Characteristics of Centrifuges, (III)

A method of numerically integrating the Navier-Stokes equations is presented for axisymmetric compressible flows. A modified Newton's method is employed to determine the steady motion of gas in a rotating cylinder without the use of a time-consuming marching process with respect to time. A suitable form of the finite difference equations gives a computationally-stable integration with reasonable representation of the spatial characteristics of the flow. The method includes a Gaussian elimination procedure which consists of the transformation of the Jacobian matrix to a triangular matrix followed by the backward substitution. By using an auxiliary constant matrix algorithm, the method gives the solution within reasonably acceptable computation time.

As an example of the method, some features of solutions are presented for the steady flow of UF₆ gas in the centrifuges which have the openings for feed and withdrawal on the end plates.     

Studies of Actinium (III) in Various Solutions, (I)

A solvent extraction method using a mixture of 0.1M thenoyltrifluoroacetone and 0.1M tributylphosphate in carbon tetrachloride has been developed for the separation and purification of ²²⁸Ac in ²²⁸Ra solutions. The ²²⁸Ra was first purified by a preliminary extraction cycle. The ²²⁸Ac which had accumulated int his ²²⁸Ra fraction after the purification was separated and purified by a second solvent extraction cycle. Since commercially available ²²⁸Ra solution very often contains ²²⁶Ra, the γ-radioactive decay products of the ²²⁶Ra have to be carefully removed. The ²²⁸Ac thus prepared was found to be pure enough for use as tracer.     

The conversion factor of Keff to K3.7 in thermoluminescence dating

In the fine-grain TL dating the full α dose must be converted into the equivalent β dose.The conversion is finished by Keff-value,which is an effective α effectiveness.But the Keff can not be measured directly for each sample and only the external radiative efficiency K3.7 can be measured.In order to obtain the Keff a special study for the conversion factor of Keff to K3.7 has been made using the ultrathin TLD.The results show that the conversion factor of the TLD for archaeological samples is 0.847,which is in agrcement with calculated value 0.85.     

Theory of conversion electron Mössbauer spectroscopy (CEMS)

A theory of conversion electron Mössbauer spectroscopy (CEMS) including second order effects, i.e. secondary electron emission, and detection coincidence corrections has been derived. The theory is applicable to surface films containing any number of distinct layers. The partial spectra are given in terms of analytical functions of the Mössbauer parameters and the physical characteristics of each layer in the sample. Numerical results are compared to available experimental data.