•A new criterion for transmutation efficiency of MAs was introduced.•A new approach for loading MAs into SD-TMSR and SMSFR was introduced.•The transmutation efficiency of 241Am in both reactors was ...calculated by using SERPENT-2.•The on-line reprocessing technique was adopted during burnup.
Up to now no definite internationally recognized quantitative criterion of minor actinides (MAs) transmutation efficiency was worked out, although this would be highly desirable. The absolute and relative total mass reduction of MAs are completely inadequate because they ignore the accumulation of higher radiotoxic long-lived MAs from the transmuted nuclide. In the current work, we introduce a new criterion for transmutation efficiency of MAs in nuclear reactors and demonstrate its efficiency by comparing two molten salt reactors; the Single-fluid Double-zone Thorium-based Molten Salt Reactor (SD-TMSR) and the Small Molten Salt Fast Reactor (SMSFR). Our proposed criterion takes into account the mass of all useful actinides, short-lived MAs, and short-lived fission products (FPs). In contrast, the mass parameters calculate the reduction in the MAs mass regardless of the produced nuclides. We introduce a new approach to load MAs into both reactors. The proposed approach merges the advantages of both homogeneous and heterogeneous approaches. The overall change in the actinides and FPs mass during the irradiation has been calculated using direct SERPENT-2 calculations. The results show that the transmutation efficiency of 241Am (the prime isotope for the transmutation) in the SD-TMSR is much higher than in the SMSFR. After 1500 days of radiation, the transmutation efficiency reaches 82.6% for SD-TMSR, however, for SMSFR it reaches 52.5%.
We have observed a significant enhancement in the energy deposition by 25–
100
GeV
photons in a
1
cm
thick tungsten crystal oriented along its
⟨
111
⟩
lattice axes. At
100
GeV
, this enhancement, ...with respect to the value observed without axial alignment, is more than twofold. This effect, together with the measured huge increase in secondary particle generation is ascribed to the acceleration of the electromagnetic shower development by the strong axial electric field. The experimental results have been critically compared with a newly developed Monte Carlo adapted for use with crystals of multi-
X
0
thickness. The results presented in this paper may prove to be of significant interest for the development of high-performance photon absorbers and highly compact electromagnetic calorimeters and beam dumps for use at the energy and intensity frontiers.
Summary
The control of the reactor energy increases the reactor fuel cycle time. In this work, a new method has been investigated to control the reactor energy instead of traditional methods. ...SERPENT2 version 2.1.30 was used to investigate the possibility of using Zirconium rods as an energy regulator in the VVER‐1000. Zirconium rods were used as water displacers. The effect of different Zr rod diameter on the infinite multiplication factor (k∞) of the reactor and the fuel concentration at different fuel burnup steps has been analyzed. Larger fuel pitches have been investigated to increase the Zr rod diameter. The main safety parameters such as the void volume reactivity coefficients, the Doppler reactivity coefficients and the Moderator temperature coefficient have been studied at different fuel pitch and different Zr rod diameter. A comparison between the effect of Zr rods and boric acid on the reactor reactivity proved the efficiency of using Zr rods as reactivity regulation.
This paper investigates the possibility of using Zr rods in the VVER‐1000 to regulate its reactivity. The Zr rods work as a water displacers.The effect of Zr rods insertion on the main related safety parameters (void reactivity coefficient, Doppler reactivity coefficient and moderator temperature coefficient) is studied.
Currently, there is a lack of computer power to perform high-precision reactor core analysis. In full-scale simulation of nuclear reactor cores using the stochastic Monte Carlo method, there are a ...number of factors that increase the excessive computational load and make calculations difficult. Among them is the large flux attenuation, which can be observed in deep penetration problems. In order to improve the efficiency of Monte Carlo calculations, various reduction techniques are used, which make it possible to reduce the statistical uncertainty of the functional evaluation without increasing the number of simulated histories. This article is devoted to the study and testing of techniques for reducing the variance in the deep penetration problem. A test problem is formulated the solution of which will make it possible to demonstrate the possibility of using various techniques of nonanalog simulation. In order to determine the quantitative efficiency of variance reduction techniques, the FOM characteristic is considered, which is a function of the relative error in a flux estimate and the computational time of the simulation. The article deals with the techniques of nonanalog simulation implemented in the MCU and OpenMC codes. As part of the study, a module of the OpenMC code has been developed which makes it possible to automatically generate weight windows. It is shown that variance reduction techniques increase the calculation efficiency by several times. In particular, the weight window technique in OpenMC increased the efficiency of neutron flux estimation by seven times, while the number of simulated histories remained unchanged. The formulated recommendations can be used in the future for the calculation of full-scale models of cores of innovative nuclear reactors.
•A new approach compared to solid-fuel reactors for MAs loading was introduced.•The transmutation performance of 241Am and 237Np in the critical SD-TMSR was investigated.•The transmutation ratio was ...calculated using the SERPENT-2 Monte-Carlo code.•The on-line reprocessing and refueling was applied during burnup.
In the current work, we introduce a new approach compared to solid-fuel reactors to load the minor actinides (MAs) into the Single-fluid Double-zone Thorium-based Molten Salt Reactor (SD-TMSR). The proposed approach merges the advantages of both homogeneous and heterogeneous approaches. Among MAs nuclides, 241Am and 237Np are selected for transmutation due to their long half-life. We simulate two separate tanks; Pu + U tank and FPs tank. In this study, a tank is a right cylinder with a volume of 1.0 m3. The Pu + U tank is used to store Pu and U isotopes extracted from the central channel of the SD-TMSR. However, the FPs tank is used to store all fission products (FPs) produced from the transmutation process in the central channel. The overall change in the actinides and FPs mass during the irradiation has been calculated using direct SERPENT-2 calculations. The results show that the transmutation ratio of 241Am and 237Np reaches 98.5% and 93.2%, respectively after 1500 days of irradiation. We notice that the major isotope in the Pu + U tank is 238Pu. Under 241Am irradiation, our proposed approach offers ≈0.3kg of 238Pu after 1 year of operation. However, under 237Np irradiation, 2.5 times more 238Pu can be extracted after the same period of operation. The produced 238Pu can be used in the radioisotope thermoelectric generators (RTG, RITEG) and radioisotope heater units.
The long-lived minor actinides (MA); americium, neptunium, and curium are main contributors to the long-term radiotoxicity of used fuel. Thus, the transmutation of these MAs is considered as an ...alternative to direct burial. Until now, no unambiguous internationally recognized quantitative criterion for the effectiveness of MA transmutation has been developed, although this would be highly desirable. The absolute and relative decrease in the total mass of MA is completely inadequate, since they ignore the accumulation of higher radiotoxic MA from the transmuted nuclide. In this paper, we propose a new criterion for the efficiency of MA transmutation in nuclear reactors and demonstrate its efficiency when comparing two molten salt reactors; Single-fluid Double-zone Thorium-based Molten Salt Reactor (SD-TMSR) and Small Molten Salt Fast Reactor (SMSFR). In addition, the proposed criterion takes into account the mass of all useful MA, short-lived MA, and short-lived fission products (FPs). We present a new approach to loading MA in SD-TMSR and SMSFR. The total change in the mass of actinides and FPs during irradiation was calculated using SERPENT-2 Monte Carlo code. The results show that the transmutation efficiency of
241
Am (a major candidate for transmutation) in SD-TMSR is much higher than in SMSFR. After 1500 days of irradiation, the transmutation efficiency reaches 82.6% for SD-TMSR, but for SMSFR it reaches 52.5%.
The excess reactivity in WWER-type pressurized water reactors is compensated using strong neutron absorbers. This leads to useless neutron consumption and reduce the breeding ratio and fuel burnup. ...In this work, one of the methods of spectral regulation of reactivity margin for fuel burnup was considered, namely, variation of the water-to-fuel ratio by inserting hollow cylindrical zirconium rods between fuel elements in the fuel assembly. Calculations were performed for a thorium–uranium-233 fuel. The range of change in the water-to-fuel ratio was estimated as a function of the diameter of inserted hollow zirconium rods. A comparison was made with the results of similar calculations for a uranium fuel at equal (3.7%) weight concentrations of fissile isotopes. The concentrations of the raw and fissile isotopes in the fuel in both fuel cycles were studied. In the Th–U-233 fuel cycle, with decreasing water-to-fuel ratio, the coefficient of accumulation of fissile isotopes can reach 0.75. The changes in the concentrations of the fission products in both fuel cycles were compared. The fuel and moderator temperature coefficients of reactivity and the control rod worth were estimated at all the considered water-to-fuel ratios. The safety parameters in the Th–U-233 fuel cycle were better than those in the UO
2
fuel cycle. It was shown that, at equal weight concentrations of the fissile isotope in the fuel, the insertion of hollow zirconium rods in the UO
2
fuel cycle changes the reactivity over a wider range than in the Th–U-233 fuel cycle.
The Single-fluid Double-zone Thorium Molten Salt reactor (SD-TMSR) has a promising future. Inherent safety, liquid fuel, and possibility of online reprocessing and refueling are unique potentials of ...the SD-TMSR. In the present study, the Monte Carlo code Serpent2 has been chosen to model the full core of the SD-TMSR. In addition, online reprocessing and refueling has been modeled based on subroutine provided by Serpent2. During the burnup time (10 years), the total mass of the fuel inside the core has been checked and found to be almost constant. Furthermore, we controlled the reactivity by adjusting the feed rate of fissile and/or fertile materials. The change of Keff, breeding ratio, Th and U-233 refill rates with burn-up time have been investigated. Additionally, the build-up of U-233 during 10 years has been calculated.
The paper formulates the main problems associated with research on transmutation, which should be paid attention to by today's young researchers. The processes of production of hazardous nuclides ...during transmutation in reactor facilities are considered. The goals of transmutation and the choice of nuclides to be transmuted are discussed. The concept of radiotoxicity is explained as a measure of the radiological hazard of radioactive nuclides, based on the maximum permissible concentration of nuclides according to the IAEA standards. The problem of the formation of secondary radioactive nuclides in nuclear fuel during generation of neutrons for transmutation is discussed. The advantages and disadvantages of various methods of transmutation in nuclear installations are considered: inclusion of transmutable nuclides in nuclear fuel in fast reactors, transmutation in specialized thermal and fast transmutation reactor installations and ADS systems. The problem of accumulation of highly radioactive actinides in a transmutation facility during long-term transmutation and the problem of a potential hazard of the transmutation facility itself are discussed. The unacceptability of application of common-type power reactors for the transmutation of long-lived fission products is demonstrated.
The standard three-neutrino oscillation paradigm, associated with small squared mass splittings Delta m super(2) << 0.1 eV super(2), has been successfully built up over the last 15 years using solar, ...atmospheric, long baseline accelerator and reactor neutrino experiments. However, this well-established picture might suffer from anomalous results reported at very short baselines in some of these experiments. If not experimental artifacts, such results could possibly be interpreted as the existence of at least an additional fourth sterile neutrino species, mixing with the known active flavors with an associated mass splitting (ProQuest: Formulae and/or non-USASCII text omitted) >> 0.01 eV super(2) and being insensitive to standard weak interactions. Precision measurements at very short baselines (5-15 m) with intense MeV nu sub(e) emitters can be used to probe these anomalies. In this article, the expected nu sub(e) signal and backgrounds of a generic experiment which consists of deploying an intense beta super(-) radioactive source inside or in the vicinity of a large liquid scintillator detector are studied. The technical challenges to perform such an experiment are identified, along with quantifying the possible source- and detector-induced systematics and their impact on the sensitivity to the observation of neutrino oscillations at short baselines.
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