20,159 research outputs found
A Feasibility Study on the Transmutation of <sup>100</sup>Mo to <sup>99m</sup>Tc with Laser-Compton Scattering Photons
No full textThis paper evaluates the effectiveness of producing 99Mo using the photonuclear giant dipole resonance (GDR) (γ, n) reaction. The focus of the study is a novel implementation of the photonuclear transmutation method by the use of laser-Compton scattering (LCS) gamma-ray beams to produce 99Mo. The use of LCS enables the production of energetic and high-intensity gamma rays with a tunable energy spectrum based on various facility parameters (i.e., electron energy, laser energy, and collimation angle). The combination of these three features have made the use of the LCS process for the production of 99Mo using the photonuclear (γ, n) reaction a concept deserving further investigation. In this study, rigorous optimization of the LCS spectrum is performed to maximize the overlapping of the GDR cross section and the LCS spectrum to optimize the production rate and activity of the 99Mo product. Furthermore, the unique innovation of the multiple laser extraction concept is also included in this paper in order to increase the gamma-ray intensity by a factor of 10 to 20.
Physics conditions of passive autonomous frequency control operation in conventional large-size PWRs
No full textThe non-base load operation of nuclear power plants is expected to be unavoidable in future due to the increasing shares of the intermittent renewables. In this paper, the physics conditions required for a passively autonomous frequency control operation (PAFO) in a 3400 MWt conventional pressurized water reactor (PWR) design is investigated. The PAFO scheme allows a PWR to passively achieve the requested power maneuverability for primary and secondary frequency regulations on the electrical grid. This study is carried out for a conventional coolant system with a typical critical boron concentration, which yields a less negative coolant temperature coefficient (CTC) than that in a soluble-boron-free (SBF) core. The PAFO scheme is expected to be more challenging in the conventional PWRs than in an SBF small modular reactor, particularly for the secondary frequency regulation. This is mainly due to the weaker coolant reactivity feedback and the higher fuel temperature, which yields a stronger Doppler reactivity feedback during the passive power transients. Numerical simulations of PAFO are performed, for typical power ranges and power ramping rates required for frequency regulations, using a lumped PWR model that is solved by an in-house Fortran-95 computer code. In conventional PWRs, the progressive dilution of the soluble-boron throughout the cycle and the fuel depletion vary the reactivity coefficients. Therefore, we perform sensitivity analyses on CTC, FTC, and Xe worth to assess the feasibility of PAFO throughout the fuel cycle. In addition, sensitivity analysis on the fuel temperature is done to study its role in altering the reactor performance during PAFO.
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No full textThe present invention relates to a nuclear reactor, more precisely a passive safety device applicable to a thermal neutron reactor and a nuclear fuel assembly equipped with the same. The nuclear fuel assembly for a thermal neutron reactor of the present invention includes multiple fuel rods; multiple guide thimbles arranged between the fuel rods; and a passive safety device including neutron absorber parts which are inserted in one or more guide thimble
Convergence analysis of the nonlinear coarse-mesh finite difference method for one-dimensional fixed-source neutron diffusion problem
No full textThe convergence rates of the nonlinear coarse-mesh finite difference (CMFD) method and the coarse-mesh rebalance (CMR) method are derived analytically for one-dimensional, one-group solutions of the fixed-source diffusion problem in a nonmultiplying infinite homogeneous medium. The derivation was performed by linearizing the nonlinear algorithm and by applying Fourier error analysis to the linearized algorithm. The mesh size measured in units of the diffusion length is shown to be a dominant parameter for the convergence rate and for the stability of the iterative algorithms. For a small mesh size problem, the nonlinear CMFD is shown to be a more effective acceleration method than CMR. Both CMR and two-node CMFD algorithms are shown to be unconditionally stable. However, the one-node CMFD becomes unstable for large mesh sizes. To remedy this instability, an under relaxation of the current correction factor for the one-node CMFD method is successfully introduced, and the domain of stability is significantly expanded Furthermore, the optimum underrelaxation parameter is analytically derived, and the one-node CMFD with the optimum relaxation is shown to be unconditionally stable
A nodal and finite difference hybrid method for pin-by-pin heterogeneous three-dimensional light water reactor diffusion calculations
No full textAn innovative hybrid spatial discretization method is proposed to improve the computational efficiency of pin-wise heterogeneous three-dimensional light water reactor (LWR) core neutronics analysis. The newly developed method employs the standard finite difference method in the x and y directions and the well-known nodal methods [nodal expansion method (NEM) and analytic nodal method (ANM) as needed] in the z direction. Four variants of the hybrid method are investigated depending on the axial nodal methodologies: HYBRID A, NEM with the conventional quadratic transverse leakage; HYBRID B, the conventional NEM method except that the transverse-leakage shapes are obtained from a fine-mesh local problem (FMLP) around the control rod tip; HYBRID C, the same as HYBRID B except that ANM with a high-order transverse leakage obtained from the FMLP is used in the vicinity of the control rod tip; and HYBRID D, the same as HYBRID C except that the transverse leakage is determined using the buckling approximation instead of the FMLP around the control rod tip. Benchmark calculations demonstrate that all the hybrid algorithms are consistent and stable and that the HYBRID C method provides the best numerical performance in the case of rodded LWR problems with pin-wise homogenized cross sections
Feasibility of passive autonomous frequency control operation in a Soluble-Boron-Free small PWR
No full textNuclear power plants should be capable of contributing safely and flexibly to the electrical grid stability. This research deliberates the feasibility of a new innovative concept of a passive and autonomous frequency control operation (PAFO) in soluble-boron-free (SBF) pressurized water reactors (PWRs). The new concept eliminates any required active control in the reactor core for attaining primary and secondary frequency control operational modes in PWRs. In particular, control rods and soluble-boron are not utilized in a PAFO. Meanwhile, the reactor power maneuvering is achieved entirely by the passive reactor feedback to the coolant temperature change. This approach is motivated by the strongly negative coolant temperature coefficient available in an SBF coolant system. In order to ascertain judiciously the practical viability of the proposed concept, numerical simulations of passive primary and secondary frequency operations are performed using a lumped PWR system model solved by an in-house FORTRAN-95 computer code. The various simulation parameters are obtained from 3D Monte Carlo simulations of an SBF 450 MWt PWR by using Serpent-2 code with ENDF/B-7.1 data library. The numerical simulations are carried out at the beginning, middle and end of the fuel cycle to emphasize the effect of fuel bumup on the proposed PAFO. Moreover, sensitivity analyses on xenon worth and nominal fuel temperature are performed to deliberate their impacts in tailoring the reactor performance. Because the reactor power matches well with the power demand with a small variation in coolant temperature during the frequency control, we conclude that there is promising potential for the proposed PAFO concept. (C) 2018 Elsevier Ltd. All rights reserved.
Numerical design of a 20 MW lead-bismuth spallation target with an injection tube
No full textA spallation target system is a key component to be developed for an accelerator driven system (ADS). It is known that a 15-25 MW spallation target is required for a practical 1000 MWth ADS. The design of a 20 MW spallation target is very challenging because more than 60% of the beam power is deposited as heat in a small volume of the target system. In the present work, a numerical design study was performed to obtain the optimal design parameters for a 20 MW spallation target for a 1000 MWth ADS. A dual injection tube was proposed for a reduction of the lead-bismuth eutectic (LBE) flow rate at the target channel. The results of the present study show that a 30 cm wide proton beam with a uniform beam distribution should be adopted for a spallation target of a 20 MW power. When the dual LBE injection tube is employed, the LBE flow rate could be reduced by a factor of 7 without reducing the allowable beam current. (C) 2007 Elsevier B.V. All rights reserved
Optimization of the laser-Compton scattering spectrum for the transmutation of high-toxicity and long-living nuclear waste
No full textThe laser-Compton scattering (LCS) phenomenon is one known method for producing energetic and high intensity gamma rays with variable photon spectrums. Availability of high-intensity gamma rays has made probing the (gamma,n)-based photonuclear transmutation possible and worth consideration. Parametric studies of LCS have shown that the gamma ray's spectrum is tunable and dependent upon various facility-related parameters. In this paper, a systematic optimization study of the LCS spectrum has been performed in view of the incident laser energy, electron beam energy and collimation angle. This optimization has been done with the aim to maximize the transmutation reaction rates of long-living fission products (LLFPs) such as I-129,Cs-135, and Cs-137 that have an isotopic composition of typical LWR spent fuel. In addition, the (gamma,n) and (gamma,2n)-reaction rates have been simultaneously calculated in order to evaluate the feasibility of photonuclear transmutation using the (gamma,n)-reaction. It has been shown that careful optimization of the LCS spectrum noticeably enhances the (gamma,n)-reaction rate without requiring any isotopic separation of the iodine and cesium targets. Furthermore, in order to enhance the energy efficiency of the LCS-based photo-transmutation system, a novel multiple laser-Compton scattering extraction (MULEX) concept has been introduced in this work, and it has been shown that the total production of the LCS photons can easily be increased by a factor of 10 or 20 in a single accelerator system. (C) 2017 Elsevier Ltd. All rights reserved.
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