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[en] Highlights: •Burnup and power distributions at the end of long-term daily load follow can be estimated by simplified load follow schemes. •Constraints imposed on simplified schemes are equal energy production and equal cycle length. •Computation time of simplified schemes is reduced by factor of 29 times at least. •Maximum error in burnup distribution of simplified schemes is less than 16.8%. •Maximum error in power distribution of simplified schemes is less than 17.7%. -- Abstract: Simulation of Daily Load Follow Operation (DLFO) for a whole cycle has long computation time as well as tedious lengthy input files. The purpose of this study is to reduce the computation burden associated with long-term DLFO simulation by developing a Simplified Load Follow Scheme (SLFS) simulation that can reproduce the core characteristics of long-term DLFO simulation (reference scheme) at End of Cycle (EOC). To achieve this aim, the SLFS employs two constraints: energy production and cycle length must equal those of the reference scheme. The solution variables in a SLFS then becomes operation time and power level satisfying the two constraints. In this paper, low power levels of 50%, 63%, 75%, and a maximum power level of 100% are employed for the SLFSs. Operation times are determined to satisfy the two constraints for the given power level. The reference scheme in this paper employs OPR1000 Mode-K daily load follow scheme for the Small Modular Reactor (SMR). The results show the SLFSs can predict Core Radial Plane Burnup (CRPB) and Core Radial Plane Power (CRPP) distributions of a long-term DLFO with errors lower than 6% across the core height. Axial Offset (AO) and Control Element Assembly (CEA) critical height of the SLFSs are also comparable with the reference scheme with low errors of 1.5% and 4.5% respectively at EOC. The computational time of the simplified schemes is reduced by more than 29 times than that of the reference scheme. Single Control Element Assembly (SCEA) Ejection is simulated to validate the applicability of the simplified schemes. The SCEA ejection simulations also show CRPP distribution errors less than 6%. In conclusion, the SLFSs can be used to simulate long-term DLFO with marginal errors of less than 6%.
[en] Highlights: ► Summary of rationale and objectives of Partitioning and Transmutation R and D. ► Nuclear fuel cycle options and transmutation technologies (ADS in particular). ► Summary of main worldwide ADS research and technology development efforts. - Abstract: The paper summarizes the rationale and the objectives of Partitioning and Transmutation (P and T) research and technology development activities. It then provides overviews of both the various nuclear fuel cycle options and the transmutation technologies (with particular emphasis on ADS), as well as a brief worldwide summary of the main research and technology development efforts in the field of ADS
[en] Highlights: • Process monitoring can strengthen nuclear safeguards and material accountancy. • Assessment is conducted at a system-centric level to improve safeguards effectiveness. • Anomaly detection is improved by integrating process and operation relationships. • Decision making is benefited from using sensor and event sequence information. • Formal framework enables optimization of sensor and data processing resources. - Abstract: In this paper, we apply an advanced safeguards approach and associated methods for process monitoring to a hypothetical nuclear material processing system. The assessment regarding the state of the processing facility is conducted at a system-centric level formulated in a hybrid framework. This utilizes architecture for integrating both time- and event-driven data and analysis for decision making. While the time-driven layers of the proposed architecture encompass more traditional process monitoring methods based on time series data and analysis, the event-driven layers encompass operation monitoring methods based on discrete event data and analysis. By integrating process- and operation-related information and methodologies within a unified framework, the task of anomaly detection is greatly improved. This is because decision-making can benefit from not only known time-series relationships among measured signals but also from known event sequence relationships among generated events. This available knowledge at both time series and discrete event layers can then be effectively used to synthesize observation solutions that optimally balance sensor and data processing requirements. The application of the proposed approach is then implemented on an illustrative monitored system based on pyroprocessing and results are discussed.
[en] Highlights: • One-dimensional multi-channel approach is applied to predict the minimum point of pressure drop under non-uniform heating. • The pressure drop-mass flow rate curves between uniform and non-uniform heating are different. • In the single-phase flow, the pressure drop curve is the same for the uniform and non-uniform heat flux cases. • In the experiment, the pressure drop is abruptly increased after the minimum pressure drop is reached. • The predicted pressure drop curve is not matched well with the experiment after the minimum pressure drop. • For a better prediction, the flow regime effect in narrow rectangular channels should be considered. - Abstract: It is necessary to accurately predict the minimum point of pressure drop to ensure the safety of nuclear reactors. However, the non-uniform heat flux distribution along the transverse direction is encountered when the plate-type nuclear fuels are used. This study shows the effect of a transversely non-uniform heat flux on the minimum point of the pressure drop. The pressure drop-flow rate curve under the non-uniform heat flux was obtained by the experiment, and the trend of curve was different with the one of uniform heat flux case. Under the non-uniform heat flux, even when the inlet mass flow rate decreased, the value of the pressure drop was constant for a while with the development of a two-phase flow. With further reduction of inlet mass flow rate, the pressure drop started to decrease until the minimum point of the pressure drop was reached. Moreover, the inlet mass flow rate at the minimum point of pressure drop is much lower than that in the uniform heat flux case. For a detail analysis, the numerical approach is proposed along with the application of multi-channel concept. A single narrow rectangular channel is divided along the transverse direction, and the heat flux is given non-uniformly to the divided channels. Although the pressure drop is separately calculated for each divided channel, the mass is transferred between the channels. In the calculation, the mass flow rate is non-uniformly distributed in the transverse direction. If the mass flow rate is uniformly distributed, the non-uniform heat flux causes an unbalanced pressure drop because of the non-uniform distribution of void fraction. As a result, at the edges where the void fraction is high, the mass flow rate is transferred to the middle of channel to balance the pressure drop in transverse direction. When the void fraction in the middle becomes significantly large, the minimum point of the pressure drop can be obtained.
[en] A set of Stylized 3D Advanced High Temperature Reactor (AHTR) benchmark problems in full core and single fuel assembly configurations is developed in this paper. The configurations include the lower support plate, the bottom reflector, the fuel zone (AHTR assemblies), the top reflector, and the upper support plate. The benchmark problems retain the multiple heterogeneities and other important neutronics features such as the detailed geometric and material distributions of the Tristructural-Isotropic (TRISO) fuel and burnable poison particles, the fluoride salt coolant, the graphite moderator, and the reflectors. Monte Carlo results are presented for the benchmark problem in both the uncontrolled and controlled single assembly configurations. These benchmark problems can be used for evaluating the performance of neutronics codes.
[en] This review of the present status of actinide production and burn-up has been prepared in accordance with the action arising from the 21st meeting of the NEACRP in November 1978. The review covers topics such as the importance of actinides in the fuel cycle, revised U-Pu cycle LWR models, comparison of one-group cross sections for fast reactors, sensitivity analysis, experimental programme and depletion study. It rests on a basis of the discussion held at the meeting of the NEACRP in the past several years. Progress in the field of reactor physics related to the actinide production and burn-up is summarized and areas in which further work should be pursued are remarked on. (author)
[en] A procedure is described to evaluate the expected cost of spent-fuel management and decommissioning. Uncertainties in the cost database are treated by assigning probability densities to fuel-cycle cost items. The cost increases due to reactor and waste-management accidents are also included in the assessment. In the illustrative once-through case studied, the deterministic cost of 2.6 mill kWh-1 is increased up to 3.8 mill kWh-1 depending on the accident assumptions. The corresponding standard deviation would be 1.23 mill kWh-1. (author)
[en] A simple mathematical model is proposed and developed for the core criticality control by burnable poisons (BPs) distributed only throughout the peripheral region of the core while its central region remains free from BPs. The numerical burnup calculations confirm the effectiveness of the considered BP distribution for the criticality control of nuclear reactors. (author)
[en] Highlights: ► A second-order adjoint perturbation method is derived for time-dependent problems ► Second order perturbations can be computed with a set of additional adjoint solutions ► The method is applied to some classical initial value problems in reactor physics - Abstract: In this paper we discuss the application of second-order adjoint based perturbation techniques to linear and nonlinear time dependent problems. These techniques are based on the property of the adjoint problem which allows calculating the set of first and second order coefficients by solving a number of adjoint systems. The derivation of a second order adjoint theory that can be used to calculate the second order Taylor components of a functional response is first presented for nonlinear problems, and then reformulated for linear systems. This implementation is based on the Adjoint Sensitivity Analysis Procedure, originally presented by Cacuci. The theoretical part is followed by the application of the technique to some classical reactor physics problems: a fuel depletion calculation, a linear and a nonlinear point-kinetic problem. The results obtained using the second order theory are compared with the values obtained using a first order approximation and a direct solution of the forward problem. Our first results show that the procedure provides good estimations in presence of higher order perturbation components, being able to reconstruct the responses of interest even in presence of large perturbations. The main differences between linear and nonlinear formulations and their computational implications are also discussed
[en] Highlights: • We propose a new numerical solution of matrix exponential in burn-up depletion calculations. • The depletion calculation with extremely short half-lived nuclides can be done numerically stable with this method. • The computational time is shorter than the other conventional methods. - Abstract: Nuclear fuel burn-up depletion calculations are essential to compute the nuclear fuel composition transition. In the burn-up calculations, the matrix exponential method has been widely used. In the present paper, we propose a new numerical solution of the matrix exponential, a Mini-Max Polynomial Approximation (MMPA) method. This method is numerically stable for burn-up matrices with extremely short half-lived nuclides as the Chebyshev Rational Approximation Method (CRAM), and it has several advantages over CRAM. We also propose a multi-step calculation, a computational time reduction scheme of the MMPA method, which can perform simultaneously burn-up calculations with several time periods. The applicability of these methods has been theoretically and numerically proved for general burn-up matrices. The numerical verification has been performed, and it has been shown that these methods have high precision equivalent to CRAM