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BackgroundMicro-reactors can be used as a lunar surface power or spacecraft power source for space exploration. Before launching the reactor, a safety analysis should be conducted to prevent a launch accident. Currently, the safety analysis of the radioactive isotope power system does not fully include the safety analysis of the reactor. The main critical safety analysis scenario is that the reactor falls and hits the concrete ground from a high altitude. The reactor may return to criticality after high-speed impact.PurposeThis study aims to investigate the nuclear safety characteristics of a space reactor subjected to dynamic shock under high-speed impact conditions.MethodsFirst of all, based on internal and surface unstructured grids, two simplified reactor models corresponding to two high-speed impact scenarios, i.e., pure fuel reactor vertical impact with ground, and cylinder reactor with a reflector layer and shielding layer impact the ground at a 30° angle were established. Then, the ABAQUS finite element method and unstructured mesh Monte Carlo method of particle transport were combined to predict the criticality properties of the pure fuel and cylindrical reactor during high-speed impact. Based on the surface and internal unstructured mesh Monte Carlo transport technology, the criticality safety analysis platform of micro-reactor under high speed impact was established.ResultsThe results show that the keff induced by the deformation may increase with time for the above mentioned two simplified reactors. The maximum increase in the keff of the pure fuel reactor can reach 1 000×10-5, whereas for the cylinder reactor, the keff is improved to a maximum of 200×10-5. Considering the non-uniform density effect, reactivities of -666×10-5 and -132×10-5 are introduced into the two reactors.ConclusionsThe critical safety characteristics of the reactor under different impact conditions should be evaluated to ensure sufficient safety margins under such accident conditions.

BackgroundWhen fusion nuclear reactor is in operation, neutron activation causes a large number of radioisotopes. Activation calculation is a very important step in both of reactor shielding calculation and radiation safety analysis.PurposeThis study aims to develop the capability of transport-activation coupling calculation for fusion reactor based on the Monte Carlo code cosRMC.MethodsFirstly, the built-in burnup solver "Depth" of cosRMC was employed to develop transport-activation internal coupling calculation function under fixed source mode with embedded calculation of activation related nuclide single group reaction cross-sections in neutron transport process without the transmission of neutron spectra to external activation programs. Then, the developed code was applied to the activation calculations of the first wall (FW) material steel and plasma facing component (PFC) material tungsten of the Chinese Fusion Engineering Testing Reactor (CFETR) using continuous energy cross-sections and multi group cross-sections, respectively, and calculated results were compared and verified with that of the activation program ALARA.ResultsThe comparison results of activation calculation of FW steel and PFC tungsten in CFETR show the consistency between cosRMC-based internal coupling method and ALARA program, which preliminarily verifies the correctness of the transport activation internal coupling calculation function of the developed cosRMC program.ConclusionThe developed cosRMC-based internal coupling method can dynamically update neutron spectra and material information, and use continuous energy cross-sections for reaction rate calculation, obtaining reaction cross-sections related to the geometry and energy spectra of actual problems, thus accurately considering the influence of resonance zone nuclear cross-sections.

BackgroundFusion reactors have the characteristics of high neutron energy, large spatial scales, complex geometric structures, and large radiation attenuation gradients, which make nuclear design and analysis more challenging.PurposeThis study aims to verify the accuracy of the calculation of Monte Carlo code cosRMC on the material shielding effect in fusion reactor applications.MethodsTwo deep penetration benchmarks, i.e., FNS-Duct (Fusion Neutron Source Dogleg Duct Streaming) and FNS-W (FNS Clean Experiment on Tungsten Cylindrical Assembly) from the Shielding Integral Benchmark Archive Database (SINBAD), were taken for simulation study of the penetration behaviors of neutrons in models under different geometric shapes and materials. First of all, detailed cosRMC models was established based on benchmark experimental models, neutron flux spectra of detectors at different penetration depths in benchmark experiments were calculated using cosRMC. Then, the variance reduction technique of cell importance was applied to improving the accuracy of cosRMC in calculating deep penetration problems. Finally, neutron flux spectra calculated by cosRMC were compared with those calculated by MCNP5, as well as the experimental results of the benchmarks.ResultsThe comparison results show that the calculations of cosRMC conform to that of MCNP5 with relative deviations of less than three times the standard errors. Both calculation results match well with the experimental values.ConclusionsThe study verifies that cosRMC can be applied to shielding calculations of fusion reactors.

This work presents the mathematical/theoretical framework of the "nth-Order Feature Adjoint Sensitivity Analysis Methodology for Response-Coupled Forward/Adjoint Linear Systems" (abbreviated as "nth-FASAM-L"), which enables the most efficient computation of exactly obtained mathematical expressions of arbitrarily-high-order (nth-order) sensitivities of a generic system response with respect to all of the parameters (including boundary and initial conditions) underlying the respective forward/adjoint systems. Responses of linear models can depend simultaneously on both the forward and the adjoint state functions. This is in contradistinction to responses for nonlinear systems, which can depend only on the forward state functions since nonlinear operators do not admit bona-fide adjoint operators. Among the best-known model responses that depend simultaneously on both the forward and adjoint state functions are Lagrangians used for system optimization, the Schwinger and Roussopoulos functionals for analyzing reaction rates and ratios thereof, and the Rayleigh quotient for analyzing eigenvalues and/or separation constants. The sensitivity analysis of such responses makes it necessary to treat linear models/systems in their own right, rather than treating them just as particular cases of nonlinear systems. The unparalleled efficiency and accuracy of the nth-FASAM-L methodology stems from the maximal reduction of the number of adjoint computations (which are "large-scale" computations) for computing high-order sensitivities, since the number of large-scale computations when applying the nth-FASAM-N methodology is proportional to the number of model features as opposed to the number of model parameters (which are considerably more than the number of features). The mathematical framework underlying the nth-FASAM-L is developed in linearly increasing higher-dimensional Hilbert spaces, as opposed to the exponentially increasing "parameter-dimensional" spaces in which response sensitivities are computed by other methods (statistical, finite differences, etc.), thus providing the basis for overcoming the curse of dimensionality in sensitivity analysis and all other fields (uncertainty quantification, predictive modeling, etc.) which need such sensitivities. [ABSTRACT FROM AUTHOR]

Vibration problems have become one of the most important factors affecting robot performance. To this end, a terminal residual vibration suppression method based on joint trajectory optimization is proposed to improve the accuracy and stability of robot motion. Firstly, based on the characteristics of the friction nonlinearity due to joint coupling and physical feasibility of dynamic parameters, a semidefinite programming method is used to identify dynamic parameters with actual physical meaning, thereby obtaining an accurate dynamic model. Then, based on the result of the residual vibration time domain analysis, a joint trajectory optimization model with the goal of minimizing joint tracking error is established. The Chebyshev collocation method is used to discretize the optimization model. The dynamic model is used as the optimization constraint, and barycentric interpolation is used to obtain the optimized joint motion trajectory. Finally, industrial robot experiments prove that the vibration suppression method proposed in this article can reduce the maximum acceleration amplitude of residual vibration by 62% and the vibration duration by 71%. Compared with the input shaping method, the method proposed in this paper can reduce the terminal residual vibration more effectively and ensure the consistency of running time and trajectory. [ABSTRACT FROM AUTHOR]