Takanori Sugawara

Sensitivity and uncertainty analysis for an accelerator-driven system with JENDL-4.0

A sensitivity and uncertainty analysis was performed for the accelerator-driven system (ADS) proposed by the Japan Atomic Energy Agency (JAEA) with the latest version of the Japanese Evaluated Nuclear Data Library (JENDL-4.0). Significant discrepancies have been found between the reactor physics parameters of JENDL-4.0 and those of JENDL-3.3. An analysis with the sensitivity coefficients showed that the major contributors to these discrepancies are the differences in the inelastic scattering cross sections of 206Pb and 207Pb, and the capture and inelastic scattering cross sections and ν value of 241Am. The uncertainty analysis with the JENDL-4.0 covariance data found that the covariances of the fission neutron spectrum of minor actinides (MAs) have a considerable impact on the uncertainties of the reactor physics parameters.

Conceptual Design Study of Beam Window for Accelerator-Driven System

The conceptual design study of the beam window of the spallation target is one of the critical issues in the R&D of the accelerator-driven system (ADS). In this study, the investigation to create a feasible concept of the beam window for the ADS was performed by changing the proton beam profile from the Gaussian distribution to the parabolic and the flat distributions. Detailed analyses were performed by considering the particle transport of protons and neutrons in the spallation target region, the thermal hydraulics of lead bismuth eutectic (LBE) around the beam window, and the structural strength of the beam window. The calculation results showed that the difference in the temperature between the inner and outer surfaces at the top of the beam window was reduced by changing the beam profile from the Gaussian to the parabolic and the flat distributions. By this reduction, in the parabolic case, the thermal stress at the top position was also reduced and the buckling pressure increased by about 20%. On the other hand, in the flat case, the thermal stress at the peripheral region instead of at the central position increased and the buckling pressure slightly deteriorated. The buckling mode was also changed in the flat case. From these calculation results and discussions, it was confirmed that all three cases, the Gaussian, the parabolic, and the flat, were feasible and it was concluded that the concept with the parabolic distribution would be the most feasible under the current ADS design condition.

Analytical Validation of Uncertainty in Reactor Physics Parameters for Nuclear Transmutation Systems

To confirm the reliability of calculated reactor physics parameters for the nuclear transmutation systems, the uncertainty deduced from the covariance data prepared in JENDL-3.3 is compared with the differences in the reactor physicsparameters in the Monte-Carlo calculation using different nuclear data libraries, ENDF/B-VII.0 and JEFF-3.1.1. The Accelerator-Driven System (ADS) and the Minor Actinide (MA)-loaded Fast Reactor (FR) are selected as the representative transmutation systems. The criticality and void reactivity of these systems are discussed. The results show that the uncertainties deduced from the JENDL-3.3 covariance data are smaller than the differences in the reactor physics parameters among the nuclear data libraries. The cause of this discrepancy is that the covariance data of main nuclides and reactions in JENDL-3.3 are smaller than the relative differences in the cross sections among the nuclear data libraries. It is required to verify the uncertainty of the reactor physics parameters by integral experiments and to discuss the uncertainty utilization for the nuclear design accuracy.

Validation of Pb nuclear data by Monte Carlo analyses of sample reactivity experiments at Kyoto University Critical Assembly

Sample reactivity experiments on the uncertainty analyses of Pb nuclear data are carried out by substituting Al plates for Pb ones at the Kyoto University Critical Assembly, as part of basic research on Pb–Bi for the coolant. Numerical simulations of sample reactivity experiments are performed with the Monte Carlo calculation code MCNP6.1 together with four nuclear data libraries JENDL-3.3, JENDL-4.0, ENDF/B-VII.0 and JEFF-3.1, to examine the accuracy of cross-section uncertainties of Pb isotopes by comparing measured and calculated sample reactivities. A library update from JENDL-3.3 to JENDL-4.0 is demonstrated by the fact that the difference between Pb isotopes of the two JENDL libraries is dominant in the comparative study, through the experimental analyses of sample reactivity by the MCNP approach. In addition, JENDL-4.0 reveals a slight difference from ENDF/B-VII.0 in all Pb isotopes and 27Al, and from JEFF-3.1 in 238U and 27Al. Based on these results, further experiments are needed to investigate the uncertainties of Bi isotopes with the use of the Pb–Bi and Bi plates.

Development of three-dimensional reactor analysis code system for accelerator-driven system, ADS3D and its application with subcriticality adjustment mechanism

ABSTRACT In order to perform the parametric survey for an accelerator-driven system (ADS) core with the subcriticality adjustment mechanism, a new calculation code system, ADS3D, was developed on MARBLE which is a comprehensive and versatile framework for reactor analysis. The application of ADS3D was also demonstrated on the neutronics design of ADS operated by control rod (CR) movement. Through the neutronics calculation, it was shown that the maximum proton beam current was decreased from 20.5 to 11.6 mA due to the switch from beam-operated to CR-operated core.

Sensitivity and Uncertainty Analyses of Lead Sample Reactivity Experiments at Kyoto University Critical Assembly

Abstract Sensitivity and uncertainty analyses of lead (Pb) isotope cross sections are conducted with the use of sample reactivity experiments at the Kyoto University Critical Assembly (KUCA). With the combined use of the SRAC2006 and MARBLE code systems, attempts are made to precisely examine the contributions of the reactions and energy regions of Pb isotope cross sections to reactivity based on the covariance data of JENDL-4.0. Moreover, the effect of decreasing uncertainty is discussed in terms of the accuracy of sample reactivity by applying the cross-section adjustment method to the uncertainty analyses. From the results of the sensitivity and uncertainty analyses, the reliability of Pb isotope cross sections, such as the Pb isotope covariance data of JENDL-4.0, is compared with the JENDL-3.3, ENDF/B-VII.0, and JEFF-3.1 libraries. Additionally, the numerical results reveal the applicability of the sensitivity and uncertainty analyses to the thermal neutron spectrum cores, such as the KUCA core, and demonstrate the improvement in the calculation results generated by the cross-section adjustment.

Reaction rate analyses of accelerator-driven system experiments with 100 MeV protons at Kyoto University Critical Assembly

ABSTRACT At the Kyoto University Critical Assembly, a series of reaction rate experiments is conducted on the accelerator-driven system (ADS) with spallation neutrons generated by the combined use of 100 MeV protons and a lead–bismuth target in the subcritical state. The reaction rates are measured by the foil activation method to obtain neutron spectrum information on ADS. Numerical calculations are performed with MCNP6.1 and JENDL/HE-2007 for high-energy protons and spallation process, JENDL-4.0 for transport and JENDL/D-99 for reaction rates. That the reaction rates depend on subcriticality is revealed by the accuracy of the C/E (calculation/experiment) values. Nonetheless, the accuracy of the reaction rates at high-energy thresholds remains an important issue in the fixed-source calculations. From reaction rate analyses, the indium ratio is newly defined as another spectrum index with the combined use of 115In(n, γ)116mIn and 115In(n, n′)115mIn reaction rates, and considered useful in examining the neutron spectrum information on ADS with spallation neutrons.