In order to refine the 3D finite element model, it is important to verify the correspondence to the seismic observation behaviors. In this study, we analyze the basic response characteristics, such as the natural frequencies and modes of the reactor building, and evaluate the effects of the amplitude of the seismic excitation on the response characteristics based on seismic observation records.

Biofilm formation and the establishment of an aerobic environment on EDZ fractures in Deep Neogene Sedimentary Rock have been observed. This aerobic environment is suggested to be formed by microbial production of dark O2.

This article shows an overview of the Country-Specific Safety Culture Forum Japan in 2024 and summarizes the major findings from having participated in it.

NRA analyzed the results of the heating test on flame-retardant electrical cables made of thermoplastic (TP) and thermosetting (TS) materials (i.e., TP/TS hybrid cable), recently conducted by University of Tsukuba to improve the knowledge of the electrical insulation performance of cables under elevated temperature conditions caused by nearby fires.

NRA has conducted a joint research program with the University of Tokyo to clarify how the pore sizes affect the adsorption reactions of different ions.

A system analysis code AMAGI (Advanced Multi-fluid Analysis code for Generation of thermal-hydraulic Information) has been developed as a best estimate code from its basic design. In the calculations using AMAGI on the void fraction experiments, technical knowledge was obtained on the differences between the AMAGI and TRACE models for each phenomenon and their impacts on the results.

Severe accident code, AZORES, is coupled with plant dynamics code for SFRs, ADYTUM. Accident progression between coupled and single AZORES simulations differs significantly.

Clearance measurement should be performed as a conformity assessment of the evaluated contamination values to the regulatory limit, considering the measurement’s uncertainty, including the uncertainty of the ratio of the activity concentration of the difficult to measure nuclide to that of the key nuclide. The key issues for the treatment of these uncertainty were summarized.

NRA Secretariat experts developed an empirical method for estimating source vicinity ground-motion levels on hard bedrock and annual exceedance probabilities for inland crustal earthquakes with sources difficult to identify in advance.

NRA conducted tube burst tests and post-test analyses on high-burnup spent nuclear fuel claddings to investigate the condition for the occurrence of macroscopic hydrogen-induced ductile-brittle transition at operational temperatures with quantitative consideration of precipitated Zr hydrides' morphology.