Study on the evaluation method of radioactivity for dismantling wastes generated from test and research reactors using ORIGEN attached to SCALE6.2.4

Tomioka, Dai; Kochiyama, Mami; Ozone, Kenji; Nakata, Hisakazu; Sakai, Akihiro

JAEA-Technology 2024-023, 38 Pages, 2025/03

JAEA-Technology-2024-023.pdf:1.54MB

Japan Atomic Energy Agency is an implementing organization of near-surface disposal for low-level radioactive wastes generated from research, industrial and medical facilities in Japan. Information on the radioactivity concentration of these radioactive wastes is dispensable for the design and conformity assessment of the waste disposal facilities for the licensing application of the disposal project and its safety review. Radioactive Wastes Disposal Center has been improving the radioactivity evaluation procedure for the dismantling waste generated from the research reactors based on the activation calculation. In order to investigate the applicability of the ORIGEN code (included in SCALE6.2.4), which enables more accurate activation calculations using multigroup neutron spectra, we performed activation calculations with the ORIGEN-code and the ORIGEN-S code (included in SCALE6.0), which has been widely used in the past, for the dismantled wastes from the Rikkyo University Research Reactor, where radioactivity analysis data for the structural materials around the reactor core were compiled. As a result, the calculation time difference between ORIGEN and ORIGEN-S was small and the evaluated radioactivity concentrations of the former were in the range of 0.8-1.0 times those of the latter, which was in good agreement with those of radiochemical analysis in the range of 0.5-3.0 times. The applicability of ORIGEN was confirmed. In addition, activation calculations assuming trace elements in structural materials of nuclear reactor were performed with ORIGEN and ORIGEN-S and the results were compared. The causes of the large differences among 170 nuclides that are important for dose assessment in near-surface disposal were assessed each nuclide.

Reactive-transport model analyses of bentonite alteration behavior at alkaline condition generated by cement-water interaction in a TRU wastes repository

Oda, Chie; Honda, Akira; Takase, Hiroyasu*; Ozone, Kenji*; Sasaki, Ryoichi*; Yamaguchi, Kohei*; Sato, Tsutomu*

Nendo Kagaku, 51(2), p.34 - 49, 2013/02

http://ci.nii.ac.jp/naid/110009594110

Proposed TRU repository designs for geological disposal envisage the use of a bentonite buffer to limit the migration of radionuclides by impeding groundwater flow. Under highly alkaline conditions due to cementitious materials could cause a complex series of coupled changes in the porewater chemistry, mineralogy and, ultimately, the mass transport properties of the bentonite buffer. To elucidate the consequences of these coupled changes, reactive-transport model analyses have been conducted for eight bentonite alteration test cases using different combinations of secondary minerals that could form in the bentonite buffer. It was found that after 100,000 years the amount of dissolved bentonite was at a maximum when metastable secondary minerals precipitated. It was also found that the diffusion and hydraulic coefficients after 100,000 years in all test cases were on the same order of magnitude as the initial values.

Evaluation of water infiltration considering impermeable sheets and other barriers in trench disposal facilities for research facility waste

Kitatani, Hikari; Nakata, Hisakazu; Ozone, Kenji; Sugaya, Toshikatsu; Abe, Daichi*

no journal, , 

In trench disposal facilities for research facility waste, radioactive materials in the waste layer migrate into the environment via infiltration water derived from precipitation, so reducing the volume of infiltration (leachate) water is required. The Japan Atomic Energy Agency (JAEA), as the implementing body for the disposal of research facility waste, is examining the application of a shallow land disposal facility and is considering an enhanced-function trench disposal facility in which an impermeable barrier - consisting of an impermeable sheet, a drainage layer, and a low-permeability clay layer - is installed around the waste layer. Because the service life of the impermeable sheet is estimated at 50 to 100 years, it is necessary to understand how a decline in barrier performance due to long-term degradation affects the infiltration water volume. This presentation reports the results of evaluating, using the one-dimensional flow analysis HELP (Hydrologic Evaluation of Landfill Performance) code, the effect of the barrier's impermeability performance on the infiltration water volume from the disposal facility. The analysis model comprised an impermeable sheet, a drainage layer, and a low-permeability clay layer above the waste layer, together with double impermeable sheets below the waste layer. A parametric study was conducted by setting the impermeable sheet's subgrade contact condition and defect count, and the hydraulic conductivities of the drainage and clay layers, at multiple stepwise levels. The infiltration water volume of a stable-type trench disposal facility without an impermeable sheet (35 mm/y) was used as the reference value, and parameter conditions under which the infiltration water volume would not exceed this reference value, even after long-term degradation of the barrier, were examined. The results showed that when the impermeable sheet's installation condition was perfect or very good, the infiltration water volume did not exceed the reference value (35 mm/y) under any of the parameter combinations examined. In contrast, when the installation condition was good or defective, the infiltration water volume exceeded the reference value once the clay layer's hydraulic conductivity exceeded 1.010 m/s. These results confirm that, when the impermeable sheet is in good condition, a low infiltration water volume can be maintained regardless of the permeability of the clay layer, whereas once the sheet degrades, the clay layer's permeability becomes the dominant factor governing the infiltration water volume. These findings demonstrate that the present findings can serve as a guideline and an indicator for designing the impermeable barrier in consideration of its performance under degraded conditions, and for managing the hydraulic conductivity during construction of the barrier.

Development of a generative AI-based PR support and technical information management system for the near surface disposal of low-level radioactive waste

Niizato, Tadafumi; Okamura, Tomohiro*; Ozone, Kenji; Nakase, Masahiko*; Saito, Tatsuo; Oi, Takao; Kamei, Gento

no journal, , 

Near surface disposal of radioactive waste from research facilities etc. is urgent in Japan. Originating from diverse sources, the project spans over 300 years, demanding consensus-building and knowledge transfer across generations. Challenges include managing vast technical documents, rapid information extraction, preventing knowledge loss, and public accessibility. A RAG system integrating a knowledge database with an LLM was adopted for accurate retrieval and natural language responses. The RAG chat system supports technical Q&A and drafting. A comprehension-support AI agent aids consensus-building. The Inventory Assessment Support System automates dose calculations and builds surrogate models. To mitigate hallucination, responses include source citations and reliability scores. Expert verification is incorporated, and AI outputs are reference only. Development proceeds in phases: prototype construction, then database expansion. Advanced RAG and multimodal capabilities will be explored.