Study on the radioactivity evaluation method of biological shielding concrete of JPDR for near surface disposal

Kochiyama, Mami; Okada, Shota; Sakai, Akihiro

JAEA-Technology 2021-010, 61 Pages, 2021/07

JAEA-Technology-2021-010.pdf:3.56MB
JAEA-Technology-2021-010(errata).pdf:0.75MB

It is necessary to evaluate the radioactivity inventory in wastes in order to dispose of radioactive wastes generated from dismantling nuclear reactor in the shallow ground. In this report, we examined radioactivity evaluation method for near surface disposal about biological shield concrete near the core generated from the dismantling of JPDR. We calculated radioactive concentration of the target biological concrete using the DORT code and the ORIGEN-S code, and we estimated radioactivity concentration Di (Bq/t). For DORT calculation, the cross-section library created from the MATXSLIB-J40 file from JENDL-4.0 was used, and for ORIGEN-S, the attached library of SCALE6.0 was used. As a result of comparing the calculation results of the radioactivity concentration with the past measured values in the radial direction and the vertical direction, we found that the trends were generally the same. We calculated radioactive concentration of the target biological concrete Di (Bq/t), and we compared with the estimated Ci (Bq/t) equivalent to the dose criteria of trench disposal calculated for 140 nuclides. As a result we inferred that the except for about 2% of target waste could be disposed of in the trench disposal facility. We also preselected important nuclides for trench disposal based on the ratios (Di/Ci) for each nuclide, H-3, C-14, Cl-36, Ca-41, Co-60, Sr-90, Eu-152 and Cs-137 were selected as important nuclides.

Design study for impermeable function of trench disposal facility for very low level waste generated from research, industrial and medical facilities (Joint research)

Sakai, Akihiro; Kurosawa, Ryohei*; Nakata, Hisakazu; Okada, Shota; Izumo, Sari; Sato, Makoto*; Kitamura, Yoichi*; Honda, Yasutake*; Takaoka, Katsuki*; Amazawa, Hiroya

JAEA-Technology 2016-019, 134 Pages, 2016/10

JAEA-Technology-2016-019.pdf:8.25MB

Japan Atomic Energy Agency has been developing to design trench disposal facility with impermeable layers in order to dispose of miscellaneous waste. Geomembrane liners have a function that prevent seepage of leachant and collect the leachant. However, the geomembrane liners do not necessarily provide the expected performance due to damage generated when heavy equipment contacts with the liner. Therefore, we studied the impermeable layers having high performance of preventing seepage of leachant including radioactivity taking into account characteristics of low permeable materials and effect of multiple layer structure. As results, we have evaluated that the composite layers composed by a drainage layer, geomembrane liners and a low permeable layer are most effective structure to prevent seepage of leachant. Taking into account disposal of waste including cesium, we also considered zeolite containing sheets for adsorption of cesium were installed in the impermeable layers.

Outline of the disposal of very low level concrete waste in JAEA

Tsuji, Tomoyuki

no journal, , 

Japan Atomic Energy Agency (JAEA), who conducted the demonstration test on a safe dismantling of Japan Power Demonstration Reactor (JPDR) in Nuclear Science Research Institute, has been performing the safe demonstration test of near-surface disposal of very low level (VLL) concrete waste arising from JPDR dismantling. Approximately 1,700 tons of VLL concrete wastes were placed in a simple disposal facility, of which dimensions are 45 m16 m and 3.5 m in depth without any engineered barrier, and covered with soil of 2.5 m thickness. The safe demonstration test of near-surface disposal of VLL concrete waste consists of a operation stage (FY 1995-1996) and a management stage (FY 1996-2024). In the operation stage, radiation dose around the disposal facility was measured, and radioactivity concentrations in groundwater and soil were analyzed. After we proceeded the management stage of disposal, radiation monitoring was continued additionally for 3 years in the management stage. An inspection such as no outflow, crack and subsidence of the covered soil is conducted at once a week. The radiation monitoring data is planned to storage properly by management department until the finishing of management stage, and an inspection data is stored in accordance with the Act on the Regulation of Nuclear Source Material, Nuclear Fuel Material and Reactors.