Takao Tanosaki

Development of Low-Activation Design Method for Reduction of Radioactive Waste Below Clearance Level

Design methodology for reinforced concrete of nuclear power plants to reduce radioactive wastes in decommission phase has been developed. To realize this purpose, (1) development of raw materials database of cements, aggregates and steel bars on concentration of radioactive target elements, (2) trial production of low activation cements and steel bars based on the material database developed in (1), and (3) development of tools for estimation and prediction of the amount of radioactive elements in reactor shielding walls have been carried out. Radioactive analysis showed that Co and Eu were the major target elements which decide the radioactivity level of reinforced concrete from wide survey of raw materials for concrete (typically aggregates and cements). Material database for the contents of Co and Eu was developed based on the chemical analysis and radioactivation analysis. Upon the above survey and execution expreiment of concrete, six types of low-activation concrete are proposed for various radioactive portion in the plant. These concrete have a 1/10 – 1/300 rasioactivity compare to the ordinary concrete, which are assumed the concrete with Andesite aggregate and ordinary Portland cement. Baed on the above data base, it was clarified that the low activation cement would be successfully manufactured by adequate selection of raw materials. The prospect to produce the low-heat portland cement which would have a 1/3 radioactivity in comparison with conventioanl cements obtained by means of selection of limestone and natural gypsum. An attempte was carried out to produece low activation heavy-mortar which would have radioactivity below the clearance level when using at the radiation shielding wall of BWR. Characterization and optimization of consturction conditions with new additives have also been carried out. These two new raw materials for low-activation concrete are conducted in pre-manufacture size, and over the laboratry level. Boron added low-activation concrete are also carried out as extreamly high performance low-activation concrete. It was claryfied that the accurcy of calculation results of the radioactivity evaluation was very high compared to available benchmark calculation for the JPDR and commercial light water reactor. The specification of the mapping system for judging the activation classification was also developed by using the general-purpose radio activation calculation tool. This work is supported by a grant-in-aid of Innovative and Viable Nuclear Technology (IVNET) development project of Ministry of Economy, Trade and Industry, Japan.Copyright

DEVELOPMENT OF LOW-ACTIVATION REINFORCED CONCRETE DESIGN METHODOLOGY—I: MANUFACTURE OF LOW-ACTIVATION CONCRETE

Abstract Screening tests using several reactors were performed to select low-activation raw materials. The number of samples was about 1500. Detailed data were obtained on the concentrations of Co and Eu in low-activation aggregates, low-activation cements, low-activation additives, and low-activation B4C sands. After that, we manufactured various types (1/10, 1/20, 1/30, 1/50, 1/100, 1/300) of low-activation concrete. The term “1/10 low-activation” concrete denotes that the activity reduction rate to ordinary concrete is designed to be 1/10. By admixing with a boron content of ~1 × 1021/cm3, the total residual radioactivity reduction rates of low-activation concrete to ordinary concrete, in units of ΣDi/Ci (Di: concentration of radionuclide i, Ci: clearance level of radionuclide i cited from IAEA-RS-G-1.7), are estimated to range from ~1/300 to 1/10 000. It was concluded that most of the shielding concrete around the advanced boiling water reactor (ABWR) or the advanced pressurized water reactor (APWR) are classified below the clearance level of decommissioning by adopting some suitable types of low-activation concrete.

Development of Low-Activation Reinforced Concrete Design Methodology - II: Concrete Activation Analyses of BWR/PWR

Abstract A precise method for estimating residual radioactivity and decommissioning cost is indispensable when deciding whether to adopt low-activation material. For this precise estimation, accurate estimation of both the thermal neutron flux and the activation cross section of the structural material is necessary. We developed a new groupwise cross-section library that has ten thermal groups for SN transport calculation and activation calculation. These libraries are tested and used for advanced boiling water reactor (ABWR) and advanced pressurized water reactor (APWR) activation analyses.