QSE

Safety Engineering of Nuclear Systems
Nuclear Energy-Flow Environmental Engineering

Front Line Research
Evolving the study and development of materials to enhance the capabilities of "barriers" to confine nuclides based on an understanding of geosphere environments!

Expected mass generation of the low-level radioactive wastes

Radioactive waste is an unavoidable problem if we are to receive the ample benefits of nuclear energy. The radioactive waste produced by nuclear plants and nuclear fuel cycle facilities are roughly grouped into "high-level radioactive waste" and "low-level radioactive waste." High-level waste is often heard of in the media, like newspapers and television, but the amount of the low-level waste is much greater. All six nuclear power plants of Fukushima Daiichi Nuclear Power Plant will be decommissioned and it is expected that a huge quantity of the low-level radioactive wastes including metallic waste and concrete waste that accompanies the dismantling of the facility will be produced within a relatively short period of time.

Low-level radioactive waste is classified based on its radioactivities and other properties, to apply safe and appropriate disposal and handling methods.

  1. Low-level radioactive waste with relatively high level activity (such as control rods and the core internals): Intermediate depth disposal (transported to and buried in artificial structures constructed at 50-100 meters below ground)
  2. Low-level radioactive waste (liquid waste, filters, and expendables): Near-surface pit disposal (transported to a concrete storage facility and the entire facility is then buried at about 10 meters below ground)
  3. Extremely low-level radioactive waste (concrete and metal): Near-surface trench disposal (disposed in landfills a few meters below ground)

Natural barriers such as soil and geological formations and engineering barriers such as casing constructions and concrete structures are methods meant to protect the human environment from radioactive waste indefinitely. Therefore, an evaluation of integrity and stability of these barriers are essential.

Focusing on cement-based materials that absorb nuclides.

Now, we are focusing on Cement-based materials as chemical barriers to confine nuclides. At Niibori Laboratory, we noticed that "calcium silicate hydrate (hereinafter called C-S-H gel)," the main constituent of cement-based materials, absorbs cation and anion nuclides. Utilizing such interactions, the laboratory works on the development and evaluation of barrier substances (cement-derived secondary minerals) that further improve confinement capabilities. Considering geological environments, the properties of C-S-H gel to absorb nuclides might change according to groundwater influences (salinity in particular). Niibori Laboratory challenges itself to reveal the influential properties of C-S-H gel in transmutation, using an understanding of mass and heat transfer and chemical reactions of the geosphere environments which constitute the ground, with state-of-the-art devices for analyzation. The study of radioactive waste storage management must always consider the ultra-long term scale of radioactive half-life. It is a project that must take place over multiple generations and it is thus necessary to pass down the knowledge and skills. The research that the future depends on – that is the motto at Niibori Laboratory.

Front Line Research

Dynamic Behavior of Silicic Acid and Alteration of Underground Environment due to the Repository Construction

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