Research Activities

Research Overview

 Further enhancement of nuclear reactor safety and safe and steady management of the radioactive wastes are most important issues for sustainable progress in nuclear energy. We are studying on fission product (FP) behavior in severe accident (SA) of light water reactor (LWR) for improvement of source term evaluation technology. We are also studying on nuclear fuels for transmutation of long-lived actinides (so called "minor actinides (MA)") included in spent nuclear fuels in the aspect of fabrication/reprocessing technologies, material properties, irradiation behavior, and resource recycling. Our research activities cover wide range of issues concerning high temperature science on fuel and FP materials, represented by characteristics of "fuel debris" for decommissioning of TEPCO’s Fukushima Daiichi Nuclear Power Station (1F).

Research on minor actinides containing nuclear fuel

 It is well known that most of MA nuclides contained in the high-level radioactive liquid waste (HLLW) are alpha-emitters with the long half-lives and/or large decay heat. From the viewpoint of mitigating the long-term toxicity of radioactive waste and the burden of final disposal of radioactive waste, an advanced fuel cycle with partitioning and transmutation (PT), in which MA are partitioned from HLLW and burnt in a transmutation system such as a fast reactor or accelerator driven system (ADS), has been investigated. Our group has been carrying out the R&D on the preparation of transuranium (TRU) compounds such as the oxide, nitride, chloride and alloy, the measurement of thermal properties, the fuel fabrication/pyrochemical-reprocessing technologies, and the evaluation of irradiation behavior in order to support the development of an advanced fuel cycle with PT.

Research activities related to MA-recycling

Research Output

• A breakthrough to realize the nuclear transmutation for reducing radioactive wastes -Opening of material property database for transmutation fuel which enables fuel performance analysis-
  

  To the Nitride Fuel Property Database, please click here.

Research Topics

• Developing a Database of Fundamental Properties for Partitioning and Transmutation -Evaluating Thermodynamic Data on Intermetallic Compounds with Electrochemical Techniques-
  
• Development of Database for a Practical Fuel Design -Formulation of Thermal Conductivity of Zr-Based TRU Nitride Fuels-
  
• Change in Fuel Microstructure Induced by Helium Accumulation and Release -Expansion and Annealing Correlation for Lattice and Bulk-
  
• Elucidating Thermal Change in Am-Containing Oxide Fuels -Investigation of Thermodynamic Properties of Nonstoichiometric Am Oxides-
  
• Demonstration of Excellent Thermal Properties of Minor Actinide Nitride Fuel -High-Quality Thermal Conductivity Data of MA Nitride Obtained from Small Samples-


• Toward High Recovery Yields of Pyrochemical Reprocessing for Minor Actinide Transmutation Nitride Fuels -Chlorination of Neptunium in Platinum Group Elements Compounds Without Using Corrosive Gases-
  
• Toward the Establishment of a Method for Treating MA Transmutation Fuels -Development of the Technology for Pyrochemical Treatment of MA Nitride Fuel-
  
• Toward the Evaluation of Minor Actinide Transmutation Fuel Behavior -Preparation of a High-Purity Curium Sample at the Milligram Scale-
  
• Toward Clarification of Minor Actinides Behavior in Pyrochemical Processes -Preparation of Minor Actinide Chlorides without the Use of Corrosive Gases-
  
• Preparation of Nitride Fuel in the Pyrochemical Reprocessing of Spent Fuel -Technological Development of Renitridation of Plutonium Recovered in Liquid Cathode-

Research on fission product behavior

 FP is released from nuclear fuel and transported from the reactor core to the Primary Containment Vessel (PCV) and Reactor Building (RB) under LWR severe accident. We have conducted systematic experiments and analyses in order to construct the dataset on FP chemistry and model of each elemental process as FP chemistry database named “ECUME”. ECUME will become a fundamental basis for improvement of source term evaluation technology.

Research activities related to chemical behavior of fission products in SA

Research Output

• Toward prediction of the radioactive material behavior in a nuclear reactor -Developing a database of cesium "chemistry" in a severe accident-
  

  Fission product chemistry database ECUME（version 1.1).

Research Topics

• Chemisorption of Cesium on Structural Materials during SA -Prediction and Verification of Thermodynamic Properties of Cesium Compounds-
  
• Estimation of Fission Product in a Light Water Reactor under a Severe Accident -Development of Fission Product Chemistry Database ECUME-
  
• Radioactive-Material Behavior during a Severe Accident -Evaluation of the Release and Transport of Radioactive Materials in a Reactor-
  
• Toward Estimating Characteristics of Radioactive Material Released in Severe Accidents -Experimental and Analytical Technologies for Evaluating Fission Product Chemistry in a Reactor-
  
• Behavior of Radioactive Cesium Deposited in the Nuclear Reactor -Investigation of Cesium-Deposition Behavior onto Stainless Steel-
  
• Prediction of the Characteristics of Radioactive Materials Released from Nuclear Fuel during Nuclear Power Plant Accidents -Evaluation of the Effects of Boron Released from BWR Control Rods on the Chemical Behavior of Fission Products-

Research on fuel debris

 Information on the properties of fuel debris is required for safe retrieval and storage of fuel debris formed during the 1F SA. Therefore, we fabricate simulated fuel debris by melting of uranium with core materials and concrete to acquire basic data on properties.

Research activities related to fuel debris

Research Topics

• How do Microscopic Particles of Debris Change in Water ? -To Understand the Chemical Effects of Hydrogen Peroxide and Boric Acid-
  
• What Has Formed from the Melted Fuel and Control Blade ? -Investigating the Characteristics of Solidified Core Melt-
  
• What Has Formed on the Fuel Debris Surface by Sea Water Injection ? -High-Temperature Reaction Products between Simulated Fuel Debris and Salt Deposits-