Design and safety evaluation of the Japanese fusion reactor DEMO with system simulations

Nuclear fusion ・ DEMO reactor ・ TRACE ・ Vacuum Vessel ・ Thermal hydraulic analysis

We are conducting safety design and simulation on fusion reactors as a next-generation energy source. We model the safety components in fusion reactors for the simulation with the TRACE code. The representative scenarios of the Japanese DEMO reactor are (1) accidental leak in the vacuum vessel, (2) pressure and temperature transients in the reactor, and (3) loss of power in the residual heat removal system of the vacuum vessel. We gain physics behind these transient and accident simulations and confidence in the safety of the reactor.

R&D for Offshore Floating Nuclear Power Plant

Floating Nuclear Power Plant・ Rocking ・ Surge ・ Heave ・ Reactor response evaluation

The offshore floating nuclear power plant is one of the next-generation nuclear reactor concepts, which is being developed in a project of the Council on Competitiveness-Nippon (COCN). We model the reactor components with TRACE code to simulate the floating reactor response for oscillating and tilting conditions. In particular, we demonstrate BWR5 simulation at the rated condition for various heaving conditions with thermal-hydraulic and neutronic feedback (void feedback). We have also developed countermeasures against sloshing with immersed obstacles with TRACE simulations and sensors to acquire the wavy motions.

Development of measures to improve cooling limits

IVR, 3D printer, additive modeling, boiling cooling, critical heat flux

Porous heat transfer plates made of specially shaped alloys that can withstand the enormous heat loads (large CHF) generated by nuclear reactors, fusion reactors, and high-power lasers have been fabricated by 3D printers, and their performance has been evaluated through experiments and analysis. Recent studies have shown that the cooling limits can be further improved by installing a chimney structure.

Development of micro-scale droplet control method

Micro Channel ・ Computational Fluid Dynamics・ Micro Droplet Control

We are developing a micro-scale micro-droplet control method for less-harmful chemical reactions of radioactive materials. There is a demand to control droplets' separation, coalescence, and formation behavior on a smaller scale. In this study, droplet generation into a single-micron scale (a few micrometers) is achieved through CFD simulations and experiments.

Multidimensional Thermal-Hydraulic Analysis
(Elucidation of temperature stratification mechanism)

Fuel pool, PIV, temperature stratification, simulation

We are investigating the mechanism of thermal stratification in a spent fuel pool to cope with a long-term power outage. When thermal stratification occurs, the evaporation of cooling water becomes significant. The working environment may be degraded. Therefore, we are trying to prevent the water level from dropping by using methods such as placing an oil film on the water surface. In our experiments, we use particle image velocimetry (PIV) and thermography to analyze the tank's temperature and flow velocity changes.

Sloshing Simulation
(Floating nuclear power station)

TRACE, Dam Break, Floating nuclear power station, Simulation, CFD, Sloshing

We have been investigating the flow dynamics, such as sloshing of a water pool in a floating nuclear power plant when subjected to shaking due to high waves. Floating nuclear power plants have the advantage of generating power in areas far from urban cities. In addition, they can move to a distant location even when topographical risks such as active faults or submarine volcanoes are discovered. Sloshing simulations with the system analysis code TRACE and CFD to be validated against experimental results for the safety of floating nuclear power plants.

Inspection of reactor internal structures from outside the vessel using ultrasonic phased array

Experiment, Analysis, Ultrasonic phased array, Nondestructive inspection, Deep learning

We are developing a method to inspect the reactor internal structures without opening the vessel, using ultrasonic phased array. This will improve the maintenance of equipment installed in sodium, shorten the inspection time, and reduce the load on the reactor internal structures.

Non-contact laser measurement Predictive Maintenance Method for Rotating Machines

Experiment, Analysis, Laser Displacement Transducer, Non-contact Predictive Maintenance Method, Deep Learning

We are developing a method to diagnose the predictive maintenance of rotating machines such as turbines used in power plants by using non-contact laser displacement meters with machine learning. Non-contact measurement can reduce the cost and labor required for installation and maintenance. Since the data is prone to noise, it can be analyzed using classification learning and deep learning to predict failures.

Simultaneous measurement of temperature and velocity fields using a fiber-optic thermometer simultaneous measurement of temperature and velocity fields

Experiment, Fiber-optic thermometer, Velocity field measurement

We are developing a method to measure both temperature and velocity fields with high temporal and spatial resolution using an optical fiber thermometer in the same device. By pulsed heating of a gold-coated optical fiber, we can measure the temperature and velocity fields simultaneously by correlating the time variation of the flow velocity and temperature.

Development of a temperature and velocity field measurement system using PIV and LIF

Experiment, Analysis, Computational Fluid Dynamics

To better understand thermal stratification phenomena in spent fuel pools of nuclear power plants, we are developing models for computational fluid dynamics (CFD) simulations by measuring temperature and velocity fields based on particle image velocimetry (PIV) and laser-induced fluorescence (LIF).

Development of an AI-based sodium leak detection method for fast reactors Leak Detection Method Using Macine Learning

Macine Learning・Experiment・Analysis・Predictive Maintenance

We are developing a technology for early detection of sodium leakage in steam generators of fast reactors. In this study, bubbles are generated in a loop that simulates a steam generator, and supervised learning of vibration data obtained from lasers and accelerometers from outside the vessel is used to detect the occurrence of an accident at an early stage.

Development of Placement Algorithm for Spent Fuel Storage Pools

Macine Learning・Analysis・Mathematical Algorithm

We are developing an algorithm to study the placement of fuel using reinforcement learning and linear programming. Fuel is heated by decay heat, so it is submerged in a water pool for storage. In order to improve cooling in the pool, we design the fuel so that the fuels with relatively high decay heat are not placed next to each other.

Creating microchannels for radioactive material diversion Microfluidic channel creation


In the nuclear fuel reprocessing process, it is important to obtain chemical reaction rate data such as solvent extraction. When handling highly radioactive solutions, a microreactor can be used to obtain transfer coefficients and other data for design purposes in a safe and efficient manner. In this study, we will develop a microdroplet generation technique in a microreactor.

Development of next-generation sensors using materials chemistry

Experiment・Curie Temperature・PTC Material・Sensor

We are developing PTC thermistors with radiation resistance as a new means of measuring the core outlet temperature of nuclear reactor (PWR) coolant. In this research, we are developing PTC thermistors with high Curie temperature (the point at which the resistance changes significantly) by adding new materials to the existing PTC materials.

Research on high performance heat transfer plates using additive manufacturing technology

Experiment・IVR・3D Printer・CHF

We use 3D printers to create porous heat-transfer plates made of specially shaped alloys that are resistant to the enormous heat loads (large CHF) generated by nuclear reactors, fusion reactors, and high-power lasers, and evaluate their performance through experiments.

Toward Ultimate Boiling Cooling

Experiment・Image Analysis・CHF・Computational Fluid Dynamics

By analyzing the growth and flow of bubbles in images, we can find the optimum flow structure for reactor design. By accurately grasping the movement of bubbles, it is possible to understand the critical power at which the cooling water dries up and make use of this information in design.

Utilization of topology by 3D modeling

3D printer・Digital Twin・Scale Effect・Topology Optimization

We are developing a digital twin technology that combines scalable experiments (3D printers) with integrated measurement and control, and simulation. The 3D printer is used as a substitute for molds and other containers. Digital twin in this research refers to a system that makes experiments and analysis compatible with only one design.

Suppression of evaporation of fuel pool water

Experiment・Safety Measure・Spent Fuel Pool

We are devising and experimenting with a method to control the evaporation of cooling water in the reactor fuel pool. We are developing measures to automatically reduce the evaporation of water and suppress the rise in temperature and humidity in the building when the power supply is lost, as in the case of the Fukushima Daiichi Nuclear Power Plant accident.

Turning carbon dioxide into a resource

Electrochemistry・Catalyst・Organic Synthesis

We are developing catalysts to recycle carbon dioxide into valuable and much-needed resources (such as ethylene). Carbon dioxide can also be used for burial deep underground to prevent global warming.

Plant diagnosis by time series analysis

Noise Analysis・Macine Learning・Plant Condition Diagnosis・Predictive Maintenance

Deep learning and time-series analysis can be used to determine the status of a plant from minute vibrations that appear to be noise. We can predict abnormalities in plants even from small signals.