Masa-aki Ochiai

Effects by Sea Wave on Thermal Hydraulics of Marine Reactor System

This paper describes the experiments of the first Japanese nuclear ship ‘Mutsu’, to investigate the effects of sea wave on the thermal hydraulics of marine reactor system while cruising through various sea conditions. The experimental data were analyzed in time-domain by RETRAN-02/GRAV code. This code was modified so as to simulate the ship motion effect on reactor thermal hydraulics. The data were also analyzed in frequency domain by Blackman Turkey method for the calculation of the spectrum and response function. The experiments involving ship maneuvering were performed by cruising on different wave heights, as well as wave directions in the northern Pacific ocean. From the experiments, vertical acceleration due to ship motion was found to induce direct variation of water levels in the SGs and the pressurizer. The water level variations were largest in the head wave, but smallest in the following wave. On the other hand, the following wave caused greater variation of the reactor power when the feed back...

Development of In-vessel Type Control Rod Drive Mechanism for Marine Reactor

A highly reliable control rod drive mechanism (CRDM) installed inside the reactor vessel has developed for use of an advanced marine reactor. This CRDM contributes to compactness and simplicity of the reactor system, and it can eliminate the possibility of a rod ejection accident. The CRDM works in the high temperature and high pressure water—310°C and 12 MPa, the same atmosphere as the primary loop. Driving force is produced by a synchronous motor with the rotor of a permanent magnet, which has been developed. An innovative latch mechanism using separable ball nuts can latch the driving shaft connecting the control rod and de-latch it for scram. The rod position detector using a magnetostrictive wire type sensor on the principle of Wiedeman effect has been developed, accuracy of which is verified to have a detecting error within 1.2 mm. Ball bearings for thrust and radial supports in rotation have been developed to be capable of working under the high temperature water for a long period. Under condition of high temperature water, the performance tests on latching, de-latching, holding and vertical movement, and durability test were conducted to verify the design conditions. This CRDM can be applied to not only the marine reactor, but also to light water reactors, PWR and BWR.

A very small LWR installed in the underground in the city

Abstract The effective of the nuclear reactor as the source of heat supply is more expected considering that the energy demand will increase and that the energy consumption structure will convert in Japan. The output scale of such reactors is to be less than 300MWt from the limit of supply area. We are studying two types of such reactors. One is the system for district heat supply with a nuclear reactor MR100 type and the other is for heat supply in buildings with a cassette type nuclear reactor MR1. The conception of these nuclear reactors is originated from the marine nuclear reactor technology. They are of highly safety with passively safe system and highly load following ability.

Simulation of a marine nuclear reactor

A Nuclear-powered ship Engineering Simulation SYstem (NESSY) has been developed by the Japan Atomic Energy Research Institute as an advanced design tool for research and development of future marine reactors. A marine reactor must respond to changing loads and to the ship`s motions because of the ship`s maneuvering and its presence in a marine environment. The NESSY has combined programs for the reactor plant behavior calculations and the ship`s motion calculations. Thus, it can simulate reactor power fluctuations caused by changing loads and the ship`s motions. It can also simulate the behavior of water in the pressurizer and steam generators. This water sloshes in response to the ship`s motions. The performance of NESSY has been verified by comparing the simulation calculations with the measured data obtained by experiments performed using the nuclear ship Mutsu. The effects of changing loads and the ship`s motions on the reactor behavior can be accurately simulated by NESSY.