Yoshikuni Shinohara

Acoustic detection of in-sodium water leaks using twice squaring method

Abstract The problem of detecting in-sodium water leaks in the steam generator of liquid metal fast breeder reactor has been studied by applying the Twice-Squaring method, originally developed for acoustic detection of sodium boiling. Through the performance tests using test data synthesized by mixing experimental leak noise with background noise from real steam generators, it was concluded that the present method can detect the leak noise with signal-to-noise ratio down to −20 dB.

Stochastic center manifold dynamics of limit cycle oscillation in power reactors and measures of nuclear reactor stability

Abstract We consider “stochastic center manifold dynamics” of a nuclear power reactor near the limit cycle oscillations in 2D phase space. The exact analytic expression of the generalized q -th order moments is obtained for the 2D probability density function of a nonlinear model in the complex normal form. A theory is presented for estimating the effective potential and the linear stability of nuclear reactor systems with the use of the q -th order moment. The relationship between the second order radial moment and the concept of the irreversible circulation is clarified. Applicability of this nonlinear theory to system identification with the use of the generalized moments, the irreversible circulation and the geometry of an effective potential is demonstrated for the power oscillations observed in the Phase-III experiment conducted in the NSRR.

Twice squaring method: Non-linear acoustic signal processing technique for real-time detection of sodium boiling

Abstract A new signal processing method, named the Twice-Squaring method, for acoustic detection of sodium boiling in liquid metal fast breeder reactor has been developed. It uses a relatively simple nonlinear signal processing technique in time domain, consisting of band-pass filtering and squaring of signal in two folds. Its advantage is that real-time detection can be realized using only simple analog circuits without any digital calculation. In the present paper, we describe details of this method and the results of evaluation tests performed for sodium boiling acoustic data from KNS-1 test rig and from BOR-60.

Qualitative analysis of nonlinear power oscillation in NSRR

Abstract The performance of the automatic control system of NSRR is investigated experimentally and theoretically in connection with the power oscillation. A subsystem in the automatic control system relevant to the onset of the power oscillation is determined, and it is found that the subsystem possesses nonlinearity. Although the detailed mechanism of the nonlinearity cannot be identified because of lack of signals measured inside the subsystem, the input and output signals imply that the nonlinearity is a sort of backlash. A simplified reactor dynamic model with backlash simulates the dynamics of the NSRR power oscillation.

Development of telerobotic manipulators for reactor dismantling work

This paper describes the amphibious electrical manipulators JARM-10, JART-25, JART-100, and JARM-25 which were developed in the programme of reactor decommissioning technology development carried out by the Japan Atomic Energy Research Institute. They are multi-functional light-duty (10 and 25 daN) and heavy-duty (100 daN) telerobotic manipulators which can be used for reactor dismantling work in hostile environments such as high radiation and underwater environments. Each manipulator can be operated in either a bilateral master-slave, a teach-and-playback, or a program control mode. By combining these modes appropriately, it is possible to perform various complex tasks of remote handling. The usefulness of these telerobotic systems for dismantling nuclear reactors has been demonstrated by the successful application of JARM-25 for remote underwater dismantlement of highly radioactive reactor internals having complex configurations of an experimental nuclear power reactor.

An experimental remote handling system

An experimental robotic remote handling system is described which has been constructed in order to investigate various engineering problems in advanced remote handling such as the man-machine interface, system control and communication. The device consists of a mobile and a control station. The mobile station comprises an electrical manipulator having seven degrees of freedom, a TV camera, a control sub-computer, a servo-control unit, radio transmitters and receivers, batteries, etc., which are mounted on a crawler-type vehicle. The control station is equipped with the master arm of the manipulator, radio transmitters and receivers, a TV monitor, a main control computer and its peripheral devices, etc. The manipulator can be operated in either a master-slave, a playback or a programmed control mode with the assistance of control computers. Communication between the mobile and the control stations is made using optical fibres or a radio link.

Development of Telerobotic Systems for Reactor Decommissioning, (III): Demonstration System

This paper describes the telerobotic system for reactor decommissioning in the scope of engineering demonstration of dismantling radioactive reactor internals of an experimental boiling water power reactor JPDR. The total system consists of a telerobotic manipulator system equipped with a multi-functional amphibious slave manipulator with a load capacity of 25 daN, a chain-driven transport system, and a computer-assisted monitoring and control system. Preceding to the application of the telerobotic system to actual dismantling operation, a mockup test was performed of dismantling the simulated reactor internals of actual-size by the method of underwater plasma arc cutting in order to study the performance of the telerobotic system in a realistic environment. The system was then successfully applied to dismantling the actual reactor internals according to the JPDR decommissioning program.

Development of Telerobotic Systems for Reactor Decommissioning, (I): Prototype Light-Duty System

This paper describes the prototype light-duty telerobotic system constructed as a cold test facility in the program of developing technology for robotic handling systems to be used for decommission...

Study on the goodness of system identification using multivariate AR modeling

Abstract In order to evaluate the goodness of system identification using a MAR modeling method, simulation study was performed using a hybrid computer. The simulated systems are low order feedback systems with independent Gaussian white noise sources. The test of system identification using MAR modeling method was performed for this simulation model. The results of the simulation study show that the MAR model gives correct estimates of power spectra of the output signals and gain factors of the transfer function between output signals. However, it will not necessarily give correct ones for the estimation of the cut-off frequencies of transfer functions for all sub-systems. The examples in which MAR modeling is applied to real reactor noise data to estimate transfer functions of the control system and the noise sources are also discussed.

Application of an AI Method to Optimal Reactor Control Problems

Since the development of mathematical theories and methods of optimization in the fifties such as the dynamic programming method by Bellman and the maximum principle by Pontryagin, a large number of analytical and numerical studies have been made on various optimal reactor control problems. One of the problems which were studied by many authors is optimal reactor shutdown control involving reactor poisoning, especially xenon poisoning.