Yasuo Nishizawa

Intelligent decision support systems for nuclear power plants in Japan

Abstract This paper describes the MITI (Ministry of International Trade and Industry) projects for decision support systems for NPPs in Japan. Main attention is paid to the new project of an advanced man-machine system for nuclear power plants, of which a conceptual design was initiated in 1984. Some of the aspects of the design and the outline of the prototype system are discussed.

On-line prediction of the power distribution within boiling water reactors

A method for on-line prediction of the power distribution within boiling water reactors has been developed. The prediction procedure consists of two parts: the first is to estimate the present traversing in-core probe (TIP) readings using local power range monitors (LPRM) readings, which is required to give the initial condition of the predictional calculation; the second is to predict the TIP readings after motion of a control rod. Results of numerical experiments show that the TIP readings are predicted, with reasonable accuracy, within a short computer time and a small core memory. It is felt that this method is suitable for on-line computer application.

Automatic Scheduling of Maintenance Work in Nuclear Power Plants

An automatic scheduling method for maintenance work in nuclear power plants has been developed using an AI technique. The purpose of this method is to help plant operators by adjusting the time schedule of various kinds of maintenance work so that incorrect ordering or timing of plant manipulations does not cause undersirable results, such as a plant trip. The functions of the method were tested by off-line simulations. The results showed that the method can produce a satisfactory schedule of plant component manipulations without interference between the tasks and plant conditions.

On-Line Test of Power Distribution Prediction System for Boiling Water Reactors

A power distribution prediction system for boiling water reactors has been developed and its on-line performance test has proceeded at an operating commercial reactor. This system predicts the power distribution or thermal margin in advance of control rod operations and core flow rate change. This system consists of an on-line computer system, an operators console with a color cathode-ray tube, and plant data input devices. The main functions of this system are present power distribution monitoring, power distribution prediction, and power-up trajectory prediction. The calculation method is based on a simplified nuclear thermal-hydraulic calculation, which is combined with a method of model identification to the actual reactor core state. It has been ascertained by the on-line test that the predicted power distribution (readings of traversing in-core probe) agrees with the measured data within 6% root-mean-square. The computing time required for one prediction calculation step is less than or equal to 1.5 min by an HIDIC-80 on-line computer.

Method for Evaluating the Local Variation of the Neutron Flux

One method of evaluating the local variation of the neutron flux is described. By regarding the variations in nuclear reactors such as control rod motion, fuel shuffling and refueling as disturbances added to the material buckling, a one-group diffusion equation is solved using the perturbation theory in one-dimensional geometry. This method is applied to an inhomogeneous reactor, which has already been disturbed, where the disturbances are approximated by a number of square pulses small enough for the method to be applicable. Good results are obtained with this method for disturbances equivalent to a reactivity of several percent. Discussion based on several examples are presented on the errors introduced by larger disturbances.

Method for detecting and removing interferences among maintenance tasks.

A method, based on AI techniques, has been developed for detecting and removing interferences among maintenance tasks in nuclear power plants. This method helps plant operators by adjusting the time schedule of the various tasks so that incorrect ordering or timing of plant manipulations does not cause undesirable results, such as a plant trip. This method consists of three main parts.(1) Checking for interference among tasks and plant conditions by analyzing effects of manipulating one component on other components.(2) Searching for a method to remove interference by isolating the problem component from the others.(3) Adding new operations and readjusting the time schedule by the branch and bound method.The performance of this method was checked by off-line simulation test. The result showed that the method can examine and remove the interferences among maintenance tasks.