Takashi Kiguchi

A Method for Generating a Control Rod Program for Boiling Water Reactors

The OPROD computer code has been developed to generate a long-term control rod program, a series of control rod patterns that optimize a cycle length within various operational constraints. In the algorithm, the optimization problem is decomposed into two hierarchies. In the inner loop, a time-invariant target power distribution is assumed, and a control rod pattern is determined so as to best fit the power distribution to the target within the constraints at each burnup step. The target is then improved in the outer loop to achieve a longer cycle length. The code consists of two major parts: a three- dimensional boiling water reactor (BWR) core simulator and MAP, the method of approximate programming. It readily generates a long-term control rod program of BWRs without trial search by core-management engineers. The OPROD has therefore facilitated prompt response to varying operating conditions and the investigation of a conflicting relationship between the thermal limitation and the cycle length. (auth)

Development of an advanced core analysis system for boiling water reactor designs

A core analysis system has been developed for the recent advanced designs of boiling water reactors. This system consists of a fuel assembly analysis code VMONT and a three-dimensional core simulator COSNEX. To cope with heterogeneous structures found in the recent high-performance fuel, VMONT employs a Monte Carlo neutron transport calculation method. COSNEX is based on a three-group nodal expansion method to treat spectral interactions among fuel assemblies. Both codes are vectorized to meet timing requirements as design tools. The analysis system is verified by the tracking of recent plant operations. Although the analyzed cores are highly heterogeneous in the multienrichment configuration, the system gives sufficient accuracy both in critical eigen values and thermal power distributions.

Knowledge Representation and Utilization for Optimal Route Search

A guidance method for route search with knowledge is developed by combining knowledge representation and utilization in the frame form with an enumeration algorithm. The knowledge-guided route search introduced is based on three key techniques: obstacle-adaptive spatial cells, direct and automatic application of routing knowledge to the path-finding process, and an extended maze routing algorithm.

Stochastic Fluctuation in a Uranium-Enriching Cascade Using the Centrifuge Process

The parameters of a uranium-enriching cascade, i.e., the cut and the separation factor, are considered to be fluctuating stochastically. The covariance matrices of the total uranium flow and 235UF6 flow were derived by the classical stochastic theory for evaluating the effect of stochastic fluctuations of these parameters to steady-state plant performance. Also the stationary random process theory is applied to the kinetic equations of the cascade, and the autocorrelation function of the 235UF6 flow and enrichment is derived for evaluating the time behavior of the plant performance caused by random fluctuation of these system parameters. Numerical values illustrate the response of product flow and enrichment to the fluctuations, which are both time independent and dependent, of the cut and the separation gain of stages and centrifuges. These data lead to a conclusion concerning the tolerances of centrifuge parameters and stage controllers.

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.

Optimization of boiling water reactor control rod patterns using linear search

A computer program for searching the optimal control rod pattern has been developed. The program is able to find a control rod pattern where the resulting power distribution is optimal in the sense that it is the closest to the desired power distribution, and it satisfies all operational constraints. The search procedure consists of iterative uses of two steps: sensitivity analyses of local power and thermal margins using a three-dimensional reactor simulator for a simplified prediction model; linear search for the optimal control rod pattern with the simplified model. The optimal control rod pattern is found along the direction where the performance index gradient is the steepest. This program has been verified to find the optimal control rod pattern through simulations using operational data from the Oyster Creek Reactor.

Man--machine communication system for boiling water reactor core management planning

A man-machine communication system has been developed for boiling water reactor (BWR) core management planning to provide a very flexible tool, which is complementary to automated optimization programs that maximize or minimize one particular performance index under certain constraints. A three-dimensional BWR simulator, which can cover a wide range of BWR operating conditions, has been developed and coupled with a graphic display serving as a main input-output controlling device. The system has been successfully applied to generate a long-term control rod programming of a BWR in which locally poisoned fuel assemblies are loaded. The time required for one cycle analysis is approximately 3 h, out of which the actual computation time is only 4 min with an average of three trials of rod pattern search per exposure step. The quick response (5 sec) and the visualized results on the screen are very helpful in understanding the complicated characteristics of the BWR core, and it is found that this kind of tool has a very great educational effect. A similar approach is expected to be applied in other fields such as core design and safety analysis, as well as in core management.

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.

Effective Use of Sensor Readings in On-Line Plant Monitoring and Its Application to Boiling Water Reactor Power Distribution Calculations

Effective use of the measured readings of sensors in on-line plant monitoring has been studied, based on an error theory. Both the measured reading and the calculated one, obtained by an analytical model of the plant, are treated as observed values, and the maximum-likelihood estimator is determined so as to minimize its mean-squared error. The difference between the estimator and the calculated reading is used to adapt the model to the current plant state and to increase accuracy of the calculated reading. The index of systematics, which indicates the mutual independence of the two observed values, has been evaluated to determine the step in the procedure where the above adaptation is to be inserted. The error-theory-based model adaptation procedure has been experimentally applied to boiling water reactor power distribution calculations, and its performance has been verified in simulation calculations at different core states and different numbers of in-core neutron monitors by evaluating the expected error of the calculated readings. Compared to the adaptation, which uses the measured readings instead of the estimator, the error is typically lowered by more than 2% and is less affected by the number of monitors.

Feasibility Study of Core Management System by Data Communication for Boiling Water Reactors

A core management system by data communication has been designed and proposed for more efficient operation of boiling water reactor (BWR) plants by faster transmission and centralized management of...