John A. Bernard

Use of a rule-based system for process control

A rule-based, digital, closed-loop controller that incorporates fuzzy logic has been designed and implemented for the control of power on the 5-MW Massachusetts Institute of Technology (MIT) Research Reactor under both steady-state and transient conditions. A comparison is made of the rule-based and analytic approaches. Differences in the division of labor between plant engineers and control specialists, the type of knowledge required and its acquisition, the use of performance criteria, and controller testing are discussed. The design, implementation, and calibration of rule-based controllers are reviewed, with specific examples taken from the completed work on the MIT Research Reactor. The possible role of rule-based technology in process control is evaluated. It is proposed that since rule-based systems are generally more robust than their analytic counterparts, they should be used both as backups to analytic controllers and as a means of improving the man-machine interface by providing human operators with the rationale for automatic control actions. >

Use Of A Rule-Based System For Process Control

A rule-based, digital, closed-loop controller that incorporates fuzzy logic has been designed and implemented for the control of power on the 5-MW Massachusetts Institute of Technology (MIT) Research Reactor under both steady-state and transient conditions. A comparison is made of the rule-based and analytic approaches. Differences in the division of labor between plant engineers and control specialists, the type of knowledge required and its acquisition, the use of performance criteria, and controller testing are discussed. The design, implementation, and calibration of rule-based controllers are reviewed, with specific examples taken from the completed work on the MIT Research Reactor. The possible role of rule-based technology in process control is evaluated. It is proposed that since rule-based systems are generally more robust than their analytic counterparts, they should be used both as backups to analytic controllers and as a means of improving the man-machine interface by providing human operators with the rationale for automatic control actions.<<ETX>>

The Fission Converter-Based Epithermal Neutron Irradiation Facility at the Massachusetts Institute of Technology Reactor

Abstract A new type of epithermal neutron irradiation facility for use in neutron capture therapy has been designed, constructed, and put into operation at the Massachusetts Institute of Technology Research Reactor (MITR). A fission converter, using plate-type fuel and driven by the MITR, is used as the source of neutrons. After partial moderation and filtration of the fission neutrons, a high-intensity forward directed beam is available with epithermal neutron flux [approximately equal to]1010 n/cm2·s, 1 eV ≤ E ≤ 10 keV, at the entrance to the medical irradiation room, and epithermal neutron flux = 3 to 5 × 109 n/cm2·s at the end of the patient collimator. This is currently the highest-intensity epithermal neutron beam. Furthermore, the system is designed and licensed to operate at three times higher power and flux should this be desired. Beam contamination from unwanted fast neutrons and gamma rays in the aluminum, polytetrafluoroethylene, cadmium and lead-filtered beam is negligible with a specific fast neutron and gamma dose, Dγ,fn/ϕepi [less than or approximately equal] 2 × 10–13 Gy cm2/nepi. With a currently approved neutron capture compound, boronophenylalanine, the therapeutically advantageous depth of penetration is >9 cm for a unilateral beam placement. Single fraction irradiations to tolerance can be completed in 5 to 10 min. An irradiation control system based on beam monitors and redundant, high-reliability programmable logic controllers is used to control the three beam shutters and to ensure that the prescribed neutron fluence is accurately delivered to the patient. A patient collimator with variable beam sizes facilitates patient irradiations in any desired orientation. A shielded medical room with a large window provides direct viewing of the patient, as well as remote viewing by television. Rapid access through a shielded and automatically operated door is provided. The D2O cooling system for the fuel has been conservatively designed with excess capacity and is fully instrumented to ensure detection and control of off-normal conditions. A wide range of possible abnormal events or accident scenarios has been analyzed to show that even in the worst cases, there should be no fission product release through fuel damage. This facility has been licensed to operate by the U.S. Nuclear Regulatory Commission, and initial operation commenced in June 2000.

Microcomputer-based fault detection using redundant sensors

The design of a prototype device that implements a redundancy management scheme for online detection and isolation of faulty sensors in strategic facilities such as nuclear reactors, hazardous chemical plants, and advanced aircraft is presented. Such a device can potentially reduce the number of display devices in the control room and relieve the plant operator(s) from the tasks of assimilation and analysis of redundant sensor data as well as enhance the processing capabilities of the main computer. The device can be used as an integral part of intelligent instrumentation systems. It was built using an 8-bit microcomputer system and commercially available electronic hardware. The software is completely portable. The operation of a prototype has been successfully demonstrated for real-time validation of sensor data at the MITR-II nuclear research reactor. >

Boron neutron capture therapy and radiation synovectomy research at the Massachusetts Institute of Technology Research Reactor

In this paper, current research in boron neutron capture therapy (BNCT) and radiation synovectomy at the Massachusetts Institute of Technology Research Reactor is reviewed. In the last few years, major emphasis has been placed on the development of BNCT primarily for treatment of brain tumors. This has required a concerted effort in epithermal beam design and construction as well as the development of analytical capabilities for {sup 10}B analysis and patient treatment planning. Prompt gamma analysis and high-resolution track-etch autoradiography have been developed to meet the needs, respectively, for accurate bulk analysis and for quantitative imaging of {sup 10}B in tissue at subcellular resolutions. Monte Carlo-based treatment planning codes have been developed to ensure optimized and individualized patient treatments. In addition, the development of radiation synovectomy as an alternative therapy to surgical intervention is joints that are affected by rheumatoid arthritis is described.

Design and evaluation of an observer for nuclear reactor fault detection

The design and evaluation via simulation of an observer for nuclear reactor fault detection is reported. The method used is an extension of that proposed by Beard (in 1971) that allows actuator, sensor, and system dynamic faults to be detected and localized by studying the asymptotic response of an error signal. Signal noise and modeling errors can cause false alarms and/or failure to detect real faults. These types of error are characterized by their respective first hitting times of a decision threshold. Cost functions are then defined for each error and optimization is used to select observer parameters. The final design was evaluated by simulation on both a one-group linear reactor model and a six-group nonlinear one. The method was shown both to detect and localize faults and to be robust against measurement noise and modeling errors.

Design and Experimental Evaluation of an Automatically Reconfigurable controller for Process Plants

A digital controller that reconfigures control strategies as a result of changes in plant operating conditions has been developed and demonstrated. The reconfiguration logic involves the organization of available plant information, the definition and identification of plant operating conditions, the selection of the appropriate control law for the given operating condition, and the verification of the control choice through on-line performance evaluation. Also included is a decision and supervisory logic which interfaces with a knowledge base to insure that plant operating guidelines, procedures, and specifications are not exceeded. This methodology is entirely general and may be used with any process system. It was demonstrated experimentally on the 5 MWt MIT Research Reactor. The reconfigurable controller successfully controlled the reactor power under steady-state, power maneuver, and experimentally-induced anomalies in the control laws.

Digital Control of Power Transients in a Nuclear Reactor

An integrated, closed-loop, control system for online operations in nuclear power plants has been developed and demonstrated with an LSI-ll/23 micro-processor on the 5 MWt fission reactor (NITR-II) that is operated by the Massachusetts Institute of Technology. This control system has inherent capabilities to perform online fault diagnosis, information display, sensor calibration, and measurement estimation. Recently, its scope has been extended to include the direct digital control of power changes ranging from 20-80% of the reactors licensed limit. This controller differs from most of those discussed in theoretical and simulation studies by recognizing the non-linearity of reactor dynamics, calculating reactivity on-line, and controlling the rate of change of power by restricting both period and reactivity. The controller functions accurately using rods of non-linear worth in the presence of nonlinear feedback effects.

Considerations in the control of PWR-type multimodular reactor plants

Issues in the control of PWR-type multimodular reactor plants are discussed with emphasis on the need for operation under conditions of unbalanced loads, operating strategies for both single- and multireactor systems, and the coordinated adjustment of power and temperature. One defining characteristic of a multimodular plant is that each unit will probably be loaded differently so as to compensate for the effects of varying maintenance outages and, if desired, to stagger refuelings. A second characteristic is interdependency in that, with several reactors connected to a common turbine, a change in any one unit will propagate to the others. The combination of these two factors makes operation of a multimodular plant differ from that of existing single-reactor ones. For example, conventional sliding-T/sub ave/ load maps cannot be applied directly to a multimodular system because, with the exception of the highest-powered unit, each reactors temperature will be a function of not only its power level but also that of the most heavily loaded one. Similarly, withdrawal of the control rods in a fully loaded PWR will, in the presence of a large negative temperature coefficient, cause hot and cold leg temperatures to rise but leave power and core /spl Delta/T unchanged. In a multimodular system, there will be a shift in power to the affected reactor. These and other differences in the behavior of multimodular and single-reactor systems are delineated. The paper concludes with some practical suggestions on the operation of PWR-type multimodular plants. >

Evaluation of 'period-generated' control laws for the time-optimal control of reactor power

Time-optimal control of neutronic power has recently been achieved by developing control laws that determine the actuator mechanism velocity necessary to produce a specified reactor period. These laws, designated as the MIT-SNL period-generated minimum-time control laws, function by altering the rate of change of reactivity so that the instantaneous period is stepped from infinity to its minimum allowed value, held at that value until the desired power level is attained, and then stepped back to infinity. The results of a systematic evaluation of these laws are presented. The behavior of each term in the control laws is shown, and the capability of these laws to control properly the reactor is demonstrated. Factors affecting the implementation of these laws are discussed. The results of an experimental study in which these laws were used to adjust the power of the 5 MWt MIT research reactor are shown. >