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Approach to Knowledge Based Man-Machine Communication for BWR Start-Up GuidanceYasuo NISHIZAWA a , Hiroshi MOTODA a , Naoyuki YAMADA a & YutakaWADA aa Energy Research Laboratory , Hitachi Ltd. , Moriyama-cho, Hitachi-shi , 316Published online: 15 Mar 2012.
To cite this article: Yasuo NISHIZAWA , Hiroshi MOTODA , Naoyuki YAMADA & Yutaka WADA (1983)Approach to Knowledge Based Man-Machine Communication for BWR Start-Up Guidance, Journal ofNuclear Science and Technology, 20:10, 877-879, DOI: 10.1080/18811248.1983.9733482
To link to this article: http://dx.doi.org/10.1080/18811248.1983.9733482
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Journal of NUCLEAR SCIENCE and TECHNOLOGY, 20, pp. 877-879 (October 1983) 877
SHORT NOTE Approach to Knowledge Based Man-Machime Communication for BWR Start-up Guidance
Yasuo NISHIZAWA, Hiroshi MOTODA, Naoyuki YAMADA and Yutaka WADA
E n e r g y Research Laboratory, Hitachi Ltd.*
Received April 13, 1983 Revised July 25, 1983
KEYWORDS: BWR type reactors, start-up, core management, infer- ence engine, predicate calculus, man-machine communication, CAD
Computer has so far been used to solve a problem by numerical computation. Many of the engineering problems, however, can be solved more efficiently by the so-called expert knowledge pertinent to the problem. The knowledge used there is sometimes heuristic and not handled by numerical com- putation. Knowledge engineering (K.E.) ()() provides a method to incorporate such knowl- edge in problem solving.
Core management is a field in which much experience useful for decision making has been accumulated. This note introduces a computer program that receives such ex- perience as pieces of knowledge and makes inference for problem solving with an ex- ample applied to a man-machine communica- tion for BWR start-up guidance.
1. Summary of Program Experts knowledge comprises not only
individual fact and relations among them but also more general or abstract concept. To express such abstract knowledge, the program developed here adopts first order predicate calculus that allows to use variables for in- definite object. In the inference process, variables are compared with individual object and bound to them by unification. Using predicate calculus, individual fact is expressed as a proposition, and a relation among the facts is represented as a production rule that
is sometimes called if-then rule. Two methods of inference are prepared,
that are, forward and backward inferences. Forward inference finds new facts that are concluded by combining rules and previously proved facts. Backward inference proves the solution of a problem by tracing the logics in a backward direction starting from an assumed conclusion. The assumed conclusion can contain variables. These methods can be used in combination.
Experts knowledge further includes the knowledge about when and how to use knowledge. Such knowledge is called meta- knowledge. Meta-knowledge can also be stored in the knowledge base and is used for inference control such as to proceed numerical computation on the way of inference, or to generate a question to users before looking into the knowledge base. Hierachical structure is employed for context of knowledge. Knowl- edge in the higher level context can be referred from the lower level context but not for reverse. The program has also the func- tion to explain the process of inference, that is, the way through which it has reached a conclusion. The language used is UTILISP and the computer M-200H.
2. Application to Start-up Guidance The program has been applied to a man-
machine communication for BWR start-up guidance. Start-up scheduling is a problem to find a way to bring reactor power to the rated value without violating any of the operating constraint^'^)'^). In the start-up process, the most difficult and troublesome problem is estimation of Xe transient state caused by reactor power change. The Xe behavior brings about a fairly complicated effect on core state. Engineers however can estimate the Xe change by reference to the power history and their experience. Although such estimation is not so accurate as that by numerical simulation, it is useful to decide the reactor operating strategy.
Utilization of such experts knowledge makes it possible to give a guidance for BWR
* Moriyama-cho, Hitachi-shi 316.
Pattern of Xenon Change
Monotonically Increasing Monotonically Decreasing Equilibrium Overshooting Undershooting
SlioRT NOTE (Y. Nishizawa et al.) J. Nucl. Sci. Technol.,
Degree of xenon Change
Remarkably Increasing Gradually Increasing Equilibrium Gradually Decreasing
start-up through man-machine communication in which the program analyses what is neces- sary to solve a problem by itself. In the following, described is an attempt of such a knowledge based guidance to the decision making of reactor operation.
The man-machine communication system consists of a knowledge base, an inference engine and a communication equipment. The rules stored in the knowledge base are those of operating constraints, corrective actions for constraint violations, Xe transient state and meta-knowledge for inference control.
Structure of the knowledge base and the flow of information are shown in Fig. 1. The amount of rules is 55, out of which, 10 is for constraints, 20 for corrective actions,
Power Change o Degree o Elapsed Time
20 for Xe transient and 5 for inference con- trolling meta-knowledge.
The Xe transient state is characterized by the two factors :
(1) Xenon concentration changing pattern (2) Degree of the change.
The former is determined by reactor power history and the latter by the degree of the power change that brought about the Xe change together with the elapsed time after the power change. The process of the Xe transient state estimation is shown in Fig. 2 with an example of the rules.
The characteristic of this system is that it adopts backward inference in combination with meta-knowledge to generate questions to the users about what computer needs to
Xnowledge of Xnowledge of Constraints Corrective A c t i o n
Question Driving Functions Questions
Fig. 1 Structure of knowledge base
Example of Rule5
(If [and (Xenon-transient Overshoot) (Power-change Great I
Fig. 2 Knowledge construction about Xe (Elapsed-trme Short 1 ) (Then (Xenon Increasing Remarkab1y)I)l
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Vol. 20, No. 10 (Oct. 1983) SHORT NOTE (Y. Nishizawa e t a l . ) 879
t Control Rod or Flow? J C R 1 Pz;;-up, Down or Hold? How Many Power-up Loops?
Set Degree of Power Chang
I Inference Process
Final Power-up Increasing Remarkably
Power Change 3 3 0 1 % )
Set Time aftez Power Change ~1 Ihr)
t I I
own by Xenon.
Fig. 3 Example of man-machine communication and inference process (in case of rod block line violation)
know. The inference starts by assuming a conclusion about corrective action if a con- straint is violated. It first finds conditions required to prove the assumed conclusion by tracing the logics in the rules and tries to prove each of them. Some of the conditions can be asked to the user for the truth by the meta-knowledge. When the answer is not known, it then looks for a chain to prove the condition as a subgoal.
Figure 3 shows an example of man- machine communication with the inference path to reach the final goal. This is a case to decide the corrective action when the reactor power exceeded its constraint Rod Block Line. By answering to the questions raised by the program, it has been concluded that (1) the Xe transient state is in the initial stage of overshooting introduced by a great power change and the Xe is increasing re- markably and, thus, (2) the corrective action is simply to wait for the power to decrease.
3. Discussions The study indicates that some complicated
problems as those encountered in a Xe trans-
ient state can be solved by using the knowl- edge about reactor operation, expressed in simplified logical statements.
For practical use, more detail and abundant knowledge should be prepared and the guid- ance should be more quantitative. Know- ledge to meet such a requirement includes numerical simulation. It is, therefore, neces- sary to couple symbolic manipulation to numeric computation.
The approach introduced here will be a useful technique for intelligent problem solv- ing. Other tasks of core management such as refueling scheduling and long term control rod programming are also handled by this technique.
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(2) OHSUGA, S. : Joho Shori, (in Japanese), 23
(3) BESSHO, Y., et a l . : J . Nucl, Sci. Technol.,
(4) NIsHizAwA, Y., et 01.: [Nucl. Technol 58,
(JO], 967-974 (1982).
lE(9], 697-704 (1981).
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