Nuclear Power Plant Applet Description

Henrik Eriksson
Dept. of Computer and Information Science
Linköping University
S-581 83 Linköping, Sweden

Power Plant Model

This applet provides a (very rough) simulation of a nuclear power plant. This power plant consists of three major components: the reactor, turbine, and condenser. Furthermore, there are three pumps, four valves, and one turbine. The reactor boils the water and the steam generated drives the turbine. After the turbine, the condenser cools the steam. In turn, external cooling water cools the condenser. The cooling pumps transport the water from the condenser tank back to the reactor tank.

The simulator calculates values for reactor-tank pressure, condenser-tank pressure, water levels, and so on, and displays them graphically. When components fail, the simulator calculates and displays the consequences for the running power-plant system. For instance, if a cooling pump fails and the corresponding valve is not closed, water may flow backwards from the reactor tank to the condenser tank. This process will then drain the reactor tank and expose the reactor core.

User Interaction

The user can start several simulation sequences where components of the power plant fail. In Sequence 1, the turbine fails, and the state of the power plant changes accordingly. In Sequences 2 and 3, cooling water pump 1 fails, and the external-cooling water pump fails, respectively. (You may have to resize the browser window to see the external-cooling water pump, because it is located to the left of the condenser.) The randomize button invokes a sequence where two random components fail. For instance, the turbine may fail and then a few seconds later a cooling pump may fail.

The simulator allows user interaction with certain components when a simulation sequence is running. The user can open and close valves by clicking on them, and can start and stop pumps by clicking on them. Moreover, the user can change the position of the moderator rods by dragging them with the mouse. The simulator disables user interaction with components immediately after a sequence is completed.

Applet Description

The applet implementation consists of two major parts: (1) the graphical user interface and (2) the power-plant simulator. In the version of the applet you seen on the demonstration WWW page, the simulator component is implemented in Java-compatible and run together with the graphical-user interface in your Java browser (e.g., HotJava and Netscape 2.0). Although this Java-based simulator is now running locally in you browser, it can be configured to communicate with a remote simulator server that receives user input and transmits simulation output data to the browser client (through a TCP/IP stream).

Learning Rule-Based Programming in CLIPS

This applet is designed primarily to teach students expert systems and rule-based programming by adding safety rules to the power-plant control system. The expert-system shell we are using to perform this task is CLIPS. Because simulator servers running remotely can be implemented in other languages than Java, students can implement (or modify existing) simulators in CLIPS. (In our approach, we use Java-to-Java communication over the TCP/IP stream and, we integrate Java and CLIPS through the C-based API on the server side.) For instance, it is possible to develop a relatively small rule base that will take appropriate actions automatically when components fail. This safety knowledge base can then be tested against random sequences, to ensure that the rules work properly.

Our goal is to use this applet as a tool in teaching students basic knowledge-engineering skills, such as rule-based programming. Currently, we are working on a document that defines the student assignment, and provides the information required to complete the exercise. We shall fine-tune the applet and the program skeleton to work with the documentation during the fall of 1995. The expert-system course starts in January 1996, and we expect to have the course material ready by then. The current version of the CLIPS program skeleton is available here.

Applet Documentation and Source Code

Class documentation (generated by javadoc) and Java source code are available.

Class documentation
Source code - main simulator, contains several class definitions
Other interesting source code: Remote simulation and CLIPS (not part of this version of the applet)

Bugs

The graphics could be cooler. In the 1.0Alpha3 version, the sequence control buttons are sometimes not redrawn correctly when the user scrolls the page in HotJava. The applet was developed using the Solaris version of HotJava. It works with the Windows 95/NT version (1.0Alpha3 or later), but there are still some rough edges on the Windows platform, such as font-geometry, color, and crash problems.

Historical Background and Acknowledgments

The approach of power-plant simulation (in this context) was originally a laboratory assignment to teach computer-science students at Linköping University rule-based programming. In 1986, Anders Nyberg and Mikael Svensson developed the original version in the expert-system shell Epitool running on Xerox D-machines. The Epitool code handled the simulation, and the Interlisp-D code displayed the simulation graphically. A few years later, the D-machines became obsolete, and where replaced by Medley running on Sun SPARCstations. Because, Epitool was no longer available for the Medley platform, the laboratory assignment had to be removed from the expert-system course.

For several years, we were frustrated we could not run the power-plant simulator. In early 1995, it was time to revise the assignments for the expert-system course. We needed a new and cool assignment to teach students rule-based programming in CLIPS. Since Java and HotJava was available, we decided to resurrect the power-plant simulation, and to use Java as the user-interface front end to CLIPS. During summer 1995, Henrik Eriksson implemented a new user interface in Java and translated the old Epitool simulator code to CLIPS. The first part of this implementation process was to create a stand-alone (i.e., complete) simulator in Java to test the Java user interface. Eva L. Ragnemalm rewrote the assignment documentation for the new power-plant simulator.