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3.5. THE NUCLEAR POWER INDUSTRY

Perhaps one of the most critical processes in the entire field of power generation is that of generating electricity with nuclear reactors. Although human operators are well trusted and are well-trained to cope with an emergency, they are not infallible, and the possible outcome of a human error could be very costly, as was demonstrated in Russia on the night of 26th April 1986. Chernobyl was the worst nuclear accident of all time, with low safety standards, ill-designed safety tests and poor construction standards all contributing to the disaster. Read (1993) in his book, describes the courage, panic and terror of the fateful night:

"Scientists and technicians -- who thought at first the war had broken out -- streamed along corridors in the dark as their instruments failed. They heaved at twisted metal doors to reach the control rods and put their hands into radioactive pools to turn safety valves. They slung injured colleagues over their shoulders as they fled for the exits, even though the radioactivity from their contaminated clothing burned deep sores into their flesh. Thirty-one people died immediately or within days. They watched their own bodies rot, their intestines dissolve and the skin on their legs fall down like loose socks."

The disaster left severe contamination to thousands of acres of farmland in Belarus, the Ukraine, and Russia as well as thousands of people being exposed to extremely high levels of radiation. Europe was also affected; for instance in Britain 400,000 acres of land and millions of sheep were contaminated by the radiation cloud that passed over on 3rd May and 4th May 1986. As a result 4.2 million sheep were slaughtered and to this day there are still restrictions on the use of some farm land.

The after effects of Chernobyl overshadow the rest of the world's nuclear power industries, with heightened public concern about safety of these power stations. Could the use of expert system and artificial intelligence products help relieve some of the public worries and prevent another Chernobyl from happening?

Their are two main types of reactor within the industry namely: Boiling Water Reactors (BWR) and Pressurised Water Reactors (PWR). A boiling water reactor works by boiling its cooling water to produce steam, which is then used to drive a turbo-generator unit. However, since the water has been in close proximity to the reactor, it will be itself radioactive, which in turn means that the turbo-generator must now be classified as a radioactive piece of machinery and the required safety or emergency procedures must be applied to it. It should also be noted that different sensors and wiring setups will be needed to connect monitoring equipment to the radioactive piece of machinery.

A pressurized water reactor works on the same principal as the boiling water reactor, only this time the cooling water is not allowed to boil. The cooling water gets extremely hot, and is used to heat water in pipes, which is allowed to boil, produce steam and drive a turbo-generator. The steam driving the turbo-generator on this type of reactor is not radioactive and can be handled as such. It should also be noted that there are also many different variations of both the boiling and pressurised water reactors.

Beck et al. (1992) note some points that future expert system or any other software developers should note when attempting to develop systems for the nuclear power industry. Most components within a nuclear power plant are Safety Rated (SR); this means that the component designer must have considered the major "what-if" scenarios to ensure that the component is safe from Design-Based Accidents (DBA) or Design-Based Events (DBE). An expert system which monitors (or even controls) a safety rated component should itself be safety rated.

Control rooms of nuclear facilities present their operators with thousands of switches, lights, meters, recorders and alarm windows, and most of this data must be presented to an expert system in some way. This is no trivial task when you consider the sheer number of sensors, the difference in signal types (which may also need converting into a symbolic form) and that interference may occur between Safety Rated and Non Safety Rated Equipment.

Beck et al. (1992) also notes that nuclear facilities hold a wealth of information in the form of diagrams, procedures and plans, but the greatest wealth of information comes from the expertise of engineers, technicians and operators who work there. Sun et al. (1989) tell us that:

"Expertise is a kind of intellectual capital which represents a substantial portion of the electric industry's worth."

Other points raised by Beck are:

  • Expert systems should be able to cope with the prospect of multiple failures occurring
  • Expert systems should be able to model reactor physics
  • Expert systems should contain knowledge about site operating licenses and regulations
  • Contradictory sensor readings should be identified in order to prevent errors from occurring

3.5.1. Systems Developed by EPRI

Nuclear facilities face the same competitive problems as other types of generating facilities and must also enhance power generation and increase productivity while also increasing the safety of the plant. To help accomplish these goals, EPRI have been using expert system technology for many years within the power generation field and believe that this technology can be safely put to use in their nuclear facilities (Sun et al., 1989).

One system developed using the commercial toolkit, Knowledge Engineering Environment (KEE) was PLEXSYS (PLant EXpert SYStem) which allows the facility operator to represent a plant schematically in the form of CAD drawings. Knowledge bases can be associated with the drawings, so that the expert system can automate the problem solving tasks associated with modifications to the plant.

The Emergency Operating Procedures Tracking System (EOPTS) is another EPRI development using a custom made inference engine and knowledge representation schema to interpret and compile Emergency Operating Procedure logic. The result is a fast running software module that interfaces to and is co-resident with the nuclear plant's Safety Parameter Display System.

A planning application that EPRI have implemented is the Refueling Insert Shuffle Planner (RISP) which determines an efficient crane moving pattern for the fuel insert shuffle of nuclear reactors. The application, based on KEE, does not find the optimal solution as this would be far too time consuming, but instead uses heuristics to find a number of efficient solutions.


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