![]() Three types of moderators are used at the MIT reactor: (1) ordinary or "light" water that is also used to cool the reactor core, (2) deuterated or heavy water (D 20), and (3) high-purity graphite, both of which are excellent at slowing neutrons without absorbing them. Since U-235 nuclei do not readily absorb the high energy neutrons that are emitted during fission, it is necessary to slow the neutrons down with a "moderator". In the MIT reactor, one other group of components is essential to the maintaining and controlling a chain reaction. The process may take place spontaneously in some cases or may be induced by the excitation of the nucleus with a variety of particles (e.g., neutrons, protons, deuterons, or alpha particles) or with electromagnetic radiation in the form of gamma rays. As fewer and fewer neutrons are absorbed, more and more neutrons are available to cause the splitting of uranium nuclei, until finally enough neutrons are available to sustain a chain reaction. ![]() To put the reactor into operation, the control blades are raised very slowly. When the control blades are fully inserted, they absorb so many neutrons from the uranium that there are not enough to allow a chain reaction to continue. Boron has the property of absorbing neutrons without re-emitting any. The rate of fissions in the uranium nuclei in the MIT reactor is controlled chiefly by six control blades of boron-stainless steel which are inserted vertically alongside the fuel elements. When it is in operation, the central active core contains a huge number of neutrons traveling in every direction at very high speeds. The MIT Research Reactor is used primarily for the production of neutrons. However, outside of the main reactor, a nuclear power plant generates electricity in a surprisingly. Hence, the possibility exists for creating a chain reaction. The nuclear reactor is the heart of any nuclear power plant. These reactors require a moderator to reduce the speed of neutrons produced by fission. Thermal reactors use slow neutrons to maintain the reaction. Each time a U-235 nucleus splits, it releases two or three neutrons. The speed of the neutrons in the chain reaction determines the reactor type (Figure 7.13. ![]() This process is known as fission (see diagram below). When a U-235 nucleus absorbs an extra neutron, it quickly breaks into two parts. The arrangement of particles within uranium-235 is somewhat unstable and the nucleus can disintegrate if it is excited by an outside source. Such an administrator would allow a plant control system to be constructed with commercially available, state-of-the-art equipment and be customized to the needs of the individual plant operator.In the nucleus of each atom of uranium-235 (U-235) are 92 protons and 143 neutrons, for a total of 235. We propose that an HCSS administrator be constructed as a standardized approach to address regulatory issues. HCSS principles can be applied to nuclear power plants in a manner that allows the off-the-shelf use of process control instrumentation while maintaining a high level of safety and enhancing the plant performance. This approach addresses the key issues of safety, security, and control while satisfying requirements for reliability and quality. This technology can be directly applied in an operating nuclear power plant more ยป provided a surety principle-based hardware system is included in parallel with the upgrade Sandia National Laboratories has developed a rigorous approach to High Consequence System Surety (HCSS). Nuclear power plant operators have been hesitant to install this technology because of the cost and uncertainty in the regulatory process. The technology is used to optimize processes and enhance the man-machine interface while maintaining control and safety of the processes. This technology includes distributed microprocessors, fiber optics, intelligent systems (neural networks), and advanced displays. The state of the art in process control and instrumentation has advanced to use digital electronics and incorporate advanced technology. Many nuclear power plants use instrument and control systems based on analog electronics.
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