9. Inherently Safe Reactor Designs

The economic advantage of the pbmr is that it can

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Unformatted text preview: low a utility to make a decision on investing about 120 million dollars rather than the 2-3 billion dollars for other power plants. In addition, the construction time can be reduced to the 18-36 months level as opposed to the 5 or more years for light water reactors. The operating costs of the concept because of the staffing characteristics and the lower fuel costs. It can satisfy the information technology needs which are increasing the load demand in the USA at 4-4 1/2 percent rate per year, for instance around Chicago. It possesses a high degree of inherent safety. The worst case scenario would produce temperatures below fuel damage temperatures. The design provides a containment structure provide for regulatory needs only the reason is that the type of accidents envisioned would take hours to days to develop, as compared to minutes in PWRs. In the USA a Nuclear Regulatory Commission (NRC) policy statement designated as SECY 93-092, provides guidance in this regard. It concludes that conventional containment is not needed for such a design. Nevertheless, the PBMR design allows for the release of the helium coolant in the case of a loss of coolant accident. The containment structure is there to intercept any fission products release within days of the initiation of any accident. Fig. 19: Conceptual Design of Pebble Bed Gas Cooled Reactor with a steam cycle rather than a gas cooled cycle.. The design would require a smaller Emergency Planning Zone (EPZ). The control rods are used only for compensating for the initial heat up and for achieving full cold shutdown. For temperature control, the helium pressure is lowered or raised. To decrease the power level, the temperature is decreased by increasing the helium pressure and vice versa. In a bridging to a helium economy in the future, high temperature systems can be used to dissociate water into oxygen and hydrogen on a global scale. This would satisfy in a nonpolluting manner the needs of both industrialized and developed nations. Expectations are for the doubling of electricity demand worldwide by 2020. DISCUSSION The core meltdown frequencies for two conventional reactor designs, the Surry PWR and the Peach Bottom BWR were estimated by the WASH-1400 reactor safety study to be 6x10-5 and 3x10-5 [accidents/reactor.year], respectively. The uncertainty in these estimates is believed to be a factor of 5-10 either way. On this basis, a core melt frequency of 10-4 cannot be ruled out. Studies before the Three-Mile Island (TMI) accident suggested that these frequencies were as high as 10-3. After the improvements mandated by TMI, it is suggested that present day reactors have frequencies 1.5-3 times higher than the WASH-1400 study. This puts them back at about 10-4. For an evolutionary PWR design built by Westinghouse and Mitsubishi, and for the evolutionary ABWR built by General Electric, the frequencies are estimated at the level of 1.1x10-6 and 5x10-6, respectively. Thus the evolutionary designs can be thought as having a core melt frequency around 10-5. The USA's Nuclear Regulatory Commission (NRC) has promulgated the value of 10-4as a safety goal. Thus it is seen that the evolutionary designs are an order of magnitude lower than the NRC goal. With a world with about 500 reactors, a core meltdown frequency of 10-4, translates into: 500 reactors x 10-4 [accident/reactor.year] = 1/20 [accident/year], or 1 accident each 20 years. With the figure associated with the evolutionary designs, at 10-5, this figure becomes 1 accident per 200 years. It does appear that the latest figure is one that could be more acceptable to the public, suggesting any new nuclear power plant construction cannot follow the older standard designs any more, and the latter should probably be retired in favor of the new evolutionary designs. If the world opts for more nuclear power plants construction, as a remedy for greenhouse emissions, and a movement towards a hydrogen based energy economy, a world with a 1,000 nuclear power plants, can be envisioned. If we desire in such a world for the core meltdown frequency not to exceed 1 accident per 200 years, this would mandate a core melt frequency design goal of less than 5x10-6. In this situation, to account for the statistical error involved at a factor of ten either way, a move to the passive designs which would provide a core melt frequency of less than 5x10-7. This appears to be the clear alternative for the world to benefit from nuclear electrical production. REFERENCES 1. S. R. Spencer, "Advanced Nuclear plants: Meeting the Economic Challenge," Energy Horizons, May 1994. 2. John R. Redding, "Advanced LWR Technology for Commercial Application," Nuclear Technical Meeting, KAIF, KNS, ANS-Korea, Seoul, Korea, November 25, 1992. 3. Llewellyn King and Debra Weiss, How Nuclear's vissitudes led to the Controversial Integral Fast Reactor," The Energy Daily, March 10, 1989. 4. Alvin M. Weinberg and Irving Spievak, "Inherently Safe Reactors and a Second Nuclear Era," Science, 224, pp.1398-1402, 1984. 5. "Safety Goals for Nuclear Power Plant Operation," NUREG-0880, Rev.1, US Nuclear Regulatory Commission, 1983. 6. J. J. Taylor, K. E. Stahlkopf, and J. C. DeVine, Jr.,"Advanced Light-Water Reactor Development in the United States." IAEA Bulletin, 3, 1989. 7. V. Galushkin, "GT-MHR- An Advanced Reactor," Nuclear Plant Journal, Jan-Feb, 2001. 8. R. Michal, "PBMR Licensing in the United States," Nuclear News, p.22, Feb., 2001. 9. F. P. Johnson, "Sensor Craft, Tomorrow's eyes and ears of the Warfighter," Technology Horizons, Vol. 2, n. 1, March 2001...
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This note was uploaded on 06/16/2010 for the course NPRE 402 taught by Professor Ragheb during the Spring '08 term at University of Illinois at Urbana–Champaign.

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