Chernobyl-What Happened? Charles H. Atwood Mercer Unlverslty, Macon, GA 31207 The nuclear reactor accident a t Chernobyl, Russia, which occurred on April 26,1986, has attracted the attention of the general public, the scientific community, and our students. Recentlv, enoueh of the dust surroundina this reactor accident has aettledto provide us with areas&ably clear view of the events and the consequences of the worst nuclear reactor accident in history. This paper will detail the hasic design of the reactor that exploded and the events that eventually caused the reactor to explode and will survey the consequences of the explosion on the population of Europe and the world. It is hoped that this information will provide the teacher with the information necessary to answer the quesin the minds of your tions and doubts that are still lineerine students and local community. Reactor Deslgn The reactor design that is used at the V. I. Lenin nuclear reactor power plant is designated the RBMK 1000 model. The Soviet Union plans to have as many as 21 of these reactors in operation. Presently there are 13 in operation with the rest in various stages of construction ( I ) . These reactors are era~hite-moderated.water-cooled. and fueled withUO2 t h g is-2.0%enriched i n 2 W (2). he; represent a modification of the reactors that were used in the Russian nuclear weapons programs to produce weapons-grade Pu for use in both fission and fusion weapons. The reactors still have some of the characteristics of the weapons production reactors, such as the abilitv to he refuelled continuousls; however, there is no evidence that the Chernobyl reactor has been used for anything other than commercial power production (3). These reactors are capable of producing 3200 MW of thermal energy that can be converted into 1000 MW of electrical enerev -" bv. the ~ l a n t ' sturboeenerators. The V. I. Lenin power plant contained four of th;, RBMK 1000 reactors. Construction of the first reactor at the plant was begun in 1970and completed in 1977. Thesecond stage of construction, which included reactor number 4 (the one that exploded),was completed in 1983. Reactor number 4 went on line shortly after construction was finished (2). The RBMK 1000's design is sufficiently different from that of the typical American commercial nuclear reactor to require a detailed explanation of its design and operation. The reactor design uses graphite to moderate, or slow down, the neutrons from the fission reactions and decay of the fission products. I t is necessary to moderate these neutrons because the neutrons from the reactions and radioactive decay are quite energetic (on the order of a few megaelectronvolts of energy) and therefore have rather high velocities. These "fast" neutrons have a fairly small probability of initiating any subsequent fission reactions. If only fast neutrons we-re present in a nuclear reactor, the chain reaction that is necessary tosustain the reactor's fission process (and therefore its power production) would stop. Instead the reThis paper was presented at the 38th Southeast Regional Meeting of the American Chemlcal Society. Louisville, Kentucky, November 3-5. 1986, and the 194th National Meetlns of the Amerlcan Chemlcal ~ociety,New Orleans, Louisiana, ~ u ~ u s t > ~ - ~ e ~ t e4,m1987. ber
Flaure 1. ARistic renderinrr of the RBMK 1000 reactor. For size com~arison nols'hetuo peop e sranamgan lne reanor core (Taw" wth permoss#onfrom re1 1 1 , copy' qnr 1986 o, the AAAS. and u r h perm so on ol The Warhlngron POStand the artist, Johnstone Oulnan.)
actor requires slower or "thermal" neutrons that have a high ~robahilitvof initiatine subseauent fission reactions to sustain the ;hain reaction. ~ h e ' ~ r a ~ h moderator ite accomplishes the task of converting fast neutrons into thermal neutrons by providing a large number of protons with which the neutrons can collide and lose some enerev. The thermal neutrons that are produced by the moderat& process then strike the 2"U in the reactor's fuel assemhlies and initiate fission reactions. In the RBMK 1000 the graphite is formed into ~arallelepipedblocks that are 250 mm on a side with a hole through the center. The holes arenecessary to provide a channel for the coolant pipes and fuel assemhlies. These blocks are stacked into a rouehlv cvlindrical s h a ~ ethat is 11.8 m in diameter and 7 m
