b'C HAPTER F OURTEENI M A G I N I N G T H E W O R S TThe reactor must also function during startup and shutdown or load change andmust be able to scram safely under a variety of postulated malfunctions.Nucleonics, 1960I t isnt clear just accessories to be working well, but In the 1950s, imagined accident scenar-something within the core of the reac- ios opened up questions for which scien-tora badly-made fuel element, per- tists had few answers. Does a risingwhen the word excursion migrated haps, or impurities in the coolantcan temperature encourage or discourage theinto the daily vocabulary of nuclear sci- affect the rate at which the uranium chain reaction? What happens while theentists. Among non-nuclear people, the atoms are fissioning. Instead of splitting fuel is heating up? Will the reaction con-word evokes picnics in the park and at a certain rate per second, the atoms tinue? At what point will it stop? If theleisurely drives in the country. Reactor split at twice that rate, or four times. If automatic controls or human operatorsscientists appropriated the word to unchecked, such an excursion could fail to scram an excursioning reactor,describe a potentially deadly hazard. overwhelm the heat-removing appara- what is the worst that can happen? Suchtus, melt the fuel, inspire chemical questions pointed the way to formulatingAmong the early preoccupations of explosions, and cause a release of fis- many parts of the overall safety researchN RTS scientists was to imagine what sion products into the environment. programs supported by the AEC .kinds of accidents might endanger peo-pleand then to minimize the chances The Nautilus prototype and the MTRof accidents. If power plants were to used water for cooling. In both casesgenerate electricity, they would most the water was pressurized to prevent thelikely be located near populated areas. water from boiling in the core or turn-For the sake of the population and the ing to steam. The conventional wisdomfuture of the nuclear power industry was that steam bubbles would somehowboth, the plants had to operate safely. affect the behavior of neutrons andcause the reactor to behave erratically,An excursion is a sudden increase in the possibly overheating.power level of a reactor. All of the reac-tors accessoriesthe vessel that con- Samuel Untermyer, a scientist attains the fuel, the pumps that circulate Argonne National Laboratory, thoughtthe coolant, the control rods and the otherwise. Based on his observation ofmachines that move them in and out an accidental withdrawal of a controlare designed with an expectation that rod at a zero-power reactor in Chicago,the reactor will not run hotter than a Argonne National Laboratory-West 201-709 he thought that if water bubbled orcertain temperature. Removing heat is BORAX-I, the runaway reactor. steamed in an overheating reactor core,the single most important way to keep the chain reaction would merely slowthe reactor safe. It is possible for the down until it died all by itself.12 8'