MOLTEN PLUTONIUM CHLORIDE FAST BREEDER REACTOR COOLED BY MOLTEN URANIUM CHLORIDE
Swiss Federal Institute of Reactor Research, Würenlingen, Switzerland
MIECZYSLAW TAUBE and J LIGOU
A fast breeder reactor of 2000 ~MWt output using molten chlorides as fuel and coolant is discussed. Some of the most significant characteristics are: The liquid fuel contains only PuCl3/NaCl. The coolant is molten UCl3/NaCl and also forms the fertile material along with the blanket system, again UCl3/NaCl: the coolant blanket system is divided into 2 or more independent circuits. The fuel circulates through the core by forced convection; the core is not divided. The thermal stability of the reactor is very good. Power excursions or fuel temperature transients are quickly damped by the phenomena of fuel expansion pushing part of the fissile material out of the critical zone. The loss of coolant accident results in a loss of half (or 1⁄3, 2⁄3) of blanket which, without relying on a reactor scram, results in an automatic adjustment of the reactor power level. Corrosion effects form the most difficult problem. Thermodynamic studies suggest the use of molybdenum alloys as structural materials.
Breeder reactors differ from other reactor types in that they are not only power-producing devices but also a source of fissile material and therefore should be considered as part of a complex “breeding system” which includes both the power reactor (producing electricity and heat) and the reprocessing and fuel preparation plant. From this point of view the fast reactor with molten fuel seems to be better adapted to the long-term secure breeding system than are the solid- fuel reactors.
The reactor system described here being a continuation of a long-term development study of a molten-chlorides breeder (Bulmer, 1956; Chasanov, 1965; Nelson et al., 1967; Taube, 1961) demonstrates some of these advantages, among others a very high inherent safety (without relying on engineered devices) against changes of power level and loss-of-coolant accident.