The Super Near Boiling Reactor The 25MW Super Near Boiling Nuclear Reactor (SNB25) in Transient States and Confirmation of its Inherent Safety

Currently, nuclear power plants are being built in the hundreds of Megawatts to Gigawatt range to produce large amounts of energy to supply densely populated areas. Although the designers of nuclear power plants take great strides to make reactors safe through complex monitoring and control systems, inventive ways to decrease decay heat, and designing containment structures, large reactors are not inherently safe. The Super Near Boiling 25MWth reactor is a small unpressurized reactor conceptually designed by Lt(N) Stephane Paquette that shows great potential for inherent safety due mainly to its large negative void reactivity coefficient of -5.17mk per % void. In order to confirm that the reactor is indeed inherently safe, a kinetic model has been developed to examine the time behaviour of the reactor.;It has been determined that the reactor does not experience large power excursions or produce temperatures that could compromise its structural integrity. Also, as the reactor is unpressurized, the coolant/moderators normal output coolant temperature is 95°C. If the temperature of the coolant/moderator rises above the saturation temperature of 100°C, the coolant begins to boil(void). Due to the large negative void coefficient, the reactivity is rapidly reduced causing the reactor to become subcritical in 0.84 seconds.;Using the kinetic model, the reactor has been examined through various positive and negative reactivity insertions as well as during abnormal conditions including a loss of coolant flow and a total loss of coolant. The first trial examines the time behaviour of the reactor through positive reactivity insertions ranging from 1mk to a maximum of 6.25mk. When the reactor operates at full power and the maximum possible reactivity of 6.25mk is inserted, the reactor increases in power and temperature until the coolant begins to void. The presence of voiding causes the reactor to decrease in power due to the large negative void coefficient. The second trial examines the reactor during abnormal conditions. These include a loss of coolant flow and a total loss of coolant. During both of these trials, the SNB25 reactor did not experience power excursions or reactor component temperatures that would compromise its structural integrity. Finally, the time behaviour of the reactor was examined with negative reactivity insertions to confirm that the reactor would shut down.