Core Design and Dynamics of the SECURE District Heating Reactor

The SECURE reactor was developed by a Finnish-Swedish project group in 1976–1977. It is a small low-pressure and low-temperature nuclear plant for district heating purposes. The special safety requirements for a reactor of this kind have led to an unconventional design with certain inherent safety features to guarantee safe shutdown without the use of any active components. The reactor is located inside a large, slightly pressurized pool containing cold water with about 1000 ppm natural boron. On shutdown, the pool water flows into the primary system to keep the reactor subcritical. Boron is also used for power control, whereas burnup is compensated for by use of the burnable absorber Gd₂O₃.