Safety analyses were carried out to confirm the sufficiency of the function of the safety protection system against the pump/diagrid link rupture. The target plant was a pool-type sodium-cooled fast reactor (SFR) of about a 600-MW(electric) class equipped with an axially heterogeneous core currently under development in Japan. In the pool-type SFR, the primary system piping that connects the primary pump and the high-pressure sodium plenum located at the inlet of fuel subassemblies is called the pump/diagrid link. Because this piping is submerged in the reactor vessel, it is difficult to detect small-scale sodium leakage in this piping, and thus a large pipe break like guillotine should be assumed and evaluated as a design-basis event.

In order to confirm the detectability of the pump/diagrid link rupture by safety protection system signals, a series of analyses of a guillotine break for a pump/diagrid link was carried out. Sensitivity analyses was also performed to consider the uncertainty of the operating power level and reactivity coefficient. The sufficiency of the function of the safety protection system against the pump/diagrid link rupture is confirmed by whether or not the development target of the system in a pool-type SFR in Japan is satisfied. The target is that at least two kinds of signals are transmitted for the detection of the event.