This accident is mitigated by isolating the group of steam generators affected via closing their steam and feedwater lines. The secondary side of the steam generators then reaches thermal equilibrium with the primary circuit, with the pressure also being equalized. Eventually, the reactor could continue its operation at reduced power.

Steam line break

Sudden depressurization of the secondary side of the steam generators increases heat removal from the primary system, resulting in a consequent core overpower. Reactor shutdown (FSS and SSS) and the residual heat removal system are actuated, and the reactor then reaches a safe state. In the case of a hypothetical failure of both shutdown systems, reactor overpower does not compromise critical safety values (DNBR and CPR) because the total primary heat removal by the steam generators is intrinsically limited by the reduced tube-side water inventory.

NPP blackout

This is an event with a major contribution to core meltdown probability in a conventional light water reactor. In CAREM, extinction and cooling of the core and decay heat removal are secured without external electric power, by the passive safety systems. Loss of electric power causes the interruption of feedwater supply to the hydraulically driven CRDs and results in the insertion of absorbing elements into the core. Nevertheless,

Effective Dose (Sv)

FIG. III-4. Acceptance criterion for BDBA.

in the case of a failure of the first and the second shutdown systems (both passive), feedback coefficients cause a self-shutdown of the fission chain reaction without compromising safety related variables. The decay heat is then removed by the RHRS with an autonomy of several days.