Transient with failure of the reactor protection system (TC)

12.102. Should there be a malfunction combined with failure of the reactor protection system, the reactor will continue to generate power. However, it is assumed that the main steam valves will isolate the reactor from the turbine generator and the recirculating pumps will trip. As a result of rising steam pressure, safety relief valves will open, releasing steam to the suppression pool, with the resulting core voiding reducing the reactor power. Subsequent events would depend on the ability of water makeup and coolant injection systems to keep the core covered. Insufficient suppression pool heat removal capacity could result in excessive pressur­ization of the containment and failure, while core uncovering would result in fuel failure and fission product release.

Transient with failure to remove residual core heat (TW)

12.103. In this type of sequence, the reactor would trip, but the suppres­sion pool would fail to remove the continuing production of residual heat. Containment failure could occur as a result of excessive pressure and the ECC systems, which use the suppression pool as a water source, becoming ineffective because the water is now saturated and cannot be pumped. Core uncovering is then likely.