The emergency cooling system of the two-phase nuclear power plant has a reserve water tank at the bottom of the reactor building.

The French nuclear regulatory authority ASN initially classified this disruption of the emergency cooling systems as stage 1 on the international scale of nuclear events (INES), but later assigned it the stage 2 classification.

The operating company EDF then built the slider so that excess pressure can no longer lead to a blockage.

In 2017 the French nuclear regulator Autorité de sûreté nucléaire (ASN) placed Belleville under increased supervision because of "several failures by the operator in identifying and analysing the consequences of anomalies affecting certain safety-critical equipment".

[1] On 2 December 2021, the International Atomic Energy Agency (IAEA)'s Operational Safety Review Team (OSART), concluded an 18-day mission to Belleville and concluded the plant's operators had demonstrated a commitment to safety by introducing additional methods to prepare for accident management and using innovative approaches in the training of plant staff.