On December 31, the management of the Tricsatin nuclear power plant declared a level 1 incident on the international nuclear and radiological events scale (INES) which has 7 to the nuclear safety authority.
A faulty nuclear reaction measuring instrument
On December 29, the control room of reactor No. 1 noticed that part of the reactor measurement chains were no longer functioning. This is an instrument which measures the homogeneity of the nuclear reaction within the reactor, more precisely the homogeneity of the neutron flux. This extremely powerful neutron flux must be well distributed within the cell. This instrument ceased to function for two days from December 27 to 29. EDF repaired this electronic card when the incident was discovered.
The specifications indicate that EDF would have had to measure the distribution of the nuclear reaction every hour in the absence of this instrument. This was not done since for two days EDF was unaware that this instrument was defective.