Unit 4 is currently off, but a team found during a recent inspection that water levels in one of the basins were lower than regulated. In case of a disruption, this water can be used to cool down the reactor. A pump is needed to ensure that this process works, but that is only the case when the water is at a certain minimum level.
A team identified and solved the problem by adding more water to the basin in question.
According to a CGDIS statement, there was no imminent threat, but in case of an accident, the circulation mechanism may have malfunctioned. As it took too long to identify the problem, the Plant alerted the authorities for nuclear safety to declare a ‘level 1' issue.
The International Nuclear and Radiological Event Scale (INES) counts seven levels in total.
