The incident was initially given an INES rating of 2 ("incident"). However a video examination of the damaged fuel elements following the successful removal of the lid caused the rating to be raised to 3 ("serious incident"). This revealed that cladding on the majority of the 30 fuel elements had been broken, with radioactive spent uranium fuel pellets spilling from the elements into the bottom of the cleaning tank. Apart from the release of radioactive material, a concern was that the accumulation of a compact mass of fuel pellets could lead to a criticality accident, as the pellets were in a tank of neutron moderating water. Water containing neutron absorbing boric acid was added into the tank to raise its concentration to 16 g/kg to prevent this. Ammonia and hydrazine were also added to the water to help with the removal of radioactive iodine-131.