Main accidents and breakdowns in nuclear power facilities in FY2012
|Cessation of operation of spent fuel pool water clean-up system pump.
|Equipment abnormality alarm activated in the A system of the containment atmosphere monitoring system (CAMS).
|Breakdown of electrical motor of the emergency cooling service seawater pump (A). Caused by the occurrence of an electrical short due to corrosion from penetration of rainwater.
|Water leak from controlled area auxiliary building air exhaust duct.
|When attempting to withdraw the control rods one notch to confirm the movement of the control rod drive mechanism after recovery of isolation of the hydraulic control unit, a problem occurred when control rods in core position 58-31 withdrew three notches. A full confirmation of the action of the control rod drive mechanism was implemented. At this time, in the action confirmation test conducted on June 12, a problem occurred when core position 02-31 control rods also withdrew two notches when the command was given to withdraw one notch. Abnormalities were found in the directional solenoid valve (valve 122).
|Defect in a residual heat removal system electrical valve.
|Damage to the bearings on the reactor building overhead crane runway.
|Onagawa 2 & 3
|As a result of an inspection conducted on the upper part of the channel boxes of fuel stored in the Unit 2 the spent fuel pool, it was confirmed that of 1807, the clip joints on the upper part of 13 channel boxes were partially damaged (max. length approximately 1.1 cm). Of the total of 1386 boxes in Unit 3, 19 were confirmed to have similar damage.
|Burnout damage to lighting cable in miscellaneous solids melting treatment building.
|Fracture due to stress corrosion cracking found in proximity to weld on one of four parts fixed to a steam dryer in order to hoist it up.
|Damage found on water circulation piping.
|Main exhaust stack radiation monitor sampling pipe found to have a defective connection.
|Tsuruga 1 & 2
|As a result of an inspection conducted on the upper part of the channel boxes in the spent fuel pools, 3 of the fuel channel boxes in Unit 1 had partially damaged or missing clip joints. No damage was found in the Unit 2 channel boxes.
|Tokai Reprocessing Facility
|Contamination was found on the surface of radioactive liquid waste piping in a utility room in the analytical laboratory.
|Seawater was found to be leaking from the air cooling tower of emergency diesel generator B.
|Shimane 1 & 2
|As a result of an inspection conducted on the upper part (clip) of all 4381 channel boxes (798 in Unit 1, 2648 in Unit 2, and 872 in Unit 3) that were loaded into the reactor core or were being stored in the spent fuel pools, it was confirmed that there was damaged parts on the clip joints of 13 channel boxes (10 in Unit 1, 3 in Unit 2).
|Tomari 1 & 2
|A defect was found in the monitor data transfer of the discharge structure of Units 1 & 2. A defect had occurred in the transmission of data in the monitoring station.
|Accident involving inability to withdraw control rods (02-27) that occurred during a control rod action test as part of a functional inspection of the control rod drive hydraulic pressure system.
|Fukushima Daiichi 5
|Dropout of the minimum flowrate bypass valve on the core spray system (B).
|Deformation of water rods in two fuel assemblies.
|Reduction in thickness of SG tubes in component cooling water heat exchanger B.
|Defective reading from neutron flux detector.
|Of 72 rotor blades detached from the 12th stage of the generator side of the low-pressure turbine (B), bending damage was discovered on the attachment base (rotary blade side) on 4 of the blades, and fissures on the attachment base (rotary blade side) on 11 of the blades.
|Foreign object discovered on the lower part of the first spacer of a fuel assembly.
|Fractures found in the attachment base of rotary blades in the 12th stage of the high-pressure turbine side and the 12th stage of the generating side of the low pressure turbine (C).
|Leakage of waste cleaning liquid outside of a controlled area.
|Corrosion on the second injection isolation valve in residual heat removal system A.
|It was confirmed that fuel rods inside the two fuel assemblies in which deformed water rods had been discovered on October 16 had come into contact with each other and that they did not possess the necessary function.
|A fracture was discovered in the attachment base of the reactor cleaning fluid pump (A) vane wheel.
|Ningyo Toge Environmental Engineering Center Refining and Conversion Facility
|Water containing radioactive substances found to be leaking from an exhaust duct in a non-controlled area.
|Fukushima Daiichi 6
|Leak from seawater sampling line of the reactor closed cooling water system heat exchanger (B).
|Damage to the turbine blade of emergency diesel generator A and bending damage to weld between the turbine blade and shaft.
|Divergence from the operating limits of system B emergency direct current bus.
|Fukushima Daiichi 5 & 6
|Leak in the intake chamber between the temporary tank storing retained water and the (reverse osmosis membrane type) desalination apparatus.
|Fukushima Daini 3
|Damage to the axis bearings of the reactor building overhead crane runway.
|Divergence from operating limits due to automatic shutdown of emergency diesel generator (A) (emergency diesel generator (B) being in shutdown for inspection).
|Of 68 fuel assemblies that had completed tests, 6 were found with deformed water rods, and of these it was confirmed that fuel rods had come into contact with each other in one assembly, and did not possess the necessary function.
|During regular testing on the residual heat removal system (A), a problem occurred when it was attempted to open one test flowrate adjustment valve (electrical motor-operated valve) from the fully closed position, but the valve would not open.