Reactor 5

Historical information and statistics about Fukushima Daiichi Reactor 5.

Fukushima I – 5

Type: BWR-4Fukushima Daiichi Unit 5
Containment: Mark I
Construction: May 22, 1972
Criticality: August 26, 1977
Commercial Operation: April 18, 1978
Electric Power: 784 MW
Reactor Supplier: Toshiba
Architecture: Toshiba
Construction: Kajima
Fuel: LEU
INES Disaster Rating: 7
Electrical output (kW million)  78.4
Prime contractor     Toshiba
Heat output (kW million)   238.1
Number of fuel assemblies (body)  548
Fuel assembly length (m)   4.47
The amount of uranium loading (t)  94
Number of control rods 137
Pressure vessel
         Inner diameter (m)   5.6
         (M) Height     22
         Total weight (t)  500
          (M) Height   34
          Diameter cylindrical section (m)  11
          The sphere diameter (m)  20
Pressure suppression pool water (t)  2980

The fifth of the Fukushima Daiichi reactors to be built. Unit 5 was in cold shutdown when the earthquake hit. No known major damage occurred at unit 5 and it managed to maintain a somewhat safe status until AC power could be restored. Unit 5 has a slightly different construction than units 1-4 including outside vertical structural beams that can be seen in the image. Unit 5 had the shroud replaced in 2000.

While Unit 5 did not suffer the massive damage units 1-4 did, there was concern about hydrogen build-up. Workers cut holes in the reactor building roof to give potential hydrogen a route out of the refueling floor. After the 2007 earthquake at Kashiwazaki Kariwa TEPCO ordered workers to weld shut blowout panels on the refueling floor level walls. This may have created the need to cut holes in the roof. Unit 5 did lose water intake access. The intake pipe heads that pull water out of the sea and into the turbine building were damaged by the tsunami. TEPCO eventually installed temporary pipes and pumps to bring water into the cooling systems.

A near accident scenario did take place at unit 5 but was not disclosed until years later in an IAEA report. Portions of the containment system were removed while some of the safety systems on the reactor were locked out in preparation for running tests. When the disaster hit, this configuration posed a very real potential for unit 5 to have gone into a dangerous scenario. In 2015 all of the fuel was offloaded from unit 5’s reactor vessel to the spent fuel pool.

Unit 5 being in a relatively undamaged state has provided a test environment for workers preparing for work in the more damaged reactors. Workers have tested robot operation and use of new scopes on Unit 5 to fine-tune the work before going into the more dangerous conditions at the other units.

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