Reactor 3

Historical information and statistics about Fukushima Daiichi Reactor 3.
For current updates, click here.

Interactive Timeline: Launch Now

Fukushima I – 3

Type: BWR-4
Containment: Mark I
Construction: December 28, 1970
Criticality: September 6, 1974
Commercial Operation: March 27, 1976
Electric Power: 784 MW
Reactor Supplier: Toshiba
Architecture: Toshiba
Construction: Kajima
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
Maximum pressure 8.24MPa
         Maximum temp 300℃ 
          (M) Height   33
          Diameter cylindrical section (m)  11
          The sphere diameter (m)  20
         Maximum pressure  0.38MPa 
         Maximum temp  140℃
Pressure suppression pool water (t)  2980
Spent fuel pool current inventory: 566
Initial reactor power: 2381 MWt (rated output)
Initial reactor pressure: 7.03 MPa [abs] (Normal operating pressure)
Initial reactor water level: about 5274 mm (normal water level: TAF standard)
RPV node split: Attachment 1 6
Effective core node split number: radial direction: 5 nodes, Axis direction: 10 node
Cladding temperature damage: 727 ℃ (1000K)
Fuel melting: Appendix 1 Table 2
Containment model: Attachment 1 7
Containment space volume:  D / W space: 4240 m3 , S / C space: 3160 m3
Suppression pool water: 2980 m3
(Adjust the parameters so that it is ORIGEN2 collapse 壊熱 equivalent that reflects the fuel loading history) ANSI/ANS5.1-1979 Models | decay heat


Reactor building dimensions:
Width (north-south): 
 46 meters
Height (grade level to roof):  46 meters
Outer wall thickness:  .5 to 1.5 meters
Material: Ferroconcrete

Material: ASME SA 516 Gr.70
(M) Height:   33
Diameter cylindrical section (m):   10.9 m
The sphere diameter (m):  20 m
Maximum pressure: 0.38MPa
Design outer pressure (gauge): 0.14 kg/cm2g
Design inner pressure (gauge): 3.92 kg/cm2g
Maximum temp:  140 °C
Design temp: 138 °C
Containment model: Appendix 1 Figure 5

Containment space volume: D / W space: 4240 m3 , S / C space: 3160 m3



1: approx. 34m
2: approx. 11m
3: approx. 20m
4: approx. 9m
5: approx. 2m
6: approx. 17-34mm
Material: Carbon steel





Pressure vessel (RPV reactor vessel):
Applicable standard:

Inner diameter: 
 5.57 m
Hydraulic equivalent diameter:  4.03 m
22.0 m
Thickness of base metal: 138 mm
Thickness of stainless liner: 5 mm
Material of base metal:  SA533 -, SA-508
Total weight: 
(t)  500t
Maximum pressure: 
Design pressure (gauge): 87.9 kg/cm2g
Maximum temp: 
300 °C
Design temp: 302 °C
Core temperature:  ?
Initial reactor power: 
Initial reactor pressure:
Operation pressure in reactor pressure vessel (gauge):  6.93 MPa
Initial reactor water level:
Total flow rate of coolant: 33.8 x 103 t/h
Steam flow rate:  4440 t/h
RPV node split:  
Attachment 1 4
Effective core node split number: 
radial direction: 5 nodes, Axis direction: 10 node
Axis direction: 

Cladding temperature damage: 
Fuel melting:  
Appendix 1 Table 2
Decay heat: 
ANSI/ANS5.1-1979 model ORIGEN2 collapse, which reflects (fuel loading history Adjust the parameters so that it is equivalent 壊熱)


1:  approx. 22m
2:  approx. 5.57m
3:  approx. 143mm
4:  approx. ?
Material:  Carbon steel
(with stainless steel lining)




Primary loop recirculation System:
Number of loops:
Inner diameter of pipe: 627 mm
Number of jet pumps: 20
Flow rate of pumps: 7800 t/h
Pump head: 152 m
Output power of pump motor: 3750 kW
Number of rotation of pump motor: 1380 rpm

Main steam system:
Number of pipes:
Inner diameter of pipe: 610 mm
Number of main steam isolation valves: 8
Number of safety relief valves: 8
Number of safety valves:  3

Fuel: LEU
Weight of UO2: 93 t
Number of fuel assemblies (body) 548
Fuel assembly length (m)  
Length of active fuel: 3710 mm

The amount of uranium loading (t): 93 (9×9(A)x2/3+MOXx1/3), 94(9×9(A))
Averaged uranium enrichment (wt%):  MOX:1.1-1.3 for U (2.7-5.3 for Pu),9×9(A):3.8 wt%
Burnup (9×9(A)): averaged 45.0 GWD/t, maximum 55.0 GWD/
Burnup MOX: averaged 33.0 GWD/t, 40.0 GWD/t

Fuel (9x9 (A) ):
Diameter of pellet:  9.6 mm
Outer diameter of cladding tube:  11.2 mm
Thickness of cladding(Thickness of zirconium liner):  0.71(0.1) mm
Fuel assembly, Number of FA(Total number): 516(548)
Number of fuel rods in one fuel assembly: 9 x 9 – 7 (2 water rods): including 8 partial length rod
Material of Channel Box:  Zircaloy-4

Fuel MOX:
Diameter of pellet:  10.4 mm
Outer diameter of cladding tube:  12.3 mm
Thickness of cladding(Thickness of zirconium liner):  0.86(0.1) mm
Fuel assembly, Number of FA(Total number): 32(548)
Number of fuel rods in one fuel assembly: 8 x 8 – 4 (Water rod)
Material of Channel Box:  Zircaloy-4

Control Rods:
Number of control rods: 
Control material: B4C
Configuration:  cross shape
Pitch: 305 mm

Reactor output:
Electrical output (kW million):  
Heat output (kW million):    238.1
Thermal output:  2381 MWt

Suppression Chamber (Torus):
Diameter of torus (torus): 33.5 m
Minor inner diameter of torus: 8.9 m
Number of vent pipe/downcomers: 8
Inner diameter of vent pipe/downcomers: 2.06 m
Inner diameter of the header: 1.46 m
Number of downcomers (inside torus tube):96
Pressure suppression pool water (t)  2980 m3
S / C space: 
Suppression pool water: 2980 m ^3 (estimate based on unit 2)

Spent fuel pool:
Spent fuel pool current inventory: 
Spent fuel pool damaged assemblies: 

Some of the specification data is from this report by FDADA.

Articles & Research on Unit 3 Can Be Found Here:

The third of the Fukushima Daiichi reactors to be built, reactor 3 had the shroud replaced in 1999. At the same time, Fukushima Daiichi received its first shipment of MOX (plutonium-uranium) fuel. Various issues and the rescinding of local government approval to run MOX in unit 3 delayed the installation of MOX fuel until September of 2010. At the time of the earthquake unit, 3 had a mixed load of MOX and LEU in the reactor. It is unclear how many total MOX shipments were received at Daiichi and how many total assemblies are stored or in use at the power plant. Records show unit 3 to be the only one running MOX but MOX fuel must be stored in a spent fuel pool even if it is unused due to volatility. Updated records show one shipment of MOX to Kashiwazaki Kariwa that was not used at that plant due to a local referendum voting down the use. The MOX assemblies were accounted for at Kashiwazaki Kariwa up until a few years ago when no further updates on the status of those assemblies were made. This leaves open the potential for those assemblies to have possibly been planned by TEPCO to be moved to Fukushima Daiichi for use there. We do not have any documents to prove or disprove this theory or any record of the current location of those MOX assemblies initially delivered to Kashiwazaki Kariwa.

Unit 3 lost all AC power at 3:42 pm JST on March 11th. Loss of the emergency core cooling function of the ECCS  was reported to authorities at 5:58 am JST on March 13th.
At 9:20 am JST on March 13th the pressure relief valve for the reactor was opened.
At 1:12 pm JST on March 13th seawater was injected into the reactor.
Pressure in the reactor reached 460 kPa beyond the design value at 6:10 am JST March 14th.
Unit 3 suffered an intense hydrogen explosion at 11:01 am on March 14th.
At 8:32 am JST an enormous amount of white smoke belched from unit 3.
Self Defense Forces attempted to drop water by helicopter at 4 pm JST on March 16th but were abandoned due to high radiation levels.
At 9:48 am JST Self Defense Forces resumed helicopter water drops.

It is now estimated that the reactor core melted to the bottom of the reactor vessel within 16 hours of the station blackout (power loss). The melted core is also likely melted through the vessel and is somewhere within the containment structure. TEPCO has not been able to send in workers to perform any sort of containment inspection. Workers entered the basement level of the building and attempted to open the torus room door. The door was found to be bowed out and jammed. In July 2012 workers were able to put the robot SurveyRunner into the torus room where it did a partial inspection of the catwalk on top of the torus. Video of that can be found here. Unit 3’s torus room was found to be in much better condition than imagined and in much better condition than Unit 1’s torus room. The 1st-floor TIPS room of Unit 3 was also inspected in May 2012. The steel door and door frame had been blown into the TIPS room hallway. This prevented any additional inspection of the TIPS room itself. Current work in late 2012 consists of attempts to remove debris from the refueling floor level with robotic heavy machinery. A steel frame and cover will be installed over the remaining building to facilitate removing fuel from the fuel pool. The containment airlock doors have been found to be leaking high levels of radioactive water in small amounts. The heavy concrete plug for the equipment hatch was pushed out of place raising more concerns about what took place in containment. Some of the interior building damage is likely due to the massive hydrogen & steam explosions at unit 3.

Radiation Readings Unit 3 (2011-2012, added readings up to 2016)



Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: