The purpose of this page is to inform people of what happened at Fukushima and the reactor incident, and to give information about the plant itself. (present tense will be used throughout this)

Fukushima Reactor

Fukushima Daiichi NPP is plant that hosts 6 BWR reactorBWR reactorA boiling water reactor uses Light Water as both coolant and neutron moderator. The second most used reactor, next to the PWR reactors, there are approximately 75 plants in current operation. The efficiency of these reactors is about 46%, with 33-34% in practice. Enriched uranium is used as nuclear fuel, as light water absorbs too many neutrons to use Uranium that is natural. Light water is not as good of a moderator compared to Heavy Water or graphite, but it is good as in the event of a LOCA os, using Light WaterLight WaterLight water, although appearing to have a fancy name, is literally just ordinary water....except it does contain a small amount of Heavy Water. The point of light water is that it can be used as a moderator --however it can only be used in certain situations, as it absorbs too many neutrons to be used with unenriched uranium (which is why light water is presumably used in Spent Fuel Pools) Light water is mainly used in BWR reactors & PWR reactors Uranium Enrichment is necessary for the usage of. This resulted in Fukushima being capable of delivering a combined power of 4.7 GWe (4700 MWe).

Units 1, 2, and 6 were made by GE, 3 & 5 by Tobisha, and 4 by Hitachi. All 6 reactors were designed by GE. Unit 3 was fueled using Mixed-Oxide fuel instead of low-enriched uranium. Unit 5 uses Mark 1 containment, 6 using Mark 2.

This chart comes from Fukushima Reactor Information

Unit	Type	Net power	Start construction	First criticality	Commercial operation	Shutdown	NSSS	A-E	Builder
1	BWR-3 (Mark I)	439 MW	July 25, 1967	October 10, 1970	March 26, 1971	May 19, 2011	General Electric	Ebasco	Kajima
2	BWR-4 (Mark I)	760 MW	June 9, 1969	May 10, 1973	July 18, 1974	May 19, 2011	General Electric	Ebasco	Kajima
3	BWR-4 (Mark I)	760 MW	December 28, 1970	September 6, 1974	March 27, 1976	May 19, 2011	Toshiba	Toshiba	Kajima
4	BWR-4 (Mark I)	760 MW	February 12, 1973	January 28, 1978	October 12, 1978	May 19, 2011	Hitachi	Hitachi	Kajima
5	BWR-4 (Mark I)	760 MW	May 22, 1972	August 26, 1977	April 18, 1978	December 17, 2013	Toshiba	Toshiba	Kajima
6	BWR-5 (Mark II)	1067 MW	October 26, 1973	March 9, 1979	October 24, 1979	December 17, 2013	General Electric	Ebasco	Kajima
7 (planned)	ABWR	1380 MW	Canceled 04/2011	Planned 10/2016
8 (planned)	ABWR	1380 MW	Canceled 04/2011	Planned 10/2017

Reactor Incident

TL;DR

Fukushima's earthquake trigged SCRAM of 3 Nuclear ReactorNuclear ReactorIn it's most simplest form, a nuclear reactor uses Uranium and other radioactive materials and the fission from uranium to create heat, and transfer that heat into steam to create power. Nuclear reactors are one of the biggest sources of energy, although not renewable, uranium has a very high energy density resulting in massive power transmissions. There are many different types of nuclear reactors, and this term serves as a broad hub/introduction for each type. After uranium is used in reactos, tsunami stopped EDGs, resulting in LOOP, lack of cooling led to meltdown; 3/6 reactors and 1/6 Spent Fuel PoolAir Traffic Control\#emptys were affected.

Information

Fukushima has 6 reactor units; 5 & 6 were undergoing maintenance and are located a bit away from the rest, and experienced no damage during the incident. unit 4 was undergoing maintenance and was damaged.

Before the incident

TEPCO (tokyo electric power company) submitted a report predicting a high tsunami; this report was originally made in 2008 but delayed.

Primary Incident

A 9.0 Magnitude earthquake strikes at the coast. At this time, a LOOP event occurs, resulting in automatic shutoff of all reactors. At this time, A & B trips occur and EDGs turn on. In general, in an emergency such as an earthquake or LOOP, SCRAM measures are indicated and even with loss of control are automatically activated. A few minutes after the reactor trips, Unit 1 ECCSECCSEmergency Core Cooling Systems encompass all of the emergency systems used in Nuclear Reactors. Inside of the RPV of a reactor is the reactor core, which gets hot due to fission during operation. In the event that primary cooling systems go offline due to a powerloss, LOCA, or other reason, ECCS systems are automatically enabled. ECCS broadly describes all of the emergency systems used, however specific emergency systems can be used in isolation. Some ECCS systems are specified for a specific d was turned on and 10 min after that turned off manually as temp dropped. This all occured at 14:46 on March 11, 2011.

At 15:27 the first tsunami of 7 struck - the seawall and plant design indicated 5.7M as the max tsunami. The emergency condenser in Unit 1 also failed, and then the big wave came - 7.5 FT. Unit 1 was flooded the turbine halls and such the EDG started to flood, batteries flooded, all seawater intake structures unavailable due to flooding, and diesel fuel tanks are flooded. At this point, ALL electrical power offline, LPCS offline, RHRRHRThis page's sources are primarily from NRC ML11223A219 (Westinghouse Section 5.1) RHR or Residual Heat Removal is a system utilized in Nuclear Reactors to manage the decay heat from the reactor. When a reactor is at its subcritical or shutdown stages, the fuel still produces heat that needs to be managed. During this period, RHR removes heat using heat exchangers and service water. During shutdown, RHR reduces temperature of the core to safe temperatures. While in shutdown, RHR maintains the sa offline, LPCI, mainpumps and ADS have all failed. What this means is that the remaining working items are the RCIC in unit 2 & 3 and isolation condenser in reactor 1. Furthermore, unit 1 IC valves fail, and decay heat results in temp increasing. Reactor decay heat is from after the scram; the rods are still hot and create remaining heat that needsto be managed,

Also, the unit 2 SFP was damaged, and needed to be pumped (spent fuel pools are often noted as a primary feature that needs to be managed as if damaged can result in major damage and hard to cool due to the lack of safety systems regarding it.)

Later, the Unit 1 reactor has a low water level, and ECCS fails to manually start, and fuel unrecovery occurs - loss of ALL water. Core temp increases and fuel damage occurs. At this time, likely the pressure was also causing the zirconium claddingCladdingCladding is the thin walled metal tube that composes the outside of a fuel rod. It's purpose is to prevent corrosion of the fuel by the coolant & release of fission contents into the coolant. Although Zirconium alloy is common, aluminum and stainless steel is also used. Cladding Types Zirconium alloy has been used for so long due to it's properties being very good for nuclear reactors. * New research suggests that there is an alternative - SiGA cladding. This cladding is made from silicon car to start a reaction creating hydrogen gas. After this, the first mobile generators arrive, and unit 2 SLCS is attempted to be started.

The next day, Unit 1 is planned to be vented; and fresh water injection begins, however, the core of reactor 1 has fallen to the bottom of the RPVRPVReactor Pressure Vessel - contains all of the reactor heat. In BWR reactors, the RPV contains the reactor core - basically the entirety of the main reactor assembly. The RPV is designed to withstand a very large amount of force considering that in a BWR it must withstand the pressure that both it operates at and at emergency designs -- this is due to the fact that in most designs, the RPV isn't considered to be at major risk: even during a major LOCA the RPV is considered to be at healthy condi. Unit 2 is also planned to be vented, and then venting occurs. a bit later, a hydrogen explosion occurs.

Hydrogen Buildup

As predicted, a hydrogen buildup occured, and the explosion occurs due to hydrogen and oxygen reacting. Primary containment is not damaged, but secondary containment is damaged, and unit 2 SLCS pump cabling is damaged. Debris covers the site which is highly radioactive, and unit 1 has seawater injection.