Tell Us about the Construction of the Fukushima Nuclear Power Plants

Celsias/MIT NSE Nuclear info Hub

 

We ,like everyone else, have been trying to come to terms with what is actually happening at Fukushima. Like others, we don't always believe the Government statements from any Government. And there are commentaries that run the spectrum from total meltdown to much more reassuring. We liked this one for the reasonably simple explanations it provided.It is part of a re-blog from a post 

We, like everyone else, have been trying to come to terms with what is actually happening at Fukushima. Like others, we don't always believe the Government statements from any Government. And there are commentaries that run the spectrum from total meltdown to much more reassuring. We liked this one for the reasonably simple explanations it provided.It is part of a re-blog from a post 

This is from a re-blog of a post published recently by‘Morgsatlarge’ , an Australian English teacher living in Japan who asked Dr Josef Oehmen, of MIT in Boston.Oehman is not a nuclear physicist.This blog is now on MIT NSE's Nuclear Information Hub.

We thought we might repost the questions but just one by one.

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nuclear1

 

 

Tell us about the Construction of the Fukushima nuclear power plants

The plants at Fukushima are Boiling Water Reactors (BWR for short). A BWR produces electricity by boiling water, and spinning a a turbine with that steam. The nuclear fuel heats water, the water boils and creates steam, the steam then drives turbines that create the electricity, and the steam is then cooled and condensed back to water, and the water returns to be heated by the nuclear fuel. The reactor operates at about 285 °C.

The nuclear fuel is uranium oxide. Uranium oxide is a ceramic with a very high melting point of about 2800 °C. The fuel is manufactured in pellets (cylinders that are about 1 cm tall and 1 com in diameter). These pellets are then put into a long tube made of Zircaloy (an alloy of zirconium) with a failure temperature of 1200 °C (caused by the auto-catalytic oxidation of water), and sealed tight. This tube is called a fuel rod. These fuel rods are then put together to form assemblies, of which several hundred make up the reactor core.

The solid fuel pellet (a ceramic oxide matrix) is the first barrier that retains many of the radioactive fission products produced by the fission process.  The Zircaloy casing is the second barrier to release that separates the radioactive fuel from the rest of the reactor.

The core is then placed in the pressure vessel. The pressure vessel is a thick steel vessel that operates at a pressure of about 7 MPa (~1000 psi), and is designed to withstand the high pressures that may occur during an accident. The pressure vessel is the third barrier to radioactive material release.

The entire primary loop of the nuclear reactor – the pressure vessel, pipes, and pumps that contain the coolant (water) – are housed in the containment structure.  This structure is the fourth barrier to radioactive material release. The containment structure is a hermetically (air tight) sealed, very thick structure made of steel and concrete. This structure is designed, built and tested for one single purpose: To contain, indefinitely, a complete core meltdown. To aid in this purpose, a large, thick concrete structure is poured around the containment structure and is referred to as the secondary containment.

Both the main containment structure and the secondary containment structure are housed in the reactor building. The reactor building is an outer shell that is supposed to keep the weather out, but nothing in. (this is the part that was damaged in the explosions, but more to that later).

For other great stories on Celsias:

Lets dream a Little: Rebuilding Christchurch Green

Are Smaller Nuclear Reactors Safer?

The Pacific Rim of Fire that So Many of us Live on 

 

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