Inside a Japanese Nuclear Power Station

The battle to tame the stricken Fukushima Daiichi nuclear power plant has filled television screens for the last few days. The massive earthquake and tsunami that hit on March 11 and subsequent cooling problems caused a nuclear accident that likely means the plant will never be restarted.

Images of the mangled power station won't easily be forgotten, but what's a nuclear plant like during better times?

In July 2007 another nuclear power station run by Tokyo Electric Power Co. (TEPCO) was also hit by a large quake. That quake, at magnitude 6.6, was nowhere near as powerful as the magnitude 9.0 quake of March 11, but it forced the Kashiwazaki Kariwa nuclear power station offline for years for seismic upgrades. Some of the reactors are still offline.

As part of a campaign to show the plant sustained no major damage, TEPCO invited journalists inside the facility and reactor 3, a reactor many worried about due to a fire in a transformer outside the reactor caused by the earthquake. Kashiwazaki Kariwa is the world's largest nuclear power plant by electricity output and is home to 7 reactors.

Both Kashiwazaki Kariwa and Fukushima are boiling water reactors, which use a controlled nuclear reaction to heat water that in turn drives turbines to produce electricity. Kashiwazaki Kariwa is newer, it was built in the mid-nineties, whereas Fukushima Daiichi is from the mid seventies.

(A video version of this story with footage from inside the reactor containment vessel is available on YouTube.)

A nuclear plant is a high security zone and there were several checks to get inside, including an airport-style metal detector and x-ray for my camera. We'd had to provide copies of our passports in advance of the trip.

I'd already seen the plant on television and checked it on Google Earth, but those images only showed buildings. It wasn't until I got up close and inside that the scale of the plant became clear.

Inside the reactor building everything is big. The construction, as you might expect, is very solid.

Pressure inside is slightly lower than outside, so air is not pushed out of the building. To keep it that way, doors in front wouldn't open, unless doors behind were closed.

As we moved towards the center of the building, we came upon a row of shiny cylinders. They were the hydraulic pumps for moving the rods that help control the reaction at the core. Reactor 3 has 185 of the pumps, one for each rod.

At the very center of the building is the containment vessel. Its wall is a couple of meters thick. If the reactor core, situated at the top of the vessel, were ever to meltdown and fuel burn through the bottom, the containment vessel is supposed to seal radioactivity in. It needs to be very strong.

Inside there are metal platforms that lead to several levels so the maze of pipework, valves and machinery can be accessed. Everything is spotlessly clean and, as TEPCO was at pains to point out, we couldn't see evidence of earthquake damage anywhere we went.

A little outside the containment vessel stood a large pump that was several meters high. It was one of the pumps that injects liquid into the reactor core to stop the nuclear reaction. Its pumps like these that are among the troubles in Fukushima.

And at the very top of the building was a spent-fuel pool. This is where used fuel rods are stored to cool down. Another problem faced in Fukushima is a loss of water from just such a pool. The rods are transported from the reactor to the cooling pool by a large crane, which permanently sit atop of the structure.

Even though it was more than 3 years ago, the memories of my visit is still fresh in my mind. A nuclear power station is an amazing piece of engineering and it was, without doubt, one of the most impressive things I've ever seen.

Martyn Williams covers Japan and general technology breaking news for The IDG News Service. Follow Martyn on Twitter at @martyn_williams. Martyn's e-mail address is martyn_williams@idg.com

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