News Navigator: Why do Japan's nuclear plants need electricity to operate?

The Mainichi Shimbun answers some common questions readers may have about the need to supply electricity to nuclear power plants after the Jan. 1 Noto Peninsula earthquake caused a power cutoff to a nuclear station in the area.

Question: What happened to the nuclear plant on the Peninsula after the quake?

Answer: Hokuriku Electric Power Co.'s Shika Nuclear Power Station in the town of Shika, Ishikawa Prefecture has two reactors, both of which have been halted since the Great East Japan Earthquake of 2011. However, shaking from the Jan. 1 Noto earthquake measuring upper 5 on Japan's 7-level seismic intensity scale destroyed two power transformers used to keep electricity flowing into the facility. Two of the five power lines were downed, with repairs reportedly expected to take at least six months.

Q: It's a power plant. Why does it need electricity?

A: Mainly for cooling the nuclear fuel, which emits heat even long after the reactors have been stopped. Water must be continuously pumped in as a coolant. As well, various parts in the plant uses energy to power different sorts of equipment and lighting.

Q: What happens when the outside power source is cut?

A: Nuclear plants are always equipped with multiple backup diesel-powered generators allowing them to avoid accidents in such a situation. However, even these backup generators at the Fukushima Daiichi plant were damaged by the tsunami triggered by the March 11, 2011 earthquake. Without any electricity, reactors No. 1 through 3 suffered meltdowns of their cores.

Q: Is it safe at the Shika plant?

A: In a test of the three generators at reactor No. 1 after the Noto quake, one shut down automatically. Investigations determined the cause as circuitry in the plant that was switched following the breakage of the transformer. It was back in operation 12 days later.

Q: Will there be any measures to prevent a recurrence?

A: Japan's Nuclear Regulation Authority has begun to study whether the facilities inside nuclear power plants should be made more earthquake-resistant. Strict safety measures are needed as electricity is the last line of defense to prevent accidents.

(Japanese original by Yui Shuzo, Lifestyle, Science & Environment News Department)