A background of the nuclear plant accident 2 :  Is it safe?

 原発事故 reactor containment vessel of Fukushima in Japan

< reactor containment vessel of Fukushima in Japan >

 This time nuclear accident in Japan was in depend on a direct cause and indirect causes.

Although the great earthquake caused the accident, the defect of the tsunami protection measures and the electric power unit in a nuclear power plant enlarged the damage.

A unified group of industry, government office, and academic society pressed down the security measures to the low level.

There are the social structure cannot reveal the corruption, and there are the peculiar corporate culture in Japan.

This time, we look back upon the safety of a nuclear power plant.








航空機離陸 A takeoff of an airplane

< A takeoff of an airplane >

What is safety?

The safety of equipment is estimated by a safety ratio, a rate of accident, and reliability.

For example, the safety ratio of an airplane is about 1.2 times.

If the maximum breaking load is 1 ton or less, it is considered that the equipment destroyed at 1.2 tons is safe.

If we consider this ordinarily, it will be fearful, but the aircraft has very few accidents compared with other vehicles.

The reason is in the thorough tests by destruction and endurance, the strict management of the manufacture and the operation, and the improvement by the accident analysis.

This has been making reliability.

For example, the rate of accident is that one piece in 10,000 pieces breaks at 20000 hours after.

Exchange of engine components etc. is the example.













阪神淡路大震災 the Great Hanshin-Awaji Earthquake in 1995 

< the Great Hanshin-Awaji Earthquake in 1995 >

 Safety of a nuclear power plant

The safety ratio of a reactor pressure vessel is 3. How do you evaluate this?

The safety ratio of an industrial machine or a plant is from several times to ten times.

At the start, the assumption of the maximum breaking load that operate on a nuclear power plant was careless.

Although the destructive power of 30 years ago was 250 gal(acceleration), only one part was raised to 1200 gal these days.

However, the maximum destructive power that was measured in an inland earthquake in Japan was 4022 gal.

It is not safe. The safety ratio is 1/16 but isn’t 3.

Furthermore, although the inland earthquake-resistant criterion was M6.5 at energy, M9.5 was measured in the Chile earthquake in 1960 (ocean trench type).

The fracture energy is 33000 times the criterion.














“The rate of a nuclear power plant disaster is lower than the probability that a meteorite will fall to Yankee Stadium.”

This utterance by a scientist was famous.

For example, the rate of accident of one cooling-water system is once in 100 years.

If the three systems is placed in parallel, a total rate of accident is once only in 1 million years.

In 435 nuclear power plants in the world, therefore, if the rate of accident is once in 1 million years, an accident will be once only in 2300 years.

However, major accidents of 12 in the world have occurred after 1957.

This difference is because the human error is not taken into consideration.

When an accident occurs in a nuclear power plant in Japan, in general, it is announced, “This is not a serious structural problem but a petty construction mistake, a check mistake, and an operation mistake, and we makes a worker put this into practice.”

Most factory accidents are human errors.

This foolish situation continued in Japan.

a lawsuit demanding to stop the nuclear power plant has been losing, and mass media promoted the nuclear power plant.


Next time, I may tell about the reliability of the industry.
























Categories: <english language, <japanese language, opinion, politics, science, Series: A background of the nuclear plant accident | Tags: , , | Leave a comment

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