Fukushima and Chernobyl: Level Comparison

Japans Fukushima Disaster has renewed anti-nuclear protesters

There is a lot that seems to set Fukushima apart from Chenobyl, it is not clear why, after over three weeks, the Japanese have suddenly chosen to upgrade to Level 7 skipping Level 6.

Have they and other countries that are helping them given up hope of retrieving the situation, asks nuclear safety expert L V Krishnan.The Japanese government upgraded the severity level of the damage to the reactors in Fukushima to Level 7 from what was described as Level 5 three weeks earlier. There is no higher level in the scale, and the Chernobyl accident is the only one rated so high in history.

Those who have been claiming from the beginning that the happenings in Fukushima are as dangerous as Chernobyl will find support from the Japanese assessment. What indeed are the parallels between the two? An examination will provide some clarification.

Chernobyl facts

The Chernobyl accident in Ukraine occurred in an operating reactor. It was caused by indiscriminate action by the operator and resulted in a sudden explosion within the core.

The reactor was completely destroyed by the explosion and the prolonged fire that ensued swept most of the radioactivity in the core including the fuel itself high into the atmosphere spreading it far and wide.

There was extensive contamination of land around the reactor in Ukraine and the neighbouring Belarus. Poverty made people return to the contaminated areas in spite of the risk of radiation exposure. Significant levels were found in other countries further away. That did not warrant evacuation or relocation but restriction was imposed on consumption of meat and other food products.

It took several months to entomb the remains of the reactor in a structure called the sarcophagus, which is now crying for repairs or replacement by a stronger structure.

Success and failure of safety measures

There are significant differences in the events that unfolded in Fukushima. Safety equipment kicked in immediately after the earthquake to shut down the reactor promptly.

Emergency cooling began but was disabled by the tsunami never to recover. Countrywide impact of the forces of nature denied vital electrical power to restore cooling, for nearly two weeks. An explosion occurred in four of the six reactors at site, but not in the reactor vessel. All of the fuel and much of the associated radioactivity remains in the reactor vessel.

The hydrogen explosions that occurred caused atmospheric release mainly of material in gaseous form like iodine and cesium. The releases came in puffs separated in time and were dispersed largely over the ocean.

Japanese authorities have estimated that the cumulative release so far is a tenth of that in Chernobyl. Remedial measures since then seem to have arrested further atmospheric release. There are no cases reported of excessively high, fatal radiation exposure among personnel working in the plant.

Exposure levels on population

Protective measures like moving people out of the vicinity of the plants were taken well in advance before the release of radioactivity. Iodine tablets were administered in good time. This has considerably minimised radiation exposure. In particular, measurements reported reveal that thyroid exposure among children is far below the conservative limits prescribed.

Estimates are that even if people continue to live there for a year, they would receive minimal exposures well within the limits adopted by the Japanese.

Containment provisions under revision?

It is the inadequate containment provision that seems to be common to the reactor in Chernobyl and those in Fukushima. A hydrogen explosion blew off the roof of the reactor building in both cases.

The crippling of four reactors at the same time each contributing to radioactive releases is perhaps the only aspect that makes the Fukushima case seem worse than Chernobyl but the magnitude of release is far less to support that conclusion.

While the Soviet Union was determined to handle the Chernobyl accident all by itself, the Japanese have sought and utilised help from various quarters, including the Russians.

On assigning levels

On March 12, the second day after the earthquake, soon after the hydrogen explosion in unit 1, Japanese authorities assigned Level 4 for the accident suspecting fuel damage and likely melting and assessing the radioactivity release to be rather low. In subsequent days, there were explosions in other units pointing to larger releases.

Without electrical power and fresh water, little could be done other than spraying seawater on the buildings and praying for lower temperatures. Meanwhile protective measures were implemented up to about 20 km. It was a clear Level 6 situation, but the authorities declared it to be Level 5 instead and that announcement came only on March 18.

With so much that seems to set Fukushima apart from Chenobyl, it is not clear why, after over three weeks, the Japanese have suddenly chosen to upgrade to Level 7 skipping Level 6. Have they and other countries that are helping them given up hope of retrieving the situation? That does not seem probable, but we will have to wait and see.

–LV Krishnan is former director, safety research, at the Indira Gandhi Centre for Atomic Research, Kalpakkam.

Sourced via: Fukushima and Chernobyl: What are the parallels? – Rediff.com News.

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Categories: Events, Health, Medicine, Politics, Law, Science, Technology

Author:Andrew Beato

CEO, Chief Editor and founder of Intentious. Passionate comment enthusiast, amateur philosopher, Quora contributor, audiobook and general knowledge addict.

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