Fukushima Storage Problems Escalate

Fukushima storage problems escalate
http://the-japan-news.com/news/article/0000114832

The Yomiuri Shimbun
Yomiuri Shimbun file photo Water contaminated with radioactive substances was found to have leaked from an underground storage pool at the Fukushima No. 1 nuclear power plant.
April 8, 2013
[The Yomiuri Shimbun]

A second discovery of leakage at an underground storage pool at Tokyo Electric Power Co.’s crippled Fukushima No. 1 nuclear power plant shows the challenges in storing an increasing amount of water contaminated with radioactive substances.

TEPCO announced Saturday night that radioactive substances had been detected in the soil around an underground storage pool for contaminated water at the Fukushima plant.

On Sunday, the utility confirmed the contamination of the soil was caused by radioactive water leaking from the pool. This discovery came after about 120 tons of water contaminated with radioactive substances was found to have leaked from a neighboring storage pool earlier last week, which TEPCO announced Friday.

Since all seven of such underground storage pools at the plant were built with the same structure, TEPCO has decided to move the contaminated water from these pools to tanks on the ground as a stopgap measure.

Observers have warned that storing radioactive water will become even more difficult in the summer given the typical increase in rainfall.

Radiation to surpass estimates

Of the seven underground storage pools at the plant, three contained contaminated water. After the leak was confirmed Friday at one pool, TEPCO quickly studied the other two, and discovered the contaminated soil on Saturday.

The soil was found around a structure measuring 56 meters long, 45 meters wide and six meters deep. The pool could hold 11,000 tons of water and was nearly at capacity when the discovery was made.

At the plant, water is filtered to reduce and remove radioactive elements after being used to cool down melted nuclear fuel in the reactors. This water is then transferred to the storage pools.

The contaminated soil contained 0.11 becquerel per cubic centimeter of radioactive substances, less than one-hundredth of the amount found in the water leaked at the first pool.

Meanwhile, work to move the contaminated water from the first pool where the leak was found to other storage tanks is expected to take three days.

In addition to the 120 tons already leaked, 21 to 47 tons of contaminated water are estimated to leak from the facility before the work is completed.

Taking into account the second leak found at the other pool Sunday, the total amount of accumulated radioactive substances leaked is certain to surpass the initial estimate of 710 billion becquerels.

The combined effect of both leaks is now considered the largest leakage of contaminated water after the reactors were shut down in December 2011.

It seems TEPCO did not plan for the possible leakage of contaminated water from the underground storage pools since most of the past leakages were found at the joints of water pipes.

The underground storage pools were designed to store as much contaminated water as possible by making effective use of land around the plant, where construction of tanks is difficult on the ground.

Seams in sheets likely damaged

The structure of the underground storage pools is similar to that of those used for storing industrial waste.

Three layers of waterproof sheets made from polyethylene or another synthetic resin line the pool to prevent contaminated water from leaking into surrounding soil. Since a single layer consists of several attached waterproof sheets, TEPCO suspects the water might have leaked through tears in the seams.

However, the company has yet to determine what might have caused such damage.

Before starting to use the pools in February, TEPCO tested the sheets to confirm they were watertight. The firm continued to check the sheets once a week to ensure no water had leaked. It did not find any issues in its last inspection March 27.

Therefore, TEPCO was surprised to find radioactive substances in water sampled outside the pool on Wednesday.

“A small hole might have been made in a seam of the waterproof sheets, which isn’t strong,” said a senior official of the company.

“Some space could have been created between the sheets depending on water temperatures,” said Atsunao Marui, a chief researcher at the National Institute of Advanced Industrial Science and Technology. An expert on underground structures, he added, “A sharp object could also have damaged the sheets.”

Since the water in the leaking pool discovered Wednesday is being moved to another pool with the same structure and the cause of the leakage is still unknown, another leak could occur.

At the plant, 276,000 tons of contaminated water is already stored in tanks and the underground pools. The plant’s remaining storage capacity is only 53,000 tons. If all the underground storage pools are rendered unusable even temporarily, the plant’s available storage capacity would drop to 24,000 tons.

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