Photo/IllutrationRows of storage tanks on the grounds of the Fukushima No. 1 nuclear power plant contain water contaminated by radioactive materials. (Asahi Shimbun file photo)

Steps to purify a radioactive water buildup at the stricken Fukushima No. 1 nuclear power plant have come to naught, forcing the operator, Tokyo Electric Power Co., to go back to the drawing board.

On Sept. 28, TEPCO acknowledged that about 80 percent of the water in giant storage tanks on the premises exceeded government standards for radioactive materials even though it had already been processed.

Some of the "processed" water showed concentrations of radioactive materials at more than about 20,000 times the standard used to determine if the water is safe enough to discharge into the ocean.

TEPCO has been treating the water with a device known as ALPS, or advanced liquid processing system. Water is accumulating at a rate of between 50,000 and 80,000 tons a year.

The latest study covered about 890,000 tons of the 940,000 tons of water that has gone through ALPS and is stored on-site.

Tests showed that strontium 90 was present in some tanks at levels of about 600,000 becquerels per liter of water, which is about 20,000 times the safety standard.

Strontium 90 has a half-life of about 29 years. It could lead to bone cancer or leukemia after being absorbed in the bones by breathing it, or ingesting it.

Until now, TEPCO had insisted that the ALPS device could remove 62 types of radioactive materials from the water. The only substance that could not be removed was tritium, a radioactive isotope of hydrogen.

When TEPCO decides on how to dispose of the contaminated water in the storage tanks, it plans to again process the water through the ALPS device before releasing it into the ocean.

This leaves TEPCO between a rock and a hard place as the device can currently process only 340 tons of water daily.

If once-processed water is sent through the device a second time, that would not only add to costs but require years of processing before all the water can be discharged safely.

TEPCO does not have the luxury of time as contaminated water continues to be generated at the rate of tens of thousands of tons annually in the form of either groundwater or water used to cool reactor cores that come into contact with the melted nuclear fuel in the three reactors that went into meltdown after the earthquake and tsunami disaster in 2011.

An additional problem is that so many storage tanks have been constructed on the grounds of the Fukushima plant that there will be no space for new ones by 2020.

TEPCO at least knows why so much of the stored water continues to register radioactive substances in alarmingly high concentrations.

It explained that a malfunction of the ALPS device in fiscal 2013 prevented processing of all highly contaminated water. Some of the water with high concentrations of radioactive materials likely mixed in with other water in the storage tanks.

Utility officials also pointed to a delay in the replacement of absorbent in the ALPS device used to remove the radioactive substances.

TEPCO promised to review the timing for the replacement of absorbent. However, it could not rule out the possibility that radioactive materials at levels exceeding safety standards would again be detected even if that step is taken.

The utility was also taken to task for releasing the measurement levels of radioactive materials on its website without providing an adequate explanation of what those figures actually meant.

At a public hearing in August in Fukushima Prefecture, local residents pointed out that the stored water contained radioactive materials other than tritium at levels exceeding safety standards.

In the seven-plus years since the triple meltdown at the Fukushima plant, TEPCO has released a voluminous amount of data about various measurements of radioactive materials, which has caused headaches for local residents who have no in-depth knowledge of what the figures mean.

The Ministry of Economy, Trade and Industry also bears some of the blame because it has been pushing TEPCO to accelerate the processing of contaminated water to show the world gathering in Japan for the 2020 Tokyo Olympics and Paralympics that the situation in Fukushima was under control and the region well on its way to rebuilding.

(This article was written by Yusuke Ogawa and Hiroshi Ishizuka. Noriyoshi Ohtsuki, a senior staff writer, and Chikako Kawahara contributed to the article.)