Tokyo Electric Power Co. has started taking measures to contain highly radioactive groundwater at the Fukushima No. 1 nuclear plant, but its strategy is based on a theory that is disputed by industry experts.
TEPCO insists that recently detected radioactive substances originated during the early stages of the disaster in 2011, and it is setting up barriers near the area of the initial water leak problems.
However, even the Nuclear Regulation Authority (NRA) says it is currently impossible to pinpoint where the latest leaks are coming from. Some say the leakage could be anywhere within the intricate system to cool the melted reactors and the underground maze of pipes at the plant site.
The utility’s measures, intended to prevent the underground radioactive water from spilling into the sea, could end up exacerbating the problem, some experts have warned.
The efforts to locate the cause of the leaks and prevent their further spread started more than a month after the problem was detected. Contaminated water is already believed to be draining into the sea.
On July 12, TEPCO said the No. 3 observation well at the plant produced a total reading of 1,400 becquerels of radioactive substances that emit beta rays, including strontium, per liter of water sampled on the previous day. No radioactivity had been detected in the No. 3 well a week earlier.
The No. 3 well is about 200 meters south of the No. 1 well, where high radioactive levels have been detected for some time.
Water sampled on July 8 from another well, 21 meters seaward of the No. 1 well, produced a record 630,000 becquerels of tritium, a radioactive isotope of hydrogen. That level is about 10 times higher than the legal safety limit.
The latest developments date back to late May, when water from the No. 1 well, on the seaside of the No. 2 reactor turbine building, produced high levels of radioactive substances. The readings were 500,000 becquerels of tritium per liter, or eight times the legal limit, and 1,000 becquerels of strontium per liter, or 30 times the legal limit.
TEPCO had earlier dug a number of observation wells to check for any new influx of radioactive water into the sea because seaborne levels of radioactive cesium had been slow to decline.
After the spread of radioactive substances was confirmed, TEPCO rushed to dig four additional observation wells near the No. 1 well. It also began analyzing seawater north of the water intakes for the reactors.
High radioactivity levels continue to be detected in the observation wells. TEPCO officials said they need more data to determine how the radioactive materials have been spreading.
But the plant operator believes it knows the origin of these substances. According to TEPCO, the materials represent the spread of highly radioactive water that leaked during the early phase of the 2011 nuclear disaster and have since permeated the ground.
Toyoshi Fuketa, a commissioner for the NRA, emphasized during a July 10 meeting that the origin of the leaks remains an open question.
“We have yet to learn in the first place if the spread represents leaks during the early phase of the disaster that subsequently remained stagnant, or if the spread represents leaks that came out later, and whether such leaks continue to this day,” Fuketa said.
NRA officials said the nuclear watchdog plans to soon set up a task force and begin efforts to identify the cause and block a further spread of the radioactive water.
During the chaotic early stages of the nuclear disaster, which began after the Great East Japan Earthquake and tsunami struck the plant on March 11, 2011, water used to cool the overheating reactors flowed into the basements of the reactor buildings. The highly radioactive water eventually entered underground pits for pipes and power cables seaward of the turbine buildings.
In April 2011, some of that water leaked from the end of a No. 2 reactor pit and flowed into the port at the plant via a water intake. Radioactive water also escaped from the end of a No. 3 reactor pit in a similar manner the following month.
At the time, TEPCO blocked the leaks by injecting concrete and liquid glass into the pit ends.
The company says the recently detected substances came from the early spread of this radioactive water.
According to TEPCO figures, the No. 2 reactor pits and the No. 3 reactor pits currently hold about 5,000 tons and 6,000 tons, respectively, of highly radioactive water.
However, industry experts say they cannot rule out the possibility that the radioactive materials detected in the wells derive from water that has leaked elsewhere and mixed with groundwater.
After high radioactive levels were found in the No. 1 observation well, TEPCO on July 8 began work to inject a water-sealing agent into the ground near a levee on the seaside of the No. 2 reactor turbine building as a stopgap measure to prevent leaks to sea. It plans to create a two-layered wall by the end of July, TEPCO officials said.
But waterproofing the levee could simply divert the flow of groundwater on the seaside of the turbine building, leading to a spread of radioactive contamination to unforeseen locations, according to some industry experts.
TEPCO is also considering pumping up radioactive water from the pits and funneling it into decontamination devices as part of efforts to dispose of the water.
However, the pits are connected with the turbine buildings, meaning that pumping up the radioactive water would only result in more water coming in from the turbine buildings.
Given the high radiation levels on the plant site, devising a method to block the water flow between the pits and the turbine buildings is expected to pose a major challenge.
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