” In a quarterly report on conditions and cleanup progress at the Fukushima Daiichi Nuclear Power Station in Japan, the Tokyo Electric Power Company (TEPCO) said that soil temperatures at more than 90 percent of the measuring points in a circumference surrounding four reactor buildings were below zero degrees Celsius or 32 degrees Fahrenheit.
TEPCO is attempting to create and impervious wall of frozen soil below the damaged plant in an area that includes reactor buildings 1 through 4. The idea is to control groundwater that has been flowing under and through the damaged buildings, picking up radioactivity along the way, then flowing back into the ambient soil below the plant on the seaside, eventually reaching the ocean.
TEPCO finished installation of 1,549 pipes to create the underground frozen blockade area in early February 2015. The coolant began flowing through the pipes on March 31 after a series of pressure tests.
The report, that shows more than 90 percent of measuring points achieving success, covers the January through March period.
Judging the bottom-line success of the soil freezing may proof difficult, but some measures of success can be defined through observations of groundwater levels inside the damaged building.
It is uncertain, for example, how water flow has changed given 10 percent of the wall is unsecured. That may allow incidental leakage or significant leakage, depending on conditions.
The report on the progress is helpful, however. The 90 percent that is frozen, the report says, includes the “entire seaside line along with preliminary freezing of some areas to the north and on the mountainside.” On that mountainside or uphill side of the frozen soil wall, there are areas “where there is significant space between freezing pipes and thus more difficult to freeze,” says the report.
Where water can be directly measured is inside the lower chambers of the damaged buildings. Along with the frozen soil and improved ditching for water control around the plant, TEPCO is pumping contaminated water inside the facility to a treatment system. In August 2015, additional transfer pumps were installed in each building and more water level gauges were mounted. At that point water levels were “down incrementally.” As of September 2015, subdrains were employed which “gradually lowered groundwater level(s) and hindered production of contaminated water.”
On March 7, the water level inside the reactor building was below the level of the connections to the turbine building, a crucial achievement. Since then, “we have verified that the water levels are being stably maintained,” another achievement. As of March 16, TEPCO determined “channels had been severed through which accumulated water had flowed between the reactor and turbine buildings.”
In the fourth quarter, work was completed on shifting the outlet of drainage channel K, which discharges rainwater around buildings at Units 1-4, from outside the port to inside the port. After a cut-off wall was completed, the switchover was completed, the report says.
Progress is also affecting workers on site. Since early March, the site has been divided into “highly contaminated areas,” which require cumbersome protective gear and areas where “regular working clothes or special on-site clothing,” is allowed. Measures such as spraying areas to keep radioactive dust down has improved worker safety, says TEPCO, which claims they have achieved an annual radiation level of 1mSv along the site boundary. ”