Ice blocks and trenches

July 24, 2014

TEPCO to use ice blocks to stem flow of radioactive water in Fukushima plant trenches

http://ajw.asahi.com/article/0311disaster/fukushima/AJ201407240054

THE ASAHI SHIMBUN

Tokyo Electric Power Co. unveiled a plan that would place blocks of ice in trenches at the stricken Fukushima No. 1 nuclear power plant to help stanch the flow of radioactive water.

The method was revealed at a July 23 meeting of the Nuclear Regulation Authority. The NRA instructed TEPCO to pump out contaminated water in the trenches as early as possible because water inside the underground tunnels could be leaking into the surrounding soil.

The trenches originate at the turbine buildings and extend to the seaward side of reactors. A large volume of radioactive water, which flowed into the tunnels after the March 2011 Great East Japan Earthquake and tsunami, still has to be removed.

In late April, TEPCO began work to prevent additional water in the turbine buildings from flowing into the trenches. The utility has been constructing "ice walls" at joint sections connecting the tunnels and turbine buildings after installing bags containing cement and clay at those points.

Although the operations were scheduled to be completed at the end of May, the cement and clay bags are still not sufficiently frozen.

During the July 23 meeting, TEPCO said a small stream of water in the trenches has hampered the freezing operations.

The utility said it will introduce additional freezing pipes and blocks of ice and dry ice to lower water temperatures, and also use liquid chemical agents to interrupt the water flow. The plan was approved by the NRA, but the nuclear watchdog said it will check on the efficacy of the new countermeasures as early as mid-August.

TEPCO is currently constructing a frozen soil wall around the plant’s No.1 through No. 4 reactor buildings to prevent more contaminated water from accumulating.

The delay in draining the radioactive water from the tunnels could slow the construction of the frozen wall on the seaward side of the reactors.

July 23, 2014

Fukushima plant measures to freeze tunnels

http://www3.nhk.or.jp/nhkworld/english/news/20140723_23.html 

The operator of the crippled Fukushima Daiichi nuclear power plant will take additional measures to accelerate the behind-schedule work of freezing radiation-contaminated water in underground tunnels.

Water used to cool melted-down fuel in damaged reactors has leaked out of reactor buildings into underground utility tunnels. The tainted runoff, mixed with ground water, is believed to be seeping into the ground and ending up in the sea.

The work is designed to prevent that outcome for the tainted water. But the tunnels have yet to be fully frozen nearly 3 months into the project.

On Wednesday, the Tokyo Electric Power Company briefed members of the Nuclear Regulation Authority about the additional measures.
These include installing more pipes that carry refrigerants in and out of the tunnels and adding ice in the tunnels by late next month. TEPCO will also use sandbags to fill sections where the pipes cannot be installed.

Regulatory officials criticized TEPCO's original plan for being too optimistic. Commissioner Toyoshi Fuketa instructed TEPCO to take the necessary measures quickly. He told it to prepare devices with extra capacity and freeze the water inside the tunnels perfectly.

A separate and larger project is now underway at the plant to freeze soil and create a wall of ice around the 4 reactor buildings. This is to prevent groundwater from coming into the damaged buildings and getting tainted with radioactivity.

But that work could also be delayed due to a suspension in freezing the water in the tunnels, because part of the work areas overlap.

Jul. 23, 2014 - Updated 04:46 UTC