Via The Guardian: Doubts over ice wall to keep Fukushima safe from damaged nuclear reactors. Excerpt:
In fading light and just a stone's throw from the most terrifying scenes during Japan's worst nuclear accident, engineers resumed their race against time to defeat the next big threat: thousands of tonnes of irradiated water.
If all goes to plan, by next March Fukushima Daiichi's four damaged reactors will be surrounded by an underground frozen wall that will be a barrier between highly toxic water used to cool melted fuel inside reactor basements and clean groundwater flowing in from surrounding hills.
Up to 400 tonnes of groundwater that flows into the basements each day must be pumped out, stored and treated – and on-site storage is edging closer to capacity. Decommissioning the plant will be impossible until its operator, Tokyo Electric Power [Tepco] addresses the water crisis.
Last month workers from Tepco and the construction firm Kajima Corp began inserting 1,550 pipes 33 metres vertically into the ground to form a rectangular cordon around the reactors. Coolant set at -30C will be fed into the pipes, eventually freezing the surrounding earth to create an impermeable barrier.
"We started work a month ago and have installed more than 100 pipes, so it is all going according to plan to meet our deadline," Tadafumi Asamura, a Kajima manager who is supervising the ice wall construction, said as workers braved rain, humidity and radiation to bore holes in the ground outside reactor No 4, scene of one of three hydrogen explosions at the plant in the early days of the crisis.
But sealing off the four reactors – three of which melted down in the March 2011 disaster – is costly and not without risks. The 32bn-yen (£185m) wall will be built with technology that has never been used on such a large scale.
"I'm not convinced the freeze wall is the best option," Dale Klein, former head of the US Nuclear Regulatory Commission and a senior adviser to Tepco, recently told Kyodo News. "What I'm concerned about is unintended consequences. Where does that water go and what are the consequences of that? I think they need more testing and more analysis."
The 1,500-metre wall will stay in use until 2020, using enough electricity every year to power 13,000 households, according to officials.
Over the next eight months, 360 workers from Tepco and Kajima will work in rotating shifts of up to four hours a day, with each shift beginning in the early evening to combat heat exhaustion. Each worker is wrapped in hazardous materials suits and full-face masks, along with tungsten-lined rubber torso bibs for added protection against radiation.
Tepco's record of mishaps in the three years since Fukushima Daiichi suffered a triple meltdown suggests the wall project will not be trouble free. The firm has had problems freezing irradiated water – using the same method being used to build the underground wall – that has accumulated in underground trenches, raising concerns that the ice technology is flawed.