Explainer: Wall of ice at Fukushima's crippled nuclear plant

Kajima

25/01/2022 09:03

By Elaine Lies and Ju-min Park
    TOKYO, Jan 25 (Reuters) - The operator of Japan's crippled
Fukushima nuclear power plant said this month that two storage
tanks had leaked about four tonnes of coolant solution used to
create an ice wall that prevented groundwater from seeping in.
    The operator, Tokyo Electric Power Co Holdings  9501.T 
(Tepco), said the leak had no impact on the wall or the
environment, however.
    But the incident highlights its struggle to clean up the
plant nearly 11 years after a massive earthquake and tsunami set
off meltdowns in the worst nuclear disaster since Chernobyl in
1986.  urn:newsml:reuters.com:*:nL1N2U3030
    It also comes just as the utility is readying to build a
tunnel https://www.reuters.com/markets/commodities/japans-tepco-build-underwater-tunnel-fukushima-water-release-2021-12-21
 to the sea to release more than 1 million tonnes of irradiated
water from the site, after treatment, in an effort set to start
around the spring of 2023.  urn:newsml:reuters.com:*:nL1N2TD074
    
    WHY AN ICE WALL?
    In operation since 2016, the ice wall, as the structure is
called, is really more like a barrier of frozen soil. Built by
Kajima Corp  1812.T , it cost 34.5 billion yen ($303 million) in
public funds.
    The ice wall https://www.reuters.com/article/us-olympics-2020-fukushima-backstory-idUSKBN1ZS0IR
 is meant to keep contaminated water within the plant while
keeping out groundwater, which becomes radioactive on seeping
into the basements of the crippled reactors and coming in
contact with highly radioactive debris there.
    That has interfered with clean-up work, forcing Tepco to
pump out the water for storage in huge tanks at an annual cost
of about 100 billion yen. 
    Now space is running out, as nearly 1.3 million tonnes of
such water has accumulated, or enough to fill about 500 swimming
pools of Olympic size. 
    
    HOW DOES IT WORK?
    Coolant pumped into freeze tubes reduces temperatures to
about -30 degrees C (-22 Fahrenheit) in about 1,500 tubes filled
with brine located at a depth of 30 meters (98.43 ft) along a
perimeter of 1.5 km (1 mile) around the plant. 
    This in turn freezes the surrounding groundwater into a
contiguous wall of frozen soil, and the coolant is recirculated.
    
    LEAKS AND PROBLEMS
    The latest leak appears to have been caused by a warping of
joints in metal pipes, despite a lack of visible cracks, a TEPCO
spokesperson said. The system is operating after the defective
parts were replaced. 
    The last of roughly eight leaks since the wall became
operative was in 2019, probably because of metal fatigue from
vibrations caused by construction vehicles.
    The spokesperson was unable to immediately confirm the cause
of earlier leaks, but said similar reasons were likely.
    In Nov 2021, Tepco said https://www.reuters.com/markets/commodities/ice-wall-japans-fukushima-nuclear-plant-may-have-partially-melted-nhk-2021-11-26
 it was launching remedial work after testing showed a partial
melting of the ice wall.
    The coolant in Sunday's leak was a solution of calcium
chloride, used in concrete mixes to hasten setting and in food
to firm it. 
    
    WATER RELEASE - AND THE TUNNEL
    In December, Tepco said it aimed to build an underwater
tunnel to release the water into the sea, in the latest stage of
a plan to discharge about 1 million tonnes after treatment and
dilution, at a point about 1 km (0.6 miles) offshore.
 urn:newsml:reuters.com:*:nL4N2T60OH
    The treated water is to be pumped from tanks for release at
a depth of 12 metres (40 ft), with construction set to start
this year.
    The water will be processed to remove all radioactive
contamination, except tritium, which will be diluted to a
seventh of the World Health Organization (WHO) standards for
drinking water. The release is set to start around spring 2023.
    Though nuclear plants worldwide routinely discharge water
with tritium in it, the plan has stirred concern from neighbours
China and South Korea, worried over food safety.
    Also alarmed are farmers and fishermen nearby who worry it
could hit prices after years of struggle to rebuild. 
    
    LAWSUIT
    Separately, a lawsuit set to be filed on Thursday against
Tepco says a group of six men and women developed thyroid cancer
due to radiation exposure from the disaster, the Mainichi daily
said. 
    In a statement, the utility said it would respond after the
filing and hearings.
($1=113.7600 yen)

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Graphics: Fukushima Site Recovery    https://graphics.reuters.com/JAPAN-DISASTER-NUCLEAR-ICEWALL/01006144292/JAPAN-DISASTER.jpg
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 (Reporting by Ju-min Park and Elaine Lies; Editing by David
Dolan and Clarence Fernandez)
 ((elaine.lies@thomsonreuters.com; +81-3-4563-2748; Reuters
Messaging: elaine.lies@thomsonreuters.com))