8 Mars 2013
March 9, 2013
Those who were at the Fukushima No. 1 power plant two years ago probably remember their fears after towering tsunami knocked out the reactor cooling systems, triggering three core meltdowns that threatened to harm the entire nation.
Today the crippled reactors require close monitoring but are in a controllable state — at least compared with the chaos of 2011.
Looking at the bigger picture, however, Tokyo Electric Power Co. isn’t making much progress decommissioning reactors 1, 2, 3 and 4 — a task expected to take at least three decades. This is because the very thing that saved the plant is now blocking the way: water.
Water is perpetually needed to keep the melted fuel cool, but the meltdowns burned holes in three of the six reactors, allowing water to leak into the basements of the containment buildings after being tainted with deadly amounts of radioactivity. This was exacerbated by hydrogen explosions, which possibly cracked the containment vessels and ripped the buildings housing the reactors apart.
While pumps are being used to drain and detoxify the water as much as possible, finding safe places to store it remains Tepco’s most pressing task.
“The work to decommission the plant is still in the beginning stage. We have to overcome many hurdles, such as taking care of the massive amounts of contaminated water, finding the source of leaks in the containment vessels and recovering the melted fuel rods,” said plant manager Takeshi Takahashi, 55, at a Feb. 28 news conference in Fukushima.
“It’s going to take a very long time to complete the work, and it’s going to be tough, but we’re committed to completing it,” Takahashi said.
As if the damage above ground isn’t enough to worry about, the 9 -magnitude earthquake apparently cracked the walls of the plant, allowing about 400 tons of groundwater to seep into the buildings and mix with the tainted coolant water. Tepco has controlled the coolant volume to ensure the inflow of groundwater is stronger, which will help keep it in the buildings.
About 260,000 tons of tainted water are stored in tanks; Tepco thinks it could probably store up to 700,000 tons if it had time to build more tanks. But as it stands today, there are only enough tanks to store about 60,000 more tons, which means they only have months before the entire site begins to flood.
“The contaminated water is a pressing issue,” said Takahashi.
Since the water could very well leave the plant and end up in the water supply and the ocean, Tepco is planning two measures.
One is to make bypasses for the groundwater by digging wells to curb the seepage into the reactor buildings. The diverted groundwater would flow to the sea.
The second measure is a new water processing system called ALPS that can remove 62 kinds of radioactive substances, including strontium, which can cause bone cancer. The existing system mainly removes cesium before recirculating some of the water into the reactors. The rest is stored.
Tepco also will have to find a way to dispose of water processed by ALPS. Since Tepco is trying to limit the amount of coolant to reduce the leak rate, any water purified by ALPS won’t be reused as coolant.
And even ALPS cannot remove tritium.
According to Tepco, the level of tritium in the contaminated water is between 1 million and 5 million becquerels per liter, and the legal limit is 60,000. Tritium has a half life of about 12 to 13 years and is about one-thousandth as radioactive as the isotopes cesium-134 and -137.
Drinking 2 liters of water containing 60,000 becquerels of tritium per liter each day for a year will give you a dose of about 0.79 millisievert, the utility said. The legal exposure limit is 1 millisievert per year.
To prevent the tanks from occupying all of the available space on site, Tepco is thinking of dumping the water processed by ALPS into the ocean, despite fierce opposition from fishermen.
Tepco said it will not do it without receiving the consent of related ministries.
Kyoto University professor Akio Koyama, an expert on radioactive waste, said Tepco seems to have no choice but to dump the water because tritium is so hard to remove. If Tepco can dilute the tritium-tainted water to legal levels, it should not be a big problem, Koyama said.
“The water will be further diluted as soon as it is dumped into the ocean. There are various estimates, but I don’t think this will be dangerous,” he said.
Still, it will be hard to convince people in the fishing industry, which was decimated by a similar release in the early stages of the crisis in April 2011.
JF Zengyoren, a national advocacy group for fishermen, visited Tepco on Jan. 25 to protest.
“Fishermen have been suffering from the impacts of the Fukushima crisis and trying to regain consumers’ trust. Dumping tainted water will destroy these efforts,” the organization said.
To end the vicious circle, Tepco must locate the leaks and plug them. But little progress has been made because the radiation levels are still lethal in the reactor buildings and a thorough examination of the machinery will be extremely hard to carry out.
The utility is planning to send robots to find the leaks and other plant makers are developing technologies to plug them.
The only progress Tepco seems to be making is on reactor 4, which was defueled prior to the crisis but had become a storage site for both fresh and spent-fuel rods — including some containing plutonium.
Experts believe the fuel rods in the spent-fuel pool of unit 4 present a critical risk and Tepco is working to remove them as quickly as possible before another major quake topples the remains of the building, which was heavily damaged by the hydrogen explosion.
Tepco claims reactor 4′s building can still withstand a quake rated at upper 6 on the Japanese intensity scale to 7 — the same as the quake that hit two years ago — but experts say it is better to move the fuel to a safer place as soon as possible.
The pool, which sits above the reactor, contains 1,533 spent-fuel rods. Tepco plans to start removing them in November and hopes to be finished by the end of 2014.