23 Juin 2013
June 22, 2013
June 22, 2013
CHERNOBYL, Ukraine--Chernobyl stands as the worst nuclear disaster yet, and 27 years later there are still no signs of when work can begin to decommission the heavily damaged No. 4 reactor.
That sobering assessment offers an important lesson for the Japanese government and Tokyo Electric Power Co., which intend to decommission the crippled reactors at the Fukushima No. 1 nuclear power plant within 30 to 40 years.
An Asahi Shimbun reporter went inside the No. 4 reactor at the Chernobyl plant on June 20 for a first-hand look at the damage and to ascertain what is being done to contain the spread of radioactive materials.
The visit provided a mountain of evidence that the task in Japan will not likely proceed according to plan.
Although a concrete sarcophagus was constructed to cover the No. 4 reactor building that was demolished in an explosion on April 26, 1986, the shield has become badly damaged. There are now plans to construct a new and even bigger shelter to cover that structure.
Radiation readings at the control room of the No. 4 reactor registered 7 microsieverts per hour. In 1990 when another Asahi Shimbun reporter visited the same reactor, the radiation level was 30 microsieverts per hour.
That's the good news: It means radiation levels have dropped to one-fourth of the previous level.
However, behind the thick concrete wall of the sarcophagus still lies the melted nuclear fuel that caused the meltdown and explosion in April 1986. The radiation levels within the sarcophagus are so high that anyone entering it would be certain to die.
The Chernobyl disaster resulted in the release of about six times the volume of radioactive materials spewed out from the Fukushima plant. More than 30 people perished putting out fires immediately after the Chernobyl accident.
The Chernobyl plant now faces a new crisis. A huge metal frame measuring about 80 meters in height has been installed to hold up the reactor building as it is in danger of collapse. Rust covers some exposed parts of the steel frame of the sarcophagus.
Despite monumental efforts to prevent the release of radioactive materials into the air, rain that leaks through cracks in the sarcophagus mixes with the radioactive materials inside and seeps into the soil.
In an attempt to prevent a further spread of radioactive materials, a new plan has been put together to construct a dome-shaped shelter that will eventually cover the entire No. 4 reactor. Plans call for completing the shelter in two years.
Oleksandor Novikov, deputy technical director for safety at Chernobyl, said: "Eventually, we want to break open the sarcophagus and remove the melted fuel. However, no decision has been made on what process will be used. We have to think that it may take 100 years."
The roof of a nearby building offers a clear view of not only the extent of damage to the nuclear plant, but also of the massive new shelter that is being constructed.
The shelter now rises 85 meters. When it is complete, it will reach a height of 110 meters, making it one of the world's largest arch-shaped buildings.
The shelter is being constructed in two parts. Once they are finished, the parts will be moved along rails to veil the No. 4 reactor entirely. In September, work will begin to remove exhaust vents that could become a hindrance if they snag on the roof.
The plan came under initial consideration in 1997, but it was not until 2012 that construction began in earnest. Construction expenses will reach 935 million euros (120 billion yen, or $1.2 billion).
More than 20 nations, including Japan, have made contributions to the Chernobyl shelter fund at the European Bank for Reconstruction and Development.
The shelter was deemed to be a priority because the sarcophagus has had to undergo a number of repairs for structural weakness. There are countless cracks in the concrete wall of the sarcophagus.
Construction of the sarcophagus began two months after the nuclear accident. A seemingly endless number of military personnel was brought in for the purpose, and construction was completed in six months. Because the high radiation levels prevented workers from getting near the structure, no welding or bolts were used in the construction. That defect has led to a shifting of the foundation through land sinking.
According to a report by experts at the International Atomic Energy Agency, the holes in the sarcophagus cover a total area of 1,000 square meters. As a result, some 2,000 tons of rainwater leaks into the reactor building over the course of a year. After mixing with the radioactive materials inside, about 1,300 tons of contaminated water is produced, which then leaks into the ground under the No. 4 reactor.
A huge hole was also clearly visible in the turbine building on the south side of the plant. The hole was made when the roof of the machinery room in the turbine building collapsed in February. Workers had to temporarily evacuate at that time. While the initial assumption was the roof had collapsed due to the weight of snow, it is now suspected that shoddy repairs led to roof braces coming off, resulting in the roof collapse.
All these problems mean that no specific plans have yet been drawn up on how to decommission the reactor at Chernobyl.
Plans calls for installing a crane to the ceiling of the shelter now under construction. The crane would be capable of lifting 50-ton loads. Once the shelter was completed, the crane would be used to first clear away the sarcophagus. The next step would be to remove melted nuclear fuel from the reactor. However, no process or deadline has yet been set for that task.
Volodymyr Holosha, head of the State Agency of Ukraine on Exclusion Zone Management, said, "The new shelter will have a service life of 100 years, which means that is about how long it will take to decommission the reactor."
Even for the No. 1 to No. 3 reactors that were not affected by the accident, estimates are that decommissioning will take at least 50 years.
Moreover, experts have only a fuzzy picture about the melted fuel. As yet, they have no way of knowing exactly where in the damaged reactor the fuel may have spread to. The high radiation levels in the reactor prevent any attempt to approach the area for an assessment.
Sergiy Paskevych, a senior researcher at the Institute for Safety Problems of Nuclear Power Plants under the National Academy of Sciences of Ukraine, said:
"There will be a need to develop robots that can operate in high radiation areas. We will also have to develop technology that will allow for the safe grabbing of the fuel for removal."
Similar work is also progressing in Japan to confirm the state of the melted fuel at the Fukushima plant as well as the damage to the reactors. Because the work now being conducted is still only in the preliminary stage, there is no specific schedule or process for the actual decommissioning work.
With workers at the Fukushima plant still struggling to keep water decontaminated with radiation from leaking into the ground or spilling into the sea, the plans set by the government and TEPCO for decommissioning the Fukushima reactors have to be considered as only theoretical.