Overblog Suivre ce blog
Editer l'article Administration Créer mon blog
Le blog de fukushima-is-still-news

Le blog de fukushima-is-still-news

information about Fukushima published in English in Japanese media info publiée en anglais dans la presse japonaise

Until the contaminated water issue is solved...

April 3, 2016

 

Contaminated water, fuel extraction stand in way of decommissioning Fukushima plant

http://mainichi.jp/english/articles/20160403/p2a/00m/0na/010000c

 

 

With about five years having passed since the start of the Fukushima No. 1 Nuclear Power Plant disaster, nuclear workers still lack a method of treating the around 1,000 tanks of contaminated water stored on site, and the start of work to remove melted nuclear fuel from the plant remains at least five years away.

"Until the contaminated water issue is solved, decommissioning of the reactors remains far off. We have to stop the water," says Tetsuo Ito, professor of nuclear energy safety engineering at the Kinki University Atomic Energy Research Institute. Akira Ono, chief of the Fukushima plant, says, "We're still at step one" of the decommissioning process, which is estimated to take until 2041 to 2051.

Tokyo Electric Power Co. (TEPCO), the plant's owner, is treating the contaminated water with its Advanced Liquid Processing System (ALPS), which can remove 62 varieties of radioactive material. However, ALPS cannot remove radioactive tritium, and because of this the treated water is stored in tanks. Tritium is extremely difficult to separate from water, because even if one of the hydrogen atoms in a water molecule is replaced by tritium, the chemical properties such as the boiling point barely change.

The International Atomic Energy Agency (IAEA) has advised that tritium-containing water be released into the ocean, because its effect on the human body is very limited. Tritium-containing water is created even during the normal operation of a nuclear power plant, and it is released into the ocean in accordance with waste-disposal standards. However, there is local opposition to doing this at the Fukushima plant because of worries about its effects on the reputation of the local fishing industry, and no decision has been made on what to do with the water.

Tritium has a half-life of 12.3 years, so storing the water until the radiation naturally lessens is another option, but there is the risk of leaks during that time if the tanks' conditions deteriorate.

As for decommissioning the plant reactors, at the end of 2011 the national government put together a roadmap that estimated the decommission work would take 30 to 40 years. To decommission the No. 1 through 3 reactors at the plant, 1,573 units of spent fuel will have to be removed from the spent fuel pools of these reactors, and 1,496 units' worth of fuel that melted from the reactors will have to be removed. Safe removal of the melted fuel represents the largest problem.

The national government and TEPCO intend to decide on a plan for the fuel's extraction in the first half of fiscal 2018, and start extraction efforts at one of the reactors within the year 2021. Toyoshi Fuketa, a member of the Nuclear Regulation Authority (NRA), argues that nuclear fuel that is too difficult to take out should be stored on-site, saying, "There is the option of just removing as much (of the melted fuel) as possible, and hardening the rest (to seal off its radiation)."

The cost for decommissioning the reactors is already estimated at 2 trillion yen, and this could grow if the decommissioning schedule is delayed.

While the No. 1 through 3 reactors at the plant were shut down at the time of the Great East Japan Earthquake on March 11, 2011, they lost all power due to the proceeding tsunami and, with no way to cool the nuclear reactors, they experienced a meltdown. The tsunami measured at up to 15.5 meters, and emergency underground power supplies were flooded and failed to function.

The No. 1 reactor was equipped with a cooling system called Reactor Core Isolation Cooling (IC), but this didn't activate, and on March 12 at 3:36 p.m. the No. 1 reactor suffered a hydrogen explosion. Then, on March 14 at 11:01 a.m. the No. 3 reactor also experienced a hydrogen explosion. The No. 4 reactor was already offline at the time of the disaster for a regular inspection, but hydrogen from the adjacent No. 3 reactor leaked in, and it suffered a hydrogen explosion as well at 6:14 a.m. on March 15. The No. 2 reactor was not hit by a hydrogen explosion, but among the No. 1 through 3 reactors it is thought to have leaked the most radiation. The disaster is rated a 7 on the International Nuclear Event Scale, the same as the Chernobyl disaster.

Masao Yoshida, the late chief of the Fukushima plant who headed up the frontline disaster-response efforts, testified to a government panel investigating the disaster, "We (who were on-site) imagined it as the destruction of eastern Japan. I really thought we were dead."

Four reports on the disaster were put together, from the national government, the Diet, TEPCO and elsewhere in the private sector. They differ on points such as why the IC in the No. 1 reactor did not activate. The Diet probe raised the possibility that the IC system's piping was damaged in the earthquake, but the national government's investigative panel denied that earthquake damage was the cause. Due to the high radiation levels in the reactor buildings, there has not yet been an on-site investigation to better understand what happened.

Partager cet article

Repost 0

Commenter cet article