Nuclear
Tuesday, 22 March 2011 14:26

Japan’s nuclear meltdown

Japan was ravaged by an 8.9 magnitude earthquake and subsequent tsunami on 11 March 2011. Besides the massive destruction and death toll in the country, Japan was almost immediately forced to deal with a nuclear crisis.

The reactors at the Fukushina Dai-Ichi Nuclear Power Plant shut themselves down, as they were supposed to do after the natural disasters, but the cooling systems of the reactors were compromised after two hydrogen explosions. The electrical systems that provide electricity to cool the nuclear reactor were knocked out in the earthquake, and the diesel-powered back-up system also failed.

Authorities maintained an emergency shutdown at the site and US President Barack Obama directed Energy Secretary Steven Chu to “provide any assistance that’s necessary, but also to make sure that if in fact there have been breaches in the safety system on these nuclear plants, that they’re dealt with right away”. NHK, the national broadcaster, said it was the first time that a nuclear-emergency evacuation order had been issued in Japan.

Japanese authorities informed the International Atomic Energy Agency (IAEA) that reactors Units 1, 2 and 3 of the plant were in cold shutdown status (on 15 March) and that teams of experts from Tokyo Electric Power Company (TEPCO), the plant’s operator, are working to restore cooling in the reactor Unit 4 and bring it to cold shutdown.

How nuclear reactors work
Both water and fuel rods made of zirconium and pellets of nuclear fuel (such as uranium) are contained in the core of a nuclear reactor. These liquids set off a controlled nuclear reaction which heats the water, creating a 550-degree Fahrenheit (287.78 Cº) steam that powers the turbine and creates electricity.

What is a meltdown?
The fuel rods can crack and release radioactive gases if the core of the nuclear reactor gets too hot. In a partial meltdown, only some of the reactor core or fuel melts, but in the worst case scenario, the fuel pellets can melt and fall to the reactor floor, where the hot, radioactive material may be able to eat through protective barriers and reach the surrounding environment.

Why the cold shutdowns in Japan?
The reactors at the Fukushina Dai-Ichi Nuclear Power Plant are designed to automatically turn off if a disaster disrupts the electric grid. The shutdown process at the plant worked properly, but even with the shutdown, the fuel still had tremendous heat. The diesel-powered back-up generators are supposed to kick in to cool the fuel, but this system failed in the tsunami that followed the earthquake.

Source: www.wsj.com

The IAEA offered its Good Offices to Japan – making available the agency’s direct support and coordination of international assistance – which the Japanese government accepted on 15 March.

Three days after the accident
The best available information at the present suggests that four reactors (at Fukushima I & II and Tokai II) are experiencing severe cooling problems, with two reactors at Fukushima experiencing at least partial meltdowns. As a result of this partial meltdown, a hydrogen explosion at Fukushima 1 has occurred and iodine-131 and caesium-137 isotopes have been released. – Earthlife South Africa


Japan’s Nuclear and Industrial Safety Agency (NISA) reported that about 185 000 residents had been evacuated from the towns listed below since 13 March.

Populations of evacuated towns near affected nuclear power plants
Hirono-cho 5 387
Naraha-cho 7 851
Tomioka-cho 15 786
Okuma-cho 11 186
Futaba-cho 6 936
Namie-cho 20 695
Tamura-shi 41 428
Minamisouma-shi 70 975
Kawauchi-mura 2 944
Kuzuo-mura 1 482
Total 184 670
Source: www.iaea.org

US evacuating military fleet
Three days after the catastrophe, the US Seventh Fleet announced that it had moved its ships and aircraft away from the nuclear power plant after discovering low-level radioactive contamination. According to Associated Press, the fleet said that the radiation was from a plume of smoke and steam released from the plant.

The aircraft carrier USS Ronald Reagan was approximately 160 km offshore when its instruments detected radiation (the dose of radiation was about the same as one month’s normal exposure to natural background radiation in the environment).

New uncertainties for the nuclear industry
Until the disaster, many country leaders believed that nuclear energy offered a large part of the answers to electricity issues and climate change. Towards the end of 2010, South Africa’s Minister of Energy confirmed that nuclear power will be part of the country’s future power mix, along with renewable energy and coal. National Planning Commission member Bobby Godsell also told delegates at a public discussion on energy that “as much as 50% of South Africa’s electricity could be comprised of nuclear energy. Between 10 000 and 20 000 megawatts of the possible 40 000 megawatts the country would need in the future could come from nuclear energy.”

But this confidence may have evaporated as quickly as confidence in Japan’s crippled nuclear reactors – and now many governments and leaders are watching the drama unfold. “I think it calls on us here in the US, naturally, not to stop building nuclear power plants, but to put the brakes on right now until we understand the ramifications of what’s happened in Japan,” said Senator Joseph I. Lieberman, an independent member of Connecticut and of the US Senate’s leading voice on energy on CBS’s “Face of the Nation”.

Lieberman noted that the Federal Emergency Management Agency (FEMA) had in recent years upgraded contingency plans for nuclear power plants in the event of a natural disaster and that the crisis in Japan could be instructive in preventing a future crisis (www.cbsnews.com).

“We’ve got 104 nuclear power plants in America now. I was informed this morning that about 23 of them are built according to designs that are similar to the nuclear power plants in Japan, which are now the focus of our concern,” said Lieberman.

“I’ve been a big supporter of nuclear power because it’s domestic, it's ours and it’s clean. We’ve had good safety with nuclear power plants here in the United States. . . I don’t want to stop the building of nuclear power plants, but I think we have got to kind of quietly, quickly put the brakes on until we can absorb what has happened in Japan as a result of the earthquake and the tsunami and then see what more, if anything, we can demand of the new power plants that are coming online. What this horrific natural disaster in Japan has to do for all of us is to go back and look at our preparedness for such a catastrophe,” said Lieberman.

SA has “nuclear safety culture” – Eskom
Commenting on Japan’s nuclear crisis, Eskom’s spokesman for nuclear power, Tony Scott, told SAPA that South Africa is “well-equipped” to have nuclear power stations and has a “nuclear safety culture”.

“Clearly we will be looking at what actually happened in Japan, but South Africa has a nuclear safety culture because of the Koeberg power station,” said Scott.

“Nuclear power is certainly complex. It requires management depending on the level of risk, but the level of risk in nuclear is low. How many people are killed on the roads every day compared to people killed in the nuclear industry? Obviously if something does go wrong in the nuclear industry the consequences are enormous,” continued Scott.

Could this happen in SA?
“This is an extremely serious nuclear accident that unfortunately poses as a stark reminder and warning of the inherent dangers and risks of nuclear power,” said Tristen Taylor from Earthlife SA in a statement on 13 March.

“We cannot discount the risk that exists at the Koeberg power station. Only last year, 91 workers at Koeberg were exposed to excess radiation,” said Taylor.

Scott explained that Japan’s Fukushina Dai-Ichi Nuclear Power Plant used boiling water reactors, whereas South Africa’s Koeberg uses pressurised water reactors. “About 70% of all new nuclear stations in the world use the pressurised system,” said Scott, before adding that Eskom was familiar with pressurised water reactors and would want to stick with that design for future nuclear power stations in the country.

“We also know that if we do build more, we would buy modern technology, and certainly the events that happened would be looked at and taken into account to see what technology should be used,” said Scott.

Sources: CBS News, Earthlife, SAPA, Eskom, IAEA, TimesLive