Meltdowns Grow More Likely at the Fukushima Reactors
Japan's government and nuclear industry, with help from the U.S. military, is inside a desperate race to stave off multiple nuclear reactor meltdowns -- as well as prospective fires in pools of spent fuel.
As of Sunday afternoon, a lot more than 170,000 individuals have been evacuated near the reactor sites as radioactive releases have increased. The number of military emergency responders has jumped from 51,000 to 100,000. Officials now report a partial meltdown at Fukushima's Unit 1. Japanese media outlets are reporting that there might be a second one underway at Unit 3. Folks living nearby have already been exposed to unknown levels of radiation, with some requiring medical consideration.
Meanwhile, Unit 2 of the Tokai nuclear complicated, which is close to Kyodo and just 75 miles north of Tokyo, is reported to have a coolant pump failure. And Japan's nuclear safety agency has declared a state of emergency at the Onagawa nuclear energy plant in northeastern Japan due to the fact of high radiation levels. Authorities are saying its three reactors are "under control."
The damage from the enormous earthquake and also the tsunamis that followed have profoundly damaged the reactor sites' infrastructure, leaving them with out power and their electrical and piping systems destroyed. A hydrogen explosion Saturday at Unit 1 severely damaged the reactor creating, blowing apart its roof.
The outcomes of desperate efforts to divert seawater into the Unit 1 reactor are uncertain. A Japanese official reported that gauges do not seem to show the water level rising inside the reactor vessel.
There stay quite a few significant uncertainties in regards to the situation's stability and a lot of questions about what may transpire next. In addition to the struggle to cool the reactors could be the possible danger from an inability to cool Fukushima's spent nuclear fuel pools. They include quite huge concentrations of radioactivity, can catch fire, and are in a lot more vulnerable buildings. The ponds, normally rectangular basins about 40 feet deep, are created of reinforced concrete walls 4 to 5 feet thick lined with stainless steel.
The boiling-water reactors at Fukushima -- 40-years-old and created by General Electric -- have spent fuel pools a number of stories above ground adjacent towards the leading of the reactor. The hydrogen explosion might have blown off the roof covering the pool, as it's not underneath containment. The pool needs water circulation to eliminate decay heat. If this doesn't happen, the water will evaporate and possibly boil off. If a pool wall or support is compromised, then drainage is really a concern. When the water drops to around 5-6 feet above the assemblies, dose rates could be life-threatening close to the reactor creating. If substantial drainage occurs, right after many hours the zirconium cladding around the irradiated uranium could ignite.
Then all bets are off.
On regular, spent fuel ponds hold five-to-ten times more long-lived radioactivity than a reactor core. Especially worrisome is the significant level of cesium-137 in fuel ponds, which contain anyplace from 20 to 50 million curies of this harmful radioactive isotope. Having a half-life of 30 years, cesium-137 offers off highly penetrating radiation and is absorbed in the food chain as if it had been potassium.
In comparison, the 1986 Chernobyl accident released about 40 percent of the reactor core's 6 million curies. A 1997 report for the Nuclear Regulatory Commission (NRC) by Brookhaven National Laboratory also identified that a severe pool fire could render about 188 square miles uninhabitable, trigger as several as 28,000 cancer fatalities, and expense $59 billion in damage. A single spent fuel pond holds far more cesium-137 than was deposited by all atmospheric nuclear weapons tests in the Northern Hemisphere combined. Earthquakes and acts of malice are thought to be to become the main events that may result in a main loss of pool water.
In 2003, my colleagues and I published a study that indicated if a spent fuel pool had been drained in the United States, a major release of cesium-137 from a pool fire could render an region uninhabitable higher than developed by the Chernobyl accident. We suggested that spent fuel older than five years, about 75 % of what is in U.S. spent fuel pools, be placed in dry hardened casks -- some thing Germany did 25 years ago. The NRC challenged our recommendation, which prompted Congress to request a evaluation of this controversy by the National Academy of Sciences. In 2004, the Academy reported that a "partially or completely drained a spent fuel pool could result in a propagating zirconium cladding fire and release big quantities of radioactive supplies to the atmosphere."
Given what's happening at the Fukushima Daiichi nuclear complicated, it is time for a severe evaluation of what our nuclear safety authorities contemplate to become improbable, particularly with regards to reactors operating in earthquake zones.
