With the deluge of often quite technical news coming out of Japan about the situation at the Fukushima Daiichi plant, the Post‘s Sarah Boesveld answers some of the most common questions:
Q: Early Tuesday morning in Japan, there was an explosion at the Unit 2 reactor at the Fukushima Daiichi plant. Officials have since reported a breach in the containment vessel at the heart of the reactor. What’s the significance of that crack?
A: A breach would cause an “uncontrolled path” for radiation to be discharged, said John Luxat, professor of engineering physics and NSERC Industrial Research Chair in Nuclear Safety Analysis at McMaster University in Hamilton, Ont. It also means it’s going to be a lot harder to pressurize the containment vessel. In its normal state, the machine, designed to condense steam to keep the reactor cool, would use power to run like a vacuum, constantly sucking in air. But now, without a source of power, the vessel is leaking gas which contains radioactive materials. While he’s unsure of the current state of the breach, he said, “There could be large leakage especially if you’ve got a lot of steam or gas which could increase the pressure inside the building.”
Q: Why are the nuclear authorities pouring seawater into the reactor? What effect does that have?
A: The seawater — the only water supply they have — hits the hot fuel rods, which are at risk of overheating and eventually melting, and acts as a cooling agent by steaming the water. Think of the rods as the element in a kettle that keeps on producing heat, said Rick Holt, professor of nuclear materials and NSERC Industrial Research Chair of Nuclear Materials at Queen’s University in Kingston, Ont. “It’s not something hot that you’re cooling down, it’s something that’s continually generating heat.” The water then boils and is released as steam, functioning much like your body does when it sweats. Energy is released through radioactive decay and the amount of energy released is reducing all the time, he said. “That’s one of the saving graces of the situation – every day there’s less heat to dispose of, so the amount of cooling is less every day.” Boric acid is also being used alongside the water to help prevent a nuclear chain reaction, Prof. Holt said.
Q: Where does the steam go?
A: Out into the atmosphere through a venting system, said Prof. Holt. That’s why people in Fukushima and beyond are being tested for traces of radiation on their bodies and told to evacuate the area. If nuclear authorities didn’t release the steam from inside the reactor where the cold seawater mixes with the hot fuel rods, the pressure could become unsafe. “You have to vent that steam somewhere,” he said. Unfortunately, they have no way of removing any radioactive materials from that steam. “Any water that leaks out is going to have radioactivity in it for certain. That’s one of the concerns with this cracked part of the containment, is that water is leaking out and that could be the reason for the spike in radioactivity they saw.”
Q: If they can’t cool down the fuel rods, which are generating the heat, will there be more explosions?
A: It’s very unlikely at this stage, said Prof. Luxat. “Especially if they have some kind of breach in containment, the hydrogen is going to go up that way. But there’s no indication they are seeing any increase that would lead to a hydrogen explosion.”
Q: What could happen if the rods began to melt?
A: Just like at the Three Mile Island nuclear disaster in Dauphin County, Pa., pieces of the rods could crack and crumble to the bottom of the reactor. As their temperature rises, the fuel rods made of zircaloy cladding and cement with ceramic fuel pellets inside would expand like a balloon, said Arthur Motta, chair of nuclear engineering program at Penn State University. In a really severe accident such as Chernobyl, “it becomes like molten metal with ceramic, a blob. This [in Japan] is all inside the pressure vessel, a cylindrical containment under pressure which is very thick.” Should the rods melt, they would eventually make their way down to the bottom of the reactor and could react with the metal there. Worst-case scenario, the blob pierces through that and into the bottom of the containment. Part of the melted rods fell to the bottom of containment at Three Mile Island, said Prof. Luxat, but luckily water there had formed a solid protective surface to prevent piercing. As Prof. Holt said, the steaming so far appears to be lowering the levels of radiation. It dropped by about 20 levels over the course of six hours on Tuesday, he observed. “That’s a very good positive sign. It would indicate they are cooling the rods.”
Q: What will happen to the Fukushima Daiichi Nuclear Power Station once it’s cooled?
A: No one will ever be able to use it again. “The reactors suffered an accident that was hundreds of times bigger than the one they were designed for,” Prof. Motta said. The saltwater poured into the reactors has a corrosive effect, he added, so that alone would deem them irreparable. It will take at least two years for the plant to cool down completely, said Prof. Luxat. Then, it will likely become the subject of intense international study. “At that point, they can go and most probably do some remote inspections, which is what they did at Three Mile Island,” he said. “They want to understand what actually happened.” Scientists dressed in protective gear will drill into the top of the reactor, without even entering it, and gather samples to study under microscopes. “They’ll look at the different structures of the materials and whether there was melting, how much melting there was, how much oxidation occurred so they can actually characterize what occurred in an almost forensic way.” Once their studies are through, it will likely be dismantled and contained in a secure, sealed place, Prof. Holt said.