Nuclear meltdowns are scary things. Most people don't understand what a nuclear reaction is. They just know it is big. Three major meltdowns have occurred: Three Mile Island, Chernobyl, and Fukushima. Most people know about the last two; Chernobyl was a true disaster, and Fukushima still is leaking radiation into the ocean. Fukushima in particular would have been easy to prevent at two stages: building a higher protective wall around the plant, and flooding the reactor early. Zero people died in Fukushima and Three Mile. Compare that to the disaster that is 11,000 premature deaths and 24,000 heart attacks per year caused in the US alone by burning coal. Moreover, modern nuclear power plants are designed to prevent these accidents from happening.
Three Mile Island
Three Mile Island occurred in 1979 in PA. A problem began, and human error allowed it to persist. A pressure release valve was stuck open. The valve allowed some irradiated coolant to escape. A poorly trained operator was not familiar with the interface and confused the warning for the loss of coolant (the human-computer interfaces were new and not well designed). When the reactor began to overheat, the control rods were fully inserted. Remnant decay heat persisted, but the chain reaction was halted. Unfortunately, the plant had its emergency cooling pumps shut down for maintenance. You would think that there would be a rule saying that if the emergency cooling pumps were shut down for maintenance, that the plant itself should shut down, right? Well, there was such a rule. It is one the the key rules that the Nuclear Regulatory Commission laid down. The plant was in violation of this key rule.
A series of events followed where the cladding of the nuclear fuel rods melted. Some radioactive gas was released into the environment. The average person living within a 10 mile radius was dosed with about 8 millirem (a measure of radioactivity). This is the equivalent to a single chest x-ray. The average person living in a high altitude city, like Denver, CO, gets 100 extra mrem a year just by being closer to the sun. The average US citizen gets 300mrem a year from the environment. A round-trip flight from New York to Europe will dose you with 3mrem. In other words, this was negligible. The consensus of epidemiological studies since shows no increase in cancer rates from this event.
One a 1-10 screw up scale, this was about a 6. The operators failed to recognize it as a loss-of-coolant event, and allowed the core to overheat. Not a single person died as a result. All the containment methods, which are 1970s technology and design, worked. The only loss was an economic one. To the tune of about $2 billion.
Chernobyl. April 26, 1986. A real, unshielded nuclear meltdown occurred. Chernobyl did not have the containment building that most other reactors had. In other words, outside of the reactor pressure vessel, there was nothing to contain leaks or explosions. 31 people died that night, and most serious epidemiological studies indicate the total death toll (counting increased incidences of cancer) has caused about 5000 premature deaths in Europe to date. Total increase in cancer by 2065 is estimated to be about 40,000 (not all of these lead to death). Let's be very clear on this. The worst nuclear disaster in history, which has proven to be avoidable just by building a concrete building around it, will have caused 40,000 cancer-related premature deaths in 80 years. This also happens to be the sum total of deaths caused by nuclear. If you look at actual deaths caused in the US alone by coal in the past 80 years, you are looking at numbers close to 1.6 million (about 20k deaths annually in the 70 years prior to strict limitations in 2004, 11k annually since then). This is a conservative estimate, not accounting for likely increase in death through the years when there were no emissions limitations. The number of heart attacks caused by coal emissions over this period is likely double this. Also compare those 40,000 increased cancer incidences to the literally hundreds of millions of unrelated cancer cases that will have occurred over that same 80 year period in Europe alone. 40,000 compared to 1,600,000, the latter produced in an era of much lower population, is pretty staggering. These numbers speak for themselves. Also compare this to the 17,000 deaths that have occurred from airplanes in the 13 years of 1999-2011.
Now that we know the death toll of Chernobyl, and we have a comparison of other deaths, let's talk about this catastrophic failure. It was a very complicated series of events, one that I could write several posts about. Instead, I will direct you to the Wikipedia article. The short version is that they were running some safety tests. They were instructed by Kiev to hold off their tests by 12 hours, making the test run during the overnight shift instead of the shift that was trained to run the test. At the end of the safety tests, they tried to insert the control rods back into the core. Because of several anomalies caused by having moved the test time, there was a minor explosion in the core as the rods were inserted. They were only 1/3 of the way in, and they broke off, preventing full insertion. Unlike modern control rods, these control rods were made of graphite. Graphite is a good moderator, but it also burns really well at high temperature. The lack of control rods allowed a small nuclear chain reaction to happen. This reaction was self-limiting; the energy from the reaction blew the fuel rods apart, making it so there was not enough uranium in one place to continue the reaction. The explosion, however, ripped through the pressure vessel and allowed atmosphere to come in. Air contains O2. Graphite is carbon. Carbon is what burns in coal to produce heat. The heat of the overheated reactor combined with the influx of oxygen was enough to make the graphite burn. This helped spread out the radioactive material. There was no giant concrete containment structure to contain it (remember how Three Mile island had a containment structure, and it worked? So did Fukushima.). The burning graphite spread radioactive material very far.
On a 1 to 10 scale of screw up, this was a 10. Bad idea to do safety tests.
Fukushima is still being studied. The latest reports indicate that people living within the immediate vicinity of the plant received 10mrem dosing. Again, this is the dosage a person gets every 10 days just for living on Earth. There have been no increases in cancer, nor is there expected to be any. There are some serious ecological impacts to be dealt with. There are some regions in the immediate vicinity of Fukushima that won't be able to produce agriculture for as much as 20 years. Other areas are uninhabitable for that amount of time. The region groundwater around Fukushima Daiichi is still contaminated and likely will be until a 100 foot deep wall of concrete and steel is built as a containment wall around it. It still leaks radiation into the ocean today. Nonetheless, no one has died from the incident. It could have easily been prevented in two circumstances. An event like this wouldn't even be possible in a modern nuclear power plant, as we will see.
Fukushima Daiichi's emergency backup generators kicked in after the 9.1 magnitude earthquake shut down the power grid. The ensuing tidal wave washed over the protective barrier of the power plant and inundated the generators. They shut down. The emergency backup batteries lasted 8 hours. Then cooling pumps stopped. This is known as a triple power failure. It is something that had been written about in the past for many plants, with measures taken against in. It was something written about with this particular plant, with no measures taken against it. TEPCO was warned by a governmental agency two years prior to this event that their sea walls were not tall enough.
What happened next is that the core melted down. They should have flooded the core with seawater and destroyed the reactor (seawater is pretty corrosive), but the plant operator thought they could contain the situation without destroying the reactor. They were wrong, and the consequences were a full nuclear meltdown. Heat and pressure built up and the explosion could not be easily contained. The surrounding area had to be evacuated. Even in all of this mess, no one was exposed to sufficient radiation to matter, and the situation is handled. It is an environmental disaster, yes. But let's compare this to coal fired power plants. Where do you think all that mercury in the fish over the entire planet comes from? Coal fired power plants.
More importantly, the new generation of power plants would prevent this type of event from happening. The emergency cooling water reservoir is contained above the core. In the event of power loss, the water can dump into the reactor using gravity. No Fukushima, no explosion and radiation.
This post is getting long, but before we go, let's visit one point we have touched on. Nuclear power has risks. Coal power has definite consequences. Far more people die from coal than from nuclear power. Grossly more. Nuclear is still scary to most people, and likely not to win the PR battle in the short run. And all these safety features make nuclear power pretty expensive. What are the other options? We haven't discussed hydro yet, nor wind and solar. For now, let's leave it between the big power plants. I personally believe that Fukushima was the last major learning point in nuclear power. Coal power is pretty gnarly, even at its best. Another solution is to use less energy. This is pretty tough one to make happen, and I don't see it happening any time soon. A post far in the future will grapple some of this.
That's all for now. Thanks for reading my longest article to date.