There is renewed interest, and actual progress, in building new nuclear power plants in the United States.¹ A news broadcast last nigh covered plans to build a new plant near existing ones on the Chesapeake Bay. The broadcasters provided an opportunity for a spokesman from the Union of Concerned Scientists to opine that such a power plant could produce an incident like Chernobyl. He specifically claimed that a loss of coolant would result in a spread of nuclear material just like Chernobyl. This claim is nonsense.

The Union of Concerned Scientists, by the way, is mainly ideologues who recruit scientists to give opinions out of their field of expertise. Thus they get distinguished physicists to make foolish declarations about engineering.

“How Stuff Works” provides an overview of plant operation. “Chernobyl was poorly designed and improperly operated. While the plant required constant human attention to keep the reactor from malfunctioning, modern plants require constant supervision to keep from shutting down.”²

Nuclear reactors require a “moderator” to slow down neutrons to sustain a chain reaction. “Commonly used moderators include regular (light) water (75% of the world’s reactors), solid graphite (20% of reactors) and heavy water (5% of reactors).”³

In Chernobyl, graphite was used as the moderator. A coolant loss due to operator error caused the reactor to overheat. The heat distorted the mechanical structure making it impossible to reinsert control rods to shut down the reactor. Ultimately the heat caused the graphite to catch fire. Chernobyl had no containment vessel, so the radioactive smoke escaped and carried the radioactive material to the surrounding population.

“There are two types of reactors used in the U.S. for the production of electricity: the Pressurized Water Reactor (PWR) and the Boiling Water Reactor (BWR). Both of these types use ordinary water as both coolant and moderator and therefore are known as Light Water Reactors (LWR).”⁴ The article provides a detailed analysis of why a Chernobyl-style accident cannot occur in the U.S.

In a US reactor a coolant loss automatically shuts down the reactor’s chain reaction and automatically limits the consequences of the accident. There is no graphite or other combustible material in the reactor, so there is nothing to catch fire. The severe consequences of Chernobyl were mainly a result of the smoke distributing the radioactive material. This cannot happen without smoke, and with nothing to burn there cannot be smoke.

The Three Mile Island nuclear accident was close to the worst possible accident with a US-style reactor. Due to mechanical failure and operator error there was a coolant loss. Loss of the water shut down the chain reaction, however the fuel is nonetheless radioactive, and it gets hot. There was a small escape of radioactive steam, but no one was injured.

If a large aircraft crashed into a US nuclear plant, it’s extremely unlikely that the containment would be breached. The outer shell is four feet of special high density concrete reinforced with 2.5 diameter steel rebar. Inside the shell are two concentric steel containment vessels. However, even if the containment were cracked and coolant lost, the reactor would still automatically shut down. The breach in the containment vessel would allow more steam to escape, but it would be nothing like a Chernobyl accident.

It is impossible for any nuclear power plant to create a nuclear explosion because the radioactive material in the fuel is not concentrated enough to reach critical mass.

A nuclear accident like Chernobyl is not now possible in the United States, but couldn’t a new reactor design pose a Chernobyl threat? That depends on the risks a new design poses, and those risks can be calculated. A study made way back in 1974 assessed the risk of a Western-style power plant.⁵ The odds of an accident causing a thousand casualties was put at one in a million per year. That’s about the same as meter strike causing that many casualties, so they judged in acceptable. Chernobyl was a 15,000+ casualty accident.

In the 45 years since the study there have been no deaths from Western nuclear reactors, so whoever figured the odds has not been contradicted. With advancing technology we expect the odds to have dropped since then.

We cannot live our lives with zero risk. The chances of dying in a motor vehicle accident are about one in 6000 and the chances of dying in a fall are about one in 15,000, both per year.⁶ It’s fair to demand that the risks of nuclear accident be considerably less than those everyday risks, but demanding zero risk is irrational. We should live comfortably with one in a million odds.

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1. Delaware Online, A New Wave of Nuclear Power Plants?
2. How Stuff Works,“How Nuclear Power Works”:http://science.howstuffworks.com/nuclear-power.htm
3. Wikipedia, Neutron Moderator
4. Could It Happen Here?
5. Time Magazine, New Nuclear Odds
6. National Safety Council, Odds of Death Due to Injury