A Chernobyl-type nuclear power accident cannot happen in the United States

There is renewed interest, and actual progress, in building new nuclear power plants in the United States. http://www.delawareonline.com... 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 certified moron 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. "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." http://science.howstuffworks.com... 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)." http://en.wikipedia.org... 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)." http://users.owt.com... 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 possible in the United States.