The Simple Physics of Nuclear Safety

The Simple Physics of Nuclear Safety
September 26, 2011

Jay Lehr, Ph.D.

Jay Lehr, Ph.D. (jlehr@heartland.org) is science director at The Heartland Institute, an... (read full bio)

Simple physics demonstrates the safety of power production in modern U.S. nuclear power plants. Despite the scaremongering of anti-nuclear activists, nuclear power can provide almost limitless safe, emissions-free power in the United States if we merely exercise the political will to allow it to happen.

Controlled Heat Production 

To create heat in a nuclear reactor, a U235 nucleus must absorb a slow neutron in order to split and give off heat. (I promise that is the most difficult concept I will present.) To make neutrons more effective for splitting the uranium nuclei, they must be slowed down from the high velocities with which they are emitted. This is done by a material we call a moderator, which will not absorb the neutrons but instead simply bumps them back into the uranium.

It turns out that the hydrogen in water is a near perfect moderator. Therefore, surrounding the fuel rods with water aids the reaction while simultaneously acting as a receiving reservoir for the heat which will eventually create steam and turn a turbine to generate electricity.

The rate of heat production can be controlled by controlling the number of neutrons allowed to create fissions, or splits, within the uranium fuel. This is easily done by utilizing control rods which are lowered between the rods containing uranium fuel. They absorb neutrons, removing them from further fissioning potential.

The control rods provide a continuous range of power output, which can span from zero power production to full capacity. Regardless of what position the fuel rods are in, the process is entirely stable and predictable.

Two Types of Reactors

Two important types of reactors use this system: Boiling Water Reactors (BWR) and Pressurized Water Reactors (PWR). In the former, water in the reactor is brought to a boil and the steam is then fed into a turbine. In the latter, the water is kept under pressure so that it cannot boil but instead transfers its heat to another water circuit outside the reactor core. The water outside the reactor core eventually becomes steam which turns a turbine.

Once the steam has been produced and fed into the turbine, the generation of electricity is the same as in fossil fuel power plants.

This brief description concerns only those components of a nuclear plant that are essential to the plant’s operation. Many other components are added to this process to increase safety. 

Safety Components

The containment building surrounding a reactor is made of four-foot-thick, heavily reinforced and steel-lined concrete, which protects the reactor from natural disasters such as Fukushima, as well as hurricanes, tornadoes, or aircraft like the ones that struck the World Trade Center. Those planes could not have destroyed any of the 444 nuclear reactors in the world today. Chernobyl was the only reactor ever constructed without such a building. 

It is important to remember the Japanese earthquake and tsunami did not destroy any reactors. It was the lack of cooling water that created the problem which led to the release of very low level radiation. While more than 10,000 people died as a direct result of the unprecedented earthquake and tsunami, not a single person died from radiation exposure from the Fukushima nuclear power complex. 

A release of low-level radiation is the only major accident that can occur at a nuclear plant. The feared meltdown is not a serious health problem; it just likely places the reactor beyond repair. It is important to remember always that a reactor can never become a nuclear bomb.

Fail-Safes in Place

An important principle is built into nuclear power plant safety: “Don’t activate safety measures when something goes wrong; instead, keep safety measures inoperable only if everything works right.” When a nuclear plant loses power, it shuts down. Control rods that absorb radiation are held above the fuel rods by an electromagnet. When electricity to the nuclear power plant is interrupted, the electromagnet no longer functions, and the control rods drop into place, cutting off the continuous radiation-producing heat. 

By way of comparison, consider what would happen if some moron inspected an oil refinery or a liquid natural gas plant with a candle. He would not be around to tell us about it. There would be an explosion of a type that you occasionally read about in the news.

Fukushima Success Story

The earthquake in Japan and the subsequent tsunami that followed did not show the weakness of nuclear safety, but rather its strength. It is estimated that 23,000 people died from these natural disasters, yet nobody died as a result of radiation from the power plants.

Although the media and anti-nuclear activists are  guilty of causing unnecessary and irrational fear throughout the world and likely slowing nuclear power development, it is actually the nuclear power industry that should shoulder the lion’s share of the blame, for making no serious effort during these past 40 years to educate the public as to what nuclear power really is and how safe it is.

Jay Lehr, Ph.D. (lehr@heartland.org) is science director of The Heartland Institute. Lehr wishes to acknowledge the help his former mentor, the late Petr Beckmann, gave him through his counsel and his book The Health Hazards of Not Going Nuclear. 

Jay Lehr, Ph.D.

Jay Lehr, Ph.D. (jlehr@heartland.org) is science director at The Heartland Institute, an... (read full bio)