The First Containment Building

The first containment building, courtesy Bing Maps

Constructed to prevent radioactive contamination from escaping during or after an accident, the containment building is a standard design feature on all modern nuclear reactors. But this wasn’t always the case.

Besides research and nuclear weapons production, one of the first applications of the nuclear reactor was in submarine propulsion.

The first nuclear submarine to be built was the Nautilus. Its development was overseen by the father of the nuclear navy, Captain Hymen G. Rickover. It launched in January of 1954. The second nuclear-powered submarine to be built was the Seawolf. She was launched on July 21, 1955. President Jimmy Carter was scheduled to be its Engineering Officer, but Wikipedia reports that he had to resign due to the death of his father in 1953 before his commission began.

The first nuclear reactors were built by the government, mostly for research purposes. The earliest reactors were used to study the atomic properties of materials in order to gain information useful to bomb makers. Nuclear physicists recognized the danger inherent in a nuclear reactor meltdown, especially in the early years in which little operating experience was available. A nuclear reactor meltdown could potentially spread radioactive contamination for miles, especially if weather patterns and surrounding hydrological conditions combined to create worst-case circumstances.

Because of that, the government implemented a basic design principle for keeping the public safe: isolation. They built their reactors as far from population centers as they could. The early reactors didn’t even have containment buildings. Some were built to utilize the natural shielding of the environment, like the Clementine plutonium reactor that was built at the bottom of Los Alamos Canyon.


This changed with the Submarine Intermediate Reactor built at West Milton, New York. A facility was built there for housing the prototype reactor that would be installed in the forthcoming Seawolf. The Seawolf submarine reactor was unique because it was not a light-water cooled reactor like that installed in the Nautilus. Rather, it was cooled by liquid (molten) sodium. The reactor powering the Nautilus was a pressurized water reactor (PWR) built by Westinghouse. The reactor inside the Seawolf would be a sodium-cooled, fast-neutron reactor designed by General Electric.

Sodium is a metal that melts at 208 degrees Fahrenheit, just shy of the boiling point of water. It has superior heat transfer properties, a property that makes it ideal as a coolant. Mercury was thought to work a little better, but the problem with mercury in nuclear applications is that it tends to slow neutrons because it has a high neutron absorption cross section. Liquid sodium is used as a coolant in fast-neutron reactors, which use highly enriched fuel without requiring a moderator. Light-water reactors require a moderator to slow down the neutrons so that they can be trapped by the fuel and carry on the chain reaction.

In the light-water reactor, regular water doubles as both the moderator and the coolant.

Sodium reactors also use electromagnetic pumps that don’t have any moving parts. They generate electromagnetic forces that propel the molten metal through the piping. With greater heat transfer efficiency, the Navy was expecting faster speeds from the Seawolf.

One of the challenges with sodium is that it reacts violently with water to produce hydrogen gas. If some coolant were to somehow escape from this reactor prototype, it may come into contact with water.

To see the explosive reaction that occurs when sodium comes into contact with water, just watch this video:

Rapid generation of hydrogen gas increases pressure. Hydrogen gas is flammable. A hydrogen gas explosion caused by a coolant leak could litter the surrounding countryside with radioactive debris.

To forestall the consequences of a dangerous, explosive event following the accidental rupture of a cooling line while testing the prototype reactor, the engineers designed a safety measure: a containment building. They even thought to include an accident mitigation system: a core spray that could cool down the containment environment following an accident in order to reduce the pressure that would be trying to rapidly build up.

If this measure wasn’t taken, then the pressure increase could damage the containment structure, similar to what would happen if you overfilled a balloon. At that point, the containment building’s purpose would be defeated because its integrity would be compromised, allowing radioactive material to escape to the surrounding environment. The core spray provides a defense against this possibility.

This early core spray system is almost identical to safety systems installed in modern power reactors.

As one newspaper article from 1953 put it when describing this facility at West Milton, “The know-how they are acquiring, say project leaders, will come in handy when the day of industrial atomic energy arrives.”


The world’s first nuclear power plant devoted entirely to peacetime purposes was the Shippingport reactor constructed by the AEC. Construction began in September of 1954. It housed a Westinghouse PWR inside a containment building. The facility built at West Milton was already in construction by 1953.

The authors in Controlling the Atom explained that the “General Electric designers of the West Milton reactor set a major safety precedent by enclosing it in a large steel containment structure….Except for a few experimental reactors constructed at remote sites and some gas-cooled reactors, all power-reactor facilities designed in the Unites States after that time included provisions for containment structures.”

The Seawolf‘s sodium-cooled reactor was replaced with a light-water PWR in 1958. Even though the Navy abandoned the idea of sodium-cooled intermediate reactors for its submarines, that reactor’s development left an important and lasting legacy on the commercial nuclear power industry.