2.5 The first reactor and the first nuclear power plant

In this video, we will set out to the very beginning of nuclear power usage to generate electricity. We will get to know the first nuclear reactor, in which a fission chain reaction was ignited and its modest, but at the same time, fully functional equipment. We will also learn, for example, what the acronym SCRAM means, which is still used today. From the first reactor, we’ll move to the first nuclear power plant to light a light bulb and see what this National Historic Landmark looked like. Finally, we will also stop at the first nuclear power plant which supplied the produced electricity to the public electricity distribution network.

The journey of nuclear energy use for electricity production began in the first half of the last century with the discovery and study of nuclear reactions caused by the bombardment of nuclei of heavy elements with slow neutrons. During these reactions, the nuclei of the bombarded elements disintegrated and new radioactive elements were formed at a significantly greater rate than during bombardment with not slowed down neutrons. This was especially important in connection with the fissionable isotopes of uranium and plutonium, which later became a basic building block in the design of the first nuclear reactors.

In the 1930s and 1940s, the Italian physicist Enrico Fermi, a Nobel Prize winner and a significant figure in the Manhattan Project in the USA, was intensively involved in the research of radioactive decay and neutron interactions leading to nuclear fission.

Chicago Pile - 1

The first nuclear reactor using a controlled fission reaction was built by Enrico Fermi and a team of collaborators in 1942 under the west stands of the University of Chicago’s Stagg Field football stadium. The reactor was called the Chicago Pile No. 1 and its goal was to prove the possibility of controlling the fission chain reaction in uranium fuel and to experimentally verify the calculations of the initial design of the reactor. A 7.5 m wide, 4 m high and 350-ton weight pile of graphite blocks interspersed with blocks of enriched uranium served as the foundation. The ellipsoid-shaped reactor core used 5.6 tons of uranium metal together with 36 tons of uranium oxide in the form of pressed spheres. The control and emergency functions of the first reactor were very simple. Simple cadmium rods manually inserted from the side of the reactor served to control the ongoing fission reaction. Cadmium was known to be an effective neutron absorber and by moving it in and out of the reactor core, it was possible to control the number of neutrons and thus the power of the reactor. A single emergency rod, suspended above the reactor, ensured that the reactor did not go out of control under any circumstances. By automatically evaluating the neutron flux sensors or cutting the suspension, this crash rod would immediately launch into the centre of the reactor if needed and stop the reaction. The final safety feature of the first nuclear reactor were dedicated workers who were prepared to pour buckets of cadmium salt solution directly into the reactor.

Fortunately, during the experiment, which took place on December 2, 1942 and lasted approximately 20 minutes, the reactor worked exactly according to the calculations and expectations of the present physicists. In the first stage, the sensitive automatic system shut down the reactor while it was still in a sub-critical state, a few hours later the reactor reached a critical state and began to slowly increase its heat output. When the power reached about 0.5 W and the entire reactor warmed up by several degrees Celsius, the automation stopped the fission chain reaction again. In another experiment, held ten days later, the reactor was started again and brought to a critical state. During more than half an hour of operation, it reached a maximum output of 200 W.

EBR-1 plant in Idaho

The world’s first experimental nuclear power plant to produce electricity was the EBR-1 plant in Idaho. The abbreviation EBR meant that the reactor used in it was the Experimental Breeder Reactor, originally known as Chicago Pile No. 4 or “Zinn’s Infernal Pile”. After all, the main goal of the reactor’s designers was not the primary production of electricity but the verification of Fermi’s multiplying principle, which states that the reactor can produce more fissionable material than it consumes. In the EBR-1 reactor, fission was caused by fast unmoderated neutrons and the reaction of these neutrons with uranium 238U produced plutonium. The resulting plutonium could then be used as additional nuclear fuel.

Fermi’s principle was verified.

The maximum power output of the power plant’s turbogenerator was only 200 kW but it was this turbogenerator that produced electricity for the four famous light bulbs, first lit on 20th December 1951. The very next day, the first nuclear power plant was able to supply electricity to the entire building.

Another first belongs to the Russian nuclear power plant with the RBMK type reactor, built in the 1950s in Obninsk. It was the first nuclear power plant in the world to be connected to the distribution network. Its output was already 5 MW and it started supplying the city of Obninsk with electricity on 27th June 1954. As with the EBR, this type of reactor was capable of producing plutonium in addition to electricity.