Nuclear Security, Part II—Fission Basics

The Overall Topic of the Nuclear Power Plant Operation and the Use of Process Control to Protect Against Nuclear Accidents

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By Béla Lipták, PE, control consultant

In the November column, (Nuclear Plant Security and Cyber Terrorism), I wrote about cyber terrorism and how process control can protect nuclear power plants or the chemical industry against it. Now I will discuss the overall topic of the nuclear power plant operation and the use of process control to protect against nuclear accidents. I will first describe the process and the reasons why some of the 100 accidents occurred in the past.

 

Want MoreRead Bela Liptak's six part series "Process Controls Prevent Nuclear Disasters," to learn how process controls could have prevented past nuclear accidents and how it could improve the safety of the nuclear power industry. Visit www.controlglobal.com/liptaknuclear.html

But first we need to familiarize ourselves with the basics of the nuclear power generation process, because we can only control a process if we fully understand it!

History

In 1905, Albert Einstein identified the relationship between matter and energy as e = mc2.  In 1923, he received the Nobel Prize in physics for it. It took 103 years to prove his theory, but this year, he was finally proven right.1 

Atomic Structure
Figure 1. The atomic structure of a stable (238U) and an unstable (235U) isotope of uranaium.  Only unstable isotopes can be used as nuclear fuel.

 

The concept of a nuclear reactor utilizing the chain reaction of fission was developed by the Hungarian-American2 scientist Leó Szilárd in 1933. He patented the process and later (1942) demonstrated it while working with a team of scientists headed by the Italian-American Enrico Fermi. This chain reaction was later used by the team of the German-American L. Robert Oppenheimer during the Manhattan Project in building the first atomic bombs.

nuclear reactor
Figure 2: In a nuclear reactor, a slow thermal neutron enters the fissionable fuel (235U) and splits that atom while energy (E) and 2 or 3 neutrons are released. Some of these neutrons are “thermal” and others are “fast” having different energy levels.

 

Another way to release the energy of the atom was taken by the Hungarian-American scientist, the Hungarian-American Edward Teller in 1952, who proved that the fusion of hydrogen atoms can also be used to initiate a chain reaction. Teller also participated in the Manhattan Project and wanted to develop this weapon only to be used as a deterrent and later did all he could to prevent its use on civilian targets. In the last years of his life, he became convinced that nuclear weapons threaten human civilization and became one of the advocates of total nuclear disarmament. Teller also understood the great importance of process control and wrote the preface to the first edition of my Instrument Engineers’ Handbook3.

Schematic Diagram of a CANDU reactor
Figure 3: Schematic Diagram of a CANDU reactor:
The primary loop is in yellow and orange, the secondary in blue and red. The cool heavy water in the calandria can be seen in pink, along with partially-inserted shutoff rods.
(Courtesy of Wikipedia http://en.wikipedia.org/wiki/CANDU

 

Here, as an energy source, I will not discuss this fusion process, (which occurs in the sun), because that process operates at millions of degrees temperature and, therefore, is unpractical on this planet. I will just mention that to date, controlled fusion has only been achieved in experimental devices although a large fusion reactor is under construction in France with international support.

Understanding Nuclear Fission

An atom is composed of a central nucleus consisting of protons, neutrons and other particles plus of electrons orbiting in shells around the nucleus at discrete energy levels. These are referred to as electron shells. The proton has a positive charge equal to that of the electron and a mass, which is a couple of thousand times greater. The neutron has no electric charge and has a mass similar to that of the proton. When basic particles combine to form an atom, a certain amount of mass is converted into the binding energy of the atom, which is needed to hold the nucleus together. As I noted earlier, Einstein defined this conversion by the equation e = mc2, where e is the energy, m is the mass, and c is the velocity of light in a vacuum.

reactor design
Figure 4: A schematic (top) and a more detailed view (bottom) of the reactor design which in 1986 at Chernobil caused the most severe nuclear accident to date. The design is referred to as the RBMK (Reactor Bolohoj Moshosztyl Kanalnyj) reactor.

In chemical reactions, the changes occur in the electron shells. In nuclear fusion, the release of energy is caused by the change in the nuclei as atomic particles are fused together. In fission, mass is converted into energy and energy is released, because the atoms of isotopes are split. Fission events release more than 2 million times more energy per event than do chemical reactions.

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