A nuclear reactor, if described in layman’s terms, is a multiplier of source neutrons, with reactor power reflecting the extent, and activities of the neutron source strength and the source multiplier. Though it has extensive usage in terms of space research, naval usage as well as generating electricity, it has its own share of skepticism owing to the frequent radioactive accidents and hazards which have taken place over the years.

Introduction: A nuclear reactor is an apparatus developed to create reactions and to capture the heat produced by fission. This heat is used to convert water into steam which in turn is used to spin huge turbines that drive generators in order to produce electricity. A nuclear reactor works in a similar way as most of the thermal power plant which operates on coal, oil or gas, however, the only difference is that the reactor uses uranium fuel to create the heat essential to generate electricity. The enormous amount of heat generated is collected and used to create steam which enables the turbines to move. This is one of the most commonly used sources of generating electricity across the globe.

Nuclear reactors are predominantly used to produce nuclear energy in a controlled manner. Though there are various types of nuclear reactors, almost all of them operate using nuclear fission. They are basically heat engines. With respect to uranium fissions which are also used in nuclear reactors, there is breaking down of atoms which results in the release of energy, most of it in the form of heat which in turn is used for various applications. It is most commonly used to generate electricity along with being used by naval, NASA, etc.

In terms of its usage in naval, in a nuclear-powered submarine, reactors’ heat results in production of steam to drive the turbines that provide the submarine its tangible power. It was a great breakthrough in early 1950s, when the development of sleek, safe and highly dependable pressurized water reactors for naval use was introduced resulting in the usage of nuclear powered submarines. [How A Nuclear Reactor Works, 2004]

It is interesting to understand how naval pressurized water reactors work. It consists of two parts - a primary coolant system and a secondary coolant system. The primary coolant system is involved in circulating water which is then pressurized to avoid boiling, in a closed loop. With the passage of water through the reactor, the water gets heated up and then converts to steam to pass through the steam generator and then it moves on to the secondary system. This whole process continues with it flowing back to the reactor to be heated again and the cycle goes on and on.
Apart from being used for naval purposes, nuclear reactors are also used by NASA for various space researches. At the centre of every nuclear power plant is the radioactive core which is the basic nuclear furnace that generates heat with the atoms splitting during the controlled chain reaction. The usage of radioisotope power sources for research in space has gone back to as long as 1961. Russia has been mainly using fission power sources. However, the new and more powerful designs have been used by NASA and are also under development in the USA.

While Russia has extensively used nuclear fission power for space missions, the USA has flown only one which is the SNAP-10A (System for Nuclear Auxiliary Power) way back in 1965. During the period 1959-73, a US nuclear rocket program called the Nuclear Engine for Rocket Vehicle Applications (NERVA) was set up, whose objective was to replace chemical rockets for the latter stages of launches by nuclear power. [Vrillon et al, 1990]
Another form of nuclear reactor called the radioisotope systems or radioisotope thermoelectric generators (RTGs) has been widely used for US space work since 1961. This system uses high decay heat of Plutonium-238 resulting as an electricity provider in the RTGs of spacecrafts, satellites, navigation beacons, among other uses. This method has been considered safe, dependable and easy to handle along with providing heat and electricity for long periods of time even under harsh conditions. [Poston, 2002]

NASA has been using many RTGs especially in space vehicles like Apollo, Pioneer, Viking etc. along with being used for civil and military satellites. The most recent Viking and Rover Landers for the exploration in Mars also rely on RTG power sources. The usage of nuclear reactors would further help in unraveling the wonders of the universe. In 2002, NASA declared its Nuclear Systems Initiative for space projects which was named as Project Prometheus in 2003. The sole objective of this mission was to facilitate advancements in the capabilities of space missions resulting in faster nuclear-powered space travel as well as manned missions to planets like Mars.

Analysis: A nuclear reactor provides a favorable environment for a moving neutron to interface with a stationary fissile atom, more commonly the U-235. This interface results in the production of enormous instability in the atom’s nucleus resulting in the splitting of the atom into two unequal pieces. This splitting of the atoms releases two or more neutrons along with the release of energy. The single neutron which has be released from the first fission results in the second fission which in turn results in the third fission, so on and so forth causing a chain reaction. [NUKEFACT #22, How a nuclear reactor works, 1997]

With regards to all operational uses of the reactors, the chain reaction is of finite length and stops eventually. The poison or the neutron absorber controls the reactor’s nuclear status which is the number of fission events in the chain reaction, the number of chain reaction which might be ongoing as well as whether these numbers are going to be same or are going to change with time. These absorbers are placed in the reactor and the most common absorber used is the boron-10 which reduces the chance of fission by fighting with the fissile atoms for free neutrons.

There have been extensive debates on the usage of nuclear energy and in turn nuclear reactors for various purposes. However, supporters of the use of nuclear energy as well as reactors are under the belief that it is a safe and effective way to produce enormous amounts of energy. With the every increasing requirement for energy and the problems connected to burning fossil fuels resulting in acid precipitation, greenhouse effect, etc., the usage of nuclear energy is the safest bet.