Nuclear fuel: What is important to know?

Most of us are aware of different types of fuel but how much we know about nuclear fuel? Because of our inadequate knowledge, we are very often get confused by various misleading statements and remarks. 

The topic of nuclear fuel is very pressing and relevant for Bangladeshi people as the country already embarked on nuclear power program and implementing their maiden nuclear power plant. 

Many of us know that the fuel used in nuclear power reactors is Uranium.Uranium (U) is a relatively common metal, found in rocks and seawater. Naturally occurring uranium is composed of three major isotopes, uranium-238 (over 99%), uranium-235 (aprox 0.7 %), and uranium-234 (below 0.006%). 

Of these of isotopes Uranium-235 is the most important thing for nuclear reactors. U-235 is a fuel (fissile) isotope. When U-235 is bombarded with neutrons in the reactor, it produces energy and new neutrons, which in its turn bombards new atoms of U-235 and thereby causing a sustained chain reaction.USA, Russia, France, China, India and others mostly use U-235 as the fuel for their nuclear power reactors. 

U-238 as it is a so-called fertile isotope of Uranium. ,To obtain nuclear fuel, namely plutonium (Pu 239), in the reactor U-238 needs to be struck by neutrons. So it is impossible to run a reactor using only the fertile isotope U-238 as this is the feed rather than the fuel. It will have no source of neutrons which are produced only from a fuel isotope. There must be the fuel isotope U-235 in the reactor. Thus, it will be an ordinary reactor Therefore, there are no U-238 fueled reactors. 

Some people talk about U-236 fuel based reactors. It also does not exist at all. U-236 is not found in nature. U-236 is produced only in a nuclear reactor as by-product of U-235 neutron bombardment. 

Use of these isotopes like U-238 and U-236 as nuclear fuel contradicts the basic principles of nuclear and radiation physics. 

Of the 450 reactors currently operating world-wide, the major part, namely 384 reactors are Light-Water Reactors (LWRs). Since Bangladesh should invest in a proven technology, the decision of the government to deal with Russia for a proven type LWRis a step in the right direction. 

The Rooppur NPP will be equipped with two U-235 fuel based Russian VVER reactors, each with a minimum capacity of 1,200 MW. The referential project for Rooppur NPP is Novovoronezh NPP in Russia, which has successfully been feeding power to Russia's grid for over a year. 

It is a unique new Generation 3+ power unit with a VVER-1200 reactor at present, the generation '3+' power units are also under construction in the USA, France and other countries. However, it is just the Novovoronezh Unit 6 that became the first last-generation power unit in the world which reached its physical start-up phase and have been connected to national power grid.