Basics of nuclear fuel: Rooppur Power Plant

An article titled "Option for safe power plants" by Engr. S.A. Mansoor was posted in the August 26, 2016 online edition of the Financial Express. [The article appears on Page-5 in the August 27 print edition of the paper.]
The topic raised in the article is very pressing and relevant, as some of us do not have a clear idea of fuel used in nuclear power plants (NPPs), though many of us know that the fuel is Uranium. Unfortunately, the article by Engr. S.A. Mansoor is highly confusing.  Some of the statements of the article contradict the basic principles of nuclear and radiation physics.
Engr. Mansoor talks about U-236 reactors. Nuclear power reactors fuelled by U-236 do not exist at all. There are no reactors fuelled by U-238 as well. Russian, American, French, Chinese and all other reactors are fuelled by U-235.
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 per cent), uranium-235 (aprox 0.7 per cent), and uranium-234 (below 0.006 per cent).
Of these 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.
Engr. S.A. Mansoor wrongly talks about U-236 fuelled nuclear power reactors, which do not exist at all. U-236 also doesn't exist in nature. U-236 is produced only in a nuclear reactor as a by-product of U-235 neutron bombardment.
There are also no reactors fuelled by U-238. U-238 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. Therefore, there must be the fuel isotope U-235 in the reactor. Thus, it will be an ordinary reactor. Of course, it will also produce some U-236.
Engr. Mansoor apparently talks about the reactor in the USA using pebbles of tennis ball size as fuel (called Pebble Bed Reactors). It is one of the six concepts being investigated for Generation IV rectors. It also uses U-235 as fuel, although it has not been tried out in production scale (current reactors operating round the world being of the Generation II, III and III-plus type). Generation IV reactors are not expected to be available for commercial operation before 2030.
Of the 450 reactors currently operating world-wide, 384 reactors are Light-Water Reactors (LWRs). Since Bangladesh should invest in a proven technology, the decision of the Bangladesh government to deal with Russia for a proven type LWR is a step in the right direction. The Rooppur Nuclear Power Plant will be constructed under the intergovernmental agreement signed between Russia and Bangladesh on November 02, 2011. The Rooppur NPP will be equipped with two 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 recently launched a unique new Generation 3+ power unit with a VVER-1200 reactor (Power Unit 6 of the Novovoronezh NPP). At the present time, 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 has been connected to national power grid.
The writer is an independent nuclear expert from Russia and Editor-in-Chief of AtomInfo.ru,
specialised nuclear energy news portal.
 [email protected]