Nuclear Electrical Power Generation – Why The Fuss? (Part 5)

Posted on Fri 07/31/2009 by

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A Single ceramicised enriched fuel pellet.

A Single ceramicised enriched fuel pellet.

The image shown here is a single enriched pellet used in a nuclear electrical power generator.

Uranium is a naturally existing material in the Earth, and deposits are vast, with further deposits being discovered on a regular basis.

The ore is mined, and the Uranium separated from that. This is called Yellowcake, and naturally existing Uranium is already in a partially enriched state, at around 0.7%. So, even while still in the ground it is partially enriched.

150 thousand tons of rock and ore will yield around 200 tons of the Uranium.

From this first stage, that of separation, it then undergoes further enrichment.

The process to enrich it to a level where it can be used for fuel in Nuclear power plants entails 5 separate steps, and at the end of those 5 steps, it is enriched to around 3 to 5%, and most typically just that 3%.

The process for enrichment to weapons grade Uranium (typically 95 to 98%) is a completely different series of processes altogether, so if the process is to manufacture Nuclear power plant fuel, it’s not just a matter of ‘holding down the button’ so to speak and just keeping on enriching it, perhaps until it reaches weapons grade enrichment. At the end of the 5 processes for manufacturing Nuclear power plant fuel that is the absolute maximum that it can be enriched, that being the 3 to 5%.

During those processes for nuclear power plant fuel, the Uranium is converted to a powder which is then pressed into pellet form. Those pellets are then fired in a high temperature furnace to create those hard ceramic pellets. The pellets are then machined into specific sizes and a single pellet is what you see above.

nuclear_fuel_pelletsThis image at left shows a handful of those pellets, and also a small section of the rod into which these pellets are then inserted. The machined pellets are then inserted into the rods, usually tubes manufactured from  Zirconium alloy material.

I mentioned above that the original ‘dirt out of the ground’ yields 200 tons of Uranium from 150,000 tons of ‘dirt’. At the end of the 5 process, you will have 24 tonnes of nuclear fuel. The cost is $2200 per kilogram, so that amount of fuel has cost $52.8 Million to produce. You might think this is an expensive process, and in later posts I will go into the costings in a little more depth, but that amount of money is not what you might think of at first. That 24 Tonnes of Nuclear fuel is what a large reactor might use in a year, and again, you may consider that a large amount but compare it with a large coal fired power plant that burns around 7 million tons of ‘steaming’ coal each year. That steaming coal costs around $60 to $110 per tonne, so the cost of the coal amounts to close on ten times as much as the nuclear fuel for a large nuclear power plant. While coal is plentiful, and there are many hundreds of years supply World wide left, then coal fired plants are still economical, so from that you can see that nuclear power plants are even more economical than that again.

The two most common forms of reactors used in the Nuclear electrical power generating area are Pressurised Water Reactors (PWR) and Boiling Water Reactors.(BWR)

Pressurised Water Reactor Fuel Rod Assembly. Click on the image to open in a new and larger window.

Pressurised Water Reactor Fuel Rod Assembly. Click on the image to open in a new and larger window.

The finished rods with the pellets in them are then installed into bundles for insertion into the reactors. The bundles for the two types of reactors are different. For PWR reactors, there are around 180 to 260 rods in the bundle and the final assembly is around 13 feet in length. There are around 120 to 190 assembly bundles in each reactor, depending on the size of that reactor.

Boiling Water Reactor Fuel Rod Assembly. Click on image to open in a new and larger window.

Boiling Water Reactor Fuel Rod Assembly. Click on image to open in a new and larger window.

For the BWR reactors, the bundle of rods assemblies are different both in the rod material and they are then also further encased as well, and those used for BWR reactors would typically contain around the low 90’s in numbers of rods, and also depending on the size of the reactor, would contain around 370 to 800 bundle assemblies.

In both cases, as the fuel is consumed by the reaction, enrichment levels are diminished somewhat and when they fall back to around 1%, they are considered to be spent in relation to their use for the reaction to boil the water. The rods are removed from the bundle, or the bundle removed from the central core, and stored in the reactor, usually for a couple of years. By this time enrichment has diminished even further, and in most cases back to the same level as Uranium existing in the ground, at around 0.7%. The rods are then removed for dry storage at the storage facility for these nuclear fuel rods.

I will explain more about the reaction process and the generation of electrical power process in the next post, but what I want to draw to your attention is the image of the pellet back at the top of the page.

When you go to any of the numerous pages indicating Either of the 2 types of solar power plants, and also for wind power plants, you will see proudly claimed that the plant can generate enough power to provide for X number of houses. These claims are entirely spurious, even though technically correct. What they have done is to calculate the total power that the plant will generate in a year. Then they take the average power consumed per individual residence, and then divide that into the total plants power production. Those plants are not directly connected to those houses,  and they also do not directly supply power for those residences at all. The power generated by the plant is supplied to the grid only.

Now why I mention this at all is look back again at that one single pellet held in the hand there. I’m going to use a similar analogy used by those renewable power plants, and read this very carefully, because it is simply amazing.

Just 5 of those enriched pellets will supply the complete electrical power needs for a single average U.S. household residence. 5 pellets.

A typical large Westinghouse PWR power plant reactor will contain around 193 fuel assemblies in all, holding 51,000 fuel rods, and almost 18 million fuel pellets.

In the post for tomorrow, I will explain the reaction process, and how this reaction produces the electrical power.

NukeSteamElec