Reactor Fuel Production; Endless Sustainability
Nuclear energy is the power source of the future. However; Similar to fossil fuels, there is a finite amount of fuel in our earth. Common reactors of today use the idea of delayed neutrons to sustain a reaction and moderators to slow fast neutrons to a thermal state so they will react. They will react with U235 in a fission reaction and release energy which can be harnessed through a thermodynamic fluid cycle to create electricity. We are writing this wiki entry to propose the idea of the breeder reactor.
The idea of a breeder reactor is to produce more fuel while using fuel. Moving into the future this has the potential to feed our society’s thirst for energy without depleting our environment or running out of recourses. The research ideas behind these reactors could lead to the production of fuel from many different elements, ideally ending in a cycle of building fission products into fissile material. Ultimately sustainable! Though, for the purpose of this essay we will examine the breeding of thorium.
For the description of this cycle we will assume the reader has a general knowledge of a typical reactor cycle, if you need refreshing you can look at one of my peers articles on nuclear cycles. The thorium recourses in this world triple that of uranium (1). 400,000 tones exist in the US alone. On the other hand this point becomes moot when we look at ultimate sustainability; we are considering the entire world, a global economy. Moreover; when coupled with a U233 fission reactor, Th232 can become fuel through the capture a free fast or slow neutron which will yield Th233. With a 22 minute half life this thorium will go through a beta decay resulting in Pa233. With a month long half life the protactinium will experience beta decay and become fissile U233. We refer to thorium as fertile. We believe that with further research many more elements can be discovered to be fertile, as stated before, ideally fission products; thus creating an endless cycle. This would become possible with the correct analysis of the chart of the nuclides and impeccable reactor control.
To be classified as a breeder reactor, the reactor must create more fissile material than it consumes. This is a very hard ratio to achieve and should be receiving a large amount of government research funding. As undergraduates we cannot claim to have the ideas necessary to design a safe breeder reactor, but with the general engineering knowledge we have, we can come up with some conceptual ideas. Sadly in 1979 president Jimmy Carter placed a ban on reprocessing of spent fuel. This is a crucial step for all breeder reactors and can greatly reduce the waste produced from the reactor. The waste produced by these breeder reactors is a fraction of that produced by current reactors (3). Jimmy Carter’s decision has slowed the process of the research in this country and has made it nearly uneconomical to research breeder reactors.
Per fission2-4 neutrons are released. In the energy ranges we are considering an average of 1.4 neutrons are needed to create fission in the next generation. This leaves .6-2.6 neutrons on average available for breeding (2). The graph below shows that the cross section area for U233, you can see that at high energies it is very unlikely that the uranium will capture a neutron. Ideally more than one element could be bred at a time so when one reaches the fissile state the other will be on its way and fuel will slowly produce itself. Another cycle under development is the uranium plutonium cycle, which breeds fuel in a similar way.
While these reactors do need large amounts of fuel to begin and have an inherent danger with high energy neutrons, when they can be researched and perfected they will be our recourse of the future.
To prove this point lets take a quick example of a common fission product (samarium 153) and we will show you what this element must go through to become fissile again. Obviously this takes much more nuclear control than is available with today's technology. However; each of these reactions is a real decay the element experiences and the neutron capture is from the free neutrons of a breeding reactor (4):
Sm15362 - Beta Decay (half life of 1.9 days)
Eu15363 - Capture Neutron(6)
Eu15763 - Beta Decay (half life of 15 hours)
Gd15764 - Capture Neutron(2)
Gd15964 - Beta Decay (half life of 19 hours)
Tb15965 - Capture Neutron(2)
Tb16165 - Beta Decay (half life of 7 days)
Dy16166 - Capture Neutron(5)
Dy16666 - Beta Decay (half life of 3.4 days)
Ho16667 - Capture Neutron(1)
Ho16767 - Beta Decay (half life of 3.1 hours)
Er16768 - Capture Neutron(4)
Er17168 - Beta Decay (half life of 7.5 hours)
Tm17169 - Capture Neutron(2)
Tm17369 - Beta Decay (half life of 8.2 hours)
Yb17370 - Capture Neutron(2)
Yb17570 - Beta Decay (half life of 4.1 days)
Lu17571 - Capture Neutron(2)
Lu17771 - Beta Decay (half life of 6.6 days)
Hf17772 - Capture Neutron(5)
Hf18272 - 2 Beta Decays (half lifes of 1 hour and 15 minutes)
W18274 - Capture Neutron(5)
W18774 - Beta Decay (half life of 24 hours)
Re18775 - Capture Neutron(1)
Re18875 - Beta Decay (half life of 17 hours)
Os18876 - Capture Neutron(5)
Os19376 - 2 Beta Decays (half lifes of 30 hours 10 days)
Pt19378 - Capture Neutron(6)
Pt19978 - 2 Beta Decay (half lifes of 30 minutes and 3.2 days)
Hg19980 - Capture Neutron(6)
Hg20580 - Beta Decay (half life of 5 minutes * lowest half life in the series but the only other radioactive Hg particle has a 50 day half life.)
Ti20581 - Capture Neutron
Ti20681 - Beta Decay (half life of 3.4 minutes * again short half life but Ti205 is stable)
Pb20682 - Capture Neutron(3)
Pb20982 - Beta Decay (half life of 3.3 hours)
Bi20983 - Capture Neutron(1)
Bi21083 - 3 Beta Decays (half lifes of 5 days, 3 hours and 8 hours)
Rn21086 - Capture Neutron(11)
Rn22186 - Beta Decay (half life of 25 minutes)
Fr22187 - Capture Neutron(1)
Fr22287 - Beta Decay (half life of 14 minutes)
Ra22288 - Capture Neutron(3)
Ra22588 - Beta Decay (half life of 15 days)
Ac22589 - Capture Neutron(1)
Ac22689 - Beta Decay (half life of 31 hours)
Th22690 - Capture Neutron(7)
Th23390 Glorious! 2 Beta Decays with half lives of 22 minutes and 27 days yields fissile U233
This is extremely theoretical but extremely sustainable. The benefits of breeder reactors are great and require the attention and research of our nation.
(1) World Nuclear Association www.world-nuclear.org July 2008
(2) http://lpsc.in2p3.fr/gpr/english/NEWNRW/NEWNRW.html July 2001(R. Brissot, D. Heuer, E. Huffer, C. Le Brun, J.-M. Loiseaux, H. Nifenecker, A. Nuttin)
(3) Nuclear Engineering by Ronald Allen Knief 1992
(4) Chart of the Nuclides - Lockheed Martin 16th edition
S. Lavoritano
N. Ingham
