الفهرس 
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Abstract
One barrier that inhibits the development of more nuclear reactors in the world is the concern over waste management. The waste generated from nuclear power plants requires disposal and therefore a repository. One goal of this thesis is to develop the technology for waste transmutation.
Waste transmutation involves transforming some of the long lived radioactive materials into short lived or even stable isotopes. The minor actinides (MA) that are of most concern include Np-237, Am-241, and Am-243 and the long-lived radio-nuclides (e.g. I-129, Tc-99, etc.) which do contribute to very long-term radio-toxicity, can only be destroyed by neutron capture, representing 4% of spent nuclear fuel. By transmuting these actinides, the long term radio-toxicity and heat load of the spent fuel can be reduced and will in turn lessen the burden for a repository. One way to transmutate these minor actinides is through an Accelerator Driven System (ADS).
A great interest has been displayed worldwide for accelerator driven subcritical reactors (ADSR or ADS) to produce energy and transmute radioactive waste in a possibly cleaner and safer way.
The physics of ADS is quite different from that of critical. Critical reactors can be operated at any power that can be safely removed whereas the power of ADS is determined, additionally, by the operating keff and the available accelerator beam current. The power in ADS is very sensitive to the value of keff and it becomes essential therefore, to accurately predict these parameters over the entire length of the burn up cycle.
Because of the target is the physical and the functional interface between the accelerator and the subcritical reactor in the ADS so it is probably the most innovative component of the ADS. The performance of the ADS are characterized by the number of neutrons emitted per incident electron, the mean energy deposited in the target for neutron produced, the neutron spectrum and the spallation products distribution. Neutron multiplicity is the number of neutron produced per one beam particle.
This study uses a neutron source driving a subcritical TRIGA core configuration. The neutron source is produced by bombarding a lead-bismuth eutectic target (Pb-Bi+Be) with a Beryllium layer in it’s downstream end with 3 GeV energy electrons. The electrons produce Bremsstrahlung photons while slowing down and the photons produce fast neutrons via photonuclear reactions. These neutrons are then multiplied through a subcritical lattice.
MCNPX will be used with in the vicinity of the TRIGA reactor. An electron source was created on the top portion of the target to simulate the accelerator. MCNPX can simulate the electron interactions within the target that produce Bremsstrahlung photons which in turn produce neutrons via photonuclear reactions.
Introducing layer of beryllium Be- to reflect those neutrons which may otherwise escape the block from the downstream end so that many of them enter the fuel assembly instead of escaping out and secondly it marginally increases their number through (n, 2n) reactions, hence we got an intense neutron spallation source INSS. By coupling the TRIGA reactor with the Pb-Bi+Be target we get an ADS system used to burn up the MA and FP in an efficient and safer way.
We can conclude from the burn up results that:
- The total core fuel mass is 126700 gm (initial mass).
- After 300 days the total core fuel mass reduced by a factor of 17.5 %;
- After 700 days the total core fuel mass reduced
by a factor of 38.5 %.