Additionally, a comparison of fast and thermal systems with equal TRU destruction rates and driven by external neutron source reported in [Bowman C.D., 2001] shows that equilibrium inventories of all the actinides including Cm are considerably smaller for the thermal system due to the higher effective cross-sections. Furthermore, the reduced Pu inventory also reduces the proliferation potential of the fuel cycle.
Coolant and fuel choice The neutron spectrum of the system largely drives the choice of the coolant which by itself has a minor impact on transmutation capabilities of the system. The fast systems are limited to liquid metal (Na, Pb) or gas (He, CO2) coolants (Figure 1.2.3). All three technologies: sodium, lead, and gas-cooled reactors are promising concepts and they were chosen for development as candidates for future nuclear energy systems by the Generation IV roadmap committee [DOE/Generation IV International Forum, 2002]. Considerable research activities are currently in progress throughout the world aiming at the development of lead or lead-bismuth eutectic cooled reactor systems for waste transmutation. Pb-Bi coolant offers a number of safety advantages over Na, while much more operating experience is available for Na cooled systems. A number of commercial as well as small scale research Na cooled fast reactors have been operated throughout the world. Transmutation of Pu and MA in sodium cooled fast reactors was successfully demonstrated by several studies [Hill R.N., 1995], [Kuraishi H. et al., 2001]. The experience with lead cooled reactors originates in the Russian navy propulsion program. The development of commercial power Pb (or Pb-Bi) cooled reactor (BREST concept) is also actively pursued in Russia [Orlov V.V., 2003]. Lead can effectively serve as a coolant and as a spallation neutron source in accelerator driven systems (discussed below). A number of Pb/Pb-Bi cooled critical fast reactor concepts were proposed and analyzed revealing a high potential for transmutation of TRU [Kuznetsov V.V. et al., 1995], [Hejzlar et al., 2001], [Romano A. et al., 2002]. He or CO2 gas can be used as a coolant in either fast or thermal systems typically in combination with a graphite moderator. The conventional light water cooled reactors and their potential for waste transmutation is the main subject of this thesis and will be discussed later.
31
