Page 155 - Managing Global Warming

Current and future nuclear power reactors and plants 121

nuclear reactor generations are as the following: (1) Generation I (1950–65)—early
prototypes of nuclear reactors; (2) Generation II (1965–95)—commercial power
reactors; (3) Generation III (1995–2010)—modern reactors and Generation III+
(2010–25)—reactors with improved parameters (evolutionary design improve-
ments); and (4) Generation IV (2025)—future reactors with new parameters and
enhanced safety features.
Furthermore, nuclear reactors can be classified, based on various parameters [1]:

1. Neutron spectrum: (a) thermal (the vast majority of current nuclear power reactors), (b) fast
(currently, only two nuclear power fast-neutron-spectrum reactors are in operation in Russia:
BN-600 and BN-800), and (c) interim or mixed spectrum.
2. Reactor-core design:
I. Neutron-core design: (a) homogeneous, i.e., the fuel and reactor coolant are mixed
together (one of the Generation IV nuclear reactor concepts) and (b) heterogeneous,
i.e., the fuel and reactor coolant are separated through a sheath or cladding (currently,
all nuclear power reactors); and
II. General core design: (a) Pressure-vessel (PV) (the vast majority of current nuclear
power reactors) and (b) Pressure-channel (PCh) or Pressure-tube (PT) reactors;
3. Coolant:
I. Light-water-cooled reactors;
II. Heavy-water-cooled reactors;
III. Gas-cooled reactors;
IV. Liquid-metal-cooled reactors;
V. Molten-salt-cooled reactors; and
VI. Organic-fluids-cooled reactors (existed only as experimental reactors some time ago).
4. Type of a moderator: (a) liquid moderator (H 2 O (light water) and D 2 O (heavy water) and
(b) solid moderator (graphite, zirconium hydride (ZrH 2 ), beryllium (Be) and beryllium oxide
(BeO)).
5. Application: (a) power reactors; (b) research reactors; (c) transport or mobile reactors
(submarines and ships (icebreakers, aircraft carriers, etc.); (d) reactors for space applica-
tions; (e) industrial reactors for isotope production, etc.; and (f ) multipurpose reactors.
6. Number of flow circuits: (a) single-flow circuit (once-through or direct-cycle); (b) double-
flow circuit; and (c) triple-flow circuit.
7. Fuel enrichment: (a) Natural-uranium fuel (NU) (99.3% wt of nonfissile isotope uranium-238
(U 238 ) and 0.7% of fissile isotope uranium-235 (U 235 )); (b) slightly enriched uranium
(SEU) (0.8–2% wt of U 235 ); (c) low-enriched uranium (LEU) (2–20% of U 235 ) (the vast
majority of current nuclear power reactors); and (d) highly enriched uranium (HEU)
(>20% wt of U 235 ).
8. Fuel used: (a) Conventional nuclear fuels (low thermal conductivity): Uranium dioxide
(UO 2 , used in the vast majority of nuclear power reactors), mixed oxides (MOX)
((U 0.8 Pu 0.2 )O 2 , where 0.8 and 0.2 are the molar parts of UO 2 and PuO 2 , used in some
reactors); and thoria (ThO 2 ) (considered for a possible use instead of UO 2 in some countries,
usually, with large resources of this type of fuel, for example, in India); and (b) alternative
nuclear fuels (high thermal conductivity): Uranium dioxide plus silicon carbide (UO 2 -SiC),
uranium dioxide composed of graphite fiber (UO 2 -C), uranium dioxide plus beryllium oxide
(UO 2 -BeO), uranium dicarbide (UC 2 ), uranium monocarbide (UC), and uranium mono-
nitride (UN); the last three fuels are mainly intended for use in high-temperature Generation
IV reactors.