of trans-uranium elements (TRUs) are becoming long-lived radioactive wastes. If
TRUs could be recycled as nuclear fuel, the benefits attained from nuclear power
would increase as a long-term energy supply and the negative environmental
impact of TRUs as radioactive wastes could be greatly reduced. For these purposes
many types of innovative reactors, including the sodium-cooled fast reactor (SFR),
have been proposed. The resource-renewable BWR (RBWR) has been proposed to
achieve the same purposes using concepts based on proven BWR technologies and
the BWR capability to control the neutron energy spectrum flexibly [1–3]. A major
characteristic of the BWR is “boiling” in the core, which includes water that
functions as both a moderator and a coolant. The neutron energy spectrum can be
hardened by reducing the hydrogen-to-uranium ratio (H/U) using the two-phase
flow and using the hexagonal tight fuel lattice, so that the transmutation of
238 U to
fissile plutonium is promoted with increasing resonance absorption: this enables the
multi-recycling process of both breeding and consuming TRUs. On the other hand,
there is a tendency that the harder the neutron spectrum becomes in the TRU-loaded
core, the more positive the void reactivity coefficient becomes. The void reactivity
coefficient is one of the main safety parameters for light water reactors (LWRs) and
must be negative. The RBWR achieves the TRU multi-recycling capability under
the constraint of the negative void reactivity coefficient by introducing the parfait
core concept [4].
This chapter reviews details of the specific design and core characteristics of
the RBWR.
14.2 RBWR System
14.2.1 Overview
Figure 14.1 shows the reactor pressure vessel (RPV) of the RBWR. The common
plant specifications of the RBWR and the latest commercial BWR, the ABWR, are
listed in Table 14.1. The rated thermal power, electric power, diameter of the RPV,
and core pressure are identical for both reactor plants. Figure 14.2 shows a horizontal cross-sectional view of the RBWR core configuration, which is composed of
720 hexagonal fuel bundles and 223 Y-type control rods. The axial configuration
uses the parfait core concept in which an internal blanket of depleted uranium oxide
is placed between the upper and lower fissile zones of the TRU oxides.
Various design concepts of the RBWR core have been proposed. Recent core
designs have focused on TRU management. The RBWR-AC is the break-even
reactor that can burn depleted uranium by using TRUs extracted from the spent fuel
bundles of LWRs without decreasing the amount of TRUs. The RBWR-TB is the
TRU burner that can fission almost all the TRUs, leaving only the minimum critical
mass of TRUs, by repeating their recycling and collecting. The RBWR-TB2 is a
modified version of the TRU burner. The RBWR-TB2 is designed to be able to burn
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T. Hino et al.
TRUs could be recycled as nuclear fuel, the benefits attained from nuclear power
would increase as a long-term energy supply and the negative environmental
impact of TRUs as radioactive wastes could be greatly reduced. For these purposes
many types of innovative reactors, including the sodium-cooled fast reactor (SFR),
have been proposed. The resource-renewable BWR (RBWR) has been proposed to
achieve the same purposes using concepts based on proven BWR technologies and
the BWR capability to control the neutron energy spectrum flexibly [1–3]. A major
characteristic of the BWR is “boiling” in the core, which includes water that
functions as both a moderator and a coolant. The neutron energy spectrum can be
hardened by reducing the hydrogen-to-uranium ratio (H/U) using the two-phase
flow and using the hexagonal tight fuel lattice, so that the transmutation of
238 U to
fissile plutonium is promoted with increasing resonance absorption: this enables the
multi-recycling process of both breeding and consuming TRUs. On the other hand,
there is a tendency that the harder the neutron spectrum becomes in the TRU-loaded
core, the more positive the void reactivity coefficient becomes. The void reactivity
coefficient is one of the main safety parameters for light water reactors (LWRs) and
must be negative. The RBWR achieves the TRU multi-recycling capability under
the constraint of the negative void reactivity coefficient by introducing the parfait
core concept [4].
This chapter reviews details of the specific design and core characteristics of
the RBWR.
14.2 RBWR System
14.2.1 Overview
Figure 14.1 shows the reactor pressure vessel (RPV) of the RBWR. The common
plant specifications of the RBWR and the latest commercial BWR, the ABWR, are
listed in Table 14.1. The rated thermal power, electric power, diameter of the RPV,
and core pressure are identical for both reactor plants. Figure 14.2 shows a horizontal cross-sectional view of the RBWR core configuration, which is composed of
720 hexagonal fuel bundles and 223 Y-type control rods. The axial configuration
uses the parfait core concept in which an internal blanket of depleted uranium oxide
is placed between the upper and lower fissile zones of the TRU oxides.
Various design concepts of the RBWR core have been proposed. Recent core
designs have focused on TRU management. The RBWR-AC is the break-even
reactor that can burn depleted uranium by using TRUs extracted from the spent fuel
bundles of LWRs without decreasing the amount of TRUs. The RBWR-TB is the
TRU burner that can fission almost all the TRUs, leaving only the minimum critical
mass of TRUs, by repeating their recycling and collecting. The RBWR-TB2 is a
modified version of the TRU burner. The RBWR-TB2 is designed to be able to burn
142
T. Hino et al.