At present, proton accelerators with megawatt-level beam power in CW mode
only exist in two basic concepts: sector-focused cyclotrons and linear accelerators
(linacs). Cyclotrons are an attractive option with respect to construction costs, but
they do not have any modularity, which means that a fault tolerance scheme cannot
be implemented. Also, an upgrade of its beam energy and intensity for industrial
application presently is not a realistic option. A linear accelerator, especially if
made superconducting, has the potential for implementing a fault tolerance scheme
and offers a high modularity, resulting in the possibility to recover the beam within
a short time and increasing the beam energy and intensity toward industrial
application of ADS technology.
7.4 Design of the Core and Primary System
Because MYRRHA is a pool-type ADS, the reactor vessel houses all the primary
systems. In previous designs of MYRRHA, an outer vessel served as secondary
containment in case the reactor vessel leaks or breaks. In the current design, the
reactor pit fulfills this function, improving the capabilities of the reactor vault air
cooling system. The vessel is closed by the reactor cover, which supports all the
in-vessel components. A diaphragm, inside the vessel, acts to separate the hot and
cold LBE plenums; it supports the in-vessel fuel storage (IVFS) and provides a
pressure separation. The core is held in place by the core support structure
consisting of a core barrel and a core support plate. Figure 7.2 shows vertical cut
sections of the MYRRHA reactor showing its main internal components.
At the present state of the design, the reactor core (Fig. 7.3) consists of mixed
oxide (MOX) fuel pins, typical for fast reactors. In subcritical mode, the central
hexagon houses a window beam tube-type spallation target. Thirty-seven positions
can be occupied by in-pile test sections (IPS) or by the spallation target (the central
one of the core in subcritical configuration) or by control and shutdown rods (in the
core critical configuration). This design gives a large flexibility in the choice of the
more suitable position (neutron flux) for each experiment.
The requested high fast flux intensity has been obtained by optimizing the core
configuration geometry (fuel rod diameter and pitch) and maximizing the power
density. We will be using, for the first core loadings, 15-15Ti stabilized stainless
steel as cladding material instead of T91 ferritic-martensitic steel that will be
qualified progressively further on during MYRRHA operation for a later use. The
use of lead–bismuth eutectic (LBE) as coolant permits lowering the core inlet
operating temperature (down to 270
C), decreasing the risk of corrosion and
allowing increasing the core ΔT. This design, together with the adoption of reliable
and passive shutdown systems, will allow meeting the high fast flux intensity target.
In subcritical mode, the accelerator (as described in the previous section) is the
driver of the system. It provides the high-energy protons that are used in the
spallation target to create neutrons which in their turn feed the subcritical core. In
subcritical mode the spallation target assembly, located in the central position of the
64
H.A. Abderrahim
only exist in two basic concepts: sector-focused cyclotrons and linear accelerators
(linacs). Cyclotrons are an attractive option with respect to construction costs, but
they do not have any modularity, which means that a fault tolerance scheme cannot
be implemented. Also, an upgrade of its beam energy and intensity for industrial
application presently is not a realistic option. A linear accelerator, especially if
made superconducting, has the potential for implementing a fault tolerance scheme
and offers a high modularity, resulting in the possibility to recover the beam within
a short time and increasing the beam energy and intensity toward industrial
application of ADS technology.
7.4 Design of the Core and Primary System
Because MYRRHA is a pool-type ADS, the reactor vessel houses all the primary
systems. In previous designs of MYRRHA, an outer vessel served as secondary
containment in case the reactor vessel leaks or breaks. In the current design, the
reactor pit fulfills this function, improving the capabilities of the reactor vault air
cooling system. The vessel is closed by the reactor cover, which supports all the
in-vessel components. A diaphragm, inside the vessel, acts to separate the hot and
cold LBE plenums; it supports the in-vessel fuel storage (IVFS) and provides a
pressure separation. The core is held in place by the core support structure
consisting of a core barrel and a core support plate. Figure 7.2 shows vertical cut
sections of the MYRRHA reactor showing its main internal components.
At the present state of the design, the reactor core (Fig. 7.3) consists of mixed
oxide (MOX) fuel pins, typical for fast reactors. In subcritical mode, the central
hexagon houses a window beam tube-type spallation target. Thirty-seven positions
can be occupied by in-pile test sections (IPS) or by the spallation target (the central
one of the core in subcritical configuration) or by control and shutdown rods (in the
core critical configuration). This design gives a large flexibility in the choice of the
more suitable position (neutron flux) for each experiment.
The requested high fast flux intensity has been obtained by optimizing the core
configuration geometry (fuel rod diameter and pitch) and maximizing the power
density. We will be using, for the first core loadings, 15-15Ti stabilized stainless
steel as cladding material instead of T91 ferritic-martensitic steel that will be
qualified progressively further on during MYRRHA operation for a later use. The
use of lead–bismuth eutectic (LBE) as coolant permits lowering the core inlet
operating temperature (down to 270
C), decreasing the risk of corrosion and
allowing increasing the core ΔT. This design, together with the adoption of reliable
and passive shutdown systems, will allow meeting the high fast flux intensity target.
In subcritical mode, the accelerator (as described in the previous section) is the
driver of the system. It provides the high-energy protons that are used in the
spallation target to create neutrons which in their turn feed the subcritical core. In
subcritical mode the spallation target assembly, located in the central position of the
64
H.A. Abderrahim