AnsaldoEnergia

Divisione Nucleare
Progetto
Project
PDS-XADS
AnsaldoEnergia
Identificativo
Document no.
XADS 20 TRIX 009
Rev.
Rev.
1
Cl. ris.
class
Pagina
Page
13
Reactor Internals
The Reactor Internals include the following parts that are supported by the Internal Support
Structure (see Fig. 3.2-3):
• Core Diagrid. The core support system comprises the diagrid welded to a perforated
cylindrical shell, which is in turn welded to a thickened strake in the base of the primary
vessel. It will be noted that the core and all internals immersed in the LBE melt are
subjected to a net upward force. The Core Diagrid has the functions to support the fuel
elements and to assist in positioning them, to guide the fuel elements during the
loading/unloading operations, to prevent placing the fuel elements into the positions
reserved for the dummy elements, to separate the Core Inlet Plenum from the Core
zone, so as to limit the Core bypass flow and to distribute the Core flow through the
various fuel elements.
• Reactor Core. The Reactor Core (see Fig. 3.2-4 and Fig. 3.2-5) is the zone in which the
nuclear reactions occur and where are locate the Fuel Assemblies (FAs), the spallation
target and the dummy element. The spallation target is arranged as a coaxial structure
that surrounds and extends from the proton beam pipe connected to the beam supply
system. It is accommodated inside a cavity at the core vertical axis, delimited by the
surrounding pattern of fuel assemblies organized in regular rounds that are encircling the
inner region. The core shape assumes the configuration of a hollow cylinder in axis with
the proton beam pipe, whose edge is extending from the top of the vessel down to a
fixed distance to the core mid-plane, at which the center of the beam spallation spark is
focused inside the target bulk material (this corresponds to 19 FA’s positions). The
surrounding 120 fuel assemblies is arranged through a honeycomb-like array forming an
annular pattern constituted by four coaxial hexagonal full rounds of fuel assemblies for a
total of 108 loaded fuel assemblies (which are delimiting a full hexagonal area with a
two-rounds cavity inside) plus another twelve fuel assemblies, distributed in couples,
each adjacent to the mid-lines of the hexagon sides of the fourth outer round. Starting
from this round the fuel core has been surrounded by an outer region arranged as
another annular honeycomb-like array of three rounds of boxed assemblies (“dummy”)
which are essentially light, FA’s alike, empty duct structures not carrying any fuel rod
bundle and related components (the nozzling at the foot is designed in such a way to
prevent important bypass from the core flow allowing the minimum coolant needed for
maintaining the necessary structures cooling from the core neutron-gamma heating). In
total, the core buffer region accounts for 174 loading positions. The buffer zone is
accomplishing the primary duty of displacing at a distance the fixed, large, nonreplaceable
core structure internal parts of the XADS, which could undergo excessive
radiation damage due to the hardest portion of the neutron spectrum that would be
detrimental for the overall plant life. Similarly, the same precaution has been
implemented in the bottom region of the fuel core, where the fixed core grid, which is
maintaining and positioning the fuel assemblies through their lower foot fitted-in, has
DNU 020/1