Comparison of square and hexagonal fuel lattices for high conversion PWRs
21st Symposium of AER on VVER Reactor Physics and Reactor Safety (2011, Dresden, Germany)
Spent fuel disposal, actinide transmutation
Abstract
This paper reports on an investigation into fuel design choices of a PWR operating in a selfsustainable Th-233U fuel cycle. Achieving such self-sustainable with respect to fissile material
fuel cycle would practically eliminate concerns over nuclear fuel supply hundreds of years into
the future. Moreover, utilization of Light Water Reactor technology and its associated vast
experience would allow faster deployment of such fuel cycle without immediate need for
development of fast reactor technology, which tends to be more complex and costly. In order to
evaluate feasibility of this concept, two types of fuel assembly lattices were considered: square
and hexagonal. The hexagonal lattice may offer some advantages over the square one. For
example, the fertile blanket fuel can be packed more tightly reducing the blanket volume fraction
in the core and potentially allowing to achieve higher core average power density. Furthermore,
hexagonal lattice may allow more uniform leakage of neutrons from fissile to fertile regions and
therefore more uniform neutron captures in Thorium blanket. The calculations were carried out
with Monte-Carlo (MC) based BGCore system, which includes neutronic, fuel depletion and
thermo-hydraulic modules. The results were compared to those obtained from Serpent MC code
and deterministic fuel assembly transport code BOXER.
One of the major design challenges associated with the SB concept is high power peaking due
to the high concentration of fissile material in the seed region. In order to explore feasibility of
the studied designs, the calculations were extended to include 3D fuel assembly analysis with
Thermal-Hydraulic (TH) feedback. The coupled neutronic – TH calculations were performed with
BGCore code system. The analysis showed that both hexagonal and square seed-blanket (SB)
fuel assembly designs have a potential of achieving net breeding. While no major neutronic
advantages were observed for either fuel lattice arrangement.