RRFM 2009 Transactions - European Nuclear Society

CD WIRES AS BURNABLE POISON FOR THE
BR2 FUEL ELEMENT
N.FRANCK
AREVA♦CERCA*
Les Bérauds, B.P. 1114, 26104 Romans Cedex - France
S.KALCHEVA & E.KOONEN
BR2 reactor SCK●CEN
Boeretang 200, B-2400 MOL Belgium
ABSTRACT
SCK-CEN intends to replace the current burnable poisons, which are mixed in the
fuel meat, by cadmium wires which should be more appropriate for a future LEU
fuel element. This paper describes the present status and planning of this
modification project. In a first step theoretical and computational evaluations have
been performed by BR2 to determine an optimum configuration of burnable
poisons for the future LEU element. Various Cd wires design were studied in order
to define an optimal solution. Mechanical studies and design modifications were
investigated at AREVA-CERCA in order to evaluate the manufacturing feasibility of
a BR2 fuel element using Cd wires inserted in the stiffeners instead of Sm 2 O 3 and
B 4 C powder mixed in the aluminium matrix of the fuel meat. It is the intention to
deliver 2 prototypes with the new design of burnable absorbers to BR2 by mid-
2010 and to irradiate them shortly there after. The final objective is to have this
new type of burnable poisons qualified by mid-2011 to be able to use them for
future LEU fuel elements.
1. Introduction
Burnable absorbers are used in most nuclear reactors. These are isotopes with high neutron
absorption cross section, which purpose is to lower the reactivity at the start up of the reactor
operation. The idea behind is that the burnable absorbers will capture neutrons and
transmute all along the cycle in order to completely disappear at the end of the cycle, thus
allowing to limit the reactivity penalties.
The BR2 reactor is a multi-purpose Material Testing Reactor which main activity is to
test advanced fuel designs, including new LEU types, and structural materials for different
reactors types like LWR, fusion reactor (ITER), ADS. BR2 belongs to the European Network
of reactor dedicated to the production of Mo99. When the BR2 was designed in the 60's, the
fuel was foreseen to be Highly Enriched Uranium (93% U5) in aluminium matrix with
burnable absorber, B 4 C and Sm 2 O 3 , homogeneously mixed in the fuel meat. HEU is a
concern in the proliferation of nuclear weapon framework, from one side and from the other
side, mixing burnable absorber (boron) in the fuel meat causes some concerns for the
fabrication of such fuel. Therefore, a 'BR2 conversion project' has been initiated in 2008
under the RERTR programme for non-proliferation of nuclear weapon, which is managed by
U.S. DOE and supported by IAEA. The first aim of this project is to re-consider the current
fuel assembly design, in particular the localization and the nature of the burnable absorber in
the fuel assembly. The requirements for the burnable absorber are: to have high absorption
cross section at beginning of life and relatively short lifetime, which allows compensating for
depletion of the fissile material at the end of cycle.
Preliminary studies for the choice of an optimal material, geometry and localization of
the burnable absorber in the fuel assembly, which provides at least the same (as for the
*AREVA-CERCA, a subsidiary of AREVA NP, an AREVA an SIEMENS company
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