atw - International Journal for Nuclear Power | 2.2024

Research and Innovation
67
Fully Ceramic Microencapsulated (FCM)
fuel based on Uranium Oxy carbide
and Uranium Nitrite as the fuel
replacement for SMART Reactor Core
› Khurram Mehboob
The system Integrated Small and Modular Reactor (SMART) has been designed with
conventional fuel or uranium dioxide (UO2). The Fully Ceramic Microencapsulated
(FCM) fuel as an Accident torrent fuel (ATF) provides a multitude of safety benefits
where the fuel length is deprioritized. In this work, uranium Nitrate (UN) and uranium
oxcarbide (UCO) have been replaced with the conventional fuel for the SMART reactor.
The fuel replacement has been investigated for
criticality with depletion (burn up), fuel and moderator
temperature coefficients, and power peaking factor
despite the alternation of assembly configuration. The
UN and UCO as Tirso Particle fuel in FCM configuration
are implanted in graphite matrices. Nitrite fuel has the
advantage of mechanical stability, enhanced thermal
conductivity, and high fuel density compared to dioxide
fuel (UO2). The neutronic assessment of UN and UCO
for the SMART reactor examined the effective multiplication
factor, thermal flux distribution, axial and
radial power distribution, and power peaking factor
at the beginning, and end of the fuel length. Results
indicate that the UN and UCO as FCM fuel are more
feasible in terms of safety with the compromising of
the fuel length.
1. Introduction
Fully ceramic microencapsulated (FCM) fuel with
an improved accident tolerance due to oxidation
resistance, fission product retention, high thermal
conductivity, and irradiation stability [1–4] has revealed
much attention as the Accident Torrent Fuel (AFT) for
the Light water Reactors (LWRs). Since the FCM provides
significant safety benefits. Therefore, it presents
a dilemma for the FCM fuel concept for the SMRs as it
has been envisioned as the transuranic-bearing TRISO
fuel particles [5–6] . Historically the TRISO fuel is developed
for the High-Temperature Gas-cooled Reactors
(HTGRs), or spherical pebble of a pebble bed modular
high-temperature gas-cooled reactor operate at a
temperature in excess of 1000C [7] . The aim of designing
FCM fuel is to improve the fission retention capacity
and to withstand during the accident process. FCM is
composed of the Tri-isotropic fuel embedded in the
fully dense and impermeable SiC matrix. The TRISO
Fig. 1.
Structure View of the Triso-coated Fuel Particle [9]
particles consist of a fuel kernel encapsulated by three
coating layers of carbon buffer, a pyrolytic carbon
layer, a SiC layer, and a dense outer pyrolytic carbon
layer [8] whereas the kernel is an oxide fuel of nitrates,
carbides, or fissile material (U, Pu, Po) as shown in
Figure 1 [9] . The concept of FCM fuel is to develop a
fuel pallet similar in dimensions to a conventional
fuel pellet that could be loaded in fuel rods. However,
the FCM fuel pellet triso fuel particles are randomly
embedded in the SiC matrix. The analogy of the
conventional fuel pellet and FCM fuel pellet is depicted
in Figure 2a [9] and the cross-section view is compared
in Figure 2b.
FCM fuel is composed of the TRISO fuel particles
embedded in the fully dense silicon carbide (SiC)
matrix. The SiC matrix can form the radiation-resistant
form of SiC of a near theoretical density at relatively
low applied pressure and temperature. This mild sintering
prevents the deformation of the SiC layers and
minimizes the consumption of OPyC. The Tri structuralisotopic
(TRISO) particle consists of the fuel kernel
surrounded by four successive layers [10] of PyC, and SiC,
low-density carbon buffer, and pyrolytic graphite
Vol. 69 (2024)