DEVELOPMENT OF SMALL MODULAR LFR DESIGNS FOR ICEBREAKER SHIP

Abstract

A conceptual development for the long-life small modular lead-bismuth eutectic fast reactor (SMLFR) has been presented in this work. The key design constraint for this fast reactor is the transportation capability in spent nuclear fuel (SNF) cask so as to be able to use as a single or cluster power propulsion for icebreakers. Another innovated feature of this suggested SMLFR is all the core components are included within a small reactor vessel, which can be immediately transferred into the SNF cask after its entire operation time. The thermal power of the SMLFR is 37.5 MW with an assumption of 40% thermal efficiency by using an advanced energy conversion system based on supercritical carbon dioxide (S-CO2) as the working fluid. It is also designed to target more than 40 years of cycle length without refuelling and a small reactivity swing by adopting a breed and burn concept. For such a long-life, small and portable reactor, an excellent neutron economy is a vital requirement. A recent study has been reported that the LBE cooled fast reactor demonstrates a better performance in neutron economy, burnup reactivity swing, and void coefficient rather than sodium fast reactor (SFR). In addition, uranium nitride (UN) with a high thermal conductivity and a high-concentrated amount of fissile fuel is chosen as one of the primary fuel candidates for LFR due to better compatibility with the LBE coolant and providing an immense improvement in neutron economy compared to uranium oxide fuel. The core inlet and outlet temperatures are 300oC and 400oC, respectively. The 15-15Ti stabilized steelis selected as cladding and structure material due to its excellent swelling resistance and stability in LBE. The performance in design and analyses of this core are conducted with the fast reactor analysis code system MC2-3/TWODANT/REBUS-3 developed by Argonne National Laboratory (ANL) and the UNIST in-house Monte Carlo code MCS with ENDF/B-VII.0 cross-section library. It is confirmed through depletion calculations that the designed reactor is capable to operate for more than 40 years without refuelling and a reactivity swing less than 500 pcm. In addition, core performance features are analysed for criticality, radial and axial power profiles and thermal-hydraulic (T-H) calculation. A preliminary T/H calculation is achieved by a T-H one-dimensional module using single-phase closed-channel model. Pin-by-pin temperature profiles are obtained as receiving the pin-wise power profiles from MCS. It is basically confirmed the outlet coolant and maximum fuel temperatures and the coolant flow velocity are within the acceptance criteria. The SMLFR core is also evaluated in view of various significant safety parameters, including control rod worth, fuel temperature coefficient, and coolant density coefficient.