The development of tritium breeder, neutron multiplier and flow channel insert materials for the breeding blanket of the DEMO reactor is reviewed. Present emphasis is on the ITER test blanket module (TBM); lithium metatitanate (Li2TiO3) and lithium orthosilicate (Li4SiO4) pebbles have been developed by leading TBM parties. Beryllium pebbles have been selected as the neutron multiplier. Good progress has been made in their fabrication; however, verification of the design by experiments is in the planning stage. Irradiation data are also limited, but the decrease in thermal conductivity of beryllium due to irradiation followed by swelling is a concern. Tests at ITER are regarded as a major milestone. For the DEMO reactor, improvement of the breeder has been attempted to obtain a higher lithium content, and Be12Ti and other beryllide intermetallic compounds that have superior chemical stability have been studied. LiPb eutectic has been considered as a DEMO blanket in the liquid breeder option and is used as a coolant to achieve a higher outlet temperature; a SiC flow channel insert is used to prevent magnetohydrodynamic pressure drop and corrosion. A significant technical gap between ITER TBM and DEMO is recognized, and the world fusion community is working on ITER TBM and DEMO blanket development in parallel.

https://iopscience.iop.org/article/10.1088/1741-4326/aa7e4e/pdf

Functional materials for breeding blankets—status and developments

Lattice models and discrete networks naturally describe mechanical phenomena at the mesoscale of fibrous materials. A disadvantage of lattice models is their computational cost. The quasicontinuum (QC) method is a suitable multiscale approach that reduces the computational cost of lattice models and allows the incorporation of local lattice defects in large-scale problems. So far, all QC methods are formulated for conservative (mostly atomistic) lattice models. Lattice models of fibrous materials however, often require non-conservative interactions. In this paper, a QC formulation is derived based on the virtual-power of a non-conservative lattice model. By using the virtual-power statement instead of force-equilibrium, errors in the governing equations of the force-based QC formulations are avoided. Nevertheless, the non-conservative interaction forces can still be directly inserted in the virtual-power QC framework. The summation rules for energy-based QC methods can still be used in the proposed framework as shown by two multiscale examples.

https://orbilu.uni.lu/bitstream/10993/17426/1/BeexPeerlingsGeers2013_acceptedJMPS.pdf

A multiscale quasicontinuum method for dissipative lattice models and discrete networks

Thermal-hydraulic analysis on the whole module of water cooled ceramic breeder blanket for CFETR

The quasicontinuum (QC) method [Tadmor, E.B., Phillips, R., Ortiz, M., 1996. Mixed atomistics and continuum models of deformation in solids. Langmuir 12, 4529–4534] is a multiscale methodology to significantly reduce the computational cost of atomistic simulations. The method ensures an accurate incorporation of small-scale atomistic effects in large-scale models. It essentially consists of an interpolation of the displacements of large numbers of atoms between representative atoms (repatoms) and an estimation of the total potential energy of the atomistic lattice by a so-called summation (or sampling) rule. In this paper a novel energy-based summation rule is presented for the QC method that allows for a seamless coupling between coarse domains and fully resolved domains. In the presented summation rule only the repatoms are used in combination with one extra sampling atom in the center of each interpolation triangle. The presented summation rule is therefore straightforward and computationally efficient. The performance of the proposed summation rule is evaluated for a number of two-dimensional and three-dimensional multiscale atomistic test problems.

https://orbilu.uni.lu/bitstream/10993/17425/1/Beex_orbi.pdf

Central summation in the quasicontinuum method

Coarse-graining atomistic ensembles can overcome the practical limitations of molecular statics and dynamics in order to facilitate simulations at much larger length scales than accessible by discrete atomistic techniques due to computational expense. The quasicontinuum (QC) method was introduced to reduce the number of degrees of freedom in crystalline solids by choosing a set of representative atoms from the fully atomistic ensemble and obtaining the positions and momenta of all remaining lattice sites by interpolation. Here, we present a new energy-based nonlocal meshless version of the QC method based on local maximum-entropy (max-ent) interpolation schemes instead of the traditional polynomial interpolation, which particularly promises advantages in model adaptation to tie atomistic resolution to crystal defects while efficiently coarse-graining away from these. To this end, we formulate the meshless QC representation and analyze its performance. One-dimensional chain problems allow for clean mathematical treatment and provide interesting insight, which allow us to quantify the approximation error as a function of representative atom distribution and support of meshless shape functions. A fully three-dimensional implementation then demonstrates the applicability of the new QC scheme and highlights its features. Overall, we show that local max-ent interpolation offers a number of advantages over previous QC realizations.

https://iopscience.iop.org/article/10.1088/0965-0393/22/3/034007/pdf

A meshless quasicontinuum method based on local maximum-entropy interpolation

Pre-conceptual design study on K-DEMO ceramic breeder blanket

An efficient three-dimensional adaptive quasicontinuum method using variable-node elements

Recent progress in the design of the K-DEMO divertor

Design updates of magnet system for Korean fusion demonstration reactor, K-DEMO

Neutronic assessment is the important foundation of Korean fusion demonstration reactor (K-DEMO) study. Previously, preliminary neutronic calculations using a simplified model have been performed [1] , and optimized structure of blanket module and shield material has been derived. Based on the previous calculation results, the advanced K-DEMO neutronic analysis model has been developed to perform more accurate and reliable neutronic assessments with the detailed configuration of vacuum vessel (VV), toroidal field (TF) coil, blanket, and shield. The advanced K-DEMO neutronic analysis model was imported into the integrated interface program by the help of Monte Carlo automatic modeling system to produce input files for the Monte Carlo neutron photon transport code analyses. The neutronic calculation on neutron wall loading (NWL) distribution, tritium breeding ratio (TBR), and nuclear heating in tokamak components was conducted for the newly developed advanced K-DEMO neutronic analysis model. In the NWL calculation, the peak was indicated at the inboard (IB) and the outboard (OB) blanket first wall with the value of 3.81 and 3.93 MW/ $\text{m}^{2}$ . The different types of models by changing gaps between the blanket modules and the thickness of separated borated steel shield blocks are calculated to check global TBR and the shield performance. The global TBR of 1.017 was achieved with the 49.7- and 76.2-cm-thick IB and OB blanket modules. The model with 1-cm-thick assembly gap between blanket modules, 22-cm-thick IB shield, 50-cm-thick OB shield, and 34-cm-thick divertor shield are considered as a reasonable shield model with the total nuclear heating in 16 TF coils and VV of 9 and 32 kW.

Development of the Advanced Neutronic Analysis Model for the K-DEMO With MCNP Code

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