Nuclear design and assessments of helical-axis advanced stellarator with dual-coolant lithium-lead breeding blanket: adaptation from DEMO tokamak reactor

Abstract

As a possible long-term alternative to a tokamak fusion power plant, the stellarator concept offers salient physics features (no external current drive, no risk of plasma disruptions and low recirculating power, among others) that could be offset by the more complex configurations and challenging maintenance schemes. Very ffew conceptual design studies have been performed compared to those in tokamaks, and the enhancement of engineering aspects should follow. With the recent start of operation of Wendelstein 7-X, the helical-axis advanced stellarator (HELIAS) line has again raised interest in the scientific and technologic EUROfusion programme. The main aim at present is showing that stellarators (particularly helical-axis stellarators) are viable as potential fusion reactors. For the conceptualisation of a mature HELIAS power reactor, different engineering and technological aspects must be studied, improved and solved. To this end, starting from a very preliminary reactor design called HELIAS 5-B (5-field-period), with a fusion power of 3000 MW, a neutronic model has been developed and analysed introducing in the baseline the relevant components of breeding blankets (BB). The vast experience achieved at CIEMAT in BB designs for the DEMO tokamak has been exploited, adapting the dual-coolant lithium-lead BB design elaborated in the frame of the WPBB programme of EUROfusion/PPPT to the HELIAS configuration. Preliminary neutronic assessments have been performed focussing on tritium production, power density distributions and damage/shielding responses such as nuclear heating, neutron fluence, dpa and helium production. Particle transport calculations have been performed with MCNP5v1.6 Monte Carlo code.

Physics design point of high-field stellarator reactors

“…To qualify the neutral wall load (NWL) numbers shown in that table we consider that, as a rule of thumb, a maximum NWL of 1.97 MW/m 2 (corresponding to a 13.5 m device) would translate into a damage rate of 19.7 dpa/fpy (displacements per atom in a full-power year) in steel and around 4 × 10 18 n/m 2 /fpy neutron flux at the first wall. This could be still acceptable under the damage of the first wall, shielding of the other structures (Vacuum Vessel and Coils) and heat recovery points of view, as preliminary assessed in [61], although some improvement on shielding and minor modification on maintenance scheme would be necessary. Nevertheless, such aspects would be not easily manageable with higher NWL.…”

Neutronic Assessments towards a Novel First Wall Design for a Stellarator Fusion Reactor with Dual Coolant Lithium Lead Breeding Blanket

“…As a consequence of previous studies [21] concerning the evaluation of the MHD resistance for different BB segmentations it has been demonstrated [22] [23] that a quasitoroidal segmentation (instead than the poloidal one, used in DEMO) would be preferred to avoid the use of FCI or coatings, and having strong impact on the simplification of the engineering BB design, especially interesting to cope with the complex 3D stellarator configuration.…”

“…As there is not yet a complete 3D model of a HELIAS Stellarator sector with a full specific DCLL BB implemented [21], alternatives has been searched that, although being preliminary study, could bring valuable information about the neutronic performances of these new FW configurations. This first approximation comes in the way of a 1-dimensional spherical modelling of the HELIAS reactor.…”

“…In addition to the geometry, a representative neutron source is also needed for the MCNP neutronic analyses. To this purpose, a pre-existing simplified MCNP HELIAS DCLL BB model used for previous neutronic studies [34] which has a prevalent homogenised BB (including the FW) but with four detailed DCLL blanket modules (Figure 3a) with a separated W coating and Eurofer FW has been used. The neutron spectrum (Figure 3b) obtained in a void cell at the front of the FW W coating of one of such BB modules has been used as the source term for the subsequent MCNP simulations in which the 1-D concentric spheres simplified approach has been considered.…”

“…In the past [34], for the simplified DCLL HELIAS extrapolated from DEMO tokamak and not optimised to the stellarator configuration the produced TBR was calculated to be around 1.24. Thus, a 5% of TBR reduction, as resulting from v7, could be still affordable, being the values still higher than the DEMO TBR target, TBR ≥ 1.15 [13] (to be still established, since the TBR target is machine dependent).…”