Elsevier

Fusion Engineering and Design

Volume 112, 15 November 2016, Pages 298-302
Fusion Engineering and Design

Effect on the Tritium Breeding Ratio due to a distributed ICRF antenna in a DEMO reactor

https://doi.org/10.1016/j.fusengdes.2016.08.028Get rights and content

Abstract

This thesis reports results of MCNP-5 calculations, with the nuclear data library FENDL-2.1, to assess the effect on the Tritium Breeding Ratio (TBR) due to a distributed Ion Cyclotron Range of Frequencies (ICRF) antenna integrated in the blanket of a DEMO fusion power reactor. A preliminary design of the antenna with a reference configuration of the DEMO reactor was used together with a parametric analysis for different parameters that strongly affect the TBR. These are the type of breeding blanket (Helium Cooled Pebble Bed, Helium Cooled Lithium Lead and Water Cooled Lithium Lead), the covering ratio of the straps of the antenna (the ratio between the surface of all the straps and the projected surface of the antenna slot: 0.49, 0.72 and 0.94), the antenna radial thickness (20 cm and 40 cm), the thickness of the straps (2 cm, 4 cm and a double layer of 0.2 cm plus 2.5 cm with the composition of the First Wall), and finally the poloidal position of the antenna (0°, which is the equatorial port, 40° and 90°, which is the upper port). For an antenna with a full toroidal circumference of 360°, located poloidaly at 40° with a poloidal extension of 1 m and a total First Wall surface of 67 m2, the reduction of the TBR is −0.35% for a HCPB blanket concept, −0.53% for a HCLL blanket concept and −0.51% for a WCLL blanket concept. In all cases covered by the parametric analysis, the loss of TBR remains below 0.61%. Such a distributed ICRF antenna has thus only a marginal effect on the TBR for a DEMO reactor.

Introduction

A DEMO fusion power reactor [1] must be self-sufficient in tritium. Hence, a net Tritium Breeding Ratio (TBR – the ratio of T produced in the blanket to the T consumed in the core reactions) greater than one is essential. Some margin is required to account for tritium losses and uncertainties. The typical design targets the global TBR required in the range of 1.05–1.15 [2]. The integration of diagnostics, plasma heating components, etc. deteriorates the TBR due to the required replacement of breeder blanket parts by non-breeding materials or volumes. Recently, a new concept for the Ion Cyclotron Range of Frequencies (ICRF) antenna integrated within the blanket has been proposed [3] (see Fig. 1). From the ICRF engineering and physics point of view, the in-blanket IC array presents large advantages (low power density, no use of equatorial ports, better definition of the k-spectrum), but the impact on the TBR is less evident. The antenna uses a large surface but, in contrast to a port opening, it does not require a large volume at expense of the blanket breeder. The effect on the TBR is due to the combination of three effects:

  • 1.

    Parasitic absorption of neutrons in the antenna

  • 2.

    Moderation of neutrons affecting the neutron spectrum

  • 3.

    A reduction of the total breeding blanket volume

The objective of this paper is to quantify this loss of TBR and thus to check if such an antenna is compatible with the TBR requirements of DEMO. The assessment has been performed for the European DEMO power reactor and three types of breeder blanket concepts, the Helium Cooled Pebble Bed (HCPB) [4], the Helium Cooled Lithium Lead (HCLL) [4] and the Water Cooled Lithium Lead (WCLL) [5]. The calculations were done at KIT (Karlsruhe Institute of Technology) using the Monte Carlo N-Particle code MCNP, version 5 [6], and nuclear cross-section data from the Fusion Evaluated Nuclear Data Library (FENDL-2.1) [7].

The antenna used is a preliminary conceptual version and it is still being developed. This study is a complement to this development in order to check its fundamental feasibility in terms of tritium self-sufficiency and provide guidance on the impact of design choices on the TBR. Because the design is only conceptual and preliminary and in order to check if other choices would greatly affect the TBR, a parametric analysis consisting of variations of the design values of the antenna has been performed. With the parameters considered in this parametric analysis all modifications of the environment and the antenna that could affect the TBR are roughly covered. These are, in addition to the breeding blanket concepts, the covering ratio of the straps of the antenna, the radial thickness of the antenna, the thickness of the straps and the poloidal position of the antenna. All they have been varied and the loss of TBR has been estimated.

Other physics or engineering design aspects are not considered within this work.

Section snippets

Blanket

The European fusion technology programme considers two blanket development lines which will be tested in ITER [8], the HCPB blanket with Lithium ceramics pebbles as breeder material and beryllium pebbles as neutron multiplier, and the HCLL blanket with the Pb-Li eutectic alloy acting both as breeder and neutron multiplier. Both, as well as the WCLL blanket, a very strong candidate which is especially attractive for using water as coolant, are considered in this paper. For the Monte-Carlo

Distributed antenna

To be acceptable the antenna must comply with the following conditions [10]:

  • The antenna must not impair any blanket function: it has to keep ensuring the tritium self-sufficiency and the capability to extract the energy from the fusion reaction. The effect in other blanket functions is not studied in this work.

  • The antenna must match the blanket modularity and not require extra openings in the vessel: each blanket module is independent from the others, so the antenna can’t require an internal

Calculations

As said above, the DEMO model developed at KIT for the HCPB blanket was used as the reference model. The CAD model of the ICRF antenna was integrated into this model using the SpaceClaim software [13]. The resulting CAD geometry model was then converted into MCNP geometry using KIT’s McCad interface [14]. The calculations were carried out using the MCNP-5 code and the FENDL-2.1 nuclear data library on 11.25° torus sector while taking symmetries into account. The track length estimator F4 [6]

Conclusions

A quantification of the loss of TBR for a distributed antenna in a DEMO reactor has been performed in this paper based on Monte Carlo calculations. The ICRF distributed antenna was shown to have only a small effect on the tritium breeding performance of DEMO. For a DEMO with HCPB blanket, there is only a reduction 0.35% of the TBR, which is equivalent to a void port opening on the equatorial plane of 1.12 m2. The reduction is bigger for the HCLL blanket concept (0.53%) than for the HCPB (0.35%).

Acknowledgments

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

References (15)

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