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Foreword Selected papers from the 23rd Topical Meeting on the Technology of Fusion Energy (TOFE 2018) Fusion Neutronics and Tungsten

Guest Editor Arkady Serikov Karlsruhe Institute of Technology, Karlsruhe, Germany

The Technology of Fusion Energy (TOFE) meeting components. Solutions to solve the problem of radiation series provides a platform for discussions and knowledge damage to the toroidal and poloidal field coil materials exchange for researchers working in many very exciting have been explored in this overview. areas, among them being fusion neutronics. In the frame of Bohm et al. provide initial neutronics investigation of TOFE 2018 technical program, we have succeeded in gath- liquid-metal -facing component (LM-PFC) con- ering worldwide neutronics specialists to present a great cepts, ensuring that radiation limits are met and that system variety of cutting-edge neutronics results of different fusion performance meets expectations. The authors explore the concepts, with one common characteristic—all of them are LM-PFC concepts in the newly developed 3-D neutronics sources: large deuterium-deuterium (DD) and deu- model on the Fusion Energy Systems Study Fusion Nuclear terium-tritium (DT) , inertial fusion devices, Science Facility (FESS-FNSF), which is a DT of hybrid fusion-fission reactors, and small-size DD genera- 518 MW . The LM-PFC FNSF design was tors. In this foreword, I want to convey briefly the content of analyzed using the DAG-MCNP5 transport code. Among these fusion neutronics papers, highlighting their interesting the four liquid-metal first wall (FW) candidates studied in points with the hope that this brief review will not spoil your this paper (PbLi, Li, Sn, and SnLi), the Li FW design is the joy of discovery when reading the full papers in this special best candidate from a neutronics perspective. issue of Fusion Science and Technology. In addition beyond Rolison et al. present neutronics calculations for the fusion neutronics papers, we include in this special issue a rather exotic and hypothetical version of a fusion reactor eight papers on the topic of tungsten for fusion systems. based on the repetitively pulsed concept of plasma-jet- The fusion neutronics section opens with an over- driven magneto-inertial fusion (PJMIF). The 14-MeV neu- view by Zucchetti et al. of neutronics scoping studies of tron source is formed in this concept by injection of hyper- high-field compact tokamaks denoted as “experimental sonic plasma jets that form both the DT plasma target and fusion devices.” The design line of presenting in the ahigh-Z spherically imploding plasma liner to compress the overview high-field compact tokamaks includes the fol- target. The associated plasma and technological lowing fusion machines: Ignitor, ALCATOR, SPARC, challenges force us to call this concept “hypothetical.” The and ARC. The calculation results of neutron damage neutronics analysis is focused on the study of FLiBe liquid and several shielding characteristics are presented using blanket parameters, with aims to provide radiation shielding the MCNP transport code and the FISPACT-II activation with adequate attenuation of and to demon- code. This paper emphasizes the design preferences of strate achievable tritium breeding ratios. The neutron fluxes, Ignitor, sharing with SPARC and ARC some design con- tritium production, neutron damage, and nuclear heating cepts, showing the convenience of this design line as well have been calculated with MCNP6.2, while activation of as progress in technological fields such as new magnet the PJMIF reactor is done by the CINDER-2008 code. superconductors and innovative structural materials. The peculiar problem of fusion devices producing A general-purpose macroscopic model, set up by some 14-MeV is activation of their cooling water. If of the authors in previous studies, has been used to a neutron spectrum is “hard” enough (i.e., if neutron estimate the radiation damage to selected machine energy is above 9 MeV), then the oxygen in water is

FUSION SCIENCE AND TECHNOLOGY · VOLUME 75 · AUGUST 2019 iv activated in nuclear reactions with the generation of Rate of IEC Fusion Device by the Fusion Reaction on the radioactive isotopes of nitrogen: 16N (emits decay Inner Surface of the IEC Chamber.” For this paper, inside gamma radiation) and 17N (emits decay neutrons). the IEC chamber, two anodes made of titanium and These nuclear reactions in the water of common fission stainless steel were used to study the effect of the anode reactors are negligible due to lower neutron flux and material on the measurements of NPR. In the second much “softer” neutron spectrum. In large tokamaks, experimental neutronics paper, titled “Preliminary such as the ITER 500 MW machine, much generated Results of Neutron Transport in Blanket Module by heat is removed by the tokamak cooling water system MCNP with Profile Analysis Using Imaging Plate,” (TCWS) equipment, and this water becomes activated. Ogino et al. lay out the achievements of their neutronic This important topic is investigated in two connected experiments supported with calculation analyses. This is papers by authors from Oak Ridge National Laboratory. an interesting methodology using imaging plates and The first paper is by Radulescu et al. and describes the activation materials (dysprosium, indium, and gold) for MCNP models for the TCWS activation evaluations. measurements of neutron flux and its energy profile in The second paper is by Royston et al. and presents the blankets of fusion devices. It was applied in an experi- results obtained with such MCNP models in the assess- mental setup of polyethylene and graphite blocks as ment of activation on level L3 of the ITER tokamak a model of the blanket module. The small-size DD dis- building due to the ITER TCWS. Both plasma neutrons charge-type fusion device was used to irradiate the blan- and neutrons from the decay of radioactive isotope 17Nin ket module with 2.45-MeV neutrons. Activation foils and the activated coolant will activate the steel of TCWS wires were placed in the assembly to measure neutron components located in the level L3 shielded region. flux distributions. To compare the fluxes, the blanket These activated TCWS components will result in module was reproduced in the MCNP model. The com- a shutdown dose rate during dwell periods after plasma parison shows that, in principle, measurements with the pulses. imaging plate method are feasible, with some restrictions Hong and Kim studied the design of a hybrid fusion- described in the paper. fission reactor for waste transmutation (Hyb-WT) in a paper This neutronics section is worthwhile reading for titled “Neutronic Analysis for Feasibility of Fusion-Driven neutronics specialists, nuclear scientists, engineers, Subcritical System with Constant Fusion Power by Online undergraduates and postgraduates—anyone interested in Feeding of Molten Salt Fuel.” Neutronic calculations have recent achievements in the fusion neutronics area. It been performed with the SERPENT2.1.29 radiation trans- provides a contemporary look at today’s challenging pro- port code. The authors focused on the evaluation of the blems, design solutions, and the horizon of future devel- feasibility of the hybrid Hyb-WT reactor with constant opments in fusion neutronics science and technology! k-eff (neutron effective multiplication factor). Because the Beyond this, we hope readers also find great interest significant change of external source rate is one of the and value in the second half of this special issue, which disadvantages of subcritical systems, including Hyb-WT, focuses on the fusion material tungsten. These eight papers various feeding scenarios were proposed to make k-eff span topics such as tungsten transport analysis, thermal and constant by using molten salt fuel. The performance mechanical properties, elemental characterization of neu- changes, such as tritium breeding, energy multiplication, tron-irradiated tungsten, irradiation of tungsten with helium and transmutation, were evaluated compared to a once- ions, morphology and erosion, the effect of rhenium doping through cycle. In other words, this paper is focused on the on tungsten properties, divertor damage characterization, feasibility of a hybrid molten salt Hyb-WT reactor concept, and development of tungsten-coated graphitic foam for instead of its design optimization. PFCs. We hope you enjoy this state-of-the-art fusion neu- Experimental neutronics work is presented in two tronics and tungsten research derived from abstracts pre- papers wrapping up the fusion neutronics section of this sented at the TOFE 2018 meeting. special issue. The first paper, devoted to measurements of total neutron production rate (NPR) in a fusion inertial ORCID electrostatic confinement (IEC) device, is written by Bakr et al. and titled “Improvement of the Neutron Production Arkady Serikov http://orcid.org/0000-0003-2053-7879

FUSION SCIENCE AND TECHNOLOGY · VOLUME 75 · AUGUST 2019