فعالیت های R & D در تولید کننده هلیوم جامد سرد TBM در کشور کره

R&D activities currently being undertaken for HCSB TBM include joining technologies of structural material, breeder and reflector pebble material development, the effect of TBM ferritic–martensitic steel on the ripple of toroidal magnetic field, and ceramic coating on graphite pebble. The HIP joining performance of FM steel is evaluated. Lithium ceramic breeder and graphite reflector pebble fabrication methods are under development using special fabrication process, and the initial characteristics of the pebbles are assessed. Silicon carbide coating on graphite pebble is also investigated and its preliminary results are mentioned. Finally, an accurate evaluation of the effect of TBM and ferromagnetic inserts on magnetic field are implemented. The current results of these R&D issues are addressed in this paper.

Korean Helium Cooled Solid Breeder (HCSB) Test Blanket Module (TBM) has been designed accounting for the performance of DEMO-relevant blanket. The HCSB TBM uses helium as coolant and purge gas, and reduced activation ferritic–martensitic (FM) steel as a structural material [1] and [2]. Lithium ceramic breeder material, beryllium neutron multiplier, and graphite neutron reflector are used in pebble-bed forms. One of the unique features of the HCSB TBM is that a reflector is used to reduce the amount of beryllium, while tritium breeding ratio remains almost unchanged with relatively low 6Li enrichment of 40%. Since joining technologies would be key factors for successful TBM fabrication, the development of various joining methods, such as Electron Beam Welding (EBW), laser welding, Tungsten Inert Gas (TIG), Hot Isostatic Pressing (HIP), is on-going. Especially, the HIP joining characteristics of FM steel have been evaluated [3]. The effect of degassing temperature on the HIP joining surface is investigated. Several pebble fabrication methods of lithium ceramic breeders and graphite reflector are under development considering mass production. The characteristics of the pebbles fabricated by various methods are assessed. A silicon carbide coating on graphite pebble is important to prohibit the reaction of graphite with steam or air. Protective SiC coatings have been widely used in steel and microelectronic industries because of their intrinsic properties such as good wear resistance, high hardness, high thermal conductivity and very high thermal stability [4] and [5]. For improving the defects at high temperature, a coating using RF sputtering widely used in industries appears to be very attractive because of its relative simplicity, low deposition temperature and high attainable deposition rates [6]. As a preliminary step to develop SiC coating method on graphite pebbles, a SiC coating on the graphite sheet by RF sputtering has been performed. Since TBM structures are made of ferromagnetic steel, they are magnetized during normal ITER plasma operation, generating parasitic non-axisymmetric magnetic field perturbations. Recently, concerns have been raised regarding the possibility of the increase of L-H transition power and the degradation of energetic particle confinement due to toroidal field (TF) ripple in the vicinity of TBM-allocated ports. In addition to the TF ripple, non-axisymmetric error fields are likely to be produced by TBMs, potentially leading to the reduction of plasma performance and/or locked mode disruptions. An accurate evaluation of TBM-produced non-axisymmetric field perturbations and their impact on the plasma performance are necessary to be investigated. The current results of all these R&D activities are described in this paper.

Recent R&D works for HCSB TBM were presented. The effect of degassing temperature on the mechanical characteristics of HIP bonding of F82H was investigated. It was found that degassing temperature is important in the HIP process. Li2TiO3 and graphite pebbles with excellent sphericity and strength were fabricated using new processes of mechanical polishing. Further advanced processes, such as automatic mechanical polishing are necessary for the mass production of pebbles. As a preliminary study on SiC coating on graphite pebbles two coating methods, wet and dry, are adopted. The results of SiC deposition by RF sputtering on the graphite sheet show that the possibility of SiC coating on graphite by RF sputtering has been proved. Finally, an evaluation of the effect of TBM and FIs on the ripple of magnetic field is investigated. The results show that the presence of TBM increases the TF ripple up to 1.45%, even though FIs reduce to 0.75%, but still exceed the design requirement of less than 0.5%. So, it is necessary to reduce the ferromagnetic contents of TBM structures by about two thirds to satisfy the design requirement for TF ripple.