Study of Processes of Hydrogen Isotope Interaction with Lithium CPS I. Tazhibayeva1, E. Kenzhin1, T. Kulsartov1, Yu. Gordienko1, Yu. Ponkratov1, E. Tulubaev1, N.Barsukov1, A. Kulsartova2  1: Institute of Atomic Energy of National Nuclear Center RK, 071100, Kurchatov, Kazakhstan 2: Nuclear Technology Safety Center, Almaty, Kazakhstan International Symposium on Lithium Applications for Fusion Devices, PPPL, Princeton, New Jersey, USA, 27-29 April, 2011

KTM Tokamak Uniqueness KTM tokamak is located in Kurchatov city, Kazakhstan, former STS. Tokamak KTM has an opportunity of operative access to vacuum chamber to replace divertor components without loss of vacuum. Parameters of energy loads, wide range of used methods and diagnostics allow for high level studies and tests in divertor volume, which is highly important for study of plasma facing materials for ITER and DEMO programs and for other experimental and power fusion reactors. These properties allow to successfully solve a problem of lithium divertor development. Trial start-up of Tokamak KTM was done September, 5,2010.

Kazakhstan Material Testing Tokamak - KTM Tokamak KTM is facility, where plasma has the configuration, extended on a vertical Working body is the mix of hydrogen and deuterium Cooling coils of electromagnetic system of tokamak KTM by water (warm windings) is used Main stream power of the plasma is directed into divertor area at the receiving tiles Research and study of the divertor tiles made from various materials and of various designs is main goal of the facility operation Potentials of the capillary-porous liquid metal units as power divertor receivers are proposed to study at the tokamak KTM.

Development and justification of lithium divertor demonstration models of KTM tokamak Work is carried out jointly by IAE NNC, Krasnaya Zvezda (Red Star) and TRINITI in framework of the ISTC project K-1561; EU financing, collaborator – ENEA, Italy. Goal – testing of the lithium divertor model at KTM and issuing the recommendations on use of lithium technologies in tokamak-reactors. 1 − vacuum chamber; 2 − lithium divertor module; 3 − pipeline for liquid metal supply (Li, Na-K); 4 − receiving divertor plates. 1 − CPS; 2 − cooling lids; 3 − collector; 4 − coolant tank; 5 − collector's lids; 6 − lithium channel; 7 − coolant channels. Principal Scheme of module of lithium CPS for KTM Tokamak Scheme of location of lithium divertor module in KTM

Characteristics of the lithium divertor module of KTM Value Power flux to the surface up to 10 MW/m2 Discharge duration up to 5 s Max. energy on PFS per plasma shot 750 kJ Initial lithium surface temperature ≥ 200oC Max. lithium surface local temperature during plasma interaction ≤550oC Number of shots in experiments > 1000 Strutural material 316 SS type CPS material 316 SS, W felt Heat transfer media of heating/cooling system Na-K eutectic alloy

Demonstration models of lithium divertor of KTM tokamak Module will replace one of 24 graphite tiles of the divertor and will be connected with module’s external components through the pipelines. Size of MLD and distribution of heat load along the surface in the lithium divertor module

Main Goal of lithium experiments in KTM Main aims of lithium experiment in KTM should be: investigation of lithium behavior under tokamak conditions, investigation of efficiency of lithium non-coronal radiation, plasma confinement in tokamak with lithium divertor and wall, investigations of plasma wall interaction, Lithium divertor module consist of: 1. In-vessel lithium unit 2. External system for thermal stabilization

In-vessel unit of the lithium divertor module Internal structure of module PF surface – Li CPS Cooling channel Na-K flow direction Lithium volume

Main Goal of Work Goal of present work is to assess parameters of hydrogen isotope interaction with lithium CPS under conditions modeling the operation modes of the tokamak KTM to regulate pre-start modes of working gases’ input. The experimental results of hydrogen isotopes interaction with Li CPS and effects of atmosphere gases in-leak are presented.

Samples and Li filling technique The samples under study were lithium CPS based on net-matrix of stainless steel 12Cr18Ni10Ti of 100 µm thickness; cell was about 100 µm. Temperature range was similar to the working temperatures of lithium divertor module and was 200 – 350oC. Eight identical squares of 10x10 mm were cut from SS. 30-mm wick,10 fragments of SS wire and 0,1 mm thickness was fastened through a hole to a SS base. The mat of 30-40% porosity was made.

Samples and Li filling technique A wick intended for filling the CPS matrix with liquid Li due to capillary forces was connected with a Li feeding tract. Vacuum filling of the sample’s matrix with liquid Li was carried out using experimental device VIKA. The experimental device, which was preliminary annealed, was filled with 3 g Li. CPS model ( at T=400 C) was filled with Li through the wick due to capillary forces.

Experimental Device Scheme Experimental Device Scheme for filling CPS with lithium: 1– fastenings; 2 – CPS; 3 – thermocouples; 4 – wick; 5 – liquid lithium; 6 – chamber frame; 7 – heat insulation; 8 – heaters; 9 – lithium vessel; 10 – watch window; 11 – sealed output for thermocouples

VIKA experimental device VIKA facility includes: Vacuum tracts and fittings providing for two-step vacuum pumping of the experimental device: fore-vacuum on the basis of the pump 2NVR-5DM and high-vacuum oil-free on the basis of the pump NORD-250; A device containing lithium CPS sample; Hydrogen/deuterium feeding system on the basis of diffusion palladium-silver filter; Measurement system consisting of pressure meters and two mass-spectrometers (quadruple mass-spectrometer RGA-100 and omegatron mass-spectrometer on the basis of RMO-13).

Experimental condition The gas absorption technique was used to study hydrogen isotope interaction with the samples of lithium CPS The experimental procedure was as follows: gas was fed to lithium CPS chamber at given temperature, then gas pressure kinetics in a chamber was measured. During the experiments residual gas composition was controlled as well. Experimental conditions were as follows: Hydrogen isotopes H2, D2; Temperature range 200 – 350°С; Input pressure of hydrogen isotopes 100 – 550 Pa; Calibration leak from atmosphere 1.2·10-10 mole/s.

Experimental results First stage of the experiments was aimed to assess effects of atmosphere gases on the parameters of hydrogen interaction with lithium CPS. As a result of the experiments the time dependencies were obtained for hydrogen pressure over the sample under various vacuum conditions (with and without leakage of atmosphere gases through calibration hole) . Lithium CPS temperature was 200°С. Initial pressure in the experimental device was 100 Pa and pressure during experiment was 100 – 550 Pa.

Determination of sorption properties of lithium CPS against atmosphere gases Changes in pressure of atmosphere gases in experimental device under CPS temperature of 200°С Leakage of atmosphere gases into experimental device through calibration hole

Experiments with deuterium Second stage – Experiments with deuterium under leak of atmosphere gases Experimental conditions: sample’s temperature was 250 and 350°С, initial pressure of deuterium was 450 – 520 Pa. Normalized graph of deuterium pressure changes in experimental device taking into account leak of atmosphere gases

Determination of parameters of hydrogen isotope interaction with lithium CPS k – constant of hydrogen isotope interaction with lithium CPS without leakage dν – moles of gas interacted with lithium CPS during time dt , V- volume of experimental device with lithium CPS; R – universal gas constant; T – gas temperature; P – gas pressure in the experimental device; P′ – rate of changes in gas pressure in experimental device; Scps – square of lithium CPS surface.  

Determination of parameters of hydrogen isotope interaction with lithium CPS   kI- constant of hydrogen isotope interaction with lithium CPS under leakage of atmosphere gases into the experimental device dvS – changes of gas concentration in a chamber with lithium CPS during time dt , dvнат – quantity of atmosphere gas leaked in the chamber during time dt; P1(t) - pressure of hydrogen isotope in a chamber during saturation. V – volume of experimental device with lithium CPS; R – universal gas constant; T – gas temperature; P – gas pressure in experimental device; P’ – rate of gas pressure changes ; SCPS – area of lithium CPS surface.

Lithium temperature, °С Determination of parameters of hydrogen isotope interaction with lithium CPS Values of hydrogen/deuterium interaction constants calculated for initial sector of sorption curves are given in the Table Using the temperature dependence curve of constant of deuterium interaction with lithium CPS we defined activation energy of interaction process – 19.23 kJ/mole. Kd=55.10-7 exp (-19,23/RT) Table . Constants of hydrogen isotope interaction with lithium CPS CPS Temperature , °С kн, Р0=100 Pa, mole/(s×Pa×m2) kн, Р0=100 Pa with leakage kн, Р0=550 Pa., with leakage kD, Р0=550 Pa With leakage 200 1,68Е-7 1,09Е-7 0,96Е-7 — 250 6,61Е-8 350 1,34Е-7 Reference data on H-Li interaction constants (Gardner M. P., Altermatt R. E., 1985) Lithium temperature, °С 520 485 455 kн, mole/(s×Pa×m2) (4,9E-6) (4,4E-6) (3,9E-6) (8,8E-7)

Thermodesorption experiments with Lithium CPS Release of hydrogen isotopes from lithium CPS Release of all residual gases from lithium CPS TDS spectra were obtained under linear heating up to 350 0С and heating rate of 13 С/min. These peaks of hydrogen/deuterium concentration were obtained for classical diffusion approximation model. Mass-transfer activation energy obtained for hydrogen and deuterium was in the ranger of 100-130 kJ/mole, pre-exponential factor in Arrhenius dependence can be in a range of 1-100 m2/s.

Thermodesorption experiments with Lithium CPS H and D concentration change at a surface of lithium CPS Rate of atom H and D concentration change at a lithium surface The pictures show ,that the temperature dependences of rate concentration changes of H and D atoms in the Li surface are equally in view of the fact that the H and D TDS peaks location are equally too.

Summary Main parameters of hydrogen isotope interaction with lithium CPS were obtained as a result of the experiments. Influence of atmosphere gases leak (permissible leak of ~1.77*10-12 Pa/(m3s)) on interaction rate of hydrogen isotopes with lithium CPS was registered: rate of hydrogen isotope sorption decreased and interaction constant was decreased in 1.5 times at least. This effect can be explained by interaction of atmosphere gases with liquid lithium and formation of poorly soluble films in lithium. The obtained parameters of hydrogen isotope interaction with lithium CPS were used for calculation of a rate of deuterium (hydrogen) supply into KTM chamber during pre-start mode.

Future work Influence of neutron irradiation on parameters of hydrogen isotopes interaction with Li CPS T and He generation and release in/from Li CPS under neutron irradiation Goal – Li technology application for fusion power reactor

Welcome to the International Workshop “Innovation Project-creation of KTM tokamak. Research program and international cooperation”, 5-7 September, 2011, Astana, Kazakhstan