Th. Giegerich

Technological exploitation of Deuterium-Tritium operations at JET in support of ITER design, operation and safety

Abstract Within the framework of the EUROfusion programme, a work-package of technology projects (WPJET3) is being carried out in conjunction with the planned Deuterium–Tritium experiment on JET (DTE2) with the objective of maximising the scientific and technological return of DT operations at JET in support of ITER. This paper presents the progress since the start of the project in 2014 in the preparatory experiments, analyses and studies in the areas of neutronics, neutron induced activation and damage in ITER materials, nuclear safety, tritium retention, permeation and outgassing, and waste production in preparation of DTE2.

The THESEUS facility — A test environment for the Torus exhaust vacuum pumping system of a fusion power plant

At KIT Karlsruhe, a new vacuum pump concept for fusion power plants is under development. This concept consists of three pump types, namely a vapour diffusion pump as primary pump, a metal foil pump that provides a sharp gas separation of unburnt fuel (pure deuterium/tritium) and a liquid ring pump as backing pump. As special feature, diffusion pump and ring pump apply mercury as working fluid due to its perfect tritium compatibility. All three pump types require a proof-of-principle testing as their performance cannot be predicted easily. For these experiments, a dedicated experimental facility called THESEUS is currently being set up. This facility allows experiments with nitrogen, argon, hydrogen, deuterium and helium as fusion relevant test gases in a pressure range from 103 to as low as 10-9 mbar. Hence, the performance of both primary pumps and backing pumps can be tested. The use of mercury and flammable gases in the facility asks for demanding safety pre-cautions and a well-designed safety system. This paper presents the test facility in full detail. It describes the safety system as well as the Supervised Control And Data Acquisition (SCADA) system, and the gas analysing system that monitors the mercury release and - migration inside the facility.

TRANSFLOW: An experimental facility for vacuum gas flows

The TRANSFLOW experimental facility represents a reliable tool for measuring the conductance of 1:1 scale components as typically used in vacuum systems in a wide range of the Knudsen number (e.g. 10−4≤Kn≤103). The main principle of this facility is the dynamic measurement of the pressure difference upstream and downstream of the duct by setting a constant mass flow rate through the test channel. Many experiments on fully developed and developing flows, based on long and short channels respectively, have been already completed and comparisons with corresponding numerical results have been successfully performed. It has been clearly proven that the TRANSFLOW experimental setup provides conductance results with overall uncertainty between 1 to 10% and it could be used as a benchmark facility for any new proposed scientific numerical method in rarefied gas dynamics and in the whole range of gas rarefaction.

Exhaust pumping of DT fusion devices: Current state-of-the-art and a potential roadmap to a fusion power plant

The main functions of the exhaust pumping system of a DT fusion device are to pump out the helium ash and to control the divertor neutral gas density. This requires the handling of large gas throughputs at high pumping speeds (but at relatively moderate vacua). The pumped exhaust gas is then usually transported to the tritium plant for cleaning, which involves impurity removal and separation of the pure hydrogenic species for re-injection as fuel. In view of a fusion power plant, a systematic technical review of primary and roughing pump technologies is conducted in order to identify potential exhaust pumping concepts which eliminate some of the disadvantages that eventually result from simple scale-up of the ITER solutions that are based on batch-wise operating cryogenic pumps. This paper also illustrates the methodology applied to come to unbiased results and describes the final configuration which is based on a vapor diffusion pump as primary pump together with a metal foil pump for hydrogen separation, and a liquid metal ring pump as roughing pump. All pumps are working continuously and do not require cryogenic temperatures. The new concept will reduce the tritium inventories of a power plant, firstly because of the continuous pumping characteristics of the pumps involved, and secondly because the metal foil pump allows for internal recycling of the unburnt fuel species directly from the divertor to the fuelling systems, bypassing the tritium plant.