Infrastructure > Experimental Devices > HTHL


Smyčka HTHL

The High-Temperature Helium Loop, (HTHL), is an experimental device built for the purpose of simulation of chemical and technical conditions of coolant of near-future gas-cooled nuclear reactors (VHTR and GFR), which belong under the so-called Generation IV nuclear energy systems. The loop is mostly designed for long-run tests of VHTR construction materials and also for the research and development in-field of chemical technology processes for the purification of advanced gas-cooled nuclear reactor coolants.

Nominal Parameters

Maximal temperature 900 °C (active channel with samples)
Gas pressure 7 MPa
Gas flow rate max. 38 kg/hod.
Thermal neutron flux 5 × 1018 n/m2s
Fast neutron flux 2.5 × 1018 n/m2s


The very High Temperature Reactor, abbreviated as the “VHTR” and Gas-cooled Fast Reactor, abbreviated as the “GFR”, belong to Generation IV nuclear energy systems, which are near-future nuclear energy systems united under the Generation IV International Forum (GIF), multinational initiative for development of high-efficiency and super-safe nuclear sources with low production of radioactive wastes. VHTR is a graphite-moderated helium-cooled thermal neutron-spectrum reactor with approx. 1000°C temperature on reactor coolant outlet, pressurized up to 10 MPa.

High coolant temperature and pressure demands lay heavy claims on construction materials and components design hence it is necessary to investigate all candidate materials very thoroughly. out of interest is that the VHTR energy unit was designed for generation of both electricity and non-electric energy products, such as hydrogen production, coal gasification and process heat production, which can be utilised in metallurgy, petrochemicals and similar. Hydrogen requires a very high coolant temperature as its thermal efficiency grows with temperature.

Equipment and experimental possibilities

The purpose of the HTHL, whose construction was also funded from 6th EC framework programme and tasks from Ministry of Industry and Trade of the Czech Republic, is to simulate technical and chemical conditions of VHTR’s coolant. The loop is intended to serve as an experimental device for fatigue tests of construction materials for gas-cooled reactors and it should also be employed for research in the field of gaseous coolant chemistry. HTHL consists of several parts:

  • active channel
  • helium purification and impurities dosing system
  • helium adjusting system
  • helium purity control system

HTHL Chart

Schéma HTHL

1 circulator;
2 heat exchanger;
3 heater;
4 mech. filter;
5 oxidation;
6 cooler;
7 molecular sieves;
8 freezing;
9 gas chromatography;
10 sampling;
11 dosing impurities;