High temperature helium loop (HTHL) safety assessment

HTHL test facility is designed for the material testing under the simulation of Gas-cooled Fast Reactor (GFR) and/or Very High Temperature Reactor (VHTR) operational conditions. The specimens being tested will be placed into the test chamber located in the active channel where high pressure/temperature helium flow parameters will be reached. In addition to that exposure, during the in-pile operation, with the active channel placed into predefined position of LVR-15 active core rectangular grid the irradiation effects on the samples will be studied.

HTHL-2 high-temperature helium loop is being developed (project, construction and production) at Research Center Řež s.r.o. in order to implement research material in both inactive and active operating arrangements. In the active operational configuration, studies requiring combinations of high temperature gas, neutron flux and g radiation effects, studies of the transport of fission products, testing of helium cleaning systems can be carried out. The flow diagram is shown in Figure.

The active channel HTHL-2 is designed to work in both inactive and active operating configurations, and its design solution is the same for both operating configurations. The basic elements of the vertically oriented assembly are the two-stage helium circulator mounted with a flange connection to the flange with the grommets to which the pressure channel of the active channel is welded from the bottom. The active channel pressure pipe is made of stainless steel. The elliptical bottom is then welded to the active channel. The bushings in the upper flange are used for the helium inlet / outlet, cooling water inlet / outlet of the secondary cooler circuit, for outlets measuring the main technological parameters - helium temperatures in the active channel.

The active channel has been modelled with the use of TRACE code in two different configurations:

  • the out-of-pile configuration that takes into consideration only pressure and temperature conditions;
  • the in-pile configuration, with the channel placed inside the LVR-15 active core, that takes into account also the gamma heating.

A series of accidental analyses were done using the TRACE code for the support of licensing process. The planned in-pile operation of both loops requires an amendment of the LVR-15 Final Safety Report providing thermohydraulic and structural integrity analyses during normal operation and during Loss of Flow Accident (LOFA) and Loss of Coolant Accident (LOCA) accident conditions. In particular, the structural integrity analyses required the temperature profile inside the Pressure Envelope (PE) as boundary condition. The analyses showed that during these scenarios the safety criteria were not violated.


Marek Ruscak, CV REZ