Ultra-Critical Water Loop (UCWL)

SuperCritical Water Loop (abbreviated as SCWL) is experimental device which serves for simulation of technical and chemical

parameters of Supercritical-Water-Cooled Reactor (abbreviated as SCWR). SCWR is water-cooled nuclear reactor

from Generation IV initiative, which uses water with parameters above critical point (374°C; 22.1 MPa) both as the coolant and

moderator, see figure no. 1. Recent nuclear power reactors are using much lower coolant parameters: temperature is usually limited

to 350°C and pressure is kept below 16 MPa (approx. 160 atmospheres). Such large increase of coolant parameters allows rising

of efficiency of employed thermal cycle, but it is also connected with problematic selection of construction materials.

Fig. 1: Working area of LWR and SCWR

Fig. 2: SCWL with mockup of active channel (cylinder far left)

SCWL heart is mockup of active channel, or alternatively UCWL module, where water reaches required physical-chemical parameters

(pressure of 25 MPa, temperature around 600°C, selected flow rate and very clean demineralised water – i.e. water with minimum of chemical impurities: in the language of water chemistry, we can speak almost of clean H2O).

Mockup of active channel serve for exposure of selected material samples. The exposure cell is cylindrical with diameter 24 mm and length 350 mm.

We use the mockup of active channel also to verify thermohydraulic calculation during the licensing process of active channel at the authority body.

UCWL module serve for exposure of selected material samples too. The exposure cell is cylindrical with diameter 28 mm and length 600 mm. UCWL module is therefore suitable for exposing a larger number of material samples.

SCWL loop with mockup of active channel or UCWL module allows our to explore:

• Corrosion processes of construction materials in supercritical water.

• Development and testing of sensors, mostly for measuring of electrochemical quantities.

• Testing and optimisation of supercritical water regimes.

Fig. 3: UCWL module

The most of SCWR engineering problems is directly or indirectly connected with chemical-mechanical material properties of construction materials. The highest priority in construction material’s properties is given to impact of increased parameters of cooling supercritical water. Recent materials display not sufficient mechanical properties (such as strength or creep resistance) and also fast corrosion rate under similar conditions.

The SCWL device will shed light upon these and similar problems and it is strongly believed it will largely contribute to the further development

of nuclear engineering.