The High Temperature Test Unit (HTTU)

The third PBMR related test facility is the High Temperature Test Unit (HTTU), which also forms part of the Heat Transfer Test Facility (HTTF). This test facility, which is located in a separate tripple volume building opposite the HPTU and PBMM facility building, was constructed and commissioned between January 2006 and August 2007.  It is now in operation and its purpose is to conduct various integrated effects tests to evaluate the thermal‑fluid phenomena in a pebble bed at very high temperatures.  The maximum temperature at certain points in the plant can be as high as 1600 ºC. The HTTU test section geometry can be described as a full‑scale distorted version of the actual PBMR reactor geometry.  The HTTF is used to measure the heat transfer characteristics of the pebble bed as a whole. The tests will be used to evaluate the pebble-to-pebble effective conductivity, pebble-to-reflector conductivity and temperature profiles through the core for different flow rates. These tests include steady-state and transient experiments with nitrogen and helium under different conditions. The high temperature pebble bed core or test section forms the heart of the HTTU plant. The test section contains about 28000 graphite spheres each with a diameter of 60 mm.

The HTTU plant and plant schematic layout, which aims to start operation in mid 2007.

The HTTU can accommodate two different test section configurations namely the Vacuum/Natural Ventilation Header (NVH) and the Forced Convection Header (FCH).

The Natural Ventilation Header (NVH) (left) and the Forced Convection Header (FCH) (right).

The layout of the high temperature graphite electrodes of the HTTU plant.

Some of the features required to ensure that there is not leakage of air into the HTTU test section under vacuum test conditions.

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