To investigate the possibility to use a diverse reactor water level measurement system in Olkiluoto 1 and 2 BWRs based on different physical principle than the currently used differential pressure sensors, a scaled down KOHO low-pressure test rig was designed and constructed at Lappeenranta University of Technology in 2011-2012. The new proposed reactor water level measurement system consists of water level sensors (i.e. float level switches) installed in the suction lines of the Reactor shutdown cooling system (321).
The test rig consists of a reactor pressure vessel tank, two float level switches, a volume swap tank, a heat exchanger, two electric heaters, piping, valves, three pumps, measurement instrumentation, CCTV system and a data acquisition system. The maximum operating pressure and temperature of the test rig are 10 bar (abs.) and 180°C, correspondingly. To reduce heat losses the test facility is insulated with mineral wool.
The test facility is equipped with temperature, pressure, pressure difference and flow rate measurements. Additional instrumentation includes a magnetostrictive level transmitter for measuring velocity of the water level in the reactor pressure vessel tank. During the experiments flow in the reactor pressure vessel tank and in the switch houses can be monitored through the sight glasses.
In 2013, both the installation position of the switches and the float level switch house configuration were modified.
In 2013, also a high-pressure test rig was designed and constructed. The test rig is attached to the DN50 hot leg of the PACTEL test facility. The main components of the high-pressure test rig are: a reactor pressure vessel tank, two float level switches, an electric heater, piping, valves, a non-condensable gas injection system, measurement instrumentation and a data acquisition system. The maximum operating pressure and temperature of the high pressure test rig are 80 bar (abs.) and 300°C, correspondingly.
In 2016, a high-pressure test rig was constructed. The test rig is attached to the PACTEL test facility, which is designed to model the thermalhydraulic behavior of VVER-440 type pressurized water reactors. In 2017, the high-pressure test rig was modified. In the KOHO 2017 high-pressure test rig configuration, altogether four Mobrey float level switches are used (same as in the KOHO 2015 high- and low-pressure test rigs). Two of the level 8 switches are used for detecting a low (L2D) and two a high (H2D) water level of the RPV. Each Mobrey float level switch is installed inside one switch house as in the KOHO 2012 and 2015 test rig configurations. The housings are connected to the test rig with DN25 impulse pipes (Ø33.4x3.38). The upper DN25 impulse pipe is connected to the extension pipe of the upper plenum and the lower one to the hot leg of the PACTEL. Connection part of the hot leg is expanded from nominal DN50 to DN100. Main differences compared to KOHO 2016 high-pressure test rig are: 1 x H2D and 1 x L2D level switches were installed in both impulse lines, insulation of the impulse piping was modified, and length of the double-side connection pipe was increased.
