MYRRHA will be equipped with instrumentation to measure parameters such as temperatures, pressures and pressure drops, neutron fluxes, PbBi flow velocities, motor electrical data, motor speeds, liquid levels and to leak detection. Safety actions will be defined and these actions will be activated by means of the 2/3 principle. The oxygen concentration in the PbBi pool is monitored by oxygen sensors installed in the upper plenum (above the diaphragm). The lower limit of the oxygen concentration is determined by corrosion aspects that are the most critical at higher temperatures, while the upper limit of the oxygen concentration is determined by the departure of precipitation of Pb-oxides that rather occurs at lower temperatures. The core is monitored by measurement of the temperature, the PbBi velocity and the neutron flux. Thermocouples (or PT100's) are installed on top of at least the hottest fuel assemblies, possibly all assemblies. The flow velocity of the PbBi will be measured with an electromagnetic flow meter installed on the top of at least three representative assemblies. Those measurements, together with the temperature measurement at the exit of the primary pumps, make it possible to estimate the thermal power of the core. Finally the pressure drop over the core is also measured. In the reflector, in total 9 neutron flux detectors will be mounted in the dummy assemblies. Three redundant neutron detectors working in pulse mode will be used to monitor the flux during the start-up hase. Three other redundant neutron detectors will be so-called logarithmic neutron detectors working in current mode to follow (rapid) changes over a large flux range (from start-up to power range). Finally three redundant neutron detectors working in current mode will be used as linear detectors to monitor small flux changes during operation at nominal power level. Additionally four fuel assemblies in the core will be equipped with one fission chamber which can be moved axially through the core. These fission chambers will be used for the calibration of the flux-to-current reactivity indicator. During power operation these fission chambers can be moved outside of the core (above the diaphragm). Therefore the central pin of all fuel assemblies is omitted to keep space for the fission chamber that is inserted from above into the assembly. One empty assembly in the reflector is equipped with a neutron source detector for a more in-depth calibration of the reactivity indicators. During normal operation of the reactor this device will be moved outside of the core. The spallation loop will be equipped with all the necessary instrumentation in order to detect conditions indicating a departure from normal operating conditions that could lead to a failure of the confinement function. The instrumentation of the spallation loop consists of the pressure measurement in the vacuum part of the spallation target, PbBi flow measurement, temperature measurement at different positions in the system, spallation target level with LIDAR system that is feed backed to the magneto hydraulic pump (MHD), PbBi level detection (buffer volume), electrical data monitoring the conditions of the PbBi pumps and electrical data monitoring of the vacuum pumps. The inlet & outlet temperatures and the pressure drops of the primary PbBi and of the secondary water coolant of the primary heat exchangers are measured. As already mentioned the PbBi temperature & flow at the exit of the primary pumps are measured and the PbBi pressure drop as well. A water leak detector is placed downstream the heat exchangers at the inlet of each primary pump. The motors driving the pumps have speed, current & temperature control. Likewise the primary system, the heat exchangers and pumps of the secondary and tertiary system will be equipped with devices to measure all inlet and outlet temperatures and pressure drops. All motors are controlled by measuring the current, speed and temperature. The pressure of the pressuriser is controlled by an electric resistant heater. The level in the pressuriser can be regulated by water coming from the feed-bleed and water chemistry control system.
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