Problems related to SPIDER Cooling Plant primary cooling circuits sensors: pH, O2 and k

SPIDER primary cooling circuits currently in operation are the so called PC01, PC02 and PC03. These circuits cool respectively SPIDER power supplies (PC01) and the beam source components (PC02 and PC03) using ultrapure water produced by an in-house purification system. This water purification system is called Chemical Control System (CCS). The CCS used to fill these SPIDER primary circuits with ultrapure water is called CCS-1. This technical note discusses the performances of the sensors that should maintain under control water purity quality produced by CCS-1; it does not discuss the processes involved in the purification treatment of water to an ultra-purity water level. It was found that the conductivity sensors installed in PC01, PC02 and PC03 were transmitting wrong values of water conductivity as they had been calibrated in the past with a wrong procedure that changed sensors cell constant. The oxygen sensors installed in CCS-1 that should ensure a maximum admissible value of dissolved oxygen in the ultrapure water produced (<= 50 ppb), were found not reliable and out of warranty since 2016. Problems related to sensors signals transmission to the local control system were discovered and corrected since the measuring range was set identical to the optimum operational range. Most of the abovementioned issues were solved and a way to calibrate correctly the sensors is proposed. Further suggestions for improving sensors maintenance procedure is discussed and the need to install new sensors in line with the primary circuits is presented.