Fiber Optic Temperature Sensor for Rigid Deformable Media

The safety of a nuclear power plant as a whole depends on the accuracy of measuring the temperature of the cement base of the dome of a nuclear power plant. The used measuring instruments should not create electromagnetic interference during measurements, therefore, fiber optic measuring instruments have been preferred recently. The subject of this study is scientific and technical solutions of fiber optic temperature sensors with compensation channel, which are part of the monitoring systems of nuclear power plant containment. The purpose of the work is to develop design and technological solutions of fiber optic temperature sensors, providing the possibility of its application in rigid deformable media with a minimum dynamic error due to inertial processes of transfer of thermal fields in the body of the sensor. The main approach to achieve the goal is adaptation of previously developed technical solutions of fiber optic temperature sensors to the conditions of measurement in rigid deformable media, which are the supporting parts of the dome of a nuclear power plant. As a result of research the structure and design of fiberoptic temperature sensors with a compensating channel of reflective type are determined. The ratios between the coefficients of thermal expansion of materials from which the structural elements of fiberoptic temperature sensors are made have been determined, providing the reduction of deformation of the protective housing and the sensitive element of fiberoptic temperature sensors at temperature change. The initial distance between the mirror surface and the ends of optical fibers opposite to the mirror surface, at which the sensor conversion function is linear, and the maximum sensitivity (up to 30%) and depth of modulation of optical signal conversion (up to 50%) are determined. Design-technological and structural solutions of fiberoptic temperature sensors with compensating channel of reflective type for systems of monitoring of stress-strain state of nuclear power plant containment placed in rigid deformable media have been developed. Application of the developed fiberoptic temperature sensor provides: reduction of internal stresses inside the deformable medium of the protective shell when its temperature changes in the range from minus 50 to +90 ℃; reduction of dynamic error of temperature measurement caused by inertial processes in the body of the sensor due to the choice of materials and determination of relations between the coefficients of thermal expansion of structural elements of the fiberoptic temperature sensor; increasing the accuracy of temperature measurement of the protective shell due to the exclusion of deformation of the protective housing of the sensor and compensatory conversion of optical signals directly in the optical system of the sensing element #CSOC1120.