Patent Number: 044141777
Section: summary

TECHNICAL FIELD This disclosure relates to an apparatus for monitoring the presence of coolant in liquid or mixed liquid and vapor, and superheated gaseous phases at one or more locations within an operating nuclear reactor core, such as pressurized water reactor or a boiling water reactor. BACKGROUND ART There exists a need for systems capable of detecting the proximate phase of coolant flow in a reactor core, and for instruments capable of detecting liquid level in the core. United States governmental regulations specify "thermal hydraulic" measurement capabilities in all operating power reactors. These needs and requirements are the result of the TMI accident. During such an "event" in a pressurized water reactor, there might be a period during which the reactor pressurizer will overfill with water while the primary pumps are operating. The reactor coolant may be in two-phase flow through the coolant loop and might have a significant void fraction. At the present time, the reactor operator has no instrumentation which would indicate a void fraction or liquid level exists in the core. If the pumps are shut off, the void fraction in the coolant will separate, exposing a portion of the core. Because of the unavailability of monitoring systems for either of these conditions, the operators of the reactor may be unaware of these conditions until serious damage results to the core itself. The present system is designed to provide continuous monitoring of coolant conditions at one or more locations within an operating reactor vessel. It can be used to determine the nominal coolant phase at a designated location. DISCLOSURE OF THE INVENTION The apparatus comprises a length of small diameter tubing having an open end positioned within the coolant at the location to be monitored. The tubing leads through the vessel or pipe walls to its exterior to deliver pressurized coolant from its open end. The exterior end of the length of tubing is closed. A temperature sensing device, such as a thermocouple, is mounted at the open end of the length of tubing. Leads from it extend through the tubing to the exterior of the vessel. A pressure sensing device, such as a pressure transducer, is operably connected to the interior of the tubing at a location exterior to the vessel. Since discernible temperature differences exist between liquid and superheated gaseous phases of coolant at reactor vessel pressures, and the saturated temperature is well defined for any given pressure, an indication of the coolant phase condition can be obtained by comparing the measured liquid temperature to the measured pressure. These two measured parameters are compared to pressure and temperature tables inserted in a programmable memory. The measured pressure is utilized to select a set of temperatures from the memory which are compared to the measured temperature. Because the liquid temperature doesn't change at T saturation, this device cannot recognize these changing phase conditions. To obtain a usable readout from this device the output must be divided into three categories: (1) T measured is below T saturation=output reading normal liquid, (2 ) T measured is above T saturation but below some preselected superheated steam temperature (say T saturation+5.degree. F.)=output reading interpreted as possible void fraction, and (3) T measured is above T saturation+5.degree. F.=output reading indicated the presence of superheated steam, therefore, liquid level is below sensing location. This can be accomplished by a properly programmed analyzer with readout capability or annunciators for indicating the condition of the coolant at the monitored location. By using a multiple number of lengths of tubing with open ends incrementally spaced at different elevations, one can then monitor coolant level.