Methods and apparatuses for monitoring nuclear reactor core conditions

A temperature sensor array (100) includes several temperature sensors (110) at different positions for installation within an instrumentation tube (50) of a nuclear reactor (10). The temperature sensors (110) measure temperature at multiple axial positions of the nuclear reactor (10), and plant operators are able to access and interpret this measurement data. Temperatures associated with vessel coolant boiling or loss and/or fuel damage can be detected by the temperature sensors (110) to permit more direct determinations of core fluid levels. Multiple temperature sensor arrays (110) permit vessel fluid levels and conditions to be measured at multiple core locations.