Sensors for measuring thermal conductivity and related methods

A method of measuring thermal conductivity, the method comprising:

• disposing a sensor in a reactor core in which a nuclear fuel undergoes irradiation and radioactive decay, the sensor comprising:
• an insulator;
• a test material over the insulator;
• a conductor over the test material;
• and
• a gas within an open volume adjacent the test material and the conductor;
• providing an alternating current from an electrical source through the conductor to heat the layer of the test material;
• measuring a voltage at a pair of leads connected to the conductor, the voltage measured as a function of time;
• and
• calculating a thermal conductivity of the test material based on the voltage measured as a function of time.

A method of forming a sensor, comprising:

• providing a test material over an insulator;
• providing a conductor over and in contact with the test material;
• sealing a gas within an open volume adjacent the test material and the conductor;
• connecting the conductor to an electrical source configured to provide an alternating current through the conductor to heat the test material;
• and
• connecting a pair of leads to the conductor, the pair of leads configured to connect to a voltmeter.