Method of and apparatus for measuring the power distribution in nuclear reactor cores

The method of monitoring elongated fuel elements of a nuclear reactor core comprising:

• providing an elongated measuring instrument and locating it adjacent, and parallel, to said elongated fuel elements,
• cooling the elongated measuring instrument with reactor cooling fluid,
• changing the direction of flow of the cooling fluid to divert the cooling fluid away from the elongated measuring instrument at a plurality of spaced limited portions of the length of said elongated measuring instrument while passing the cooling fluid in contact with the elongated measuring instrument at other portions of said elongated measuring instrument while the reactor is in operation, and
• separately making a plurality of temperature difference measurements, with each such measurement being between one of said portions about which the cooling fluid was diverted and one of said portions which is contacted by the cooling fluid.

In apparatus for monitoring elongated fuel elements that emit gamma rays, of a nuclear reactor core:

• an elongated measuring instrument having a plurality of thermocouples with their hot junctions spaced apart along the instrument and respectively responsive to the temperatures of the portions of the instrument where the hot junctions are located,
• each said hot junction being spaced apart from its complementary cold junction,
• means for guiding said cooling fluid along said elongated measuring instrument to cool the instrument where the cooling fluid contacts it while the reactor is in operation,
• each said cold junction being responsive to the temperature of a part of the instrument cooled by said cooling fluid,
• insulating means surrounding a portion of the measuring instrument where each hot junction is located to insulate such portion of the instrument from the cooling fluid;
• whereby the gamma rays may heat the portion of the instrument to which the hot junctions are responsive;
• said insulating means including means for diverting said cooling fluid away from said measuring instrument at the places where said hot junctions are located.

The method of monitoring the elongated fuel elements of a nuclear reactor core which elements emit gamma rays, comprising:

• providing an elongated measuring instrument constructed to be heated to a greater extent by said gamma rays at certain zones along its length than at least, one other zone along its length,
• calibrating said instrument which electrical resistance heating that provides heating at each zone of the same magnitude to that of said gamma rays while the reactor is in operation,
• locating said instrument adjacent, and parallel, to said elongated fuel elements, and
• making measurements, based on the heating contributed by said gamma rays to at least some of said zones, which in view of said calibrations enables a determination of the power outputs of the fuel elements at different positions along their lengths.

The method of monitoring elongated fuel elements, which emit gamma rays, of a nuclear reactor core, comprising:

• (a) providing a flow path for the flow of a cooling fluid to be used for calibration purposes, and passing said cooling fluid along said flow path for calibration purposes,
• (b) providing an elongated instrument element including electrical conducting material having first and second zones,
• (c) locating said instrument in said flow path and exposing it to said fluid so that the temperature of the second zone depends on said temperature and rate of flow of said cooling fluid more than the temperature of the first zone depends on the temperature and rate of flow of said cooling fluid,
• (d) passing an electrical current, for calibration purposes, through said electrical conducting material to supply heat to both of said zones with the first zone rising in temperature more than the second zone due to cooling effect of said cooling fluid on said second zone,
• (e) measuring the temperature difference between said first and second zones to calibrate the instrument,
• (f) placing the instrument parallel to and adjacent said elongated fuel elements,
• (g) passing a cooling fluid past the instrument while it is adjacent said elongated fuel elements,
• (h) the step of passing a cooling fluid past the instrument for calibration purposes as aforesaid involving fluid cooling conditions substantially identical to those characterizing the cooling fluid that is passed by the instrument while it is adjacent to the elongated fuel elements, and
• (i) measuring the temperature difference between said two zones while the instrument is adjacent the elongated fuel elements with cooling fluid flowing past the same and without said electrical current flowing, whereby in view of the previous calibration of the instrument with said flow of current the output of the elongated fuel elements may be determined.

In apparatus for monitoring fuel elements, a nuclear reactor core:

• a measuring instrument comprising a thermocouple having a "hot" junction and a "cold" junction,
• said measuring instrument having a body, said body having an outer wall,
• said measuring instrument including means for mounting said "hot" junction inside said body and spaced from any and all liquid and solid material,
• said measuring instrument including solid material surrounding said "cold" junction and providing a heat conduction path from said cold junction to said outer wall,
• means for passing a cooling fluid along the outer wall of said body, and
• means for positioning said body in the path of said gamma rays to thus directly heat said hot junction, whereby the heat from said gamma rays elevates the temperature of the "hot" junction above that of the "cold" junction due to the better thermal contact between the "cold" junction and the cooling fluid than between the "hot" junction and the cooling fluid.