Fixed incore wide range neutron sensor

A method of measuring neutron flux over a wide range in a nuclear reactor having a containment vessel and reactor core, comprising the steps of:

• (a) sealing two spaced apart electrodes inside a chamber which includes a seal;
• (b) positioning and maintaining the chamber in the reactor core with the seal at at location adjacent to core within the vessel having a neutron flux which is at least two decades lower than the neutron flux experienced by the electrodes;
• (c) pressurizing an ionizable gas in the space between the electrodes to a pressure above six atmospheres;
• and
• (d) positioning a layer of a mixture of an active and a breeding material within the chamber, the active material and breeding material being respectively U-235 and U-234;
• (e) applying power across said electrodes;
• and,
• (f) measuring power across said electrodes from 10.sup.3 to 10.sup.14 nv.

In combination with a nuclear reactor including a reactor core, a reactor vessel, a fixed site interior of said core for disposing a neutron sensor, cables running from said fixed site interior of said core to a location exterior of said pressure vessel, a power supply capable of delivering power exterior of said core, and a signal processor capable of analyzing electrical signals including current exterior of said core, the improvement of a wide range neutron detector connected across said cables comprising:

• (a) a sealed chamber, having first and second spaced electrodes positioned therein, disposed in said core having a neutron flux, with the first electrode connected to receive power from the power supply and the second electrode connected to deliver current to the signal processor through said cables, which chamber is hermetically sealed with a seal which is disposed exterior of said core within said vessel having a neutron flux which is substantially at least two decades below the neutron flux in the core location of the detector;
• (b) an ionizable gas, disposed within the space between the electrodes, pressurized to a pressure above one atmosphere;
• and
• (c) a layer of a mixture of an active material and a breeding material, positioned within the chamber, the active material and the breeding material being respectively U-235 and U-234, the layer having a thickness of at least 0.2 milligrams per square centimeter, which active material when struck by the neutron flux is capable of ionizing the gas to cause conduction of electric current from the first electrode through the second electrode to the signal processor, which current is proportional to the intensity of the neutron flux.