A measuring system includes a detector having an optical waveguide including a primary dopant capable of transmuting, by neutron capture, into a stable secondary dopant that is less neutron-absorbent than the primary dopant, a moderation layer suitable for slowing down fast neutrons, and an analysis device connected to the detector. The analysis device is configured to inject, into the waveguide, an interrogation wave having a wavelength corresponding to an absorption peak of the secondary dopant, detect a response wave emitted by the waveguide, calculate, from the detected response wave, a piece of information relating to a concentration of secondary dopant in the waveguide, and, based on the information relating to the calculated concentration of secondary dopant, determine a fluence of fast neutrons during a predetermined secondary period.

A self-powered in-core detector arrangement for measuring flux in a nuclear reactor core includes a first in-core detector and a second in-core detector. The first in-core detector includes a first flux detecting material, a first lead wire extending longitudinally from a first axial end of the first flux detecting material, a first insulating material surrounding outer diameters of the first flux detecting material and the first lead wire and a first sheath surrounding the first insulating material. The first sheath includes a first section surrounding the first flux detecting material and a second section surrounding the first lead wire. The first section of the first sheath has a greater outer diameter than the second section of the first sheath. The second in-core detector includes a second flux detecting material, a second lead wire extending longitudinally from a first axial end of the second flux detecting material, a second insulating material surrounding outer diameters of the second flux detecting material and the second lead wire, and a second sheath surrounding the second insulating material. The second sheath includes a first section surrounding the second flux detecting material and a second section surrounding the second lead wire. The first section of the second sheath has a greater outer diameter than the second section of the second sheath. The first section of the first sheath is axially offset from the first section of the second sheath and radially aligned with the second section of second sheath.

An excore detector assembly for measuring flux outside of a nuclear reactor core. The excore detector assembly includes a housing and at least one self-powered detector inside the housing for measuring flux generated by the nuclear reactor core. The at least one self-powered detector includes a sheath, a detector material section inside the sheath, an insulator between the sheath and the detector material, and a flux signal output line.

A neutron position detector according to an embodiment includes a tubular enclosure used as a cathode, an anode located at an axial center inside the enclosure, and a gas that includes a .sup.3He gas and an additive gas and is sealed inside the enclosure. The additive gas includes nitrogen as a quenching gas, and argon as a gas that reduces the ranges of reaction products as neutron and .sup.3He gas.

A temperature measurement sensor for use in a nuclear reactor is described. The sensor includes a first neutron detector member and a second neutron detector member. The first neutron detector includes an outer shield material with an effective neutron capture cross section that is temperature dependent. The first neutron detector member outputs a first current signal and the second neutron detector member outputs a second current signal. An electrical connection between the first and second neutron detector members produces a net current that is the difference in current between the first and second signals. The difference is proportional to changes in temperature.

A method for evaluating a single-photon detector signal includes duplicating the single-photon detector signal into a first and a second signal. The first signal is processed and the second signal is either not processed or is processed in a manner different from the first signal. A differential signal is formed between the unprocessed or differently processed second signal and the processed first signal. The differential signal is evaluated to determine pulse events.

A Disclosed is a long-lifespan in-core instrument having an extended lifespan due to an enhanced combustion lifespan of an emitter. A central tube and an outer sheath tube distanced from the outer circumferential surface of the central tube are provided. Self-powered neutron detectors are placed between the central tube and outer sheath tube. Each self-powered neutron detector includes an emitter of a material having a neutron reaction cross section that is comparatively smaller than that of rhodium. A background detector for compensating for the background noise signal; core exit thermocouples for detecting the core exit temperature; and filler wires filling in the space between the self-powered neutron detectors, background detector and core exit thermocouples are provided.

A method whereby signals that are output by replacement SPNDs are converted into equivalent signals that would have been detected by legacy SPNDs for input to the legacy software. The replacement SPNDs have a different geometry than the legacy SPNDs and also have a different neutron sensitivity than the legacy SPNDs. The replacement SPNDs are subjected to a neutron flux in a core of a reactor and responsively output a set of signals. The set of signals and the geometry of the replacement SPNDs are employed to create a characterization of the neutron flux in the form of a curve that represents flux as a function of location along the core of the reactor. The legacy geometry of the legacy SPNDs is then employed to find the values on the curve that correspond with the positions where the legacy SPNDs had been located to create inputs for the legacy software.

Disclosed are a radioisotope activity surveillance system and methods. The system includes a fuel rod assembly having a plurality of nuclear fuel rods and a target assembly having a top nozzle including an orifice plate and at least one target material rod fixedly coupled to the orifice plate. The least one target material rod is slidably disposed within the fuel rod assembly. A sensing assembly defines an opening sized and configured to receive the target assembly therethrough. The sensing assembly includes a self-powered detector assembly to detect radioisotope activity of the target rod material. Also disclosed is a method for measuring a self-powered detector signal to calculate radioisotope activity of a target assembly and a method for analyzing total activity of a desired radioisotope.

A detector for generating an electrical current that is proportional to a flux of neutrons includes a neutron sensitive emitter, a conductive collector, an insulator between the neutron-sensitive emitter and the collector, an electrical connection to the neutron sensitive emitter, and an electrical connection to the conductive collector. The neutron sensitive emitter includes an emitter material with no more than 2 stable isotopes, and which upon impact by a neutron having an energy of from 100 keV to 1000 keV will generate electrons in proportion to the flux of neutrons in less than 10 minutes, and any generated electrons not generated in less than 10 minutes will be generated in no less than 30 days. A method of detecting neutrons generated by a nuclear reactor is also disclosed.