System for measuring fast neutron fluence for a nuclear reactor, associated installation, measurement method and computer program product

Patent metadata

Field	Value
Publication number	US-12111432-B2
Application number	US-202017789545-A
Country	US
Kind code	B2
Filing date	Dec 29, 2020
Priority date	Dec 30, 2019
Publication date	Oct 8, 2024
Grant date	Oct 8, 2024

Abstract

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.

First claim

The invention claimed is:

1. A system for measuring fast neutron fluence for a nuclear reactor, comprising at least one detector and an analysis device connected to each detector,
each detector comprising:
an optical waveguide including a primary dopant capable of transmuting, by neutron capture, into a secondary dopant, the secondary dopant having an atomic number different from that of the primary dopant, the secondary dopant being stable and being less neutron-absorbent than the primary dopant; and
a moderation layer configured to slow down fast neutrons and arranged between the optical waveguide and an external surface of a wall of a reactor vessel; and
the analysis device being configured, for each detector, to:
inject, into a corresponding optical waveguide, a secondary interrogation wave having a secondary wavelength at which the secondary dopant has an absorption peak, a smallest difference between the secondary wavelength and a wavelength corresponding to an absorption peak of the primary dopant being greater than or equal to a first predetermined minimum difference;
detect a secondary response wave emitted by the corresponding optical waveguide from the secondary interrogation wave;
calculate, from the detected secondary response wave, a piece of information relating to a concentration of secondary dopant in the corresponding optical waveguide; and
based on the calculated piece of information relating to the concentration of the secondary dopant, and conversion data relating to the nuclear reactor, determine a fast neutron fluence experienced by the wall of the vessel for a predetermined secondary period.

2. The measurement system according to claim 1 , wherein the primary dopant is thulium and/or europium, the secondary dopant being ytterbium or samarium, respectively.

3. The measurement system according to claim 1 , further including a thermal neutron barrier layer configured to be arranged between the moderation layer and the external surface of the wall of the vessel.

4. The measurement system according to claim 3 , wherein the thermal neutron barrier layer is made of cadmium.

5. The measurement system according to claim 1 , wherein
the analysis device is configured, for each detector, to determine, by time-domain reflectometry or by frequency-domain reflectometry, from the detected secondary response wave, an attenuation profile of the corresponding optical waveguide at the secondary wavelength according to a position along the optical waveguide, and
the analysis device is configured to calculate the piece of information relating to the concentration of secondary dopant from the determined attenuation profile at the secondary wavelength.

6. The measurement system according to claim 1 , wherein the analysis device is also configured, for each detector, to:
inject, into the corresponding optical waveguide, one or two optical complementary secondary interrogation waves each having a complementary secondary wavelength corresponding to a respective foot of the absorption peak associated with the secondary wavelength;
for each complementary secondary interrogation wave, detect a corresponding complementary secondary response wave emitted by the corresponding optical waveguide; and
determine, by time-domain reflectometry or by frequency-domain reflectometry, from each detected complementary secondary response wave, an attenuation profile of the corresponding optical waveguide at the complementary secondary wavelength according to a position along the optical waveguide,
the analysis device being configured to calculate the piece of information relating to the concentration of secondary dopant from a result of a correction of the attenuation profile at the secondary wavelength by the attenuation profile associated with each complementary secondary wavelength.

7. The measurement system according to claim 1 , wherein the analysis device is configured, for each detector, to determine, from the detected secondary response wave, a secondary total amount of fluorescence light emitted by the corresponding optical waveguide over its entire length in a secondary fluorescence spectral band associated with the secondary dopant, the piece of information relating to the concentration of secondary dopant in the corresponding optical waveguide being calculated from the total secondary amount.

8. The measurement system according to claim 1 , wherein
for each detector, the primary dopant is also capable of being transformed into a tertiary dopant by irradiation by a photon, the tertiary dopant having a same atomic number as the primary dopant but a different valence; and
the analysis device is also configured, for each detector, to:
inject, into the corresponding optical waveguide, an optical tertiary interrogation wave having a tertiary wavelength at which the tertiary dopant has an absorption peak, the tertiary wavelength being such that a smallest difference between the tertiary wavelength and a wavelength corresponding to an absorption peak of the primary dopant or of the secondary dopant is greater than or equal to a third predetermined minimum difference;
detect a tertiary response wave emitted by the corresponding optical waveguide from the tertiary interrogation wave;
calculate, from the detected tertiary response wave, a piece of information relating to a concentration of tertiary dopant; and
determine, based on the piece of information relating to the concentration of tertiary dopant and the conversion data, a dose of photon radiation absorbed by the wall of the vessel for a predetermined tertiary period.

9. The measurement system according to claim 8 , wherein the tertiary dopant is divalent thulium and/or divalent europium, the primary dopant being trivalent thulium or trivalent europium, respectively.

10. The measurement system according to claim 8 , wherein
the analysis device is configured, for each detector, so as to determine, by time-domain reflectometry or by frequency-domain reflectometry, from the detected tertiary response wave, an attenuation profile of the corresponding optical waveguide at the tertiary wavelength, according to a position along the optical waveguide; and
the analysis device is configured to calculate the piece of information relating to the concentration of tertiary dopant from the attenuation profile at the tertiary wavelength.

11. The measurement system according to claim 8 , wherein the analysis device is also configured, for each detector, to:
inject, into the corresponding optical waveguide, one or two optical complementary tertiary interrogation waves, each having a complementary tertiary wavelength corresponding to a respective foot of the absorption peak associated with the tertiary wavelength;
for each complementary tertiary interrogation wave, detect a corresponding complementary tertiary response wave emitted by the optical waveguide; and
determine, by time-domain reflectometry or by frequency-domain reflectometry, from each detected complementary tertiary response wave, an attenuation profile of the corresponding optical waveguide at the complementary tertiary wavelength according to a position along the optical waveguide,
the analysis device being configured to calculate the piece of information relating to the concentration of tertiary dopant from a result of a correction of the attenuation profile at the tertiary wavelength by the attenuation profile associated with each complementary tertiary wavelength.

12. The measurement system according to claim 8 , wherein the analysis device is configured, for each detector, to determine, from the detected tertiary response wave, a total tertiary amount of fluorescen

Assignees

• Commissariat Energie Atomique

Inventors

• Dumazert Jonathan
• Magne Sylvain
• Coulon Romain
• Laffont Guillaume

Classifications

• G21C17/108

  Measuring reactor flux · CPC title

• G01N23/222

  using neutron activation analysis [NAA] · CPC title

• Y02E30/30

  Nuclear fission reactors · CPC title

• G01T3/006 Primary

  using self-powered detectors (for neutrons as well as for Y- or X-rays), e.g. using Compton-effect (Compton diodes) or photo-emission or a (n,B) nuclear reaction (radioisotopic generators G21H1/00, e.g. G21H1/02, G21H1/04; photo-tubes H01J40/00; thermionic generators H01J45/00) · CPC title

• G01T3/00 Primary

  Measuring neutron radiation (G01T5/00 takes precedence) · CPC title