Optical Waveguide Fast Neutron Fluence Monitoring
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Solution Overview
Problem
Conventional methods for measuring fast neutron fluence on reactor vessel walls are quasi-punctual, require extensive dosimeter deployment, and provide infrequent, costly, and labor-intensive data, limiting the ability for continuous, spatially resolved monitoring of neutron fluence over time.
Innovation Solution
A measurement system comprising optical waveguides with primary and secondary dopants, where the secondary dopant is stable and less neutron-absorbent, allowing for continuous operation and cartographic monitoring of fast neutron fluence integrated over time, using a moderation layer to slow down neutrons and an analysis device to determine fluence based on dopant concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If niobium film dosimeters are distributed on the vessel wall to map fast neutron fluence, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The vessel wall is divided into multiple measurement zones, with optical waveguides positioned at strategic locations to represent different regions. Each waveguide acts as an integrated sensor for its zone, reducing the total number of sensors needed while maintaining comprehensive spatial coverage of neutron fluence distribution
Solution Approach 2:
The optical waveguide system serves multiple functions: it acts as both the neutron detection medium (through dopant atoms) and the signal transmission pathway. The same waveguide structure that captures neutron information also guides the optical signal to the detection system, eliminating the need for separate dosimeter and readout components
2Reliability
If niobium film dosimeters are used for fast neutron fluence measurement, then measurement capability is achieved, but ease of operation deteriorates due to lengthy preparation and processing requirements
Solution Approach 1:
The optical waveguide system is self-contained and requires no external preparation or specialized processing. The waveguide itself contains the dopant atoms that capture neutron information, and the optical signal can be read directly by standard interrogation equipment, eliminating the need for specialized gamma measurement services and complex sample preparation procedures
Solution Approach 2:
The mechanical and chemical processing steps required for traditional dosimeters (encapsulation, mounting, specialized gamma spectrometry analysis) are replaced by an optical interrogation system that can remotely and automatically read the neutron fluence information stored in the waveguide's dopant atoms
3Measurement precision
If niobium film dosimeters are deployed for neutron fluence monitoring, then measurement data is obtained, but loss of time increases due to infrequent measurement intervals
Solution Approach 1:
The optical waveguide system enables continuous or near-continuous monitoring of fast neutron fluence, as the waveguide constantly accumulates neutron information and can be interrogated at any time. This eliminates the decade-long intervals between measurements with traditional dosimeters, allowing for real-time assessment of vessel wall aging
Solution Approach 2:
The system provides continuous feedback on neutron fluence accumulation through optical interrogation of the waveguide. This allows operators to monitor the aging process in real-time and adjust operational parameters or maintenance schedules based on actual accumulated dose, rather than relying on periodic snapshots
4Reliability
If niobium film dosimeters are used to measure fast neutron fluence, then measurement capability is provided, but loss of substance increases due to consumption of specialized processing services
Solution Approach 1:
The optical waveguide system is self-contained and requires no external preparation or specialized processing. The waveguide itself contains the dopant atoms that capture neutron information, and the optical signal can be read directly by standard interrogation equipment, eliminating the need for specialized gamma measurement services and complex sample preparation procedures
Solution Approach 2:
The neutron fluence information is captured and stored in the optical properties of the waveguide's dopant atoms, creating a permanent record that can be read repeatedly without consuming or depleting the measurement medium. This optical 'copy' of the neutron information can be interrogated multiple times, eliminating the need to consume specialized processing services for each reading
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables reliable, continuous, and cost-effective monitoring of fast neutron fluence, reducing the need for frequent dosimeter replacement and providing detailed spatial distribution and aging analysis of reactor vessel walls.
Implementation Method 1
a moderation layer suitable for slowing down fast neutrons and intended to be arranged between the optical waveguide and an external surface of a wall of a reactor vessel
Implementation Method 2
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
Implementation Method 3
inject, into the corresponding optical waveguide, a secondary interrogation wave having a secondary wavelength at which the secondary dopant has an absorption peak
Implementation Method 4
detect a secondary response wave emitted by the corresponding optical waveguide from the secondary interrogation wave
Data Source
AI summary
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.