The Key Role and Application of Vanadium Wire in Online Monitoring of Neutron Flux Rate in Nuclear Reactors

Vanadium wires (usually made of highly pure vanadium-51) are the key component for "online monitoring of neutron fluence rate" in nuclear reactors: When vanadium-51 captures thermal neutrons, it instantly generates radioactive vanadium-52 (with a half-life of 3.74 minutes), and the intensity of the released gamma rays is proportional to the neutron flux in the reactor core; by real-time measurement of gamma counts, the power distribution or abnormal fluctuations can be inversely calculated within a second-scale timeframe, without the need for an external power source, achieving a truly "self-powered" detection.

In the operation control of the reactor, the data of vanadium wires is directly connected to the DCS system: During normal operation, the system adjusts the control rods or coolant flow based on the feedback of neutron flux to maintain the set power. Once there is a sudden increase in flux or other precursors of criticality, the signal immediately triggers an emergency shutdown. The accumulated long-term flux curve can also be used to evaluate the fuel burnup and provide a basis for the refueling plan.

Compared with other detector materials such as silver and rhodium, vanadium wire has a high thermal neutron cross-section, long service life with high temperature resistance and high radiation tolerance, as well as reliable all-passive operation, making it indispensable in fast neutron reactors and even in future fusion reactors; however, trace impurities will interfere with the capture cross-section, so the purity of vanadium wire needs to be ≥ 99.95%, and at the same time, the high-temperature resistance drift needs to be compensated through algorithms.

Typical deployment scenarios include: In pressurized water reactors, a wire array is placed around the core to create a three-dimensional power map; for fast neutron reactors, a shielding layer is added around the wires to filter high-energy neutrons; for fusion devices, the wire is planned to be inserted into the tritium breeding cladding to monitor the fusion neutron flux.

With the rise of small modular reactors and fourth-generation reactors, vanadium wire monitoring technology is integrating with AI diagnosis and edge computing, forming an "perception - analysis - decision" integrated nerve plexus, driving the nuclear power industry towards a smarter and safer future.

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