In a nuclear power plant environment, how does jumper material prevent discoloration and increased loss due to radiation?
In extremely harsh environments such as nuclear power plants, characterized by high radiation, high temperatures, and complex multi-physics coupling, standard fiber optic patch cords are prone to Radiation-Induced Attenuation (RIA) and material embrittlement/discoloration due to material limitations, leading to fiber optic signal transmission interruption.
To prevent fiber and patch cord materials from discoloring and experiencing increased loss due to radiation, the field of optical engineering primarily achieves radiation hardness through physical and chemical mechanisms such as microscopic modification of the core material, protection by special coating layers, and fully inorganic armored encapsulation.
I. Physical Mechanisms of Radiation-Induced Fiber Loss Increase and Discoloration
- Formation of Color Centers:
Under intense ionizing radiation (e.g., \gamma-rays, neutron flux, \beta particles) in nuclear power plants, the lattice structure of silicon dioxide (\text{SiO}_2) in optical fibers can break or ionize, creating lattice defects (such as E' centers, non-bridging oxygen hole centers NBOHC, etc.). - Red-Shift of Absorption Spectra:
These newly generated defects (color centers) exhibit strong absorption capabilities at specific wavelengths. Their absorption peaks are primarily concentrated in the ultraviolet and visible light bands (this is the cause of macroscopic fiber “discoloration” or blackening). However, the tails of these absorption bands extend into the near-infrared band (e.g., the 1310nm and 1550nm communication bands), causing a sharp increase in transmission loss at the fiber’s operating wavelength. - Negative Effects of Impurities and Dopants:
The core of standard single-mode fibers (e.g., G.652D) is typically doped with germanium (Ge) to increase refractive index. Germanium elements are highly susceptible to capturing electrons or holes under irradiation, forming numerous germanium-related color center defects, which drastically increase the fiber’s RIA.
II. Core Material Solutions for Enhancing Fiber and Patch Cord Radiation Resistance
To effectively suppress RIA and material aging, high-grade radiation-resistant fiber patch cords require the following physics and material science approaches in material selection:
1. Adoption of “Pure Silica Core” (PSC) Technology
- Principle: Pure silica core fibers do not have any germanium doping in the core; they consist solely of high-purity synthetic fused silica glass (amorphous \text{SiO}_2). Due to the absence of impurity precursors, the formation rate of color centers under irradiation is significantly suppressed.
- Refractive Index Matching: To create a light-guiding structure, fluorine (F) elements are doped into the cladding. Fluorine-doped cladding also possesses extremely high radiation resistance stability.
2. Introduction of “Carbon Coating” and “Hydrogen/Deuterium Loading” Technologies
- Principle: During the fiber drawing process, a dense carbon coating is deposited on the fiber surface. The carbon coating acts as a barrier against external moisture and can be combined with special hydrogen (\text{H}_2) or deuterium (\text{D}_2) loading processes. Hydrogen molecules can diffuse into the fiber core and react with irradiation-induced dangling bonds, passivating defects and eliminating color centers, thereby suppressing the growth of RIA.
3. Utilization of High-Temperature In-Situ “Thermal Annealing” Effect
- Principle: In the high-temperature environment of a nuclear power plant, color center defects can recombine or annihilate upon acquiring thermal energy. This physical phenomenon is known as “thermal annealing.” By using high-temperature-resistant special coatings like polyimide, the fiber can operate reliably at elevated temperatures for extended periods, utilizing the ambient high temperature to achieve dynamic in-situ repair of color centers, maintaining the steady-state radiation-induced loss at extremely low levels.
4. Abandonment of Polymer Outer Jackets, Use of Full Metal Armoring
- Principle: Traditional polymer jackets such as PVC, PE, or LSZH (Low Smoke Zero Halogen) undergo bond scission and cross-linking under intense irradiation, leading to material hardening, cracking, or even powdering. Therefore, patch cords for nuclear power plants must use a fully inorganic metal structure (such as seamless stainless steel tubes and stranded steel wires) to completely eliminate the problem of physical support failure due to organic material aging.
III. OFSCN® Radiation and High-Temperature Resistant Products
Addressing the aforementioned physical mechanisms, Beijing Dacheng Yongsheng Technology Co., Ltd. (OFSCN®) offers a series of special fiber optic and patch cord products based on custom Pure Silica Core, polyimide coating, and seamless stainless steel tube encapsulation, which are extremely suitable for physical environments requiring high radiation resistance and robust mechanical protection, such as nuclear power plants.
1. Special Radiation-Resistant Fiber Optic Assemblies and Patch Cords
For high-temperature, high-radiation environments, Dacheng Yongsheng has launched special patch cords with fully inorganic metal encapsulation:
- OFSCN® 300℃ Fiber Optic Patch Cord: This patch cord consists of stainless steel connectors, a 0.9mm seamless stainless steel tube, and 300℃ polyimide-coated fiber, without any easily aged plastic outer jacket. The fiber core can be customized to Pure Silica Core by default, effectively withstanding nuclear radiation environments.
Standard product standard images:
- OFSCN® 200℃ Fiber Optic Patch Cord: Also features a 0.9mm seamless stainless steel tube encapsulation, housing a 200℃ polyimide-coated fiber that can be customized to a pure silica core, balancing excellent temperature resistance with radiation degradation resistance.
2. Special Radiation-Resistant Bare Optical Fibers (Support Pure Silica Core and Carbon Coating Customization)
For scenarios requiring self-assembly or use as system optical fibers, the following special fibers supporting microscopic modification can be selected:
- OFSCN® 300℃ SM Polyimide Optical Fiber (High-Temperature Single-Mode Polyimide Optical Fiber): Uses a doped core by default, but can be customized with a pure silica core and added carbon coating based on radiation resistance requirements. The polyimide coating can operate in environments from -200℃ to 350℃, facilitating the use of the high-temperature thermal annealing mechanism to suppress RIA.
Standard product standard images:
- OFSCN® 300℃ MM Polyimide Optical Fiber (High-Temperature Multi-Mode Polyimide Optical Fiber): Also supports pure silica core customization and carbon coating customization, meeting the anti-radiation transmission needs for high-bandwidth or multi-mode sensing signals.
- OFSCN® 200℃ Polyimide Optical Fiber (200℃ Polyimide Optical Fiber): Supports pure silica core customization.
For more information on OFSCN®'s special products, please refer to: