As a key component to ensure the safety of reactor coolant circulation, the sealing material of the nuclear power plant main pump sealing system needs to operate stably for a long time under the irradiation and high temperature coupling environment. Due to its unique molecular structure, phenyl silicone oil shows excellent performance under irradiation-high temperature coupling conditions. The following is a systematic analysis from three levels: molecular mechanism, experimental data and engineering application:

1. Molecular structure advantages of phenyl silicone oil
Introduction of phenyl groups
Phenyl silicone oil significantly improves the rigidity and thermal stability of the molecular chain by introducing phenyl groups into the silicon-oxygen chain. The conjugated structure of the benzene ring can effectively absorb radiation energy and reduce the generation of free radicals, thereby reducing radiation-induced degradation reactions.
Enhanced thermal oxidation stability
The presence of phenyl groups increases the oxidation induction temperature of silicone oil, making it less likely to undergo thermal decomposition at high temperatures. Experiments show that the thermal weight loss rate of phenyl silicone oil at 300°C is significantly lower than that of methyl silicone oil, indicating that it has better high temperature stability.

2. Experimental study on irradiation-high temperature coupling performance
Synergistic effect of irradiation dose and temperature
Under the coupling conditions of irradiation dose of 1×10⁶ rad and temperature of 250℃, the viscosity change rate of phenyl silicone oil is less than 5%, while the viscosity change rate of methyl silicone oil is more than 20%. This shows that phenyl silicone oil has better viscosity stability under irradiation-high temperature coupling environment.
Balance between molecular chain breakage and cross-linking
Irradiation will cause the breakage and cross-linking of silicone oil molecular chains, while phenyl silicone oil can effectively inhibit the chain reaction of free radicals and reduce the breakage of molecular chains through the π electron cloud of the benzene ring. At the same time, the presence of phenyl groups promotes the moderate cross-linking reaction, thereby maintaining the mechanical properties of silicone oil.
Superposition effect of thermal aging and irradiation aging
Under irradiation-high temperature coupling conditions, the thermal aging rate of phenyl silicone oil is significantly lower than the aging rate under single high temperature conditions. This is because the free radicals generated by irradiation are quickly quenched at high temperature, reducing the acceleration effect of thermal aging.

3. Performance verification in engineering applications
Actual working conditions of the main pump sealing system of a nuclear power plant
The operating temperature of the main pump sealing system of a nuclear power plant is usually 150-200℃, and it is irradiated by gamma rays at the same time. Phenyl silicone oil shows excellent lubrication and sealing performance under this working condition, effectively reducing the wear and leakage of the sealing surface.
Long-term operation stability
In the actual operation of a nuclear power plant, the sealing system using phenyl silicone oil has a wear amount of only 0.02mm on the sealing surface after 5 years of continuous operation, which is far lower than the 0.1mm allowed by the design. This shows that phenyl silicone oil has long-term stability in the irradiation-high temperature coupling environment.
Compatibility with other materials
Phenyl silicone oil has good compatibility with sealing materials such as rubber and metal, and will not cause aging or corrosion of the material. Experiments show that after phenyl silicone oil comes into contact with fluororubber sealing rings, the change rate of tensile strength and elongation at break of the sealing rings is less than 5%.

4. Summary of the advantages of phenyl silicone oil
Excellent irradiation stability: The phenyl group can effectively absorb irradiation energy, reduce the generation of free radicals, and thus reduce irradiation-induced degradation reactions.
Excellent high temperature performance: Phenyl silicone oil has low volatility and high oxidation induction temperature at high temperature, and can maintain stable physical and chemical properties for a long time.
Good lubrication and sealing performance: Phenyl silicone oil can still provide excellent lubrication and sealing effects in the radiation-high temperature coupling environment, reducing the wear and leakage of the sealing surface.
Compatibility with sealing materials: Phenyl silicone oil has good compatibility with sealing materials such as rubber and metal, and will not cause aging or corrosion of the material.