Temperature resistant material for use in nuclear power plant doors
The safety of nuclear power plants is of paramount importance to the nuclear energy sector. Robust armored doors installed in critical areas are an essential part of nuclear power plants. A study published in Frontiers of energy research presented research on new temperature resistant materials for these critical elements of power plant infrastructure.
Study of a shielding material resistant to high temperatures for the armored doors of nuclear power plants. Image Credit: Parilov / Shutterstock.com
The importance of nuclear shielding
At the start of the atomic age, the potential of radiation to cause death was discovered. This discovery led to the urgent need to create effective protective materials and infrastructure for nuclear power plants to ensure the safety of workers and the environment, as well as to protect vital equipment outside the protected area.
Samples of the polyethylene lead-boron shielding composite. Image credit: Xiao-ling, L et al., Frontiers in Energy Research
Elements of nuclear power plants that require shielding include reactors, pressure valves and main circuit systems. Conventional materials used for shielding doors include boron steel, epoxy resin, and lead-boron polyethylene. Because armored doors are close to radioactive areas, they must be designed to withstand high levels of temperature, humidity and radiation.
For this reason, shielding materials should not only exhibit superior mechanical properties, performance, and aging resistance to irradiation and hydrothermal pressures over their recommended 20-year lifespan. They must also be able to withstand extreme temperatures of up to 190oC when a loss of coolant accident (LOCA) occurs.
Doors and shielding materials go through intense 48-hour LOCA simulations before being approved for installation in nuclear power plants. After this period, the armored doors must remain intact and show no significant deformation. They should also be easy to repair and replace, and all performance indicators should be within acceptable ranges.
Combination of materials in armored doors
The optimal design of an armored door for nuclear power plants combines different materials to protect against neutrons and gamma radiation. Materials like lead absorb and scatter gamma rays through effects such as the Compton effect and the photoelectric effect, and slow down fast neutrons through inelastic scattering. High carbon polyethylene can further moderate intermediate neutrons by elastic scattering, which are then absorbed by tenB of boron carbide.
Test parameters of the environmental conditions of the simulated design basis accident. Image credit: Xiao-ling, L et al., Frontiers in Energy Research
However, polyethylene-based shielding materials exhibit lower melting temperatures and heat distortion temperatures, which means they cannot withstand the high temperatures caused by a coolant loss accident. This leads to mechanical deformations of materials such as softening and spattering, which affects the effectiveness of the shielding and increases the risk of radiation leakage.
Even when fitted with protective elements such as lead or steel plates, temperatures can still exceed the safe level on the surface of polyethylene-based materials.
Improve materials used in radiation shielding
To study how to improve the thermal resistance and mechanical properties of radiation shielding doors, the study published in Frontiers of energy research introduced a lead-based polyethylene composite shielding material. This material would perform better during the intense heat of a coolant loss accident scenario and would prevent radiation leakage, thereby improving safety levels at nuclear power plants.
The modification of the raw materials and the optimization of the composition design further improved the properties and performance of the composite armor material presented in the research. The door design has been subjected to rigorous and comprehensive performance testing and sample testing. The shielding design was evaluated in the gallery of the Hualong One reactor chamber under normal and accident conditions.
The shielding material composition report was designed using the Monte Carlo method and genetic algorithm. Ultra-high molecular weight polyethylene has been used with block and graft copolymerizations throughout the mixing process. This improved the resistance of the material to high temperatures and achieved the maximum protective effect.
Simplified MCNP calculation model for the armored door of the reactor pit chamber. Image credit: Xiao-ling, L et al., Frontiers in Energy Research
The modification molecule chosen was maleic anhydride. This modifier molecule optimized the uniformity and mechanical properties of elements such as lead and boron carbide which were mixed with polyethylene. Extensive environmental testing has been carried out on factors such as the neutron shielding properties of the composite material, its mechanical performance, its resistance to hydrothermal and irradiation-induced aging, and performance in the event of PRA.
The results of intensive testing of the material have shown superior overall performance. The integrity of the armor was maintained even in the severe atmospheric temperature of a coolant loss accident. Adding a 60mm thick layer of this new material to the reactor tunnel shielding door has been further demonstrated3d to reduce gamma radiation dose levels by five times and the gamma radiation dose levels by ten times. neutron levels. This met the zoning requirements for the armored door.
Research has demonstrated a composite armor material that displays superior performance even under catastrophic crash conditions. Widespread use of the material would significantly improve personnel safety and protect sensitive equipment from damage caused by exposure to radiation.
Xiao-ling, L et al. (2021) Study of a shielding material resistant to high temperatures for the armored doors of nuclear power plants [online] Before. Energy Res. | bordersin.org. Available at: https://www.frontiersin.org/articles/10.3389/fenrg.2021.751654/full#h1