Aging reactors require a concrete solution

Aging reactors require a concrete solution
by Riko Seibo
Tokyo, Japan (SPX) Feb 03, 2025

The structural integrity of concrete in nuclear reactors has long been understood to be affected by radiation exposure, but the specifics remained unclear until now. Researchers from the University of Tokyo have identified key properties influencing concrete's resilience under varying neutron radiation loads. Their findings reveal both concerning and reassuring aspects, such as the ability of quartz crystals within concrete to self-heal, potentially extending reactor operational lifespans.

Nuclear power remains a contentious topic, particularly following notable incidents at power plants. However, its role in achieving carbon neutrality is widely acknowledged, increasing the urgency for improved safety, reliability, and cost-efficiency. A critical aspect of nuclear plant longevity is the material used in construction - especially concrete, a material known for its durability but whose response to neutron radiation has only now been deeply examined.

"Concrete is a composite material consisting of multiple compounds, which vary based on factors like geographical location. Rock aggregate, a major component of concrete, often contains quartz. Understanding how quartz reacts to radiation helps predict the overall behavior of concrete under these conditions," explained Professor Ippei Maruyama from the Department of Architecture.

"Neutron radiation-induced degradation is a challenging and costly research area, limiting extensive studies. Our team has tackled this issue since 2008, compiling literature reviews and consulting with experts to develop investigative strategies. Our recent work involved X-ray diffraction analysis of irradiated quartz crystals," Maruyama added.

A major aspect of their research focused on two neutron radiation properties: total dosage and flux rate. The team discovered that higher dose rates resulted in greater expansion of quartz crystals, whereas lower dose rates allowed for partial recovery, mitigating expansion. As an analogy, Maruyama compared this to sun exposure - short-term intense exposure has a greater impact than the same exposure spread over an extended period.

"The flux effect demonstrates that neutron radiation distorts quartz's crystalline structure, leading to amorphization and expansion, but also shows that recovery occurs at lower dose rates. Larger quartz grains exhibited less expansion, indicating a size-dependent effect. These findings suggest that neutron-induced concrete degradation may be less severe than previously believed, potentially enhancing reactor longevity and safety," he noted.

The research team now seeks to deepen its understanding of how various rock-forming minerals expand under radiation. Their goal is to refine predictive models for concrete expansion based on material composition and environmental conditions.

They also aim to study how mineral expansion influences crack formation, which could inform the selection of construction materials and design of future nuclear power plants. Additionally, these insights may prove valuable for the stability and durability of inorganic materials in extraterrestrial structures for space exploration.

Research Report:Neutron flux impact on rate of expansion of quartz