Assessment of Concrete Cracking at Nuclear Waste Disposal Facilities via Fiber Optic Sensors

Fiber optic sensors offer a novel approach to monitoring of fractures in concrete waste disposal vaults and offer the possibility of determining the quantity, width and location of the cracks as they form. Fiber optics can directly detect cracks if they form within the path of a fiber optic as well as monitor secondary indicators of cracking such as temperature changes and strain. When cracks form in concrete waste disposal vaults they can fill with water which has a high heat capacity, this enables cracks to be observed by monitoring temperature variations near the crack. An analytical solution for heat transfer is applied to estimate the propagation of temperature waves around cracks. It is demonstrated that discharge rates through the concrete which are less than 10-5 m3/m-s do not produce a meaningful temperature wave through the concrete. Fractures in the concrete must be larger than 0.07 cm to produce a measurable result and temperature sensors must be located within 0.5 meters of a crack to detect a change in temperature produced by seasonal groundwater flow through a crack. A distributed system of fiber optic sensors may be embedded in the concrete vault and used to monitor crack formation, temperature variations and strain.