Ventilated Canister Insulation for SCC Mitigation
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Solution Overview
Problem
Stress Corrosion Cracking (SCC) of stainless steel nuclear waste canisters in storage, particularly in coastal marine environments, is a concern due to surface temperature dependence on heat generation rates and corrosive elements, with the risk increasing as the heat generation rate of spent nuclear fuel decreases over time.
Innovation Solution
A ventilated storage system with a cask body and inlet ducts arranged to maintain a predetermined percentage of the canister's vertical height above a threshold temperature, using a distributed inlet duct design and sealing ducts over time to manage heat rejection and minimize SCC risk, combined with radiation shielding and natural convective cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the heat generation rate of spent nuclear fuel decreases over time, then the storage period extends, but the surface temperature of the canister decreases and SCC risk increases
Solution Approach 1:
The patent applies preliminary action by providing insulation to the canister surface before the SCC problem occurs. The insulation layer is installed in advance to maintain surface temperature above the SCC threshold temperature throughout the entire storage period, preventing the harmful effect rather than addressing it after it occurs.
Solution Approach 2:
The patent converts the harmful heat generation (which causes temperature increase) into a beneficial effect by using the decay heat to maintain the canister surface temperature above the SCC threshold. The insulation layer traps this heat and redirects it to prevent SCC, transforming what could be a thermal management problem into a protective mechanism.
2Reliability
If the canister surface temperature is maintained above threshold temperature, then SCC risk is reduced, but heat rejection capability is compromised
Solution Approach 1:
The patent applies local quality by providing insulation only at specific locations on the canister surface, particularly at the lower portion where SCC risk is highest. This localized insulation maintains temperature above the SCC threshold in critical areas while allowing other areas to reject heat effectively, thus balancing SCC protection with thermal management.
Solution Approach 2:
The patent changes the thermal parameters of the canister system by introducing an insulation layer with specific thermal conductivity properties. This modification alters the heat transfer characteristics to maintain surface temperature above the SCC threshold while managing overall heat rejection, effectively changing the thermal regime from one that prioritizes heat rejection to one that prioritizes SCC prevention.
3Reliability
If insulation is added to maintain surface temperature, then SCC risk decreases, but device complexity increases
Solution Approach 1:
The patent employs a simple, cost-effective insulation layer that can be easily applied and removed if necessary. This disposable-like insulation solution provides SCC protection without creating complex permanent modifications to the canister structure, maintaining simplicity while achieving the reliability goal.
Solution Approach 2:
The patent uses composite material structures by combining the metal canister with an insulation layer having different thermal properties. This composite construction leverages the strengths of each material - the metal canister for structural integrity and the insulation layer for thermal management - creating a simple yet effective solution that doesn't significantly increase system complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively reduces the length of the canister surface prone to SCC, maintaining temperatures above the vulnerable range for an extended period, thereby minimizing structural integrity compromise and extending the service life of storage solutions.
Implementation Method 1
these VVOs are passive cooling systems as they use a natural convective flow of air induced by the heated air to rise within the VVO (also know as the chimney effect)
Implementation Method 2
cool air enters the VVO chamber through air-inlet ducts, flows upward past the loaded canister as it is warmed from the heat emanating from the canister, and exits the VVO at an elevated temperature through air-outlet ducts
Implementation Method 3
it is also imperative that the VVO provide adequate radiation shielding and that the SNF not be directly exposed to the external environment
Data Source
AI summary
A system and method for storing high level radioactive waste, such as spent nuclear fuel. In one embodiment, the invention is a method of storing high level radioactive waste comprising: a) positioning a metal canister containing high level radioactive waste having a heat generation rate in a storage cavity of a ventilated system comprising a cask body, a cask lid positioned atop the cask body, at least one outlet duct extending from a top of the storage cavity to an ambient atmosphere, and a plurality of inlet ducts, each of the inlet ducts extending from a first opening in the outer surface of the cask body to a second opening in the inner surface of the cask, body; and b) sealing selected ones of the plurality of inlet ducts over time as a function of a decay of the heat generation rate to maintain more a predetermined percentage of a vertical height of the metal canister above a predetermined threshold temperature.