Annular Cooling Header for Nuclear Waste Cask Heat Dissipation
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Solution Overview
Problem
Current methods for cooling high-level radioactive waste in nuclear fuel casks during transfer and storage are inadequate, particularly under high heat loads, as natural convection may not suffice to prevent boiling, posing risks to the integrity of the weld and safety of the system.
Innovation Solution
A passive or actively pumped cooling water system is integrated into the cask, featuring a detachable annular cooling water header that encircles the cask, providing uniform cooling through spray nozzles or orifices, and is coupled to a water source via a reservoir or pumps to maintain subcooled conditions without relying on electric power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If natural convection cooling is used for the cask, then the system complexity is reduced, but the cooling effectiveness is insufficient under high heat loads
Solution Approach 1:
The cooling system is segmented into multiple functional components: an annular header divided into segments, multiple spray nozzles distributed around the cask, and separate water supply/drainage lines. This segmentation allows the system to maintain cooling effectiveness under high heat loads while keeping each component relatively simple and modular.
Solution Approach 2:
Cooling water serves as an intermediary substance between the heat source (cask) and the environment. The water absorbs heat from the cask surface through spray cooling and then dissipates it through evaporation and drainage, effectively mediating the heat transfer process without requiring complex active cooling machinery.
2Loss of energy
If the canister water is allowed to boil, then the heat dissipation is improved, but the weld integrity is compromised
Solution Approach 1:
The cooling system is activated before the welding operation begins and maintains subcooled conditions throughout the welding process. By preliminarily cooling the canister water and maintaining it below boiling point during the critical welding phase, the system prevents vapor formation that would compromise weld quality, ensuring heat dissipation occurs without sacrificing weld integrity.
Solution Approach 2:
The system controls the temperature parameter of the canister water to remain below the boiling point (100°C at atmospheric pressure) during welding operations. By maintaining this critical temperature parameter within safe limits through active cooling, the system prevents phase change while still achieving effective heat dissipation through the cooling water film on the cask exterior.
3Temperature
If the cask is made larger to accommodate better cooling, then the cooling capacity is improved, but the storage density is reduced
Solution Approach 1:
The cooling system transitions from internal volumetric cooling to external surface cooling. By applying cooling water spray to the exterior surface of the cask through the annular header and nozzles, the system achieves effective heat dissipation without increasing the internal volume available for waste storage. The cooling function is added in the external dimensional space rather than consuming internal storage space.
Solution Approach 2:
The cooling function is extracted from the internal canister environment and relocated to the external cask surface. Instead of cooling the water inside the canister directly, the system extracts heat through the canister walls and cask exterior using external spray cooling, thereby maintaining the internal storage volume while achieving effective heat removal.
4Reliability
If active cooling systems with pumps are used, then the cooling reliability is improved, but the device complexity increases
Solution Approach 1:
The cooling system utilizes gravity-driven water flow and natural evaporation to achieve cooling without requiring powered pumps or complex control systems. Water is supplied through gravity feed from an elevated reservoir, distributes through the annular header by gravity, and dissipates heat through natural evaporation and drainage, making the system self-service and highly reliable without active mechanical components.
Solution Approach 2:
The system employs hydraulic principles using water as the cooling medium, utilizing gravity-induced pressure differentials to drive water flow through the header and nozzles. The hydraulic design leverages natural pressure gradients and flow dynamics rather than mechanical pumping, achieving reliable cooling through passive hydraulic action.
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 keeps the canister water subcooled under high heat loads up to 50 kW, preventing boiling and ensuring safe welding operations without time limits, enhancing the safety and reliability of the nuclear waste handling process.
Implementation Method 1
The cooling water header comprises a plurality of dispensing outlets configured to drip or spray cooling water supplied to the header onto the external surface of the cask which is wetted by the water
Implementation Method 2
natural convection from the transfer cask's external surface is adequate to keep the water sub-cooled
Implementation Method 3
The canister to transfer cask annulus is also kept filled with water to provide additional shielding and to serve as the heat transmission bridge from the canister to the outside surface of the cask from which the heat is dissipated to the ambient environment
Data Source
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AI summary
A system for externally cooling a radiation shielded cask containing heat-emitting high level radioactive waste such as spent nuclear fuel. The system includes the cask defining an internal cavity configured to hold an unshielded canister containing the spent nuclear fuel. An annular cooling water header extends circumferentially around the entire circumference of the cylindrical sidewall of the cask. The header comprises plural dispensing outlets which direct cooling water onto the cask, thereby wetting the entire sidewall of the cask. The cooling water provides an external heat sink for absorbing the heat emitted through the external wall surface of the cask generated by the spent nuclear fuel. In various embodiments, the cooling water header may have a continuous annular structure, or be formed by two or more header segments. The header may be supported directly from the cask by detachably mounted brackets.