Adjustable Ventilation Shutter for Spent Fuel Cask Temperature Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing ventilated casks for storing spent nuclear fuel lack provisions for adjusting and controlling ventilation airflow rates, which is crucial for maintaining the canister at a desired temperature to prevent stress corrosion cracking (SCC) as the heat emission from the canister decreases over time.
Innovation Solution
A radiation-shielded ventilated cask with a user-adjustable and variable ventilation airflow system, where the airflow rate can be adjusted over time using adjustable shutter plates or fixed flow restrictors to maintain the canister at or near a maximum temperature limit, thereby mitigating the risk of SCC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If fixed ventilation openings are used in the cask, then the structure is simple and manufacturing is easy, but the ventilation airflow rate cannot be adjusted to maintain canister temperature as heat emission decreases over time
Solution Approach 1:
The ventilation system transitions from fixed openings to adjustable openings that can dynamically change their effective area. Shutter plates mounted on rotation axes allow the opening area to be adjusted based on the canister's heat emission rate over time, enabling the system to adapt to changing thermal conditions while maintaining structural simplicity.
Solution Approach 2:
The effective area of ventilation openings is changed as a adjustable parameter rather than being fixed. By modifying the opening area parameter through shutter plate rotation, the system can control airflow rate to match the declining heat emission from the canister, thereby maintaining optimal canister temperature throughout its service life.
2Temperature
If larger ventilation openings are used to increase cooling airflow, then heat removal is improved, but the canister temperature drops too low increasing risk of stress corrosion cracking
Solution Approach 1:
The ventilation system incorporates a feedback mechanism where the adjustable openings respond to the canister's thermal state. By monitoring or estimating the heat emission rate and adjusting the opening area accordingly, the system maintains canister temperature within a safe range that prevents stress corrosion cracking while still providing adequate cooling.
Solution Approach 2:
The system takes preliminary action to prevent stress corrosion cracking by maintaining the canister temperature above the dew point. Adjustable openings are designed to restrict airflow when necessary, proactively preventing the temperature conditions that would lead to condensation and subsequent corrosion, rather than waiting for the problem to develop.
3Reliability
If smaller ventilation openings are used to reduce cooling airflow, then canister temperature is maintained higher, but heat removal becomes insufficient risking overheating
Solution Approach 1:
The ventilation openings dynamically adjust their size based on the canister's thermal requirements. When the canister emits more heat, larger openings allow greater cooling airflow; when heat emission decreases, smaller openings maintain appropriate temperature. This dynamic adjustment prevents both overheating and excessive cooling throughout the canister's service life.
Solution Approach 2:
The opening area parameter is adjusted to match the changing heat emission characteristics of the canister over time. By varying this parameter, the system ensures sufficient heat removal when needed while preventing temperature drops that would cause corrosion, thereby balancing thermal management and structural integrity.
4Device complexity
If fixed flow restrictors are used instead of adjustable shutter plates, then device complexity is reduced, but adaptability to changing heat emission rates over time is lost
Solution Approach 1:
The system uses simple rotational shutter plates mounted on axes rather than complex automated control systems. This mechanical approach provides adjustability while maintaining simplicity in the control mechanism. The shutter plates can be rotated to different positions to change the effective opening area, offering adaptability without requiring motors, sensors, or complex electronics.
Solution Approach 2:
The adjustable opening system allows operators to manually adjust the ventilation rate based on observed or measured thermal conditions. This self-service approach enables adaptability to changing heat emission rates without requiring complex external control systems, maintaining operational simplicity while providing the necessary flexibility.
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 adjustable ventilation system effectively maintains the canister temperature, reducing the risk of stress corrosion cracking and ensuring the longevity of the canister by accommodating the changing heat emission rates over time.
Implementation Method 1
Ambient cooling air is drawn into the bottom of the cask interior cavity which holds the canisters, flows upward via natural thermal-siphon effect between the cask and canister as the air is heated by the canister, and the heated air is rejected back to the ambient environment through the air outlet vents at top.
Implementation Method 2
flows upward via natural thermal-siphon effect between the cask and canister as the air is heated by the canister
Implementation Method 3
a relatively thin-walled stainless shell to effectively transmit heat emitted by the decaying the SNF assemblies across the canister's wall boundary
Implementation Method 4
A radiation-shielded ventilated cask with a user-adjustable and variable ventilation airflow system, where the airflow rate can be adjusted over time using adjustable shutter plates or fixed flow restrictors
Data Source
AI summary
A natural passively cooled ventilated cask includes a cavity which holds a canister containing heat and radiation emitting spent nuclear fuel assemblies. Cooling air inlet ducts draw ambient cooling air inwards into a lower portion of the cavity. The air heated by the canister flows upwards along the canister and is discharged from at least one air outlet duct formed by the cask lid to atmosphere via natural convective thermo-siphon flow. The air inlet ducts or at least one outlet duct in one embodiment may be fitted with an adjustable shutter plate which allows the flowrate of air entering the cask to be increased or decreased to maintain a predetermined canister maximum temperature limit selected in part to prevent the onset of stress corrosion cracking of the canister welds. Other embodiments may use a fixed orifice plate replaceable over time to maintain the minimum temperature.