Below-Grade Spent Fuel Storage with Ventilation Ducts
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Solution Overview
Problem
Current systems for storing spent nuclear fuel are inefficient in terms of space usage, radiation shielding, and earthquake resistance, and pose security risks due to their above-ground placement and large size, which complicates transfer and storage processes.
Innovation Solution
A below-grade storage system with a ventilated vertical module design that includes a shell with inlet and outlet ventilation ducts, allowing for efficient heat removal and radiation shielding, while minimizing the structure's height and exposure, using a concrete body with a metal shell and lid to enclose the canister and facilitate ergonomic transfer and enhanced safety features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If spent nuclear fuel is stored in above-ground ventilated vertical overpacks (VVOs), then heat removal is achieved through ventilation, but the structure becomes extremely heavy (over 150 tons) and requires significant vertical space with height greater than 16 feet
Solution Approach 1:
The patent transitions from above-ground storage to below-grade (underground) storage, utilizing the third dimension (vertical depth) to relocate the storage structure. This dimensional change allows the VVO to be positioned underground, reducing above-ground footprint and structural requirements while maintaining heat removal capabilities through modified ventilation systems that intake air at below-grade levels
2Temperature
If spent nuclear fuel is stored in above-ground VVOs, then ventilation can remove heat, but radiation exposure risk increases for security and surveillance personnel who must work in close vicinity of the ducts
Solution Approach 1:
By relocating the VVO below grade, the patent creates physical separation between the radiation source and personnel working areas. The below-grade position utilizes the earth as a natural barrier, reducing radiation exposure to personnel while maintaining ventilation functionality through strategically positioned air inlets that draw cool air from below-grade levels
3Temperature
If above-ground VVOs are used for storage, then heat can be vented effectively, but the structure becomes vulnerable to terrorist attacks and natural disasters
Solution Approach 1:
The patent embeds the VVO structure below grade, utilizing the earth as protective cover. This positional change in the vertical dimension provides natural shielding against terrorist attacks and reduces vulnerability to certain natural disasters while maintaining heat removal through modified ventilation pathways that intake air at below-grade levels
4Ease of operation
If transfer cask is stacked atop storage VVO for fuel transfer, then transfer operation is enabled, but the overall stack height becomes excessively large requiring more vertical space
Solution Approach 1:
By positioning the storage VVO below grade rather than above ground, the patent reduces the overall vertical clearance required for transfer operations. The transfer cask can still be stacked atop the below-grade VVO structure, but the earth cover provides additional structural support and reduces the effective height above ground level, minimizing vertical space requirements
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 below-grade storage system reduces the height of the stack assembly, minimizes radiation exposure, enhances safety by utilizing subgrade radiation shielding, and provides effective heat removal and earthquake resistance, while reducing the risk of terrorist attacks and natural disaster damage.
Implementation Method 1
cool air enters the VVO chamber through bottom ventilation ducts, flows upward past the loaded canister, and exits the VVO at an elevated temperature through top ventilation ducts
Implementation Method 2
enhances safety by utilizing subgrade radiation shielding
Data Source
AI summary
Systems and methods for storing spent nuclear fuel below grade that afford adequate ventilation of the spent fuel storage cavity. In one aspect, the invention is a system comprising: a shell forming a cavity for receiving a canister of spent nuclear fuel, at least a portion of the shell positioned below grade; and at least one inlet ventilation duct extending from an above grade inlet to a below grade outlet at or near a bottom of the cavity; the inlet ventilation duct connected to the shell so that the cavity is hermetically sealed to ingress of below grade fluids. In another aspect, the invention is a method comprising: providing a below grade hole; providing a system comprising a shell forming a cavity for receiving a canister of spent nuclear fuel, at least a portion of the shell positioned below grade, and at least one inlet ventilation duct extending from an inlet to an outlet at or near a bottom of the cavity, the inlet ventilation duct connected to the shell; positioning the apparatus in the hole so that the inlet of the inlet ventilation duct is above grade and the outlet of the inlet ventilation duct into the cavity is below grade; filling the hole with engineered fill; and lowering a spent fuel canister into the cavity.