UF6 Storage Cylinder Segmentation for Criticality Control
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Solution Overview
Problem
Current containers for transporting and storing Uranium Hexafluoride with enrichments of U235 greater than 5 weight percent but less than 20 weight percent do not ensure a Keff less than 1.0, increasing the risk of critical events, especially when exposed to water or damage, as they lack a safe geometric design to prevent neutron moderation and subsequent criticality.
Innovation Solution
A container with an annulus base that segregates internal space into two isolated volumes, incorporating a valve system protected by caps and bases to prevent water ingress and maintain safe storage conditions, ensuring a Keff less than 1.0 by controlling the effective storage volume and preventing neutron moderation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional cylinders are used to store enriched UF6 with U235 greater than 5 weight percent, then the storage capacity is sufficient, but the container cannot ensure a Keff less than 1.0 and may become critical when exposed to water or damage
Solution Approach 1:
The container interior is segmented into two isolated volumes by introducing a second volume within the first volume. This segmentation reduces the effective storage volume to maintain Keff less than 1.0 while still providing sufficient capacity for enriched UF6 storage. The segmentation creates geometric constraints that prevent criticality even when U235 content exceeds 5 weight percent.
Solution Approach 2:
The annulus base structure creates local geometric modifications at the bottom of the container. This local quality change in the base geometry (annular shape with specific dimensions) is designed to control neutron moderation and maintain Keff less than 1.0 while preserving overall storage capacity.
2Reliability
If the container volume is reduced to maintain Keff less than 1.0, then criticality safety is improved, but the storage capacity for enriched UF6 is limited
Solution Approach 1:
By segmenting the container interior into two isolated volumes, the design maintains a reduced effective storage volume necessary for criticality safety (Keff less than 1.0) while the outer volume provides sufficient overall capacity. The segmentation allows the container to hold more material than a single-volume design would permit while maintaining safety.
Solution Approach 2:
The second volume is nested within the first volume, creating a concentric arrangement. This nesting approach allows the container to utilize the full outer volume for storage while the inner volume provides the geometric constraints necessary for criticality safety, effectively decoupling storage capacity from safety-constraining volume.
3Reliability
If valves and plugs are made more robust to prevent water ingress, then protection against criticality is improved, but the device complexity increases
Solution Approach 1:
The annulus base structure is designed in advance to prevent water ingress before it can cause criticality. The geometric configuration of the annulus base inherently resists water penetration and neutron moderation, providing preliminary protection without requiring complex additional valve or plug mechanisms.
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 container design effectively prevents critical events by maintaining a Keff less than 1.0, ensuring safe transportation and storage of enriched Uranium Hexafluoride by controlling the internal volume and isolating the hazardous substance from water, thus reducing the risk of neutron-induced criticality.
Implementation Method 1
Moderators slow the movement of emitted neutrons thereby increasing the possibility of a collision, which can trigger a critical event. Water is one such moderator of UF6.
Implementation Method 2
The container functions to prevent a critical event by controlling the internal volume of the container. The annulus base segregates internal space into two isolated volumes; one used for storage of substances like UF6 and the other volume sealed from receiving substances.
Data Source
AI summary
A vessel for storing and transporting hazardous substances, like for example Uranium Hexafluoride, includes a body having an internal region that is subdivided into two or more isolated regions. The vessel further includes end members that house ingress and egress valves. A cover assembly is affixed to the vessel to shield the valves from damage due to exposure and/or impact.