Removable Sealing Plug for Nuclear Reactor Neutron Shielding
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Solution Overview
Problem
In sodium-cooled fast breeder nuclear reactors, the existing Upper Neutron Shielding (UNS) designs fail to provide a sufficient seal between the hot and cold collectors, leading to undesirable thermomechanical stresses and gas retention issues, which can compromise the mechanical strength and longevity of reactor components, as well as pose risks to cooling faults.
Innovation Solution
A removable sealing plug with a cone-shaped sealing block and internal cone-shaped surface is introduced, allowing for a tight seal and minimizing clearance, while also facilitating the corium flow and neutron shielding functions, and enabling compatibility with in-core handling and washing procedures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed Upper Neutron Shielding design is used, then the neutron shielding function is provided, but the seal between hot and cold collectors is insufficient leading to thermomechanical stresses and gas retention
Solution Approach 1:
The UNS device is divided into two main segments: a fixed upper neutron shielding head and a removable sealing plug. The sealing plug can be separated from the shielding head, allowing independent optimization of sealing performance while maintaining the neutron shielding function. This segmentation enables the sealing interface to be specifically designed with cone-shaped surfaces for leak-tight closure.
Solution Approach 2:
The UNS device transitions from a completely fixed design to a partially removable design. The sealing plug can be removed and reinstalled, providing dynamic access to the mitigation assembly for maintenance and inspection while maintaining a secure seal during operation. This dynamic capability resolves the contradiction between reliable sealing and operational accessibility.
2Ease of operation
If the UNS is made removable for maintenance, then accessibility for washing and inspection is improved, but the sealing performance may be compromised
Solution Approach 1:
The sealing interface employs cone-shaped surfaces with precise curvature profiles. The cone-shaped sealing surface on the mitigation assembly and the complementary cone-shaped interface on the sealing plug create a self-aligning, leak-tight joint. This curved geometric design ensures reliable sealing even after repeated removal and reinstallation cycles, enabling maintenance accessibility without compromising sealing performance.
3Stress or pressure
If a tight seal is achieved with minimal clearance, then thermomechanical stresses are reduced, but the corium flow may be restricted
Solution Approach 1:
The sealing plug design applies local quality by providing a tight seal only at the specific interface between the plug and the mitigation assembly head. The cone-shaped sealing surfaces create a localized seal zone that minimizes clearance and reduces thermomechanical stresses at the joint, while the rest of the mitigation assembly interior maintains sufficient space for corium flow. This localized sealing approach resolves the contradiction between stress reduction and flow maintenance.
Data Source
AI summary
A mitigation assembly for a nuclear reactor including a box with an upper portion forming the head of the assembly housing an upper neutron shielding device, including a head including removable lock and a slug installed free to move in translation relative over a given travel distance, the lock being configured such that locking/unlocking between the head and the box can be made by displacement of the slug with an extraction grab with its pawls attached in the slug. The lower part of the upper neutron shielding device includes a cone-shaped sealing block with the tip of the cone oriented downwards, cooperating with a cone-shaped internal surface of the box, a sealing device being formed between the two, the assembly created forming a removable sealing plug.