Passive Nuclear Reactor Protection Device Using Molten Metal and Fusible Links
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Solution Overview
Problem
Existing nuclear reactor protection systems for fast neutron reactors face reliability issues due to material swelling and geometrical changes under high neutron flows and temperatures, leading to inefficient actuation of absorbing rods, especially in reactors with heavy heat carriers like lead, where buoyancy forces hinder rod insertion and alter actuation thresholds.
Innovation Solution
A passive protection device comprising two interconnected vessels with a ring-shape hollow space, where the upper vessel is filled with molten metal of high neutron absorption and high vapor pressure, and the lower vessel is filled with inert gas, connected by a safety buckling rupture disc, allowing for reliable actuation of negative reactivity insertion during emergency conditions caused by neutron flux growth or heat carrier temperature rise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical rod systems are used for emergency protection, then the reactor core can be protected against emergencies, but the reliability of actuation is reduced due to material swelling and geometrical changes under high neutron flows and temperatures
Solution Approach 1:
The patent replaces the mechanical rod insertion system with a passive system based on physical effects. Instead of using motor-driven or gravity-dependent mechanical rods that are sensitive to geometrical changes, the invention employs a system where a rod is held by a elastic element (spring) and a fusible link, which responds automatically to temperature changes through melting, eliminating the need for complex mechanical actuation mechanisms that are affected by material swelling and dimensional instability.
Solution Approach 2:
The invention utilizes changes in physical parameters (temperature-induced phase change) to trigger the protection mechanism. The fusible link is designed to melt at a specific temperature threshold, causing the elastic element to release and insert the absorbing rod into the reactor core. This parameter-based triggering mechanism is inherently more reliable than mechanical systems because it directly responds to the critical temperature parameter without being affected by gradual material degradation or geometrical changes.
2Reliability
If absorbing rods are used for emergency protection, then the chain reaction can be suppressed, but the rods are subject to significant buoyancy force in heavy heat carriers that makes it difficult for the rods to fall down into the reactor core
Solution Approach 1:
The patent employs an elastic element (spring) that provides a counteracting force to overcome the buoyancy force exerted by the heavy heat carrier on the absorbing rod. The spring is pre-loaded to exert sufficient force to push the rod downward into the reactor core against the upward buoyancy force, ensuring reliable insertion even in reactors with liquid metal coolants where buoyancy would otherwise prevent gravity-driven rod insertion.
3Ease of operation
If bi-metal elements and rocket arms are used for passive protection actuation, then the system can respond to emergency temperature rise, but the geometry and actuation characteristics change significantly under intense neutron irradiation and high temperatures
Solution Approach 1:
The patent replaces the bi-metal element and rocket arm mechanism with a simpler thermal-response system based on fusible links and elastic elements. Instead of relying on bi-metallic bending or complex mechanical linkages that change geometry under irradiation, the invention uses a fusible link that melts at a predetermined temperature, directly releasing the elastic element to insert the absorbing rod. This eliminates the intermediate mechanical components whose geometrical stability deteriorates under neutron irradiation and high temperatures.
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 device ensures rapid and reliable actuation of negative reactivity introduction, reducing response time and increasing reliability by utilizing molten metals like mercury and cadmium isotopes, which absorb neutrons effectively, even under conditions of heat carrier temperature rise, thereby preventing chain reactions and ensuring reactor safety.
Implementation Method 1
the emergency heat carrier temperature rise makes the bi-metal plate bend
Implementation Method 2
the growth of the melted substance's volume
Implementation Method 3
a fusible link, which melts when the heat carrier temperature reaches the device actuation temperature
Implementation Method 4
casts the absorbing rod bunch in the reactor core to suppress the nuclear reaction
Data Source
AI summary
The invention relates to nuclear reactor protection systems and can be used when building nuclear reactors, in particular, the fast neutron reactors. The Technical result of the invention consists in the expansion of 5 functional capabilities of the negative reactivity passive insertion device by securing its reliable actuation in various emergency conditions. The device has two vessels located in a common enclosure one under another with a ring-shape hollow space between the vessels and the enclosure to let the heat carrier flow. Fuel elements are located in the ring-shape hollow space, as well as the tooling for the heat carrier flow formation to cool the fuel elements and heat the upper vessel. The upper vessel is located above the reactor core and is divided with an internal partition wall to the central cylindrical and ring-shape hollow spaces. The partition wall has low thermal conductivity in the transverse direction. In the central hollow space of the upper vessel the cadmium isotope is mainly located, while in its ring-shape space—mercury. Lower vessel is mainly located in the active core of the reactor and filled with inert gas. The vessels and are connected with a pipe with a partition, made in the form of buckling rapture disc.