Passive Decay Heat Removal via Modular PCM Cold Source
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Solution Overview
Problem
Current decay heat removal (DHR) systems in liquid metal cooled fast neutron nuclear reactors are not completely passive, rely on instrumentation and human intervention, and lack diversified heat sink solutions, making them vulnerable to failures and external attacks.
Innovation Solution
A DHR system featuring a closed circuit with U-shaped pipes and monotube exchangers that utilize natural convection and a modular phase change material (PCM) cold source, allowing for passive decay heat removal and reducing the risk of chemical interaction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If current DHR systems are used in liquid metal cooled reactors, then decay heat removal function is provided, but the systems are not completely passive and require instrumentation and human intervention
Solution Approach 1:
The DHR system is designed to operate autonomously without external control or human intervention. The natural circulation of liquid metal coolant through the primary circuit and heat exchangers provides self-regulating decay heat removal, where the system automatically responds to temperature differences and heat loads without requiring active control systems.
Solution Approach 2:
The patent replaces active mechanical control systems (pumps, valves, instrumentation) with passive thermal-hydraulic mechanisms. Natural circulation driven by density differences and thermal gradients substitutes for mechanically pumped flow systems, eliminating the need for electrical power and control instrumentation during accident scenarios.
2Temperature
If liquid metal/air exchangers are used as final cold source, then heat removal is achieved, but chemical interaction risks and external attack vulnerabilities increase
Solution Approach 1:
The patent introduces an intermediate heat transfer fluid (liquid metal) that circulates in a closed secondary circuit between the primary reactor circuit and the air-cooled heat exchangers. This intermediate fluid acts as a barrier, preventing direct contact between the radioactive liquid metal in the primary circuit and the air environment, thereby eliminating chemical interaction risks while maintaining effective heat removal.
Solution Approach 2:
The closed secondary circuit containing the intermediate liquid metal creates an inert barrier environment that isolates the radioactive primary coolant from the external atmosphere. This prevents any potential chemical reactions between the liquid metal and air, and also protects against external attacks on the final cold source by containing the hazardous material within the sealed circuit.
3Volume of moving object
If DHR systems are arranged inside the primary vessel, then compactness is improved, but reactor shutdown is required for component handling
Solution Approach 1:
The DHR system is segmented into modular components (heat exchangers, pipelines, isolation valves) that are distributed throughout the reactor structure but can be independently accessed. The secondary circuit components are positioned in accessible locations outside the primary vessel, while maintaining compact integration through strategic routing of connections, allowing maintenance without full reactor shutdown.
Solution Approach 2:
The system incorporates isolation valves and disconnect mechanisms that allow preliminary separation of the secondary DHR circuit from the primary vessel before maintenance activities. This enables component handling and replacement in the secondary circuit without requiring reactor shutdown or opening the primary vessel, improving ease of manufacture and maintenance.
4Productivity
If active forced convection systems are used, then heat removal efficiency is improved, but system complexity and power requirements increase
Solution Approach 1:
The system utilizes periodic natural circulation cycles driven by thermal density differences. During normal operation, controlled thermal gradients create sustained circulation patterns that efficiently remove heat without mechanical pumps. The periodic thermal responses to load changes provide adaptive heat removal that maintains efficiency while avoiding complex active control systems.
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 system ensures completely passive decay heat removal, reduces the risk of chemical interaction, and provides enhanced safety features by utilizing natural convection and a modular PCM cold source, making it more resilient to failures and external attacks.
Implementation Method 1
The circuit is configured such that the heat transfer liquid flows by natural convection
Implementation Method 2
the PCM present in each module being designed... to transition to the liquid state in an accident condition of the nuclear reactor in which decay heat is released
Implementation Method 3
each module containing a phase change material (PCM) of solid-liquid type... to transition to the liquid state
Data Source
AI summary
A nuclear reactor incorporates a fully passive decay heat removal system with a modular cold source. The decay heat removal system is configured to remove heat passively, via the outside of a primary vessel included in the nuclear reactor. The cold source has a plurality of modules grouped together in assemblies. Each module is filled with a phase change material. Each module is cooled by a monotube heat exchanger. The decay heat removal system includes a hot collector and a cold collector to ensure the distribution of a heat transfer fluid in the plurality of monotube heat exchangers.