Integral Molten Salt Reactor Unit Design
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Solution Overview
Problem
Molten salt nuclear reactors face challenges with graphite moderator lifetime, reactor vessel longevity, and primary heat exchanger replacement, leading to design complexities and economic disadvantages due to the need for large reactors or frequent graphite replacement, and potential radioactive contamination during servicing.
Innovation Solution
The integration of the graphite moderator, reactor vessel, and primary heat exchangers into a single replaceable unit, allowing for a higher power density design with a shorter operational life, eliminating the need for graphite replacement and incorporating decay heat removal and volatile gas storage, which can function as a storage container after shutdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If graphite moderator is used in MSR, then reactor control is improved and starting fissile inventory is reduced, but graphite lifetime is limited due to shrinkage and expansion under neutron flux
Solution Approach 1:
The graphite moderator is divided into replaceable elements or modules that can be individually replaced when they reach their lifetime limit, while the rest of the reactor continues operating. This segmentation allows maintenance without complete shutdown and extends overall system lifetime.
Solution Approach 2:
The reactor design incorporates the capability to dynamically replace graphite elements during operation or during scheduled outages, transitioning from a static graphite structure to a dynamic system where components can be renewed without replacing the entire moderator assembly.
2Duration of action of stationary object
If large reactor size is used to extend graphite lifetime, then graphite can remain in vessel for design life, but capital costs and material requirements increase significantly
Solution Approach 1:
The reactor is designed with modular graphite elements that can be replaced independently, allowing a compact overall reactor size while maintaining long operational lifetime through component renewal rather than requiring an oversized graphite structure.
Solution Approach 2:
Graphite elements are designed for controlled replacement after reaching their neutron fluence limit, with spent elements being removed and replaced by fresh ones, extending the reactor's operational lifetime without increasing initial graphite volume or reactor size.
3Power
If periodic graphite replacement is implemented, then higher power density is achieved, but reactor must be shut down and opened every few years causing radioactive contamination risks
Solution Approach 1:
The graphite elements are designed to be extractable from the reactor vessel through dedicated access ports or removable end caps, allowing replacement without completely opening the vessel and minimizing exposure of personnel to radioactive environments.
Solution Approach 2:
Graphite elements are designed as disposable or limited-life components that are replaced periodically, with the replacement process simplified through standardized interfaces and minimal disassembly requirements, reducing both cost and radioactive exposure risk.
4Quantity of substance
If graphite is omitted from MSR, then starting fissile load is reduced, but neutron spectrum becomes harder requiring five times the starting fissile load
Solution Approach 1:
The reactor design allows adjustment of neutron spectrum characteristics through control rod positioning, moderator density changes, or core configuration modifications, providing flexibility to achieve criticality with reduced fissile load without requiring traditional graphite moderation.
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
This approach simplifies reactor design, reduces economic costs, and manages radioactive materials effectively by allowing for the IMSR to be replaced as a unit, eliminating the need for frequent graphite replacement and minimizing radioactive exposure during maintenance, while maintaining the advantages of a sealed system.
Implementation Method 1
it gives a softer or more thermalized neutron spectrum which provides improved reactor control
Implementation Method 2
a molten salt circulating at least in the vessel... The heat exchanger system to receive heat from the molten salt
Implementation Method 3
a molten salt circulating at least in the vessel
Implementation Method 4
a vessel, a graphite moderator core positioned in the vessel, and a molten salt circulating at least in the vessel
Data Source
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AI summary
The present relates to the integration of the primary functional elements of graphite moderator and reactor vessel and/or primary heat exchangers and/or control rods into an integral molten salt nuclear reactor (IMSR). Once the design life of the IMSR is reached, for example, in the range of 3 to 10 years, it is disconnected, removed and replaced as a unit. The spent IMSR functions as the medium or long term storage of the radioactive graphite and/or heat exchangers and/or control rods and/or fuel salt contained in the vessel of the IMSR.