Research on lithium-water interactions for the safety analysis of tokamak reactors

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Posted by NewAdmin on 2025-01-16 13:12:35 |

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The Nuclear Research Team at the University of Pisa, led by Professor Nicola Forgione, is working to enhance the understanding of lithium-water interactions to improve the safety of tokamak reactors. Magnetic confinement fusion reactors have the potential to provide a nearly limitless and sustainable energy source. Unlike conventional nuclear reactors, fusion reactors aim to replicate the processes occurring in the sun, where hydrogen nuclei fuse to form helium and release vast amounts of energy. One of the key components of any fusion reactor is the Breeding Blanket, which generates additional tritium fuel (necessary for the fusion reaction) and captures the thermal energy produced by the plasma.

Breeding Blanket Candidates

Four different concepts are being developed as candidates for the Breeding Blanket, each with its own advantages and challenges:

1. Water Cooled Lead Lithium (WCLL)
   The WCLL system uses water as a coolant, operating under conditions similar to those of Pressurized Water Reactors (PWRs), with a pressure of 15.5 MPa and temperatures ranging from 295 to 328°C. The PbLi eutectic serves as the breeder material, and tritium is extracted from the PbLi outside the reactor.
   The system’s two main advantages are:

   • Compatibility with existing nuclear technology: It shares operational conditions with PWRs, making it easier to integrate with current infrastructure.
   • Safety and Tritium Management: Tritium extraction from the PbLi outside the reactor enhances operational safety, ensuring that the radioactive isotope can be managed more safely.

2. Helium Cooled Pebble Bed (HCPB)
   The HCPB system uses helium as a coolant (operating at a pressure of 8 MPa and temperatures from 300 to 500°C). Helium is an inert gas with high thermal conductivity, and it is paired with breeder materials like Li4SiO4 or Li2TiO3 and beryllium for efficient tritium breeding and heat transfer. Tritium extraction happens within the blanket using a purge gas, simplifying design and operation.

3. Helium Cooled Lead Lithium (HCLL)
   The HCLL system uses helium as a coolant (at a pressure of 8 MPa and temperatures from 300 to 500°C) and PbLi eutectic as the breeder material. This combination allows for efficient heat transfer and tritium breeding, with tritium extraction occurring outside the reactor, which is advantageous for maintenance and safety.

4. Dual Coolant Lead Lithium (DCLL)
   The DCLL system uses a dual coolant approach, with helium cooling the first wall at 8 MPa and temperatures from 300 to 400°C, while PbLi serves as both coolant and breeder, with a maximum operational temperature of 500°C. This design allows for higher operational temperatures and efficient heat transfer, with tritium extraction located outside the reactor for enhanced safety and easier maintenance.

The Role of the Nuclear Research Team at the University of Pisa

The Nuclear Research Team, led by Professor Nicola Forgione at the Department of Civil and Industrial Engineering at the University of Pisa (DICI-UNIPI), is focused on improving the safety of the WCLL concept, particularly with respect to In-Box Loss of Coolant Accidents (LOCAs) involving lithium-water interactions.

The chemical reaction between lithium, contained within the Li-Pb alloy, and water is a critical factor influencing the overall interaction. These reactions are highly exothermic, leading to rapid temperature increases and hydrogen gas formation. Therefore, the main aim of the research is to enhance the validation of numerical codes used for safety analysis of magnetic confinement fusion reactors, with a focus on understanding the transient phenomena during LOCAs. This involves complex chemical reactions and thermal dynamics that could pose safety risks.

The research uses computational methods to model lithium-water interactions, supported by available experimental data. The team’s Nuclear Thermal-Hydraulic Simulation Laboratory has modeled LOCAs, considering controlled amounts of water in a lithium-lead environment under the operating conditions expected for fusion reactors.

The team has developed calculation models implemented in numerical codes that can predict the behavior of lithium-water interactions in various scenarios. These models have been validated against experimental data from the literature to ensure their accuracy and reliability.

In conclusion, the work conducted by the team at DICI-UNIPI represents a significant step in the development of safe and efficient magnetic fusion reactors. By understanding and addressing the risks associated with lithium-water interactions during LOCAs, the team is contributing to the advancement of fusion energy as a credible, sustainable, and future-proof energy source.

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