The tritium breeding blanket in Tokamak fusion reactors

The tritium breeding blanket in Tokamak fusion reactors T. Onjun 1), S. Sangaroon 2), J. Prasongkit 3), A. Wisitsorasak 4), R. Picha 5), J. Promping 5) 1) Thammasat University, Pathumthani, Thailand 2) Mahasarakham University, Mahasarakham, Thailand 3) Nakhon Phanom University, Nakhon Phanom, Thailand 4) King Mongkut’s University of Technology Thonburi, Thailand 5) Thailand Institute of Nuclear Technology, Bangkok, Thailand

Kingdom of Thailand • Thailand is a country on Southeast Asia’s Indochina peninsula • Previous called “Siam” • Member of “ASEAN” • Capital: Bangkok • Population: 65. 12 million (2015) • Currency: Thai baht

Thailand: Land of Smiles Rich of Nature and Culture

Fusion reactions for future energy q The fuels for fusion reactions are in the plasma state. Thus, they are confined by magnetic field of the tokamak. q Alpha particles are trapped inside while neutrons can escape from the core of the tokamak. Neutrons can be used to heat up water to produce electricity, similar to a fission power plant.

International Thermonuclear Experimental Reactor (ITER) q to demonstrate the scientific and technical feasibility of fusion power ITER parameter Achieved Total fusion power 500 MW Major radius, a 6. 2 m Minor radius, R 2. 0 m Additional heating 73 MW Electron density, ne 1 1020 m-3 Pulse length > 400 s Plasma volume 837 m 3 One key success of ITER is an R&D on first wall material and blanket

Understanding plasma in tokamak • Transport code is used to simulate plasma evolution To be published in NF 2016

Fusion Reactors

Surface Material is a Key Item for Fusion Development Challenges for fusion materials technology • • Very high heat loads for materials facing the plasma Damage to the structure caused by high-energy neutrons Hydrogen isotope retention Helium embrittlement Material candidates: beryllium , tungsten and carbon fibre composite

Plasma facing material Tungsten, with its very high melting point and high thermal conductivity is an attractive candidate as fusion wall material. Nevertheless it can melt within one millisecond when in direct contact with the plasma. (Photo: Egbert Wessel, Julich Research Centre) A tungsten bulk sample after exposure to the edge plasma in Jülich's TEXTOR Tokamak. Even the chemical element with by far the highest melting point of 3422 °C can melt—good to know for ITER's envisaged all-tungsten divertor.

Blanket (including first wall) Blanket functions: 1. Power extraction • • Absorb plasma radiation on the first wall Convert kinetic energy of neutron and secondary gamma-ray into heat 2. Tritium breeding • • Tritium breeding, extraction, and control Must have lithium in some form for tritium breeding 3. Physical boundary for the plasma • • Physical boundary surrounding the plasma, inside the vacuum vessel Provide access for the plasma heating, fueling Must be compatible with plasma operation Innovation blanket concept can improve plasma stability and confinement 4. Radiation shielding of the vacuum vessel

Self-cooled lithium blanket q Tritium breeding fusion blankets with vanadium alloys as structural materials and liquid lithium as breeding and cooling materials (self-cooled Li/V blankets) have been designed as advanced concepts for DEMO and commercial fusion reactors q the neutron multiplying beryllium is in most cases not necessary for obtaining the required Tritium Breeding Ratio (TBR) The blanket is composed of q Li cooling channels; q Reflectors; q Shielding area

Li/V blanket concept

Advantage q Replacements frequency of the blanket will be reduced once long life structural materials are developed, because the blanket system is free from periodic replacement due to the life time of beryllium q High heat transfer capability due to physical property of vanadium alloys and high heat transfer characteristics of liquid lithium, and low tritium leakage because of high solubility of tritium in liquid lithium

Simulation of Blanket using MCNP • Material and structure of self-cooled liquid lithium blanket used in this study • The 3 -D modeling of the mock-up blanket was created using the MCNP

Tritium Breeding • The tritium production and the tritium to neutron ratio in the breeder zone are simulated using MCNP

Simulation Results • Tritium production to neutron ratio in the local breeder zone Percent 6 Li enrichment Tritium to neutron ratio 0% 0. 369 Natural lithium 0. 506 75% 1. 528 95% 1. 747 100% 1. 798 Design point

Summary • The 3 -D modeling of the mock-up blanket was created using the MCNP – Tritium production increases with the percent 6 Li enrichment – At the design point, the ratio of tritium to neutron is 1. 528