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DTT Vacuum Vessel Cooling Circuit: Borated Water Chemistry Assessment

Water chemistry definition in nuclear fusion research experiments is under development. Many nuclear fusion experiments, such as the Italian Divertor Tokamak Test Facility (DTT)[1], the Korea Superconducting Tokamak Advanced Research (KSTAR) [2] and Japan Torus-60 Super Advanced (JT60SA) [3] reactors consider the use of enriched boric acid (up to 95% 10B) in water to shield the superconducting coils by neutrons generated from nuclear fusion reactions in the plasma chamber.

Product Number: ED22-17307-SG
Author: Claudia Gasparrini, Luigi Di Pace, Nicholas Terranova, Rosaria Villari, Emanuela Martelli, Piergiorgio Sonato, Mauro Dalla Palma, Giuseppe G Scatigno
Publication Date: 2022
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A preliminary water chemistry assessment for the nuclear fusion experiment called Divertor Tokamak Test facility Vacuum Vessel (VV) was performed using both experiments and simulations. The requirement to use 8000 ppm B in water enriched with 95% 10B as a neutron shield implies that water has a pH60C=3.6. Materials in contact with the borated water are stainless steel type, 316LN, resistant to general corrosion from borated water. Corrosion, however, is a complex phenomenon affected both by water chemistry and material characteristics. No water chemistry guidelines exist for nuclear fusion experiments cooling circuits so the assessment was based on nuclear fission power plants operational experience. The need to raise the pH of the DTT VV borated water to minimize corrosion has been assessed using metal release experiments and simulations with the use of computer codes devoted to the estimation of activated corrosion products (ACPs) production and transport. The release of ions was found to be more influenced by water chemistry, more releases were measured in the borated water environment than ultrapure water (UPW), than by microstructure (base metal vs welds). The addition of hydrogen in the DTT VV cooling circuit was also assessed, but without considering water radiolysis at this stage. It was found that at these low temperatures (60-80°C) the addition of hydrogen is not beneficial if the oxygen content can be maintained low.

A preliminary water chemistry assessment for the nuclear fusion experiment called Divertor Tokamak Test facility Vacuum Vessel (VV) was performed using both experiments and simulations. The requirement to use 8000 ppm B in water enriched with 95% 10B as a neutron shield implies that water has a pH60C=3.6. Materials in contact with the borated water are stainless steel type, 316LN, resistant to general corrosion from borated water. Corrosion, however, is a complex phenomenon affected both by water chemistry and material characteristics. No water chemistry guidelines exist for nuclear fusion experiments cooling circuits so the assessment was based on nuclear fission power plants operational experience. The need to raise the pH of the DTT VV borated water to minimize corrosion has been assessed using metal release experiments and simulations with the use of computer codes devoted to the estimation of activated corrosion products (ACPs) production and transport. The release of ions was found to be more influenced by water chemistry, more releases were measured in the borated water environment than ultrapure water (UPW), than by microstructure (base metal vs welds). The addition of hydrogen in the DTT VV cooling circuit was also assessed, but without considering water radiolysis at this stage. It was found that at these low temperatures (60-80°C) the addition of hydrogen is not beneficial if the oxygen content can be maintained low.