Protection of the primary circuits and effect on the design of the inner deuterium/tritium fuel cycle of ITER

Abstract

The confinement of tritium within its respective processing systems is clearly one of the most important safety objectives for fusion reactors. Consequently, the functional safety of all the subsystems of the inner deuterium/tritium fuel cycle of ITER need to be carefully analyzed and the results implemented into the design of the Tritium Plant as a whole. The basic principles for the management of functional safety are laid out in the international standard IEC 61508. The tritium bearing systems need to be particularly protected against over-pressure and over-temperature, even at levels significantly below values at which sensors or components would loose their mechanical integrity. The design shall take into account the necessity to validate and test the protection measures, noting the contamination of the equipment with tritium and the restricted access due to multiple barriers. Any protection measure has its characteristic but limited credibility. Software based safeguarding, for example, is not fully satisfactory in certain cases. In spite of the developments in software and the increasing possibilities to assure its quality, hard-wired signal processing is still considered to be necessary within the ITER Tritium Plant.