Safety analysis for the Divertor Tokamak Test (DTT)

Abstract

The Divertor Tokamak Test (DTT) facility will emit ionizing radiation during its operation, both due to d-D (deuterium-deuterium) reactions and to accelerating electrons and other particles within the plasma. Therefore, the plant shall be designed and operate according to the Italian legislation and regulations applicable to facilities using ionizing radiations.The licensing process involves the execution of safety analyses dedicated to demonstrating compliance with the legal limits in the various operational phases and in the incidental/accidental conditions that could occur.Accordingly, safety analyses begin at an early stage of the project development. A functional failure mode and effect analysis (FFMEA) was performed when the DTT design was at conceptual level. The output of this first assessment was the identification of a set of safety concerns and a set of hazards (e.g. possible source terms). Preliminary reference accident sequences have also been outlined for the transient deterministic analyses to be performed in order to demonstrate that safety requirements are met and that structural containment is not challenged.Evaluations of source terms such as tritium, activated dust in the plasma chamber and activated corrosion products (ACPs) in cooling circuits have started and are still ongoing. In parallel, as the design has progressed significantly, component-level failure mode and effects analyses (FMEA) have been initiated, as well as deterministic assessments.FMEAs allow the confirmation/identification of the complete set of hazards, the possible initiating events and the selection of reference accident sequences. Deterministic assessments will evaluate the possible consequences related to the reference accidents and demonstrate compliance with safety limits.In this work, the following studies are presented:•functional analysis, which defines the process and safety functions provided by the systems, structures and components (SSC) in the DTT;•the functional FMEA in terms of methodology used and results obtained when the design was only in a pre-conceptual phase;•the analysis of ACPs related to the primary heat transfer system (PHTS) of the vacuum vessel (VV);•the FMEA at component level both in terms of results obtained and design improvements necessary to reduce safety risks.