Claudio Rizzello

Analysis of the SEAFP Reactor Fuel Cycle

The safety aspects of a fusion reactor fuel cycle, which handles substantial quantities of tritium, have been assessed in the framework of the European Programme on Safety and Environmental Assessment of Fusion Power Long Term (SEAL). This study focused on the assessment of the tritium inventory that could be released from interlinked systems in accidental scenarios. A systematic review of the fuel cycle systems was performed by focusing attention on the main interfaces and to the possible propagation of accident sequences through these interfaces. For the bounding accident sequences identified, deterministic analyses were carried out to determine the accident consequences. Both process source terms (PST) and environmental source terms (EST) were estimated. Simultaneous failure of the primary and secondary containment was considered to be beyond the design basis, nevertheless a preliminary analysis has been carried out; a bounding accident sequence related to a double failure, involving a hydrogen fire, has led to a tritium environmental release of 5.3 g and the wall mechanical load deriving from the maximum hypoth-esizable hydrogen detonation has been defined. Tritium releases into the secondary containment are treated by the appropriate detritiation and by the vent detritiation system. The related EST has been estimated based on an overall tritium cleanup efficiency of 99%, deliberately chosen low to cause the EST to be overestimated. The maximum tritium environmental release is less than 11 g and corresponds to an in-vessel LOCA. For accidents initiating in the fuel cycle only, the maximum tritium release is at most 3.1 g.

Main Results of the Analyses Related to a Few Reference Accident Sequences of NET/ITER Tritium Systems

Based on the existing conceptual design, a set of Reference Accident Sequences (RAS) has been defined by tritium system experts. This paper presents the main results related to a preliminary analysis of the following RAS for fuel cycle systems: hydrogen detonation in the isotopic separation system, rupture of a cryoline in a cryopump, fire in the long-term storage beds, and mechanical faulty operation in the pellet injector. The systems and the component mode of operation have been analyzed, as well as the characteristics of all streams, the inventory of T, D, and H, and the energy released under accident conditions. Failures that could give rise to the release of tritium and/or to the formation and ignition of oxygen/hydrogen mixtures and failures that could lead to containment pressure transients are discussed and examined.

Dust and corrosion product effluents assessment in ITER

A detailed assessment of the activated corrosion products (ACPs) and tokamak dust escaping to the environment during international thermonuclear experimental reactor (ITER) normal operation, including scheduled maintenance, is presented. Calculation models were developed to assess ACPs environmental release through main pathways. The dust air transport to the environment was assessed by the NAUA-Mod.5 code and dedicated computational models. The analysis confirms the conservatism used in non-site specific safety report no.-2 (NSSR-2).

NET-ITER HYDROGEN ISOTOPE SEPARATION SYSTEM SAFETY ASSESSMENT

A safety analysis of the Hydrogen Isotope Separation System of the NET/ITER tritium plant has been performed. The study has been splitted in two steps: a probabilistic safety assessment and a deterministic study of the reference accident sequences. Safety relevant initiating events, related to accidental losses of tritium from process equipment, have been identifed and their propagation within the plant and to the environment has been evaluated. For the accident sequences resulting in severe consequences for the public health, a quantitative evaluation has been performed. Results have been compared with the design safety targets for the tritium plant. The analysis has been completed by a deterministic assessment of some reference accident sequences. These have been analyzed in detail by evaluating the amount of hydrogen isotopes that can give rise to a deflagration or to a detonation and the related effects, even if preliminarily, on the surroinding structures.