Preliminary accident analysis of Flexblue^®underwater reactor

Abstract

Flexblue ® is a subsea-based, transportable, small modular reactor delivering 160 MWe. Immersion provides the reactor with an infinite heat sinkthe oceanaround the metallic hull. The reference design includes a loop-type PWR with two horizontal steam generators. The safety systems are designed to operate passively; safety functions are fulfilled without operator action and external electrical input. Residual heat is removed through four natural circulation loops: two primary heat exchangers immersed in safety tanks cooled by seawater and two emergency condensers immersed in seawater. In case of a primary piping break, a two-train safety injection system is actuated. Each train includes a core makeup tank, an accumulator and a safety tank at low pressure. To assess the capability of these features to remove residual heat, the reactor and its safety systems have been modelled using thermal-hydraulics code ATHLET with conservative assumptions. The results of simulated transients for three typical PWR accidents are presented: a turbine trip with station blackout, a large break loss of coolant accident and a small break loss of coolant accident. The analyses show that the safety criteria are respected and that the reactor quickly reaches a safe shutdown state without operator action and external power.

Flexblue® Underwater Reactor: Introduction To The Concept And To The Passive Safety Strategy For A Steam Generator Tube Rupture Accident

“…9. The accident analysis of this transient is presented in [8]. This strategy is acceptable: all the safety criteria are respected.…”

Flexblue®core design: optimisation of fuel poisoning for a soluble boron free core with full or half core refuelling

“…A complete description of the Flexblue ® concept, including market analysis, regulation and public acceptance, security and environmental aspects can be found in reference [1]. A more detailed description of the PWR reactor design and the thermal-hydraulic accident analysis can also be found in reference [2].…”

“…Moreover, concerning the main steam line break accident, as there is no criticality after automatic shutdown (thanks to the increased control rod worth) in soluble free reactor, it is much less an issue. 2 These results have been obtained with QUABOX/CUBBOX, using cross-section libraries generated with DRAGON (Sect. 4).…”