Severe Accident Considerations for the Lead-Cooled Fast Reactor

The Lead-Cooled Fast Reactors (LFR) has in some cases advantages from a safety point of view compared to other fast reactors. Conversely, the LFRs also have some unresolved issues that need further investigation. Among the advantages is the high coolant boiling temperature of 1780°C, which makes voiding of the core from coolant boiling very unlikely. Since the LFR has low operating pressures, the risk for Loss-Of-Coolant Accidents is reduced. The natural circulation capacity of lead is excelent, which is useful during loss of forced pumping power. The natural circulation is futher improved by that the LFRs usually have a low-pressure drop core with relatively large pitch-to-diameters (PTD) and simple flow paths. For example, some smaller LFR designs, as the STAR-LM [1], by employing this achieves a purely natural circulation cooled core during normal operation. Unresolved issues for LFRs match often the category of material issues. Today the highest temperature that steel, with aluminun coating of the GESA method, can endure for longer times is 600°C and lead velocities should not exceed 2.5 m/s. The most critical structures are the pumps (high velocities), the core and the heat-exchangers (HX). Alternative steels are being considered like for example the MATHAL (Ti3SiC2), but their performance needs to be proven in the lead environment at high temperatures and velocities for longer times. Another uncertainty concerning the LFR is the consequence of a steam generator tube rupture. High-pressure steam would then enter the primary circuit. The strenth of the pressure wave is uncertain as well as where the steam bubbles would move. In case the bubbles reach the core region positive reactivity would increase its power. Research began on LBE and lead cooled Accelerator-Driven Systems (ADS) about ten years ago within European projects called PDS-XADS and later IP EUROTRANS [3]. The latter concerns the developmend of a European Facility Industrial Transmutation (EFIT). This paper compares the performance of the EFIT reactor during the Unprotected Loss-of-Flow (ULOF) accident.

CARLSSON Johan;  TUCEK Kamil;  WIDER Hartmut; 

2008-02-11

American Nuclear Society - ANS

JRC43300