Study on Unprotected Transients for LFRs of 600 MWe Power and Two Different Core Radii and Heights

This paper investigates the influence of core radii and height on core outlet temperatures during unprotected transients for a 600 MWe (1426 MWth) lead-cooled reactor fuelled by (U,TRU)O2. Two core geometries were examined, one compact core of 2 m height and 4 m diameter, and a pancake core of 1.2 m height and 5 m diameter. UZrH1.6 pins were added into core sub-assemblies in order to improve reactivity coefficients (increase the negative Doppler reactivity feedback and decrease the coolant temperature reactivity coefficient). The pin diameter was 12.5 mm and the pitch-to-diameter ratio was 1.6. Each fuel pin had a 3 mm diameter concentric hole in order to reduce the maximum fuel temperatures. For the thermal hydraulics calculations the computational fluid dynamics code STAR-CD was used, and the neutronic and burn-up performance was evaluated by the Monte Carlo codes. It was found that during an unprotected Loss-of-Flow accident, for which it was assumed that the core power remained constant during the whole transient, the pancake core had a temperature increase of only 100 K, compared to almost 200 K for the compact core. During an unprotected Loss-of-Heat-Sink accident at full power the heat up of the coolant is independent of the core type, i.e. the reactor vessel reaches the fast creep temperature (1173 K) within 400 seconds. A Total-Loss-of-Power accident would lead to a temperature peak of 1080 K two days after accident initiation.

TUCEK Kamil;  WIDER Hartmut; 

CARLSSON Johan; 

2006-06-01

SCK-CEN

JRC33516

https://publications.jrc.ec.europa.eu/repository/handle/JRC33516,