Thermal hydraulic analysis of ALFRED by RELAP5 code & by SIMMER code G. Barone, N. Forgione, A. Pesetti, R. Lo Frano CIRTEN Consorzio Interuniversitario per la Ricerca Tecnologica Nucleare UNIVERSITA’ DI PISA Dipartimento di Ingegneria Meccanica, Nucleare e della Produzione LEADER Technical Meeting, Karlsruhe 2012

Content ALFRED reactor TD-5 Loss of one primary pump: RELAP5 preliminary nodalization  Steady state Needed improvements TRB-1 Steam system piping break at SG outlet: SIMMER III preliminary model  Preliminary obtained results Needed improvements LEADER Technical Meeting, Karlsruhe 2012

ALFRED reactor LEADER Technical Meeting, Karlsruhe 2012

TD5-Relap5 preliminary nodalization 8 STEAM GENERATORS LEADER Technical Meeting, Karlsruhe 2012

RELAP geometrical parameters are fixed according to ALFRED core: FA, 108 Dummy elements, -127 pins/FA, P/D=1.32, D=10.5 mm HTC is evaluated by RELAP5 according to Ushakov correlation. 2 % of the total flow rate crosses the core through the Dummy elements. The gap (5 mm) between adjacent FA and Dummy, together with the core annular zone has been modeled; the lead is in stagnant conditions. FAs, Dummy and gap/core-annulus zones are connected to ALFRED core upper plenum, in this branch the hot FAs lead mass flow mixes with the by-pass one from Dummy elements, to reach (by means of TDPJUN) the SGs. ALFRED 300 MWth core fuel assemblies (FA) are modeled by PIPE 876. The associated heat structure has a vertical length of 0.6 m (FA active height) and power is assumed being generated uniformly; heat transfer is simulated by vertical bundle convective option. Lead mass= 3.58E6 kg LEADER Technical Meeting, Karlsruhe 2012 TD5-Relap5 preliminary nodalization

RELAP5 preliminary nodalization ALFRED reactor includes 8 SGs: once through double wall bayonet type (T91). Each SG unit consists of 508 tubes with feed-water MFR of 24.1 kg/s; lead shell side MFR of kg/s. Secondary side pressure is 180 bar and feed-water enters the inner tube with a temperature of 335 °C (subcooled, T sat (180 bar)= 357 °C). RELAP5 bayonet tube nodalization: - Inner tube, water flows downwards - Annular zone, up-flow water stars to boil The two zones are thermally insulated by a paint layer (0.05 W/(m K)) to avoid steam condensation. Water reaches inner tube bottom at a temperature of 340 °C (subcooled) and enters the annular zone reaching saturated steam conditions (quality=1) at about 3 m height (half tube active length). Water/Steam exchange power with liquid lead that flows in counter-current on the tube outer surface, through double wall high conductivity gap (55 x He conductivity). Superheated steam is obtained at 6 m SG active length with a temperature of °C reaching the SG Steam Plenum at a temperature of 450 °C and quality of Heat exchange with lead above SG active length (6 m) has been neglected. LEADER Technical Meeting, Karlsruhe 2012

Model set up (steady state) LEADER Technical Meeting, Karlsruhe 2012

Model set up (steady state)

Model set up (ULOF) LEADER Technical Meeting, Karlsruhe 2012

Model set up (ULOF)

LEADER Technical Meeting, Karlsruhe 2012 Model set up (ULOF)

RELAP5 model improvements The ongoing improvements are:  Modeling the reactor kinetics (reactivity feedback)  Introduce hot FA and hot pin in the model  Power profile along FA active length (from Monte Carlo simulations)  Primary pumps with appropriate characteristic curve instead of time dependent junctions, if available. LEADER Technical Meeting, Karlsruhe 2012

7 pumps 1 pump 7 SGs 1 SG core 7 pump-SG connections 1 pump-SG connection 7 core-pump connections 1 core-pump connection 7 pump channels 1 pump channel Fuel assembly extended downcomer lower plate Lead Water Argon Non calculation regions feed-water tank Partial vertical section of the ALFRED reactor Axial-symmetric SIMMER III model TRB-1-SIMMER III model for SGTR analysis LEADER Technical Meeting, Karlsruhe 2012

Ø = 7.4 mm Failure plane T H2O = 335 °C P H2O = 180 bar T LEAD = 440 °C P ARGON = 1 bar Bayonet tube with rupture plane In SIMMER III model the flow areas and the axial dimensions have been conserved. Bayonet tube, water tank and injector orifice detail Lead Water Argon Non calculation regions LEADER Technical Meeting, Karlsruhe 2012 TRB-1-SIMMER III model for SGTR analysis Tube t=5 mm

Lead velocity vectors, in stationary conditions, before the water injection (V LEAD < 2 m/s) Pressure distribution, in stationary conditions, before the water injection and computational grid SGTR analysis: preliminary model set-up LEADER Technical Meeting, Karlsruhe 2012 Vbase 5 m/s

SGTR analysis: preliminary results LEADER Technical Meeting, Karlsruhe 2012 The steam, that arises from the LWI, seemed to propagate in the bottom part of core region. The analysis is at the beginning, about 3.5s of the foreseen transient (that is assumed to begin after the system has reached a steady state condition).

SGTR analysis: preliminary results LEADER Technical Meeting, Karlsruhe 2012 A detail of the previous figure showing the propagation of steam in the whole considered system : it is a preliminary results of TRB-1 analysis. Final results will be available soon: compatible with the time required by the simulations and the analysis of the obtained results

The model developed takes into account the real volume of the main components of the ALFRED reactor, the flow areas and the axial dimensions have been conserved. The results will allow to evaluate: the pressure trends inside the ALFRED reactor the evaporated water flowing through the core the possible lead freezing In the future work, one bayonet tube rupture in the ALFRED Steam Generator will be analyzed by the axial-symmetric model developed by the 2D SIMMER III code SIMMER III model: conclusions and needed improvements LEADER Technical Meeting, Karlsruhe 2012