Some thermal hydraulic challenges in sodium cooled fast reactors

A proper assessment of core thermohydraulics under natural circulation conditions is important so that the full potential of the inherent, passive feature of a fast reactor can be used. When the he...

Investigation of core thermohydraulics in fast reactors: Interwrapper flow during natural circulation

Natural convection test in Phenix reactor and associated CATHARE calculation

Natural circulation plays a significant role in the decay heat removal function of a sodium-cooled reactor. A recent design of the Japan Sodium-Cooled Fast Reactor (JSFR) fully uses natural circulation for a decay heat removal system (DHRS). A dipped heat exchanger (DHX) is immersed in the reactor upper plenum as the DHRS. The DHX provides cold sodium in the upper plenum during the decay heat removal operation. This cold sodium covers the top of the core under the low-flow-rate conditions of natural circulation. Several water experiments of natural circulation in fast reactors revealed that the cold fluid in the reactor upper plenum might partially and temporally penetrate into the low power core channels, e.g., the radial blanket fuel subassemblies. Sodium experiments were carried out to find the onset conditions and the penetration depth of such partial reverse flow driven by buoyancy force. A blanket subassembly and the upper plenum were modeled in the test section including the axial upper neu...

Sodium Experiments of Buoyancy-Driven Penetration Flow into Low-Power Subassemblies in a Sodium-Cooled Fast Reactor During Natural Circulation Decay Heat Removal

CFD analysis of the flow in the MICAS experimental facility, a water model of the hot pool of a sodium cooled fast reactor

This paper reports, to examine the function of the safety-related SNR-2 decay heat removal concept, natural convection experiments performed in two-and three-dimensional water models, scaled 1:20, under conditions of symmetric and nonsymmetric loads of the immersed coolers installed in the upper plenum at 180-deg positions with respect to each other. The temperature and velocity distributions were measured and the flow patterns recorded for different configurations of the instrumented plug. For symmetric load conditions, symmetric temperature and flow distributions were measured in two- and three-dimensional models. Nonsymmetric load conditions produce remarkable temperature differences between the two separated plenums of the two-dimensional model if fluid circulation is suppressed by a closed plug. An open plug allows fluid to pass through and shows lower temperature differences. In contrast, in the three-dimensional experiment, azimuthal fluid flow inside the plenum prevails even with the plug closed, and identical temperature distributions are measured. The calculations using the COMMIX-1B code are generally in good agreement with the measurements.

Thermohydraulic Investigations of Decay Heat Removal Systems by Natural Convection for Liquid-Metal Fast Breeder Reactors

In this paper, thermohydraulic studies on the transition from forced to natural convection are carried out using the 1:20 scale RAMONA three-dimensional reactor model with water as the simulant fluid. In the investigations, a scram from 40% load operation of a fast reactor is simulated. The core mass flows and the core as well as the hot plenum temperatures are measured as a function of time for various core power levels, coastdown curves of the primary- and secondary-side pumps, and for various delay times for the start of the immersion coolers after a scram. These parameters influence the onset of the natural circulation in the reactor tank. The main result is that the longer the intermediate heat exchanger coolability is ensured and the later the immersion coolers start to operate, the higher is the natural-circulation flow and, hence, the lower are the core temperatures.

Thermohydraulic model experiments on the transition from forced to natural circulation for pool-type fast reactors

After a reactor scram, the decay heat removal (DHR) is of decisive importance for the safety of the plant. A fully passive DHR system based on natural circulation alone is independent of any power source. The DHE system consists of immersion coolers (ICs) installed in the hot plenum and connected to air coolers, each via intermediate circuits. During the postscram phase, the decay heat is to be removed by natural circulation from the core into the hot plenum and via the ICs and intermediate loops to the air coolers. The function of this DHR system is investigated and demonstrated in model tests with a geometry similar to the reactor, though on a different scale RAMONA is such a three-dimensional model set up on a 1:20 scale. It is operated with water. The steady-state tests for natural-circulation DHR operations have been conducted over a wide range of operational and geometric parameters. To study the transition from nominal to DHR conditions, experiments were defined to investigate the onset of natural circulation in the postscram phase (transient tests). The experiments were analyzed using the one-dimensional LEDHER code. LEDHER is a network analysis code for the long-term DHR of a fast reactor developed atmore » Power Reactor and Nuclear Fuel Development Corporation in Japan. The results of the experiments and conclusions are summarized.« less

H. Hoffmann

Papers

Thermohydraulic Investigations of Decay Heat Removal Systems by Natural Convection for Liquid-Metal Fast Breeder Reactors

Thermohydraulic model experiments on the transition from forced to natural circulation for pool-type fast reactors

Thermohydraulic model experiments and calculations on the transition from forced to natural circulation for pool-type fast reactors