DC Conduction pump immersed in sodium forms a part of Failed Fuel Location Module (FFLM) of 500 MWe Fast Breeder Reactor (PFBR) currently under construction. FFLM housed in control plug of the reactor, is used to locate the failed fuel sub-assembly due to clad rupture in the fuel pin. The DC conduction pump sucks the sodium from the top of fuel sub-assemblies through the selector valve and pumps the sodium to hold up for detecting the presence of delayed neutrons. Presence of delayed neutron is the indication of failure in the sampled fuel sub-assembly. The DC Conduction Pump was chosen because of its low voltage operation (2 V) where argon/alumina ceramic can provide required electrical insulation even at operating temperature of 560°C without much complication on the manufacturing front. Sampling of sodium from top of different sub-assemblies is achieved by operation of selector valve in-conjunction with the drive motor. FFLM requires the pump to be immersed in sodium pool at ∼560°C located above the fuel sub-assemblies in the reactor. The Pump of 0.36 m3/h capacity and developing 1.45 Kg/ cm2 pressure was designed, manufactured and tested. The DC Conduction Pump has a stainless steel duct filled with liquid sodium, which is to be pumped. The stainless steel duct is kept in magnetic field obtained by means of electromagnet. The electromagnet is made of soft iron and the coil made of copper conductor surrounds the yoke portion of electromagnet. The external DC source of 2000 Amps, 2 Volt is used to send current through sodium placed in the stainless steel duct and the same current is sent through copper coil of electromagnet for producing required magneto motive force, which in turn produces required magnetic field. The interaction of current in sodium (placed in stainless steel duct) and magnetic field produced by the electromagnet in the duct region produces pumping force in the sodium. Electromagnet, copper coil, stainless steel duct, copper bus bar etc. are encapsulated in stainless steel shell. Hydraulic characteristics, efficiency, cavitation free operation at operating temperatures was ascertained by conducting tests in sodium loop called Large Component Test Rig (LCTR). The pump was also endurance tested for 750 hrs. The performance tests on DC Conduction Pump indicate that the pump meets the target specification at reactor operating condition. This paper deals with design, construction and performance testing of DC Conduction Pump.
In a fast reactor safety analysis determination of the molten core conditions when it reaches the core catcher plate is one of the main factors after a postulated MFCI event. If large fragmentation and quenching is accomplished in the coolant column no major problems for main vessel attack would occur. If instead, a significant amount of melt would remain as a solid molten cake, potential for lower head penetration would exist. In the present study towards development of a model for core melting and debris settling on to a core catcher plate, early phase of liquid stream fragmentation progression due to hydrodynamic consideration was investigated with woods metal melt water system. The system selected simulates the hydrodynamic physical properties more closely that of liquid UO2-sodium system. Assessment of debris-bed forming characteristics was carried out with different coolant column and different melt temperatures with melt inventories up to 20 kg released from a nozzle of 8 mm diameter. Bed height, debris spread area, jet break up length and repose angle obtained are presented for a melt release rate of ∼ 600 g/s. Only solidified debris constituted the bed for a melt temperature of 100°C and water temperature of 29 °C, with 720 mm water height. The estimated average bed height, bed porosity and heap repose angle were 15 cm, ∼0.6 and 43° respectively. Solidified central columnar lump of height 30 cm was seen for a water column of 360 mm. Relative bed forming characteristics for melt temperatures of 120 °C and 220 °C are also presented. High speed video imaging was taken to assess the stream break up distance and heap formation dynamics. Bulk coolant temperatures close to the melt stream were also monitored. Dependence of particulate debris and bed characteristics on melt temperature, interaction height and melt inventory have been brought out.
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