Inlet plenum

Factory-welded subassemblies are based on separate fabrication of bag housing, dust hopper, inlet plenum, outlet plenums, etc., to form the largest subassemblies that can be shipped over the road. Connections are made to adjacent components by welding or bolting at the job site. Bags can be already... 

Figure 2.40 shows the unsteady flow upstream of the ONE in one of the parallel micro-channels of d = 130 pm at = 228kW/m, m = 0.044 g/s (Hetsroni et al. 2001b). In this part of the micro-channel single-phase water flow was mainly observed. Clusters of water appeared as a jet, penetrating the bulk of the water (Fig. 2.40a). The vapor jet moved in the upstream direction, and the space that it occupied increased (Fig. 2.40b). In Fig. 2.40a,b the flow moved from bottom to top. These pictures were obtained at the same part of the micro-channel but not simultaneously. The time interval between events shown in Fig. 2.40a and Fig. 2.40b is 0.055 s. As a result, the vapor accumulated in the inlet plenum and led to increased inlet temperature and to increased temperature and pressure fluctuations.

A Fonr Field Hamon Research-Cottrell Inc. Refinery ESP with top inlet plenum and weather enclosnre is shown in Fignre 18.11. 

Table 4 shows the results of the seismic margin evaluations and the seismic capacity of KALIMER reactor internal structures including the reactor vessel and containment vessel. From the results, the containment vessel, reactor vessel, inlet plenum, and core support have large seismic stress margins but the reactor vessel liner, support barrel, separation plate, and baffle plate have small margins. The maximum stress occurs in reactor vessel liner parts coimected with the separation plate due to the vertical seismic loads. 

The primary components of each RS (core, reflectors, and associated supports, restraints, and controls) are contained in the reactor vessel. The nuclear heat is generated in the reactor core. Removal of the heat energy is provided by the Heat Transport System (HTS) with the main circulator providing the driving force to supply helium coolant into an upper core inlet plenum and to draw heated coolant from a bottom core outlet plenum. The primary coolant is distributed to numerous coolant channels running vertically through the core. The outlet plenum directs the flow to the central portion of the coaxial cross duct which channels the helium flow to the steam generator vessel (see Chapter 5). 

The upper plenum thermal protection structure consists of metallic plates formed into a shroud within the top head of the reactor vessel to create the core inlet plenum. It includes a thermal barrier attached to the outside of... 

The 12 primary coolant inlet channels with internal dimensions of 152 mm x 660 mm (6 in. x 26 in.) are located on the outside surface of the core barrel to direct the primary coolant to the top inlet plenum. During loss of forced circulation, these channels, in conjunction with the core barrel and the... 

The blowers and fans for the reactor aiir system take their air. from an inlet plenum chamber beneath the building and exhaust it to another, also beneath the building. ... 

Hydraulic tests to assess the flow distribution and measure vibration of tube bundle are carried out on a 60 degree sector model of SG (fig 13a). The velocity distribution measured in the inlet plenum was found matching with prediction of the 3D hydraulic calculations (fig 13b). Vibration measurements are carried out in the straight spans and expansion bend regions. Although the vibration level is found higher in the inlet span where cross flow takes place across the tube bundle, it is within the acceptable values based on structural mechanics analysis (fig 13c). 

Fig. 4.12. Schematic of pebble recirculation system being studied at the University of California at Berkeley, showing pebble insertion into the coolant cold legs for injection at 32 locations around the bottom inlet plenum of the reactor.

Concentric holes in both plates accept the circular nose pieces of the subassemblies. The weight of the subassemblies is supported at a conical seal face on the top grid plate. This grid structure is the coolant inlet plenum, coolant entering side holes in the nose pieces. Close fits of the nose pieces in the lower grid plate provide a hydraulic hold-down, the area between the lower grid plate and the reactor vessel being opened to the primary tank. 

The calculational models should allow calculation of the fuel pin characterisation for the End of Equilibrium Cycle Core Loading Scheme and during the transient as well as the transient thermal and hydraulics processes in the reactor and in the primary circuit taking into account the sodium boiling. The models should include multichannel representations of the core (12-30 channels), with appropriate models of the out- and inlet plenum and the IHX, or prespecified in-/outlet boundary conditions (pressure and temperature). 

The cold 1 piping enters the reactor vessel at the same level as the hot leg nozzles, and the 260°C return flow is directed downwards to the reactor core inlet via the down- comer. On its way down, the flow velocity is increased in a siphon breaker arrangement with open connections to the pressurizer. The siphon breaker is intended to prevent siphoning ofT too much reactor pool water inventory in the hypothetical event of a cold leg rupture. During normal operation, the siphon breaker does not affect the water circulation. At the bottom of the annular downcomer the return flow enters the reactor core inlet plenum. 

Four primary reactor auxiliary cooling systems (PRACS) are used A cooling coil is installed in the inlet plenum of each IHX and a heat transfer coil is installed in the mr cooler of ultimate heat sink Coolant is circulated by EM pumps supported by emergency AC power The air cooler consists of a blower, a stack, vanes and dampers The blower is supported by the emergency AC power The vanes and the dampers are operated by the emergency DC power Decay heat removal by natural circulation is possible to mitigate a total blackout event (loss of all AC power)... 

Two ring spargers, one for LPCS and the other for HPCS, are mounted inside the core shroud in the space between the top of the core and the steam separator base. The core spray ring spargers are provided with spray nozzles for the injection of cooling water. The core spray spargers and nozzles do not interfere with the installation or removal of fuel from the core. A nozzle for the injection of the neutron absorber (sodium pentaborate) solution is mounted below the core in the region of the recirculation inlet plenum. 

The reactor core support consists of a redundant beam structure on the bottom and the sides of the reactor vessel. A core barrel and support cylinder extends from the inlet plenum to above the core to contain the core and storage racks for temporary storage of offloaded fuel assemblies. The internal core structure is shown in Figure 6.8. 

PRISM has four submersed EM pumps to provide primary sodium circulation within the reactor vessel. The pumps are inserted through penetrations in the reactor closure. These pumps have no moving parts and no external shaft penetrations. The pumps draw cold pool sodiiun from an inlet plenum beneath the pump. Within the pump, the sodium enters the tapered inlet section of the pump duct. The sodium is discharged from the top of the pump and is passed radially outward into the pump outlet plenum from which it flows to the core inlet pleraun. 

During normal operation the reactor core coolant outlet temperature is kept constant at 290°C, the inlet temperature varies with the power level (260°C at full power). The primary circuit coolant and the pool water are in direct contact below the core inlet plenum and at the top of the riser. The heated water from the core will rise up through the riser since its density is lower than the pool water density (the chimney effect), and the flow rate is determined by the temperature differences. By controlling the speed of the recirculation pump its flow is adjusted to the flow rate up through the riser to maintain the lower hot/cold Interface at a constant position - no pool water will enter the primary circuit. 

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