Lower plenum

Because of their low thermal conductivity, high temperature capability, low cost, and neutron tolerance, carbon materials make ideal thermal insulators in nuclear reactor environments. For example, the HTTR currently under construction in Japan, uses a baked carbon material (Sigri, Germany grade ASR-ORB) as a thermal insulator layer at the base of the core, between the lower plenum graphite blocks and the bottom floor graphite blocks [47]. 

Analyses of the effects of breaking instrument tubes at the PWR vessel lower plenum (Fletcher and Bolander, 1986) One safety concern for nuclear reactors is related to... 

The amount of fluidization gas required to maintain constant fluidization velocity scales linearly with the cross section of the bed. However, for large fluidized beds, one of the major concerns is the even distribution of the fluidization gas across the whole area of the bed. Thus redesign of the air distributor and lower plenum modification may be required. 

Figure 3 shows the nodalisation of the HTTR-IS system model. The reactor consists of the internal flow path (P2), permanent reflector blocks (HS25), upper plenum (B4), reactor pressure vessel (RPV) (HS30), vessel cooling system, reactor core bypass flow (P10), lower plenum (B12) and reactor core. The... 

Using this approach, corrosion potentials have been calculated for various components in the heat-transport circuit of a BWR, as shown in Fig. 19, as a function of the concentration of hydrogen added to the feedwater. The calculations predict that the lower plenums and recirculation systems of many BWRs can be protected by hydrogen water chemistry, but that those components that are exposed to high radiation fields and/or high concentration of radiolysis products cannot be protected, at least under full-power operating conditions. Similar calculations have been carried out [46] for in-vessel materials in PWRs, in order to explore the susceptibility of various components to intergranular fracture. 

CC Core channel CB Core bypass UP Upper plenum MP Mixing plenum UD Upper downcomer LD Lower downcomer RS Recirculation system JP Jet pump BLP Bottom lower plenum TLP Top lower plenum. . . . . ... 

Fig. 25 Plots of the concentrations of oxygen (ppb), hydrogen (ppb), and hydrogen peroxide (ppb), and the calculated ECP (mVsHE) at the top inner surface of core shroud as a function of time along the CEP. Note that the concentration of hydrogen is considerably lower than the feedwater hydrogen, because of the mixing of flows from the lower plenum and because hydrogen is stripped from the coolant by boiling in the core.

Lower Plenum Support Structure Failure Modes ... 

Lower Plenum Floor Failure Modes and Effects 4.4-16... 

Includes all fluid flowing into the lower plenum via the core exit... 

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