Temperature Conditions 1 Design Criteria

In contrast to the combustion in stabilized flames, flameless oxidation is mixture and temperature controlled and is achieved by specific flow and temperature conditions. A prerequisite for a stable flame front is a balance between flow and flame velocity. This is true in premixed and in diffusion flames and stability depends on species concentrations, flow velocity, flow field, temperature, pressure, and other parameters. Creating flow conditions for flame stabilization is an essential burner design criterion. Swirl or bluff body are most often used to create stagnation points or areas of low velocity for stabilization. The species concentration also plays an important role. Air, with an oxygen content of 21% can create a flammable mixture with... 

For the specific jacket-cooled CSTR process considered in this section and the next, a simple heuristic approach can be used to incorporate quantitatively the limitations of controllability into the steady-state design. The idea is to specify a design criterion that ensures good controllability. In the reactor temperature control problem we use the criterion of a specified ratio of the maximum heat removal rate to the heat removal rate at design conditions. This simple approach is easily understood by designers and operators, and it requires no dynamic simulation or control analysis. We illustrate its usefulness in the following section to determine the besf reactor operating temperature. 

From the thermal considerations in Sect. 5.3.3.2, the core power, feedwater flow rate and feedwater temperature are designed as 20 and 35% of the rated values and 280°C, respectively. The decay ratios of coupled neutronic thermal-hydraulic stability are then calculated with these conditions. The results are shown in Fig. 5.55 [10]. The stability criterion is satisfied with sufficient margin during... 

This gives point b in Fig. 19.4, thus the amount of catalyst needed in the first stage as well as the outlet temperature from that stage. Especially in preliminary design it may not be convenient to use the criterion of Eq. 1. A simple alternative is a trial-and-error search. Usually two or three carefully chosen trials keeping away from low rate conditions will yield a good design, close to the optimum. 

FUNCTION Remove Core Heat This function refers to the necessity to remove the reactor heat during off-normal conditions so that fuel temperatures are not excessive. Since the design selections needed to meet Criterion II and Criterion III limit chemical attack and fission heat generation, the principal requirement is to assure reliable decay heat removal. 

If pressure is redueed, the walls of the vessel will be exposed to less foree and the risk of explosion if the temperature increases will be lower. As a general criterion, API recommends the installation of devices able to reduce the pressure up to approximately 7 bar (relative) or up to half of the design pressure in 15 minutes. If the ground is sloped and the vessel is thermally insulated, this time can be longer. The depressurization can require a remote control valve besides the safety valve. The released material should be eliminated in safe conditions (Shebeko et al., 1996), e g., with a torch. It should also be taken into account that in some eases a strong depressurization ean cause extremely low temperatures, leading to fragile eonditions in the steel. 

Creep. The gradual extension of a lap-shear joint can be observed under conditions in which the adhesive is near or above its Tg, the stress is relatively high and its shear component much greater than the cleavage (hydrostatic) component. What little data is available refers to polyvinyl-P/F and to a modified epoxy of undisclosed composition. If the absence of creep is important in design then an adhesive with Tg well above the important working temperature must be chosen. In the absence of other data, the heat distortion temperature can be used as a criterion. 

The same plant characteristics as in Chap. 4 are used for the safety analyses. The initial conditions are shown in Table 6.10. The hottest cladding temperature of 650°C is the same as the criterion applied in the three-dimensional core design... 

The AFS delay after detecting one of the actuation conditions is taken from that of the turbine driven RCIC system of BWRs. Its influence on the peak temperature for the loss of offsite power event is checked. Due to the water source effect of the water rods, the core coolabihty is not influenced by the AFS delay. On the other hand, the net reactivity tends to increase with the shorter AFS delay because the AFS supplies cold coolant to the core. The peak temperature is higher with the shorter AFS delay. The increase in the cladding temperatiue is about 450°C for a delay time of 15 s and 330°C for 100 s. In spite of the wide variatiOTi of the AFS delay that would cover the actual design point, the degree of the temperature variation is well below that of the safety margin to the criterion. 

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