Hot-cold interface

As a last illustration, return to the original problem of Figure 1 and ask how much time the family in the suite has, if they are to be able to safely run at 1.65 m/sec to exit at the open end of the corridor. In order to run, the program HAZARD assumes that the hot-cold interface is at least 1.2 meters from the floor. The latest they could leave the suite is at 160 seconds following the dashed line F-F in Figure 6. 

Under these conditions, natural circulation between the cold pool, the core and the riser pipe will be established through the two hot-cold interfaces along an always-open natural circulation path. The pool of cold, borated water will then enter into the core and will shut the reactor down and remove the decay heat. In a certain sense, PIUS safety is based on the use of an essentially unstable coohng circuit, which needs active pump action to ensure stability during normal operation in off-normal conditions, the system automatically switches to its stable condition which also is a safe shutdown condition. 

A variable speed operation is required to control the "hot-cold interface in the lower density lock. The variable frequency electric supply is provided by two generators driven by a common variable-speed turbo coupling wth a flywheel of high mechanical inertia (about 5000 Kg m ). 

Both the IE I C systems (Protection and Safety related monitoring) and the control systons (characterized by the absence of control rods and by the "hot-cold" interface regulation inside the Density Locks) are designed utilizing a proven, distributed microprocessor-based technology. An advanced control room, vrith a wall panel information station and work stations for operators and supervisor is foreseen, taking into account the most recent achievements and improvements in the man-machine interface systems. 

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. 

REFERENCE PLANT The reactor concept is new, and there Is no reference plant yet. Develop programs under way are related to the thermal-hydraulic functions, the hot/cold Interface functions, the wet thermal insulation and the Once-Through Steam Generator design. References to plants in operation are valid for other systems and components, however. 

Fig. 8.26. Position at interwrapper hot-cold interface measured in HIPPO...

There is another "density lock" arrangement at a high location in the pool, connected to the upper riser plenum - the volume on top of the riser from which the water is drawn into the hot leg pipes. This upper density lock has a similar arrangement of tube bundles and a buffer volume above the hot/cold water interface level. There are also a number of small openings between the riser and the density lock. 

The hot/cold intraface level in the upper density lock is determined by the total volume of the primary loop water mass, when the position of the interface level in the lower density lock is kept constant. The temperature measurements for the interface level in the upper lock are basically used for reactor pool volume control purposes. (The reactor primary loop volume control utilizes level measurements in the pressurizer.)... 

Figure 3.25 Schematics and SEM micrographs of cross-sections of PLA vessel tubular elements realized under different temperature gradients. The warmer and the colder walls are inverted in the two sets of panels (left and right panels, respectively). The size of the radially oriented voids decreases by moving from the hot to the cold interface with the external template material. In both the investigated cases, PLA benzene solutions at different concentrations are used (A) 2.5%, (B) 5.0%, (C) 7.5%, (D) 10.0% (weight/volume). Adapted with permission from Ref. 308, Adv. Funct. Mater., 2010, 20, 2833-2841. Doi 10.1002/ adfm.201000922. Copyright 2010, Wiley-VCH Verlag GmbH Co. KGaA.

Consider a planar premixed flame front, such as that sketched in Figure 5.1.1. For the moment, we will be interested only in long length scales and we will treat the flame as an infinitely thin interface that transforms cold reactive gas, at temperature and density T p, into hot burnt gas at temperature and density T, A.-The flame front propagates at speed Sl into the xmbumt gas. We place ourselves in the reference frame of the front, so cold gas enters the front at speed = Su and because of thermal expansion, the hot gases leave the front at velocity 14 = Sl(Po/a)- The density ratio, Po/Pb, is roughly equal to the... 

Figure 6. Height above the floor of the interface between the upper (hot) and lower (cold) layers in the corridor, m, predicted by FAST (A-A) Mother-baby escape route (B-B) Father-boy escape route ...

Henry and Fauske (1975, 1976) have proposed a model to describe the events leading to a large-scale vapor explosion in a free contact mode. Their initial, necessary conditions are that the two liquids, one hot and the other cold, must come into intimate contact, and the interfacial temperature [Eq. (1)] must be greater than the homogeneous nucleation temperature of the colder liquid. Assuming the properties of both liquids are not strong functions of temperature, the interface temperature is then invariant with time. Temperature profiles within the cold liquid may then be computed (Eckert and Drake, 1972) as... 

Thermal uniformity in the cold zone was found to be from 0.01 to 0.02 °C, and that in the hot zone was found to be better than + 0.5 °C vertically and + 0.1 °C horizontally. Thermal gradients near the solid-liquid interface were achieved in excess of 30 °C cm " in the crystal region and up to 20 °C cm" in the melt. The growth of crystals was performed in a sealed transparent silica ampoule, which has two rooms for As source and GaAs polycrystalline, respectively, separated by a quartz diffusion barrier. For details of the growth process the reader is referred to Ref. 43. In this experiment the As source temperature T. was systematically reduced by 2 °C at 3 h intervals from 620 °C to 614 °C. 

Theories of a direct impact effect of gas molecules may also be called temperature discontinuity theories they make sense only when the cold powder and hot reaction products are adjacent to one another. If the temperature of the powder and gas at the interface are identical, then activation as a result of thermal motion in the solid body is much more probable, not activation by the impact of a gas molecule. 

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