Hot channel factors

T4. Tong, L. S., Chelmer, H., and McCabe, E. A., Hot channel factors for flow distribution and mixing in core thermal design, WCAP-2211 (1963). 

The monitoring uncertainty and operational transient margin is to ensure that the minimum DNB ratio is calculated at the worst operating condition. The assumed worst operating condition consists of a power surge of 12% in a worst power distribution (power skew at top), accompanied by an inlet coolant temperature elevation of 4°F (2°C) and a pressure swing of 30 psi (0.2 MPa). A set of worst hot channel factors in core life should also be used in evaluation of the worst power distribution. Such an assumed worst operating condition is obviously overly... 

The subassemblies are designed to reach a peak temperature rise of 300 X 1.177 = 353°F. The hot-channel factor of 1.29 results in a maximum temperature rise of 456°F. The average core temperature rise is 319°F. 

Measurement of hot channel factors (as allowed by facility design and operational limits and conditions) and effects of control rod positions on nuclear instrument indications. 

The design criteria are to have no coolant boiling and no fuel melting and to ensure that temperature does nor exceed 650°C for the primary boundary structure. Temperatures are evaluated for the nominal hottest pin, which is assumed to have a nominal hot channel factor of 1.53 without the engineered safety factor. The outlet coolant temperature is 593°C in normal operation. 

An upper limit for the steam quality or, correspondingly, a lower limit for the water content are substantially dictated by the heat transfer crisis. The CIRENE design Is based on a critical flux correlation derived both from full-scale experiments performed in a purposely made 7 MWe heat transfer loop and from the analysis of literature data. A safety factor of 1.5 was adopted against the crisis (i.e., the ratio of channel power in nominal conditions to channel power at the crisis), including the intrinsic uncertainty margin of the correlation and the hot channel factor as well. 

Axial and radial power distribution and hot channel factor ... 

Limits on the power distribution of the core and margins to these limits must be established to preclude fission product release from the fuel due to fuel and cladding failure. In pressurized water reactors (PWRs) the ultimate limit is the limit on the departure from nucleate boiling ratio (DNBR), which quantifies how close the core is to experiencing fuel melting. Inherent to the DNBR determination are core power distribution parameters such as assembly average powers and hot channel factors (HCFs). Since these parameters help make up the DNBR, limits placed on the DNBR can be translated into limits on these power parameters. 

The engineering temperature rise hot channel factors account for flow conditions and tolerances of the hot coolant channel. They arise from the tolerances of dimensions, fissile contents, data processing, and so on. The engineering factors consist of two parts. One is the coolant temperature rise hot channel factor. The other is the film temperamre rise hot channel factor. The engineering temperature... 

The uncertainty of heat transfer correlation can be treated in two ways one is to use a corresponding engineering hot channel factor, the other is to treat this uncertainty separately with parametric uncertainties. The latter is applied to this study as is done for the Super LWR in Chap. 2. The uncertainty of the heat transfer correlation is evaluated by comparing with the Oka-Koshizuka correlation and the Dittus-Boelter correlation in the high coolant enthalpy region. The uncertainty is evaluated as 6.33°C. It is taken as the correlation uncertainty because the hot spot is always in the high coolant enthalpy region. 

Next, the axial profile of the hot-channel coolant temperature can be computed using the axial power profile and the engineering hot-channel factor. The former can be estimated with sufficient accuracy for design since the analysis is relatively insensitive to the uncertainty involved. However, the hot-channel factor is of considerable importance and represents a design challenge. The subject will be discussed separately later. 

Hot-channel factors play the same important role in the thermal design of LMFBR cores as they do for light water reactor cores, namely, they relate performance limitations to average values upon which reference specifications are usually based (7). 

The nuclear hot-channel factor is therefore 1.071 for the enthalpy rise in a given coolant channel. 

As for local thermohydraulic characteristics, such as hot spot factors, temperature nonuniformity in the irregular arrangement of pins etc., of critical importance are the processes of inter-channel exchange. Comprehensive studies of inter-channel heat and mass transfer in the bundles of smooth pins with ribs or wires provided a basis for development of calculation techniques. 

In addition to the more relevant case that is defined as the average core, the coolant flow and heat transfer for the hot channel was analysed.The main results of the HEATHYD calculation have been compiled on Table 2 for the average and hot channel case at nominal power and overpower of the 114 %, respectively. In all cases, hydraulic calculations show 4.08 m/s for the coolant velocity and 0.44 bar as total pressure loss. The result of the heat transfer part depends on the total power. In case of overpower and hot chaimel, it amounts to 3.56 including axial radial and engineering factor. The results of all calculations have been depicted in the folloAving figures. In Fig. 4 and Fig. 5, the clad surface and coolant temperatures have been represented for four cases as a function of the active length of the fuel plate. 

Nuclear hot factors are employed in the calculation to consider the effects of the power distribution in the core, including the radial nuclear hot assembly factor /, the axial nuclear hot assembly factorand the linear heat flux nuclear hot spot factor/p. The factoris defined as the ratio of the hot assembly power to the core average assembly power and is used to determine the power level of the hot assembly. The factor is defined as the ratio of the maximum planar power to the average planar power in the hot assembly and is used to describe the axial power distribution in the hot assembly. The factor fp is defined as the ratio of the maximum linear heat flux to the core average linear heat flux and is used to determine the power distribution of the hot channel and the power of the hot spot of the core. 

Subfactors may be combined either statistically or by the product method, as appropriate, or through the use of a computer code. In one computer approach (8), parallel cases of the nominal and hot-channel enthalpy rise are calculated under the same pressure potential corresponding to each of the limits expressed by the statistical factors affecting flow... 

The Mean particle size (MPS) of coal is an important factor for the COREX Process because a decrease in the MPS reduces the permeability of the char bed resulting in gas channelling, which drops the hot metal temperature and quality. To maintain consistency, the MPS of the coal should be maintained within 20-30 mm, which is a very important factor for efficient plant operation. The COREX technology coal should be sized at +16 mm with a top size as high as 70-80 mm. Fines coal (—16.0 mm) included with the sized coal is separated at the COREX steel mill and used for either... 

Touch Includes the Sensing of Pressure, Temperature, and Other Factors Touch, detected by the skin, senses pressure, temperature, and pain. Specialized nerve cells called nociceptors transmit signals that are interpreted in the brain as pain. A receptor responsible for the perception of pain has been isolated on the basis of its ability to bind capsaicin, the molecule responsible for the hot taste of spicy food. The capsaicin receptor, also called VRl, functions as a cation channel that initiates a nerve impulse. 

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