Pin power distribution

Pin power distribution / (burnup history, density, CR insertion)... 

For the verification of this code, three typical steady-states are calculated and compared to the results by the steady-state subchannel analysis code. Table 6.24 summarizes the three steady-state cases. Figure 6.62 shows the pin power distributions in those cases. The steady-state cmiditions are obtained using the transient... 

Core depiction ealcidation with pin power distribution... 

Reconstructed pin power distribution Fig. 7.23 Example of pin power reconstruction. (Taken from [1])... 

The main control module automatically prepares the inputs required for both neutronic and thermal-hydraulic calculations. It also produces the pin power distribution and bumup distribution, and then prepares the peak and average channels for each fuel assembly. The neutronic and thermal-hydraulic calculations are executed by the main control module internally and coupled to each other by pin power and coolant density distributions. 

In order to evaluate the influence of the subchannel heterogeneity, the pin power distribution is set as imiform and the axial power distribution is set as cosine with the maximum linear heat generation rate of 39 kW/m. Figure 7.43 [1] shows the mass flux distribution at the assembly outlet. Due to a relatively large hydraulic... 

Based on the two fuel assembly designs (Cases 2 and 3 in Table 7.18 [1]), subchannel analysis is carried out with the pin power distributions taken from the thermal-hydraulic coupled neutronic calculation in order to evaluate the MCST... 

The most advanced implementation of cofired-ceramic-packaging technology is the thermal conduction module (TCM) used in large-scale computers (IBM) (4, 72, 74). This package can accommodate over 100 flip-chip-bonded ICs on a 90 by 90 mm cofired ceramic substrate. The multilayer ceramic substrate contains 33 metal layers for chip pad redistribution, signal interconnection, and power distribution (Figure 14). Each chip contains 120 bonding pads, and 1800 pins are brazed to the bottom of the substrate for connection to a PWB. 

A velocity peaking factor of 1.15, derived from the radial power distribution, results in a peak velocity of 21.0 fps in the inner subassembly of the outer zone. These subassemblies are unorificed, thus setting the core pressure drop. The resultant pressure drop is 40.5 psi due to fuel pins, 16.5 psi due to the spiral wire wrap, and 6.4 psi due to entrance and exit losses. Pressure drop through the rest of the primary loop is 30.5 psi, giving a total pump head of 93.9 psi. Assuming a 75 % efficient pump and motor, this requires 1.25% of the net plant output to drive the primary pumps. 

Flux and power distributions near room temperature were made with Mn-Cu wire and a special bundle of individually removable pins. These measurements show good agreement with machine calculations. 

The power distribution in the Phoenix Core was determined from fission product activity traverses of " U pins, Pu wands, and removable fuel plates. The peak power, used to determine maximum operating power, was found to occur in the fuel-follower section of an interior shini element, about an inch below the bottom of the fixed fuel core. The ratio of this peak to the core average was 4.3 0.5. 

Additional data" also concern heterogeneous systems containing PuOa end UQ) in fuel pins that were made critical in water and in boronated water. Reported also are similar measurements with V(2.35)0> fuel i ns. Close agreement between calculated and observed gen-values, power distributions and rod worths was obtained."... 

Traditionally, the detailed power distribution within each assembly is deconstructed by using the combinations of the results from each of the previous reactor analysis steps. That is, the within-pin power profiles from Step 3 (based ultimately on the flux energy shapes from Steps 1 and 2) are superimposed on the power... 

The reactivity holddown supplied initially by borosilicate rods will be evaluated versus fuel depletion. These analyses will lead to determining the pin-pitch range as well as the fuel cycle length and the desired fuel shuffling patterns for optimal power distributions. 

The cladding temperature that was obtained by the three-dimensional coupled core calculation is the average temperature over the assembly. The peak cladding temperature of a fuel rod is necessary for the evaluation of the fuel cladding integrity. The subchannel analysis code of the Super LWR is coupled with the fuel assembly bum-up calculation code for this purpose [25]. Fuel pin-wise power distributions are produced for various bum-ups, coolant densities, and control rod positions. The pin-wise power distributions are combined with the homogenized fuel assembly power distribution to reconstmct the pin-wise power distribution of the core fuel assembly. The power distribution over the fuel assembly is taken into account as shown in Fig. 1.11. The reconstracted pin-wise power distribution is used in the evaluation of peak cladding temperature with the subchaimel analysis. 

Fig. 1.11 Coupling of subchannel analysis with three-dimensional core calculation (Reconstruction of pin-wise power distribution for the subchannel analysis)...

From these calculations, the interfuel assembly gap size is determined to be 4.0 mm. In this case, the local power peaking factor takes the lowest value of 1.06 without fuel rod enrichment controls. The relative fuel rod power distribution for the case with inter-fuel assembly gap size of 4.0 mm is shown in Fig. 2.38 [9]. The pin number (from 1 to 46) on the x axis of this figure corresponds to the pin number position shown in Fig. 2.37 [9]. Although the pin powers tend to be relatively high near the middle of the water rods, and relatively low at the corners of the water rods, the overall power distribution is flat. 

The original SRAC system does not include the capability for pin power reconstmction. It only provides the neutron fluxes and power distributions for the homogenized mesh structure. If the intra-assembly heterogeneity is not significant, the fluxes and power distributions for homogenized regions must be similar to those of local ones. On the other hand, the local power distribution in a fuel assembly may... 

The fuel pin temperature pattern as a function of burnup is influenced by the effect of fuel management on the neutron flux distribution. An indication of trends is shown in Fig. 3 for an idealized case where the linear pin power is maintained at a constant value of 16.2 kW/ft. The temperature gradient across the gas gap increases as fission gases dilute the helium in the gap. An increase in the center void is also expected with burnup with a resulting lowering of the maximum temperature. In the actual case, however, the effects of fuel cracking and restructuring could lead to a different pattern. 

---