DEPLETION CALCULATIONS

Shine, K. P., R. S. Freckleton, and P. M. de F. Forster, Comment on Climate Forcing by Stratospheric Ozone Depletion Calculated from Observed Temperature Trends, by Zhong et al. Geophys. Res. Lett., 25, 663-664 (1998). 

Shine, K.P., R.S. Frcckleton and P.M. de F.Forster. Comment on Climate forcing by stratospheric ozone depletion calculated from observed temperature trends , Geophys.Res.lMt., 25. 663-664.1998. 

A third critical test for current ozone depletion calculations is the diurnal behavior of CIO as a function of altitude. Figure 15, taken from a recent treatment by Ko and Sze [6], summarizes the distinctive signature... 

As has been indicated in previous sections, the isotopic content at the end of the final burn cycle may be determined for each assembly or fuel subgroup by interpolating between burnups for which SAS2H/ORIGEN-S depletion calculations have been performed, based on the final burnup of the fuel. For a criticality condition obtained after the shutdown of the last cycle, it is necessary to perform decay calculations to account for the change in composition due to radioactive decay during the downtime prior to criticality. 

Reactivity allowances for manufacturing tolerances, uncertainty in depletion calculations, and other correction factors are added to the rack to determine... 

Contrary to ceramic fuel, such as UO2, the total fission product gases may be released into the plenum rather than locked in the fuel structure. Clearly some gases will be locked in pockets in the fuel alloy. However, the initial backfill pressure in the plenum and the total plenum size should be determined based on a 100% plutonium bumup. The time-dependent fission product gas source term can be determined from appropriate isotopic generation and depletion calculations. The pressure and clad requirements can be calculated from the corresponding fuel performance models. 

The nominal peak rod is defined as the fuel rod with the highest linear heat rate during normal operation. The highest linear heat rate is limited by the nominal design criterion of the MLHGR (39 kW/m), with which the cladding surface temperature is calculated by a single channel analysis and also hmited by the nominal MCST of 650°C. The nominal peak rod is determined by the thermal hydraulic coupled neutronic depletion calculation introduced in Sect. 7.4. 

The local peaking factor is considered in the three-dimensional core depletion calculation of the Super FR, while it is separately considered by the assembly bumup analyses coupled with the subchaimel analyses in the Super LWR (see Chap. 2). The reason is that the local power peaking is mainly caused by the zirconium hydride (ZrHi 7) layers located in the blanket assemblies, introduced in Sect. 7.3. The local power peaking must be calculated along with the radial power distribution considering the arrangement of both the seed and blanket assemblies in the whole core, while it instead depends on the control rods and burnable poisons inside a fuel assembly in the Super LWR. 

The unit cell depletion calculation reflects spatial and neutron energy group self shielding effects coming from the spatial distribution of group neutron flux and change of neutron spectrum. At first, one representative cell containing a fuel rod... 

For the thermal-hydraulic coupled core depletion calculation, the macroscopic cross sections for various states of coolant densities and bumup are calculated by a branch calculation. A reference depletion calculation is made first with the core average coolant density, in which the nuclide concentrations for each given bumup states are calculated with the reference neutron spectmm. Then, the branch calculation is conducted with the same nuclide concentrations but different coolant densities over the bumup, whose cross sections are to be interpolated in the core depletion calculation for given bumup states and coolant densities. The macroscopic cross sections are prepared at eight different coolant densities from 0.001 to 0.8 g/cc and at 11 bumup states up to 150 MWd/kgHM to cover aU the operatiOTi ranges of the coolant density and bumup. 

A fuel assembly is described by the 1/6 symmetric model as shown in Fig. 7.19 [1]. The assembly calculations are conducted for the same coolant densities and bumup state by the branch calculation as in the unit cell depletion calculation. Figure 7.20 [1] shows the concept of the branch calculation for the coolant densities. ASMBURN implemented in the SRAC system is used for the assembly depletion calculations. ASMBURN is also based on the integral neutron transport calculation of CPM. 

The core depletion calculation is based on the fine mesh Tri-Z finite difference neutron diffusion solution of the CITATION module. The core is described as the 1/6 symmetric Tri-Z fine mesh stmcture as shown in Fig. 7.21 [1], in which a black boundary condition and a rotational boundary condition are applied to the outer radial direction and symmetric line, respectively. The radial water reflector is placed in the outer region of the core, and it denotes the downcomer. The axial reflectors are placed in the bottom and top of the core and denote the lower and upper plenums. 

Fig. 7.21 Tri-Z description for core depletion calculation. (Taken from [1])...

The thermal-hydraulic coupling is not conducted at the individual bumup states, but after the core depletion calculation is finished this reduces overall calculation time. Figure 7.25 [1] shows the schematic diagram for the thermal-hydraulic coupling and equilibrium cycle search. The white boxes in the figure mean the original SRAC system. The shaded boxes represent the newly developed modules here. The cylindrical boxes are modified from the previous design method based on a two-dimensional R-Z model. 

From the previous discussion it is clear that we have no direct experimental evidence for stratospheric ozone depletion as a result of nuclear explosions. However, at least for altitudes above 30 km the sudden input of significant amounts of NO has clearly been shown to lead to large ozone destmctions. In August 1972 a major solar proton event deposited large amounts of nitrogen oxides in the stratosphere, leading to ozone depletions poleward of about 60°N. The estimated ozone depletions calculated with a photochemical model were confirmed by satellite observations of stratospheric ozone [61]. 

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