Calculation of Reactor Parameters

Analysis of Heavy- and Light-Water-Moderat Thermal Reactor Lattices Using ENDF/B Data, W. Rotkenstein (BNL) 

A number of water-moderated thermal reactor lattices which have been described in the literature have been reanalyzed with the HAMMER code using ENDF/B data. The calculations have revealed several areas in which ttie present analysis differs from those made previously. 

The most detailed comparisons between the present and previous calculations have been made for some of Hie standard heavy-water lattices for which full computattonal details were available at BNL. These lattices covered a wide range of rod sizes and volume ratios. The critical bucklii obtained by Roneck were used as iiqput to the HAMMER calculations and the broad- up ou t was for the same 4 groups with boundaries at 0.821 MeV, 

The thermal calculations made with the aid of THERMOS in the RAhlMER program yielded identical values of f as before, not withstanding the use of the Haywood kernel, as opposed to the Nelkin kernel which had been employed in the past. The value of was lower, however, by amounts ranging from 1.1% tor the tight and 0.9% for the loose lattices. The difference was traced down to ath and Oq (2200) of U. hi the 

In the epithermal groups, the ENDF/B data lead to rather larger values of S, Hie fast effect. For the standard latttces, Roneck bad not taken heterogeneity effects into account in group 2, from 0.821 MeV to 

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Model of ideal desaturation (model with plug flow regime) is the favorable approximation for calculation of reactor parameters [3,4,6] any cross-section normal for flow, weight hour space velocity w and flow s properties (pressure, temperature and reaction mixture structure) are uniform narrow distribution of reagents residence times in reaction zone Xpr diffusion in the axial line (coplanar mixing or turbulence) in comparison with weight hour space velocity is negligible low. 

D. Measurements and Calculations of Reactor Parameters The one-group (all thermal) model chosen to describe neutron behavior in a multiplying system yields the following critical equation ... 

In Fig. 1, various elements involved with the development of detailed chemical kinetic mechanisms are illustrated. Generally, the objective of this effort is to predict macroscopic phenomena, e.g., species concentration profiles and heat release in a chemical reactor, from the knowledge of fundamental chemical and physical parameters, together with a mathematical model of the process. Some of the fundamental chemical parameters of interest are the thermochemistry of species, i.e., standard state heats of formation (A//f(To)), and absolute entropies (S(Tq)), and temperature-dependent specific heats (Cp(7)), and the rate parameter constants A, n, and E, for the associated elementary reactions (see Eq. (1)). As noted above, evaluated compilations exist for the determination of these parameters. Fundamental physical parameters of interest may be the Lennard-Jones parameters (e/ic, c), dipole moments (fi), polarizabilities (a), and rotational relaxation numbers (z ,) that are necessary for the calculation of transport parameters such as the viscosity (fx) and the thermal conductivity (k) of the mixture and species diffusion coefficients (Dij). These data, together with their associated uncertainties, are then used in modeling the macroscopic behavior of the chemically reacting system. The model is then subjected to sensitivity analysis to identify its elements that are most important in influencing predictions. 

A number of important parameters, such as manium-235 RC loading, which provides the set energy output of RC RC dimensions, type and characteristics of heterogeneity etc. have been estimated according to intermediate multiversion neutron-physical calculations of reactors imder the known values of Nop, s and RC lifetime T =... 

Electrochemical reaction engineering deals with modeling, computation, and prediction of production rates of electrochemical processes under real technical conditions in a way that technical processes can reach their optimum performance at the industrial scale. As in chemical engineering, it centers on the appropriate choice of the electrochemical reactor, its size and geometry, mode of operation, and the operation conditions. This includes calculation of performance parameters, such as space-time yield,... 

Kinetic and hydrodynamic analyses, and methods for the calculation of the parameters of industrial reactors are sufficiently developed today [2-6]. Computer simulation is also popular because if we know the kinetic and hydrodynamic parameters of processes and the principles of reactor behaviour, it is not a problem to calculate process characteristics and final product performance. This principle is an adequate tool for the description of low and medium rate chemical transformations with uniform concentration fields and isothermic conditions which are easy to achieve. In this case, it is easy to calculate and control all the characteristics of a chemical process under real conditions. 

X-5] GRISHANIN, E.I., DENISOV, E.E., LIUBIN, A.YA., FALKOVSKY L.N.,. Mathematical model for calculation of coolant parameters in fuel assembly of light water cooled reactor with micro fuel elements. Tyazheloye Mashinostroyenie, No. 9, 11-20 (1995, in Russian). 

It is clear that although the exponential pile and criticality experiments would be required ultimately in any large-scale reactor development program, it would be desirable to obtain some preliminary experimental verification of reactor calculations by means of other more modest tests. One experiment which appears to be eminently suited to this purpose is based on the pulsed neutron-beam technique. This technique has been applied by several investigators to the determination of the thermal-diffusion coefficient and macroscopic absorption cross sections of reactor materials.More recently, it has been used by E. C. Campbell and P. H. Stelson in the study of short-lived isomers and for the measurement of reactor parameters of multiplying media. The experiment con-... 

There are several principal sets of problem layouts in chemical reaction engineering the calculation of reactor performance, the sizing of a reactor, the optimization of a reactor, and the estimation of kinetic parameters from the experimental data. The primary problem is, however, a performance calculation that delivers the concentrations, molar amounts, temperature, and pressure in the reactor. Successful solutions of the remaining problems—sizing, optimization, and parameter estimation—require knowledge of performance calculations. The performance of a chemical reactor can be prognosticated by mass and energy balances, provided that the outlet conditions and the kinetic and thermodynamic parameters are known. 

The main source of uncertainty for the majority of reactor parameters (such as k-eff) is the nuclear data used. However, calculational errors can be of large magnitude if appropriate numerical analysis is not done, for example if the diffusion approximation is used to analyse the sodium void effect in sodium plena [4.20]. 

Calculation of reactor pressure rise. The variable of interest is the maximum value of core pressure for a given set of parameter values. Although not exact, an analytic expression for the maximum pressure rise, Pm %, can be derived [36] for the case of an instantaneous reactivity addition. This is given by... 

The calculation of heat balance around the reactor is illustrated in Example 5-6. As shown, the unknown is the heat of reaction. It is calculated as the net heat from the heat balance divided by the feed flow in weight units. This approach to determining the heat of reaction is acceptable for unit monitoring. However, in designing a new cat cracker, a correlation is needed to calculate the heat of reaction. The heat of reaction is needed to specify other operating parameters, such... 

The utihty stream gets started at operating temperature and flow rate. In the following experiments, the utihty stream is heated so as to initiate the reaction. The main and secondary process tines are fed with water at room temperature and with the same flow rate as one of the experiments. Once steady state is reached, operating parameters are recorded. Process tines are then fed with the reactants, hydrogen peroxide and sodium thiosulfate. At steady state, operating parameters are recorded, and a sample of a known mass of reactor products is introduced in the Dewar vessel. Temperature in the Dewar vessel is recorded until equilibrium is reached, that is, until the reaction ends. This calorimetric method is aimed at calculating the conversion rate at the product outlet and thus the conversion rate in the reactor. The latter is also determined by thermal balances between process inlet and outlet of the reactor. Finally, the reactor is rinsed with water. This procedure is repeated for each experiment... 

Nevertheless, these modeling efforts are of little value when the practical implementation does not corroborate the above-calculated results. Ensuring the constancy of any parameter in the catalytic testing workflow, the reactor performance with regard to temperature distribution, gas distribution, constant feed... 

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