Neutron kinetics

Inelastic neutron scattering, on the other hand, usually employs a monochromatic neutron beam and records the intensity of the scattered neutron beam as a function of neutron kinetic energy. Such inelastic collision spectra are monitored as a function of the applied field and the (usually low) temperature. The observed peaks then represent the energy differences of thermally populated and excited unpopulated multiplet states. Inelastic neutron scattering experiments can be conducted using triple-axis, backscattering, or time-of-flight spectrometers. 

To determine physical and heat engineering SRU parameters, a calculated study of potential emergency situations related to water penetration into the core was performed. Mathematical description of the processes was based on dot description of both the neutron kinetics and the equations for heat transfer in the storage facility container (under such container SRU arranged within steel cup with frozen alloy was understood). 

The neutron kinetics was described with due regard for six groups of delayed neutrons. The core reactivity changes were determined by temperature effects of reactivity of fuel elements and the alloy as well as by water penetration into the core. 

Summary of neutron kinetics equations reactor power... 

The neutron kinetic energy E is related to the neutron speed by... 

If B + AT /iA + 1) E, fission may occur and the final state is the one shown as fission products in Fig. 3.18. For E = 5.3 MeV and B = 6.4 MeV. Therefore, even a neutron with zero kinetic energy may induce fission, if it is absorbed. For which is formed when a neutron is absorbed by U, B = 4.9 MeV and E = 5.5 MeV. Therefore, fission cannot take place unless the neutron kinetic energy satisfies... 

Example 11.4 The following table gives neutron-absorption cross-section values and their errors as a function of neutron kinetic energy. Determine the analytic function that fits this data set. 

The cross section for this exothermic reaction peaks at a deuteron kinetic energy of about 120 keV with a value of about 5 b. The neutrons produced have an energy of about 14 MeV. (The neutron kinetic energy changes slightly with the direction of neutron emission.) The maximum neutron flux provided by a neutron generator is of the order of 10 neutrons/(m s). 

In order to get a realistic picture of the nature and safety significance of a LPS event, it is sometimes necessary to do a very detailed and comprehensive analysis. A good example of this is a boron dilution event for which models of mixing and 3D neutron kinetics are needed in combination with modelling of primary circuit thermal hydraulics. 

WWER neutron kinetics, simple models of coolant mixing test facility... 

RBMK reactors have large cores, where local effects play a significant role in safety analyses of the several initiating events. For this reason, it is appropriate to use a 3-D neutronics code with a built-in multichannel thermohydraulic model. In addition, a 3-D neutronics code should be employed for compiling input data for point neutron kinetics (commonly involved in thermohydraulic codes) when events such as LOCAs are analysed. 

The spectrum of thermal neutrons is characterized by an equilibrium of the neutrons kinetic energy with that of the surrounding moderator. Like for any gas the speed distribution can be described by the MaxweU equation ... 

The spherical critical mass of 93% " ll enriched uranium metal which has teen used as a benchmark problem for verification of calculational methods is based on foe delayed critical mass measurements made on Godiva corrected to standard conditions. A near Spherical mass of U(93.2), recently surplused from an ei erimental program examining fast reactor behavior with an accelerator booster, was re-machined to a spherical radius of 3.466 in. Tte device is to be used in a study of neutron kinetic parameters. The data obtained for the delayed critical configuratian confirm the reevaluated critical parameters recently reported by Man-sen and Paxton. ... 

She heat transfer and neutron kinetics equations were standard. (See Section 7 8) Delayed neutron constants were characteristic of fuel exposed to 1000 IM)/T Safety r strengths of 20 kO and 60 x 10" considered. 

It is sometimes more convenient to describe the neutron population in terms of the neutron kinetic energy instead of the speed. In this event, the neutron density and the flux are defined per unit of energy. In order to show the relationship between the speed and the energy definitions, let us consider the function... 

Fuel channel box bow is a well known problem for BWRs. In principle, channel box bow is considered in the core design by neutron-kinetic and thermal-hydraulic calculations. Therefore, the degree of box bow must be supervised. Additionally, minimizing the box bow must be achieved by specific measures during design and construction of the channel boxes. 

TWINKLE is a multidimensional spatial neutron kinetics code, whieh is patterned after steady-state codes currently used for reactor core design. The code uses an implicit finite-difference method to solve the two-group transient neutron diffusion equations in one, two, and three dimensions. The code uses six delayed neutron groups and contains a detailed multi-region fuel-clad-coolant heat transfer model for calculating point-wise Doppler and moderator feedback effects. The code handles up to 2000 spatial points and performs its own steady-state initialisation. Aside from basic cross-section data and thermal-hydraulic parameters, the code accepts as input basic driving functions, such as inlet temperature, pressure, flow, boron concentration, control rod motion, and others. Various edits are provided (for example, channel-wise power, axial offset, enthalpy, volumetric surge, point-wise power, and fuel temperatures). 

The plant response to an inadvertent core makeup tank or CVS actuation is analysed by using a modified version of the computer program LOFTRAN which simulates the neutron kinetics, reactor coolant system, pressuriser, pressuriser safety valves, pressuriser spray, steam generator. 

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