Neutronics model

It is evident that the Periodic Table of the elements does not have room to include information about all the isotopes of the elements. For that purpose the chart of the nuclides has been designed, which is based on the proton-neutron model of atomic... 

Table 2.1. Proton-neutron model of the nuclides [P = number of protons N = number of neutrons).

On the basis of the proton-neutron model of atomic nuclei the following combinations may be distinguished ... 

LOADING PATTERN EVALUATION 2.1. Reference neutronics model... 

GPT is a method of evaluating the effects of cross-section perturbations on quantities that can be formulated as integral responses, such as reactivity and power density. An initial requirement is an exact solution of a reactor physics model for a reference core configuration. In FORMOSA-P the reference neutronics model is a two-dimensional Cartesian [x-y] geometry implementation of the nodal expansion method (NEM) to solve the two-group, steady-state neutron diffusion equation ... 

This reference neutronics model gives excellent agreement with nuclear design licensing codes, such as the Electricitd de France code COCCINELLE (Version 2.2) [4], and therefore provides a suitable basis for the GPT model that is essential to the computational viability of the optimization process. 

Figure XXII-7 shows the SSTAR core map. The fuel lattice consists of cylindrical fuel rods arranged on a triangular pitch (the hexagonal geometry does not imply that the core is formed of individual hexagonal fuel assemblies or bundles it merely reflects the assumed nodalization used for neutronics modelling.) A central two low enrichment zones blanket, the three enrichment zones, and locations for shutdown and control rods are indicated in the figure.

The general field of problems described above, except in some special areas, may be treated by the well-known methods and analytical models of mathematical physics. It has already been noted that the most general description of the neutron population usually starts with a neutron-balance relation of the Boltzmann type. The Boltzmann equation was developed in connection with the study of nonuniform gas mixtures, and the application to the neutron problem represents a considerable simplification of the general gas problem. (Whereas in gas problems all the particles are in motion, in reactor problems only the neutrons are in motion. ) The fundamental equation of reactor physics, then, is already a familiar one from the kinetic theory. Further, many of the most useful neutron models obtained from approximations to the Boltzmann equation reduce to familiar forms, such as the heat-conduction, Helmholtz, and telegraphist s equations. These simplifications result from the elimination of various independent variables in the... 

Related to core design, neutronic modelling needs have been covered by benchmark data available worldwide. 

The TFM approach (Laureau et ah, 2015b Laureau, 2015c) has been developed specifically as a neutronic model able to take into account the precursor motion-associated phenomena and to perform coupled transient calculations with an accuracy close to that of MC calculations for the neutronics while incurring a low computational cost. This approach is based on a precalculation of the neutronic reactor response through time before the transient calculation. The results of the SERPENT MC code (Leppanen, 2013) calculations are condensed in fission matrices, keeping the time information. These hssion matrices are interpolated to take into account local Doppler and density thermal feedback effects due to temperature variations in the system. With this approach, an estimation of the neutron flux variation for any temperature and precursor distribution in the reactor can be very quickly obtained. 

Currently, LFR R D in ROK is focused on the further development of computer codes and corrosion-resistant materials as weU as the safety design criteria. System design codes for URANUS have been focused on neutronic models and safety analysis codes. It is planned that the developed codes will be verified by independent experts. Thermomechanical processing of corrosion-resistant materials developed for long-life core will be explored to achieve desirable combinarion of proven mechanical properties in fast neutron environment and innovalive corrosion resistance. The ROK LFR R D community has been participating in the GIF LFTi provisional Systems Steering Committee as an observer. It is planned that the safety design criteria for URANUS will be derived from the international collaboration. 

The block diagram used for coupled neutronic and thermal-hydraulic stability of the Super LWR is shown in Fig. 1.28. The neutronic model is used to find the forward transfer function G(i) and the thermal-hydraulic heat transfer and ex-core models are used to determine the backward transfer function H(s). The fi-equency... 

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