Moving meshes to solve the time-dependent neutron diffusion equation in hexagonal geometry

A new solution for the control rod cusping problem in the three-dimensional pin-by-pin core calculation is proposed in this paper. The current advanced nodal code resolves this issue by estimating ...

A Simple and Efficient Control Rod Cusping Model for Three-Dimensional Pin-by-Pin Core Calculations

Control rod treatment for FEM based radiation transport methods

Comparison of two three-dimensional heterogeneous variational nodal methods for PWR control rod cusping effect and pin-by-pin calculation

A nonoverlapping local/global iterative method with 2-D/1-D fusion transport kernel and p-CMFD wrapper for transient reactor analysis

In neutronics calculations control rods are modeled incrementing the cross sections by an amount interpolated in parametric tables. This amount depends on the average physical conditions of the node. For nodes containing the tip of a rod, a weighting factor must be applied in order to keep the correct reaction rate. Several methods exist to compute this factor. The simplest one is to take the volume fraction occupied by the tip of the control rod in the node. This method produces what is known as rod cusping: a strong discontinuity appears in the control rod worth versus rod insertion curve. The method developed here, based on a physical equivalence, allows a significant reduction of this effect.

Reducing rod cusping effect in nodal expansion method calculations

Core monitoring systems based on online 3D calculations need algorithms to permit to compensate the inaccuracies in the neutronic model and in the process and incore detectors signals. It is presented here a method to reset the core neutronic model in order the computed flux be in agreement with the detectors response. The method is based on an equivalence procedure which permits to determine a reset parameter, called pseudo buckling, acting on the data of the model. It will be then presented some results showing the performance of the method.

A method to reset a 3d on line core model on incore measurements

A generalization is proposed of a recent method (the Migration Mode Method) based on the expansion in energy of the flux in terms of base functions. This new method, which we shall identify as Generalized Mode Method (GMM), aims at extending a similar approach to systems the physics of which is particularly sensitive to neutron distribution in energy, in particular, MOX fuelled PWRs and HTGRs. With this new method the (model and physical) parameters entering into the base functions are adjusted through fitting procedures basing on integral data obtained from precise numerical simulations and, possibly, from measurements. First tests relevant to a simple mathematical example at zero dimensions, considering an average composition representative of the DB-MHR reactor core and using two and four base functions have been made. In this exercise, the 26 group ABBN nuclear data library has been used, the 26 th , thermal group of which is substituted by a maxwellian distribution truncated at 0.215 eV. As well known, the ABBN library is formed by infinite dilution cross sections and factors allowing to take into account for each element for the self-shielding effects as function of the background macroscopic total cross-section. These factor are pre-calculated assuming within each group a neutron distribution t E / 1 Σ , which is the same distribution, considered for the definition of the base function above the thermal energies. The results are encouraging, indicating that the neutron spectrum is well reproduced in a variety of different system states and conditions. Further spacedependent tests are however required to validate the method.

Framatome Anp

Papers

Reducing rod cusping effect in nodal expansion method calculations

A method to reset a 3d on line core model on incore measurements

The generalized mode method (gmm) for reactor calculations