Session: 02-13: Structural Evaluation, Performance Assessment, Multiphysics Coupling - III

Paper Number: 135973

135973 - Improvement of Thermal Feedback Model in Bamboo-Core From Parallel-Channel to Subchannel 

Abstract: 

     The coupling between neutronics and thermal-hydraulics is critical for PWR-core analysis, because it has a direct impact on the core power distribution. In most analysis codes, the parallel-channel model, which neglects the transversal mixing phenomena between adjacent channels, is usually employed. Furthermore, most of them assume that the flow distribution at the inlet of the core is uniform since it is hard to know exactly. However, the actual distribution of flow at the core inlet exhibits certain unevenness, maybe 10% difference according to typical experiments. And in actual operation, variations in operational conditions can also lead to changes of inlet flow distribution.

 

     Thus, the parallel-channel model of thermal feedback in the core calculation program Bamboo-Core was improved to a subchannel model. The sub-channel model can reduce the impact of errors in the input parameter of core inlet flow distribution by considering the interaction between adjacent channels. The subchannel model is based on a homogeneous model for the two-phase condition employed for the light water within the reactor core and is capable of simulating both steady-state and transient scenarios. In the model, only the velocity in the axial direction exists, without considering the velocity in other directions. Its essence is to consider the influence of adjacent channels on the axial velocity through additional source terms. The empirical factors used in the subchannel code can come from COBRA or can be determined through the PSBT database. It is worth noting that these values are used for mixing between subchannels of the rod bundle, not between assemblies. By introducing a transport coefficient, the subchannel code can define an assembly or 1/4 assembly as a subchannel and can simulate the transversal mixing between those channels. The strategy of N/TH coupling is Picard iteration, which can achieve high-order time precision.

 

     The improved software was validated by comparing it with measured data from the Nuclear Power Plant. The first three operational cycles of a M310 unit are going to be shown in this summary. From the quantitative results, it can be found that the thermal feedback using the subchannel model, compared to using the parallel-channel model, will make the assembly with higher local power, higher power, and the assembly with lower local power, lower power. At the same time, through simulation calculations using the parallel-channel model and sub-channel model for two different inlet flow distributions in a CNP650 core, it was observed that alterations in flow distribution had a lesser influence on power distribution with the sub-channel model compared to the parallel-channel model. In other words, the results with the sub-channels model were more robust.

Presenting Author: Hengrui Zhang Xi'an Jiaotong University

Presenting Author Biography: Hengrui Zhang (1998-), a male, master's degree candidate, is currently mainly engaged in research and software development of physical analysis methods for pressurized water reactor cores.

Authors:

Hengrui Zhang Xi'an Jiaotong University
Yunzhao Li Xi'an Jiaotong University
Sicheng Wang Xi'an Jiaotong University
Yisong Li Xi'an Jiaotong University
Yiling Liang Xi'an Jiaotong University