Session: 02-10: Physics and Transport Theory - II

Paper Number: 132052

132052 - Further Research on Neutron Noise Calculation Under Plate Fuel Failure Conditions Based on Frequency Domain Finite Element Method 

Abstract: 

During reactor power operation, fuel element cladding damage may occur due to design and manufacturing defects, fluid erosion, flow induced vibration, abrasion between the grid and fuel cladding, chemical corrosion, and interaction between the fuel core and cladding. Under normal operating conditions of reactors, a certain degree of fuel element damage is allowed. Currently, the design index for the fuel element damage rate of pressurized water reactors at home and abroad is 0.25%. There are currently two measurement methods for operating units in response to fuel element damage accidents: fuel accident monitoring and primary circuit dose monitoring. Fuel accident monitoring depends on the measurement of delayed neutron activity flowing out of the core to determine whether there is fuel damage, while primary dose monitoring depends on measuring the activity of fission products and the concentration of inert gases flowing into the primary coolant to determine whether there is fuel damage. The two measurement methods require a long time for the measured fluid to be discharged from the core outlet to the measurement device, and the limited damage event is also troubled by the lower limit of dosimeter measurement after being widely diluted by the total flow rate of the first circuit. For plate shaped fuel cores, the axial flow of delayed neutron precursors after fuel element failure will disrupt the inherent balance of the normal core, resulting in transient changes in neutron noise. Based on this approach, the author conducted the following work in the ICONE30 report: 1) Based on the Galerkin finite element framework, a transient frequency domain calculation model for fuel cladding damage conditions was established, and the original FEMN program was extended to calculate neutron noise caused by transient flow of delayed neutron precursors; 2) Based on the transient situation of fuel damage in a specific core, an extended FEMN is used for quantitative calculation. It was found that: 1) after the damage of the plate fuel assembly, the neutron noise excited by the delayed neutron precursors flow is the superposition of global and local effects in space, rather than a linear amplification of static flux; 2) For typical plate shaped fuel assembly faults, from the observation results of detector position numerical calculation, the neutron noise spectrum excited by transient operating conditions rapidly decays along the frequency axis, and the noise spectrum waveforms of fast group neutrons, thermal group neutrons, and delayed neutron precursors are not significantly different; 3) It is necessary to study component faults at different positions and degrees, and compare their noise spatial distribution with the observed spectrum of detector positions. On the basis of the above work, this study investigates the damage of plate shaped fuel assemblies at different component positions and degrees in the core, and investigates their impact on neutron noise at detector positions. This subtle difference is expected to be further used for online monitoring and accurate positioning of component faults in reactors.

Presenting Author: Baoxin Yuan China Academy of Engineering Physics, Insititute of Nuclear Physics and Chemistry

Presenting Author Biography: PhD, Associate Researcher, long-term dedicated to reactor operation and application research, mainly focusing on reactor physics, neutron noise, and multi physical field numerical calculations

Authors:

Baoxin Yuan China Academy of Engineering Physics, Insititute of Nuclear Physics and Chemistry
Huiyi Lv SouthWest University of Science and Technology
Herong Zeng China Academy of Engineering Physics
Jie Zheng China Academy of Engineering Physics
Zihan Chen China Academy of Engineering Physics
Huan Huang China Academy of Engineering Physics
Songbao Zhang China Academy of Engineering Physics
Dazhi Qian China Academy of Engineering Physics