Modal analysis of the helical tube in a small nuclear reactor's steam generator using a finite element method

A finite element method was used to simulate the vibration characteristics of helical tubes in a SMART reactor. It was found that vibrational characteristics of larger coil diameter helical tubes are different from smaller coil diameter tube (142 mm). The natural frequencies of the smaller ones were reduced by increasing helix angle. Natural frequencies of doubled length tube were also calculated. The difference in natural frequencies between the first order and the last order modes of the longer tube was found to be less than one third of the corresponding frequency difference in the original tube. It was also found that when the helix angle of a tube with 8 supports and coil diameter smaller than 100 mm is larger than 80°, the natural frequencies of the tube are lower than 700 Hz and this maybe induce fretting from the fluid through the tube.