The fluctuating mechanical forces on a pipe-bend in a PWR system

Measurements and calculations are reported which represent and attempt to estimate the magnitude of the fluctuating mechanical forces in a pipe forming part of the primary loop of the H B Robinson 2 PWR system. The power spectral density of the fluctuations of the force exerted by water flowing through a smooth pipe bend of 900C, and also the probability density of force fluctuations were shown to have the same shape as that of the flow fluctuations. Fluctuations in flow as evidences by the output of a primary loop flowmeter were amplified and recorded on magnetic tape in the form of a time-series in digital form. The time series was analysed to give a power spectral density an probability density function. The estimation was made for a frequency range of 6.5 to 7.5 Hz. The number of cycles of fluctuating stress may be calculated as approximately 2 x 108/y. (U.K.)