29. The determination of the internal free volume and pressure of irradiated U0₂ Zircaloy-clad fuel pins

A technique is described for the measurement of the free volume and gas pressure inside BWR type fuel pins. The method employed is to pierce the pin and extract the fission gas into a volume measuring device. The evacuated pin is filled to a known pressure with helium. The volume of helium is measured. The internal free volume together with a known unavoidable dead volume can then be determined, and the internal pressure of the extracted fission gases can be calculated from the data obtained. The error of the system is less than 1# for free volumes of approximately 20 cc, and the