Considerations on the Detection of Failed Nuclear Fuel for CANDU Type Reactors

The defective nuclear fuel is the main source of contamination of the Primary Heat Transport System in a PHWR CANDU NPP. Thus, the continuous monitoring of the radioactivity of the heavy water in the PHTS to detect the failed nuclear fuel becomes a major objective. The radioisotopes monitored for the detection of the failed nuclear fuel are: ¹³³Xe, ⁸⁸Kr, ¹³⁵Xe, and ¹³¹I, respectively. The experiments performed at Institute for Nuclear Research (INR) Pitesti provided information related on the interval of the interest energies as well as about the moment of occurrence for these radioisotopes during the evolution of the fuel rod defect. The paper also describes the analysis mode of a gamma-ray spectrum, two on-line gamma-ray monitoring systems: GFP and DGFP (Gaseous Fission Products, respectively Digital Gaseous Fission Products) Monitor, both manufactured at INR Pitesti, and the qualitative analysis of the indicators for estimating the number of defective fuel elements. (author).