Investigation of the CRUD Layer in Failed PWR Fuel Using an EPMA

This study characterizes a failed discharged fuel rod with 53 000 MWd/tonne U from a nuclear power plant in Korea. Chalk River Unidentified Deposits (CRUD) and the oxide layer were observed using an electron probe micro-analyzer (EPMA, SX-50 R, CAMECA, France) with wavelength dispersive (X-ray) spectroscopy. A normally irradiated cladding specimen was analyzed for comparison with the failed fuel rod. The analysis revealed an oxide layer with a thickness of about 10 μm and double-stratified agglomerates of CRUD species shapes. In contrast, sound fuel rods irradiated under conditions similar to failed fuel showed clusters in which Fe, Ni, and Cr were distributed. The main elements constituting the CRUD material, notably Ni and Fe, were located in the same position. Moreover, the thickness of the oxidized layer of the failed fuel rod was found to be significantly different from the thickness of the sound fuel rod.

Consequently, EPMA techniques offer the possibility of identifying and analyzing the CRUD phases and segregations in spent pressurized water reactor fuel. Although phases and segregations are small in terms of the amount expected to be present in background radiation, they nevertheless present a significant analytical challenge.