Laser system for boring and sampling in coated-particle fuel

A pulsed four-level solid-state laser (Nd3+ : yttrium-aluminum-garnet) was developed to determine concentration profiles of the fission product cesium in multilayered spherical coated-particle fuel. In addition, the system can be used for the simulation of cracked coatings by radial borings. The laser system with a Fabry-Perot-type resonator fulfills the requirements of small pulse width, absence of higher modes, and consistency of pulse energy. Control and timing is maintained with a ''Q switch'' and a ''Brewster polarisator''. Single-bore holes are approx. = 10 μm in diameter, and hole depths range up to 200 μm. The evaporated radioactive material is sampled with an efficiency > 95% on a glass plate which is used for γ and β counting. The formation of ''deep'' holes is theoretically explained by a self-channeling mechanism and briefly discussed. Techniques used for radial-distribution measurements for the fission product 137Cs in different irradiated coated particles are presented. Radially bored particles simulating cracked coatings are heat treated and fractional releases are measured