Local heterogeneity effects on small-sample worths

An ideal technique for measuring small-sample worths would introduce the sample without otherwise disturbing the core unit cell. The standard technique used in ANL fast reactor critical experiments entails several distortions to the unit cell (local heterogeneities) that currently must be neglected in calculations. A large set of experiments is presented that were designed to determine how large the neglected local heterogeneity effects are. The experiments show that the size of the effects varies with sample type and reactor type. Fissile sample worths are affected by up to 6%, which accounts for a significant portion of the long standing central worth discrepancy