The activities performed in verification of reactor fuel rods and assemblies by International Atomic Energy Agency (IAEA) safeguards inspectors include measurements of the length of the enriched uranium sections in fuel assemblies and fuel rods. These measurements are normally made with the IAEA hand-held gamma monitor (HM-4) on fuel elements containing only enriched uranium. Many fuel rods currently in use contain natural uranium end sections and several different {sup 235}U enrichment zones. To support development of standard procedures for IAEA nondestructive assay (NDA) measurements, a field measurement campaign was carried out to evaluate the FM-4 measurements and to investigate the feasibility of extending the HM-4 measurements to fuel rods and assemblies containing both natural and enriched uranium sections. The results show that the enriched fuel length can be measured to within {plus_minus} 1 to 2 cm in the presence of natural uranium sections and to within {plus_minus} 0.5 = when only enriched uranium is present. Based on the results from these measurements, a standard procedure, ``Measurement of Active Fuel Length in Fuel Assemblies and Fuel Rods Using the HM-4,`` has been drafted for review by the IAEA.

The activities performed in verification of reactor fuel rods and assemblies by International Atomic Energy Agency (IAEA) safeguards inspectors include measurements of the length of the enriched uranium sections in fuel assemblies and fuel rods. These measurements are normally made with the IAEA hand-held gamma monitor (HM-4) on fuel elements containing only enriched uranium. Many fuel rods currently in use contain natural uranium end sections and several different [sup 235]U enrichment zones. To support development of standard procedures for IAEA nondestructive assay (NDA) measurements, a field measurement campaign was carried out to evaluate the FM-4 measurements and to investigate the feasibility of extending the HM-4 measurements to fuel rods and assemblies containing both natural and enriched uranium sections. The results show that the enriched fuel length can be measured to within [plus minus] 1 to 2 cm in the presence of natural uranium sections and to within [plus minus] 0.5 = when only enriched uranium is present. Based on the results from these measurements, a standard procedure, Measurement of Active Fuel Length in Fuel Assemblies and Fuel Rods Using the HM-4,'' has been drafted for review by the IAEA.