Irradiation is requested in support of an ASTM International Inter-Laboratory Study (ILS) of the E1297 Standard Test Method for Measuring Fast-Neutron Reaction Rates by Radioactivation of Niobium. The Nb-93 (n,n′) Nb-93m reaction is widely used for neutron metrology in nuclear power and test reactors. This reaction is desirable because its energy response range is similar to the fast neutron (E > 1.0 MeV) fluence rate response function that is commonly used as a material damage correlation parameter. In addition, the 16-year half-life of the reaction product enables monitoring of materials over relatively long time intervals. Alternative reactions with similar energy response ranges and reaction product half-lives require fissile target material, such as U-238(n,f) and Np-237(n,f), which may be undesirable because of regulatory and logistical challenges associated with handling fissile material. In spite of its utility and its increasingly common use - particularly for nuclear power reactors - there has never been a formal comparison of measurement practices for the Nb-93 (n,n′) Nb-93m reaction using this ASTM standard. This ILS aims to establish obtainable precision and bias associated with the use of ASTM International Standard E1297 to make this measurement. ASTM has agreed to support shipping and material costs associated with this study, but irradiation of the Nb-93 samples is requested.
One sheet of IRMM-526B Niobium will be cut to create approximately 24 samples of target material, with each sample approximately 0.8 cm^2 in size and 70 mg in mass. The Radiation Measurements Laboratory (RML) at INL possesses precision punches and a calibrated scale for this purpose.
The prepared foils will be transferred to the Neutron RADiography (NRAD) facility at the Hot Fuel Examination Facility (HFEF) at INL for irradiation in the F1 dry port for a total fluence of approximately 1E16 n/cm^2. Following irradiation, the Nb-93m activity levels are expected to be on the order of 1 Bq/mg, characteristic of the activity levels seen in niobium sensors irradiated in reactor cavity dosimetry positions at operating power reactors.
The E1297 ILS is open to all domestic (USA-based) and international laboratories. ASTM will support shipping to domestic laboratories. Participating laboratories must cover their own costs (e.g. staff time, consumables, etc.) to measure the samples per ASTM E1297. At least one measurement must be performed. The organizers encourage the participants to perform multiple measurements of the sample material, thereby enabling an “intra-laboratory” estimate of precision.
The sample-preparation and irradiation components of the proposed work will take approximately 6 months, while the sample analysis (not part of the proposed work, but part of the ILS) may take up to 1 year for all participating laboratories to complete.
However, sample analysis at the RML, one participating laboratory at INL, will be completed within 3 months of the irradiation.
The results of this study will be used to determine the precision and biases associated with the use of ASTM E1297 standard and will be published in an appropriate manner (likely at the International Symposium for Reactor Dosimetry, ISRD18).