Breeding Rate Measurements in Solid Fusion Blankets with Metallic Lithium Samples

Measurement of the local breeding rate in a large assembly of fusion blanket candidate materials, irradiated by a fusion neutron source, serves the dual purpose of blanket design support and, perhaps more importantly, of testing analytical methods and cross-section libraries. In this report, we present technical details of a tritium production rate measurement scheme based on the use of neutron irradiation of encapsulated lithium metal samples and subsequent thermal digestion of the samples in a metered carrier hydrogen stream, conversion to THO and LS-counting. A comparison of the scheme to other means of tritium production rate (TPR) measurement with respect to accuracy and other characteristics indicates that its potential accuracy exceeds that of wet-chemistry tritium extraction from lithium salt pellets or TLD deployment and is comparable to the best accuracy of lithium-glass traversing schemes. The sample fabrication and tritium extraction techniques that will be described evolved from well-tested equipment that was previously used in critical (fission) reactor work and cross section measurements, but needed some modification to increase the throughput and thus allow processing the large number of samples required in blanket assay. The applicability of this scheme to measurements at arbitrarily high neutron flux and higher temperatures will be briefly commented on.