TWO NOVEL TECHNIQUES OF TRITIUM MEASUREMENT AT THE FUSION NEUTRONICS FACILITY LOTUS
Institut de Génie Atomique, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
@Present Address: M.A.N.E.D., UCLA, Los Angeles, CA 90024, USA
+Present Address: O.F.A.C. - Geneva - Switzerland
The tritium measurement in deep locations of a fusion blanket by the conventional techniques, based on liquid scintillation and thermoluminiscent dosimetry, is subject to limitation because of their low sensitivity, the low neutron flux and the constraint of limited operation time of the D-T neutron generator. Two novel techniques have been developed and tested at the LOTUS facility, based on: (i) Lithium Glass Scintillation (LGS), and (ii) Solid State Nuclear Track Detection (SSNTD). The LGS has been conventionally used for the measurement of low-energy flux because of 1/v cross-section behaviour of 6Li(n,α)t reaction. The lithium glass scintillator (NE912 or NE913) used in the present experiment is only 1 mm thick. For the SSNTD method, we have used 6Li and 7Li enriched 2 mm thick LiF foils as the source for the commercially available LR115 type II detector. A benchmark experimental assembly consisting of 10 cm thick Pb followed by 22 cm thick Li2CO3 slabs was irradiated by 14 MeV neutrons. The tritium production rates (TPR) were measured at a number of axial locations. The comparison of normalized spatial profiles shows that the two techniques give matching result. However, both the profiles have significant discrepancies with the computed profile by a 2D code. The SSNTD technique also yields the profile for TPR from 7Li(n,n'α)t that is close to the one from the 2D code.
KEYWORDS: tritium measurement, lithium glass scintillator, solid state nuclear track detector, benchmark experiment