Abstract
We compare existing experimental decay heat data sets measured at the JAEA fusion neutron source (FNS), which employed a fast extraction rabbit system that in certain cases allowed the measurements to capture, at short cooling times, the decay profile of 16N in a range of oxides. Focussing on those data points and timescales that can be attributed to 16N, we compare measurements to simulations performed using the FISPACT-II inventory code together with evaluated nuclear data libraries. Making small corrections for other contributions at these short times, we derive integral cross section data estimates for 16O(n,p)16N from 12 oxide sample measurements and compare with previously obtained measurements in the IAEA EXFOR database and evaluations in the nuclear data libraries themselves.
Highlights
Cooling water in the primary circuit in both fission and fusion nuclear reactors is unavoidably exposed to neutrons leading to the generation of problematic short-lived isotopes, most importantly, 16N (T1/2=7.3s) via the 16O(n,p)16N reaction
We compare existing experimental decay heat data sets measured at the JAEA fusion neutron source (FNS), which employed a fast extraction rabbit system that in certain cases allowed the measurements to capture, at short cooling times, the decay profile of 16N in a range of oxides
ITER is designed to operate at 500 MW fusion power, where the 14 MeV neutron emission rates from the deuterium-tritium plasma will be 1.77 × 1020 n s−1 and the neutron fluence experienced by some first wall water-cooled components will exceed 1014 n cm−2 s−1
Summary
Cooling water in the primary circuit in both fission and fusion nuclear reactors is unavoidably exposed to neutrons leading to the generation of problematic short-lived isotopes, most importantly, 16N (T1/2=7.3s) via the 16O(n,p)16N reaction This presents a significant itinerant radiation source to consider for operational dose and impact on radiation sensitive equipment, such as electronics and cryogenic components such as superconducting magnets, due to the intense 6.13 MeV gamma ray that is emitted during 16N decay. Activities are ongoing to seek experimental justification to reduce these factors via coolant loop experiments at the Frascati Neutron Generator [2,3,4], which has incorporated an ITER first wall mock up component incorporating water coolant channels, irradiated with 14 MeV neutrons and the 16N emissions measured via a high efficiency CsI detector at different water flow rates
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