Description
The Joint European Torus (JET) was the largest operational facility for controlled deuterium–tritium (DT) fusion. The DT neutron spectrum at JET, with its characteristic 14.1 MeV DT peak, provided an experimental testbed to probe material activation that will be similar to future fusion machines such as ITER. Although neutron fluences at JET were many orders of magnitude lower than those anticipated for ITER, they remain the highest fluences achieved at a tokamak ($7\times10^{15}~\mathrm{n\cdot cm^{-2}}$ for the final JET DT campaign vs.\ $3.4\times10^{21}~\mathrm{n \cdot cm^{-2}}$ expected for 14 years of ITER operation). Consequently, JET provided a valuable opportunity to irradiate materials from ITER’s structural components.
Representative ITER material samples and a set of dosimetry foils were placed in an activation holder within the long-term irradiation station (LTIS), located close to the JET vacuum vessel and irradiated during 2023 JET operations, including the last JET deuterium–tritium campaign (DTE3). The discussed samples were exposed to 2925 JET shots, corresponding to a total neutron yield of $7.88\times10^{20}~\mathrm{n}$. After irradiation, the samples were removed from the cassette and distributed for gamma-ray spectrometry measurements.
Out of 69 ITER material samples and 20 dosimetry foils irradiated at LTIS during DTE3, this paper analyzes results for nine ITER samples (five 316L stainless steel, tungsten (W), EUROFER97, Al-bronze, 304 stainless steel) and three iron dosimetry foils. High-resolution gamma-ray spectrometry was performed at IPPLM to determine the activities of nuclides produced in the samples during neutron irradiation. Experimental activities were compared with predictions from the FISPACT-II inventory code, using neutron yield data from JET KN1 fission chambers and a high-fidelity Monte Carlo N-Particle (MCNP) model of JET.
The calculated/experimental (C/E) ratios for the discussed samples show overall satisfactory agreement: 2/3 of the obtained ratios deviate from unity by at most 35\% (C/E ratios lie within the interval 0.65-1.35). However, certain discrepancies - most notably the broad spread of C/E values for $^{60}Co$ in stainless steel samples - indicate that the neutronics model and simulation methodology may require refinement to improve predictive accuracy for ITER and future fusion devices.