New prompt fission gamma-ray spectral data from 239Pu(nth, f) in response to a high priority request from OECD Nuclear Energy Agency.

Benchmark reactor calculations have revealed an underestimation of γ -heat following fission of up to 28%. To improve the modelling of new nuclear reactors, the OECD/NEA initiated a nuclear data High Priority Request List (HPRL) entry for the major isotopes (²³⁵U, ²³⁹Pu). In response to that HPRL entry, we executed a dedicated measurement program on prompt fission γ -rays employing state-of-the-art lanthanum bromide (LaBr3) detectors with superior timing and good energy resolution. Our new results from ²⁵²Cf(sf), ²³⁵U(nth, f) and ²⁴¹Pu(nth, f) provide prompt fission γ -ray spectra characteristics : average number of photons per fission, average total energy per fission and mean photon energy; all within 2% of uncertainty. We present preliminary results on ²³⁹Pu(nth, f), recently measured at the Budapest Neutron Centre and supported by the CHANDA Trans-national Access Activity, as well as discussing our different published results in comparison to the historical data and what it says about the discrepancy observed in the benchmark calculations. [ABSTRACT FROM AUTHOR]