Prompt Gamma Rays
Prompt gamma rays are released directly after a nucleus undergoes its fission. Most prompt gamma rays are emitted after prompt neutrons. The fission reaction releases approximately ~7 MeV in prompt gamma rays and an additional ~7 MeV (for 235U) in delayed gamma rays. This is a significant portion of energy (~7 % of fission energy released), and it must be considered in many fields of reactor design or the design of nuclear reactor shields. A particular challenge is the calculation of the gamma heat deposition in core baffles (reflectors), pressure vessels, or excore detector channels.
In past the comparisons of various benchmarks experiments with calculated gamma heating showed a systematic underestimation for the main fuel isotopes 235U and 239Pu. Discrepancies observed for C/E ratios in various benchmarks range from 10 to 28%, while required accuracy is 7.5%. Therefore requests for new measurements of prompt gamma rays in the reactions 235U(n,f) and 239Pu(n,f) have been formulated in the Nuclear Data High Priority Request List of the Nuclear Energy Agency.