W.E. Ang, S. Prasad, and S.S. Chirayath, “Antineutrino detection for temporal monitoring of fuel burnup in a large nuclear reactor”, Nuclear Instrumentation and Methods in Physics Research A, 1028 (2022).
The objective of this work is to determine if coherent-elastic-neutrino-nucleus scatter (CENS) in natural germanium detectors can be used to detect antineutrinos from an AP1000-type fission reactor. In this work, we first modeled the AP1000 core using Monte Carlo N-Particle Transport Code 6.2 (MCNP) to estimate the number of fissions from each fissile isotope in the core. Next, the reactor antineutrino spectrum was computed using the summation method for fuel burnup from 10 to 60 GWd/MTU. It was found that with the increasing fuel burnup, as the 239Pu inventory builds-up in the fuel and the 235U inventory depletes, the contributions from 239Pu to fission is enhanced. Thus, the antineutrino energy spectrum begins to skew more towards lower energies as seen by the quantification of third and fourth central moments. Increased fuel burnup also results in greater antineutrino production. The detection setup assumes a 100-kg CENS based natural germanium detector, which is placed outside the reactor containment, 25 m away from the core. The detector has a 100-eV nuclear recoil (NR) threshold and experiences a background level of 100 differential rate units (DRU), per kg.keV.day, due to surrounding radiation interacting in the detector. We then computed the differential pulse height distribution responses for two 235U enrichment cases: 3.3-wt-% and 4.4-wt-% at burnup levels of 10, 20, 40, and 60 GWd/MTU. Overall, the detection rate decreases when the burnup increases. This study indicates that germanium pulse height distribution end-point energies decrease with increasing fuel burnup and become less separable. Thus, we note that the CENS detector resolution would need to be higher for more burned fuel. A 16-eV is sufficient for distinguishing fresh fuel from that burned to 20 GWd/MTU. We also investigate the ability to detect a difference between burnups: 10 and 20 GWd/MTU, 10 and 40 GWd/MTU, 10 and 60 GWd/MTU, based on the integral detector counts after accounting for background and detection threshold. We determined that fuel burnup deviations can be detected with confidence much greater than 20%, as required by the IAEA, for low likelihood events. For 3.3-wt-% 235U enrichment, the confidence levels to distinguish burnup between 10 and 20 GWd/MTU, 10 and 40 GWd/MTU, 10 and 60 GWd/MTU are 80.60%, 100%, and 100%, respectively. For 4.4-wt% 235U enrichment, but the same three burnup comparisons, the confidence levels decreased marginally to 65.52%, 100%, and 100%, respectively.