Orateur
Description
In the context of a nuclear power reactor operation, decay heat is a thermal power
which continues to be generated after shut down. This is due to the radioactive decay of
fission products, minor actinides, and delayed fission of fissile nuclide. Hence, a proper
characterization of decay heat and is essential for reactor safety system design, spent
fuel transportation, and repository management.
Decay heat can be calculated using reactor codes that have the capability to simulate
nuclide depletion by solving the Bateman equation coupled to the summation method.
As the name indicates, the summation method is the sum of decay power contributions
from the above-mentioned depleted fuel components at a given time. Since the data
required for this calculation, i.e., decay constants, fission yield data, and mean decay
energies are evaluated from experimental data, they have a certain level of uncertainty
which propagates to the decay heat calculation.
To this end, the objective is to analyze the impact of these uncertainties on decay
heat calculation, and a Monte Carlo method is chosen to propagate the decay heat
uncertainties through the fuel depletion. As a first step, a benchmarking work on a
sample from a PWR assembly is done to estimate the spent fuel nuclide inventory at
different cooling times. The benchmarking was done as a participation for the NEA
working group of criticality safety related to uncertainty on nuclide inventory. The
sample chosen for this purpose is the ARIANE GU3 sample. Two Monte Carlo codes
(Serpent and OpenMC) and two nuclear data libraries (JEFF3.2 and ENDF7.1) were
used for the depletion calculation. The results are compared with experimental values
and with other participants’ results. It has been shown that for most of the nuclide,
the simulation results are in agreement within the error margins with the experimental
values and other computational outputs. The subsequent steps will be to develop a
code which is capable of sampling on the decay data uncertainties (fission yields, decay
constants, mean decay energies) and calculate decay heat uncertainties. It will be first
applied to the ARIANE GU3 sample and fission pulse calculations and later on the
molten salt fast reactor concept.
