Uncertainty assessment on the calculated decay heat of the ASTRID basic design core based on the DARWIN-2.3 package

• Published in: Annals of nuclear energy Vol. 120; pp. 378 - 391
• Main Authors: Lebrat, Jean-François, Vallet, Vanessa, Coquelet-Pascal, Christine, Venard, Christophe, Eschbach, Romain
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.10.2018
• Subjects: APOLLO3; ASTRID; CFV; COMAC; CYRUS; DARWIN; Decay heat; Depletion calculation; DOUBLON; ERANOS; Fission pulse; JEFF311; Nuclear data; Pandemonium effect; PHENIX; PUIREX; Sodium Fast Reactor; TRAPU; Uncertainty propagation; Validation; Validation; DARWIN; CYRUS; Sodium Fast Reactor; Depletion calculation; PHENIX; TRAPU; ASTRID; DOUBLON; APOLLO3; PUIREX; CFV; Decay heat; COMAC; Fission pulse; Uncertainty propagation; Nuclear data; ERANOS; JEFF311; Pandemonium effect
• ISSN: 0306-4549; 1873-2100
• DOI: 10.1016/j.anucene.2018.05.043

•A good knowledge of a reactor decay heat and its uncertainty is very important.•The current uncertainty assessment for fast neutron reactors decay heat is obsolete.•It is based on old nuclear data libraries, codes and methods.•This is penalizing for the design of the ASTRID technological demonstrator.•We have revisited the decay heat and uncertainty calculations with up-to-date data and codes.•Our uncertainty assessment never exceeds 2.6%, compared to 6.6% previously. A good knowledge of the decay heat of the various elements of the core (fissile and fertile zones, structures, sodium…) as well as the associated uncertainties is critical for the safe operation of a nuclear facility, but also at the design stage as in the case of the ASTRID technological demonstrator. For this reactor, the amount of decay heat is all the more important as it will strongly impact the design of the dedicated EPur (Evacuation de la PUissance Résiduelle = disposal of the decay heat) system. The uncertainties on the decay heat calculations of a sodium fast rector that are currently used at CEA were defined several decades ago and are now considered very conservative, because of the method that was used in their evaluation. They may thus be penalizing for the design and operation of ASTRID. These past uncertainty assessments were based on a semi-empirical approach - a combination of physical considerations and experimental results - and on calculations using conservative methods and obsolete nuclear data libraries that need to be updated. We have used up-to-date calculation tools in order to reduce these uncertainties: ERANOS-2.2 for the neutronic calculations and DARWIN-2.3 for the depletion calculations. The uncertainty on the decay heat is estimated with the CYRUS tool, which performs the propagation of all the relevant nuclear data uncertainties (decay constants, branching ratios, cross sections, independent fission yields). For some parameters, we have completed the JEFF-3.1.1 uncertainties database with values from other nuclear data libraries, for instance the branching ratio for the decay of 137gCs to 137mBa, of 90gKr to 90gRb and the branching ratio for the capture of 241gAm to 242gAm. The resulting 1σ uncertainty on the decay heat calculation never exceeds 2.6%, which shows a major improvement compared to the previous uncertainty evaluation that could reach 6.6%. Additional sources of uncertainties will have to be considered in the future in order to evaluate the full uncertainty on decay heat calculations: the reactor operation conditions variations, the accuracy of the nominal power measurement and the uncertainty on the neutron flux calculated with the new APOLLO3® code system, which will be dedicated to the ASTRID neutronic calculations.