Evaluation of BETA eff measurements from BERENICE programme with Tripoli 4 ® and uncertainty qualification
Résumé
The effective delayed neutron fraction (beff ) is an important characteristic of nuclear reactors since it
affects transients significantly. It is therefore important to characterise it correctly. The use of bestestimate
codes and data together with an evaluation of the uncertainties is required not only for their
use in safety studies but also to assess reactivity effects which are being measured relative to the effective
delayed neutron fraction (beff) in $.
The use of the Iterated Fission Probability method in the Monte Carlo code TRIPOLI4® confirms results
obtained with deterministic codes such as ERANOS for calculating beff . The asset of TRIPOLI4® is the
possibility to get a better representation of experimental cores. Its use for evaluating the calculated parts
of the “experimental” beff of the BERENICE experimental programme has led to significant improvements
of the C/E ratios, especially the R2 experimental core.
This work is in support of the ASTRID project which developed the concept of a Sodium cooled Fast
Reactor (SFR). In order to get a reduced uncertainty it is recommended to repeat the beff measurement
within the future GENESIS experimental programme in the refurbished zero power reactor (ZPR)
MASURCA with an improved noise measurement technique.
The nuclear data uncertainty propagation has led to a 2.8% uncertainty for U-Pu core and 2.6% for
enriched uranium cores (with JEFF-3.2) with main contributors being the delayed neutron fission yield
and the fission cross section of U238.