CIELO U-235
Date: 3 February 2014
Place: Phone conference
Time: 16:00 (Paris, GMT+1), 8:00 (Los Alamos, GMT-7)
Participants:
BNL: M.Herman, D.Brown
CEA: G.Noguère (DEN), P.Romain and E.Bauge (DAM)
LANL: M.Chadwick, A.Kahler
ORNL: L.Leal
IAEA: R.Capote Noy
NEA: E.Dupont
The objective of this phone conference is to share progress and plans on the 235U evaluation for theCIELO pilot project. A short-term milestone is to have a starter file by May 2014.
M.Chadwick opened the discussion and proposed to hear progress in the resonance region and in thecontinuum region from L.Leal and P.Romain, respectively.
Resonance region
L.Leal reminded participants of the issues identified by WPEC Subgroup 29 in the keV energy region
for the 235U(n,g) cross section. The re-evaluation work in the resolved resonance region (RRR, up to2.25 keV) was initiated to solve this problem. The new analysis includes recent data measured at RPI(capture and fission) and at LANL (capture) up to a few keV (but data at higher energy were alsomeasured). The preliminary integral validation results are encouraging when the new resonanceparameters are included in JENDL-4.0 (but the results are not as good when using ENDF/B-VII.1). Thiswork was summarised in the presentation he gave at the NEMEA/CIELO workshop in November 20131.
The new resolved resonance parameter set is now almost ready for released, but L.Leal suggested
updating the unresolved resonance region (URR, up to 25 keV) before repeating the integral validation.
G.Noguère reported that the new URR evaluation that was presented at the NEMEA/CIELO workshop
is available for testing.
It was agreed that L.Leal and G.Noguère will finalise a complete MF2 file (RRR+URR) and will
perform a few integral tests before releasing the new parameters for additional validation.
Continuum region
P.Romain reported on preliminary results he obtained when trying to better reproduce the standard
235
U(n,f) cross section (see Appendix). The objective of this work is to keep the overall consistency ofthe evaluation when replacing the calculated values by the standard ones. Of course, the change in thefission cross section affects the other channels and there is still work to be done, e.g. to get closer to theJENDL-4.0 capture cross section below 100 keV. E.Bauge inquired about the necessity to adopt
standards data in the evaluated files.
R.Capote and M.Chadwick answered that it is certainly a good strategy to try to reproduce the standard
values as closely as possible.

1

www.oecd-nea.org/science/wpec/nemea7/presentations.html

1

M.Chadwick asked about the deficiency in the modelling of the capture cross section. P.Romain
answered that additional coupled channels are probably required in OM calculations. R.Capote
commented that this point will be further discussed in March with T.Kawano when they will be visiting
P.Romain at Bruyères (in conjunction with the ESNT workshop at CEA Saclay2).
R.Capote stressed the importance of the RPI scattering experiments on 238U to guide the evaluation of
the elastic and inelastic cross sections and recommended to perform a similar measurement with 235U.
E.Dupont reported that they need to check if they have tens of grams available in their inventory for thisexperiment. M.Chadwick agreed to see if anything can be done to help.
Starter file – Integral validation
It was suggested not to use any new prompt fission neutron data (nu-bar, PFNS) for the moment and toinclude the new MF2 resonance parameters from ORNL-CEA in the existing files (e.g. JEFF-3.2,ENDF/B-VII.1, JENDL-4.0) in order to start the integral validation and to disentangle effects from theresonance and continuum regions.
Adjourn2

http://esnt.cea.fr/Phocea/Page/index.php?id=372

2.4

1.4235

2.2

n+ U

1.35

2σn,f1.31.25

1.8

1.2

1.6

1.15
1.1

1.4

1.05
1.2
1110-2100.95-11101235

235

Cross Section (b)n+ Uσn,γ1101010n+ U
1σn,2n-1

Test for CIELO
ENDF/B-VII
JENDL4.0

σn,3n0.5-2-310-310-210-11

Neutron Energy (MeV)

10051015

Neutron Energy (MeV)20