Program - Brookhaven National Laboratory

for the combined use of integral experiments and covariance data” in 2009. In its mandate “it is proposed
for this WPEC subgroup to study methods and issues of the combined use of integral experiments and
covariance data, with the objective of recommending a set of best and consistent practices in order to
improve evaluated nuclear data files. Indication should be provided on how to best exploit existing integral
experiments, define new ones if needed, provide trends and feedback to nuclear data evaluators and measurers.”
Based on major conclusions reached by the activity of the WPEC Subgroup 26 on “Uncertainty
and Target Accuracy Assessment for Innovative Systems Using Recent Covariance Data Evaluations,” this
is the first international expert activity in this field. It reflects the growing interest for science-oriented
methodologies in order to improve nuclear data for a wide range of applications and to meet more and more
stringent requirements for safety and economic purposes, without necessarily deploying new resources for
performing expensive and time consuming experiments. The first stage has been devoted for producing
the description of different adjustment methodologies and assessing their merits. A detailed document
related to this first stage has been issued. Eight leading organizations (often with a long and recognized
expertise in the field) have contributed to the document: ANL, CEA, INL, IPPE, JAEA, JSI, NRG, and
ORNL. Among the different information provided in the document we can list: identification of merit and
drawbacks of existing methodologies, comparison of mathematical formulations and specific features (such
as a-posteriori correlation matrices), criteria for assessing methodologies. In the second stage a practical
exercise was defined in order to test the reliability of the nuclear data adjustment methodology. The goal
of the exercise is:
• Assess if in a multigroup nuclear data adjustment one ends up with the same (or very close) set of
isotope cross sections when a common shared set of integral experiments is used and different data
adjustment methodologies are used.
• Assess the impact of using different starting evaluated libraries and/or different covariance matrices.
The convergence of trends (e.g. cross section energy shapes) is investigated.
• Assess if the attained reduced uncertainties on a target design for a set of integral parameters of
interest is consistent among the different solutions.
A set of 20 well defined integral parameters from 7 fast assembly experiments was used in the exercise to
adjust the main nuclear data (major cross section reactions including capture fission elastic and inelastic
scattering, but also relevant mu-bar, nu-bar and fission spectrum) of 11 major isotopes in a 33 group energy
structure. Seven organizations have already provided their solution at different degrees of completeness.
Three more plan to participate. In the final paper comparison of results and major lessons learned in the
exercise will be provided. *Member Organizations: ANL, BNL, CEA, CIAE, INL, IPPE, IRSN, JAEA,
JSI, KAERI, NRG, ORNL, PSI
EA 2 9:15 AM
Electron-Antineutrino Disappearance Seen by Daya Bay Reactor Neutrino Experiment
Yuekun Heng, On behalf of the Daya Bay Collaboration
Institute of High Energy Physics, Beijing, 100049, China
The Daya Bay Reactor Neutrino Experiment has measured a nonzero value for the neutrino mixing angle
with a significance of 7.7 standard deviations. Antineutrinos from six 2.9 GW reactors were detected by six
20-ton target-mass detectors of identical design, deployed in two near and one far underground experimental
halls. With a 116.8 kton-GW-day live-time exposure in 139 days, 28909 and 205308 electron-antineutrino
candidates were detected at the far hall and near halls respectively. The ratio of the observed to expected
80