Better knowledge of the neutron population in reactors is crucial to improve the accuracy of neutronics simulations of present day or future reactor cores. This population is partially driven by (n, ...xn) reactions. However, the cross sections of these reactions are not precisely known. This is particularly true for the 238U(n, n’γ) cross section, which is on the High Priority Request List. One method to measure this cross section is to use the prompt γ-ray spectroscopy coupled to time-of-flight measurements. This allows the total (n, n’) cross section to be inferred from the measured (n, xnγ) cross sections and the level scheme information. However, the knowledge of the 238U level scheme is still very incomplete, so an initiative to experimentally revisit the 238U structure has been launched using γ-γ coincidences spectroscopy. The v-Ball γ-spectrometer was coupled to the LICORNE directional neutron source of the ALTO facility, allowing study of inelastic scattering on 238U via γ-γ coincidences. The analysis of data obtained during the first v-Ball campaign was performed using the Radware escl8r software. At the present time, 73 γ-transitions and 50 levels registered in ENSDF have been confirmed and 120 new γ-transitions and 50 new levels have been found.
The necessary improvement of evaluated nuclear data for nuclear applications development is possible through new and high quality experimental measurements. In particular, improving (n, n’) cross ...section evaluations for fast neutrons is a goal of interest for new reactor fuel cycles, such as 232 Th/ 233 U or 238 U/ 239 Pu. Our group at CNRS-IPHC developed an experimental program to measure (n, n’γ) cross section using prompt γ-ray spectroscopy and neutron energy determination by time-of-flight with a focus on reaching the highest achievable level of accuracy. The collected partial cross sections can then be used to infer the total (n, n’) one and contribute to evaluation improvement. The extraction of the exclusive (n, n’γ) cross sections from the recorded data involves using many parameters and processing that may introduce uncertainties and correlations. In that case, the usual method for combining and computing uncertainties based on the perturbation theory can be long and complex. It also makes the calculation of covariance hard and the inclusion of some unusual forms of uncertainty even more difficult. To overcome this issue, we developed a process relying on random sampling methods that processes intermediate analysis data to compute cross sections, uncertainties and covariance. As a benchmark, we used this Monte Carlo method on 232 Th, 233 U and 238 U data and reproduced the central values and uncertainties calculated using the analytical method, while also producing covariance matrices for (n, n’γ) cross sections. For particular cases, the random sampling method is able to produce uncertainties that better reflect the input data, compared to the analytical method.
This paper highlights the strong need for precise nuclear structure and decay data measurements in order to perform high-quality modelling on nuclear reactors and other applications. The context of ...nuclear data evaluation, as well as the importance of low uncertainty evaluations, will be first presented. The importance of such data for interpreting nuclear data experimental measurements is stressed throughout. To demonstrate this, we will explain how mass and charge-dependent fission yields, decay data (in particular for the purpose of residual heat calculations), and inelastic neutrons scattering cross section rely on nuclear structure and decay information and how new and higher quality in such data can lead to improved accuracy in the precision of evaluated nuclear data.
This paper shows how Total Monte Carlo (TMC) method and Perturbation Theory (PT) can be applied to quantify uncertainty due to nuclear data on reactor static calculations of integral parameters such ...as
k
eff
and
β
eff
. This work focuses on thorium fueled reactors and it aims to rank different cross sections uncertainty regarding criticality calculations. The consistency of the two methods are first studied. The cross sections set used for the TMC method is computed to build adequate correlation matrices. Those matrices are then multiplied by the sensitivity coefficients obtained thanks to the PT to obtain global uncertainties that are compared to the ones calculated by the TMC method. Results in good agreement allow us to use correlation matrix from the state of the art nuclear data library (JEFF 3-3) that provide insight of uncertainty on
k
eff
and
β
eff
for thorium fueled Pressurized Water Reactors. Finally, maximum uncertainties on cross sections are estimated to reach a target uncertainty on integral parameters. It is shown that a strong reduction of the current uncertainty is needed and consequently, new measurements and evaluations have to be performed.
GAINS (Gamma Array for Inelastic Neutron Scattering), currently installed at the GELINA (Geel Electron Linear Accelerator) neutron source of the EC-JRC (European Commission-Joint Research Centre), is ...one of the best instruments available worldwide for measuring high resolution, low uncertainty neutron inelastic cross-section data relevant for both fundamental research and nuclear physics applications (like Generation IV facilities). It features 12 HPGe detectors coupled with a
235
U fission chamber for neutron flux monitoring. The paper presents a short history of the GAINS development over the years and reviews some of the main experimental results together with plans for future experiments.
The extended dataset of 56Fe(n,n’γ) cross sections measured by our group more than a decade ago at GELINA (Geel Linear Accelerator) was used in many recent evaluations like ENDF, JEFF and CIELO. ...Despite the special measures we took to ensure reliability and accuracy, concerns were raised by various groups with regard to several features of this dataset (absolute normalization and/or shape) and therefore the 56Fe(n,inl) cross section is still under the evaluation by the International Nuclear Data Evaluation Network (INDEN). Consequently, a new experiment is now under preparation aiming to take advantage of the numerous experimental improvements of the GAINS (Gamma Array for Inelastic Neutron Scattering) setup implemented over the years. While γ spectroscopy combined with the time-of-flight method will remain the main technique involved, several other experimental details will differ substantially.
This paper reports partial results of a (n, n’γ) measurement on nickel. The inelastic channel was measured using the Gamma Array for Inelastic Neutron Scattering (GAINS) spectrometer at the 100-m ...measurement cabin of the Geel Electron Linear Accelerator (GELINA) neutron source of the European Commission’s Joint Research Centre (EC-JRC) in Geel, Belgium. Using γ spectroscopy, we were able to extract angle-integrated production cross sections for several γ rays but we report here only the results for the main transition in 58Ni. We discuss however in detail the observed discrepancy between our data and other experiments (especially the work of Voss et al.). We also shortly comment on the quality of the neutron-target optical model potential in describing the inelastic data in this mass region. The calculations were performed using the talys 1.9 code in the default settings.
GRAPhEME is a γ-spectrometer developed by CNRS/IPHC Strasbourg (France), in collaboration with EC-JRC Geel (Belgium) and IFIN-HH Bucharest (Romania). With its 6 High Purity Planar Germanium detectors ...and one fission chamber, GRAPhEME, installed at the EC-JRC GELINA facility, was optimized for measurements of accurate (
n
,
xnγ
) cross sections on actinides. The experimental methodology is based on the prompt γ-ray spectroscopy coupled to time-of-flight measurements. In this paper, we present an overview of fifteen years of experiments with GRAPhEME at EC-JRC GELINA facility, illustrated by main achievements to highlight the performances reached by our spectrometer. Beyond the experimental work, a close collaboration with theoreticians has emerged allowing the use of the data produced with GRAPhEME to test and constraint nuclear reaction codes like TALYS, CoH and EMPIRE. In a near future, GRAPhEME will be available to start measurement campaigns at the new neutron beam facility SPIRAL2/NFS. There, studies of (
n
, 2
n
) and (
n
, 3
n
) reactions will be possible and will complete the work done at EC-JRC GELINA on (
n
,
n
) reactions. Despite the amount of cross section data provided by GRAPhEME up to now, the prompt
γ
-ray spectroscopy method presents some weaknesses that our collaboration tries to overcome. This goes through new calculation schemes based on theoretical modeling constrained on experimental data to infer the total (
n
,
xn
) cross section, new instrument to measure conversion electrons but also by being proactive in dissemination activities to make the nuclear structure community aware of our needs about new accurate nuclear structure information on actinides.
The production of useful and high-quality nuclear data requires measurements with high precision and extensive information on uncertainties and possible correlations. Analytical treatment of ...uncertainty propagation can become very tedious when dealing with a high number of parameters. Even worse, the production of a covariance matrix, usually needed in the evaluation process, will require lenghty and error-prone formulas. To work around these issues, we propose using random sampling techniques in the data analysis to obtain final values, uncertainties and covariances and for analyzing the sensitivity of the results to key parameters. We demonstrate this by one full analysis, one partial analysis and an analysis of the sensitivity to branching ratios in the case of (n,n’γ) cross section measurements.
The necessary improvement of evaluated nuclear data for nuclear applications development is possible through new and high-quality measurements, often combined with appropriate nuclear-reaction ...modelling. In particular, improving inelastic cross-section evaluations requires new and high-quality data. We measure (n, n’γ) cross-sections using prompt γ-ray spectroscopy and neutron energy determination by time-of-flight. To extract, from these partial data, the total inelastic cross-section, we rely on theoretical model as well as nuclear structure data such as γ ray emission probabilities. This structure information, tabulated in databases, comes with uncertainty. This directly affects the precision of our results, regardless of how good the measurement is. In this paper, we will present the issue of limited precision structure data and its impact on nuclear reaction data quality in the case of neutron inelastic scattering measurements. We will also discuss how to foresee and mitigate the issue.
PDF