| 1. |
- Rochman, Dimitri, et al.
(författare)
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The TENDL library : Hope, reality and future
- 2017
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Ingår i: Nd 2016 Bruges. - Les Ulis : EDP Sciences. - 9782759890200
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Konferensbidrag (refereegranskat)abstract
- The TALYS Evaluated Nuclear Data Library (TENDL) has now 8 releases since 2008. Considerable experience has been acquired for the production of such general-purpose nuclear data library based on the feedback from users, evaluators and processing experts. The backbone of this achievement is simple and robust: completeness, quality and reproducibility. If TENDL is extensively used in many fields of applications, it is necessary to understand its strong points and remaining weaknesses. Alternatively, the essential knowledge is not the TENDL library itself, but rather the necessary method and tools, making the library a side product and focusing the efforts on the evaluation knowledge. The future of such approach will be discussed with the hope of nearby greater success.
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| 2. |
- Alhassan, E., et al.
(författare)
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Bayesian updating for data adjustments and multi-level uncertainty propagation within Total Monte Carlo
- 2020
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Ingår i: Annals of Nuclear Energy. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0306-4549 .- 1873-2100. ; 139
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a method is proposed for combining differential and integral benchmark experimental data within a Bayesian framework for nuclear data adjustments and multi-level uncertainty propagation, using the Total Monte Carlo method. First, input parameters to basic nuclear physics models implemented within the TALYS code, were randomly varied to produce a large set of random nuclear data files. Next, a probabilistic data assimilation was carried out by computing the likelihood function for each random nuclear data file based first on only differential experimental data and then on integral benchmark data. The individual likelihood functions from the two updates were then combined into a global likelihood function. The proposed method was applied for the adjustment of n+Pb-208 in the fast energy region below 20 MeV. The adjusted file was compared with available experimental data as well as evaluations from the major nuclear data libraries and found to compare favourably.
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| 3. |
- Alhassan, E., et al.
(författare)
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In search of the best nuclear data file for proton induced reactions : Varying both models and their parameters
- 2020
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Ingår i: ND 2019. - : EDP Sciences. - 9782759891061
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Konferensbidrag (refereegranskat)abstract
- A lot of research work has been carried out in fine tuning model parameters to reproduce experimental data for neutron induced reactions. This however is not the case for proton induced reactions where large deviations still exist between model calculations and experiments for some cross sections. In this work, we present a method for searching both the model and model parameter space in order to identify the 'best' nuclear reaction models with their parameter sets that reproduces carefully selected experimental data. Three sets of experimental data from EXFOR are used in this work: (1) cross sections of the target nucleus (2) cross sections of the residual nuclei and (3) angular distributions. Selected models and their parameters were varied simultaneously to produce a large set of random nuclear data files. The goodness of fit between our adjustments and experimental data was achieved by computing a global reduced chi square which took into consideration the above listed experimental data. The method has been applied for the adjustment of proton induced reactions on Co-59 between 1 to 100 MeV. The adjusted files obtained are compared with available experimental data and evaluations from other nuclear data libraries.
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| 4. |
- Alhassan, E., et al.
(författare)
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TENDL-based evaluation and adjustment of p+111Cd between 1 and 100 MeV
- 2023
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Ingår i: Applied Radiation and Isotopes. - : Elsevier. - 0969-8043 .- 1872-9800. ; 198
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Tidskriftsartikel (refereegranskat)abstract
- Proton induced reaction data are needed in the optimization of various radioisotope production routes, among others. In this work, the evaluation of proton-induced reactions on 111Cd between 1 and 100 MeV using the TALYS code system within an iterative Bayesian Monte Carlo (iBMC) framework, is presented. The method involves the simultaneous variation of a large number of nuclear reaction models included in the TALYS code system as well as their parameters. Each random TALYS calculation yields a vector of calculated values of cross section observables as well as the angular distributions, among others, which were compared with corresponding vectors of carefully selected differential experimental data for reaction channels where data were available. The random nuclear data file with the maximum likelihood function value obtained from combining the individual chi 2s computed for the considered reaction channels was chosen as the parent vector and the starting point for the generation of a further set of random TALYS calculations. This was repeated multiple times until a targeted convergence of 5% was reached. The final evaluated file was compared with available experimental data from the EXFOR database as well as with the evaluations from the TENDL-2021 and JENDL5.0 libraries, and found to compare favorably.
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| 5. |
- Dokhane, A., et al.
(författare)
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Analysis of Oskarshamn-2 stability event using TRACE/SIMULATE-3K and comparison to TRACE/PARCS and SIMULATE-3K stand-alone
- 2017
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Ingår i: Annals of Nuclear Energy. - : Elsevier. - 0306-4549 .- 1873-2100. ; 102, s. 190-199
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Tidskriftsartikel (refereegranskat)abstract
- With the goal to enhance the capability to perform best-estimate simulations of Light Water Reactors (LWRs) transients, with strong coupling between core neutronics and plant thermal-hydraulic, a coupling between TRACE and SIMULATE-3K (TS3K) was developed in collaboration between PSI and Studsvik for analyses involving interactions between system and core. In order to verify the coupling scheme and the coupled code capabilities to simulate complex transients, the OECD/NEA Oskarshmn-2 (O-2) Stability benchmark was modeled with the coupled code TS3K. The main goal of this paper is to present TS3K analyses of the Oskarshamn-2 stability event, noting that this constitutes the first reported assessment of this code system for a BWR stability problem. A systematic analysis is carried out using different time-space discretization schemes in order to identify an optimized methodology to simulate correctly the O-2 stability event. In this context, the TS3K results are compared to the available benchmark data both for steady-state and transient conditions. The results show that using a refined model in space and time, the TS3K model can successfully capture the entire behavior of the transient qualitatively, i.e. onset of the instability with growing oscillation amplitudes, as well as quantitatively, i.e. Decay Ratio and resonance frequency. In addition, the results are compared also to those obtained using TRACE/PARCS and S3K stand-alone, which allows a systematic comparison between different codes.
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| 6. |
- Rochman, D., et al.
(författare)
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A Bayesian Monte Carlo method for fission yield covariance information
- 2016
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 95, s. 125-134
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Tidskriftsartikel (refereegranskat)abstract
- The present work proposes a Bayesian method to combine theoretical fission yields with a set of reference data. These two sources of information are merged using a Monte Carlo process, and leads to a so-called Bayesian Monte Carlo update. Examples are presented for the independent fission yields of four major actinides, using the GEF code as a source of theoretical calculations and an evaluated library of fission yields for the reference data. The impact of the updated fission yields and their covariances is shown for two distinct applications: a UO2 pincell with burn-up up to 40 GWD/tHM and decay heat calculations of a thermal neutron pulse on U-235 and Pu-239.
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| 7. |
- Rochman, D., et al.
(författare)
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Correlation (nu)over-bar(p) - sigma for U-Pu in the thermal and resonance neutron range via integral information
- 2019
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Ingår i: The European Physical Journal Plus. - : SPRINGER HEIDELBERG. - 2190-5444. ; 134
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an application of the Backward-Forward Monte Carlo (BFMC) method using measured critical boron concentrations for a specific PWR cycle. The considered prior nuclear data are the fission cross sections, nu for U-235 and Pu-239 and the capture cross section of U-238. The posterior nuclear data exhibit cross-isotope correlations, moderate changes for the average quantities and reduced uncertainties. This work is the first one considering the BFMC method and an integral system mostly sensitive to thermal neutrons. It contributes to show the impact of integral experimental data for the evaluation of nuclear data and their covariance matrices, leading to cross-isotope correlations and a nuclear data uncertainty reduction.
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| 8. |
- Rochman, D., et al.
(författare)
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Nuclear Data Uncertainties for Typical LWR Fuel Assemblies and a Simple Reactor Core
- 2017
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Ingår i: Nuclear Data Sheets. - : Elsevier BV. - 0090-3752 .- 1095-9904. ; 139, s. 1-76
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Tidskriftsartikel (refereegranskat)abstract
- Abstract The impact of the current nuclear data library covariances such as in ENDF/B-VII.1, JEFF-3.2, JENDL-4.0, SCALE and TENDL, for relevant current reactors is presented in this work. The uncertainties due to nuclear data are calculated for existing PWR and BWR fuel assemblies (with burn-up up to 40 GWd/tHM, followed by 10 years of cooling time) and for a simplified PWR full core model (without burn-up) for quantities such as k ∞ , macroscopic cross sections, pin power or isotope inventory. In this work, the method of propagation of uncertainties is based on random sampling of nuclear data, either from covariance files or directly from basic parameters. Additionally, possible biases on calculated quantities are investigated such as the self-shielding treatment. Different calculation schemes are used, based on CASMO, SCALE, DRAGON, MCNP or FISPACT-II, thus simulating real-life assignments for technical-support organizations. The outcome of such a study is a comparison of uncertainties with two consequences. One: although this study is not expected to lead to similar results between the involved calculation schemes, it provides an insight on what can happen when calculating uncertainties and allows to give some perspectives on the range of validity on these uncertainties. Two: it allows to dress a picture of the state of the knowledge as of today, using existing nuclear data library covariances and current methods.
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| 9. |
- Rochman, D., et al.
(författare)
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Nuclear data uncertainty for criticality-safety : Monte Carlo vs. linear perturbation
- 2016
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 92, s. 150-160
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Tidskriftsartikel (refereegranskat)abstract
- This work is presenting a comparison of results for different methods of uncertainty propagation due to nuclear data for 330 criticality-safety benchmarks. Covariance information is propagated to key using either Monte Carlo methods (NUSS: based on existing nuclear data covariances, and TMC: based on reaction model parameters) or sensitivity calculations from MCNP6 coupled with nuclear data covariances. We are showing that all three methods are globally equivalent for criticality calculations considering the two first moments of a distribution (average and standard deviation), but the Monte Carlo methods lead to actual probability distributions, where the third moment (skewness) should not be ignored for safety assessments.
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| 10. |
- Rochman, D., et al.
(författare)
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Radiative neutron capture : Hauser Feshbach vs. statistical resonances
- 2017
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Ingår i: Physics Letters B. - : ELSEVIER SCIENCE BV. - 0370-2693 .- 1873-2445. ; 764, s. 109-113
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Tidskriftsartikel (refereegranskat)abstract
- The radiative neutron capture rates for isotopes of astrophysical interest are commonly calculated on the basis of the statistical Hauser Feshbach (HF) reaction model, leading to smooth and monotonically varying temperature-dependent Maxwellian-averaged cross sections (MACS). The HF approximation is known to be valid if the number of resonances in the compound system is relatively high. However, such a condition is hardly fulfilled for keV neutrons captured on light or exotic neutron-rich nuclei. For this reason, a different procedure is proposed here, based on the generation of statistical resonances. This novel technique, called the "High Fidelity Resonance" (HFR) method is shown to provide similar results as the HF approach for nuclei with a high level density but to deviate and be more realistic than HF predictions for light and neutron-rich nuclei or at relatively low sub-keV energies. The MACS derived with the HFR method are systematically compared with the traditional HF calculations for some 3300 neutron-rich nuclei and shown to give rise to significantly larger predictions with respect to the HF approach at energies of astrophysical relevance. For this reason, the HF approach should not be applied to light or neutron-rich nuclei. The Doppler broadening of the generated resonances is also studied and found to have a negligible impact on the calculated MACS.
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