| 471. |
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| 472. |
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| 473. |
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| 474. |
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| 475. |
- Sjöstrand, Henrik, 1978-, et al.
(författare)
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Monte Carlo integral adjustment of nuclear data libraries : experimental covariances and inconsistent data
- 2019
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 211:07007
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Tidskriftsartikel (refereegranskat)abstract
- Integral experiments can be used to adjust nuclear data libraries. Here a Bayesian Monte Carlo method based on assigning weights to the different random files is used. If the experiments are inconsistent within them-self or with the nuclear data it is shown that the adjustment procedure can lead to undesirable results. Therefore, a technique to treat inconsistent data is presented. The technique is based on the optimization of the marginal likelihood which is approximated by a sample of model calculations. The sources to the inconsistencies are discussed and the importance to take into account correlation between the different experiments is emphasized. It is found that the technique can address inconsistencies in a desirable way.
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| 476. |
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| 477. |
- Sjöstrand, Henrik, 1978-
(författare)
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Neutron Spectroscopy : Instrumentation and Methods for Fusion Plasmas
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- When the heavy hydrogen isotopes deuterium (D) and tritium (T) undergo nuclear fusion large amounts of energy are released. At the Joint European Torus (JET) research is performed on how to harvest this energy. Two of the most important fusion reactions, d+d→3He+n (En = 2.5 MeV) and d+t→4He+n (En = 14 MeV), produce neutrons. This thesis investigates how measurements of these neutrons can provide information on the fusion performance. The Magnetic Proton Recoil (MPR) neutron spectrometer has operated at JET since 1996. The spectrometer was designed to provide measurements on the 14 MeV neutron emission in DT operation, thereby conveying information on the state of the fuel ions. However, a majority of today’s fusion experiments are performed with pure D fuel. Under such conditions, the measurements with the MPR were severely hampered due to interfering background. This prompted an upgrade of the instrument. The upgrade, described in this thesis, included a new focal plane detector, a phoswich scintillator array, and new data acquisition electronics, based on transient recorder cards. This combination allows for pulse shape discrimination techniques to be applied and a signal to background of 5/1 has been achieved in measurements of the 2.5-MeV neutrons in D experiments. The upgrade also includes a new control and monitoring system, which enables the monitoring and correction of gain variations in the spectrometer’s photo multiplier tubes. Such corrections are vital for obtaining good data quality. In addition, this thesis describes a new method for determining the total neutron yield and hence the fusion power by using a MPR spectrometer in combination with a neutron emission profile monitor. The system has been operated at JET both during DT and D experiments. It is found that the systematic uncertainties are considerably lower (≈6 %) than for traditional systems. For a dedicated system designed for the next generation fusion experiments, i.e, ITER, uncertainties of 4 % could be attained. Neutron spectroscopy can also be an important tool for determining the neutron emission from residual tritium in D plasmas. This information is combined with other measurements at JET in order to determine the confinement of the 1 MeV tritons from the d+d→t+p reactions.
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| 478. |
- Sjöstrand, Henrik, 1978-
(författare)
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New chromium evaluation for EuroFusion
- 2017
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- •A new TALYS / TMC based chromium evaluation in the fast energy range for the stable chromium isotopes are proposed by adding integral constrains and Gaussian Processes. –Including co-variance for angular distributions and angular distributions / cross-sections. –Including co-variances between isotopes in random-files. –GP → Realistic uncertainties where scarce / contradicting experimental data is present Alternatively, we can address, e.g., copper or tungsten with the same methodology
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| 479. |
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| 480. |
- Sjöstrand, Henrik, 1978-, et al.
(författare)
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Nuclear Data Uncertainty Quantification for the Nuclear Fuel Cycle Using the TMC Method
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Reactor, criticality and transport simulations are widely used in the nuclear community to e.g. determine safety parameters, evaluate transients, and calculate the fuel inventory. These simulations use nuclear data (ND) as one of their most important inputs. ND is obtained by performing experiments and using theoretical nuclear models. Both experiments and theory are associated with uncertainties and consequently all ND are associated with uncertainties. There are also strong correlations in the uncertainties between different energies, reaction channels and isotopes, in both experiments and modelling. Many ND libraries (e.g. JEFF-3.2 and ENDF/B-VII.1) contain information on the ND uncertainties and their correlations in covariance files. However, this information relies on assumptions of normal distributions and is not complete. Furthermore, many reactor codes do not use ND uncertainties as input, and when they do, they rely on different assumptions, which tend to underestimate the propagated uncertainty. In order to address these issues the Total Monte Carlo (TMC) methodology has been developed [1]. The basic principles of the TMC method are illustrated in Figure 1. Figure 1. The TMC uncertainty propagation and TENDL production. In the TMC uncertainty propagation the final result is the spread in a macroscopic parameter. This spread is the systematic uncertainty in the calculation due to ND in the investigated parameter. (CS = cross section, FY = fission yield) In the TMC method a large set of random files are derived by sampling nuclear model parameters in the nuclear model codes TALYS. The random files are subsequently compared to experimental values [2]. Consequently, each random file is a complete nuclear data library containing one possible representation of the nuclear data given the uncertainties from theory and experiments. By running a reactor simulation multiple times, each time with a new random file as input, distributions of the different nuclear engineering parameters (e.g. keff, temperature coefficient, inventory, fuel temperature) are derived. These distributions are interpreted as the uncertainties in the engineering parameters due to ND. The TMC method can also be used to produce nuclear data for all open reaction channels including covariances; the “TALYS Evaluated Nuclear Data Library” (TENDL) is an example [3]. In order to select the best file to be included in the TENDL library, the random nuclear data files produced are compared against differential experimental data taken from the EXFOR database and a large set of integral measurements. The TMC method can be used for any neutronic-system and in this contribution we present results from both thermal and fast neutron systems. The importance to include nuclear data uncertainty from angular distribution and thermal scattering are highlighted. [1] A.J.Koning, and D.Rochman, Modern Nuclear Data Evaluation with the TALYS Code System. Nuclear Data Sheets 113 12 2841-2934 (2012)[2] P. Helgesson, H.Sjöstrand, A.J.Koning, D.Rochman, E.Alhassan, S.PompNuclear Data Sheets, Volume 123, Pages 214-219, 2015.[3] "TENDL-2014: TALYS-based evaluated nuclear data library", A.J. Koning, D. Rochman, S. van der Marck, J. Kopecky, J. Ch. Sublet, S. Pomp, H. Sjostrand, R. Forrest, E. Bauge, H. Henriksson, O. Cabellos, S. Goriely J. Leppanen, H. Leeb, A. Plompen and R. Mills, www.talys.eu/tendl-2014.html
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