A new DT campaign (DTE2) is planned at JET in 2020 to minimize the risks of ITER operations. In view of DT operations, a calibration of the JET neutron monitors at 14 MeV neutron energy has been performed, using a well-calibrated 14 MeV neutron generator (NG) deployed together with its power supply and control unit, inside the vacuum vessel by the JET remote handling system. The NG was equipped with two calibrated diamond detectors, which continuously monitored its neutron emission rate during the calibration, and activation foils which provided the time-integrated yield. Cables embedded in the remote handling boom were used to power the neutron generator, the active detectors and the pre-amplifier, and to transport the detectors' signal. The monitoring activation foils were retrieved at the end of each day for decay gamma-ray counting, and replaced by fresh ones. About 76 hours of irradiation, in 9 days, were needed, with the neutron generator in 73 different poloidal and toroidal positions in order to calibrate the two neutron yield-measuring systems available at JET: the U-235 fission chambers (KN1) and the inner activation system (KN2). The NG neutron emission rates provided by the monitoring detectors were in agreement within 3 %. Neutronics calculations have been performed using MCNP code and a detailed model of JET to derive the response of the JET neutron detectors to DT plasma neutrons, starting from the response to the NG neutrons, and taking into account the anisotropy of the neutron generator and all the calibration circumstances. These calculations have made use of a very detailed and validated geometrical description of the neutron generator and of the modified MNCP neutron source subroutine producing neutron energy-angle distribution for the neutrons emitted by the NG. The KN1 calibration factor for a DT plasma has been determined with ±4.2 % experimental uncertainty. Corrections due to NG and remote handling effects and the plasma volume effect have been calculated by simulation modelling. The related additional uncertainties are difficult to estimate. However, the results of the previous calibration in 2013 have demonstrated that such uncertainties due to modelling are globally ? ±3 %. It has been found that the difference between KN1 response to DD neutrons and that to DT neutrons is within the uncertainties in the derived responses. KN2 has been calibrated using the 93Nb(n,2n)92mNb and 27Al(n,a)24Na activation reactions (energy thresholds 10 MeV and 5 MeV, respectively). The total uncertainty on the calibration factors is ±6 % for 93Nb(n,2n)92mNb and ±8 % 27Al(n,a)24Na (1?). The calibration factors of the two independent systems KN1 and KN2 will be validated during DT operations. The experience gained and the lessons learned are presented and discussed, in particular with regard to the 14 MeV neutron calibrations in ITER.
COBISS.SI-ID: 31611431
A fission rate profile benchmark experiment has been performed at the Jožef Stefan Institute TRIGA Mark II reactor. The measurements were made using absolutely calibrated miniature fission chambers developed and manufactured by the Commissariat a l'Energie Atomique et aux Energies Alternatives. The aim of the paper is to describe the experimental set-up, fission rate measurements and to present the detailed Monte Carlo computational model of the TRIGA reactor, which was constructed with as used to compute absolute fission rate distributions in the core at a fixed control rod position, taking into account the detailed description of the experimental configuration. The paper focuses on the extensive evaluation of experimental and calculational uncertainties and biases following the International Reactor Physics Experiment Evaluation Project methodology. A comparison between the measured and computed absolute reaction rates concludes the paper, with the agreement being within one sigma standard uncertainty.
COBISS.SI-ID: 30868775
We describe the new ENDF/B-VIII.0 evaluated nuclear reaction data library. ENDF/B-VIII.0 fully incorporates the new IAEA standards, includes improved thermal neutron scattering data and uses new evaluated data from the CIELO project for neutron reactions on 1H, 16O, 56Fe, 235U, 238U and 239Pu described in companion papers in the present issue of Nuclear Data Sheets. The evaluations benefit from recent experimental data obtained in the U.S. and Europe, and improvements in theory and simulation. Notable advances include updated evaluated data for light nuclei, structural materials, actinides, fission energy release, prompt fission neutron and %-ray spectra, thermal neutron scattering data, and charged-particle reactions. Integral validation testing is shown for a wide range of criticality, reaction rate, and neutron transmission benchmarks. In general, integral validation performance of the library is improved relative to the previous ENDF/B-VII.1 library.
COBISS.SI-ID: 31264039
An evaluation of the criticality and relative fission rate radial distribution experiments in an 69.2-cm diameter aluminium sphere filled with intermediately enriched UO2F2 aqueous solution is presented. An evaluation of the total experimental uncertainty has been performed within the framework of the International Criticality Benchmark Evaluation Project (ICSBEP) and International Reactor Physics Benchmark Evaluation Project (IRPhEP). In addition, the uncertainty due to the uncertainties in the nuclear data is evaluated in this paper. It has been determined that the highest contribution to the overall uncertainty in the effective multiplication factor keff is due to the uncertainty in the uranium enrichment (550 pcm in keff due to the 4% uncertainty in 235U enrichment). The highest experimental uncertainties in the relative fission rate profile in terms of the relative standard uncertainty (Lrs) are 0.032, 0.016, and 0.020 due to the uncertainty in guide tube diameter, filling tubes position, and detector position, respectively. It is estimated that the uncertainty in the nuclear data contributes approximately 400 pcm%1200 pcm to the uncertainty in keff depending on the covariance data library used. keff and radial fission rates have been calculated with MCNP and COG Monte Carlo neutron transport codes and have been compared to the experimental benchmark values. In general, the various Monte Carlo codes have given similar results with deviations within uncertainties.
COBISS.SI-ID: 31863591
The rod insertion method for control rod worth measurement is explained and past as well as recent developments are outlined. The original methodology is updated with a more consistent use of the flux redistribution correction, conversion from dynamic to static reactivity and a new procedure to account for the so-called reactivity overshoot. As an example, the procedure is applied to real measured data from Krško NPP. Resulting integral and differential worth curves are compared with reference measurements by the boron dilution method, where a previously unattainable match is observed. Additional research is presented in order to assess the remaining small deviations. Besides other advantages, the rod insertion method is demonstrated to produce results that are in excellent agreement with those of boron dilution method and can therefore be used as replacement.
COBISS.SI-ID: 30971175
The use of Monte Carlo transport method with the Serpent code for generating unit cell cross sections of a light-water reactor is investigated. The geometry is a 3 % 3 array of cells, where homogenization is performed over the central cell, while the neighboring cells represent a kind of color-set scheme to model the radial leakage from the central cell. Instead of the default homogenization method of Serpent, the Effective Diffusion Homogenization method is applied externally, which conserves reaction rates, as well as the boundary partial currents of the central cell. The exercise serves to explore the potential of the Monte Carlo method for core design calculations and to validate and improve the existing computational scheme in which unit-cell calculations are based on the 1-D deterministic transport model in the WIMSD code. The cross sections by both methods are compared and applied to predict the hot-zero-power critical boron concentration and radial power distribution of the Krško NPP in comparison with measured values. The results confirm applicability of Monte Carlo transport calculations with EDH homogenization at the unit-cell level and warrant further extension to burnup and whole-assembly Monte Carlo modeling, at least for validation purposes due to present computational time constraints.
COBISS.SI-ID: 29443879
The Fission Track Thermal Ionization Mass Spectrometry (FT-TIMS) method is considered as the reference method for particle analysis in the field of nuclear Safeguards for measurements of isotopic compositions (fissile material enrichment levels) in micrometer-sized uranium particles collected in nuclear facilities. An integral phase in the method is the irradiation of samples in a very well thermalized neutron spectrum. A bilateral collaboration project was carried out between the Jožef Stefan Institute (JSI, Slovenia) and the Commissariat a l%Énergie Atomique et aux Énergies Alternatives (CEA, France) to determine whether the JSI TRIGA reactor could be used for irradiations of samples for the FT-TIMS method. This paper describes Monte Carlo simulations, experimental activation measurements and test irradiations performed in the JSI TRIGA reactor, firstly to determine the feasibility, and secondly to design and qualify a purpose-built heavy water based irradiation device for FT-TIMS samples. The final device design has been shown experimentally to meet all the required performance specifications.
COBISS.SI-ID: 31120679
PURPOSE: To characterize proliferative changes in tumors during the sunitinib malate exposure/withdrawal using 3'-deoxy-3'-[(18)F] fluorothymidine (FLT) positron emission tomography (PET)/computed tomography (CT) imaging. PATIENTS AND METHODS: Patients with advanced solid malignancies and no prior anti-VEGF exposure were enrolled. All patients had metastatic lesions amenable to FLT PET/CT imaging. Sunitinib was initiated at the standard dose of 50 mg p.o. daily either on a 4/2 or 2/1 schedule. FLT PET/CT scans were obtained at baseline, during sunitinib exposure, and after sunitinib withdrawal within cycle #1 of therapy. VEGF levels and sunitinib pharmacokinetic (PK) data were assessed at the same time points. RESULTS: Sixteen patients (8 patients on 4/2 schedule and 8 patients on 2/1 schedule) completed all three planned FLT PET/CT scans and were evaluable for pharmacodynamic imaging evaluation. During sunitinib withdrawal (change from scans 2 to 3) median FLT PET standardized uptake value (SUV (mean)) increased +15% (range: -14% to 277%; P = 0.047) for the 4/2 schedule and +19% (range: -5.3% to 200%; P = 0.047) for the 2/1 schedule. Sunitinib PK and VEGF ligand levels increased during sunitinib exposure and returned toward baseline during the treatment withdrawal. CONCLUSIONS: The increase of cellular proliferation during sunitinib withdrawal in patients with renal cell carcinoma and other solid malignancies is consistent with a VEGF receptor (VEGFR) tyrosine kinase inhibitor (TKI) withdrawal flare. Univariate and multivariate analysis suggest that plasma VEGF is associated with this flare, with an exploratory analysis implying that patients who experience less clinical benefit have a larger withdrawal flare. This might suggest that patients with a robust compensatory response to VEGFR TKI therapy experience early angiogenic escape.
COBISS.SI-ID: 25278759
The first-derivative probe technique was applied to derive data for plasma parameters from the IV Langmuir probe characteristics measured in the plasma boundary region in the COMPASS tokamak and in the TJ-II stellarator. It is shown that in the COMPASS tokamak in the vicinity of the last closed flux surface (LCFS) the electron energy distribution function (EEDF) is bi-Maxwellian with the low-temperature electron fraction predominating over the higher temperature one, whereas in the far scrape-off layer (SOL) the EEDF is Maxwellian. In the TJ-II stellarator during NBI heated plasma the EEDF in the confined plasma and close to the LCFS is bi-Maxwellian while in the far SOL the EEDF is Maxwellian. In contrast, during the ECR heating phase of the discharge both in the confined plasma and in the SOL the EEDF is bi-Maxwellian. The mechanism for the appearance of a bi-Maxwellian EEDF in the vicinity of the LCFS is discussed. The comparison of the results from probe measurements with ASTRA package and EIRENE code calculations suggests that the main reason of the appearance of a bi-Maxwellian EEDF in the vicinity of the LCFS is the ionization of the neutral atoms. Results for the electron temperatures and densities obtained by the first-derivative probe technique in the COMPASS tokamak and in the TJ-II stellarator were used to evaluate the radial distribution of the parallel power flux density. It is shown that in the SOL the radial distribution of the parallel power flux density is a double exponential. It is pointed out that in the calculations of the parallel power flux density at the LCFS the energy losses from ionization mechanisms must be taken into account.
COBISS.SI-ID: 28955943
A neutronics benchmark experiment on copper assembly was performed end 2014 beginning 2015 at the 14-MeV Frascati neutron generator (FNG) of ENEA Frascati with the objective to provide the experimental database required for the validation of the copper nuclear data relevant for ITER design calculations, including the related uncertainties. The paper presents the pre- and post-analysis of the experiment performed using cross-section sensitivity and uncertainty codes, both deterministic (SUSD3D) and Monte Carlo (MCSEN5). Cumulative reaction rates and neutron flux spectra, their sensitivity to the cross sections, as well as the corresponding uncertainties were estimated for different selected detector positions up to 58 cm in the copper assembly. This permitted in the pre-analysis phase to optimize the geometry, the detector positions and the choice of activation reactions, and in the post-analysis phase to interpret the results of the measurements and the calculations, to conclude on the quality of the relevant nuclear cross-section data, and to estimate the uncertainties in the calculated nuclear responses and fluxes. Large uncertainties in the calculated reaction rates and neutron spectra of up to 50%, rarely observed at this level in the benchmark analysis using today's nuclear data, were predicted, particularly high for fast reactions. Observed C/E (dis)agreements with values as low as 0.5 partly confirm these predictions. Benchmark results are therefore expected to contribute to the improvement of both cross section as well as covariance data evaluations.
COBISS.SI-ID: 29191975