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Nuclear data is the basis of reactor physics analysis. This paper aim at studying the influence of major evaluated nuclear data libraries, CENDL-3.2, ENDF/B-VIII.0, JEFF-3.3, and JENDL-4.0u, on the neutronics modelling of CEFR start-up tests. Results show these four libraries have a good performance and consistency in the modelling CEFR start-up tests. The JEFF-3.3 results exhibit only an 8 pcm keff difference with the measurement. The difference in criticality is decomposed by nuclide, which shows the large overestimation of CENDL-3.2 is mainly from the cross-section of 52Cr. Except for few cases, the calculation results are within 1σ of measurement uncertainty in control rod worth, sodium void reactivity, temperature reactivity, and subassembly swap reactivity. In the evaluation of axial and radial reaction distribution, there are about 65% of relative errors that are less than 5% and 82% of relative errors that are less than 10%.

High-fidelity nuclear data libraries and neutronics simulation tools are essential for the development of fast reactors. The IAEA coordinated research project on “Neutronics Benchmark of CEFR Start-Up Tests” offers valuable data for the qualification of nuclear data libraries and neutronics codes. This paper focuses on the verification and validation of the CEFR start-up modelling using OpenMC Monte-Carlo code against the experimental measurements. The OpenMC simulation results agree well with the measurements in criticality, control rod worth, sodium void reactivity, temperature reactivity, subassembly swap reactivity, and reaction distribution. In feedback coefficient evaluations, an additional state method shows high consistency with lower uncertainty. Among 122 relative errors in the benchmark of the distribution of nuclear reaction, 104 errors are less than 10% and 84 errors are less than 5%. The results demonstrate the high reliability of OpenMC for its application in fast reactor simulations. In the companion paper, the influence of cross-section libraries is investigated using neutronics modelling in this paper.

The China Experimental Fast Reactor (CEFR) is a small, sodium-cooled fast reactor with 20 MW(e) of power. Start-up tests of the CEFR were performed from 2010 to 2011. The China Institute of Atomic Energy made some of the neutronics start-up-test data available to the International Atomic Energy Agency (IAEA) as part of an international neutronics benchmarking exercise by distributing the experimental data to interested organizations from the member states of the IAEA. This benchmarking aims to validate and verify the physical models and neutronics simulation codes with the help of the recorded experimental data. The six start-up tests include evaluating criticality, control-rod worth, reactivity effects, and neutron spectral characteristics. As part of this coordinated research, the IAEA performed neutronics calculations using the Monte Carlo codes Serpent 2 and OpenMC, which can minimize modeling assumptions and produce reference solutions for code verification. Both codes model a three-dimensional heterogeneous core with an ENDF/B-VII.1 cross-section library. This study presents the calculation results with a well-estimated criticality and a reasonably good estimation of reactivities. The description and analysis of the core modeling assumptions, challenges in modeling a dense SFR core, results of the first phase of this project, and comparative analysis with measurements are presented.

Drilling fluids usually gel at rest in order to avoid cuttings to precipitate over the drill bit when circulation is interrupted. At flow start-ups, pumping pressures higher than the steady-state circulation pressure are usually required to surpass the gel strength. The gel-liquid transition may have significant importance, especially in ultra-deep waters where high pressures and low temperatures take place. In the current work, controlled shear rate rheometric tests were conducted to investigate the yielding of an oil based drilling fluid. An algebraic equation, that accounts for both shear rate and shear history, is proposed to predict the gel breaking. This equation requires less fitting parameters than the current structural kinetic models available in literature, and is quite useful to represent the pressure peaks that take place during drilling fluid flow start-ups. The equation fit to rheometric data and is able to predict satisfactorily the start-up shear stress of a gelled drilling fluid at different shear rates. [ABSTRACT FROM AUTHOR]

• CEFR benchmark start-up tests were analyzed with FARCOB and ERANOS 2.1 systems. • Transport and heterogeneity corrections were estimated for accurate prediction of k-eff. • Flux weighted self-shielded cross sections are used for reflectors with ABBN-93. • Experimental and 3-step methods predict reactivity coefficients within measured errors. • Simulated results are agreeing well the measured values by FARCOB and ERANOS. The neutronics analysis of selected start-up tests conducted from 2010 to 2011 in China Experimental Fast Reactor (CEFR) is carried out using in-house FARCOB and European ERANOS-2.1 code systems as a part of IAEA coordinated research project (CRP) on "Neutronics Benchmark of CEFR Start-Up Tests". This exercise has the main objective of validation and verification of physical models, neutronics simulation methodology including cross-section libraries that is used for fast reactor core simulations. It is challenging to simulate such a small compact core of enriched uranium with high neutron leakage having stainless steel radial reflector by using 3-D diffusion theory codes. This benchmark analysis used a new simplified approach such as a 3-step method and experimental method for simulating temperature and sodium void reactivity coefficients. Net criticality, control rod worth, temperature and sodium void reactivity coefficients and swap reactivity could be predicted well within their measured error values. This exercise provided an additional validation of the FARCOB system against small sodium-cooled fast reactor (SFR) cores, and it can be confidently used for the design and analysis of small experimental reactor cores. [ABSTRACT FROM AUTHOR]

The China Experimental Fast Reactor (CEFR) is a small, sodium-cooled fast reactor with 20 MW(e) of power. Start-up tests of the CEFR were performed from 2010 to 2011. The China Institute of Atomic Energy made some of the neutronics start-up-test data available to the International Atomic Energy Agency (IAEA) as part of an international neutronics benchmarking exercise by distributing the experimental data to interested organizations from the member states of the IAEA. This benchmarking aims to validate and verify the physical models and neutronics simulation codes with the help of the recorded experimental data. The six start-up tests include evaluating criticality, control-rod worth, reactivity effects, and neutron spectral characteristics. As part of this coordinated research, the IAEA performed neutronics calculations using the Monte Carlo codes Serpent 2 and OpenMC, which can minimize modeling assumptions and produce reference solutions for code verification. Both codes model a three-dimensional heterogeneous core with an ENDF/B-VII.1 cross-section library. This study presents the calculation results with a well-estimated criticality and a reasonably good estimation of reactivities. The description and analysis of the core modeling assumptions, challenges in modeling a dense SFR core, results of the first phase of this project, and comparative analysis with measurements are presented. [ABSTRACT FROM AUTHOR]

• MCS code system has been verified and validated by using China Experimental Fast Reactor start-up tests numerical simulation. • The start-up tests including criticality, control rod worth, sodium voided reactivity, temperature reactivity and subassembly swap reactivity are analyzed and compared with MCNP6.1 results. • The start-up tests including criticality, control rod worth, sodium voided reactivity, temperature reactivity, subassembly swap reactivity and foil activation are analyzed and compared with measurement data. • The difference between the no wire, smeared wire, and spiral wire models at the critical state are evaluated. The International Atomic Energy Agency and the China Institute of Atomic Energy proposed a coordinated research project (CRP) to establish a benchmark, based on the China Experimental Fast Reactor (CEFR) start-up tests which include fuel loading and criticality, measurements of control rod worth and reactivity coefficients, and foil activation measurements. As a participant in the CRP, the computational reactor physics and experiment laboratory of the Ulsan National Institute of Science and Technology has been studying and analyzing the neutronic performance of the CEFR. The verification and validation are performed for the simulations in the CEFR analysis. A verification process of the methodology was conducted to compare the predicted results with those obtained by a well-known MCNP6.1 Monte Carlo code. The results obtained by the MCS code were compared against the experimental data. The difference in various wire models at the critical state are evaluated in this study. [ABSTRACT FROM AUTHOR]