Strengthening the SSTC NRS Scientific and Technical Potential through Participation in the IAEA Coordinated Research Projects

The State Scientific and Technical Center for Nuclear and Radiation Safety (SSTC NRS), a Ukrainian enterprise with a 29-year experience in the area of scientific and technical support to the national nuclear regulator (SNRIU), has been actively involved in international research activities. Participation in the IAEA coordinated research activities is among the SSTC NRS priorities. In the period of 2018–2020, the IAEA accepted four SSTC NRS proposals for participation in respective Coordinated Research Projects (CRPs). These CRPs address scientific and technical issues in different areas such as: 1) performance of probabilistic safety assessment for multi-unit/multi-reactor sites; 2) use of dose projection tools to ensure preparedness and response to nuclear and radiological emergencies; 3) phenomena related to in-vessel melt retention; 4) spent fuel characterization. This article presents a brief overview of the abovementioned projects with definition of scientific contributions by the SSTC NRS (participation in benchmarks, development of methodological documents on implementing research stages and of IAEA technical documents (TECDOC) for demonstration of best practices and results of research carried out by international teams).

BOUNDARY CONDITION MODELING EFFECT ON THE SPENT FUEL CHARACTERIZATION AND FINAL DECAY HEAT PREDICTION FROM A PWR ASSEMBLY

In this paper, two main exercises have been carried out to describe the effect that varying an albedo boundary condition has in the computation of observables such as decay heat, neutron emission rate and nuclide inventory from a PWR fuel assembly (or a configuration of assemblies) during a depletion scenario. The SERPENT2 code was then employed to emphasize the importance of modeling a proper boundary condition for such purposes. Moreover, the effect of taking into account more than a single fuel-pin region for depletion studies while varying the type of boundary condition, was also accounted for. The first exercise has the main objective of comparing in a single fuel assembly the albedo variations ranging from 1.1 up to full vacuum conditions. By comparing to the reference assembly (considered to be the case of full reflective conditions), relative differences up to +17% were observed in decay heat and up to almost -30% in neutron emissions. Also, a clear dependence on the albedo was detected if more than one depletable zone was considered while computing the integral value of observables of interest. Regarding the second exercise, where a 3 × 3 configuration of fuel assemblies is being now considered with a reflector section in the middle, a negligible effect on the observables was observed for the single fuel pin zone case; instead, an effect in the 244Cm computation when analyzing two fuel pin-zones produced a change in the neutron emission rate during cooling time up to 2.5% (while comparing it to the reference single assembly case).

Analysis for the ARIANE GU3 sample: nuclide inventory and decay heat

This study presents an analysis of the ARIANE GU3 sample, in terms of nuclide inventory, as well as sample rod and assembly decay heat. The validation of a number of CASMO5 and library versions are performed with regards to the measured nuclide inventory, taking into account two dimensional lattice simulations. Uncertainties due to various sources (nuclear data, operating conditions and manufacturing tolerances) are also provided, and are combined with biases into expanded uncertainties. This study is similar to a previous one on the GU1 sample and fit in the framework of code validation, as well as in the estimation of code predictive power for spent fuel characterization.

DEVELOPMENT OF FUEL CHARACTERIZATION TOOL BASED ON LIBRARY INTERPOLATION

The feasibility of using Origen+ARP code for depletion and decay calculations for Krško NPP was tested by performing depletion and decay calculations using interpolated libraries and comparing the results to the ones calculated from non-interpolated libraries in order to evaluated the number of libraries needed in order to interpolate fuel properties with sufficient precision for any realistic burnup scenario. For Krško NPP fuel, using three interpolation libraries with different decay heat parameters was enough to bring the approximation error bellow 0:5 % when comparing fuel decay heat through the decay interval.

Fuel Characterization of Agro-wastes and Briquettes Produced from Rice Husk, Groundnut Shell and Corncob Blends

The choice of agro waste for the production of briquettes for domestic and industrial cottage utilization depends on the residues’ physical and fuel characteristics. This study investigate the physical and fuel characteristics for both the residues and blends of rice hull, groundnut shell and corncob. The residues were subjected to size reduction process and variance analysis was used to establish the influence of each sample blends. Different samples of briquettes were produced by blending rice hull (R), groundnut shell (G) and corncob(C) with different ratios of R:G:C respectively using cassava starch as a binder. The residue’ dimensions and densifications of the sample briquettes were determined using standard methods.The results revealed the following ranges of values; For the compressed residues, density (0.075 - 0.099Kg/m3), volume (0.001 - 0.002m3), height (1.0357 - 1.0343m). For the relaxed residues, density (0.049 - 0.210Kg/m3), volume (0.0001 -0.0002m3), height (1.0357 - 1.0343m). The residual density of rice hull, groundnut shell and corncob are 104, 105, and 103 (Kg/m3) respectively. The densification; compressed density (461.22 - 627.24 Kg/m3), relaxed density (285.47 - 393.63 Kg/m3), density ratio (0.56 - 0.66), relaxation ratio (1.52 - 1.79), and compaction ratio (1.46 to 2.01). Blend formulations affected the combustion characteristics of the briquettes, with low moisture briquettes possessing higher calorific values. The briquette formulation containing ratio 50:20:30 of rice hull: groundnut shell: corncob respectively had more positive attributes of biomass fuel such as lower relaxation ratio and high compaction ratio than the control and other formulated briquettes in this study. Generally, significant (p<0.05) differences existed between the samples in almost all the parameters.Keywords: Briquettes, Corn comb, Densification, Fuel Characterization, Groundnut shell, Rice hull.