Residual activity evaluation: a benchmark between ANITA, FISPACT, FLUKA and PHITS codes

The activity of residual nuclides dictates the radiation fields in periodic inspections/repairs (maintenance periods) and dismantling operations (decommissioning phase) of accelerator facilities (i.e., medical, industrial, research) and nuclear reactors. Therefore, the correct prediction of the material activation allows for a more accurate planning of the activities, in line with the ALARA (As Low As Reasonably Achievable) principles. The scope of the present work is to show the results of a comparison between residual total specific activity versus a set of cooling time instants (from zero up to 10 years after irradiation) as obtained by two analytical (FISPACT and ANITA) and two Monte Carlo (FLUKA and PHITS) codes, making use of their default nuclear data libraries. A set of ~40 irradiating scenarios is considered, i.e. neutron and proton particles of different energies, ranging from zero to many hundreds MeV, impinging on pure elements or materials of standard composition typically used in industrial applications (namely, AISI SS316 and Portland concrete). In some cases, experimental results were also available for a more thorough benchmark

Residual activity evaluation: a benchmark between ANITA, FISPACT, FLUKA and PHITS codes

The activity of residual nuclides dictates the radiation fields in periodic inspections/repairs (maintenance periods) and dismantling operations (decommissioning phase) of accelerator facilities (i.e., medical, industrial, research) and nuclear reactors. Therefore, the correct prediction of the material activation allows for a more accurate planning of the activities, in line with the ALARA (As Low As Reasonably Achievable) principles. The scope of the present work is to show the results of a comparison between residual total specific activity versus a set of cooling time instants (from zero up to 10 years after irradiation) as obtained by two analytical (FISPACT and ANITA) and two Monte Carlo (FLUKA and PHITS) codes, making use of their default nuclear data libraries. A set of ~40 irradiating scenarios is considered, i.e. neutron and proton particles of different energies, ranging from zero to many hundreds MeV, impinging on pure elements or materials of standard composition typically used in industrial applications (namely, AISI SS316 and Portland concrete). In some cases, experimental results were also available for a more thorough benchmark

New infrastructure for studies of transmutation and fast systems concepts

In this work we report initial studies on a low power Accelerator-Driven System as a possible experimental facility for the measurement of relevant integral nuclear quantities. In particular, we performed Monte Carlo simulations of minor actinides and fission products irradiation and estimated the fission rate within fission chambers in the reactor core and the reflector, in order to evaluate the transmutation rates and the measurement sensitivity. We also performed a photo-peak analysis of available experimental data from a research reactor, in order to estimate the expected sensitivity of this analysis method on the irradiation of samples in the ADS considered

A low power ADS for transmutation studies in fast systems

In this work, we report studies on a fast low power accelerator driven system model as a possible experimental facility, focusing on its capabilities in terms of measurement of relevant integral nuclear quantities. In particular, we performed Monte Carlo simulations of minor actinides and fission products irradiation and estimated the fission rate within fission chambers in the reactor core and the reflector, in order to evaluate the transmutation rates and the measurement sensitivity. We also performed a photo-peak analysis of available experimental data from a research reactor, in order to estimate the expected sensitivity of this analysis method on the irradiation of samples in the ADS considered

High blood flow shear stress values are associated with circulating tumor cells cluster disaggregation in a multi-channel microfluidic device

Metastasis represents a dynamic succession of events involving tumor cells which disseminate through the organism via the bloodstream. Circulating tumor cells (CTCs) can flow the bloodstream as single cells or as multicellular aggregates (clusters), which present a different potential to metastasize. The effects of the bloodstream-related physical constraints, such as hemodynamic wall shear stress (WSS), on CTC clusters are still unclear. Therefore, we developed, upon theoretical and CFD modeling, a new multichannel microfluidic device able to simultaneously reproduce different WSS characterizing the human circulatory system, where to analyze the correlation between SS and CTC clusters behavior. Three physiological WSS levels (i.e. 2, 5, 20 dyn/cm2) were generated, reproducing values typical of capillaries, veins and arteries. As first validation, triple-negative breast cancer cells (MDAMB- 231) were injected as single CTCs showing that higher values of WSS are correlated with a decreased viability. Next, the SS-mediated disaggregation of CTC clusters was computationally investigated in a vessels-mimicking domain. Finally, CTC clusters were injected within the three different circuits and subjected to the three different WSS, revealing that increasing WSS levels are associated with a raising clusters disaggregation after 6 hours of circulation. These results suggest that our device may represent a valid in vitro tool to carry out systematic studies on the biological significance of blood flow mechanical forces and eventually to promote new strategies for anticancer therapy

A new hybrid fast-slow ADS for research and applications

We report on the studies of an irradiation facility based on an accelerator-driven subcritical nuclear research reactor, which can simultaneously provide a fast flux in the core and a thermal flux in the reflector, that we will call a hybrid fast-slow ADS. The conceptual design presented here, inspired by [1], starts from a 432 kW (keff=0.967) ADS composed by 110 solid lead fuel assemblies each with size 9.7 x 9.7 x 87 cm3, filled with 81 MOX pins (16.5% Pu+Am) of 0.357 cm radius and surrounded by a 0.068 cm thick AISI steel cladding. Source neutrons are produced by a 70 MeV 1 mA proton beam impinging on a beryllium target (~ 8 x 1014 n/sec) [2].The core is cooled by helium flowing in very thin pipes, 0.25 cm in diameter and is surrounded by a 80 cm lead reflector. Core and reflector are contained within a 2 cm steel vessel. The hybrid version (keff 0.972= P=527 kW) is instead composed by 59 fuel assemblies, each hosting 81 MOX pins (22% Pu+Am) where: - The lead reflector has been replaced by three concentric layers, the first of 35 cm lead, followed by 50 cm graphite and finally 10 cm lead. - In the cooling system water flows in wider pipes, 0.5 cm in diameter, which allows to increase keff while maintaining the fast character of the spectrum. We simulated the neutron flux in three core positions (internal, intermediate and external) and in two graphite reflector positions (internal, intermediate), finding that the flux is still mostly fast in the core, while it exhibits a strong thermal component in the reflector, as shown in the following table. This work is partially supported by the 7th Framework Programmes of the European Commission (Euratom) through the CHANDA contract FP7-Fission-2013-605203

An ADS irradiation facility for fast and slow neutrons

We studied a flexible ADS-based irradiation facility with fast neutrons inside the core and slow neutrons in the composite reflector containing light materials. The fast reactor core has been designed using MCNP-6 code with a mixed reflector formed by three concentric cylindrical layers (lead+graphite+lead) in order to have different neutrons spectra to perform various types of measurements without perturbing the ADS core fast characteristics. We also included in the ADS design three irradiation points external to the core, in positions such to have different neutron spectra, for measurements to be performed out of the ADS system. Moreover, we performed a thermal-hydraulic assessment of the behavior of target and core cooling systems. In order to investigate the capabilities of the system, we studied different kinds of possible measurements that could be performed in various positions, both inside and outside the ADS