A preliminary criticality analysis for novel pyrochemical apparatuses for the reprocessing of mixed uranium-plutonium nitride spent nuclear fuel from the BREST-OD-300 reactor was performed. ...High-temperature processing apparatuses, “metallization” electrolyzer, refinery remelting apparatus, refining electrolyzer, and “soft” chlorination apparatus are considered in this work. Computational models of apparatuses for two neutron radiation transport codes (MCU-FR and MCNP) were developed and calculations for criticality were completed using the Monte Carlo method.
The criticality analysis was performed for different loads of fissile material into the apparatuses including overloading conditions. Various emergency situations were considered, in particular, those associated with water ingress into the chamber of the refinery remelting apparatus. It was revealed that for all the considered computational models nuclear safety rules are satisfied.
•Models development and criticality calculations of apparatuses of pyrochemical reprocessing of spent nuclear fuel.•Criticality analysis for pyrochemical apparatuses for regular operation, i.e., using the nominal loading rate of fissile material (FM) into the apparatus, and for violations of regular operation, i.e., with an increased mass of one-time loading of the FM•Criticality analysis for pyrochemical apparatuses in case of other violations of regular operation (cooling the apparatuses, forming the FM spillages, water ingress into the apparatuses).
The nuclear physical properties of austenitic chromium-nickel steel EK-164 (Fe–16Cr–19Ni–2Mo–2Mn–Nb–Ti–B) and its manganese-based modifications EK-164Mn (Fe–16Cr–20Mn–2Mo–Nb–Ti–B) and EK-164MnW ...(Fe–16Cr–20Mn–2W–Nb–Ti–B) under irradiation (up to 5 effective years) in the neutron spectra of fast power (BN-600) and thermonuclear (DEMO-C) reactors and after irradiation (nuclear cooling up to 1000 years) were determined. The investigations were based on using the ACDAM-2.0 calculation complex with consideration of the elemental (alloying and impurity) compositions of steels and typical neutron spectra of fission (BN-600) and fusion (DEMO-C) reactors. The entire set of nuclear physical characteristics of steels (primary radiation damage; transmutation of elements; radiogenic accumulation of elements, including hydrogen, helium, and boron; γ-dose rate; radioactivity; nuclear energy release; isotope contributions) is obtained and their comparative analysis is performed. The time intervals for fulfilling the criteria of low activation of steels after irradiation (γ-dose rate less than 10 mSv/h, radioactivity less than 10
10
Bq/kg, energy release less than 10 W/m
3
) were determined.
The results of complex studies of static and dynamic performance of 1550 nm range VCSELs, which were created by direct bonding (wafer fusion technique) InAlGaAs/InP optical cavity wafers with ...AlGaAs/GaAs distributed Bragg reflector wafers grown by molecular beam epitaxy, are presented. The VCSELs with a buried tunnel junction diameter less than 7 μm demonstrated a single-mode lasing with a side-mode suppression ratio more than 40 dB; however, at diameters less than 5 μm, a sharp increase in the threshold current is observed. It is associated to the appearance of a saturable absorber due to penetration of optical mode into the non-pumped regions of the active region. The maximum single-mode output optical power and the –3 dB modulation bandwidth reached 4.5 mW and 8 GHz, respectively, at 20°C. The maximum data rate at 20°C under non-return-to-zero on-off keying modulation was 23 Gb/s for a short-reach link based on single-mode fiber SMF-28. As the length of the optical link increased up to 2000 m, the maximum data rate dropped to 18 Gbit/s. The main factors affecting the high-speed operation and data transmission range are defined and discussed, and the further ways to overcome themit are proposed.
A combination of advanced light engineering concepts enables a substantial improvement in photon extraction efficiency of micro-cavity-based single-photon sources in the telecom O-band at ∼1.3 µm. We ...employ a broadband bottom distributed Bragg reflector (DBR) and a top DBR formed in a dielectric micropillar with an additional circular Bragg grating in the lateral plane. This device design includes a doped layer in pin-configuration to allow for electric carrier injection. It provides broadband (∼8-10 nm) emission enhancement with an overall photon-extraction efficiency of ∼83% into the upper hemisphere and photon-extraction efficiency of ∼79% within numerical aperture NA=0.7. The efficiency of photon coupling to a single-mode fiber reaches 11% for SMF28 fiber (with NA=0.12), exceeds 22% for 980HP fiber (with NA=0.2) and reaches ∼40% for HNA fiber (with NA=0.42) as demonstrated by 3D finite-difference time-domain modeling.
High power single mode wafer-fused 1300-nm VCSELs with a gain region based on InGaAs/InAlGaAs short period superlattice are fabricated. An InP-based optical cavity and two AlGaAs/GaAs distributed ...Bragg reflector heterostructures were grown by molecular beam epitaõy. The current and optical confinement is provided by a lateral-structured buried tunnel junction with etching depth of <inline-formula> <tex-math notation="LaTeX">\sim 25 </tex-math></inline-formula> nm. It is shown that optimal diameter of the buried tunnel junction for high-power single mode emission is <inline-formula> <tex-math notation="LaTeX">\sim 5 </tex-math></inline-formula>-<inline-formula> <tex-math notation="LaTeX">6~\mu \text{m} </tex-math></inline-formula>. The VCSEL demonstrates more than 6 mW single mode continuous-wave power and a threshold current less than 1.5 mA at 20 °C. The output optical power exceeds 1 mW at 85 °C. A -3dB modulation bandwidth up to 8 GHz and 6 GHz is obtained at 20 °C and 85 °C, respectively. The gain coefficient of <inline-formula> <tex-math notation="LaTeX">\sim 650 </tex-math></inline-formula> cm −1 and the transparency current density of <inline-formula> <tex-math notation="LaTeX">\sim 630 </tex-math></inline-formula> A/cm 2 are estimated at zero gain-to-cavity detuning (\sim 60 °C). The ultimate low internal optical losses about 0.08 % per round-trip (distributed losses ~3.2 cm −1 ) at 20 °C and 0.13 % per round-trip (distributed losses ~5.5 cm −1 ) at 100 °C were obtained.
Introduction. In 1275, two drafts of town law of Freiburg im Breisgau were created. This article presents an analysis of one of these texts, namely the short draft. Methods and materials. The main ...research method is comparative historical analysis. The contents of two charters are compared, namely the 1218 Rodel draft and the short draft of 1275. Analysis. There are 6 thematic clusters uniting the laws by branches of law: 1) privileges of citizens and rights of the Town Lord; 2) criminal procedure law; 3) civil law; 4) town administration; 5) trade law; 6) various laws. The first part of the laws from the short draft is a translation of the Rodelian laws, the second one represents reformulated Rodelian norms, while the last one contains new laws in the legislation of Freiburg. Results. Though the document did not become an official town charter, it manifested the changes in the town law of the 13th century, compared to the previous 1218 Town Charter. In addition, the laws in the draft reflected the political struggle for power between the Town Lord of Freiburg, the City Council of 24 and the town community. The Town Lord regained his previously lost rights, in particular the legislative initiative. However, at the same time, the short draft significantly limited Lord’s arbitrariness towards the property of citizens as well as Freiburg citizens themselves. According to the short draft, the City Council of 24 strengthened and expanded its power in the town, becoming a full-fledged legislative and executive body of the town administration. The town community, on the other hand, was losing its privileges and rights, for example, it lost the opportunity to elect some of the civil servants and members of the Council of 24.
A generalized diffusion model of rotational depolarization of luminescence of polyatomic molecules with internal rotors is developed assuming independent collision statistics for internal rotations ...and rotation of the molecules as a whole. The model is used to calculate the collisional depolarization of non-rigid oligonucleotides with fluorescent labels that are in the free state in solutions and in complexes with nanoparticles. Changes in the fluorescence anisotropy during relaxation are analyzed as functions of the ratio of moments of inertia of the moving parts of the molecule and the transition moment orientations. The conditions for possible enhancement of anisotropy and control of structural changes of biomolecules immobilized on nanoparticle surfaces are evaluated.
The results of experiments aimed at fabricating and studying the properties of photodetector structures based on single-layer graphene produced by chemical vapor deposition are presented. The ...configuration of a Ta
2
O
5
vertical microcavity with a resonance wavelength of about 850 nm and a lower dielectric SiO
2
/Ta
2
O
5
distributed Bragg reflector is taken as the base structure. The conditions for the transfer and fabrication of mesas in the graphene layer on the microcavity surface are optimized. The diagnostics by Raman spectroscopy of the structural quality of graphene after fabrication of the mesas in the graphene layer and contact pads are indicative of the single-layer structure of graphene with a low intensity of features in its spectrum, responsible for imperfection of the structure. The photocurrent is measured under local optical pumping.
The optical characteristics of vertical cylindrical micropillars with AlGaAs distributed Bragg reflectors and InAs/GaAs quantum dots, which are designed for the fabrication of single-photon sources, ...have been studied. The effect of parameters such as the inclination angle of sidewalls, partial oxidation of AlGaAs layers, and deviation of quantum dots from the central axis of a micropillar on the Purcell factor and the radiation extraction efficiency has been numerically simulated by the finite-difference time-domain method. The allowable ranges of the listed parameters have been determined for cylindrical vertical 920-nm micropillars. The comparison of the calculations performed with the refined refractive indices of the used materials at cryogenic temperatures with the measured characteristics of the fabricated micropillar structures has confirmed the adequacy of the used models.
The influence of the substrate temperature and the flux of In adatoms on the structural and optical characteristics of InAs quantum dots with a low surface density is experimentally studied. An ...increase in the substrate temperature under conditions of a high flux of In adatoms promotes an increase in their surface migration and a certain decrease in the density of the array of quantum dots (down to ~(1–2) × 10
10
cm
–2
), however, in this case a significant short-wavelength shift of the photoluminescence spectrum is observed despite an increase in lateral sizes of dots. A decrease in the incident flux of In adatoms at optimal substrate temperatures makes it possible to reduce the dot density more efficiently (down to ~(1–2) × 10
9
cm
–2
).
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