Plutonium Mononitride Research Articles

First-Principles Study of Nitrogen Adsorption and Dissociation on PuH2 (111) Surface.

Plutonium mononitride is one of the main fuels for Generation IV reactors and can be prepared from nitrogenation of plutonium hydride. We investigated the adsorption and dissociation of nitrogen on PuH2 (111) surface to elaborate the initial stage of nitrogenation. The adsorption energies varied greatly with respect to the adsorption sites and orientations of the adsorbed molecule. The nitrogen exhibited preferential adsorption above the ccp site, where the molecular nitrogen was nearly parallel to the PuH2 surface and pointed to the nearest Pu atom. The orbital hybridization and the electrostatic attraction between the Pu and N weakened the N-N bond in the adsorbed molecule. The mechanism of the dissociation process was investigated within transition state theory, and the analysis of the activation barrier indicated that dissociation of nitrogen is not the rate-determining step of nitrogenation. These findings can contribute to a better understanding of the nuclear fuel cycle.

Exploring the sub-stoichiometric behavior of plutonium mononitride

The intriguing and controversial sub-stoichiometric behavior of plutonium mononitride is investigated here using first-principles calculations combined with special quasirandom structures. It is found that NaCl-type plutonium mononitride is stable for only stoichiometric levels, and the formation enthalpy of plutonium mononitride is in good agreement with others. By comparing with plutonium monocarbide, the main reason for the absence of sub-stoichiometric behavior is the lower N-2p orbital energy, resulting in less hybridization and weaker Pu–N bonds. The weaker Pu–N bonds cannot support the formation of vacancies.

A first principle calculation on electronic properties of plutonium mononitride: Insights from dynamical mean field theory

We perform a first principles calculation on electronic properties of plutonium mononitride (PuN) using a many-body method merging local density approximation (LDA) with dynamical mean field theory (the so called LDA + DMFT scheme), taking into account the on-site Coulomb interaction between Pu 5f states and spin-orbit coupling due to high atomic number of plutonium element. We find that PuN is a mixed-valentnf = 4.823 moderately correlated system and a triplet of quasiparticle peaks below the Fermi level corresponding to multiplet of many-body quasiparticle peaks are due to valence fluctuations and the Pu atomic multiplet structure, which is agreement with the photo-electron spectroscopy observation. The calculation result reveals that the low energy scattering rate from the imaginary part of the self energy is very large, indicating that PuN is a bad metal, which is also in agreement with the density of states (DOS) analysis and other theoretical calculation. In order to compare with experimental angle-resolved photoemission spectrum (ARPES), we also calculate momentum-resolved electronic spectrum function, and analyze electronic excitation across the Fermi level.

Modeling thermal properties of plutonium mononitride

The thermal properties of plutonium mononitride (PuN) were investigated by molecular dynamics method. The interatomic potentials of PuN were fitted by using Chen–Möbius multiple lattice inversion technique. Based on these interatomic potentials, the lattice constant, bulk modulus, compressibility, cohesive energy and heat capacity of PuN were obtained and the results are well consistent with experimental data and previous reports. It indicates that the potentials we build in this study are effective for studying thermal properties of PuN.

Post-reactor studies of plutonium mononitride and oxide fuel with an inert matrix and burnup of about 19% h.a. in BOR-60

An experiment investigating the behavior of different fuel compositions with high content of plutonium for the conditions of a BOR-60 reactor was performed in 1996-2007. The results of post-reactor studies of the experimental fuel elements with 40% PuN + 60% ZrN and 40% PuO 2 + 60% MgO are presented here. The microstructure, density change, crystal lattice parameters of the fuel compositions, and the fission product distribution were investigated. Burnup ∼19% was attained. The swelling per 1% burnup of the fuel was 0.1% for the nitride composition and 0.7-0.9% for the oxide composition. The gas release did not exceed 1% for the nitride fuel and 9% for the oxide fuel.

Combined reprocessing of weapons plutonium into high-purity oxide fuel

The main results of a study of regimes for dissolution of plutonium oxide and mononitride powders, obtained by the pyrochemical method from weapons plutonium, in acids for subsequent extraction removal of gallium, americium, and ballast impurities and obtaining ceramic-type plutonium oxide powder suitable for fabricating mixing oxide fuel are presented. It is established experimentally that plutonium oxide and mononitride obtained by the pyrochemical method dissolve rapidly in the acid mixture HNO 3 12 moles/liter and HF 0.1 moles/liter. Plutonium extraction into solution reaches >99%.

Pyrochemical method of salvaging weapons plutonium in oxide for fabricating mixed fuel for fast reactors

Experimental results of investigations of pyrochemical conversion of weapons plutonium into plutonium oxide for fabricating fast-reactor fuel are presented. Weapons plutonium was hydrogenized by hydrogen at 220°C, after which the plutonium hydride obtained was acidified at 550–560°C with the formation of PuO2. To increase fire and explosion safety of the process, a mixture of oxygen with nitrogen, helium, or argon was used or nitriding with nitrogen and oxidation of plutonium mononitride were introduced. The particle size of the plutonium oxide powders obtained was less than 15 μm. The powders showed poor flowability, but after granulation they were suitable for fabricating kernels with mixed fuel. The gallium was removed by reduction of Ga2O3 by hydrogen to Ga2O, which was sublimated. The mixed-fuel kernels sintered at 1600–1700°C in a hydrogen atmosphere contained <0.001 wt.% gallium, and their density was 94–97% of the theoretical value.

Pyrochemical conversion of weapons plutonium into plutonium mononitride, monocarbide and mixed uranium-plutonium fuel for fast reactors

The main directions and results of research on pyrochemical reprocessing of weapons plutonium in fuel for fast reactors are presented. It is shown that this technology is economical and ecologically validated, compact, fire and explosion safe, especially for reprocessing in carbide-nitride as well as oxide fuel for fast reactors. It satisfies the principle of nonproliferation. For reprocessing weapons plutonium in oxide fuel with deep removal of 241 Am and Ga, a combined process which combines pyrochemical conversion of plutonium into oxide or nitride powder, and dissolution in acids and extraction of impurities. It is shown that the fuel kernels made from nitride, carbide, and oxide powers both from individual PuN, PuC 0.86 , and PuO 2 powders as well as mixed plutonium compounds with uranium are fabricated by means of the conventional regime and provide the required density and content of gallium of <0.001 wt. %.

Tests of Models of BREST-OD-300 Reactor Fuel Elements in an Autonomous Lead-Cooled Channel of a BOR-60 Reactor

A special feature of the BREST-OD-300 reactor that is now being designed is that it employs a container-type heat-conducting fuel element with mixed uranium–plutonium mononitride fuel, a lead sublayer, and an expansion volume at the top to collect gaseous products. The fuel elements are arranged in a square array with a wide spacing and are spaced by laminated spacing lattices.

Heat Capacity of Neptunium Mononitride

Heat capacity of neptunium mononitride was measured with a differential scanning calorimeter(DSC) in the temperature range from 323 to 1023K. In order to know the accuracy of our instrument, heat capacity measurements of uranium mononitride, plutonium mononitride and uranium dioxide were also carried out. DSC measurements were conducted in a glovebox with Ar gas purified system. Heat capacity was determined using 'scanning method'. Sapphire was used as a standard material. In the case of powder sample, oxidation occurred during the measurements. In the case of sintered samples, such oxidation was found to be avoidable. The heat capacities of uranium dioxide, uranium mononitride and plutonium mononitride agreed with the reference data within experimental errors. On the other hand, the heat capacity of neptunium mononitride almost agreed with those of uranium mononitride and plutonium mononitride.

A molecular dynamics study on plutonium mononitride

The physico-chemical properties of plutonium mononitride (PuN) were estimated by molecular dynamics (MD) calculation. The parameters of the interatomic potential were determined by fitting the changes in the lattice parameters with temperature and pressure to the literature data. The thermal expansion coefficient ( α) and the compressibility ( β) were calculated. The heat capacity at constant volume ( C V) was evaluated from the variation of the internal energy of the system by the fixed volume MD calculation. The lattice dilational contribution to the heat capacity ( C d) was calculated from α and β. The MD calculation results ( C V+ C d) agree with the reported values. The thermal conductivity ( λ) was calculated using the Green–Kubo relation in the temperature range of 300 to 2000 K. The temperature dependence of the calculated thermal conductivity followed a 1/ T law, which indicates that the lattice contribution to the thermal conductivity ( λ lat) could be evaluated by the molecular dynamics calculation. In the present study it was found that the MD simulation technique is useful and applicable to estimate the physico-chemical properties of PuN.

Studies of the neptunium-plutonium diboride system

The diborides of neptunium and plutonium and their solid solutions Np 1 − x Pu x B 2 were synthesized by reaction between boron and actinide hydrides at 900 °C. The solid solution is observed for the whole range of composition. The variations in the lattice parameters obey Vegard's law: a = 0.31622(4) + 0.00247(5) x nm and c = 0.39720(5) − 0.00228(7) x nm. An attempt to form the plutonium monoboride at low temperature (800 °C) was made without success. The earlier reported PuB was probably the isotypic plutonium mononitride.

Carbothermic synthesis of plutonium mononitride from the dioxide

Carbothermic synthesis of plutonium mononitride from the dioxide

The chemical thermodynamic properties of nuclear materials III. Plutonium mononitride

The high-temperature enthalpy { H o( T) − H o(298.15 K} of plutonium mononitride, PuN, has been determined from 298 to 1562 K using a copper-block calorimeter of the isoperibol type. The experimental results can be expressed by: {H°(T)−H°(298.15 K)}/ J mol −1=45.002(T/ K)+7.710×10 −3(T/ K) 2−1.410×10 4 The heat capacity of plutonium mononitride is expressed as C° p JK −1mol −1 =45.002+1.542×10 −2(T/ K) Combination of these results with the heat capacity and entropy at 298.15 K available from a recent study has made it possible to calculate the high-temperature thermodynamic functions for plutonium mononitride.

Vaporisation du mononitrure de plutonium

We have measured by the Knudsen method the vapour pressure of the plutonium mononitride. We have confirmed the dissociation of PuN given by the following reaction: PuN(s)→ Pu(g)+ 1 2 N 2( g) . The enthalpy of formation at 298°K (ΔH=−72,8 Kcal) obtained from this study agree very well with the other thermodynamic measurements for this compound.

The enthalpies of formation of plutonium dioxide and plutonium mononitride

The energies of combustion in oxygen of α-plutonium metal and plutonium mononitride were measured in a bomb calorimeter. The standard enthalpies of formation, ΔH f o(298.15 K), of PuO 2(c) and PuN(c) were calculated to be −(1055.85±0.72) kJ mol −1 [−(252.35±0.17) kcal mol −1] and −(299.2±2.6) kJ mol −1 [−(71.51±0.62) kcal mol −1], respectively.

A Consistent Set of Thermodynamic Values for Plutonium Mononitride

Values given in the literature for the heat of formation of plutonium mononitride range from — 70 to — 76 kcal/mole. This paper shows that if estimated entropy and high‐temperature heat capacity data are used to derive a reasonable set of high‐temperature thermal functions for the mononitride, ΔH0f,298 (PuN) values obtained by both second‐and third‐law methods from equilibrium data agree. The equilibrium data are from measurements reported in the literature and cover a range from 700° to about 3040°K. A calorimetric value of —70.2 kcal/mole reported for the PuN heat of formation appears to be in disagreement with the derived equilibrium value of — 76.0 kcal/mole, but this difference can be explained by a composition uncertainty.

Thermodynamic Properties of Plutonium Mononitride from Electromotive Force Measurements

Thermodynamic Properties of Plutonium Mononitride from Electromotive Force Measurements