Plutonium Solutions Research Articles

Installation Places of Criticality Accident Detectors in the Plutonium Conversion Development Facility

At the Plutonium Conversion Development Facility (PCDF) in the Nuclear Fuel Cycle Engineering Laboratories, the co-conversion technologies to purify the mixed plutonium and uranium nitrate solution discharged from a reprocessing plant have been developed. The probability of a criticality accident in PCDF is extremely low. However, the criticality accident alarm system (CAAS) has been in place since 1982 to reduce the radiation dose to workers in case of such a rare criticality accident. The CAAS contains criticality accident detector units (CADs), one unit consisting of three plastic scintillation detectors, and using the 2 out of 3 voting system for the purpose of high reliability. Currently, eight CADs are installed in PCDF evaluating the dose using a simple equation allowing for a safety margin. The purpose of this study is to show the determination procedures for the adequate relocation of the CADs which adequately ensures safety in PCDF.

α-Particle and γ-ray spectrometry of a plutonium solution for impurity determination

A highly enriched 240Pu solution was measured by α-particle and γ-ray spectrometry to determine other radionuclides present in the material as impurities. Low activities of 238Pu, 241Am, 243Cm and 244Cm were determined by measuring thin sources, made from the original solution, in a high-resolution alpha-particle spectrometer. The sources were prepared by evaporating the plutonium solution on quartz plates in a vacuum chamber. From the ingrowth of 241Am in the original solution, the amount of 241Pu could be calculated. After radiochemical separation of 241Am, the plutonium was measured by high-efficiency alpha-particle spectrometry to determine the amount of 238Pu. The enriched 240Pu material was also measured by high-resolution gamma-ray spectrometry, using two different HPGe detectors to determine the impurities of 239Pu and 241Am. The preparation of the sources and the measurement methods are described and discussed. The measured impurities, given in % of the 240Pu activity, are compared with the values on the certificate.

Optimization of a dried residue specimen preparation method for quantifying analytes in plutonium metal using WDXRF

A novel method for preparing thin films was investigated for quantifying gallium and iron in plutonium solutions using WDXRF. This technique was developed to eliminate the potential for radioactive liquid to leak into the spectrometer, decrease specimen preparation time, and minimize waste. Samples were cast in μL quantities onto Kapton, and a surfactant was added to disperse the solution uniformly across the Kapton. After drying the specimens, they were sealed in a cell for analysis. Results to date indicate the method can provide a relative precision of ∼0.5% for gallium and ∼2% for iron, which is more than sufficient for routine sample analyses.

Solubility of plutonium(VI) carbonate in saline solutions

Among the plutonium oxidation states found to form in the environment, mobile plutonium(VI) can exist under oxidizing conditions and in waters with high chloride content due to radiolysis effects. We are investigating the solubility and speciation of plutonium(VI) carbonate under conditions relevant to natural waters and brines such as those found near some geologic radioactive waste repositories. The solid Pu(VI) phase PuO 2CO 3(s) was prepared and its solubility was measured in NaCl and NaClO 4 solutions in a CO 2 atmosphere as a function of pH and ionic strength (0.1–5.6 m). The concentration of soluble plutonium in solution was calculated from spectroscopic data and liquid scintillation counting. Spectroscopic measurements also revealed the plutonium oxidation state. The apparent solubility product of PuO 2CO 3(s) was determined at selected electrolyte concentrations to be, log K s,0 = −13.95 ± 0.07 (0.1 m NaCl), log K s,0 = −14.07 ± 0.13 (5.6 m NaCl), and log K s,0 = −15.26 ± 0.11 (5.6 m NaClO 4). Specific ion interaction theory was used to calculate the solubility product at zero ionic strength, log K s, 0 ∘ = − 14.82 ± 0.05 .

Multi-isotopic determination of plutonium ( 239Pu, 240Pu, 241Pu and 242Pu) in marine sediments using sector-field inductively coupled plasma mass spectrometry

Among the transuranic elements present in the environment, plutonium isotopes are mainly attached to particles, and therefore they present a great interest for the study and modelling of particle transport in the marine environment. Except in the close vicinity of industrial sources, plutonium concentration in marine sediments is very low (from 10 −4 ng kg −1 for 241Pu to 10 ng kg −1 for 239Pu), and therefore the measurement of 238Pu, 239Pu, 240Pu, 241Pu and 242Pu in sediments at such concentration level requires the use of very sensitive techniques. Moreover, sediment matrix contains huge amounts of mineral species, uranium and organic substances that must be removed before the determination of plutonium isotopes. Hence, an efficient sample preparation step is necessary prior to analysis. Within this work, a chemical procedure for the extraction, purification and pre-concentration of plutonium from marine sediments prior to sector-field inductively coupled plasma mass spectrometry (SF-ICP-MS) analysis has been optimized. The analytical method developed yields a pre-concentrated solution of plutonium from which 238U and 241Am have been removed, and which is suitable for the direct and simultaneous measurement of 239Pu, 240Pu, 241Pu and 242Pu by SF-ICP-MS.

Benchmarking ENDF/B-VII.0

The new major release VII.0 of the ENDF/B nuclear data library has been tested extensively using benchmark calculations. These were based upon MCNP-4C3 continuous-energy Monte Carlo neutronics simulations, together with nuclear data processed using the code NJOY. Three types of benchmarks were used, viz., criticality safety benchmarks, (fusion) shielding benchmarks, and reference systems for which the effective delayed neutron fraction is reported. For criticality safety, more than 700 benchmarks from the International Handbook of Criticality Safety Benchmark Experiments were used. Benchmarks from all categories were used, ranging from low-enriched uranium, compound fuel, thermal spectrum ones (LEU-COMP-THERM), to mixed uranium-plutonium, metallic fuel, fast spectrum ones (MIX-MET-FAST). For fusion shielding many benchmarks were based on IAEA specifications for the Oktavian experiments (for Al, Co, Cr, Cu, LiF, Mn, Mo, Si, Ti, W, Zr), Fusion Neutronics Source in Japan (for Be, C, N, O, Fe, Pb), and Pulsed Sphere experiments at Lawrence Livermore National Laboratory (for 6Li, 7Li, Be, C, N, O, Mg, Al, Ti, Fe, Pb, D2O, H2O, concrete, polyethylene and teflon). For testing delayed neutron data more than thirty measurements in widely varying systems were used. Among these were measurements in the Tank Critical Assembly (TCA in Japan) and IPEN/MB-01 (Brazil), both with a thermal spectrum, and two cores in Masurca (France) and three cores in the Fast Critical Assembly (FCA, Japan), all with fast spectra. In criticality safety, many benchmarks were chosen from the category with a thermal spectrum, low-enriched uranium, compound fuel (LEU-COMP-THERM), because this is typical of most current-day reactors, and because these benchmarks were previously underpredicted by as much as 0.5% by most nuclear data libraries (such as ENDF/B-VI.8, JEFF-3.0). The calculated results presented here show that this underprediction is no longer there for ENDF/B-VII.0. The average over 257 benchmarks deviates only 0.017% from the measured benchmark value. Moreover, no clear trends (with e.g. enrichment, lattice pitch, or spectrum) have been observed. Also for fast spectrum benchmarks, both for intermediately or highly enriched uranium and for plutonium, clear improvements are apparent from the calculations. The results for bare assemblies have improved, as well as those with a depleted or natural uranium reflector. On the other hand, the results for plutonium solutions (PU-SOL-THERM) are still high, on average (over 120 benchmarks) roughly 0.6%. Furthermore there still is a bias for a range of benchmarks based on cores in the Zero Power Reactor (ANL) with sizable amounts of tungsten in them. The results for the fusion shielding benchmarks have not changed significantly, compared to ENDF/B-VI.8, for most materials. The delayed neutron testing shows that the values for both thermal and fast spectrum cases are now well predicted, which is an improvement when compared with ENDF/B-VI.8.

Acidity changes in plutonium solutions: Generalized proportional equations method

Disproportionation reactions change the pH of a plutonium solution. The method of generalized proportional equations is used to estimate the magnitude of the change. It is illustrated by examples and it is easy to apply.

Improvement of precision spectrophotometric method with internal reference and its application to analysis of plutonium solutions

A spectrophotometric precision method with internal reference [1, 2] was applied to analysis of straight Pu solutions for certifying Pu reference materials and for studying the PuO2 solubility in the framework of developing methods for accounting and control of nuclear materials. In the context of the activities mainly concerned with certification of reference materials, a two-channel spectrophotomer and the corresponding technique were further improved in order to decrease the error of the method. This allowed the random component of the relative error of the method to be decreased from 0.1 to 0.04% at the confidence level p = 0.95 and the number of degrees of freedom f = 25. The fixed component of the error of the method was studied in relation to impurities of U, Np and corrosion products of structural materials. Also, the extent of Pu oxidation during sample preparation was studied as influenced by the fluoride ion. The revealed lack of such influence within the limits of the study indicates that the method is suitable for analysis of Pu in mixed solutions.

Work surface for soluble plutonium

A three-dimensional work surface for aqueous plutonium is illustrated. It is constructed by means of estimating work as a function of the ambient pH and redox potential in a plutonium solution. The surface is useful for illustrating the chemistry of disproportionation reactions. Work expressions are easier to use than work integrals.

Hydrogen generation in nitric acid solutions of plutonium

Literature data on the radiolytic generation of hydrogen in nitric acid solutions of plutonium are used to construct a model that predicts G(H2) as a function of the nitric acid and plutonium concentrations. The model indicates that G(H2) decreases with increasing concentration of nitric acid, in agreement with most experimental observations. The effect of the plutonium concentration on G(H2) is secondary to the effect of the acid concentration. An equation for interpolating Gvalues for total gas is included.

Acid dependence of the Pu(V) disproportionation reaction

The disproportionation of pentavalent plutonium is traditionally represented by two inconsistent equations. The inconsistency puts the widely-accepted, fourth-power hydrogen-ion dependence of the reaction into question. The balanced reaction equation suggests that both the stoichiometry and the acid-dependence of Pu(V) disproportionation depend on the pH of the plutonium solution.

Validation of the Continuous-Energy Monte Carlo Criticality-Safety Analysis System MVP and JENDL-3.2 Using the Internationally Evaluated Criticality Benchmarks

Validation of the continuous-energy Monte Carlo criticality-safety analysis system, comprising the MVP code and neutron cross sections based on JENDL-3.2, was examined using benchmarks evaluated in the “International Handbook of Evaluated Criticality Safety Benchmark Experiments.” Eight experiments (116 configurations) for the plutonium solution and plutonium-uranium mixture systems performed at Valduc, Battelle Pacific Northwest Laboratories, and other facilities were selected and used in the studies. The averaged multiplication factors calculated with MVP and MCNP-4B using the same neutron cross-section libraries based on JENDL-3.2 were in good agreement. Based on methods provided in the Japanese nuclear criticality-safety handbook, the estimated criticality lower-limit multiplication factors to be used as a subcriticality criterion for the criticality-safety evaluation of nuclear facilities were obtained. The analysis proved the applicability of the MVP code to the criticality-safety analysis of nuclear fuel facilities, particularly to the analysis of systems fueled with plutonium and in homogeneous and thermal-energy conditions.

Eutectoid equilibria relationships in binary plutonium phase diagrams

The applicability of a universal relationship of invariant transformations for analyzing eutectoid transformations in binary plutonium systems is demonstrated in this article. This relationship requires a favorable temperature factor for the formation of eutectoid reactions. This work confirms the validity of previously established values for decomposition of δ-phase solid solution and compounds of plutonium with group III-B elements at atmospheric and elevated pressures. It is demonstrated that in alloys of plutonium with elements of group III-B, the parameters of eutectoid transformations of the δ-phase change monotonically with increasing atomic number of the element.

Preparation of a stable tracer solution of plutonium(IV)

Summary A method is given for the preparation of a Pu tracer solution in 0.10M NaHSO4 containing only Pu(IV). This solution is stable for several years.

Molecular interfacial reactions between Pu(VI) and manganese oxide minerals manganite and hausmannite.

The sorption of Pu(VI) onto manganite (MnOOH) and hausmannite (Mn3O4) was studied as a function of time, solution pH, and initial plutonium concentration. Kinetic experiments indicate that the surface complexation of plutonium occurs over the first 24 h of contact with the mineral surface. The sorption increases with pH beginning at pH 3 until it reaches a maximum value of 100% at pH 8 (0.0011-0.84 micromol of Pu/m2 of manganite and 0.98-1.2 micromol of Pu/m2 of hausmannite) and then decreases over the pH range from 8 to 10. The ratio of solid to solution was 10 mg/mL for manganite experiments and 4 mg/mL for hausmannite samples. Carbonate was not excluded from the experiments. The amount of plutonium removed from the solution by the minerals is determined by a combination of factors including the plutonium solution species, the surface charge of the mineral, and the mineral surface area. X-ray absorption fine structure taken at the Pu L(III) edge were compared to plutonium standard spectra and showed that Pu(VI) was reduced to Pu(IV) after contact with the minerals. Plutonium sorption to the mineral surface is consistent with an inner-sphere configuration, and no evidence of PuO2 precipitation is observed. The reduction and complexation of Pu(VI) by manganese minerals has direct implications on possible migration of Pu(VI) species in the environment.

The Aqueous Corrosion Behavior of Plutonium Metal Exposed to Nitric Acid Solutions

Although plutonium is of great technological importance, the electrochemical behavior of the metal exposed to aqueous solution has not been studied. Anecdotal evidence has suggested that plutonium can be passivated. However, there have no been no electrochemical studies to date. This work is the first to examine the polarization behavior of plutonium metal. Studies using 1 mM to 1 M nitric acid solutions show that plutonium is spontaneously passive. Polarization results contradict the predicted active behavior in equilibrium potential/pH diagrams. In contrast to prior plutonium solution chemistry work using inert electrodes, a significant overpotential is required to produce hexavalent plutonium. Thus, transpassivity occurs at very noble potentials and a broad passivity range is observed in acidic solutions. Pitting is observed upon polarization in 1 mM solutions. © 2002 The Electrochemical Society. All rights reserved.

Mechanisms of Positive Temperature Reactivity Coefficients of Dilute Plutonium Solutions

Mechanisms of a positive temperature reactivity coefficient that occurs in a dilute plutonium solution are investigated based on the perturbation theory and the four-factor formula. The temperature coefficient of a solution fuel is positive if the adjoint flux increases with neutron energy between 0.05 and 0.2 eV. As compared to 239Pu, 241Pu has a tendency to make the temperature coefficient of a plutonium solution positive because of the energy dependence of the capture cross section of 241Pu. As 241Pu in a plutonium solution decays into 241Am with time, the temperature coefficient of the solution becomes more positive. Since the capture cross sections of most neutron absorbers such as boron and gadolinium decrease with increasing neutron energy between 0.05 and 0.2 eV, soluble absorbers in a plutonium solution make the temperature coefficient positive for higher-concentration plutonium solutions. Cadmium and samarium dissolved in a dilute plutonium solution can exceptionally keep the temperature coefficient negative because of the energy dependence of the capture cross sections. A fixed neutron absorber generally makes the temperature coefficient of a plutonium solution negative regardless of the property of absorber materials.

Complexation and Redox Interactions Between Aqueous Plutonium and Manganese Oxide Interfaces

The sorption of Pu(VI) and Pu(V) onto manganite (MnOOH) and Hausmannite (Mn3O4) was studied at pH 5. Manganite sorbed 21-24% from a 1×10-4 M plutonium solution and the hausmannite removed between 43-66% of the plutonium. The increased sorption by hausmannite results from its larger surface area (about twice that of manganite) plus a larger number of active surface sites. X-ray absorption near-edge structure (XANES) spectra taken at the Pu LIII edge were compared to standard spectra of plutonium in single oxidation states. Based on these spectra, it appears that both manganite and hausmannite reduce the higher valent plutonium species to Pu(IV). Between 53-59% of the plutonium was present as Pu(IV) in the manganite samples while 55-61% of the plutonium complexed to the hausmannite had also been reduced to Pu(IV). The exact mechanism behind this redox interaction between the plutonium and the manganese needs to be identified.

Kinetics of the oxidation of Pu(IV) by manganese dioxide

SummaryThe kinetics of the oxidation of plutonium(IV) by manganese dioxide were studied in 1.0 M NaCl over the pH range from 2.5 to 8.2 with variable concentrations of manganese dioxide from 0.01 m2/L to 4.97 m2/L at a constant temperature of 19 ± 2 °C. The concentration of plutonium in solution was 6.0(± 1.0) × 10−10M. Fractions of Pu(IV), (V) and (VI) as a function of time were determined by removal of plutonium from the solid phase followed by an ultrafiltration/solvent extraction procedure using TTA and HDEHP as extractants. Appropriate removal conditions were established for Pu(IV), Pu(V) and Pu(VI) using Th(IV), Np(V) and U(VI) as oxidation state analogs.In the pH range from 2.0 to 3.5, the oxidation of Pu(IV) by manganese dioxide was first order with respect to the concentration of manganese dioxide and −0.21 with respect to the hydrogen ion concentration. Consequently, assuming a first order dependence with respect to the concentration of Pu(IV), the oxidation reaction can be described by the following rate equation:withk= 3.72(± 0.13) × 10−3(m−2L)(mol−1L)−0.21(min)−1. Using the kinetic data determined in this study, the influence of manganese dioxide on the oxidation state distribution of plutonium under various environmental conditions as well as in waste solutions can be estimated.

Acidity changes and balanced equations for plutonium disproportionation reactions

Disproportionation reactions in plutonium solutions alter the solution acidity. The acidity after reaction is related to the changes in the concentrations of the plutonyl cations. The final acidity can be estimated by a BASIC language program or by the method of proportional equations. The method is used to illustrate balanced equations for disproportionation reactions.