Chemical leaching behavior of237Np from intertidal coastal sediment in the Irish Sea

Chemical leaching experiments of²³⁷Np in the sediments from the Esk Estuary and the Ribble Estuary in the Irish Sea, U. K., have been carried out, in comparison with those of^{239, 240}Pu and²⁴¹Am, to understand the geochemical associations of these long-lived radionuclides with sediment. Experimental results show that partitioning behavior of²³⁷Np is obviously different from those of^{239, 240}Pu and²⁴¹Am.     

Measurements of99Tc,137Cs,237Np, Pu isotopes and241Am in sediment cores from intertidal coastal and estuarine regions in the Irish Sea

Long-lived radionuclides,⁹⁹Tc,¹³⁷Cs,²³⁷Np, Pu isotopes and²⁴¹Am were determined in the long sediment cores collected from nine intertidal sites around the west Cumbria of the Irish Sea, UK. The inventories of all nuclides measured varied considerably among the sampling sites, but generally their inventories decreased with increasing distance from Sellafield. Furthermore, the inventory ratios with respect to relationship with distance from Sellafield enabled comparison of transport behavior of⁹⁹Tc,¹³⁷Cs,²³⁷Np and²⁴¹Am compared with^239,240Pu. As a consequence, the apparent fractional rate of solution transport to the intertidal sediment was found to increase as follows:⁹⁹Tc>¹³⁷Cs>²³⁷Np>^239,240Pu≥²⁴¹Am.     

Radioisotopes of thirteen elements in intertidal coastal and estuarine sediments in the Irish Sea

A survey has been carried out of⁴⁰K,⁶⁰Co,⁹⁹Tc,¹⁰⁶Ru,¹²⁵Sb,¹²⁹I,¹³⁴Cs,¹³⁷Cs,¹⁵⁴Eu,²²⁶Ra,²²⁸Ra,²³⁷Np,²³⁸Pu,^239,240Pu,²⁴¹Pu,²⁴¹Am,²⁴²Cm, and^243,244Cm activities in sediments from the Irish Sea. Several of these radionuclides were measured independently at two separate laboratories to enable the intercomparison of the results produced. The comprehensive data set generated allows the present spatial distributions of these radionuclides in coastal sediments to be examined in relation to sediment textural characteristics and by comparison with earlier survey, enables the temporal trends in their activities to be determined. In general all artificial radionuclides showed lower activities in sediments in response to falling discharges from Sellafield and relationships with either grain size, distance from Sellafield or both. Isotope ratios were similar to cumulative weighted activity ratios rather than present day values due to sediment mixing. Pu levels supplied evidence for the lag in response of sediment deposits with increasing distance from Sellafield due to sediment transport.     

Distribution and behaviour of99Tc,237Np,239,240Pu,and241Am in the coastal and estuarine sediments of the Irish Sea

Intertidal coastal and estuarine sediments from 24 sites in the Irish Sea have been analyzed for⁹⁹Tc,²³⁷Np,²³⁸Pu,^239,240Pu and²⁴¹Am. The²³⁷Np activity and²³⁹Pu/²⁴⁰Pu ratio were measured simultaneously by ICP-MS, and⁹⁹Tc was determined by HR-ICP-MS which is ten times more sensitive than Q-ICP-MS.The activities of⁹⁹Tc,²³⁷Np,^239,240Pu and²⁴¹Am were distributed over a wide range of 1.5–70.5, 0.01–13.3, 2.3–1589, 2.6–1894 Bq/kg, respectively. Activities of these radionuclides decreased exponentially with distance from the Sellafield source. The²⁴¹Am/^239,240Pu and²³⁷Np/^239,240Pu ratios were almost constant with distance from the Sellafield. This result suggests that the distribution and behavior of Np and Pu are controlled by complicated factors such as the influence of transport, the variation with time of Np/Pu ratio in the Sellafield discharges and sedimentary mixing processes in the Irish Sea.     

Mapping of the distribution of 137Cs in Irish Sea sediments

The Sellafield nuclear fuel reprocessing plant released a total of 41 PBq of ¹³⁷Cs into the Irish Sea in the period 1952–1998. The present work integrates a series of surveys of the ¹³⁷Cs distribution in sediment offshore Sellafield which was aimed at obtaining a detailed picture of the patterns of sediment contamination and their time evolution, and an estimate of the ¹³⁷Cs inventory in sediment. The authors applied NaI(Tl)-based underwater -ray spectrometry to record a series of 1800 one-minute spectra along 14 transects totaling 160 Nm. The dominant feature of the contamination pattern obtained from this survey remains a stripe extending northwestwards along the coast from the discharge point, as reported for previous surveys. Steep gradients are observed perpendicular to the coast, with ¹³⁷Cs countrates decreasing to half the recorded maximum over a distance of less than 2000 m.     

Magnetic normalization of particle size effects in a heavy metal pollution study of intertidal sediments from the Yangzte Estuary

Magnetic, granulometric and geochemical analyses were conducted on an intertidal sediment core from the Yangtze Estuary to evaluate the possibility of normalizing samples for particle size effects in a heavy metal pollution study by means of magnetic proxies. It has been found that the magnetic parameter XARM, indicating fine grained ferrimagnetic minerals, correlates well with the clay content and organic matter concentration of the sediments. XARM also shows significant relationship with heavy metals. Therefore XARM is proposed as a proxy for clay content in the sediments, and can be used to compensate for the particle size effect in sedimentary heavy metal records, where magnetic minerals are not subject to significant post-depositional alteration.     

Magnetic normalization of particle size effects in a heavy metal pollution study of intertidal sediments from the Yangzte Estuary

Magnetic, granulometric and geochemical analyses were conducted on an intertidal sediment core from the Yangtze Estuary to evaluate the possibility of normalizing samples for particle size effects in a heavy metal pollution study by means of magnetic proxies. It has been found that the magnetic parameter_ϰARM, indicating fine grained ferrimagnetic minerals, correlates well with the clay content and organic matter concentration of the sediments._ϰARM also shows significant relationship with heavy metals. Therefore_ϰARM is proposed as a proxy for clay content in the sediments, and can be used to compensate for the particle size effect in sedimentary heavy metal records, where magnetic minerals are not subject to significant post-depositional alteration.

     

Distribution of global fallout237Np,Pu isotopes,and241Am in lake and sea sediments

In order to investigate the sedimentary behaviour of neptunium,²³⁷Np together with Pu isotopes and²⁴¹Am have been measured for the sediment cores collected from Lake Mikata (freshwater) and from Lake Kugushi (brakish water) both belonging to the Mikata Five Lakes, and from Nyu Bay (sea water). In all sediment core samples²³⁷Np was detected, and its concentrations were far below those of^239,240Pu and²⁴¹Am measured for the same samples. Inventories of²³⁷Np in Lake Mikata, Lake Kugushi and Nyu Bay were estimated to be 0.53, 0.29 and 0.34 MBq/km², respectively. The activity ratio of²³⁷Np/^239,240Pu calculted from the inventories in each sediment core was 0.29% for Lake Mikata, 0.15% for Lake Kugushi and 0.10% for Nyu Bay. These values except for the value for Lake Mikata are two or three times lower than the value of 0.3–0.4% observed for surface soils of 0–20 cm depth, suggesting that Np is more soluble compared with Pu.     

Determination of 237 Np in marine sediment and seawater

Procedures for determination of neptunium in marine sediment and seawatersamples are described. Iron hydroxide Fe(OH)₂ –Fe(OH)₃ is used for preliminary pre-concentration of neptunium. Secondly,neptunium Np⁴⁺ and Pu³⁺ are separated by tri-isooctylamine-(TIOA)extraction in 8–10M HCl by redox with SO₃ ^2–-Fe³⁺ Neptunium Np⁴⁺ and uranium U⁶⁺ areseparated by back extraction the Np⁴⁺ with 2M HCl. Finally, theneptunium is purified from the uranium and thorium by anion exchange in 8MHNO₃ and 12M HCl. The stripping of 6M HCl + NH₂ OH HClfurther separates the neptunium Np³⁺ and uranium. Reduction bySO 3_2– –Fe³⁺ appeared to be an efficientway to obtain Np⁴⁺ The decontamination factors of the procedureare 4.0. 10⁴ for ²³² Th, 5.6 . 10⁴ for uraniumand 1.6 . 10⁴ for plutonium.     

Determination of237Np in urine by reversed-phase partition chromatography

A sensitive, rapid and selective method for the determination of²³⁷Np in urine is described. Neptunium(IV) is isolated by batch-extraction with a slurry of Microthene-710 (microporous polyethylene) supporting a cyclohexane solution of tri-n-octylphosphine oxide, the slurry is transferred into a column and neptunium eluted by oxidation to Np(V) with a mixture of HCl+Cl₂. After electroplating on a stainless steel disc, neptunium is counted with a solid-state alpha-detector. The final recovery is 83.2%; the decontamination factors are sufficiently high and the sensitivity limit is suitable for radiotoxicological purposes.     

Calculation of 237Np and 241Am detector calibration constants from first principles

The Analytical Development Section of Savannah River Technology Center (SRTC) was requested by the Facilities Disposition Projects (FDP) to determine the holdup of enriched uranium in the 321-M facility as part of an overall deactivation project of the facility. The 321-M facility was used to fabricate enriched uranium fuel assemblies, lithium-aluminum target tubes, neptunium assemblies, and miscellaneous components for the production reactors. The results of the holdup assays are essential for determining compliance with the Waste Acceptance Criteria, Material Control & Accountability, and to meet criticality safety controls. This report covers calibration of the detectors in order to support holdup measurements in the C and D out-gassing ovens. These ovens were used to remove gas entrained in billet assembly material prior to the billets being extruded into rods by the extrusion press. A portable high purity germanium detection system was used to determine highly enriched uranium (HEU) holdup and to determine holdup of ²³⁵U, ²³⁷Np, and ²⁴¹Am that were observed in these components. The detector system was run by an EG&G Dart system that contains the high voltage power supply and signal processing electronics. A personal computer with Gamma-Vision software was used to control the Dart MCA and provide space to store and manipulate multiple 4096-channel -ray spectra. The measured ²³⁷Np and ²⁴¹Am contents were especially important in these components because their presence is unusual and unexpected in 321-M. It was important to obtain a measured value of these two components to disposition the out-gassing ovens and to determine whether a separate waste stream was necessary for release of these contaminated components to the E-Area Solid Waste Vault. This report presents determination of the calibration constants from first principles for determination of ²⁴¹Am and ²³⁷Np using this detection system and compares the values obtained for ²³⁷Np with the calibration factors obtained with a subsequent measurement using a point source of radioactive equilibrium ²³⁷Np/²³³Pa.     

Inherent isotope dilution analysis of237Np in spent nuclear fuels

A combined -spectrometric and mass-spectrometric determination of²³⁷Np in spent nuclear fuels using²³⁹Np as an inherent spike has been developed. In spent fuel²³⁹Np is in radiochemical equilibrium with²⁴³Am. Neptunium in the tetravalent state is separated by TTA solvent extraction from the other actinides and most of the fission products and the -activity ratio of²³⁷Np to²³⁹Np is measured. The²³⁷Np activity is via²³⁹Np directly linked to the²⁴³Am mass in a sample, which is determined by mass-spectrometric isotope dilution analysis.     

Determination of237Np in spent fuel by use of inherent239Np as a chemical yield monitor

A method for analyzing the content of²³⁷Np in spent fuel has been developed using inherent²³⁹Np as a chemical yield monitor. After ion-exchange separations for the dissolved fuel solution, the²³⁷Np content in the neptunium fraction was determined from the activity of²³⁷Np or of²³³Pa, which is in radioactive equilibrium with²³⁷Np. The chemical yield in the separations was determined both from the content of²⁴³Am which is in radioactive equilibrium with²³⁹Np before the separations and from the²³⁹Np content in the neptunium fraction after the separations by alpha- and gamma-ray spectrometry.     

Photoluminescence of crystallophosphors for the determination of 237Np and 239Pu

The photoluminescence of crystallophosphors, activated by neptunium and plutonium has been studied in connection with the necessity of discovering and elaborating on new analytical methods for actinides determination. Crystallophosphors on the base of fluorides, molybdates and tungstates have been prepared by introducing neptunium and plutonium solutions into the powder matrix, further drying and blend calcination. Luminescence spectra at room temperature have been found to have some broad bands in the near i.r. region independently of the method of crystallophosphor preparation, the oxidation state of introduced elements and the conditions of u.v. irradiation. The effect of matrix nature, flux content and concentration of quenching elements in analyzed solution on crystallophosphors luminescence has been studied. The methods of neptunium and plutonium     

Measurement of237Np in the marine environment of coastal nuclear sites in India

Nepturium-237 levels in sea water and sediments from Indian coastal waters receiving radwaste discharges have been investigated. The method used for the estimation is neutron activation and using this method,²³⁷Np activity as low as 10^–7 Bq/l in sea water could be measured. Neptunium-237 levels found are compared with the values reported for other areas.     

Measurement of 237Np in environmental water samples by accelerator mass spectrometry

Accelerator mass spectrometry (AMS) was used to measure 237Np in environmental water samples extracted from Irish Sea sediments. The samples were of limited volume (approximately 700 ml) and of low activity (0.06-0.79 mBq l-1; 2.30-30.3 pg l-1). AMS proved to have the required sensitivity for measuring these samples, and was in principle capable of measuring much smaller amounts, as low as 0.4 microBq (3.9 x 10(7) atoms). However, the background level in the procedural blanks showed that there was a systematic low level 237Np contamination of each sample, arising from the 239Np yield monitor used in the separations procedure, which effectively increased the detection limit of these analyses.     

Determination of237Np in environmental samples using inductively coupled plasma mass spectrometry

Ammonium uranates (AU) obtained by the addition of aqueous NH₄ OH to a solution of UO₂ (NO₃)₂ or the equilibrium reaction of UO₃ · 2H₂ O with the vapour over concentrated NH₄ OH have been studied by X-ray diffraction (XRD) analysis, diffuse reflectance Fourier transform infrared spectrometry (DR-FTIR) and chemical analysis. Ammonia can be present as either NH₃ or NH ₄ ⁺ . For precipitates obtained at a pH of 3.7, ammonia in the form of NH₃ is predominant. For ammonium uranate obtained by reaction over concentrated NH₄OH, most of the ammonia is bonded as NH ₄ ⁺ . The reaction mechanism and structures of the products are also discussed.     

Mössbauer spectroscopy of237Np in solid solutions of actinide dioxides

Emission Mössbauer (nuclear gamma-resonance) spectra of²³⁷Np resulting from the alpha-decay of²⁴¹Am in solid solutions AmO₂–ThO₂ and AmO₂–UO₂ prepared by precipitation from LiF–NaF eutectic melts under fluorine-oxygen exchange were first investigated in the temperature range from 77 to 296 K. The resonant absorbers are NpO₂ and NpAl₂. The possibility is stated of managing the form of the emission Mössbauer spectra of²³⁷Np in dioxides by the directed change of the matrix stoichiometry or by its irradiation by visible light. At temperatures from 77 to 230 K the authors measured for the first time the NGR absorption spectra of²³⁷Np in solid solution NpO₂–ThO₂ with various concentrations of neptunium dioxide. An increase of the absorption line width (approximately by a factor of 4) with a decrease in the NpO₂ contents (to 10 mol.%) was explained by the influence of fast electron exchange between Np⁴⁺ and Np⁵⁺ states observed in the NpO₂–ThO₂ solid solution at low concentrations of neptunium dioxide.     

Pilot measurements of <Superscript>237</Superscript>Np in forest litter from Poland

Described are results and the procedure for a pilot study on ²³⁷Np content in forest litter samples from Poland in relation to their plutonium activity. Neptunium was determined by inductively coupled plasma mass spectrometry (ICP-MS) and Pu by alpha spectrometry. Two samples originated from a location with pure global fallout and two others from a place with about 65% of the plutonium from Chernobyl. Plutonium activities were determined twice: at Krakow and in Monaco. The two results were consistent and ^239 + 240Pu activities ranged from about 1 to about 7 Bq/kg dry weight (dw). The chemical recovery for Np was between 27 and 89%. Results for ²³⁷Np activity concentrations were between 0.099 ± 0.005 and 2.21 ± 0.076 mBq/kg dw. Observed activity ratios were lower than expected and could be explained by fractionation of Np against Pu in forest litter.     

Sorption characteristics of237Np,238Pu and241Am in sedimentary materials

Adsorption experiments were performed to measure distribution coefficients of²³⁷Np(V),²³⁸Pu(IV) and²⁴¹Am(III) for sedimentary sequential chemical extraction of the adsorbed radionuclides was carried out with water, CaCl₂, KCl, NH₂OH−HCl, K-oxalate and H₂O₂ solutions, to elucidate their dominant sorption mechanisms. The distribution coefficient of²³⁷Np was two orders of magnitude smaller than that of²³⁸Pu and²⁴¹Am. Most of²³⁷Np adsorbed was extracted with CaCl₂ solution and its sorption was controlled by a reversible ion exchange reaction. The adsorbed²³⁸Pu was mainly extracted with NH₂OH−HCl+K-oxalate solution and its sorption was possibly controlled by irreversible reactions.