Verification measurements of the IRMM-1027 and the IAEA large-sized dried (LSD) spikes

In the frame of the accountancy measurements of the fissile materials, reliable determinations of the plutonium and uranium content in spent nuclear fuel are required to comply with international safeguards agreements. Large-sized dried (LSD) spikes of enriched ²³⁵U and ²³⁹Pu for isotope dilution mass spectrometry (IDMS) analysis are routinely applied in reprocessing plants for this purpose. A correct characterisation of these elements is a pre-requirement for achieving high accuracy in IDMS analyses. This paper will present the results of external verification measurements of such LSD spikes performed by the European Commission and the International Atomic Energy Agency.

     

Age determination of plutonium using inductively coupled plasma mass spectrometry

The age of plutonium is defined as the time since the last separation of the plutonium isotopes from their daughter nuclides. In this paper, a method for age determination based on analysis of ²⁴¹Pu/²⁴¹Am and ²⁴⁰Pu/²³⁶Pu using ICP-SFMS is described. Separation of Pu and Am was performed using a solid phase extraction procedure including UTEVA, TEVA, TRU and Ln-resins. The procedure provided separation factors adequate for this purpose. Age determinations were performed on two plutonium reference solutions from the Institute for Reference Materials and Measurements, IRMM081 (²³⁹Pu) and IRMM083 (²⁴⁰Pu), on sediment from the Marshall Islands (reference material IAEA367) and on soil from the Trinity test site (Trinitite). The measured ages based on the ²⁴¹Am/²⁴¹Pu ratio corresponded well with the time since the last parent-daughter separations of all the materials. The ages derived from the ²³⁶U/²⁴⁰Pu ratio were in agreement for the IRMM materials, but for IAEA367 the determination of ²³⁶U was interfered by tailing from ²³⁸U, and for Trinitite the determined age was biased due to formation of ²³⁶U in the detonation of the “Gadget”.     

What is new in certified reference materials and measurements at IRMM?

IRMM is developing more and more isotopic spike reference materials since these are increasingly needed in trace analysis. In addition, they appear to play an increasingly important role in ensuring traceability to the SI system of isotope-specific measurements made by e.g. isotope dilution mass spectometry (IDMS). Their present availability and future development is summarised. IDMS is also applied in a definitive way to establish reference measurements for IRMM's international measurement evaluation programme (IMEP), which aims at the realisation of traceability for field laboratories. IRMM uses its advanced technology for the preparation and contamination-free handling of large quantities of biological and environmental reference materials. These facilities are used for the preparation of both BCR CRM's (orange juice, sheep milk curd, sediments, etc.) and reference materials for private customers (catalytic converter materials, apple powder, flour, animal innards, tomato powder, etc.).     

Determination of the plutonium concentration by isotope dilution mass spectrometry using239Pu as a spike

A method is described for the determination of plutonium concentration in the presence of a bulk of other impurities by isotope dilution mass spectrometry /IDMS/ using²³⁹Pu as a spike. The method involves the addition of²³⁹Pu spike / 90 atom%/ to samples with²³⁹Pu / 70 atom%/ and vice versa. After ensuring chemical exchange between the sample and the spike isotopes, plutonium is purified by conventional anion exchange procedure in 7M HNO₃ medium.²³⁹Pu/²⁴⁰Pu atom ratio in the purified spiked sample is determined with high precision /better than 0.1%/ using a thermal ionization mass spectrometer. Concentration of plutonium in the sample is calculated from the changes in²³⁹Pu/²⁴⁰Pu atom ratio in the spiked mixture. Results obtained on different plutonium samples using²³⁹Pu as a spike are compared with those obtained by the use of²⁴²Pu spike. Precision and accuracy comparable to those achieved by using²⁴²Pu are demonstrated. The method provides an alternative in the event of non-availability of enriched²⁴²Pu or²⁴⁴Pu required in IDMS of plutonium and at the same time, offers certain advantages over the use of²⁴²Pu or²⁴⁴Pu spike.     

Estimation of isotopic composition of plutonium from thermal reactors by neutron coincidence counting through isotopic correlation technique

Correlations have been established between %Eff ²⁴⁰Pu and various plutonium isotopes formed in thermal reactors. Based on these correlations, a method has been developed for the estimation of isotopic composition of plutonium obtained from thermal reactors. The method is simple, fast, non-destructive and finds application for the verification of plutonium isotopic composition in the finished products of known plutonium content. The method could be applied in the nuclear fuel fabrication to verify and confirm the fissile content (²³⁹Pu+²⁴¹Pu) specification. It has also been shown that in principle, similar correlations could be established for Pu obtained from different thermal reactor fuels with reactor specific fitting parameters.     

A combined method for the determination of the isotopic vector of plutonium isotopes in environmental samples

A combination of alpha-spectrometry, liquid scintillation counting (LSC) and accelerator mass spectrometry (AMS) was used for the determination of plutonium isotopes. ²³⁸Pu and ^239+240Pu were measured by alpha-spectrometry after separation of Pu by anion-exchange using ²³⁶Pu tracer as recovery monitor. After alpha-measurement, one part of the sample was dissolved for determining ²⁴¹Pu by LSC. Another part was used for the measurement of the ²⁴⁰Pu/²³⁹Pu atom ratio by AMS at VERA. Thus, it was possible to obtain complete information on the Pu isotopic composition of the samples. This method was applied to environmental reference samples and samples contaminated from nuclear reprocessing.     

Origin and release date assessment of environmental plutonium by isotopic composition

The origin and release date of environmental plutonium have been assessed by the measurement of plutonium and americium isotopic composition. The applicability and sensitivity of different plutonium isotope ratios, ²⁴⁰Pu/²³⁹Pu and ²⁴¹Pu/²³⁹Pu measured by inductively coupled plasma sector field mass spectrometry and ²³⁸Pu/²³⁹Pu analysed by alpha spectrometry, have been evaluated for origin determination in several types of environmental samples. With use of mixing models the contribution of different sources (e.g. global fallout or Chernobyl) can be calculated. By the measurement of the ²⁴¹Am/²⁴¹Pu isotope ratio, the release date (i.e. formation of ²⁴¹Pu by irradiation) can be estimated in environmental samples, which is an important parameter to distinguish recent plutonium release from previous (e.g. Chernobyl) emissions.     

Low-level determination of plutonium by gamma and L X-ray spectroscopy

We have developed an analytical method for detection of²³⁹Pu in aqueous samples at concentrations as low as 10^–10M. This nuclear counting technique utilizes the uranium L X-rays, which follow the alpha-decay of plutonium. Because L X-rays are specific for the element and not for the individual isotope, the isotopic composition of the plutonium sample must be known. The counting efficiency in the 11–23 keV range is determined from a plutonium standard, and the concentration of the sample is then calculated from the L X-ray count and the isotopic composition. The total L X-ray count is corrected for possible contributions from other radionuclides present as impurities by measuring the low-energy gamma-spectrum for each contaminant to establish specific photon/X-ray ratios. The ratios are important when²⁴¹Pu and²⁴²Pu are measured, because the respective decay chain members produce non-U L X-rays. This new method can replace the use of labor-intensive radiochemical separation techniques and elaborate activation methods for analysis of²³⁹Pu in aqueous samples. It is also applicable for assaying plutonium in liquid wastes that pose possible hazards to the environment.     

Characterizing uranium oxide reference particles for isotopic abundances and uranium mass by single particle isotope dilution mass spectrometry

Uranium and plutonium particulate test materials are becoming increasingly important as the reliability of measurement results has to be demonstrated to regulatory bodies responsible for maintaining effective nuclear safeguards. In order to address this issue, the Institute for Reference Materials and Measurements (IRMM) in collaboration with the Institute for Transuranium Elements (ITU) has initiated a study to investigate the feasibility of preparing and characterizing a uranium particle reference material for nuclear safeguards, which is finally certified for isotopic abundances and for the uranium mass per particle. Such control particles are specifically required to evaluate responses of instruments based on mass spectrometric detection (e.g. SIMS, TIMS, LA-ICPMS) and to help ensuring the reliability and comparability of measurement results worldwide. In this paper, a methodology is described which allows quantifying the uranium mass in single micron particles by isotope dilution thermal ionization mass spectrometry (ID-TIMS). This methodology is characterized by substantial improvements recently achieved at IRMM in terms of sensitivity and measurement accuracy in the field of uranium particle analysis by TIMS. The use of monodisperse uranium oxide particles prepared using an aerosol generation technique developed at ITU, which is capable of producing particles of well-characterized size and isotopic composition was exploited. The evidence of a straightforward correlation between the particle volume and the mass of uranium was demonstrated in this study. Experimental results have shown that the uranium mass per particle can be measured via the ID-TIMS method to a relative expanded uncertainty of about 10% (coverage factor k = 2). The availability of reliable and validated methods for the characterization of uranium particles is considered to be essential for the establishment of SI-traceable measurement results. It is therefore expected that the method developed in this study is valuable for the certification of particulate materials in which the isotopic composition and the content of uranium must be accurately known.     

Preparation and calibration of a 231Pa reference material

A ²³¹Pa reference material has been characterized for amount of protactinium. This reference material is primarily intended for calibration of ²³³Pa tracers produced for ²³⁵U–²³¹Pa model age measurements associated with nuclear forensics and nuclear safeguards. Primary measurements for characterization were made by isotope dilution mass spectrometry of a purified ²³¹Pa solution using a ²³³Pa isotopic spike. The spike was calibrated by allowing multiple aliquots of the ²³³Pa spike solution to decay to ²³³U and then measuring the ingrown ²³³U by isotope dilution mass spectrometry using a certified uranium assay and isotopic standard as a reverse-spike. The new ²³¹Pa reference material will simplify calibration of the ²³³Pa isotope dilution spikes, provide metrological traceability, and potentially reduce the overall measurement uncertainty of model ages.

     

Determination of isotopic composition and concentration of uranium,plutonium and neodymium by mass-spectrometric isotope dilution in the irradiated fuel of the Czechoslovak atomic power station A-1

Determination of the isotopic composition and concentration of uranium, plutonium and neodymium by mass-spectrometric isotope dilution is described. Isotopes²³³U,²⁴²Pu and¹⁵⁰Nd were used as spikes. Isotopic composition was measured with a Varian-TH 5 mass spectrometer. Optimum amounts loaded onto the filament were 2–5 μg U, ∼0.1 μg Pu and <0.1 μg Nd. The accuracy and reproducibility of the isotopic ratio and concentration measurements were evaluated.     

Analysis of plutonium isotopes in marine samples by radiometric, ICP-MS and AMS techniques

IAEA reference materials (radionuclides in the marine environment) collected in areas affected by nuclear reprocessing plants and nuclear weapons tests have been analysed by semiconductor alpha-spectrometry (SAS), liquid scintillation spectrometry (LSS) and mass spectrometric techniques (high resolution ICP-MS and AMS) with the aim of developing analytical procedures and to study the geochemical behavior of plutonium in the marine environment. The Pu results obtained by SAS, ICP-MS and AMS were in reasonably good agreement (R ² = 0.99). The mean atom ratios of ²⁴⁰Pu/²³⁹Pu in IAEA reference materials, IAEA-134, 135 and 381 were (0.212±0.010), (0.211±0.004) and (0.242±0.004), respectively. IAEA-384 (Fangataufa Lagoon Sediment) gave a ²⁴⁰Pu/²³⁹Pu mean atom ratio of 0.051±0.001. The results of ²⁴¹Pu obtained by ICP-MS and LSS also show reasonable agreement (R ² = 0.91). Pu isotopic signatures were useful in tracing Pu origin and in interpreting biogeochemical processes involving Pu in the marine environment.     

Experimental evaluation of239Pu,238Pu and233U spikes for determining plutonium concentration by thermal ionization mass spectrometry and alpha-spectrometry

Experimental evaluation on the use of²³⁹Pu spike in Isotope Dilution-Thermal Ionization Mass Spectrometry (ID-TIMS),²³⁸Pu spike in Isotope Dilution Alpha Spectrometry (IDAS) and²³³U as a Non-Isotopic Diluent in Alpha Spectrometry (N-IDAS), for determing plutonium concentration in samples with burn-up values in the range of 1,000–10,000 MWD/TU is done. Precision is determined by analyzing replicate aliquots from different samples using each of the three spikes. Accuracy is established by comparing the results with those obtained by using well recognized spike²⁴²Pu in ID-TIMS. It is shown that the use of²³⁹Pu spike with the latest generation thermal ionization mass spectrometers gives the best precision (0.2%), whereas the precision values of 0.5 and 1% can be obtained by using²³⁸Pu and²³³U spikes, respectively, on a routine basis. Reasons for the difference in the precision values are discussed, along with the merits and drawbacks on the use of different spike isotopes.     

Determination of the plutonium concentration by Isotope Dilution Alpha-Spectrometry without purification from americium-241 and a bulk of other impurities

Summary A method is described for determining the plutonium concentration by Isotope Dilution Alpha Spectrometry (IDAS) using²³⁸Pu as a spike. It involves the addition of a pre-calibrated spike solution to a known aliquot of the plutonium sample solution followed by source preparation using TEG as a spreading agent. The results obtained on a number of samples using this method are compared with those of IDMS using²⁴²Pu as a spike as well as with those obtained by IDAS using TTA for purification, with respect to precision and accuracy. Precision of 0.3–0.5% and an accuracy of 0.5% is demonstrated. This method eliminates the need of any separation and purification of plutonium from²⁴¹ Am and a bulk of other impurities.

---

Plutoniumbestimmung durch Isotopenverdünnungs-Alpha-Spektrometrie ohne Abtrennung von Americium-241 und anderen Verunreinigungen

Zusammenfassung Bei dem beschriebenen Verfahren der Isotopenverdünnungs-Alpha-Spektrometrie (IDAS) wird²³⁸Pu als Spike benutzt. Eine vorgeeichte Spike-Lösung wird zu einem bekannten Aliquot der Probe gegeben und anschließend die Strahlungsquelle unter Verwendung von Tetraethylenglykol als Spreading-Reagens vorbereitet. Die nach diesem Verfahren erhaltenen Ergebnisse werden in bezug auf Präzision und Genauigkeit mit solchen verglichen, die mit Isotopenverdünnungs-Massenspektrometrie unter Verwendung von²⁴²Pu als Spike oder mit IDAS unter Verwendung von Thenoyltrifluoraceton zur Reinigung erhalten wurden. Eine Präzision von 0,3–0,5% und eine Genauigkeit von 0,5% wurden erzielt. Durch das beschriebene Verfahren erübrigt sich eine Reinigung des Pu von²⁴¹Am und anderen Verunreinigungen.

     

Preparation, certification and validation of a stable solid spike of uranium and plutonium coated with a cellulose derivative for the measurement of uranium and plutonium content in dissolved nuclear fuel by isotope dilution mass spectrometry.

A stable solid spike for the measurement of uranium and plutonium content in nitric acid solutions of spent nuclear fuel by isotope dilution mass spectrometry has been prepared at the European Commission Institute for Reference Materials and Measurements in Belgium. The spike contains about 50 mg of uranium with a 19.838% (235)U enrichment and 2 mg of plutonium with a 97.766% (239)Pu abundance in each individual ampoule. The dried materials were covered with a thin film of cellulose acetate butyrate as a protective organic stabilizer to resist shocks encountered during transportation and to eliminate flaking-off during long-term storage. It was found that the cellulose acetate butyrate has good characteristics, maintaining a thin film for a long time, but readily dissolving on heating with nitric acid solution. The solid spike containing cellulose acetate butyrate was certified as a reference material with certified quantities: (235)U and (239)Pu amounts and uranium and plutonium amount ratios, and was validated by analyzing spent fuel dissolver solutions of the Tokai reprocessing plant in Japan. This paper describes the preparation, certification and validation of the solid spike coated with a cellulose derivative.     

Rapid separation and purification of uranium and plutonium from dilute-matrix samples

This work describes a streamlined approach to the separation and purification of trace uranium and plutonium in environmental swipe samples that contain a small amount of collected bulk material. We describe key modifications to conventional techniques that result in a relatively rapid, safe, cost-effective, and efficient U and Pu separation process. Simulated samples were produced by loading appropriate ²³⁵U, ²³⁸U, and ²⁴⁰Pu onto high purity cotton swipes. Uranium concentration and isotopic composition were measured by multi-collector inductively coupled mass spectrometry. Corresponding plutonium measurements were conducted with a three stage thermal ionization mass spectrometer. Quantitative U and Pu recoveries were observed with this method.     

Development of a SIMS Method for Isotopic Measurements in Nuclear Forensic Applications

 Methodologies based on secondary ion mass spectrometry (SIMS) for isotopic measurements in nuclear forensic applications relevant to the age determination of Pu particles and isotopic composition of oxygen for geolocation assignment are described. For the age determination of Pu particles, a relative sensitivity factor (RSF) to correct for the different ionisation efficiencies of U and Pu, was obtained by analysing standard Pu materials with known ages. An RSF of 2.41±0.05 was obtained for PuO₂ from measurements on samples with different Pu/U ratios. In a sample of known origin, using this RSF value, the age calculated from the ²³⁸Pu/²³⁴U and ²⁴⁰Pu/²³⁶U ratios agreed well with the reported age of 2.3 years. For geolocation assignment, a new approach based on the measurement of differences in the natural abundance of ¹⁸O and ¹⁶O isotopes and their ratio was developed. The instrumental mass discrimination of the ¹⁸O/¹⁶O ratio was determined using three O-isotope samples of different chemical composition. The measured precision (the standard error of 100 cycles/analysis) obtained for the oxygen isotopic measurement on the samples was typically ±1.1‰.     

Age determination of single plutonium particles after chemical separation

Age determination of single plutonium particles was demonstrated using five particles of the standard reference material, NBS 947 (Plutonium Isotopic Standard. National Bureau of Standards, Washington, D.C. 20234, August 19, 1982, currently distributed as NBL CRM-137) and the radioactive decay of ²⁴¹Pu into ²⁴¹Am. The elemental ratio of Am/Pu in Pu particles found on a carbon planchet was measured by wavelength dispersive X-ray spectrometry (WDX) coupled to a scanning electron microscope (SEM). After the WDX measurement, each plutonium particle, with an average size of a few μm, was picked up and relocated to a silicon wafer inside the SEM chamber using a micromanipulator. The silicon wafer was then transferred to a quartz tube for dissolution in an acid solution prior to chemical separation. After the Pu was chemically separated from Am and U, the isotopic ratios of Pu (²⁴⁰Pu/²³⁹Pu, ²⁴¹Pu/²³⁹Pu and ²⁴²Pu/²³⁹Pu) were measured with a thermal ionization mass spectrometer (TIMS) for the calculation of Pu age. The age of particles determined in this study was in good agreement with the expected age (35.9 a) of NBS 947 within the measurement uncertainty.     

Determination of Am and Cm in spent nuclear fuels by isotope dilution inductively coupled plasma mass spectrometry and isotope dilution thermal ionization mass spectrometry after separation by high-performance liquid chromatography

Elemental and isotopic determination of americium and curium in spent nuclear fuels is necessary to validate neutronic calculation codes and for nuclear waste disposal purposes. Prior to mass spectrometric analysis, it is mandatory to perform separations in order to eliminate isobaric interferences between U, Pu, Am and Cm. In the spent fuels samples analyzed, a separation of U and Pu has been first realized with an anion-exchange resin. Then a rapid Am/Cm separation has been developed by high-performance liquid chromatography (HPLC) with an on-line detection using the Am and Cm α-emission. The influence of the different parameters on the chromatographic separation are described and discussed. Inductively coupled plasma mass spectrometry (ICP-MS) and thermal-ionization mass spectrometry (TIMS) have been used to measure the isotopic composition of U, Am and Cm and to determine the ²⁴¹Am/²³⁸U and ²⁴⁴Cm/²³⁸U ratios with the double spike isotope dilution method. The measurement procedures and the accuracy and precision of the results obtained with a quadrupole ICP-MS on different spent fuels samples are discussed and compared with those obtained by TIMS, used as a reference technique. Received: 30 November 1998 / Revised: 8 January 1999 / Accepted: 12 January 1999     

Determination of Am and Cm in spent nuclear fuels by isotope dilution inductively coupled plasma mass spectrometry and isotope dilution thermal ionization mass spectrometry after separation by high-performance liquid chromatography

Elemental and isotopic determination of americium and curium in spent nuclear fuels is necessary to validate neutronic calculation codes and for nuclear waste disposal purposes. Prior to mass spectrometric analysis, it is mandatory to perform separations in order to eliminate isobaric interferences between U, Pu, Am and Cm. In the spent fuels samples analyzed, a separation of U and Pu has been first realized with an anion-exchange resin. Then a rapid Am/Cm separation has been developed by high-performance liquid chromatography (HPLC) with an on-line detection using the Am and Cm α-emission. The influence of the different parameters on the chromatographic separation are described and discussed. Inductively coupled plasma mass spectrometry (ICP-MS) and thermal-ionization mass spectrometry (TIMS) have been used to measure the isotopic composition of U, Am and Cm and to determine the ²⁴¹Am/²³⁸U and ²⁴⁴Cm/²³⁸U ratios with the double spike isotope dilution method. The measurement procedures and the accuracy and precision of the results obtained with a quadrupole ICP-MS on different spent fuels samples are discussed and compared with those obtained by TIMS, used as a reference technique. Received: 30 November 1998 / Revised: 8 January 1999 / Accepted: 12 January 1999