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Environmental Radiochemical Analysis IV
By Peter Warwick
The Royal Society of Chemistry
Copyright © 2011 The Royal Society of ChemistryAll rights reserved.
ISBN: 978-1-84973-294-9
CHAPTER 1
A SEARCH FOR LONG LIVED 242mAm ISOTOPE IN FOREST LITTER SAMPLES FROM POLAND
J.W. Mietelski and E. Tomankiewicz
The Henryk Niewodniczanski Institute of Nuclear Physics, Polish Academy of Sciences; Radzikowskiego str. 152, 31-342 Krakow, Poland.
1 INTRODUCTION
The 242mAm is a long lived (T1/2=143 years) transuranic isotope which is produced in nuclear reactors mainly as a result of a neutron capture of 241Am. It can be also produced in this way by high neutron fluxes during nuclear explosion. For many particular environmental sources, as for example global fallout, one can expect the 242mAm activity on the level of about 1% of that of 241Am. 242mAm decays by internal transition into 242Am (T1/2=16 h). The ground state 242Am decays by beta minus (83%) or electron capture (16%) into an alpha emitter, 242Cm (T1/2=163 days), which then decays into another alpha emitter, 238Pu (T1/2=88 years). As discussed elswhere the direct detection of 242mAm at environmental levels is not technically possible and only indirect methods are suitable. In our approach, the ingrowth of 238Pu was determined on an old alpha source of americium. The original forest litter samples were collected in Poland in 1991 or 1987. Samples were subjected to typical radiochemical methods during 1991-1996. Americium was separated and alpha spectrometric sources were prepared (using NdF3 method), measured and results were published. For the same set of samples, data on Pu activity (including 241Pu) are also available. In the present paper original codes are kept to enable any further comparisons. Some of the litter samples showed clear dominant Chernobyl influence (for example traces of 244Cm, strongly enhanced activity ratios 238Pu to 239+240Pu and 241Pu to 239+240Pu), although for the majority global fallout was concluded to be the main origin of transuranic isotopes. In our laboratory 25 sources from this project were preserved and still available. After about 12 years (on average: 4065 days) which elapsed since the preparation of the Am alpha sources (plastic foil filters with several micrograms of NdF3 crystals on it glued on to a metal plate) were taken for radiochemical separations in order to determine the ingrowth of plutonium alpha activity within them.
2 METHOD AND RESULTS
Prior to the radiochemical procedures all samples were re-measured by alpha spectrometry to ensure the self consistency between our past and present measurement techniques. The average ratio between past and present 241Am results (decay corrected) was 0.95 with standard deviation of 0.12. Thus it was considered satisfactory. Radiochemical work started with the dismounting of alpha sources. Filters were carefully removed from the metal discs and then dissolved in hot aqua regia with some boric acid added. A spike of 242Pu was added (13.3 mBq) to each sample. After evaporation a few drops of perchloric acid was added to destroy any remains of filter material. Then the Pu oxidation state was adjusted to +4 using hydrazine and NaNO2 followed later by a standard procedure used to separate Pu from 8 M HNO3 on Dowex 1x8 anion-exchange resin. The NdF3 sources were then prepared and measured by means of alpha spectrometry.
In the original study we used a relatively high activity of 243Am tracer (usually 226 mBq per sample) and in some samples traces of 244+243Cm were observed. These isotopes all result in the production of 239Pu or 240Pu, and the decay of americium tracer is the dominant source. Spectra therefore revealed traces of 239+240Pu as well as 238Pu. The results of Pu measurements in Am sources are presented in Table 1. The last column of this table shows the 242mAm activity calculated from Beteman equation. In about half of our samples an excess of 239+240Pu activity above that expected from 243Am decay is noticed, which suggests possible contamination of original Am fraction with tiny traces of Pu. This means that the observed 238Pu activities are the upper limits of that ingrown from 242mAm decay. The calculated 242mAm activities do not correlate with measured 241Am activity (see Fig. 1), which is of mixed Chernobyl and global fallout origin.
The mean value for 242mAm/241Am activity ratio is 0.023 with standard deviation of 0.033 so, in general, the 242mAm to 241Am ratio is on the level of a single percent. The high standard deviation reflects the mix of two sources (global fallout and Chernobyl) which differ in 242mAm to 241Am activity ratio. Moreover, 242mAm activities (or rather upper limits) correlate with the 244Cm activity measured in 1995 (see Fig. 2), which is of solely Chernobyl origin. This suggests that Chernobyl is the dominant source of 242mAm in this area. The slope of the correlation line is 0.87±0.28; after decay correction of activities back to 1986 this ratio equals 0.63 and this is an estimation of the upper limit of 242mAm to 244Cm activity ratio for fresh Chernobyl fallout. This is about order of magnitude higher than reported in the past. Taking into account the estimated released 6.2 TBq of 244Cm gives an upper limit for release of 242mAm from Chernobyl of 3.9 TBq. Available data allows to estimate, that the 242mAm to 241Am ratio in Chernobyl fallout at present (including 241Am ingrown from 241Pu) may be even as high as 7%.
3 CONCLUSION
Analyses of 238Pu traces present in americium sources obtained from forest litter samples was used to estimate the upper concentration limit of long lived 242mAm. The phrase "upper limit for activity" instead of "activity concentration" reflect the potential for tiny traces of plutonium to be present in the original americium sources. The current results confirm a previous estimation that 242mAm activity is on level of single percent of 241Am. Moreover, a correlation between the 242mAm upper limit and the 244Cm activity concentration (as measured in 1995) was found, which allowed the 242mAm to 244Cm upper limit ratio in fresh Chernobyl fallout to be 0.63 (in 1986). This leads to a maximum release of 242mAm from Chernobyl, of 3.9 TBq. Thus, the 242mAm to 241Am activity ratio for Chernobyl fallout at present is estimated to be equal up to 7%.
CHAPTER 2THE FATE OF TECHNETIUM-99 (99Tc) IN THE NORTH AND NORDIC SEAS AFTER REDUCTION IN THE DISCHARGES FROM SELLAFIELD
H.M. Karlsen and H.E. Heidal
Institute of Marine Research (IMR), PO Box 1870 Nordnes, N-5817 Bergen, Norway
1 INTRODUCTION
Technetium-99 (99Tc) is a long-lived, pure β-emitting (Emax = 292 keV) radionuclide with a half-life of 2.13 x 105 years. During the period 1994-2004, large amounts of 99Tc were discharged into the Irish Sea from the nuclear reprocessing plant Sellafield (UK) (Figure 1). In oxygenated seawater, 99Tc is transported over long distances as the highly soluble pertechnetate ion, TcO4-. As a result of the increased discharges, the concentrations of 99Tc increased in seawater and marine organisms in Norwegian and adjacent waters during the late 1990s. This caused serious concerns in Norwegian fisheries and seafood industries although there was no known health or environmental impact from the measured concentrations. The issue also attracted strong criticism from Norwegian Ministers, media, NGOs and community groups at the beginning of the new millennium. In 2004, the implementation of a new treatment process for spent nuclear fuel led to a reduction in the discharges of 90%.
The Institute of Marine Research (IMR) participates in the Norwegian national monitoring programme RAME (Radioactivity in the Marine Environment), coordinated by the Norwegian Radiation Protection Authority (NRPA), where concentrations of 99Tc in Norwegian waters have been monitored. The aim of the present study was threefold: to present IMR's monitoring data on 99Tc in Norwegian waters from the period 2003-2010; to follow and document the decrease in concentrations of 99Tc in Norwegian waters after the reduction in the discharges from Sellafield; and to extend already existing datasets which can be used to model developments and validation.
2 MATERIALS AND METHODS
2.1 Sample collection
Sample collection took place during cruises conducted by IMR in the North and Nordic Seas and by local fishermen along the Norwegian coast in the period 2003-2010. Surface seawater (50-100 L from a depth of 0-5m) was collected in 25 L polyethylene carboys using a shipboard pump or by lowering the carboy into the seawater. Since the samples were collected in open sea areas with low concentrations of suspended materials, filtering prior to analysis was not necessary.
In July 2010, 20 samples from the North Sea, Skagerrak and the Norwegian Coastal Current (NwCC) were collected during a cruise aboard R/V Johan Hjort. The sampling stations are shown in Figure 2.
2.2 Analytical Method
Radiochemical separation of 99Tc from the sample matrix removes interference from other β-emitting radionuclides, and is necessary for quantitative analysis. The analytical method for determination of 99Tc in seawater used at IMR, is based upon Harvey et al. This method uses rhenium, in the form of KReO4, as a non-isotopic carrier and yield monitor. After adding rhenium, a preliminary extraction of 99Tc (and Re) based on anion-exchange separation is performed. Iron hydroxide scavenging is thereafter performed to remove unwanted components such as alkaline and rare-earth elements and phosphates. 99Tc and Re are further extracted by a second anion-exchange separation and eluted with an alkaline sodium perchlorate solution. Next, two subsequent sulphide precipitations are performed in order to remove perchlorate ions. Finally, the tetraphenyl arsonium salts of 99Tc and Re are isolated. Perchlorate ions will also form an insoluble tetraphenyl arsonium salt, and need therefore to be removed before the final precipitation. The yield of the rhenium tetraphenyl arsonium salt is determined gravimetrically. 99Tc is beta-counted using a RISØ low-level beta GM multicounter system. Count times were of the order of 48 hours and all counts were corrected for background (typically 0.0025 cps). The theoretical detection limit for 100 L seawater is 0.05 Bq m-3.
3 RESULTS AND DISCUSSION
Time-series of 99Tc activity concentrations in the North and Nordic Seas are shown in Figure 3, also including data from an IMR/CEFAS (Centre for Environment, Fisheries and Aquaculture Science) study conducted during the years 1998-2000.
The highest concentrations are measured in samples from the east coast of Britain, the North Sea, Skagerrak and the NwCC, reflecting the closeness to Sellafield and the general circulation pattern of surface water in this area. The concentrations in the Norwegian, Greenland and Barents Seas have been generally low (below 1 Bq m-3) during the whole period. The time-series show that the 99Tc concentrations in the North and Nordic Seas are generally decreasing. However, measurements from the North Sea and the NwCC in 2008 showed somewhat higher concentrations than anticipated (0.72-2.0 Bq m-3). The reason for this is not clear.
In 2010, the concentrations of 99Tc in the North Sea and the Skagerrak ranged from 0.12-0.77 Bq m-3. The highest concentration was observed off the Scottish coast. The average concentrations in the North Sea, Skagerrak and the NwCC south of Stad were 0.26, 0.35 and 0.34 Bq m-3, respectively. These results are similar to the levels reported by Herrmann et al. of 0.4 and 0.3 Bq m-3 in the NwCC and the Skagerrak, respectively, in July 1991. However, the source of the 99Tc contamination observed by Herrmann et al. was mainly elevated discharges from the French reprocessing plant La Hague during the 1980s.
Although the 99Tc concentrations in the North and Nordic Seas has decreased after the reduction in the discharges from Sellafield, the levels in the North Sea off the Scottish coast are still significantly higher today than before 1994 (0.1-0.2 Bq m-3 in 1992 and 1993). Further, the present levels are much higher than the 'fallout background level' of 0.005 Bq m-3 reported for oceanic Atlantic water.
CHAPTER 3FURTHER DEVELOPMENT OF A FAST METHOD FOR DETERMINING PLUTONIUM AND AMERCIUM IN SOILS IN GERMANY
D. Tait and B. Kock
Max Rubner-Institut, Bundesforschungsinstitut für Ernährung und Lebensmittel, Institut fur Sicherheit und Qualität bei Milch und Fisch, Hermann-Weigmann-Str. 1, D-24103 Kiel
1 INTRODUCTION
The ubiquity of the plutonium nuclides Pu-238 (t½ = 88 a), Pu-239 (t½ = 24 000 a), Pu- 240 (t½ = 6 500 a) and Pu-241 (t½ = 14 a) in soil today results mainly from the fallout after the atmospheric testing of nuclear weapons in the period 1950 to 1963. Additional amounts of Pu-238 were globally dispersed after a satellite burned out in the upper atmosphere in 1964. Local increases in plutonium contamination of soil have been caused by emissions during the early years of nuclear technology and by accidents at nuclear installations. Am-241 (t½ = 430 a) occurs in soil as a result of Pu-241 decay. Thus the activity of Am-241 has been increasing since the nuclear wepons tests. Owing to their relative half-lives, almost equal activities of Pu-241 and Am-241 are to be expected in the environment today.
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Excerpted from Environmental Radiochemical Analysis IV by Peter Warwick. Copyright © 2011 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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Table of Contents
A Search for Long Lived 242mAm Isotope in Forest Litter Samples from Poland;The Fate of Technetium-99 (99Tc) in the North and Nordic Seas after Reduction in the Discharges from Sellafield; Further Development of a Fast Method for Determining Plutonium and Amercium in Soils in Germany; Accelerator Mass Spectrometry Measurement of 129I in Solid Samples by a Microwave Based Procedure ; Using Time Resolved Laser Fluorescence Spectroscopy as an Internal Probe for the Phase Changes in Zirconium Oxide ;Determination of Thorium and Uranium Isotope Ratios in NORM and NORM-polluted Sample Leachates using ICP-QMS; Fast Method to Separate AM and PU from Soil Matrix; Biosorption of Uranium using Modified Leaf Powder of Platanus Orientalis; Development and Validation of the Radiochemical Determination of 99Tc in Environmental Samples; Radioactivity in the Irish Sea; 129I in Macroalgae (Fucus Vesiculosus) from the Swedish Coast; The Effect of Cement Superplasticiser on the Solubility of Radionuclides under Repository Conditions; Performance and Characteristics of a Low-Background Germanium Well Detector for Low-Energy Gamma-ray Nuclides; Interlaboratory Comparison on the Determination of Radio-Nuclides in Raw Milk in the Year ; Deep Geological Disposal of Intermediate and Low Level Waste in UK: Experiments to Demonstrate Chemical Containment. Part I ;Leaching of 239,240Pu and 241Am from Thule Nuclear Bomb Particles Investigated by Sequential Extraction; Caesium-137 in Norwegian Coastal Areas; Marine Radioactivity in the Channel Islands, 1990 - 2009; Development of a Small Mobile Unit for Emergency Radiological Monitoring of the Foodchain; Comparison of Analytical Methods and ICP-MS Correction Schemes; Ultra-Trace Determination of Plutonium in Coral Samples using Multi-Collector ICP-MSWhat People are Saying About This
Review of previous edition:
"The book presents the latest information concerning environmental analysis of radionuclides and will be an essential reading for practising radioanalysts, as well as for professionals in academia and industry."
International Journal of Environmental Analytical Chemistry, 2008