Kristina Stenström

Levels of 14C in the Terrestrial Environment in the Vicinity of Two European Nuclear Power Plants

Radiocarbon is produced in all types of nuclear reactors. Most of the C-14 released into the environment is in the form of gaseous emissions. Recent data on the C-14 concentration found in terrestrial samples taken in the vicinity of nuclear power plants in Romania and Lithuania are presented. We found increased C-14 levels in the surroundings of both power plants. At the Romanian power plant Cernavoda, we found excess levels of C-14 in grass within a distance of about 1000 in, the highest C-14 specific activity being 311 Bq/kg C (approximately 28% above the contemporary C-14 background) found at a distance of 200 in from the point of release (nearest sampling location). At the Lithuanian power plant Ignalina, samples of willow, pine, and spruce showed a C-14 excess of similar magnitude, while significantly higher values were found in moss samples. The samples were analyzed at the accelerator mass spectrometry facility in Lund, Sweden. (Less)

Dating Components of Human Atherosclerotic Plaques

Rationale: Atherosclerotic plaques that give rise to acute clinical symptoms are typically characterized by degradation of the connective tissue and plaque rupture. Experimental studies have shown that mechanisms to repair vulnerable lesions exist, but the rate of remodeling of human plaque tissue has not been studied. Objective: In the present study, we determined the biological age of different components of advanced human atherosclerotic plaques by analyzing tissue levels of 14C released into the atmosphere during the nuclear weapons tests in the late 1950s and early 1960s. Methods and Results: Atherosclerotic plaques were obtained from 10 patients (age 46 to 80 years) undergoing carotid surgery. Different regions of the plaques were dissected and analyzed for 14C content using accelerator mass spectrometry. At the time of surgery, the mean biological age of the cap region was 6.4±3.2 years, which was significantly lower than that of the shoulder region (12.9±3.0 years, P<0.01), the interface toward the media (12.4±3.3 years, P<0.01), and the core (9.8±4.5 years, P<0.05). Analysis of proliferative activity and rate of apoptosis showed no signs of increased cellular turnover in the cap, suggesting that the lower 14C content reflected a more recent time of formation. Conclusions: These results show that the turnover time of human plaque tissue is very long and may explain why regression of atherosclerotic plaque size rarely is observed in cardiovascular intervention trials.

Application of accelerator mass spectrometry (AMS) for high-sensitivity measurements of 14CO2 in long-term studies of fat metabolism

Long-term measurements of 14C in CO2 expired after ingestion of 14C-labelled triolein were performed using accelerator mass spectrometry (AMS). About 30% of a given amount of 14C-labelled triolein was catabolized rapidly, while the remaining 70% had a very slow turnover. The study shows the potential of the AMS technique for the study of the long-term biokinetics of 14C-labelled pharmaceuticals. The AMS technique allows the administered activity to be reduced by several orders of magnitude without compromising the study. It may also allow studies of rare drug metabolites.

Development of graphitization of μg-sized samples at Lund University

To be able to successfully measure radiocarbon with accelerator mass spectrometry (AMS) in atmospheric aerosol samples, graphitization of small sample sizes (< 50 µg carbon) must provide reproducible results. At Lund University, a graphitization line optimized for small samples has been constructed. Attention has been given to minimize the reduction reactor volume and each reactor is equipped with a very small pressure transducer that enables constant monitoring of the reaction. Samples as small as 25 µg of carbon have been successfully analyzed, and the mass detection limit of the system has probably not been reached.

Biokinetics and radiation dosimetry for patients undergoing a glycerol tri[1-14C]oleate fat malabsorption breath test.

The glycerol tri[1-14C]olein test for fat malabsorption was carried out in two male volunteers and measurements of the loss of 14C in expired air, urine and faeces and the retention of 14C in biopsy samples of abdominal fat were made using accelerator mass spectrometry. Exhalation accounted for 73% and 55% of the administered activity and could be described by three-component exponential functions with halftimes of about 1h, 2 days and 150 days, respectively. Urinary excretion accounted for 24% of the administered activity, almost all during the first 24h after administration; about 2% was excreted in the faeces in 48h. The halftime of retention of 14C in fat ranged from 137 to 620 days. Absorbed dose calculations indicate that for a normal adult the largest dose, 1.5-7.0mGy/MBq is received by the adipose tissue, and that the effective dose is 0.3-0.5mSv/MBq. It is concluded that no restrictions need to be placed on radiation safety grounds on the administration of 0.05-0.1MBq 14C-triolein for the triolein breath test.

Environmental levels of carbon-14 around a Swedish nuclear power plant measured with accelerator mass spectrometry

Abstract 14 C is one of the radionuclides which are produced by nuclear power plants. The main part of the 14 C, which is released during normal operation, is produced through neutron induced reactions in the cooling water and is released as airborne effluents (such as CO 2 and hydrocarbons) through the ventilation system of the plant to the surrounding environment. Because of the biological importance of carbon and the long half-life of 14 C, it is of interest to measure the releases and their incorporation into living material in the environment of the power plants. In this pilot study the accelerator mass spectrometry (AMS) facility at the University of Lund has been used to measure the 14 C activity concentration in vegetation around a Swedish nuclear power plant. AMS is suitable mainly because of the accuracy obtained within a short measuring time, which makes it possible to analyze a sufficient number of samples for a thorough investigation. The results of this study demonstrate that the AMS method is suitable for investigations of the influence on the local environment of reactor-released 14 C by analysis of living material. To test dispersion models, however, air sampling both of emission source and in the surrounding of the plant seems more suitable.

14C content in vegetation in the vicinities of Brazilian nuclear power reactors

(14)C specific activities were measured in grass samples collected around Brazilian nuclear power reactors. The specific activity values varied between 227 and 299 Bq/kg C. Except for two samples which showed (14)C specific activities 22% above background values, half of the samples showed background specific activities, and the other half had a (14)C excess of 1-18%. The highest specific activities were found close to the nuclear power plants and along the main wind directions (NE and NNE). The activity values were found to decrease with increasing distance from the reactors. The unexpectedly high (14)C excess values found in two samples were related to the local topography, which favors (14)C accumulation and limits the dispersion of the plume. The results indicate a clear (14)C anthropogenic signal within 5 km around the nuclear power plants which is most prominent along northeastwards, the prevailing wind direction.

14C levels in the vicinity of two swedish nuclear power plants and at two clean-air sites in Southernmost Sweden

(super 14) C is one of the radionuclides that are produced to different degrees by neutron-induced reactions in all types of nuclear reactors. Part of the (super 14) C created is continuously released into the surrounding environment during normal operation as airborne effluents in various chemical forms (such as CO (sub 2) , Co and hydrocarbons) through the ventilation system of the plant. Because of the biological importance of carbon and the long half-life of (super 14) C, it is of interest to measure the releases and their incorporation into living material. We report here on the (super 14) C activity concentrations in annual tree rings and the air around two Swedish nuclear power plants, as well as the background (super 14) C activity levels from two reference sites in southern Sweden from 1973-1996. We used both accelerator mass spectrometry (AMS) and decay counting in the investigation.

Bomb-pulse dating of human material – modelling the influence of diet.

The atmospheric testing of nuclear weapons during the 1950s and early 1960s produced large amounts of radiocarbon. This 14C bomb pulse provides useful age information in numerous scientific fields, e.g. in geosciences and environmental sciences. Bomb-pulse dating can also be used to date human material (e.g. in forensics and medical science). Bombpulse dating relies on precise measurements of the declining 14C concentration in atmospheric carbon dioxide collected at clean-air sites. However, local variations in the 14C specific activity of air and foodstuffs occur, which are caused by natural processes as well as by various human activities. As 14C enters the human body mainly through the diet, variations of 14C concentration in foodstuffs need to be considered. The marine component of the diet is believed to be of particular importance due to the non-equilibrium in 14C specific activity between the atmosphere and aquatic reservoirs during the bomb pulse. This article reviews the 14C concentration in marine foodstuffs during the bomb-pulse era, and models how the marine component in one’s diet can affect the precision of bomb-pulse dating of human material. (Less)

A one-year study of the total air-borne14C effluents from two Swedish light-water reactors, one boiling water- and one pressurized water reactor

The results of a one-year study of the total air-borne14C effluents from two Swedish light-water reactors, one boiling water reactor (BWR) at Forsmark and one pressurized water reactor (PWR) at Ringhals, are presented. Air emitted from the stacks has been collected continuously over two-week periods and the14C content in the samples has been analysed using accelerator mass spectrometry (AMS). The14C activity concentration in the air issuing from the stack of the PWR varied between 2 and 1132 Bq/m3 with a mean value of 200 Bq/m3, while from the BWR the activity concentration varied between 4 and 146 Bq/m3, with a mean value of 95 Bq/m3. The corresponding14C release rate was 0.27 TBq/GWel·year for the PWR and 0.48 TBq/GWel·year for the BWR. During the same period of time, for comparison, the14C activity in continuously collected air from the stack of the PWR was also measured by liquid scintillation counting. In most cases the results of these measurements were in fair agreement with the corresponding AMS results.