(14)C levels in the vicinity of the Fukushima Dai-ichi Nuclear Power Plant prior to the 2011 accident

Impact of the Fukushima Accident on 3H and 14C Environmental Levels: A Review of Ten Years of Investigation

The investigation of the impact of the Fukushima accident is still going on although more than ten years have passed since the disaster. The main goal of this paper was to summarize the results of tritium and radiocarbon determinations in different environmental samples, possibly connected with the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. A document containing compiled data may serve as a solid basis for further research in the selected fields. To accomplish such effort, we went through dozens of relevant published papers, reporting 3H and 14C activity concentrations in precipitations, groundwater, seawater, river systems, tree rings, and, in some more extraordinary samples, such as herbaceous plants or debris from the damaged reactor buildings. As the referenced results would not be obtainable without adequate analytical techniques, the most common methods for routine measurement of tritium and radiocarbon concentrations are discussed as well. We believe that the correct identification of the affected environmental compartments could help quantify the released 3H and 14C activities and track their following fate, which could be especially important for plans to discharge contaminated water from the FDNPP in the upcoming years.

Some mycoheterotrophic orchids depend on carbon from dead wood: novel evidence from a radiocarbon approach

Mycoheterotrophic plants depend entirely on fungal associations for organic nutrients. While most mycoheterotrophic plants are associated with the mycorrhizal partners of surrounding green plants, some mycoheterotrophs are believed to obtain carbon from decaying litter or dead wood by parasitising saprotrophic fungi, based on culture experiments and ¹³ C and ¹⁵ N isotopic signatures. The carbon age (the time since carbon was fixed from atmospheric CO₂ by photosynthesis) can be estimated by measuring the concentration of ¹⁴ C arising from the bomb tests of the 1950s and 1960s. Given that mycorrhizal fungi obtain photosynthate from their plant partners, and saprotrophic wood-decaying fungi obtain carbon from older sources, radiocarbon could represent a new and powerful tool to investigate carbon sources of mycoheterotrophic plants. We showed that the Δ¹⁴ C values of mycoheterotrophs exploiting ectomycorrhizal fungi were close to 0‰, similar to those of autotrophic plants. By contrast, the Δ¹⁴ C values of mycoheterotrophs exploiting saprotrophic fungi ranged from 110.7‰ to 324.8‰, due to the ¹⁴ C-enriched bomb carbon from dead wood via saprotrophic fungi. Our study provides evidence supporting that some mycoheterotrophic orchids depend on forest woody debris. Our study also indicates that radiocarbon could be used to predict the trophic strategies of mycoheterotroph-associated fungal symbionts.

Distribution of radiocarbon in sediments of the cooling pond of RBMK type Ignalina Nuclear Power Plant in Lithuania

The vertical distribution of radiocarbon (14C) was examined in the bottom sediment core, taken from Lake Drūkšiai, which has served as a cooling pond since 1983 for the 26 years of the Ignalina Nuclear Power Plant (INPP) operation using two RBMK-1500 reactors (Russian acronym for"Channelized Large Power Reactor"). 14C specific activity was measured in alkali-soluble and -insoluble fractions of the sediment layers. Complementary measurements of the 210Pb and 137Cs activity of the samples provided the possibility to evaluate the date of every layer formation, covering the 1947-2013 period. In addition, 14C distribution was examined in the scales of pelagic fish caught between 1980 and 2012. Our measurements reveal that, during the period 1947-1999, the radiocarbon specific activity in both fractions exhibits a parallel course with a difference of 5 ± 1 pMC (percent of modern carbon) being higher in alkali-soluble fraction, although 14C specific activity in both fractions increased by 11.4-13.6 pMC during the first 15 years of plant operation. However, during the 2000-2009 period, other than previously seen, a dissolved inorganic carbon (DIC) → aquatic primary producers → sediments 14C incorporation pattern occurred, as the radiocarbon specific activity difference between alkali-soluble and -insoluble fractions reached 94, 25, and 20 pMC in 2000, 2006, and 2008, respectively. Measurements in different sediment fractions allowed us to identify the unexpected organic nature of 14C contained in liquid effluences from the INPP in 2000-2009. The discrepancy between 14C specific activity in fish scales samples and DIC after 2000 also confirmed the possibility of organic 14C contamination. Possible reasons for this phenomenon might be industrial processes introduced at the INPP, such as the start of operation of the cementation facility for spent ion exchange resins, decontamination procedures, and various maintenance activities of reactor aging systems and equipment.

Application of synthetic benzoic acid technology in environmental radiocarbon monitoring

Environmental radiocarbon (¹⁴C) monitoring is gaining importance in China due to the recent rapid development of the nuclear industry. In this study, synthetic benzoic acid samples with the fingerprint of environmental ¹⁴C were generated by using the synthesis method, and the specific activity of ¹⁴C was determined using the liquid scintillation counting (LSC) method. The ultra-performance liquid chromatography (UPLC) analysis was performed in chemical properties test and results showed that the mean assay and yield of synthetic benzoic acid were 91.8% ± 2.4% and 84.5% ± 2.0%, respectively. Under adopted LSC counting conditions, the minimum detectable activity (MDA) of 64 Bq/kg C was achieved in our laboratory. The method's linearity was examined using a series of spiked samples, along with the ¹⁴C-free samples. The results showed a wide linear range up to 2000 Bq/kg C. Reproducible results were obtained from three batches of experiments with deviations in the intra-group and inter-group of 0.38%-3.06% and 1.24%-3.55%, respectively. Long-term evaluation of the system was found to be very stable (over 5 months storage) with the relative standard deviations of <1%. In addition, field applications in the vicinity of a nuclear power plant demonstrated that ¹⁴C data measured by our method was consistent with the accelerator mass spectrometry (AMS) method, suggesting the method's precision can meet the requirement of ¹⁴C monitoring near the nuclear facility. This is the first study to report the use of synthetic benzoic acid in environmental ¹⁴C monitoring, and it provides a new approach for improving the environmental ¹⁴C monitoring network.

Advanced atmospheric 14C monitoring around the Paks Nuclear Power Plant, Hungary

Atmospheric air samples were collected at 9 monitoring stations (A1 to A9) less than 2 km from the Paks Nuclear Power Plant (Paks NPP) and a background station (B24). The monthly integrated CO₂ and total carbon (CO₂+hydrocarbons (C_nH_m)) samples were collected to determine the excess ¹⁴C activity at the vicinity of the NPP. The measurements providing the ¹⁴C/¹²C ratio of the monthly integrated samples were carried out on a MICADAS type AMS at HEKAL. Due to the relatively low ¹⁴CO₂ emission of PWR type Paks reactors and the local Suess effect, there was negligible excess ¹⁴C activity at the investigated stations in the pure CO₂ fraction during the investigated 2 years period (2015-2016). On the contrary, there was a detectable (although minor) excess at every station in the C_nH_m fraction. In case of CO₂, the average Δ¹⁴C excess was 3.8‰ and the highest measured value was 91.2‰ at the A3 station in February 2015. In case of C_nH_m, the average excess was 31.1‰ and the highest measured value was 319.1‰ at the A4 station in February 2016. We applied PC-CREAM 08 modelling to investigate the observed excess ¹⁴C activity at the environmental sampling stations, which depends on the distance from the NPP and the meteorological conditions, such as wind direction and wind speed. Meteorology data was collected at the operating area of the Paks NPP in a meteorology tower. The direct C-14 emission through the 120 m high stacks was measured in the NPP by liquid scintillation counting. These emission data and our model calculations explain the excess activity in the C_nH_m fraction at the A4 station, which is located only 915 m far from the NPP's stacks in the prevailing wind direction. The excess activity at A3 station (the farthest unit) probably came from the nearby NPP wastewater discharge point. The recently observed average excess and highest excess data is similar to the published data in former studies (Molnár et al., 2007; Veres et al., 1995) on Paks NPP, the highest ¹⁴CO₂ and ¹⁴C_nH_m excess are just a little higher than it was in the earlier studies, but in these former studies, the A3 station was not equipped with a radiocarbon monitoring unit and the level of radiocarbon emission was almost invisible from the wastewater discharge point.

Tritium and radiocarbon in the western North Pacific waters: post-Fukushima situation

Impact of the Fukushima Dai-ichi Nuclear Power Plant (FNPP1) accident on tritium (³H) and radiocarbon (¹⁴C) levels in the water column of the western North Pacific Ocean in winter 2012 is evaluated and compared with radiocesium (^134,137Cs) data collected for the same region. Tritium concentrations in surface seawater, varying between 0.4 and 2.0 TU (47.2-236 Bq m^-3), follow the Fukushima radiocesium trend, however, some differences in the vertical profiles were observed, namely in depths of 50-400 m. No correlation was visible in the case of ¹⁴C, whose surface Δ¹⁴C levels raised from negative values (about -40‰) in the northern part of transect, to positive values (∼68‰) near the equator. Homogenously mixed ¹⁴C levels in the subsurface layers were observed at all stations. Sixteen surface (from 30 in total) and 6 water profile (from 7) stations were affected by the Fukushima tritium. Surface and vertical profile data together with the calculated water column inventories indicate that the total amount of the FNPP1-derived tritium deposited to the western North Pacific Ocean was 0.7 ± 0.3 PBq. No clear impact of the Fukushima accident on ¹⁴C levels in the western North Pacific was observed.

Local variance of atmospheric 14C concentrations around Fukushima Dai-ichi Nuclear Power Plant from 2010 to 2012

Radiocarbon (¹⁴C) has been measured in single tree ring samples collected from the southwest of the Fukushima Dai-ichi Nuclear Power Plant. Our data indicate south-westwards dispersion of radiocarbon and the highest ¹⁴C activity observed so far in the local environment during the 2011 accident. The abnormally high ¹⁴C activity in the late wood of 2011 ring may imply an unknown source of radiocarbon nearby after the accident. The influence of ¹⁴C shrank from 30 km during normal reactor operation to 14 km for the accident in the northwest of FDNPP, but remains unclear in the southwest.

Radiocarbon Releases from the 2011 Fukushima Nuclear Accident

Radiocarbon activities were measured in annual tree rings for the years 2009 to 2015 from Japanese cedar trees (Cryptomeria japonica) collected at six sites ranging from 2.5–38 km northwest and north of the Fukushima Dai-ichi nuclear power plant. The ¹⁴C specific activity varied from 280.4 Bq kg⁻¹ C in 2010 to 226.0 Bq kg⁻¹ C in 2015. The elevated ¹⁴C activities in the 2009 and 2010 rings confirmed ¹⁴C discharges during routine reactor operations, whereas those activities that were indistinguishable from background in 2012–2015 coincided with the permanent shutdown of the reactors after the accident in 2011. High-resolution ¹⁴C analysis of the 2011 ring indicated ¹⁴C releases during the Fukushima accident. The resulted ¹⁴C activity decreased with increasing distance from the plant. The maximum ¹⁴C activity released during the period of the accident was measured 42.4 Bq kg⁻¹ C above the natural ambient ¹⁴C background. Our findings indicate that, unlike other Fukushima-derived radionuclides, the ¹⁴C released during the accident is indistinguishable from ambient background beyond the local environment (~30 km from the plant). Furthermore, the resulting dose to the local population from the excess ¹⁴C activities is negligible compared to the dose from natural/nuclear weapons sources.