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

Abstract

The vertical distribution of radiocarbon ( 14 C) 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”). 14 C specific activity was measured in alkali-soluble and -insoluble fractions of the sediment layers. Complementary measurements of the 210 Pb and 137 Cs activity of the samples provided the possibility to evaluate the date of every layer formation, covering the 1947–2013 period. In addition, 14 C 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 14 C 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 14 C 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 14 C contained in liquid effluences from the INPP in 2000–2009. The discrepancy between 14 C specific activity in fish scales samples and DIC after 2000 also confirmed the possibility of organic 14 C 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.

Modeling of 14C Vertical Distribution in Bottom Sediments of the Ignalina Nuclear Power Plant Cooling Reservoir

“…The 62 cm core was separated into layers of 1 cm thickness in situ soon after sampling, transported to the laboratory in plastic beakers and stored frozen until analysis. Sediment chronology for the period of 1947-2013 was determined using the 210 Pb technique supported by anthropogenic 137 Cs as a chronostratigraphic marker [13]. DIC samples were collected once or twice a year from 1979 to 2009, usually at station no.…”

“…14 C specific activity values in atmosphere were taken from [16]. Measured values of radiocarbon activity in alkali-soluble and alkali-insoluble organic sediment fractions (red and black circles, respectively) taken from [13].…”

“…Earlier performed investigation of radiocarbon concentration in AS and AIS fractions of Drūkšiai Lake bottom sediments [13] layers revealed that prior to the commissioning of the INPP and during the first 15 years of its operation, the radiocarbon specific activity in both fractions exhibited a parallel course. As expected, this indicates that the main 14 C source was in DIC (dissolved inorganic carbon) form, especially considering that the main sediment organic matter source was of autochthonous origin.…”

“…In this study, we performed analysis of radiocarbon concentration time series in water of Lake Drūkšiai and vertical layers of bottom sediments by considering available measurements and application of the mathematical model for radiocarbon accumulation. The analysis took into account both: airborne and aqueous discharges, and the 14 C measured data obtained for two bottom sediment organic fractions: alkali-soluble (AS) and alkaliinsoluble (AIS) [13], as well as available water volumetric activity [14] and radiocarbon specific activity measurements in the tree rings collected in the vicinity of the INPP [15,16]. Therefore, it is a complex study which should generalize available knowledge collected over the decades of the INPP operation.…”

Feasibility of an environmentally friendly method of contaminant flushing in water distribution systems using containment ponds

“…Ponds are constructed for various purposes, such as cooling, stabilization, settling, and oxidation. Cooling ponds are used to store and eventually cool down heated water from the nearby industries (Ryan et al 1974;Mann & Mann Technology Limited Partnership 1991;Ramamoorthy et al 2001;Barisevicǐutėet al 2020). Stabilization ponds are used to remove or reduce turbidity, solid pollutants, and/or pathogens in many industries including wastewater treatment, mining, agriculture, aquaculture, etc.…”