Research Article 
Corresponding author: Galina V. Lavrentyeva ( lavrentyeva_g@list.ru ) Academic editor: Georgy Tikhomirov
© 2023 Boris I. Synzynys, Thi Kim Phung Nguyen, Olga A. Momot, Galina V. Lavrentyeva.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Synzynys BI, Nguyen TKP, Momot OA, Lavrentyeva GV (2023) Radiation risk assessment for the population from C14 emissions of the World’s first NPP and Smolensk NPP. Nuclear Energy and Technology 9(4): 233237. https://doi.org/10.3897/nucet.9.116651

The results of the internal radiation dose calculations for the population and the assessment of the radiation risk from radioactive carbon C14 during the normal operation of the World’s First Nuclear Power Plant in Obninsk and Smolensk NPP are presented. Calculations were carried out using two methods, taking into account the inhalation and oral intake of C14 with food into the human body. Radiation doses are 5.69·10^{9} Sv/year and 5.95·10^{9} Sv/year (for Obninsk NPP), 3.77·10^{7} Sv/year and 3.96·10^{7} Sv/year (for Smolensk NPP), which is orders of magnitude less than the established minimum significant dose (10 μSv). The assessed levels of radiation risk for the population does not exceed the risk established by NRB 99/2009 (1·10^{5}). It was found that the main contribution to the formation of the dose and risk of internal radiation of the population from C14 radiation, released by the respective NPP, was the incorporation of radionuclide with locally produced food products, which is confirmed by the results of calculations using two methods, taking into account the influence of two nuclear power plants.
carbon14, nuclear power plant, internal radiation dose, radiation risk, inhalation, food consumption
After the World’s First NPP was put into operation in Obninsk in 1954, and in the course of introducing nuclear technologies, public safety of radiation facilities was of paramount importance. In the early days of the nuclear industry evolution, however, the regulatory framework in the field of health physics was not so perfect which caused difficulties in assessing operating safety of radiologically hazardous facilities for the public. Currently, a comprehensive framework has been established for the radiological safety regulation, and technologies have been developed for its implementation. One of the key radiation safety criteria is a constraint, that is, a preintroduced value of individual risk involved in the radiation from the given source (risk constraint), which is used in situations with scheduled exposure as one of the parameters for optimizing protection and safety as applied to the source in question, and serves as a constraint for determining the range of options in the process of optimization (
The accumulated knowledge makes it possible to assess retrospectively the radiation situation in the observation area of the World’s First NPP (with the AM1 reactor: AM is the Russian abbrevation for Peaceful Atom) in the course of its operation years. For comparion, we shall characterize the radiological hazard for the population currently residing in the observation area of the Smolensk NPP with RBMK1000 reactors.
In this paper, the radiological hazard from radioactive carbon (C14) generated in NPPs in appreciable quantities will be chosen for comparison and demonstration of the NPP public safety. İt should be noted that expert studies show that gas and aerosol C14 emissions account for much of the contribution to the exposure dose for the population residing in the vicinity of nuclear power and industry sites (
The purpose of the study is to assess comparatively the radiation risk from radioactive carbon emissions for the Obninsk population in the course of operating the World’s First NPP and for the population residing in the Smolensk NPP observation area.
The purpose of the study is to investigate C14 emissions from the Obninsk and Smolensk NPPs. The Obninsk NPP with the AM1 pressuretube graphitewater reactor was in operation in 1954–2002. Along with electricity and heat production, the AM1 reactor with an electric power of 5 MW and a thermal power of 30 MW was used for generation of isotopic products, neutronic and solid body physics studies, and many other investigations, specifically for incore detectors and reactivity control rods (
The internal exposure doses and risks were estimated using a number of methods to minimize the risk estimation uncertainties.
The C14 emission data required for the calculations were borrowed from (
Further estimates require determining the C14 volumetric activity in the Obninsk NPP affected area. The yearly averaged Obninsk NPP emissions amount to 0.18 TBq/g.
The C14 volumetric activity in the atmospheric air is assumed to depend linearly on the radionuclide annual emission:
$\frac{\text{C14 volumetric activity for the Smolensk NPP}}{\text{C14 volumetric activity for the Obninsk NPP}}=\frac{\text{Total C14 emission for the Smolensk NPP}}{\text{Total C14 emission for the Obninsk NPP}}$
The calculated volumetric activity of C14 in the Obninsk NPP affected area is assumed to be equal to 3.24·10^{4} Bq/m^{3}.
Method 1 for calculating the public internal exposure dose in the NPP observation area is based on data contained in
A number of assumptions were made to calculate the committed annual internal dose and estimate the public radiation risk from C14 emissions.
The annual internal exposure dose for C14 emissions is calculated based on assumed inhalation and ingestion human exposure pathways.
The current methodologies for calculating the committed annual exposure dose based on calculated volumetric activities of radionuclides in atmospheric air rely on the assumption that equilibrium of the radionuclide specific activity in air and biological tissue is achieved (
D _{C14} = ε_{inh}UC_{C14_a} + ε_{f}Σa_{i}R_{i}C_{C14_p,i}, (1)
where ε_{inh} is the dose conversion factor for the C14 inhalation equal to 2.0·10^{9} Sv/Bq (
Most of the models take into account only atmospheric carbon pollution as the result of gas and aerosol emissions. In the process of photosynthesis, СО_{2} is incorporated into the plant organic substance. Equilibrium is achieved then between the specific activity of radioactive carbon in СО_{2} and С14 as part of the plant organic substance being “built” (
In connection with the foregoing, the content of C14 in plant products was estimated using formula
C ^{р} _{C14_p,i} = f_{v,i} C_{C14_a} /C_{C12_a}, (2)
where f_{v,i} is the share of carbon in the i^{th} plant product, kgC/kg (in accordance with
The content of radioactive carbon in plant products is calculated using formula
C _{C14_p,i} = f_{ap,i} f_{cont,i} C_{C14_a} / C_{C12_a}, (3)
where f_{ap,i} is the share of carbon in the i^{th} animal product, kgC/kg (in accordance with
Method 2 for estimating the exposure dose formed by the C14 radionuclide incorporated into the human body is based on the IAEA publication (
The effective annual dose from beta radiation of the C14 contained in food products is calculated using the formula below
E = Af_{C,a} g, (4)
where E is the effective dose, Sv/year; A is the specific activity of C14 (Bq/gC) in local food products; f_{C,a} is the share of carbon in locally produced foods (assumed to be equal to 1); and g is the effective dose factor (the ratio between the annual dose rate (Sv/year) and the concentration of C14 per g of carbon in human body) assumed to be equal to 5.6·10^{5} Sv/year per Bq/gC.
The value of the C14 specific activity in atmospheric air is calculated using formula
A = C_{C14_a} /C, (5)
where A is the C14 specific activity value, Bq/gC; C_{C14_a} is the volumetric activity of C14 in the NPP deployment area air, Bq/m^{3}; and С is the average concentration of carbon in atmospheric air (equal to 0.18 g/m^{3}) which fits the average concentration of СО_{2} in the atmosphere equal to 330 ррm.
The contribution to the human exposure via the inhalation intake of C14 was estimated in the same way as with Method 1.
The calculated specific activities of C14 in food products are: 0.12 and 7.76 Bq/kg for milk, 0.36 and 23.89 Bq/kg for meat, and 0.08 Bq/kg and 5.49 Bq/kg for potato for Obninsk and Desnogorsk respectively.
The public radiation risk for the NPP affected area was estimated based on recommendations contained in the methodology provided in
According to the classical definition, the lifetime risk magnitude is directly proportional to the effective exposure dose with the radiation risk factor taken into account
r_{i} = E_{i} r_{E}_{,i}, (6)
where r_{i} is the individual lifetime risk, person^{1}; E_{i} is the effective exposure dose, Sv; and r_{E}_{,i} is the lifetime risk factor, Sv^{1}.
The risk was estimated taking into account the assumptions formulated for the public exposure dose calculation. The lifetime risk factor is determined for the human inhalation intake of C14 and for the ingestion intake with locally produced foods.
The radiation risk for the human inhalation intake of C14 during the year was calculated using formula
r_{E} _{,inh} = r_{inh} U C_{C14_a}, (7)
where r_{inh} is the radiation risk factor for inhalation of the C14 carbon, risk/Bq (r_{inh} = 1.3·10^{10} risk/Bq (
The radiation risk from the C14 beta radiation during the C14 dietary intake is determined using the following formula
r_{E} _{,ing} = r_{ing} ΣC_{f}_{,i} R_{i} B_{i}, (8)
where r_{ing} is the radiation risk factor for the C14 intake with food assumed to be equal to 7.9·10^{11} risk/Bq (
The estimated internal exposure dose for adult population from the C14 emission in the event of the human radionuclide intake when inhaling contaminated air and with local food products is presented in Table
NPP  Calculated annual exposure dose from C14, Sv (Method 1)  Calculated annual exposure dose from C14, Sv (Method 2)  

Inhalation intake of C14  Ingestion intake of C14  Inhalation intake of C14  Ingestion intake of C14  
Obninsk  1.63·10^{11}  5.67·10^{9}  1.63·10^{11}  5.93·10^{9} 
Smolensk  1.08·10^{9}  3.76·10^{7}  1.08·10^{9}  3.95·10^{7} 
The major contributor to the public internal exposure dose from the C14 radiation is the radionuclide intake with food products which is confirmed by the results of the calculations based on two methods, taking into account the effects from two NPPs (Table
The calculated values of the annual internal exposure doses were taken into account to estimate the individual radiation risk from the C14 radionuclide emissions (Table
Individual lifetime radiation risk from C14 emissions for Desnogorsk and Obninsk residents
NPP  Risk, person^{1}  Cumulative risk (Method 1)  Cumulative risk (Method 2)  

Inhalation  For food products  
(Method 1)  (Method 2)  
Obninsk  5.55·1^{21}  3.50·10^{17}  3.65·10^{17}  3.50·10^{17}  3.65·10^{17} 
Smolensk  2.45·10^{17}  1.54·10^{13}  1.61·10^{13}  1.54·10^{13}  1.61·10^{13} 
Most of the risk from the C14 internal beta radiation for the public in the NPP observation area adjoining localities is formed via the consumption of locally produced foods.
No excessive values of the risk constraint (1·10^{5} (
It has been found based on the obtained estimates for the exposure dose from the NPPemitted atmospheric C14 radiation that the annual effective public internal exposure dose in the normal operation mode of the World’s First Nuclear Power Plant in Obninsk and the Smolensk NPP is much below the minimum significant dose of 10 µSv.
The value of the total individual lifetime risk (from inhalation and ingestion of food products contaminated with C14) for the public is much smaller than the specified constraint of the generalized public radiation risk (1·10^{5} person^{–1} (