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Systematic and continuous monitoring 14C activity in atmospheric CO2 and biological samples in the vicinity of the Krško Nuclear Power Plant (NEK) in Slovenia has been performed since 2006. The aim of the monitoring was to determine 14C distribution in a close vicinity of the power plant and to estimate a possible contribution of NEK to the effective dose to the local population through food chain. This paper describes a model of food origins developed for the purpose of estimating the effective dose from ingestion of 14C via local food. Some other approaches of diet estimation are also discussed. The slightly increased 14C specific activity in plants very close to NEK could not change significantly the effective dose to the local population due to ingestion of 14C when compared to the effective dose from the ingestion of natural 14C. Sustavni monitoring specifične aktivnosti 14C u atmosferskom CO2 i u biološkim uzorcima iz neposredne okolice Nuklearne elektrane Krško (NEK) u Sloveniji provodi se od 2006. godine. Cilj monitoringa je odrediti prostornu raspodjelu specifične aktivnosti 14C u neposrednoj okolici NEK-a, te njenu ovisnost o razdobljima promjene goriva koja se obavlja svakih 18 mjeseci. Na osnovu izmjerenih specifičnih aktivnosti 14C može se procijeniti doprinos NEK-a efektivnoj dozi koju lokalno stanovništvo primi zbog konzumacije (ingestije) hrane porijeklom iz okolice NEK-a. Budući da je ugljik, pa time i 14C, sastavni dio sve hrane, nije potrebno poznavati detaljne prehrambene navike lokalnog stanovništva. Međutim, potrebno je poznavati ili procijeniti udio hrane iz okolice NEK-a u ukupnoj prehrani. U ovom radu opisano je nekoliko scenarija za porijeklo hrane, počevši od vrlo konzervativnog i malo vjerojatnog scenarija konzumacije samo hrane iz neposredne okolice NEK-a do realističnijeg (iako još uvijek konzervativnog) scenarija od 17 % hrane iz okolice NEK-a, a ostalih 83 % s kontrolne točke na kojoj nije opažen utjecaj 14C iz NEK-a. Malo povišenje specifične aktivnosti 14C u biljkama iz neposredne okolice NEK-a, koje je opaženo tijekom monitoringa, ne utječe značajno na procjenu efektivne doze zbog ingestije 14C, jer je razlika u odnosu na efektivnu dozu zbog ingestije "prirodnog" 14C usporediva ili manja od prirodnih varijacija.

Sustavno praćenje aktivnosti 14C atmosferskog CO2 i bioloških uzoraka (voće – uglavnom jabuke, povrće, žitarice, kukuruz) u neposrednoj okolici Nuklearne elektrane Krško (NEK) provodi se od 2006. godine s ciljem procjene mogućeg utjecaja NEK-a na razinu aktivnosti 14C u okolišu te na efektivnu dozu koju primi lokalno stanovništvo putem prehrane. Posebna je pozornost posvećena praćenju utjecaja remonta elektrane, koji se provodi svakih 18 mjeseci, na aktivnost 14C u okolišu. U radu će se pokazati značajke aktivnosti 14C u okolišu elektrane i neki zaključci zasnovani na dugogodišnjem iskustvu monitoringa. Atmosferski CO2 sakuplja se na dvije lokacije unutar kruga NEK-a, obično u dvomjesečnim intervalima te u kraćim intervalima tijekom i neposredno nakon remonta. Biološki materijal koji integrira 14C iz atmosfere tijekom relativno kratkog vegetacijskog razdoblja (plodovi jabuke, kukuruz, žitarice i slično) skuplja se na početku vegetacijskog razdoblja (lipanj ili srpanj) te ujesen (prije berbe, rujan ili listopad) na više lokacija u unutarnjem i vanjskom krugu. Referentni uzorci bilja sakupljaju se na kontrolnoj točki kraj Dobove, 11, 2 km (zračna udaljenost) jugoistočno od NEK-a, na kojoj se ne očekuje utjecaj zračnih ispusta iz NEK-a. Praćenje aktivnosti 14C u okolici NEK u razdoblju od 2006. do kraja 2016. godine pokazuje da je utjecaj 14C ispuštenog u okoliš zračnim putem mjerljiv i u atmosferskom CO2 i u biljkama koje koriste CO2 za fotosintezu. Taj je utjecaj kratkoročan i prostorno ograničen na najbližu okolinu. Uočena je korelacija između ukupno ispuštene aktivnosti A14C i izmjerenih vrijednosti a14C u CO2 i u bilju. Systematic and continuous monitoring 14C activity in atmospheric CO2 and biological samples (mostly apples, vegetable, cereals, corn) in the vicinity of the Nuclear Power Plant Krško (NEK) in Slovenia has been performed since 2006. The aim of the monitoring is to determine 14C distribution in a close vicinity of the power plant and to estimate possible contribution of NEK to the effective dose of the local population through food chain. In this paper we describe some characteristics of the 14C distribution in the environment of NEK. The 14C activity of atmospheric CO2 at two locations inside the NEK area is on the average slightly higher than that in Zagreb. It depends on the 14C activity (A14C) released in air-born effluent. The influence of the 14C releases has been observed also in plants. Higher 14C activity in plants is most pronounced shortly after spring refuelling, when plants use atmospheric CO2 that contains 14C released from NEK. The influence of the released air-born 14C activity is measurable in both atmospheric CO2 and in plants; the higher the activity of gaseous effluent, the higher the atmospheric and plant 14C activity. However, the influence is temporally and spatially limited. Average 14C activity in plants at the control location Dobova does not differ from the average atmospheric 14C activity in Zagreb. It was shown earlier that the slightly increased 14C activity in plants does not contribute significantly to the effective dose of the local population due to ingestion of 14C. According to the experience of the whole monitoring, 14C is the only released radionuclide detected in the environment of NEK (Report IJS-DP-12059).

In this presentation we will summarize the 10-year-long experience in monitoring 14C activity in the close vicinity of the Krško Nuclear Power Plant (NPP) in Slovenia. Atmospheric CO2 samples have been taken in 2-month periods during the regular operation of the power plant, or in shorter periods during refuelling periods. Biological samples (apples, corn, wheat, grass, vegetables) have been samples twice a year (in summer and autumn) in two circles around the NPP, inner and outer, and at the control point 12 km from the plant. The aim of the monitoring was to estimating a possible influence of the NPP on environmental 14C levels and on the effective dose of local population through food chain. Increase of 14C activity in atmospheric CO2 was observed during and immediately after the refuelling of the power plant, performed every 18 months. Good correlation between the total 14C activity released in gaseous effluents and the 14C activity of the atmospheric CO2 has been observed. 14C activity in plants collected close to the Krško NPP is always higher than the activities on the control point, and depends both on the distance from the exhaust of the plant ventilation system and on wind direction: it is higher on the location in the SW-NE direction that coincided with the most pronounced wind directions. Higher 14C activities have been determined in plants collected in summer after the spring refuelling than in those collected during the following vegetation period after the autumn refuelling. This can be explained by the uptake of the CO2 of higher 14C activity for the process of photosynthesis after spring refuelling. To estimate the realistic effective dose due to ingestion to the population in the vicinity, a model of food consumption has been proposed. The calculated dose for the population at the NPP vicinity is not significantly different from the dose for the population at the control point.

Systematic and continuous monitoring 14C activity in atmospheric CO2 and biological samples in the vicinity of the Krško Nuclear Power Plant (NEK) in Slovenia has been performed since 2006. The aim of the monitoring was to determine 14C distribution in a close vicinity of the power plant and to estimate a possible contribution of NEK to the effective dose to the local population through food chain. This paper describes a model of food origins developed for the purpose of estimating the effective dose from ingestion of 14C via local food. Some other approaches of diet estimation are also discussed. The slightly increased 14C specific activity in plants very close to NEK could not change significantly the effective dose to the local population due to ingestion of 14C when compared to the effective dose from the ingestion of natural 14C. Sustavni monitoring specifične aktivnosti 14C u atmosferskom CO2 i u biološkim uzorcima iz neposredne okolice Nuklearne elektrane Krško (NEK) u Sloveniji provodi se od 2006. godine. Cilj monitoringa je odrediti prostornu raspodjelu specifične aktivnosti 14C u neposrednoj okolici NEK-a, te njenu ovisnost o razdobljima promjene goriva koja se obavlja svakih 18 mjeseci. Na osnovu izmjerenih specifičnih aktivnosti 14C može se procijeniti doprinos NEK-a efektivnoj dozi koju lokalno stanovništvo primi zbog konzumacije (ingestije) hrane porijeklom iz okolice NEK-a. Budući da je ugljik, pa time i 14C, sastavni dio sve hrane, nije potrebno poznavati detaljne prehrambene navike lokalnog stanovništva. Međutim, potrebno je poznavati ili procijeniti udio hrane iz okolice NEK-a u ukupnoj prehrani. U ovom radu opisano je nekoliko scenarija za porijeklo hrane, počevši od vrlo konzervativnog i malo vjerojatnog scenarija konzumacije samo hrane iz neposredne okolice NEK-a do realističnijeg (iako još uvijek konzervativnog) scenarija od 17% hrane iz okolice NEK-a, a ostalih 83% s kontrolne točke na kojoj nije opažen utjecaj 14C iz NEK-a. Malo povišenje specifične aktivnosti 14C u biljkama iz neposredne okolice NEK-a, koje je opaženo tijekom monitoringa, ne utječe značajno na procjenu efektivne doze zbog ingestije 14C, jer je razlika u odnosu na efektivnu dozu zbog ingestije "prirodnog" 14C usporediva ili manja od prirodnih varijacija.

Systematic and continuous monitoring 14C activity in atmospheric CO2 and biological samples in the vicinity of the Krško Nuclear Power Plant (NEK) in Slovenia has been performed since 2006. The aim of the monitoring was to determine 14C distribution in a close vicinity of the power plant and to estimate a possible contribution of NEK to the effective dose to the local population through food chain. This paper describes a model of food origins developed for the purpose of estimating the effective dose from ingestion of 14C via local food. Some other approaches of diet estimation are also discussed. The slightly increased 14C specific activity in plants very close to NEK could not change significantly the effective dose to the local population due to ingestion of 14C when compared to the effective dose from the ingestion of natural 14C.

Sustavno praćenje aktivnosti 14C atmosferskog CO2 i bioloških uzoraka (voće – uglavnom jabuke, povrće, žitarice, kukuruz) u neposrednoj okolici Nuklearne elektrane Krško (NEK) provodi se od 2006. godine s ciljem procjene mogućeg utjecaja NEK-a na razinu aktivnosti 14C u okolišu te na efektivnu dozu koju primi lokalno stanovništvo putem prehrane. Posebna je pozornost posvećena praćenju utjecaja remonta elektrane, koji se provodi svakih 18 mjeseci, na aktivnost 14C u okolišu. U radu će se pokazati značajke aktivnosti 14C u okolišu elektrane i neki zaključci zasnovani na dugogodišnjem iskustvu monitoringa. Atmosferski CO2 sakuplja se na dvije lokacije unutar kruga NEK-a, obično u dvomjesečnim intervalima te u kraćim intervalima tijekom i neposredno nakon remonta. Biološki materijal koji integrira 14C iz atmosfere tijekom relativno kratkog vegetacijskog razdoblja (plodovi jabuke, kukuruz, žitarice i slično) skuplja se na početku vegetacijskog razdoblja (lipanj ili srpanj) te ujesen (prije berbe, rujan ili listopad) na više lokacija u unutarnjem i vanjskom krugu. Referentni uzorci bilja sakupljaju se na kontrolnoj točki kraj Dobove, 11, 2 km (zračna udaljenost) jugoistočno od NEK-a, na kojoj se ne očekuje utjecaj zračnih ispusta iz NEK-a. Praćenje aktivnosti 14C u okolici NEK u razdoblju od 2006. do kraja 2016. godine pokazuje da je utjecaj 14C ispuštenog u okoliš zračnim putem mjerljiv i u atmosferskom CO2 i u biljkama koje koriste CO2 za fotosintezu. Taj je utjecaj kratkoročan i prostorno ograničen na najbližu okolinu. Uočena je korelacija između ukupno ispuštene aktivnosti A14C i izmjerenih vrijednosti a14C u CO2 i u bilju.

14C activity in the atmospheric CO2 and in biological samples in the close vicinity of the Krško Nuclear Power Plant (NPP) in Slovenia has been regularly monitored since 2006 with the aim of estimating a possible influence of the NPP on environmental 14C levels and on the effective dose of local population through food chain. Atmospheric CO2 on two locations was collected every two months, or in shorter periods during some refuelling periods. Biological samples (apples, corn, wheat, grass, vegetables) were collected twice a year (in summer and autumn) in two circles around the NPP, inner and outer, and at the control point 12 km from the plant. Increase of 14C activity in atmospheric CO2 was observed during and immediately after the refuelling of the power plant, performed every 18 months. Good correlation between the total 14C activity released in gaseous effluents and the 14C activity of the atmospheric CO2 has been observed. 14C activity in plants collected close to the Krško NPP is always higher than the activities on the control point, and depends both on the distance from the exhaust of the plant ventilation system and on wind direction: it is higher on the location in the SW-NE direction that coincided with the most pronounced wind directions. Higher 14C activities have been determined in plants collected in summer after the spring refuelling than in those collected during the following vegetation period after the autumn refuelling. This can be explained by the uptake of the CO2 of higher 14C activity for the process of photosynthesis after spring refuelling. To estimate the realistic effective dose due to ingestion to the population in the vicinity, a model of food consumption has been proposed. The calculated dose for the population at the NPP vicinity is not significantly different from the dose for the population at the control point.

14C activity in the atmospheric CO2 and in biological samples in the close vicinity of the Krško Nuclear Power Plant (NPP) in Slovenia has been regularly monitored since 2006 with the aim of estimating a possible influence of the NPP on environmental 14C levels and on the effective dose of local population through food chain. Atmospheric CO2 on two locations was collected every two months, or in shorter periods during some refuelling periods. Biological samples (apples, corn, wheat, grass, vegetables) were collected twice a year (in summer and autumn) in two circles around the NPP, inner and outer, and at the control point 12 km from the plant. Increase of 14C activity in atmospheric CO2 was observed during and immediately after the refuelling of the power plant, performed every 18 months. Good correlation between the total 14C activity released in gaseous effluents and the 14C activity of the atmospheric CO2 has been observed. 14C activity in plants collected close to the Krško NPP is always higher than the activities on the control point, and depends both on the distance from the exhaust of the plant ventilation system and on wind direction: it is higher on the location in the SW-NE direction that coincided with the most pronounced wind directions. Higher 14C activities have been determined in plants collected in summer after the spring refuelling than in those collected during the following vegetation period after the autumn refuelling. This can be explained by the uptake of the CO2 of higher 14C activity for the process of photosynthesis after spring refuelling. To estimate the realistic effective dose due to ingestion to the population in the vicinity, a model of food consumption has been proposed. The calculated dose for the population at the NPP vicinity is not significantly different from the dose for the population at the control point.

Sustavno praćenje 14C aktivnosti atmosferskog CO2 i bioloških uzoraka (voće – uglavnom jabuke, povrće, žitarice, kukuruz) u neposrednoj okolici Nuklearne elektrane Krško (NEK) provodi se od 2006. godine sa ciljem procjene mogućeg utjecaja NEK na razinu 14C u okolišu te na efektivnu dozu koju primi lokalno stanovništvo putem prehrane. Posebna je pozornost posvećena praćenju utjecaja remonta elektrane, koji se provodi svakih 18 mjeseci, na aktivnost 14C u okolišu. Atmosferski CO2 skuplja se apsorpcijom CO2 u zasićenoj otopini NaOH na dvije lokacije u dvomjesečnim intervalima, a u vrijeme trajanja remonta razdoblja sakupljanja uzoraka su nešto kraća. Biološki uzorci skupljaju se na početku vegetacijskog razdoblja (lipanj ili srpanj) te ujesen (prije berbe, rujan ili listopad) na lokacijama u okolici NEK koje se mogu podijeliti u tzv. unutarnje i vanjske, kao i na kontrolnoj točki u Dobovi, 12 km jugoistočno od NEK. Porast 14C aktivnosti u atmosferskom CO2 unutar NEK opažen je za vrijeme i neposredno nakon remonta koji se provodi svakih 18 mjeseci. 14C aktivnost bilja u okolici NEK ovisi o udaljenosti od ventilacijskog ispusta i o smjeru vjetrova. Najviše 14C aktivnosti u bilju izmjerene su u ljetnim sakupljanjima u godinama kad je remont proveden u proljeće (2006., 2009. i 2012.), a najniže u jesenskim sakupljanjima 2007. i 2010., prije jesenskog remonta. Nije opažena značajna razlika u efektivnim dozama zbog unosa hranom za stanovnike iz okolice NEK i iz Dobove.

Monitoring 14C activity in the atmospheric CO2 and in biological samples (apples, corn, wheat, grass) in the close vicinity of the Krško Nuclear Power Plant (NPP) was performed regularly since 2006 to estimate the possible influence of the plant on environmental 14C levels and the possible contribution to the effective dose of local population through food chain. Atmospheric CO2 on two locations was collected regularly every two months. Biological samples were collected twice a year (in June/July and September/October) on several locations very close to the plant, in a radius of about 1 km from NPP, and on the control point at Dobova, 12 km from the plant. Increase of 14C activity in atmospheric CO2 was observed during and immediately after the refuelling of the power plant, performed every 18 months. It is more pronounced on the location in the SW-NE direction that coincided with the most pronounced wind directions. 14C activities in biological samples collected close to the Krško NPP are higher than the activities on the control point, and depend both on the distance from the plant ventilation exhaust system and on wind direction. Significantly higher activities were measured in biological samples collected after the spring refuelling (2006 and 2009). They can be explained by the influence of plant effluents on the photosynthesis process, while autumn effluents (2007 and 2010) do not significantly influence the 14C activity in biological samples. The increase of total annual effective dose to local population through ingestion in the years of spring refuelling was estimated to 0.015 %. However, this increase in the effective dose is much lower than the total uncertainty of the estimate, obtained by combined variations in 14C activity in biological samples, measurement uncertainties and uncertainties in the ingestion model, and thus it may be neglected.

Monitoring 14C activity in the atmospheric CO2 and in biological samples (fruits and vegetables) in the close vicinity of the Krško Nuclear Power Plant (NPP) was performed regularly since 2006 to estimate the possible influence of the plant on environmental 14C levels and the possible contribution to the effective dose of local population through food chain. Atmospheric CO2 on two locations was collected regularly every two months, while the biological samples (apples, corn, wheat and grass) were collected twice a year (in June/July and September/October) on several locations very close to the plant in a radius of about 1 km from the Krško NPP, as well as on the control point at Dobova, 12 km from the plant. Increase of 14C activity in atmospheric CO2 was always observed during and immediately after the refuelling of the power plant, which has been performed every 18 months, and it is more pronounced on the location in the SW-NE direction that coincided with the most pronounced wind directions. 14C activity in plants collected close to the Krško NPP is always higher than the activities on the control point, and depends both on the distance from the exhaust of the plant ventilation system and on wind direction. Significantly higher activities in plants collected after the spring refuelling in 2006 and 2009 was measured. This can be explained by the influence of plant effluents during the summer when the process of photosynthesis is the most prominent, while autumn effluents (2007 and 2010) do not significantly influence the 14C activity in plants. The maximum increase of total dose to local population due to the release of 14C from the Krško NPP in the years of spring refuelling was estimated to be 0.015 %, which is negligible.

Monitoring 14C activity in the atmospheric CO2 and in biological samples (fruits and vegetables) in the close vicinity of the NPPK was performed regularly since 2006 to estimate the possible influence of the plant on environmental 14C levels and the possible contribution to the effective dose of local population through food chain. Mean values of 14C activity in atmospheric CO2 in the years when the refuelling was not performed represent a barely visible increase in relation to the activities of 14C in the atmosphere at the control point. Immediately after refuelling the atmospheric 14C activity was increased for a short period of time. Spatial distributions of 14C activities in biological samples show the dependence on distance and orientation. In all campaigns the highest activities were obtained at the same locations in the SW-NE direction that coincided with the most pronounced wind directions. Estimated contribution of 14C released by NPPK to the natural dose is less than 1 μSv.

Monitoring 14C aktivnosti u atmosferskom CO2 i u bilju u okolici Nuklearne elektrane Krško provodi se redovito od 2006. godine. Opažen je porast 14C aktivnosti u atmosferi za vrijeme i neposredno nakon remonta elektrane zbog povišenih aktivnosti 14C ispuštenih u okoliš u tom razdoblju. 14C aktivnost u biljkama također ovisi o vremenu remonta: ako se remont provodi u proljeće, bilje uzorkovano u ljeto i jesen te godine pokazuje nešto povećanu 14C aktivnost. Prostorna raspodjela 14C aktivnosti određena je prevladavajućim smjerom vjetra i udaljenošću od ventilacijskog ispusta.

Radioaktivni izotop 14C nastaje interakcijom kozmičkih neutrona i dušika u visokim slojevima atmosfere, te se zajedno s ostalim izotopima ugljika raspoređuje u atmosferi i biosferi. Zbog istovremenog radioaktivnog raspada stvorena je ravnotežna koncentracija 14C. Zbog nuklearnih i termonuklearnih pokusa ova se koncentracija u šezdesetim godinama 20. stoljeća udvostručila, da bi nakon stupanja na snagu ugovora o zabrani tih pokusa u atmosferi postupno opadala. Koncentracija 14C u atmosferi može varirati lokalno kao posljedica rada nuklearnih elektrana. Cilj ovog rada je utvrditi eventualni doprinos rada elektrane povećanju specifične aktivnosti 14C u bližem okolišu Nuklearne elektrane Krško (NEK), a time i povišenju efektivne doze stanovništva. Istražit će se utjecaj remonta elektrane, koji se provodi u redovitim 18-mjesečnim razmacima. Monitoriranje raspodjele 14C u okolišu NEK se provodi redovito od 2006. mjerenjem specifične aktivnosti 14C u atmosferskom CO2 na dvije lokacije, te dva puta godišnje u biološkim uzorcima sakupljenim na više lokacija na različitim udaljenostima od NEK, kao i na kontrolnoj točki kod Dobove, 12 km od NEK. Aktivnost 14C mjeri se scintilacijskim brojačem Quantulus 1220. Specifična aktivnost 14C u atmosferskom CO2 na lokaciji B je gotovo redovito viša nego na točki A, budući da se B nalazi u smjeru izraženijih vjetrova. To je posebno vidljivo u razdobljima remonta i neposredno nakon njega. Tri do četiri mjeseca nakon remonta aktivnosti 14C padaju na svoje uobičajene vrijednosti. Pokazuje se odziv atmosferske aktivnosti 14C na 14C aktivnosti izmjerene u ispustu elektrane. Povišene aktivnosti a14C opažene su u biološkom materijalu koji koristi CO2 u razdoblju za vrijeme i nakon remonta obavljenog neposredno prije vegetacijskog perioda. U godinama 2006. i 2009. je remont elektrane obavljan u proljeće, tako da su jabuke, čije je razdoblje vegetacije započelo neposredno nakon toga, za fotosintezu koristile nešto aktivniji CO2. Kad je 2007. i 2010. remont obavljan ujesen, tj. nakon razdoblja vegetacije i nakon što su jabuke već pobrane, izmjerena je niža a14C. Praćenjem 14C aktivnosti u atmosferi i bilju dobiveni su podaci o njenoj vremenskoj i prostornoj raspodjeli u neposrednoj okolini NEK. Specifična aktivnost 14C u atmosferskom CO2 u neposrednoj okolini elektrane odražava aktivnost 14C na ispustu elektrane – povišene vrijednosti opažene su samo u vrijeme izmjene gorivih elemenata (remonta) i kratko vrijeme nakon toga, a tijekom redovnog rada elektrane 14C aktivnost u atmosferskom CO2 nije značajno povišena u odnosu na "čista" područja. Prostorna raspodjela 14C aktivnosti u bilju određena je prevladavajućim smjerom vjetrova, a vrijednosti su nešto više ako se vegetacijsko razdoblje podudara s razdobljem remonta.

Human activities disturbed the natural 14C distribution in the atmosphere in the last half of the 20th century. Besides the big amounts of 14C released by nuclear bomb tests it is produced also by nuclear power plants and in form of 14CO2 enters the carbon cycle contributing through food chain to the dose of the local population. The aim of this study was to determine distribution of 14C in a close vicinity of the Nuclear Power Plant Krško (NEK) in Slovenia, and to estimate possible contribution of NEK to the effective dose. Atmospheric CO2 was collected since 2006 on a monthly basis at two locations (A and B) inside the NEK area by absorption of CO2 in saturated NaOH. The CO2 recovered from the carbonate was used for benzene synthesis and measured in LSC Quantulus 1220. Sampling campaigns of biological samples (apples, corn, cereals, grass) were performed twice a year and sampling sites were chosen in the immediate vicinity and in the wider environment of the NEK smokestack, and at a control site 10 km away. 14C activity was measured in LSC by direct absorption method. 14C activity of the atmospheric CO2 at site A inside NEK showed no observable deviation from 14C activities at clean-air sites, but that at site B was slightly higher, because lies in the dominant wind direction. However, significantly higher 14C activities were measured at both sites during the period of regular maintenance of the reactor in Oct 2007 and April 2009. 14C activities in biological samples around NEK showed slightly higher 14C activities than at the control site, and depend on the distance and on the most pronounced wind direction. Higher 14C activities were recorded in periods following the maintenance of NEK and can be explained by an order of magnitude higher discharge of 14C from the smokestack. An estimate of the effective dose received by ingestion of food (fruits and vegetables) grown in the vicinity of NEK results in the contribution of NEK to the natural dose of less than 1 uSv.

Monitoring of 14C in biological material and in the atmospheric CO2 in the close environment of Krško Nuclear Power Plant (NEK) in Slovenia has been performed since 2006. Sampling campaigns of biological samples (apples, corn, cereals, grass) from the sites in the immediate vicinity of the plant, as well as at a control site 10 km away, were performed twice a year. Carbon 14C activity was measured by direct absorption technique in LSC Quantulus 1220. Atmospheric CO2 was collected in bimonthly periods at two locations inside the NEK area by absorption of CO2 in saturated NaOH. The CO2 recovered from the carbonate was used for benzene synthesis, used for subsequent measurement in LSC. Most of the locations in the immediate vicinity of NEK showed slightly higher 14C activities in plants than the control site. Spatial distribution of 14C activities around NEK showed the dependence on the distance and on the direction. In all campaigns the highest activities were obtained at the locations that coincided with the most pronounced wind directions. At the control site the measured activities were more-or-less constant. Different biological materials taken at the same location gave the same 14C activity. 14C activity in atmospheric CO2 at the location inside the NEK area, which lies in the dominant wind direction, was always higher than at the other location, where no evident deviation from natural 14C activities was observed during regular operation of NEK. However, during the refueling outage periods and 2-3 months after it, higher 14C activities were detected at both sites. Based on the measurements, an assessment of the effective dose to the public could be obtained. The dose received by ingestion of food (fruits and vegetables) grown in the vicinity of the Krško Nuclear Power Plant resulted in the contribution to the total dose of most exposed individual of less than 1 μ Sv.

Lagrangean model is used at Krško Nuclear Power Plant (NPP) for calculation of dispersion coefficients and dose in the environment. To show compliance to the authorized dose limits it is required to present a realistic calculation of the dose to the public. Five years ago the numerical model was installed to calculate hypothetical air pollution dispersion in the area of 25km x 25km. The model uses on-line local meteorological measurements. The wind field is reconstructed using a three-dimensional mass-consistent wind-field model. The same model was already verified for another location around a coal- fired power plant based on emission and environmental measurements of SO2. But each of the location is specific. Krško NPP is placed near the Sava River in a semi-opened basin surrounded with several hills. The region is characterized by low winds and often thermal inversions. This paper presents first practical verification of the short range dispersion model based on the fact that the airborne carbon 14C concentration can be slightly increased close to the nuclear power plant. The other radioactive effluents are not detectable in the environment and carbon 14C measurements are accurate enough to detect small deviations from the natural 14C levels and to be used for comparison with the calculated concentration based on 14C effluents. The most of airborne 14C is released during refueling outage from the opened reactor. Within the pre-selected period of ten days increased effluents of 14C in the form of CO2 were sampled from the plant ventilation. The average atmospheric dispersion parameters were calculated for two locations in the environment where CO2 sampling plates were installed. Increased 14C activities were detected at the both locations close to the plant for this short time period of ten days. The model has been thus verified for the two points within 500 m distance from the reactor using average dispersion coefficients. There is also described a method how to estimate the emission rates to minimize the uncertainties.

14C nastaje i kao posljedica rada reaktora nuklearnih centrala, a emitira se u okoliš u obliku CO2, koji ulazi u prirodni ciklus ugljika u okolici elektrane, a putem hrane može doprinijeti i dodatnom ozračenju (povećanju doze) lokalnog stanovništva. Mjerenjem specifične aktivnosti 14C u biološkom materijalu u neposrednoj okolici Nuklearne elektrane Krško (NEK) pokušat ćemo utvrditi eventualni doprinos rada reaktora povećanju specifične aktivnosti 14C u okolišu, odnosno stvoriti bazu podataka o radioaktivnosti okoliša. Aktivnost 14C u neposrednoj blizini Nuklearne elektrane Krško ovisi o količini ispusta 14C iz dimnjaka elektrane, a prostorna raspodjela a14C određena je dominantnim smjerom vjetrova (jugozapad-sjeveroistok). Najviša aktivnost u biološkim uzorcima (132, 4 pMC) u odnosu na aktivnost na kontrolnoj točki Dobova udaljenoj oko 10 km od elektrane (104 pMC) je nađena u srpnju 2006, a to odgovara razdoblju sazrijevanja voća nakon remonta elektrane s izmjenom gorivih elemenata u travnju 2006. Uz konzervativnu procjenu da prosječni stanovnik Krškog pojede 23 kg jabuka s lokacije na kojoj je zamijećena najviša aktivnost, doprinos njegovoj efektivnoj dozi bila bi 0, 2 promila, što je zanemarivo.

Nuclear power plants represent a small source of carbon 14C that enters the carbon cycle together with the 14C produced naturally in the atmosphere. The present-day natural 14C distribution can be slightly disturbed in the close vicinity of the power plants. In this paper we report on monitoring of 14C in the atmospheric CO2 and in biological material in the close environment of Nuclear power Plant Krško (NEK) in Slovenia. Based on the regulation, sampling campaigns of biological samples (apples, corn, cereals, grass) were performed twice a year during 2006 and 2007. Sampling sites were chosen in the immediate vicinity (250 m – 700 m from the plant) and in the wider environment (1000 m – 1500 m) of the plant, as well as at a control site 10 km away. Carbon 14C activity was measured by direct absorption method in LSC Quantulus 1220. Atmospheric CO2 was collected at two locations (A and B) inside the NEK area by absorption of CO2 in saturated NaOH. The CO2 recovered from the carbonate was used for benzene synthesis. Most of the locations in the immediate vicinity of NEK showed slightly higher 14C activities than the control site. Spatial distribution of 14C activities around NEK showed the dependence on the distance and on the direction. In all campaigns the highest activities were obtained at the locations that coincided with the most pronounced wind directions. 14C activity of the atmospheric CO2 at site A inside NEK showed no observable deviation from natural 14C activities, while it was always slightly higher at site B that lies in the dominant wind direction. However, higher 14C activities were detected at both sites during the refuelling outage periods. Based on the measurements, an accurate assessment of the effective dose to the public can be obtained. The dose received by ingestion of food (fruits and vegetables) grown in the vicinity of the Krško Nuclear Power Plant results in the contribution to the dose of most exposed individual of less than 1 micro Sv.