Evaluation of C-14 Based Radiation Doses from Standard Food Ingestion in Korea

Transcription

1 Evaluatio of C-14 Based Radiatio Doses from Stadard Igestio i Korea Gab-Bok Lee 1), Daechul Cho, I Hyoug Rhee ad Byug Gi Park 2) 1) Korea Electric Power Research Istitute Muji-dog, Yusug-gu, Taejo Soochuhyag Uiversity 646 Eupae-ri, Sichag-myo, Asa 2) FNC Techology, Seoul REPUBLIC OF KOREA Abstract: - Korea s uclear power plats are i practice of reviewig radiatio doses exposed to the residets durig routie operatio. They use a evaluatio tool that computes the radiatio exposure exploitig food itake pathway. This work attempts to itroduce ewly updated parameter values to ru the program, resultig i more practical evaluatio of the residetial radiatio dose. Updated or corrected parameters are carbo fractios icorporated i the food which is routiely cosumed i the Korea diig way, ad the ig s of the food based o the total cosumptio rate for recet decade i Korea. The results show that the C-14 radiatio dose calculated with the updated data reasoably agreed with that with the covetioal data based o AECL ad/or CSA model. We also tried to validate the robustess of the data by aalyzig samples which were take from several regios earby the power plats. Key-Words: - C-14, radiatio dose, carbo fractio i food, food ig, food igestio pathway, dose evaluatio, KDOSE-60 1 Itroductio C-14 is oe of the most cotributig ucleus to radiatio dose from ormally operated uclear power plats i Korea (see Fig. 1). To evaluate C-14 radiatio doses of the residets who are apt to be exposed, they used a specific activity model (USNRC; Killough ad Rohwer, 1978)[1-2] i which C-14 cocetratio i food ca be calculated from the origial C-14 cocetratio i eviromet. The C-14 cocetratio i food requires water cotet, hydroge ad carbo fractio i food a priori. Killough et al (1984)[3] suggested a evaluatio method that ca calculate carbo fractio of each categorized food item theoretically from its protei, fatty acid, ad carbohydrate cotets. Diabate ad Strack (1993)[4] also calculated hydroge fractio from the three mai compoets of food. Up to ow, AECL (Atomic Eergy of Caada, Limited) protocol based o Diabates ad Killough s methods, is beig applied to all uclear plats i Korea (KEPRI, 2001). However, as they are kow the hydroge ad carbo fractios used are based o foreig agricultural products such as barley, cor, wheat, asparagus, brawcoli, cabbage, etc. Moreover, those values are used as arithmetic averages without cosideratio of frequecy or ig of food itake by people. Therefore the eed to get the practical values represetig domestic food itake characteristics is about to rise. I this paper a literature survey ad a theoretical developmet were coducted i order to obtai critical values of the iput variables for the evaluatio tool (KDOSE-60), ad i additio aalyzed the food samples that were cautiously collected from effective regio aroud the power plats. All the data were reviewed for regulative applicatio (ICRP-60 based) to the power plats. depositio plume plats igestio aimals depositio direct Nuclei air soil huma ihalatio Fig. 1. Radiatio exposures to humas via airways durig ormal operatio of uclear plats

2 2 Overview of C-14 Evaluatio 2.1 C-14 releases to Eviromet A uclear reactor creates C-14 with O-17 i D 2 O ad moderator via 17 O(, a) 14 C reactio. The chemical compouds released to the eviromet i terms of C-14 are 14 CO 2, 14 CO, ad 14 C-hydrocarbo. From the measuremets at Bruce-B#7 ad Getilly#2 i Caada, 14 CO 2 are foud to be domiat as % whereas 14 CO as % ad 14 C-hydrocarbo as % (Peterso ad Davis, 1997). Ad 14 CO 2 is regarded as default i case o specific data is give. C-14 is oe of the most critical ucleus sice it is hudreds times more toxic tha H-3 i air eviromet ad has a much loger half-life eve if the discharge of C-14 is much less tha that of H-3 (from Wolsug power plat). Refer to Table 1 i order to figure yearly C-14 discharge ad relative abudace to H-3. Table 1. Discharges of C-14 ad its ratio with respect to H-3(uit; discharges: TBQ, ratio: %) Year Wolsug Plat 1-gaseous releases C-14 H-3 ratio 1994 ot measured 4.83E ot measured 4.43E ot measured 3.09E ot measured 6.24E E E E E E E E E E E Evaluatio of C-14 Radiatio Dose by Itake To evaluate the residetial radiatio doses attributed to C-14 some specific activity models [2,5], Regulatory Guide (USNRC [1]) ad CSA-N288.1 model (CSA [6]) have bee used. These models basically assume cocetratio equilibrium amog evirometal media. The differeces amog the models lie o classificatio of plats, cocetratio equilibrium coefficiets betwee air ad plats, ad related values of the exposure pathways. Because C-14 is highly circulative i air, the cocetratio of C-14 i air ca be obtaied from its specific activity i CO 2. USNRC ad CSA models use 0.16 g-c/m 3 of CO 2 desity i air. However, more reliable value of CO 2 desity i air is suggested to be 0.18 g-c/m 3 with the steady icrease i CO 2 productio worldwide. Now, we evaluate the specific activity of C-14 as air X A = (1) 0.18 Where A air is the the specific activity of C-14 i air (Bq/g-C) ad X is C-14 cocetratio i air (Bq/m 3 ). I livig plats, C-14 cocetratio ca be calculated uder a assumptio that specific activities of C-14 i air ad i plats are equal: veg air A = RA (2) veg air C = A M (3) c Where R represets cocetratio equilibrium costat betwee air ad plats, A veg is specific activity i plats i regio, C veg ad Mc deote C-14 cocetratio i plat ad carbo cotet i plats, respectively. R is reported to be about 0.5, ratio of C-14 releasig time over time durig photosythesis. To obtai C-14 cocetratio i a plat, oe has to kow the carbo fractio of the plat. We, therefore, figure out the carbo fractios of food take routiely i Korea ad simultaeously compared the suggested values to the aalyzed oes from the samples collected aroud the power plats. 2.3 Calculatio of Weight Factors As the most importat radiatio exposure pathway, food itake was cosidered. The food take has bee categorized. USNRC model uses two food groups (leaf vegetable ad the others) while CSA model regards oly oe group. Curretly, Korea power plats choose four food groups icludig grais, leaf vegetable, root vegetable, ad fruit, which fully reflects the domestic food itake patter. Additioally the Korea plats cosider food which is calculated o a basis of yearly food cosumptio. The food ca be used to help stadardizig the iput variables for dose calculatio. Table 2 shows the localized food s of idividual food. 3 Results ad Discussio 3.1 Determiatio of Carbo Fractio i

3 C-14 cocetratio i food ca be predicted if the carbo fractio of each food is kow. Curretly the stadard carbo fractio i air is employed to be 0.18 g-c/m 3.[7] The carbo fractio i idividual food used, suggested by AECL i 1998, did ot comply the diig patter of the Koreas. We used a approach for carbo fractio values usig a model which was proposed by Killough et al (1984). I this model, carbo is assumed to be icorporated i protei by 50%, i fat (lipid) by 76%, ad i carbohydrate by 44%. Ad the the followig formula is applied: Carbo = 0.5P F C (4) Where P,F ad C are fractios of protei, fat, ad carbohydrate, respectively. They ca be foud Igrediet Table published by Agricultural Life Istitute i Some selected iformatio was tabulated i Tables 3 ad 4. Table 2. Fruits ad their s estimated i four seasos ame mo Witer Sprig Summer Fall Yearly Average Table 3. Protei, fat, carbohydrate ad carbo fractios i each food item (%, boby basis) group ame Strawberry ame prot ei ame Watermelo apple apple melo ame fat Carbo-h ydrate idivi dual carbo fractio Repre set tative ame pear apple mo mo pear pear peach grape Watermelo grape melo plum apple pear mo peach Straw-berr y grape melo peach plum grais leaf veget able root veget able fruit rice barley sweet rice bea Chie se cabba ge gree oio youg pumpki cucumb er spiach tomato lettuce pepper cabbag e radish leaf & stem bracke pumpki mallow radish potato oio garlic carrot sweet potato apple mo waterm elo pear strawberr y grape melo

4 peach plum Table 4. Represetative values of carbo fractio i categorized food groups (%, body basis) This work US NRC Default Curret Default Grais Leaf vegetable Root vegetable Fruit 5.23 All agricultural product Computatio of Radiatio Dose with Updated Data Newly updated carbo fractio values ad food s were applied to KDOSE-60 program (Computig code for evaluatig radiatio dose; KAERI) i order to produce more reliable radiatio dose values. Fig. 2 is a comparative graph showig the chage caused by the ew data. The figure says there is o sigificat chage betwee the computed radiatio doses (C-14 part) because the carbo fractios i leaf vegetable pay off the effect of those i root vegetable. O the other had, we aalyzed samples collected earby the power plats sites to validate the suggested values from Igrediet Table (see Fig. 3.). From the figure, may of the aalyzed food samples reasoably agree to FIT. Also, the computatio of the radiatio dose shows that use of the measured values did ot make ay sigificat differeces (ot show here). 4 Coclusio Korea s uclear power plats are i practice of reviewig radiatio doses exposed to the residets durig routie operatio usig a evaluatio tool that computes the radiatio exposure exploitig food itake pathway. This work itroduced ewly updated parameter values to ru the program, called KDOSE-60 programmed o a basis of ICRP-60 guidelie, resultig i more practical evaluatio of the residetial radiatio dose. Four food groups which match the Korea diig patter were suggested alog with updated carbo fractio values of the cautiously selected food ad the ig s of the food based o the total cosumptio rate for recet decade i Korea. The results show that the C-14 radiatio dose calculated with the updated data reasoably agreed with that with the covetioal data based o AECL ad/or CSA model. We also validated the reliability of the data with supportive samples aalyzed. % grais leaf vege. root vege. fruit ifat tee adult sum Fig. 2. Recalculated C-14 radiatio dose by food itake with updated carbo fractio values Carbo Fractio(%) chiese cabbage sample alyzed food igrediet table cucumber tomato youg pumpki gree oio lettuce gree pepper radish tpotato watermelo Fig. 3. Compariso of carbo fractios from the food table to those aalyzed from collected samples ear the power plat sites. apple pear

5 Refereces: [1] Uited States Nuclear Regulatory Commissio, Calculatio of Aual Doses to Ma from Routie Releases of Reactor Effluets for the Purpose of Evaluatig Compliace with 10CFR Part 50 Appedix I, Rev. 1, Regulatory Guide 1.109, [2] Killough G.G. ad P.S. Rohwer, A New Look at the Dosimetry od C-14 Released to the Atmospher as Carbo Dioxide, Health Physics, Vol. 34, 1978, pp [3] Killough,G.G., J.E. Till, ad B.D. Murphy, Dose Equivalet due to Atmospheric Releases of Carbo-14," Chapter 11 i Models ad Parameters for Evirometal Radiological Assessmet, DOE/TIC-11468, [4] Diabate, S. ad S. Strack, "Orgaically Boud Tritium," Health Physics, Vol. 65, 1993, pp [5] Till, J.E. ad H.R, Meyer(Eds), Radiological Assessmet: A Tectbook o Evirometal Dose Aalysis, Uited States Nuclear Regulatory Commissio, NUREG/CR-3332, [6] Caadia Stadard Associatio, Guidelie for Calculatig Derived Release Limits for Radioactive Material i Airbore ad Liquid Effluets for Normal Operatios of Nuclear Power Facilities, CAN/CSA-N288.1-M87, [7] Peterso, S-R. ad R.R. Davis, Modelig Doses from Tritium ad C-14 i the Eviromet, Atomic Eergy of Caada Limited, RC-1951, 1997.