Radioecological Studies on Terrestrial Food Chain Analysis for Accidental Release
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KAERI/RR-2035/99 KR0000196 M Development of Environmental Radiation Protection Technology Radioecological Studies on Terrestrial Food Chain Analysis for Accidental Release 7) 7| 31/ 40 KAER1/RR-2035/99 2=| Development of Environmental Radiation Protection Technology Radioecological Studies on Terrestrial Food Chain Analysis for Accidental Release 71 Please be aware that all of the Missing Pages in this document were originally blank pages n\ 2000^ o| o| 0| o| a o| 0| I. n. 16 tfltb ^ 71^ III. ifl-g- ~-S- Co-57, Sr-85, Ru-103, Cs-134) ^ H-3 D/B H Sr-90 ^ Rl Ill tp#te [opt 001 ^ '((« 005 ^ fr IbU-te a ^ >9-«IAI -R T *AI 2. H-3 HT0 H-3 HTO -f 101000% TFWT > #71 > > TFWT HTO H-3) ^ TFWT ^ TFWT 0.04-0.05% 6]^-ifl OBT ^ TFWT ^3Efi| 0.6-0.8% ^elA] OBT OBT TFWT 0.01~0.4% 0.13-0.35%, 0.02-0.66%^! 3. 5.1 IV 10"2~ 2.1 xiO'1, fe- 2.4X10''1 1-8.5x10"" ^ 6)^4 1 7}^ fe. 7.6-22.0%, 7.6xl0""4~9.7xl0""34 fe 1^ 99% I 7> >i 1.6 /g 0.03-0.04 -Al z]- «- ^ < 6.5 4. ^ D/B D/B 5 , Co, Sr, Cs, Ru f-) s.^ visual Basic^- A °g^^- Visual Basic4 ^ o]s.^x]^ ACCESS ^^l-^4. D/B 5 RTRACK(Radionuclide TRAnsfer data for Crop plants of Korean 5. Rr 5~6 ^iE^jL -fi-7]!- ^£- 2~3% Cs-1373f Sr-90 ^£^ 44 4.5-13.4 Bq/kg-dry 0.7-2.5 # ^ ^ Cs-1374 Sr- (m2/kg-dry)^ AA £°oHl 4^- 3.8xi0"5-2.0xl0"4 ^ 9.5XlO~5~6.5x 10"4^] ^^^ Sr-90 ^*]^l^r7l- Cs-137 ^A 20-30 aflM- ^7>§l-^3l Sr-90^1 ^ 2-3 Cs-137 Q°]A^A Sr-90 ^^^^^4 0^^^ 2 ^ Cs-1375] ^4- j/ej A4 Sr-90^] ^-f 2-3 afl ^S. fe^^-4 Sr-90^ ^-f 20-50 tifl ^£14 ^^4. Cs-137^ «l«ll 2|3L 20 tifl 3 30-70 VI 6. A>JL^^ *i|#i>J Yi^H! T^^r A* fe 2.5X1O"5~8.3X 35-60% 45-61% ^S^^-M- Sr-90^1 ^-f 4.6x 10""33-2.4x 4-8 tifl ^ 50-150 7. 7]^ lysimeterl- V. *}3L*} D/B^r tB«J-o]4 Ef SI4. 3% vin SUMMARY I . Project Title Radioecological Studies on Terrestrial Food Chain Analysis for Accidental Release II. Objectives and Importance A lot of Korean people are concerned about the environmental safety issue of nuclear facilities including 16 nuclear power plants operating in Korea. Especially, because of the site characteristics that agricultural land is widely distributed in the vicinity of Korean NPPs, it is urgently required to have a capability of doing the environmental impact assessment and counter-measure implementation timely and realistically. When the terrestrial ecosystem is contaminated with radionuclides by an accidental release from nuclear facilities, contaminated crop plants would contribute to human internal exposure through food chain. Therefore, understanding the migrational behavior of radionuclides in the ecosystem and their pathways to human is necessary in predicting the environmental impact and implementing a reasonable counter- measure plan for human safety. Since plant contamination parameters of radionuclides are dependent on site-specific factors such as the meteorological condition, soil properties and agricultural practice, the generation of domestic data is quite important. IX This study was carried out to experimentally analyze the direct contamination pathways of some major radionuclides in Korean staple food crops and produce domestic data on various model parameters concerning the plant direct contamination. Experimental studies were also performed for investigating root uptake by rice in soils collected around NPP sites to produce short-term and long-term site-specific transfer factors. HI. Scope and Contents For investigating the contamination pathways of major radionuclides in staple food crops, greenhouse experiments in which rice, Chinese cabbage and radish were exposed to mixed r radionuclides of Mn-54, Co-60, Sr-85, Ru-103 and Cs-134 and H-3 at different growth stages, were conducted to generate data on parameters concerning the direct contamination of those crops. Experiments of the exposure to iodine gas were also performed for rice and radish at their various growth stages to obtain contamination parameters of elemental iodine. Based on data obtained from the experiments mentioned above, a database program was constructed to make it possible to search parameter values for different radionuclides, crops and deposition times in an easy way and have an graphic output of the variation in the contamination parameter with deposition times. Paddy-field soils were collected from 5 or 6 places around Kori and Youngkwang NPPs and physicochemical properties and background radioactivity levels of the soils were investigated. Soil-to-rice transfer factors of Sr-90 and Cs-137 in the collected soils were determined for different RI application times. For Kori soils, transfer factors were also measured in the second year to investigate the yearly variation. In addition, the conceptual design of an automatized experimental greenhouse was performed to be used as a basic material for a detailed design for the construction in the future. IV. Results 1. Analysis of the contamination pathway of mixed gamma radiomiclides in staple food crops For rice, Chinese cabbage and radish, the plant interception factor showed little difference among applied radionuclides of Mn-54, Co-57, Sr-85, Ru-103 and Cs-134 and tended to increase as the application time approached the harvest. It increased very rapidly during the early part of growth and very slowly during the late part. The maximum value measured was 0.94 for rice, 0.87 for Chinese cabbage and 0.86 for radish. The remaining percentage at harvest varied with plants and radionuclides. As the application time approached the harvest, the value usually increased. For rice, the remaining percentage was highest in Ru-103 at the earliest application and in Cs-134 at the latest application while for Chinese cabbage and radish, it was highest in Cs-134 at the earliest application and in Ru-103 at the latest application. XI Translocation factors decreased in the order of Cs-134 > Co-57 > Mn-54 > Sr-85 > Ru-103 for hulled rice seeds, and Co-57 > Cs-134 > Sr-85 > Mn-54 > Ru-103 for radish root. Difference in the translocation factor among radionuclides was by a factor of up to 500 in rice seeds and by a factor of up to 100 in radish root. Variation in the translocation factor with the application time was greater in hulled seeds than in radish root. Of the 5 radionuclides, Cs-134 showed the smallest variation. It was indicated that rain played an important role in determining the remaining percentage in Chinese cabbage and radish. The rain frequency turned out, however, not to significantly affect the remaining percentage in rice when the frequency difference was by a factor of less than 2. Tying the upper end of Chinese cabbage shortly before RI application reduced effectively radionuclide concentrations in the edible portion of the mature plant. 2. Analysis of the H-3 contamination pathway in staple food crops HTO absorption coefficients in leaf, which are realtive TFWT (tissue free-water H-3) concentrations (percent of the average H-3 concentration in air moisture) in leaf at the end of 1 h exposure of crop plants to HTO vapor in an exposure box, were about 100% in rice but less than 50% in Chinese cabbage and radish. The absorption coefficient decreased in the order of leaf > stem > ear for rice, outer leaves > inner leaves for Chinese cabbage, and leaf > upper root > lower root for radish. The TFWT concentrations at harvest were lower than those at the end of exposure by factors of several hundreds to xn several hundred-thousands. In the nighttime experiment for rice, absorption coefficients were in the range of 6—37% depending on plant parts and exposure times and dilution factors were also somewhat different from those in the daytime experiment. In the exposure experiments carried out a few days before and after rice heading, the leaf OBT (organically-bound H-3) concentration (Bq per m# of combustion water) at the end of exposure was about 1% of the initial leaf TFWT concentration but the leaf OBT concentration at harvest was only about 0.04 — 0.05% of the initial TFWT concentration. In ear at the end of rice exposure performed during the early seed development, OBT concentrations were 0.6 ~ 0.8% of TFWT concentrations, which were much higher than observed in exposure experiments made during the late seed development. The OBT production factor (percent ratio of the OBT concentration in the edible part at harvest to the initial leaf TFWT concentration) in hulled rice seeds was in the range of 0.01—0.4% depending on exposure times and highest when the exposure was made at the stage of an active seed development. The OBT production factor varied 0.1 3 — 0.35% in outer leaves of Chinese cabbage, 0.02 — 0.66% in inner leaves of Chinese cabbage and 0.1—0.3% in radish on the whole. 3. Analysis of the I gas contamination pathway in staple food crops Absorption coefficients (deposition coefficients, i/g) of I gas (elemental iodine) for rice at its different growth stages were in the range of 5.1xl0"2-2.1xl0"1 in straw and 2.4xl0"1~8.5xl0"1 in ear. In both parts, the absorption coefficient was highest at the exposure made Xlll on Aug.