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Characteristic analysis and optimum management plan of disused sealed radioactive sources in Korea
Annals of Nuclear Energy 102 (2017) 268–273
Contents lists available at ScienceDirect
Annals of Nuclear Energy journal homepage: www.elsevier.com/locate/anucene
Characteristic analysis and optimum management plan of disused sealed radioactive sources in Korea Juyoul Kim ⇑, Sukhoon Kim, Seunghee Lee FNC Technology Co., 32F, 13 Heungdeok 1-ro, Giheung-gu, Yongin-si, Gyeonggi-do 16954, Republic of Korea
a r t i c l e
i n f o
Article history: Received 24 June 2016 Received in revised form 14 October 2016 Accepted 31 December 2016
Keywords: Disused sealed radioactive sources Radioisotope waste Disposal facility
a b s t r a c t This study reviewed the current status of disused sealed radioactive source (DSRS) in Korea and analyzed its characteristics according to three factors, i.e., IAEA recommended classification system of radioactive waste based on the half-life of radionuclides, potential risk index based on activity divided by the corresponding radionuclide-specific ‘D value’ and legal classification scheme of radioactive waste based on the concentration of radionuclides. The optimum management procedure was derived based on above three factors above and applied to DSRS which are currently being stored in the centralized temporary storage facility for the radioisotope (RI) waste operated by Korea Radioactive Waste Agency (KORAD). The results of this study would be used as technical background document to draw up an optimum management plan of DSRS in the near future. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction Currently, most of disused sealed radioactive sources (DSRSs) generated in Korea are stored in the temporary storage facility of Korea Radioactive Waste Agency (KORAD). On July 2015, seven DSRSs (four boxes of 63Ni nuclide) were transferred to the rock cavern type disposal facility in Gyeongju for the first time. KORAD will receive DSRSs and the annual amount of acceptance is expected to be 33 drums on average. Therefore, the future plan on DSRS disposal should be established as soon as possible in accordance with the construction and operation plan of disposal facility. Since DSRSs have a great variety of characteristics, the domestic disposal environment and source-specific characteristics should be considered for optimizing the disposal method. In this study, the optimum management plan for the disposal of DSRS has been suggested based on the characteristics of DSRS and relevant regulatory requirements. 2. Characteristic Analysis of disused sealed radioactive sources in Korea The Notice No. 2014-3 of Nuclear Safety and Security Commission (NSSC) categorizes the radioactive waste into five groups; high-level radioactive waste (HLW), intermediate-level radioactive waste (ILW), low-level radioactive waste (LLW), very low-level ⇑ Corresponding author. E-mail address: [email protected] (J. Kim). http://dx.doi.org/10.1016/j.anucene.2016.12.036 0306-4549/Ó 2017 Elsevier Ltd. All rights reserved.
radioactive waste (VLLW) and exempt waste (EW) (NSSC, 2014a). Radionuclide-specific clearance level of EW for self-disposal and concentration limit of LLW are shown in Tables 1 and 2, respectively. If the concentration of waste is between clearance level in Table 1 and centuple of clearance level, the radioactive waste is classified as VLLW. Also, if the concentration is between one hundred times of clearance level and concentration limit in Table 2, the radioactive waste is classified as LLW. Fig. 1 shows the classification system of radioactive waste in accordance with the Korean regulation. From 1991 to 2014, 34 radionuclides of DSRS have been generated in various area including industry, hospital, research and education organization. They are as follows: - 23 radionuclides whose half-lives are lower than 30 years; 210 Bi, 125I, 124Sb/Be, 192Ir, 75Se, 210Po, 153Gd, 68Ge, 57Co, 109Cd, 134 Cs, 22Na, 147Pm, 252Cf, 55Fe, 60Co, 133Ba, 85Kr, 3H, 152Eu, 244 Cm, 90Sr, 90Sr/90Y. - 9 radionuclides whose half-lives are higher than 30 years; 137Cs, 63 Ni, 241Am, 241Am/Be, 226Ra, 226Ra/Be, 14C, 235U, 238U. - 2 mixed sources including 60Co and 90Sr, respectively. Among these DSRSs, 7 radionuclides are alpha sources including Po, 252Cf, 244Cm, 241Am, 226Ra, 235U, 238U and remaining radionuclides are beta sources. The radionuclides containing Beryllium such as Sb/Be, Am/Be and Ra/Be are neutron sources. Although most of DSRSs are solid form, some DSRS such as 85Kr and 3H exist as gaseous form in the sealed container with unbreakable and
210
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J. Kim et al. / Annals of Nuclear Energy 102 (2017) 268–273 Table 1 Radionuclide-specific clearance level of exempt waste (NSSC, 2014a). Radionuclide
Clearance Level (Bq/g)
I-129 Na-22, Sc-46, Mn-54, Co-56, Co-60, Zn-65, Nb-94, Ru-106, Ag-110m, Sb-125, Cs-134, Cs-137, Eu-152, Eu-154, Ta-182, Bi-207, Th-229, U-232, Pu238, Pu-239, Pu-240, Pu-242, Pu-244, Am-241, Am-242m, Am-243, Cm-245, Cm-246, Cm-247, Cm-248, Cf-249, Cf-251, Es-254 C-14, Na-24, Cl-36, Sc-48, V-48, Mn-52, Fe-59, Co-57, Co-58, Se-75, Br-82, Sr-85, Sr-90, Zr-95, Nb-95, Tc-96, Tc-99, Ru-103, Ag-105, Cd-109, sn113, Sb-124, Te-123m, Te-132, Cs-136, Ba-140, La-140, Ce-139, Eu-155, Tb-160, Hf-181, Os-185, Ir-190, Ir-192, Tl-204, Bi-206, U-233, Np-237, Pu-236, Cm-243, Cm-244, Cf-248, Cf-250, Cf-252, Cf-254 Be-7, F-18, Cl-38, K-43, Ca-47, Mn-51, Mn-52m, Mn-56, Fe-52, Co-55, Co-62m, Ni-65, Zn-69m, Ga-72, As-74, As-76, Sr-91, Sr-92, Zr-93, Zr-97, Nb93m, Nb-97, Nb-98, Mo-90, Mo-93, Mo-99, Mo-101, Tc-97, Ru-97, Ru-105, Cd-115, In-111, In-114m, sn-125, Sb-122, Te-127m, Te-129m, Te131m, Te-133, Te-133m, Te-134, I-126, I-130, I-131, I-132, I-133, I-134, I-135, Cs-129, Cs-132, Cs-138, Ba-131, Ce-143, Ce-144, Gd-153, W-181, W-187, Pt-191, Au-198, Hg-203, Tl-200, Tl-202, Pb-203, Po-203, Po-205, Po-207, Ra-225, Pa-230, Pa-233, U-230b, U-236, Np-240, u-241, Cm242, Es-254m H-3, S-35, K-42, Ca-45, Sc-47, Cr-51, Mn-53, Co-61, Ni-59, Ni-63, Cu-64, Rb-86, Sr-85m, Sr-87m, Y-91, Y-91m, Y-92, Y-93, Tc-97m, Tc-99m, Rh105, Pd-109, Ag-111, Cd-115m, In-113m, In-115m, Te-129, Te-131, I-123, I-125, Cs-135, Ce-141, Pr-142, Nd-147, Nd-149, Sm-153, Eu-152m, Gd-159, Dy-166, Ho-166, Er-171, Tm-170, Yb-175, Lu-177, re-188, Os-191, Os-193, Ir-194, Pt-197m, Au-199, Hg-197, Hg-197m, Tl-201, Ra-227, U-231, U-237, U-239, U-240, Np-239, Pu-234, Pu-235, Pu-237, Bk-249, Cf-253, Es-253, Fm-255 Si-31, P-32, P-33, Fe-55, Co-60m, Zn-69, As-73, As-77, Sr-89, Y-90, Tc-96m, Pd-103, Te-125m, Te-127, Cs-131, Cs-134m, Pr-143, Pm-147, Pm-149, Sm-151, Dy-165, Er-169, Tm-171, W-185, re-186, Os-191m, Pt-193m, Pt-197, At-211, Th-226, Pu-243, Am-242, Cf-246 Co-58m, Ge-71, Rh-103m, Fm-254
0.01 0.1
Table 2 Radioactivity Concentration limit for low-level waste (NSSC, 2014a). Radionuclide
Radioactivity concentration (Bq/g)
H-3, Cs-137 C-14 Co-60 Ni-59, Sr-90 Ni-63 Nb-94 Tc-99 I-129 Gross-alpha
1.11 106 2.22 105 3.70 107 7.40 104 1.11 107 1.11 102 1.11 103 3.70 101 3.70 103
non-corrosive material. The majority of DSRSs have been generated from industrial organizations, and it took about 87.5% in volume.
1
10
100
1000 10,000
The next is medical institute followed by public, research, educational and military institution in order. As shown in Fig. 2, the total number of DSRSs was 52,176 over the past 24 years. 192Ir took about 69.7% and its number was 36,382. 3H took about 10.5%, followed by 147Pm (3.9%), 241Am (3.7%), 60Co (3.3%), 137Cs (2.5%), 147Pm (1.7%), 85Kr (1.0%), 226Ra (0.9%), 90Sr (0.7%). In terms of radioactivity, total radioactivity was estimated as 1.514 109 Bq as of 2014. 137Cs took the highest portion of radioactivity, which was about 59.3% of total activity. 60 Co took 37.5% of total activity followed by 241Am (2.0%), 85Kr (0.6%), 241Am/Be (0.2%), 226Ra (0.1%), 63Ni (0.09%), 90Sr (0.04%), 147 Pm (0.04%), 244Cm (0.02%). The total volume of DSRS including the storage container was 6.43 104 L, and 60Co took 55.1% followed by 137Cs (16.8%), 192Ir (9.8%), 57Co (4.9%), 241Am/Be (3.6%), 85 Kr (2.1%), 226Ra (1.6%), 63Ni (1.5%), 241Am (1.4%), and 147Pm (0.8%). In summary, 60Co, 137Cs, 192Ir, 241Am and 241Am/Be took
Fig. 1. Classification system of radioactive waste in Korea.
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Fig. 2. The variation of number (top), radioactivity (middle) and volume (bottom) of disused sealed radioactive sources between the year of 1991 and 2014 in Korea.
the top 5 ranking, and it meant these 5 radionuclides should be significantly considered for the optimum management of DSRS. In case of 192Ir, it has mainly been used for radiography in industrial field. Because of its short half-life, however, it results in the greatest number of 192Ir waste. As 137Cs has been used for
industrial gauge and has long half-life, its radioactivity is relatively high. 60Co is used in various fields such as a nondestructive testing, food sterilization, industrial gauge and so on. Especially, as there are lots of 60Co used in gamma irradiation facility (100,000 Ci), its volume takes a large portion of total volume of DSRS.
J. Kim et al. / Annals of Nuclear Energy 102 (2017) 268–273 Table 3 Grouping of disused sealed radioactive sources based on half-life of radionuclide.
271
3. Optimum management plan
Half-life (T1/2)
Number of radionuclides
Radionuclide contained in DSRS
3.1. IAEA standards and guidances
T1/2 < 100 days {Very shortlived} 100 days 6 T1/2 < 30 years {Short-lived} T1/2 P 30 years {Long-lived}
4
210
17
75
IAEA (2006) provides the guide on safety of radiation generators and sealed radioactive sources, and IAEA (2014) provides the comprehensive guide on DSRS management. The management option for certain source depends on several factors such as activity, contents of isotopes, half-life, purchase condition and physical condition. General management options for DSRS are transfer to other user, return to supplier/manufacturer, interim storage, conditioning, centralized storage or disposal. Very short-lived nuclides such as 32P, 125I, 192Ir and 210Po may be disposed of as general wastes after decay storage. Low activity and short-lived source is proper to near surface disposal option, but it may be rejected by the acceptance criteria since the activity can be locally high. If the activity of long-lived source exceeds the acceptance criteria for near surface disposal option, deep geological disposal option is proper. Also, borehole disposal facility may be an alternative option for DSRS. All options should be licensed in advance and safety analysis should be performed. IAEA (2009) provides the guide on classification of radioactive waste. IAEA (2005a) categorizes radioactive sources based on half-life; less than 100 days, from 100 days to 30 years, and more than 30 years. Also, IAEA (2005b) classifies radioactive sources into
Bi,
125
I, Sb-Be,
192
Ir
Se, 210Po, 153Gd, 68Ge, 57Co, 109Cd, Cs, 22Na, 147Pm, 252Cf, 55Fe, 60Co, 133 Ba, 85Kr, 3H, 152Eu, 244Cm 90 * 90 Sr , Sr/90Y*, 137Cs, 63Ni, 241Am, 241 Am/Be, 226Ra, 226Ra/Be, 14C, 235U, 238 U, Mixed sources (such as three (3) nuclides including 60Co, and three (3) nuclides including 90Sr) 134
13
* Although the half-life of 90Sr and 90Sr/90Y (i.e. 28.79 years) is less than 30 years, it is categorized into this group in compliance with IAEA recommendation (IAEA, 2005a).
Korean classification system categorizes the radioactive waste as 5 groups; EW, VLLW, LLW, ILW and HLW. EW took 58.52% of the number of DSRS. It means that 58.52% of DSRS could be disposed of as industrial waste when following the classification system. The number of VLLW was 3300 (6.32%), followed by LLW (2.25%) and ILW (5.57%).
Fig. 3. Proposed optimum management procedure for disused sealed radioactive sources in Korea.
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J. Kim et al. / Annals of Nuclear Energy 102 (2017) 268–273
five categories based on the risk. The risk of source is defined as D value which causes deterministic effects to the human body. The ratio of source activity to D value (i.e. A/D) is a fundamental criterion for each classification. Besides A/D value, physical and chemical form of source and type of shielding or containment are considered to decide the classification of source. 3.2. Derivation of optimum management measures In order to derive the most suitable management measures of DSRS, the following three factors are considered; IAEA recommended classification system of radioactive waste based on the half-life of radionuclides, potential risk index based on activity divided by the corresponding radionuclide-specific ‘D value’ and legal classification scheme of radioactive waste based on the concentration of radionuclide. For keeping consistency with recommendations specified in the technical guideline issued by IAEA, the terms of 100 days and 30 years are set up as the category boundaries for the half-life, resulting in three sub-groups. Table 3 shows the classification result of DSRS based on half-life of radionuclides. IAEA also provides a five-category system for radioactive sources based on the dimensionless normalized ratio of A/D, which is the activity divided by the corresponding radionuclide-specific
‘D value’. Since this categorization scheme is primarily based on the potential to cause deterministic health effects resulting from the corresponding source, the ‘D values’ are considered to be reasonable normalizing factors for determining the numerical relative ranking or sources, which represent the potential risk to workers and the general public. Accordingly, for maintaining consistency with the technical guideline recommended by IAEA, ‘the activity ratio of A/D = 1000, 10, 1 and 0.010 are set up as the boundary values for A/D, resulting in five categories. According to NSSC Notice (2014a,b), the disposal strategy of radioactive wastes generated from the nuclear installation are classified on the basis of the concentration of radionuclides, i.e., trench type disposal, engineered vault type disposal, rock cavern type disposal, deep geological disposal. In case of DSRSs that is not reusable or recyclable, the different procedure is applied based on the half-life of radionuclide contained in the source. Details are illustrated in Fig. 3. For DSRSs equipped with the very short-lived radionuclide whose half-life is less than 100 days, those are in a state of decay storage after packaging in consolidating or separate storage container until the specific activity of the corresponding radioactive source is less than 100 times the allowable concentration for clearance. At the time of disposal after a certain period of time, it is recommended that IAEA Category 1–4 sources (i.e. A/D P 0.01)
Table 4 Quantity of DSRS to be managed by the proposed procedure as of 2020.
Note: *Ratio to total quantity (i.e. 41,753) of sources that can be categorized in accordance with classification system in Korea and A/D value at the time of management and disposal; Since neutron sources cannot be classified into specific category in accordance with the Korean regulation, these are excluded from calculating the total volume to be managed.
J. Kim et al. / Annals of Nuclear Energy 102 (2017) 268–273 Table 5 Volume of DSRS to be managed by the proposed procedure as of 2020.
273
Within the limit: Self disposal in case the specific activity is less than the clearance level, otherwise engineered vault type disposal. Exceeds the limit: Rock cavern type (or borehole) disposal. As part of case studies, the proposed management procedure shown in Fig. 3 was applied to DSRS that are being stored in the temporary storage facility for DSRS waste. Considering the operational (60 years) and institutional control period (100 years) of Wolsong LILW Disposal Center (WLDC), a case study for assessing the change of quantity and volume of DSRS was performed for the year of 2020, 2035, 2050, 2065, 2080 and 2180, respectively. An example for the year of 2020 is shown in Tables 4 and 5. From these studies, it is confirmed that method (i.e. schematized in Fig. 3) for management and disposal of DSRSs derived from this study can be applied to all of the domestic DSRSs being temporarily stored in the disposal facility. However, the method is only applicable to DSRSs that the specific characteristics are already identified at present. 4. Conclusion
Note: *Ratio to total volume (i.e. 39,561.7 L) of sources that can be categorized in accordance with classification system in Korea and A/D value at the time of management and disposal; Since neutron sources cannot be classified into specific category in accordance with the Korean regulation, these are excluded from calculating the total volume to be managed.
keep in a state of decay storage, and IAEA Category 5 sources (i.e. A/ D < 0.01) be disposed of by means of the clearance or trench type disposal on the basis of the clearance level specified in the domestic legislation and technical standards in force. In principle, DSRSs can be disposed of in conventional landfills through clearance from regulatory control provided that the legal requirements for exemption or exclusion are met. However, disposal of DSRSs in the landfill site should be prudently determined considering public acceptance. For DSRSs with the short-lived (i.e. 100 days 6 half-life < 30 years) or long-lived (i.e. half-life P 30 years) radionuclide, those are in a state of temporary storage after conditioning. In this process, since DSRSs with the alpha-emitter can cause the significant consequence in case the radioactive material is released into ecosystem, it would be reasonable to exclude from the subject of disposal and subsequently to manage by means of the long-term storage followed by conditioning. At the time of disposal after a certain period of time in the process of the temporary storage, it is suggested to manage DSRSs to be disposed of by means of the following methods on the basis of the A/D value and the radioactivity concentration limit specified in the domestic legislation and technical standards in force. - IAEA Category 1 and 2 sources (i.e. A/D P 10): Long-term storage. - IAEA Category 3 sources (i.e. 1 6 A/D < 10): Determination of disposal method on the basis of the radioactivity concentration limit for ILW (Intermediate-Level Waste), which represents the allowable concentration for rock cavern type disposal. Within the limit: Rock cavern type (or borehole) disposal. Exceeds the limit: Long-term storage. - IAEA Category 4 and 5 sources (i.e. A/D < 1): Determination of disposal method on the basis of the radioactivity concentration limit for LLW (Low-Level Waste), which represents the allowable concentration for engineered vault type disposal.
According to the increasing usage of sealed radioactive sources, the necessity of management practices for disused sealed radioactive sources (DSRS) has getting attention in Korea. Since the final approval for the operation of WLDC in December 2014, all of the radioactive waste except HLW could be disposed of at WLDC. Because the disposal plan of DSRS has not been determined yet, the optimum management procedure proposed in this study would be valuable in the stage of pre-disposal of DSRS. Three important management aspects of DSRS including half-life of radionuclide, ratio of source activity to D value and concentration limit specified in Korean legislation were comprehensively incorporated. Although concentration limit is related with acceptance criteria of disposal facility, treatment and conditioning processes of high levels of DSRS (hot spot) to meet the acceptance criteria are beyond the scope of this research paper. Through this case study, it is confirmed that the proposed management procedure can be applied to all of the domestic DSRSs being temporarily stored in the temporary storage facility of KORAD. However, for enhancing applicability of the results derived from this study, it is essential to identify the inherent characteristics for the following sources; i) DSRSs without information on the radioactivity, ii) DSRSs that are not possible to calculate the specific activity and/or the source-specific A/D value. Acknowledgements This work was supported by the Energy Efficiency & Resources of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Trade, Industry and Energy (20141720100560). References International Atomic Energy Agency (IAEA), 2005a. Disposal Options for Disused Radioactive Sources, Technical Reports Series No. 436. IAEA, Vienna. IAEA, 2005b. Categorization of Radioactive Sources, IAEA Safety Standards Series No. RS-G-1.9. IAEA, Vienna. International Atomic Energy Agency (IAEA), 2006. Safety of Radiation Generators and Sealed Radioactive Sources, IAEA Safety Standards Series No. RS-G-1.10. IAEA, Vienna. International Atomic Energy Agency (IAEA), 2009. Classification of Radioactive Waste, IAEA Safety Standards Series No. GSG-1. IAEA, Vienna. International Atomic Energy Agency (IAEA), 2014. Management of Disused Sealed Radioactive Sources, IAEA Nuclear Energy Series No. NW-T-1.3. IAEA, Vienna. Nuclear Safety and Security Commission (NSSC), 2014a. Regulations for Classification of Radioactive Waste and Criteria on Clearance, Notice No. 2014-3. NSSC. Nuclear Safety and Security Commission (NSSC), 2014b. Standards for Radiation Protection, Etc., Notice No. 2014-34. NSSC.
Contents lists available at ScienceDirect
Annals of Nuclear Energy journal homepage: www.elsevier.com/locate/anucene
Characteristic analysis and optimum management plan of disused sealed radioactive sources in Korea Juyoul Kim ⇑, Sukhoon Kim, Seunghee Lee FNC Technology Co., 32F, 13 Heungdeok 1-ro, Giheung-gu, Yongin-si, Gyeonggi-do 16954, Republic of Korea
a r t i c l e
i n f o
Article history: Received 24 June 2016 Received in revised form 14 October 2016 Accepted 31 December 2016
Keywords: Disused sealed radioactive sources Radioisotope waste Disposal facility
a b s t r a c t This study reviewed the current status of disused sealed radioactive source (DSRS) in Korea and analyzed its characteristics according to three factors, i.e., IAEA recommended classification system of radioactive waste based on the half-life of radionuclides, potential risk index based on activity divided by the corresponding radionuclide-specific ‘D value’ and legal classification scheme of radioactive waste based on the concentration of radionuclides. The optimum management procedure was derived based on above three factors above and applied to DSRS which are currently being stored in the centralized temporary storage facility for the radioisotope (RI) waste operated by Korea Radioactive Waste Agency (KORAD). The results of this study would be used as technical background document to draw up an optimum management plan of DSRS in the near future. Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction Currently, most of disused sealed radioactive sources (DSRSs) generated in Korea are stored in the temporary storage facility of Korea Radioactive Waste Agency (KORAD). On July 2015, seven DSRSs (four boxes of 63Ni nuclide) were transferred to the rock cavern type disposal facility in Gyeongju for the first time. KORAD will receive DSRSs and the annual amount of acceptance is expected to be 33 drums on average. Therefore, the future plan on DSRS disposal should be established as soon as possible in accordance with the construction and operation plan of disposal facility. Since DSRSs have a great variety of characteristics, the domestic disposal environment and source-specific characteristics should be considered for optimizing the disposal method. In this study, the optimum management plan for the disposal of DSRS has been suggested based on the characteristics of DSRS and relevant regulatory requirements. 2. Characteristic Analysis of disused sealed radioactive sources in Korea The Notice No. 2014-3 of Nuclear Safety and Security Commission (NSSC) categorizes the radioactive waste into five groups; high-level radioactive waste (HLW), intermediate-level radioactive waste (ILW), low-level radioactive waste (LLW), very low-level ⇑ Corresponding author. E-mail address: [email protected] (J. Kim). http://dx.doi.org/10.1016/j.anucene.2016.12.036 0306-4549/Ó 2017 Elsevier Ltd. All rights reserved.
radioactive waste (VLLW) and exempt waste (EW) (NSSC, 2014a). Radionuclide-specific clearance level of EW for self-disposal and concentration limit of LLW are shown in Tables 1 and 2, respectively. If the concentration of waste is between clearance level in Table 1 and centuple of clearance level, the radioactive waste is classified as VLLW. Also, if the concentration is between one hundred times of clearance level and concentration limit in Table 2, the radioactive waste is classified as LLW. Fig. 1 shows the classification system of radioactive waste in accordance with the Korean regulation. From 1991 to 2014, 34 radionuclides of DSRS have been generated in various area including industry, hospital, research and education organization. They are as follows: - 23 radionuclides whose half-lives are lower than 30 years; 210 Bi, 125I, 124Sb/Be, 192Ir, 75Se, 210Po, 153Gd, 68Ge, 57Co, 109Cd, 134 Cs, 22Na, 147Pm, 252Cf, 55Fe, 60Co, 133Ba, 85Kr, 3H, 152Eu, 244 Cm, 90Sr, 90Sr/90Y. - 9 radionuclides whose half-lives are higher than 30 years; 137Cs, 63 Ni, 241Am, 241Am/Be, 226Ra, 226Ra/Be, 14C, 235U, 238U. - 2 mixed sources including 60Co and 90Sr, respectively. Among these DSRSs, 7 radionuclides are alpha sources including Po, 252Cf, 244Cm, 241Am, 226Ra, 235U, 238U and remaining radionuclides are beta sources. The radionuclides containing Beryllium such as Sb/Be, Am/Be and Ra/Be are neutron sources. Although most of DSRSs are solid form, some DSRS such as 85Kr and 3H exist as gaseous form in the sealed container with unbreakable and
210
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J. Kim et al. / Annals of Nuclear Energy 102 (2017) 268–273 Table 1 Radionuclide-specific clearance level of exempt waste (NSSC, 2014a). Radionuclide
Clearance Level (Bq/g)
I-129 Na-22, Sc-46, Mn-54, Co-56, Co-60, Zn-65, Nb-94, Ru-106, Ag-110m, Sb-125, Cs-134, Cs-137, Eu-152, Eu-154, Ta-182, Bi-207, Th-229, U-232, Pu238, Pu-239, Pu-240, Pu-242, Pu-244, Am-241, Am-242m, Am-243, Cm-245, Cm-246, Cm-247, Cm-248, Cf-249, Cf-251, Es-254 C-14, Na-24, Cl-36, Sc-48, V-48, Mn-52, Fe-59, Co-57, Co-58, Se-75, Br-82, Sr-85, Sr-90, Zr-95, Nb-95, Tc-96, Tc-99, Ru-103, Ag-105, Cd-109, sn113, Sb-124, Te-123m, Te-132, Cs-136, Ba-140, La-140, Ce-139, Eu-155, Tb-160, Hf-181, Os-185, Ir-190, Ir-192, Tl-204, Bi-206, U-233, Np-237, Pu-236, Cm-243, Cm-244, Cf-248, Cf-250, Cf-252, Cf-254 Be-7, F-18, Cl-38, K-43, Ca-47, Mn-51, Mn-52m, Mn-56, Fe-52, Co-55, Co-62m, Ni-65, Zn-69m, Ga-72, As-74, As-76, Sr-91, Sr-92, Zr-93, Zr-97, Nb93m, Nb-97, Nb-98, Mo-90, Mo-93, Mo-99, Mo-101, Tc-97, Ru-97, Ru-105, Cd-115, In-111, In-114m, sn-125, Sb-122, Te-127m, Te-129m, Te131m, Te-133, Te-133m, Te-134, I-126, I-130, I-131, I-132, I-133, I-134, I-135, Cs-129, Cs-132, Cs-138, Ba-131, Ce-143, Ce-144, Gd-153, W-181, W-187, Pt-191, Au-198, Hg-203, Tl-200, Tl-202, Pb-203, Po-203, Po-205, Po-207, Ra-225, Pa-230, Pa-233, U-230b, U-236, Np-240, u-241, Cm242, Es-254m H-3, S-35, K-42, Ca-45, Sc-47, Cr-51, Mn-53, Co-61, Ni-59, Ni-63, Cu-64, Rb-86, Sr-85m, Sr-87m, Y-91, Y-91m, Y-92, Y-93, Tc-97m, Tc-99m, Rh105, Pd-109, Ag-111, Cd-115m, In-113m, In-115m, Te-129, Te-131, I-123, I-125, Cs-135, Ce-141, Pr-142, Nd-147, Nd-149, Sm-153, Eu-152m, Gd-159, Dy-166, Ho-166, Er-171, Tm-170, Yb-175, Lu-177, re-188, Os-191, Os-193, Ir-194, Pt-197m, Au-199, Hg-197, Hg-197m, Tl-201, Ra-227, U-231, U-237, U-239, U-240, Np-239, Pu-234, Pu-235, Pu-237, Bk-249, Cf-253, Es-253, Fm-255 Si-31, P-32, P-33, Fe-55, Co-60m, Zn-69, As-73, As-77, Sr-89, Y-90, Tc-96m, Pd-103, Te-125m, Te-127, Cs-131, Cs-134m, Pr-143, Pm-147, Pm-149, Sm-151, Dy-165, Er-169, Tm-171, W-185, re-186, Os-191m, Pt-193m, Pt-197, At-211, Th-226, Pu-243, Am-242, Cf-246 Co-58m, Ge-71, Rh-103m, Fm-254
0.01 0.1
Table 2 Radioactivity Concentration limit for low-level waste (NSSC, 2014a). Radionuclide
Radioactivity concentration (Bq/g)
H-3, Cs-137 C-14 Co-60 Ni-59, Sr-90 Ni-63 Nb-94 Tc-99 I-129 Gross-alpha
1.11 106 2.22 105 3.70 107 7.40 104 1.11 107 1.11 102 1.11 103 3.70 101 3.70 103
non-corrosive material. The majority of DSRSs have been generated from industrial organizations, and it took about 87.5% in volume.
1
10
100
1000 10,000
The next is medical institute followed by public, research, educational and military institution in order. As shown in Fig. 2, the total number of DSRSs was 52,176 over the past 24 years. 192Ir took about 69.7% and its number was 36,382. 3H took about 10.5%, followed by 147Pm (3.9%), 241Am (3.7%), 60Co (3.3%), 137Cs (2.5%), 147Pm (1.7%), 85Kr (1.0%), 226Ra (0.9%), 90Sr (0.7%). In terms of radioactivity, total radioactivity was estimated as 1.514 109 Bq as of 2014. 137Cs took the highest portion of radioactivity, which was about 59.3% of total activity. 60 Co took 37.5% of total activity followed by 241Am (2.0%), 85Kr (0.6%), 241Am/Be (0.2%), 226Ra (0.1%), 63Ni (0.09%), 90Sr (0.04%), 147 Pm (0.04%), 244Cm (0.02%). The total volume of DSRS including the storage container was 6.43 104 L, and 60Co took 55.1% followed by 137Cs (16.8%), 192Ir (9.8%), 57Co (4.9%), 241Am/Be (3.6%), 85 Kr (2.1%), 226Ra (1.6%), 63Ni (1.5%), 241Am (1.4%), and 147Pm (0.8%). In summary, 60Co, 137Cs, 192Ir, 241Am and 241Am/Be took
Fig. 1. Classification system of radioactive waste in Korea.
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Fig. 2. The variation of number (top), radioactivity (middle) and volume (bottom) of disused sealed radioactive sources between the year of 1991 and 2014 in Korea.
the top 5 ranking, and it meant these 5 radionuclides should be significantly considered for the optimum management of DSRS. In case of 192Ir, it has mainly been used for radiography in industrial field. Because of its short half-life, however, it results in the greatest number of 192Ir waste. As 137Cs has been used for
industrial gauge and has long half-life, its radioactivity is relatively high. 60Co is used in various fields such as a nondestructive testing, food sterilization, industrial gauge and so on. Especially, as there are lots of 60Co used in gamma irradiation facility (100,000 Ci), its volume takes a large portion of total volume of DSRS.
J. Kim et al. / Annals of Nuclear Energy 102 (2017) 268–273 Table 3 Grouping of disused sealed radioactive sources based on half-life of radionuclide.
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3. Optimum management plan
Half-life (T1/2)
Number of radionuclides
Radionuclide contained in DSRS
3.1. IAEA standards and guidances
T1/2 < 100 days {Very shortlived} 100 days 6 T1/2 < 30 years {Short-lived} T1/2 P 30 years {Long-lived}
4
210
17
75
IAEA (2006) provides the guide on safety of radiation generators and sealed radioactive sources, and IAEA (2014) provides the comprehensive guide on DSRS management. The management option for certain source depends on several factors such as activity, contents of isotopes, half-life, purchase condition and physical condition. General management options for DSRS are transfer to other user, return to supplier/manufacturer, interim storage, conditioning, centralized storage or disposal. Very short-lived nuclides such as 32P, 125I, 192Ir and 210Po may be disposed of as general wastes after decay storage. Low activity and short-lived source is proper to near surface disposal option, but it may be rejected by the acceptance criteria since the activity can be locally high. If the activity of long-lived source exceeds the acceptance criteria for near surface disposal option, deep geological disposal option is proper. Also, borehole disposal facility may be an alternative option for DSRS. All options should be licensed in advance and safety analysis should be performed. IAEA (2009) provides the guide on classification of radioactive waste. IAEA (2005a) categorizes radioactive sources based on half-life; less than 100 days, from 100 days to 30 years, and more than 30 years. Also, IAEA (2005b) classifies radioactive sources into
Bi,
125
I, Sb-Be,
192
Ir
Se, 210Po, 153Gd, 68Ge, 57Co, 109Cd, Cs, 22Na, 147Pm, 252Cf, 55Fe, 60Co, 133 Ba, 85Kr, 3H, 152Eu, 244Cm 90 * 90 Sr , Sr/90Y*, 137Cs, 63Ni, 241Am, 241 Am/Be, 226Ra, 226Ra/Be, 14C, 235U, 238 U, Mixed sources (such as three (3) nuclides including 60Co, and three (3) nuclides including 90Sr) 134
13
* Although the half-life of 90Sr and 90Sr/90Y (i.e. 28.79 years) is less than 30 years, it is categorized into this group in compliance with IAEA recommendation (IAEA, 2005a).
Korean classification system categorizes the radioactive waste as 5 groups; EW, VLLW, LLW, ILW and HLW. EW took 58.52% of the number of DSRS. It means that 58.52% of DSRS could be disposed of as industrial waste when following the classification system. The number of VLLW was 3300 (6.32%), followed by LLW (2.25%) and ILW (5.57%).
Fig. 3. Proposed optimum management procedure for disused sealed radioactive sources in Korea.
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five categories based on the risk. The risk of source is defined as D value which causes deterministic effects to the human body. The ratio of source activity to D value (i.e. A/D) is a fundamental criterion for each classification. Besides A/D value, physical and chemical form of source and type of shielding or containment are considered to decide the classification of source. 3.2. Derivation of optimum management measures In order to derive the most suitable management measures of DSRS, the following three factors are considered; IAEA recommended classification system of radioactive waste based on the half-life of radionuclides, potential risk index based on activity divided by the corresponding radionuclide-specific ‘D value’ and legal classification scheme of radioactive waste based on the concentration of radionuclide. For keeping consistency with recommendations specified in the technical guideline issued by IAEA, the terms of 100 days and 30 years are set up as the category boundaries for the half-life, resulting in three sub-groups. Table 3 shows the classification result of DSRS based on half-life of radionuclides. IAEA also provides a five-category system for radioactive sources based on the dimensionless normalized ratio of A/D, which is the activity divided by the corresponding radionuclide-specific
‘D value’. Since this categorization scheme is primarily based on the potential to cause deterministic health effects resulting from the corresponding source, the ‘D values’ are considered to be reasonable normalizing factors for determining the numerical relative ranking or sources, which represent the potential risk to workers and the general public. Accordingly, for maintaining consistency with the technical guideline recommended by IAEA, ‘the activity ratio of A/D = 1000, 10, 1 and 0.010 are set up as the boundary values for A/D, resulting in five categories. According to NSSC Notice (2014a,b), the disposal strategy of radioactive wastes generated from the nuclear installation are classified on the basis of the concentration of radionuclides, i.e., trench type disposal, engineered vault type disposal, rock cavern type disposal, deep geological disposal. In case of DSRSs that is not reusable or recyclable, the different procedure is applied based on the half-life of radionuclide contained in the source. Details are illustrated in Fig. 3. For DSRSs equipped with the very short-lived radionuclide whose half-life is less than 100 days, those are in a state of decay storage after packaging in consolidating or separate storage container until the specific activity of the corresponding radioactive source is less than 100 times the allowable concentration for clearance. At the time of disposal after a certain period of time, it is recommended that IAEA Category 1–4 sources (i.e. A/D P 0.01)
Table 4 Quantity of DSRS to be managed by the proposed procedure as of 2020.
Note: *Ratio to total quantity (i.e. 41,753) of sources that can be categorized in accordance with classification system in Korea and A/D value at the time of management and disposal; Since neutron sources cannot be classified into specific category in accordance with the Korean regulation, these are excluded from calculating the total volume to be managed.
J. Kim et al. / Annals of Nuclear Energy 102 (2017) 268–273 Table 5 Volume of DSRS to be managed by the proposed procedure as of 2020.
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Within the limit: Self disposal in case the specific activity is less than the clearance level, otherwise engineered vault type disposal. Exceeds the limit: Rock cavern type (or borehole) disposal. As part of case studies, the proposed management procedure shown in Fig. 3 was applied to DSRS that are being stored in the temporary storage facility for DSRS waste. Considering the operational (60 years) and institutional control period (100 years) of Wolsong LILW Disposal Center (WLDC), a case study for assessing the change of quantity and volume of DSRS was performed for the year of 2020, 2035, 2050, 2065, 2080 and 2180, respectively. An example for the year of 2020 is shown in Tables 4 and 5. From these studies, it is confirmed that method (i.e. schematized in Fig. 3) for management and disposal of DSRSs derived from this study can be applied to all of the domestic DSRSs being temporarily stored in the disposal facility. However, the method is only applicable to DSRSs that the specific characteristics are already identified at present. 4. Conclusion
Note: *Ratio to total volume (i.e. 39,561.7 L) of sources that can be categorized in accordance with classification system in Korea and A/D value at the time of management and disposal; Since neutron sources cannot be classified into specific category in accordance with the Korean regulation, these are excluded from calculating the total volume to be managed.
keep in a state of decay storage, and IAEA Category 5 sources (i.e. A/ D < 0.01) be disposed of by means of the clearance or trench type disposal on the basis of the clearance level specified in the domestic legislation and technical standards in force. In principle, DSRSs can be disposed of in conventional landfills through clearance from regulatory control provided that the legal requirements for exemption or exclusion are met. However, disposal of DSRSs in the landfill site should be prudently determined considering public acceptance. For DSRSs with the short-lived (i.e. 100 days 6 half-life < 30 years) or long-lived (i.e. half-life P 30 years) radionuclide, those are in a state of temporary storage after conditioning. In this process, since DSRSs with the alpha-emitter can cause the significant consequence in case the radioactive material is released into ecosystem, it would be reasonable to exclude from the subject of disposal and subsequently to manage by means of the long-term storage followed by conditioning. At the time of disposal after a certain period of time in the process of the temporary storage, it is suggested to manage DSRSs to be disposed of by means of the following methods on the basis of the A/D value and the radioactivity concentration limit specified in the domestic legislation and technical standards in force. - IAEA Category 1 and 2 sources (i.e. A/D P 10): Long-term storage. - IAEA Category 3 sources (i.e. 1 6 A/D < 10): Determination of disposal method on the basis of the radioactivity concentration limit for ILW (Intermediate-Level Waste), which represents the allowable concentration for rock cavern type disposal. Within the limit: Rock cavern type (or borehole) disposal. Exceeds the limit: Long-term storage. - IAEA Category 4 and 5 sources (i.e. A/D < 1): Determination of disposal method on the basis of the radioactivity concentration limit for LLW (Low-Level Waste), which represents the allowable concentration for engineered vault type disposal.
According to the increasing usage of sealed radioactive sources, the necessity of management practices for disused sealed radioactive sources (DSRS) has getting attention in Korea. Since the final approval for the operation of WLDC in December 2014, all of the radioactive waste except HLW could be disposed of at WLDC. Because the disposal plan of DSRS has not been determined yet, the optimum management procedure proposed in this study would be valuable in the stage of pre-disposal of DSRS. Three important management aspects of DSRS including half-life of radionuclide, ratio of source activity to D value and concentration limit specified in Korean legislation were comprehensively incorporated. Although concentration limit is related with acceptance criteria of disposal facility, treatment and conditioning processes of high levels of DSRS (hot spot) to meet the acceptance criteria are beyond the scope of this research paper. Through this case study, it is confirmed that the proposed management procedure can be applied to all of the domestic DSRSs being temporarily stored in the temporary storage facility of KORAD. However, for enhancing applicability of the results derived from this study, it is essential to identify the inherent characteristics for the following sources; i) DSRSs without information on the radioactivity, ii) DSRSs that are not possible to calculate the specific activity and/or the source-specific A/D value. Acknowledgements This work was supported by the Energy Efficiency & Resources of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Trade, Industry and Energy (20141720100560). References International Atomic Energy Agency (IAEA), 2005a. Disposal Options for Disused Radioactive Sources, Technical Reports Series No. 436. IAEA, Vienna. IAEA, 2005b. Categorization of Radioactive Sources, IAEA Safety Standards Series No. RS-G-1.9. IAEA, Vienna. International Atomic Energy Agency (IAEA), 2006. Safety of Radiation Generators and Sealed Radioactive Sources, IAEA Safety Standards Series No. RS-G-1.10. IAEA, Vienna. International Atomic Energy Agency (IAEA), 2009. Classification of Radioactive Waste, IAEA Safety Standards Series No. GSG-1. IAEA, Vienna. International Atomic Energy Agency (IAEA), 2014. Management of Disused Sealed Radioactive Sources, IAEA Nuclear Energy Series No. NW-T-1.3. IAEA, Vienna. Nuclear Safety and Security Commission (NSSC), 2014a. Regulations for Classification of Radioactive Waste and Criteria on Clearance, Notice No. 2014-3. NSSC. Nuclear Safety and Security Commission (NSSC), 2014b. Standards for Radiation Protection, Etc., Notice No. 2014-34. NSSC.