Derivation and Comparison of Preliminary Derivation Concentration Guideline Level (DCGL) According to Scenarios of Kori Unit 1 Using RESRAD-BUILD

2019 ⦽ǎႊᔍᖒ⠱ʑྜྷ⦺⫭ ⇹ĥ⦺ᚁݡ⫭ םྙ᫵᧞Ḳ

371

Derivation and Comparison of Preliminary Derivation Concentration Guideline Level

(DCGL) According to Scenarios of Kori Unit 1 Using RESRAD-BUILD

SangJune Park*, Jihyang Byon, and Seokyoung Ahn

Pusan National University, 2, Busandaehak-ro 63beon-gil, Geumjeong-gu, Busan, Republic of Korea *

[email protected]

1. Introduction

This study provides a method of calculating a Kori Unit 1 preliminary DCGLs by using RERAD-BUILD code and, for radionuclides on the surface of buildings. Additionally, this study provides a method for calculating the exposure dose to receptors such that it satisfied the site release criteria of South Korea.

2. RESRAD-BUILD Code Description

The RESRAD-BUILD code is an exposure path analysis code for assessing the potential exposure dose of an individual or worker in a building contaminated with residual radioactive material. In the RESRAD-BUILD code, radioactive particulates in the air, aerosol indoor radon decay products, and tritium water vapor, including external exposure to penetration radiation, due to the air submersion of the radioactive material and radioactive particulates that have accumulated at the source, are considered. Additionally, consideration is given to the intake and ingestion pathways of materials emitted from the source and to materials that have accumulated on the building surface. The Fig. 1 shows exposure pathway of RESRAD-BUILD

Fig. 1. Exposure pathway considered in RESRAD-BUILD [1].

RESRAD-BUILD allows the conduct of probabilistic analysis by the input of various parameters. The deterministic analysis derives a single output dose value according to the each single input parameters, while the probabilistic analysis uses the probability distribution of the input parameters to derive various output values. The Fig 2 shows difference of deterministic analysis and probabilistic analysis.

Fig. 2. Difference of deterministic analysis and probabilistic analysis [1].

3. Input Values for RESRAD-BUILD

The dose/risk library used in this study was ICRP 60. This library contains the latest data and is suitable to industrial workers. In this scenario, the ceilings were not considered because their contamination was assumed to be negligible.

The Indoor fraction was 97.4 d·yr-1 which based on the occupancy scenario in NUREG/CR-5512, Vol. 3 [2]. The direct ingestion rate is 0.88×10-6 ‡K-1 that was 1.1×10-4 m2‡K-1

divided by the total contaminated area of 124.8 m2. When entering a deterministic value, for which a probability distribution is developed, the most conservative dose is derived using the mean, median, or most likely value (for the triangular distribution) in the parameter distribution. Therefore, the area of Source 1 is the most likely value of triangular distribution, section A.1.3 Room area of NUREG/CR-6755. The area of source 2, 3, 4, 5 is calculated by multiplying the square root of 36 which is the most likely value of triangular distribution, NUREG/CR-6755 section A.1.3 Room Area and 3.7 that is most likely value of triangular distribution, NUREG/CR-6755 section A.1.4 Room Height [3].

With regard to the area and height of the room, the room size was set to the median value of the distribution in the RESRAD-BUILD code (based on NUREG/CR-5512, Vol. 1 [4]) and fixed at an area of 64 m² and height of 3 m. We assumed that the variation of the structure was large; therefore, we input it as a distribution.

The radionuclides for calculating DCGL were selected from the radionuclides detected both at the Zion NPP and Rancho Seco NPP, which was selected as a reference NPP. Table 1 shows the radionuclides used in this study.

372

2019 ⦽ǎႊᔍᖒ⠱ʑྜྷ⦺⫭⇹ĥ⦺ᚁݡ⫭םྙ᫵᧞Ḳ Table 1. Radionuclides detected in Rancho Seco and Zion NPP buildings [5, 6]

4. DCGL Calculation

To derive the DCGL, it was assumed that there was a large variation in the size of the indoor structure that will be left on the Kori Unit 1 site. Additionally, the assigned value of the room height and room area were selected and calculated conservatively. With regard to the deposition rate, receptor breathing rate, and source life, the value was assigned in order to provide consistency during the calculation process.

Table 2. DCGL according to scenario (dpm/100cm2) Radio-nuclides 0.1 mSv/yr Radio-nuclides 0.1 mSv/yr 3 H 1.33×108 137Cs 2.26×104 14 C 3.64×106 152Eu 1.31×104 55 Fe 1.39×107 154Eu 1.20×104 59 Ni 3.18×107 155Eu 2.28×105 60_{Co 6.17×10}3 237_{Np 1.17×10}3 63 Ni 1.32×107 238Pu 1.67×103 90 Sr 3.72×104 239Pu 1.49×103 94 Nb 9.52×103 240Pu 1.49×103 99 Tc 5.32×106 241Pu 8.06×104 108m_{Ag 9.09×10}3 241_{Am 1.46×10}3 125 Sb 3.34×104 244Cm 2.41×103 134 Cs 9.00×103

The scenario 1 is on-site building worker scenario and scenario 2 is containment building worker scenario.

Table 3. Comparison of DCGLs (dpm/100cm2)

Radio-nuclides Scenario1 Scenario2

Radio-nuclides Scenario1 Scenario2

3_{H 1.33×10}8 _1.70×108 137_{Cs 2.26×10}4 _2.18×103 14_{C 3.64×10}6 _8.13×105 152_{Eu 1.31×10}4 _1.49×103 55 Fe 1.39×107 7.84×107 154Eu 1.20×104 1.87×103 59_{Ni 3.18×10}7 _8.06×106 155_{Eu 2.28×10}5 _6.77×106 60_{Co 6.17×10}3 _1.65×103 237_{Np 1.17×10}3 _3.67×102 63_{Ni 1.32×10}7 _3.22×106 238_{Pu 1.67×10}3 _5.79×102 90_{Sr 3.72×10}4 _1.45×104 239_{Pu 1.49×10}3 _4.70×102 94_{Nb 9.52×10}3 _5.55×102 240_{Pu 1.49×10}3 _4.73×102 99 Tc 5.32×106 1.16×106 241Pu 8.06×104 1.80×104 108m_{Ag 9.09×10}3 _6.72×102 241_{Am 1.46×10}3 _4.67×102 125_{Sb 3.34×10}4 _7.27×104 244_{Cm 2.41×10}3 _1.35×103 134_{Cs 9.00×10}3 _4.62×104

5. Conclusion

In this study, DCGL is derived through the probabilistic analysis of the RESRAD-BUILD code. Deterministic and probabilistic parameters that reflect the characteristics of Kori Unit 1 are applied then sensitivity analysis are performed for the scenario. Through this process, we derived the Kori Unit 1 preliminary DCGL.

The DCGL of Containment building worker scenario (scenario 2) is lower than on-site building worker scenario (scenario 1) except 134Cs, 155Eu.

Scenario 2 shows a lower DCGL than scenario 1 because of receptor location, source location, source area and other parameter difference. Additional research is needed to determine why the DCGL values of 134Cs and 155Eu are higher.

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[6] Sacramento Municipal Utility District, DTBD-05- ³5DQFKR 6HFR 1XFOHDU *HQHUDWLQJ 6WDWLRQ Decommissioning Technical Basis Document, &RQWDLQPHQW%XLOGLQJV'&*/V´ Radionuclide 3 H 90Sr 137Cs 239Pu 14 C 94Nb 152Eu 240Pu 55 Fe 99Tc 154Eu 241Pu 59 Ni 108mAg 155Eu 241Am 60 Co 125Sb 237Np 244Cm 63_Ni 134_Cs 238_Pu