H. "Yamanishi

H. Hirabayashi

H. Nakatsuka

H. Nakayoshi

H. Obayashi

K." Achiwa

N. Tsuji

T. Uda

Y. Sakuma

National Institute for Fusion Science (NIFS-Repository)

§6. Effect of Humidity on Radon Exhalation Rate from Concrete Yamanishi, H., Obayashi, H., Sakuma, Y ., Uda, T., Hirabayashi, H. Nakatsuka, H., Tsuji, N., Nakayoshi, H., Achiwa, K. (Japan Air-conditioning Service Co. LTD.) The experimental hall for nuclear fusion experiments is required to keep airtight in order not to leak airborne radioactivities which are induced by neutrons. It is necessary to monitor air change rate and air quality in that room. Tracer gas methods are generally applied for measuring method of air change rate. We have investigated measuring method of air change rate using radon 222 ( Rn) as a tracer gas. In order to get to the goal, it is necessary to evaluate factors of time variation of radon exhalation rate. The objective of the present study is evaluation of seasonal humidity effect on radon exhalation rate from concrete. Figure 1 shows the system of controlled humidity environment. Three sealed boxes are placed in a container whose temperature is controlled 30 oC. The three fixed humidities are selected 3, 10, 25 g m-3 in absolute humidity, those correspond to dry condition as control, winter and summer, respectively. In each box, a concrete piece (No.2, No.3 and No.4) whose size is 15 em diameter and 5 em thickness has been set. Radon exhalation rate from each concrete piece is measured every one month during this humidity exposure. No.2 sample has been exposed to dry circumstance. No.3 and No.4 have been set low humidity and high humidity, respectively. After 500 days exposure, No.4 sample was moved to low humidity place. Figure 2 shows the results, measured water content (W) and radon exhalation rate (E) are plotted with elapsed time. W and E are increased with elapsed time. In the high humidity, they are increased up to 2.4 % and 0.43 mBq m-2 s-1, respectively. In the low humidity environment, they are saturated early period and increased up to 0.88% and 0.13 mBq m-2 s- 1, respectively. It takes 80 days for low humidity, 180 days for high humidity to saturate these value. After saturation of W, E follows the variation of water content. W and E of No.4 sample are decreased to 1.65% and 0.25 mBq m-2 s- 1 after placed low humidity. Sealed box Fig. 1 Humidity exposure system -c 2 c: Q) c: 1.5 0 (J 11-Q) n; 3: 0.5 100 200 300 400 500 Elapsed time (day) 3 g /mA3 High Humidity (-summer) R.H . 90% A. H. 25 g /m/\3 JJ OJ 0.4 a. _o 3 ::J m <D 0.3 .c ~ 3, ~ 0.2 1/)N:::!; • 0 ~::J 0.1 i» co Fig. 2 Rn exhalation rate and water content 285 

Effect of Humidity on Radon Exhalation Rate from Concrete

Effect of Humidity on Radon Exhalation Rate from Concrete

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