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Reduction factors for wooden houses due to external γ-radiation based on in situ measurements after the Fukushima nuclear accident.

Yoshida-Ohuchi H, Hosoda M, Kanagami T, Uegaki M, Tashima H - Sci Rep (2014)

Bottom Line: The results indicated no statistically significant difference in the median reduction factor to the representative value of 0.4 given in the International Atomic Energy Agency (IAEA)-TECDOC-225 and 1162.However, with regard to the representative range of the reduction factor, we recommend the wider range of 0.2 to 0.7 or at least 0.2 to 0.6, which covered 87.7% and 80.7% of the data, respectively, rather than 0.2 to 0.5 given in the IAEA document, which covered only 66.5% of the data.We found that the location of the room within the house and area topography, and the use of cement roof tiles had the greatest influence on the reduction factor.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3 Aramaki-Aoba, Aoba-ku, Sendai, Miyagi 980-8578, Japan.

ABSTRACT
For estimation of residents' exposure dose after a nuclear accident, the reduction factor, which is the ratio of the indoor dose to the outdoor dose is essential, as most individuals spend a large portion of their time indoors. After the Fukushima nuclear accident, we evaluated the median reduction factor with an interquartile range of 0.43 (0.34-0.53) based on 522 survey results for 69 detached wooden houses in two evacuation zones, Iitate village and Odaka district. The results indicated no statistically significant difference in the median reduction factor to the representative value of 0.4 given in the International Atomic Energy Agency (IAEA)-TECDOC-225 and 1162. However, with regard to the representative range of the reduction factor, we recommend the wider range of 0.2 to 0.7 or at least 0.2 to 0.6, which covered 87.7% and 80.7% of the data, respectively, rather than 0.2 to 0.5 given in the IAEA document, which covered only 66.5% of the data. We found that the location of the room within the house and area topography, and the use of cement roof tiles had the greatest influence on the reduction factor.

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Related in: MedlinePlus

Map of the measurement locations and evacuation zones.The size of the blue, closed circles depends on the number of houses investigated at each location. The map was created using Microsoft Power Point software (version 14.4.5).
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f1: Map of the measurement locations and evacuation zones.The size of the blue, closed circles depends on the number of houses investigated at each location. The map was created using Microsoft Power Point software (version 14.4.5).

Mentions: The Great East Japan Earthquake of magnitude 9.0 and the tsunami on 11 March 2011 resulted in major damage to the Fukushima Daiichi nuclear power plant (FDNPP). Following plural hydrogen explosions, a large amount of radioactive material was released into the environment and moved as a radioactive plume with the wind1234. On 15 March, rain began to fall and turned to sleet and snow. Due to the wind direction and the rainfall, large amounts of radionuclides were deposited northwest of the FDNPP5. On 12 March, the Japanese government designated the 20-km radius around the FDNPP as a restricted area, and the residents within a radius of 20 to 30 km were ordered to “stay in house”. The “stay-in-house” area was changed to the “deliberate evacuation area” on 22 April1. By 8 August 2013, these areas to which evacuation orders were issued were rearranged into three areas responding to the annual cumulative dose, as shown in Fig. 1. Areas 1, 2 and 3 were those to which the evacuation orders were ready to be lifted, in which the residents were not permitted to live, and where it is expected that the residents will have difficulty returning for a long time, respectively6. Nearly 80,000 people, including 6,000 from Iitate village and 13,000 from Odaka district, are still taking refuge6. At present, external exposure to radionuclides which were deposited in the environment is the dominant contribution to whole-body dose to the public. To estimate the exposure dose and/or the cumulative dose properly is required for the government or the local government to determine the area to be decontaminated and is necessary for residents to plan temporary access to the area. To estimate the annual cumulative dose, the reduction factor, which is the ratio of the indoor dose to the outdoor dose, is essential, as most individuals spend a large portion of their time indoors. Shielding due to house materials and structures can reduce the dose from external penetrating gamma radiation. Most of the houses in the evacuation zone are made of wood and are one- or two-story structures. Wooden houses offer less protection than do reinforced concrete buildings due to the light outer walls. The shielding factor is sometimes used and has the same meaning and definition as the reduction factor7. Both factors include not only the shielding effect by house materials and structures, but also the effect from the ground right under the building, which is not contaminated by artificial radionuclides. Thus, the term reduction factor is used in this paper instead of the shielding factor.


Reduction factors for wooden houses due to external γ-radiation based on in situ measurements after the Fukushima nuclear accident.

Yoshida-Ohuchi H, Hosoda M, Kanagami T, Uegaki M, Tashima H - Sci Rep (2014)

Map of the measurement locations and evacuation zones.The size of the blue, closed circles depends on the number of houses investigated at each location. The map was created using Microsoft Power Point software (version 14.4.5).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4269877&req=5

f1: Map of the measurement locations and evacuation zones.The size of the blue, closed circles depends on the number of houses investigated at each location. The map was created using Microsoft Power Point software (version 14.4.5).
Mentions: The Great East Japan Earthquake of magnitude 9.0 and the tsunami on 11 March 2011 resulted in major damage to the Fukushima Daiichi nuclear power plant (FDNPP). Following plural hydrogen explosions, a large amount of radioactive material was released into the environment and moved as a radioactive plume with the wind1234. On 15 March, rain began to fall and turned to sleet and snow. Due to the wind direction and the rainfall, large amounts of radionuclides were deposited northwest of the FDNPP5. On 12 March, the Japanese government designated the 20-km radius around the FDNPP as a restricted area, and the residents within a radius of 20 to 30 km were ordered to “stay in house”. The “stay-in-house” area was changed to the “deliberate evacuation area” on 22 April1. By 8 August 2013, these areas to which evacuation orders were issued were rearranged into three areas responding to the annual cumulative dose, as shown in Fig. 1. Areas 1, 2 and 3 were those to which the evacuation orders were ready to be lifted, in which the residents were not permitted to live, and where it is expected that the residents will have difficulty returning for a long time, respectively6. Nearly 80,000 people, including 6,000 from Iitate village and 13,000 from Odaka district, are still taking refuge6. At present, external exposure to radionuclides which were deposited in the environment is the dominant contribution to whole-body dose to the public. To estimate the exposure dose and/or the cumulative dose properly is required for the government or the local government to determine the area to be decontaminated and is necessary for residents to plan temporary access to the area. To estimate the annual cumulative dose, the reduction factor, which is the ratio of the indoor dose to the outdoor dose, is essential, as most individuals spend a large portion of their time indoors. Shielding due to house materials and structures can reduce the dose from external penetrating gamma radiation. Most of the houses in the evacuation zone are made of wood and are one- or two-story structures. Wooden houses offer less protection than do reinforced concrete buildings due to the light outer walls. The shielding factor is sometimes used and has the same meaning and definition as the reduction factor7. Both factors include not only the shielding effect by house materials and structures, but also the effect from the ground right under the building, which is not contaminated by artificial radionuclides. Thus, the term reduction factor is used in this paper instead of the shielding factor.

Bottom Line: The results indicated no statistically significant difference in the median reduction factor to the representative value of 0.4 given in the International Atomic Energy Agency (IAEA)-TECDOC-225 and 1162.However, with regard to the representative range of the reduction factor, we recommend the wider range of 0.2 to 0.7 or at least 0.2 to 0.6, which covered 87.7% and 80.7% of the data, respectively, rather than 0.2 to 0.5 given in the IAEA document, which covered only 66.5% of the data.We found that the location of the room within the house and area topography, and the use of cement roof tiles had the greatest influence on the reduction factor.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3 Aramaki-Aoba, Aoba-ku, Sendai, Miyagi 980-8578, Japan.

ABSTRACT
For estimation of residents' exposure dose after a nuclear accident, the reduction factor, which is the ratio of the indoor dose to the outdoor dose is essential, as most individuals spend a large portion of their time indoors. After the Fukushima nuclear accident, we evaluated the median reduction factor with an interquartile range of 0.43 (0.34-0.53) based on 522 survey results for 69 detached wooden houses in two evacuation zones, Iitate village and Odaka district. The results indicated no statistically significant difference in the median reduction factor to the representative value of 0.4 given in the International Atomic Energy Agency (IAEA)-TECDOC-225 and 1162. However, with regard to the representative range of the reduction factor, we recommend the wider range of 0.2 to 0.7 or at least 0.2 to 0.6, which covered 87.7% and 80.7% of the data, respectively, rather than 0.2 to 0.5 given in the IAEA document, which covered only 66.5% of the data. We found that the location of the room within the house and area topography, and the use of cement roof tiles had the greatest influence on the reduction factor.

Show MeSH
Related in: MedlinePlus