• Journal of Radiation Protection and Research
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• v.36 no.3
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• pp.154-159
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• 2011

To evaluate the radiation exposure of workers participating in task where high radiation exposure is expected, two-dosimeter is typically provided radiation workers, one on the chest and the other on the back, at Korean nuclear power plants (NPPs). In a previous study, the NCRP (55:50) algorithm was selected as the optimal two-dosimeter algorithm (TDA) with various field tests and this TDA has been applied to all Korean NPPs since 2006. In 2007, the International Commission on Radiological Protection (ICRP) published the new ICRP recommendation, ICRP 103, which provides the revised weighting factors for both radiation and tissues and the new reference phantom. In this study, the applicability of current NCRP (55:50) algorithm at Korean NPPs for ICRP 103 was analyzed. As a result, it was found that the NCRP (55:50) algorithm is still effective to estimate the effective dose of workers under ICRP 103.

• Journal of Radiation Protection and Research
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• v.33 no.4
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• pp.151-160
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• 2008

In Korean nuclear power plants (NPPs), two thermoluminescent dosimeters (TLD) were provided to workers who work in an inhomogeneous radiation field; one on the chest and the other on the head. In this way, the effective dose for radiation workers at NPPs was determined by the high deep dose between two radiation dose from these TLDs. This represented a conservative method of evaluating the degree of exposure to radiation. In this study, to prevent the overestimation of the effective dose, field application experiments were implemented using two-dosimeter algorithms developed by several international institutes for the selection of an optimal algorithm. The algorithms used by the Canadian Ontario Power Generation (OPG) and American ANSI HPS N13.41, NCRP (55/50), NCRP (70/30), EPRI (NRC), Lakslumanan, and Kim (Texas A&M University) were extensively analyzed as two-dosimeter algorithms. In particular, three additional TLDs were provided to radiation workers who wore them on the head, chest, and back during maintenance periods, and the measured value were analyzed. The results found no significant differences among the calculated effective doses, apart from Lakshmanan's algorithm. Thus, this paper recommends the NCRP(55/50) algorithm as an optimal two-dosimeter algorithm in consideration of the solid technical background of NCRP and the convenience of radiation works. In addition, it was determined that a two-dosimeter is provided to a single task which is expected to produce a dose rate of more than 1 mSv/hr, a difference of dose rates depending on specific parts of the body of more than 30%, and an exposure dose of more than 2 mSv.

• Journal of Radiation Protection and Research
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• v.34 no.4
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• pp.165-169
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• 2009

Two dosimeters are provided to radiation workers participating in tasks where high radiation exposure is expected during maintenance at nuclear power plants. At Korean nuclear power plants, two dosimeters are currently provided for tasks where exposure rates exceed 1 mSv/hr, the difference of equivalent dose to specific parts of the body is more than 30% and an exposure of more than 2 mSv is expected in a single task. These conditions for the provisioning of two dosimeters are based on previous field test results, and it is recommended that the dosimeters be worn on the chest and back. It was also found that the workers felt it was more convenient when they wore two dosimeters on chest and back rather than on chest and head. After the application of previous field test results to practice, it was found that the calculated effective dose for workers during radiation work was lower than the maximum dose of chest or back dosimeter by approximately 10%-30%. This performance is regarded not only to meet the international guideline but also to provide convenience for workers during radiation work.

• Proceedings of the Korean Nuclear Society Conference
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• 2005.10a
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• pp.830-831
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• 2005

• Journal of Radiation Protection and Research
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• v.34 no.4
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• pp.176-183
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• 2009

Maintenance on the water chamber of steam generator during outage in nuclear power plants (NPPs) has a likelihood of high radiation exposure to whole body of workers even short time period due to the high radiation exposure rates. In particular, it is expected that hands would receive the highest radiation exposure because of its contact with radiation materials. In this study, characteristic analysis of inhomogeneous radiation fields for contact operations was conducted using thermoluminescent dosimeter (TLD) readouts from the application tests of two-dosimeter algorithm to Korean NPPs in 2004. It is regarded that inhomogeneous radiation fields for contact operations in NPPs are dominated by high energy photons. In addition, field tests for workers who participated in maintenance on the steam generator during outage at Ulchin NPPs in 2009 and pressure tube replacement at Wolsong NPPs in 2009 were conducted to analyze radiation fields and to estimate the extremity dose. As a result, radiation fields were dominated by high energy photons.

• Journal of Radiation Protection and Research
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• v.23 no.3
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• pp.159-174
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• 1998

Personal dosimetry system is required to measure the personal dose equivalent accurately in a wide range of radiation fields, but the dose evaluation algorithms have been developed with the X-ray fields described in MOST Ordinance (equivalent to the ANSI N13.11) from which the actual fields to be monitored may be significantly different. To evaluate the dose more accurately when workers are exposed to the non-ANSI N13.11 radiation fields, two algorithms for monochromatic radiations (one algorithm was used for various ratios of TL dosimeter and the other for matrix approximation) were developed with the experimental data of the energy responses of the $CaSO_4:Dy$ TL materials irradiated by monochromatic X-ray fields recently established in KAERI, and compared with the another algorithm developed on the basis of the ANSI N13.11 continuous spectrum X-ray fields. Then it follows the discussions for some results of the algorithm testing including mixed fields irradiations and angular response conducted in IAEA/RCA intercomparison as well as ANSI and ISO continuous spectrum X-ray and monochromatic radiation fields. The developed algorithms were successfully performed the test not only in the continuous spectrum X-ray fields given by MOST Ordinance but also in the several non-MOST Ordinance radiation fields which could be encountered in the practical working environments.

• The Journal of Korean Society for Radiation Therapy
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• v.25 no.1
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• pp.15-24
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• 2013

Purpose: In Asan Medical Center, Two parallel opposite beams are employed for total body irradiation. Patients are required to be in supine position where two arms are attached to mid axillary line. Normally, physical compensators are required to compensate the large dose difference for different parts of body due to the different thicknesses compared to the umbilicus separation. There was the maximum dose difference up to 30% in lung and chest wall compared to the prescription dose. In order to resolve the dose discrepancy occurring on different body regions, the feasibility of using Fieid-in-Field Technique is investigated in this study. Materials and Methods: CT scan was performed to The RANDO Phantom with fabricated two arms and sent to Eclipse treatment planning system (version 10.0, Varian, USA). Conventional plan with physical lead compensator and new plan using Field-in-Field Technique were established on TPS. AAA (Anisotropic Analytical Algorithm) dose calculation algorithm was employed for two parallel opposite beams attenuation. Results: The dose difference between two methods was compared with the prescription dose. The dose distribution of chest and anterior chest wall uncovered by patient arms was 114~124% for physical lead compensator while Field-in-Field Technique gave 106~107% of the dose distribution. In-vivo dosimetry result using TLD showed that the dose distribution to the same region was 110~117% for conventional physical compensator and 104~107% for Field-in-Field Technique. Conclusion: In this study, the feasibility of using FIF technique has been investigated with fabricated arms attached Rando phantom. The dose difference was up to 17% due to the attached arms. It is shown that the dose homogeneity is within ${\pm}10%$ with the CT based 3-dimensional 4 step FIF technique. The in-vivo dosimetry result using TLD was showed that 95~107% dose distribution compared to prescription dose. It is considered that CT based 3-dimensional Field-in-Field Technique for the total body irradiation gives much homogeneous dose distribution for different body parts than the conventional physical compensator method and might be useful to evaluate the dose on each part of patient body.