High-radiation-exposure tasks in Korean pressurized heavy-water reactors.

This study analysed the occupational dose in Korean pressurized heavy-water reactors (PHWRs) and identified tasks involving high radiation exposure. The average individual dose was sufficiently low to be below the annual effective dose limit for radiation workers and is even lower than the dose limit for the general public. However, some workers received relatively higher doses than others. Furthermore, most PHWR workers are exposed to radiation during planned maintenance periods. In this study, the radiation dose was normalized (radiation dose per unit time) to determine the high-radiation-exposure tasks in Korean PHWRs. Consequently, end-fitting lapping, delayed neutron tube work and fuel channel fixed-end change tasks were identified as high-radiation-exposure tasks in Korean PHWRs. If appropriate radiation protection measures are prioritized for the identified high-dose exposure tasks, optimization of radiological protection will be effectively achieved by reducing the dose that is relatively higher than the average.

Applicability test of methods for discrimination between external and internal contamination using an ORTEC whole body counter.

Whole-body counters (WBCs) are generally used for monitoring internal radioactive contamination of radiation workers in nuclear power plants. However, it has been found that external contamination is occasionally counted as internal contamination. The previous study was conducted to provide guidance on measuring the exact internal radioactivity using a Canberra WBC. However, there is strong need to verify the application of the previous study to whole-body counting using a different type of WBC, ORTEC StandFAST II. Thus, in this study, several experiments were conducted focusing on the discrimination between external and internal contamination. Finally, it was found that counts from the front and back are still effective to distinguish external contamination from internal contamination for whole-body counting.

Radiological effluents released and public doses from nuclear power plants in Korea.

As of the end of 2010, there were 20 commercially operating nuclear reactors in Korea. Releases of radioactive effluents from nuclear power plants (NPPs) have increased continuously; the total radioactivity of effluent amount released in 2010 was 547.12 TBq. From 2001 to 2010, the annual average radioactivity of gaseous and liquid effluents per reactor was 11.61 TBq for pressurised water reactors and 118.12 TBq for pressurised heavy water reactors. Most of the radioactivity from gaseous and liquid effluents came from tritium. Based on the results of release trends and analyses, the characteristics of effluents have been investigated to improve the management of radioactive effluents from NPPs.

A A field test for extremity dose assessment during outages at Korean nuclear power plants.

During maintenance on the water chamber of a steam generator, the pressuriser heater and the pressure tube feeder in nuclear power plants, workers are likely to receive high radiation doses due to the severe workplace conditions. In particular, it is expected that workers' hands would receive the highest radiation doses because of their contact with the radioactive materials. In this study, field tests for extremity dose assessments in radiation workers undertaking contact tasks with high radiation doses were conducted during outages at pressurised water reactors and pressurised heavy water reactors in Korea. In the test, the radiation workers were required to wear additional thermoluminescent dosemeters (TLDs) on their backs and wrists and an extremity dosemeter on the finger, as well as a main TLD on the chest while performing the maintenance tasks.

Dosimetry experiences and lessons learned for radiation dose assessment in Korean nuclear power plants.

Since the first Korean nuclear power plant (NPP), Kori 1, commenced operation in 1978, a total of 21 NPPs had been put into operation in Korea by the end of 2011. Radiation doses of NPP workers have been periodically evaluated and controlled within the prescribed dose limit. Radiation dose assessment is carried out monthly by reading personal dosemeters for external radiation exposure, which have traceability in compliance with strict technical guidelines. In the case of the internal radiation exposure, workers who have access to the possible area of polluted air are also evaluated for their internal dose after maintenance task. In this article, the overall situation and experience for the assessment and distribution of radiation doses in Korean NPPs is described.

An analysis of the radiation field characteristics for extremity dose assessment during maintenance periods at nuclear power plants in Korea.

Workers who maintain the water chambers of steam generators during maintenance periods in nuclear power plants (NPPs) have a higher likelihood of high radiation exposure, even if they are exposed for a short period of time. In particular, it is expected that the hands of workers would receive the highest radiation exposure as a consequence of hand contact with radioactive materials. In this study, a characteristic analysis of inhomogeneous radiation fields for contact operations was conducted using thermoluminescent dosemeters for the whole body and extremities during maintenance periods at Korean NPPs. It was observed that inhomogeneous radiation fields for contact operations at NPPs were dominated by high-energy photons.

An analysis of workers' tritium concentration in urine samples as a function of time after intake at Korean pressurised heavy water reactors.

In general, internal exposure from tritium at pressurised heavy water reactors (PHWRs) accounts for ∼20-40 % of the total radiation dose. Tritium usually reaches the equilibrium concentration after a few hours inside the body and is then excreted from the body with an effective half-life in the order of 10 d. In this study, tritium metabolism was reviewed using its excretion rate in urine samples of workers at Korean PHWRs. The tritium concentration in workers' urine samples was also measured as a function of time after intake. On the basis of the monitoring results, changes in the tritium concentration inside the body were then analysed.

A bioassay experience and lessons learned on the internal contamination of (131)I during a maintenance period in a Korean nuclear power plant.

During a maintenance period at a Korean nuclear power plant, internal exposure of radiation workers occurred by the inhalation of (131)I that was released into the reactor building from a primary system opening due to defective fuels. The internal activity in radiation workers contaminated by (131)I was immediately measured using a whole body counter (WBC). A whole body counting was performed again a few days later, considering the factors of equilibrium in the body. The intake and the committed effective dose were estimated based on the WBC results. The intake was also calculated by hand, based on both the entrance records to the reactor building, and the counted results of the air concentration for (131)I were compared with the whole body counting results.

Radiation fields and dose assessments in Korean nuclear power plants.

In the primary systems of nuclear power plants (NPPs), various radionuclides including fission products and corrosion products are generated due to the complex water chemistry conditions. In particular, (3)H, (14)C, (58)Co, (60)Co, (137)Cs, and (131)I are important or potential radionuclides with respect to dose assessment for workers and the management of radioactive effluents or dose assessment for the public. In this paper, the dominant contributors to the dose for workers and the public were reviewed and the process of dose assessment attributable to those contributors was investigated. Furthermore, an analysis was carried out on some examples of dose to workers during NPP operation.

Selection of the most appropriate two-dosemeter algorithm for estimating effective dose equivalent during maintenance periods in Korean nuclear power plants.

The application of a two-dosemeter system with its algorithm, as well as a test of its use in an inhomogeneous high-radiation field, is described in this study. The goal was to improve the method for estimating the effective dose equivalent during maintenance periods at Korean Nuclear Power Plants (NPPs). The use of this method in Korean and international NPPs, including those NPPs in the USA and Canada, was also investigated. The algorithms used by the the American National Standards Institute, Lakshmanan, the National Council on Radiation Protection and Measurements (NCRP), the Electric Power Research Institute and Kim were extensively analysed as two-dosemeter algorithms. Their possible application to NPPs was evaluated using data for each algorithm from two-dosemeter results that were obtained from an inhomogeneous high-radiation field during maintenance periods at Korean NPPs. The NCRP algorithm (55:50) was selected as an optimal two-dosemeter algorithm for Korean NPPs by taking into account the field test results and the convenience of wearing two dosemeters.

Application of an improved in vivo counting program to Korean nuclear power plants.

During the in vivo counting of individuals using a whole body counter at nuclear power plants (NPPs), external skin contamination is occasionally mistaken for internal radioactive contamination. This not only confuses the degree of external contamination and internal contamination, but can also result in the excessively conservative estimation of radioactive contamination. In this paper, previous experiments to improve in vivo counting at NPPs are introduced briefly and the practical application of techniques presented in those experiments to Korean NPPs is demonstrated in detail.

Application and experience of a two-dosimeter algorithm for better estimation of effective dose during maintenance periods at Korea nuclear power plants.

The application of a two-dosimeter and its algorithm and a test of its use in an inhomogeneous high radiation field are described. The goal was to develop an improved method for estimating the effective dose during maintenance periods at Korean nuclear power plants (NPPs). The application and experience to KNPPs was evaluated using data for each algorithm from two-dosimeter results for an inhomogeneous high radiation field during maintenance periods at Korean NPPs.

Improvement to whole-body counting procedures at nuclear power plants.

A whole-body counter (WBC) is a device employed in nuclear power plants (NPPs) to identify radionuclides and measure the content of radioactivity in humans. In this study, several experiments were conducted to suggest an optimal and practical method to improve the accuracy of in vivo measurements using WBCs at NPPs. First, countings from the front and back using a phantom were carried out to set up a discrimination programme between internal and external radioactive contamination in NPPs. Second, experiments were performed to select the optimal geometry of the WBC and to locate the contaminated area of radionuclides.