A Backward Method to Estimate the Dai-ichi Reactor Core Damage Using Radiation Exposure in the Environment

The Fukushima accident resulted in the melting of the reactor core due to loss of supply of coolant when the reactor stopped from operating conditions. The earthquake and tsunami caused loss of electricity due to the flooding that occurred in the reactor. The absence of the coolant supply after reactor shutdown resulted in heat accumulation, causing the temperature of the fuel to rise beyond its melting point. In the early stages of the accident, operator could not determine the severity of the accident and the percentage of the reactor core damaged. The available data was based on the radiation exposure in the environment that was reported by the authorities. The aim of this paper is to determine the severity of the conditions in the reactor core based on the radiation doses measured in the environment. The method is performed by backward counting based on the measuring radiation exposure and radionuclides releases source term. The calculation was performed by using the PC-COSYMA code. The results showed that the core damage fraction at Dai-ichi Unit 1 was 70%, and the resulting individual effective dose in the exclusion area is 401 mSv, while the core damage fraction at Unit 2 was 30%, and the resulting individual effective dose was 99.1 mSv, while for Unit 3, the core damage fraction was 25% for an individual effective dose of 92.2 mSv. The differences between the results of the calculation for estimation of core damage proposed in this paper with the previously reported results is probably caused by the applied model for assessment, differences in postulations and assumptions, and the incompleteness of the input data. This difference could be reduced by performing calculations and simulations for more varied assumptions and postulations.Received: 30 October 2015 ; Revised: 29 March 2016; Accepted: 31 March 201

Estimation Of Routine Discharge Of Radionuclides On Power Reactor Experimental RDE

Experimental power reactor (RDE) which is planned to be constructed by BATAN is a kind of High Temperature Gas Cooled Reactor (HTGR) with 10 MWth power. HTGR is a helium gas-cooled reactor with TRISO-coated fuel that is able to confine fission products remained in the core. Although the fission products released into the environment are very small, in order to comply the regulations the study about environmental radiation on normal or routine operation condition need to be performed. Estimation of radiology in the environment involves the source term released into the environment under routine operation condition. The purpose of this study is to estimate the source term released into the environment based on postulation of normal or routine operations of RDE. The research approach starts with an assumption that there are defects and impurities in the TRISO fuel because of limitation during the fabrication. Mechanism of fission products release from the fuel to the environment was created based on the safety features design of RDE. Radionuclides inventories in the reactor were calculated using ORIGEN-2 whose library has been modified for HTGR type, and the assumptions of defects of the TRISO fuel and release fraction for each compartment of RDE safety system used a reference parameter. The results showed that the important source terms of RDE are group of noble gases (Kr and Xe), halogen (I), Sr, Cs, H-3, and Ag. Activities of RDE source terms for routine operations have no significant difference with the HTGR source terms with the same power.Keywords: routine discharge, radionuclide, source term, RDE, HTG

Atmospheric Dispersion Analysis for Expected Radiation Dose due to Normal Operation of RSG-GAS and RDE Reactors

BATAN is planning to build an experimental power reactor, the RDE, to complement the RSG-GAS reactor that is already operating in the Serpong Nuclear Zone (KNS). The experimental power reactor is an HTGR (high-temperature gas-cooled reactor) with 10 MWt power, while the RSG-GAS is a pool-type water-cooled reactor with 30 MWt power. According to standard regulatory practices, under normal operating conditions of the plant, radiological assessment of atmospheric releases to the environment and assessment of public exposures are considered essential. The purpose of this study is to estimate the dose acceptance in Serpong Nuclear Zone (KNS) after operate the RDE operates in KNS-2. To assess the doses, the PC-CREAM 08 computer code was used. It uses a standard Gaussian plume dispersion model and composes a suite of models and data for estimation of the radiological impact assessments of routine and continual discharges from a nuclear reactor. The input data include sourceterm from the RDE and the RSG-GAS, a stack the height of 60 m annual radionuclides release, meteorological data from the Serpong local meteorological station, and agricultural products data from Serpong site. Results show that the highest individual dose in the area around KNS for adults is 6.16×10-3 mSv/y in the S (South) direction and 300 m distance from the stack of RSG. The highest collective dose around KNS within 3 km radius is 6.37×10-3 man-Sv/yr. The results show that the radiological impact of the KNS on the critical groups of public and the individual effective doses satisfy the limits given by the Nuclear Regulatory Agency of Indonesia (BAPETEN). The operation of RDE in KNS-2 does not add significantly to acceptance radiation dose in the environment in KNS. It can also be concluded that the estimated effective doses are lower than the dose constraint of 0.3 mSv/y associated with this plant

A Backward method to estimate the dai-ichi reactor core damage using radiation exposure in the environment

The fukushima accident resulted in the melting of the reactor core due to loss of supply of coolant when the reactor stopped from operating conditions. the earthquake and tsunami causesd loss of electricity due to the flooding that occured in the reactor. the absence of the coolant supply afer reactor shutdown resulted in heat accumulation,causing the temperature of the fuel to rise beyond its melting point. in the early stages of the accident,operator could not determine the severity of the accident and the percentage of the reactor core damaged. the available data was based on the radiation exposure in the environment that was reported by the authorities. the aim of this paper is to determine the severity of the conditions in the reactor core based on the radition doses measured in the environmet. the method is performed by backward counting based on the measuring radiation exposure and radionuclides releases source term. the calculation was performed by using the PC-COSYMA code. the results showed that the core damage fraction at Dai-ichi unit 1 was 70%,and the resulting individual effective dose in the exclusion area is 401 mSv,while the core damage fraction at unit 2 was 30%,and the resulting individual effective dose was 99.1 mSv,while for unit 3,the core damage fraction 25% for an individual effective dose of 92.2 mSv. the differences between the results of the calculation for estimation of core damage proposed in this paper with the previously reported result is probably caused by the applied model for assessment,differences in postulations and assumptions,and the incompleteness of the input data. this defference could be reduced by performing calculations and simulations for more varied assumptions and postulations