[en] This paper describes the numerical simulations of a decay tank, which will be utilized in KIJANG Research Reactor (KJRR) project. In the research reactor, the heat generated in the core is removed by primary cooling system (PCS), thus primary coolants contain many kinds of radioactive nuclides. N-16 comprises a majority of radiation level for PCS due to the generation of high strength γ-rays. Since the half-life of N-16 is 7.13 seconds, the radiation level could be decreased by installing the decay tank at the core outlet pipe of PCS. The N-16 activity is decreased by the sufficient flow residence time in the decay tank. The residence time distribution at outlet boundary is shown at Fig. 2. The increased time is about 6.0 seconds from the time distribution, so N-16 activity is reduced about 45%. This result is consistent with the preliminary calculation. The numerical simulations were conducted with a commercial program, ANSYS-CFX. More accurate and elaborate flow simulation will be performed with hexahedral meshes to enhance the resolution of unsteady flow phenomena. Furthermore, Fluid Structure Interaction (FSI) simulation will be also conducted to assess the structural safety analysis on decay tank

[en] Here we review the evolutionary history of radiation therapy technology through the festschrift of articles in celebration of the 30th anniversary of Korean Society of Medical Physics (KSMP). Radiation therapy technology used in clinical practice has evolved over a long period of time. Various areas of science, such as medical physics, mechanical engineering, and computer engineering, have contributed to the continual development of new devices and techniques. The scope of this review was restricted to two areas; i.e., output energy production and functional development, because it is not possible to include all development processes of this technology due to space limitations. The former includes the technological transition process from the initial technique applied to the first model to the latest technique currently used in a variety of machines. The latter has had a direct effect on treatment outcomes and safety, which changed the paradigm of radiation therapy, leading to new guidelines on dose prescriptions, innovation of dose verification tools, new measurement methods and calculation systems for radiation doses, changes in the criteria for errors, and medical law changes in all countries. Various complex developments are covered in this review. To the best of our knowledge, there have been few reviews on this topic and we consider it very meaningful to provide a review in the festschrift in celebration of the 30th anniversary of the KSMP

[en] Primary cooling system (PCS) circulates the coolant from the reactor core to the heat exchanger. Therefore the heat generated from the fuel assembly in the reactor core is removed continuously. The PCS is designed based on the required thermal design flow rate of the reactor core, uncertainty of measuring instruments and the safe functions. Primary coolant is generally dumped into the pool and goes to the reactor core through the flow guide. The fission heat generated from the fuel assembly is transferred to the coolant, and then heated coolant goes to the PCS equipment room in order to remove the heat through the heat exchanger. SRHSR is designed based on the required flow rate and system constraints. Centrifugal pump of Case 1 with a non-dimensional specific speed of 0.97 [-] and specific diameter of 3.33 [-] is chosen as the SRHRS pump for the KJRR

[en] The main fluid systems are composed of a primary cooling system (PCS), a primary purification system (PPS), a pool water management system (PWMS), a hot water layer system (HWLS), and a safety residual heat removal system (SRHRS). Unlike a nuclear power plant, the KIJANG Research Reactor (KJRR) is constructed and operated for multi-purpose utilizations: mainly radio-isotope production for medical treatment, irradiated silicon ingot production for the semiconductor industry, and irradiation facility operation for other objectives. For these multiple purposes, the reactor should be designed as an open-pool type, and the pool water should be managed within the allowable water chemistry limits to minimize the corrosion of the nuclear fuel cladding and systems through the operation of purification systems. Since the purification half-life is one of the dominant factors to design the sizing of the ion exchanger, it is of importance to determine the appropriate value not only to satisfy the water chemistry requirements but also to optimize the dimension of the ion exchanger. In this study, the purification half-life is discussed to design the optimized ion exchanger for the KJRR. To optimize the design of the ion exchanger in the PPS, the adjusted purification half-life is adopted to manage in the water chemistry of the reactor pool. From this analysis, the adjusted purification half-life is verified to be reasonable in the application of purification of the reactor pool. Moreover, the conductivity in the reactor pool is confirmed to be managed within the allowable operation limit

[en] There are two reflector types, such as in-core and out-core reflectors. This reflector is particularly important in research reactors, since it is the region in which much of the experimental apparatus is located. The out-core reflectors provide site for NTD (Neutron Transmutation Doping) and PTS (Pneumatic Transfer System). In accordance with reactor operation, large heat is generated at the out-core reflector block. Thus, cooling shall be performed to reflector to maintain the structural integrity. To cool the out-core reflector, sufficient coolant and flow path are required. Therefore, in the present study, the simulation of the cooling characteristics for the out-core reflectors was performed in consideration of generated heat on reflectors. In the present study, cooling performances are analyzed for the out-core reflector block. The reflector cooling is performed by coolant of 0.25kg/s mass flow rate per each inlet hole. It is shown that cooling of reflector block is suitably performed by the force convection. And, it is also presented that vertical force balance is maintained to ensure the structural integrity. This study could be utilized to design the flow path for various types of out-core reflector blocks.

[en] This paper presents the numerical studies of several parts of decay tank from a viewpoint of residence time. The main objective of decay tank installation is to decrease the N-16 activity by increasing the residence time. To assess the design adequacy of the tank, the residence time should be predicted. The dead zone inside the device is represented to long tail of time distribution. To obtain the accurate time distribution, several numerical methods are compared by simulating the simple geometric cases. This paper describes a comparison of residence time distributions using various numerical methods. To assess the design adequacy of decay tank, an accurate residence time calculation is required. In the present study, two particle methods, DPM and streamline, and two tracer methods, mixture and UDS, are utilized and compared by simulating the validation case. DPM shows higher exit particle ratio and accurate time estimation than streamline method. UDS methods shows better performance than mixture model for the scalar conservation. Therefore, it is concluded that the DPM methods is more proper at the stage of initial design. And at detailed design phase, UDS method could be utilized to assess the accurate tank performance. This study will be applied to design the decay tank and internal flow devices.

[en] A research reactor provides multi-purpose utilization of neutron sources such as radio-isotopes production, irradiation operation, and so on. In this type of research reactor, the reactor core is submerged in the lower part of the pool to provide core cooling and reactor safety. Therefore, the water in the lower part of the pool is highly radioactivated and is heated up by the core as well. If natural circulation occurs in the pool due to the heat from the core, the radioactivated water can rise to the surface of the pool where numbers of workers and researchers are nearby. To solve this problem, a Hot Water Layer (HWL) is often implemented in the upper part of the pool to reduce the radiation level on the pool top. The HWL is maintained at a sufficiently higher temperature than the lower part of the pool to produce a thermally stratified region in the middle part of the pool, which suppresses the natural circulation. In this study, the flow and temperature distributions in the pool are investigated by preliminary numerical simulations. The effects of HWL temperature on flow stratification are further studied by changing the discharge temperature of the hot water in the upper part of the pool. The basic design of the on-going KIJANG research reactor (KJRR) project is considered in this study using commercial computational fluid dynamics software ANSYS FLUENT 13.0

[en] Segmental analysis of volumetric modulated arc therapy (VMAT) is not clinically used for compositional error source evaluation. Instead, dose verification is routinely used for plan-specific quality assurance (QA). While this approach identifies the resultant error, it does not specify which machine parameter was responsible for the error. In this research study, we adopted an approach for the segmental analysis of VMAT as a part of machine QA of linear accelerator (LINAC). Two portal dose QA plans were generated for VMAT QA: a) for full arc and b) for the arc, which was segmented in 12 subsegments. We investigated the multileaf collimator (MLC) position and dosimetric accuracy in the full and segmented arc delivery schemes. A MATLAB program was used to calculate the MLC position error from the data in the dynalog file. The Gamma passing rate (GPR) and the measured to planned dose difference (DD) in each pixel of the electronic portal imaging device was the measurement for dosimetric accuracy. The eclipse treatment planning system and a MATLAB program were used to calculate the dosim etric accuracy. The maximum root-mean-square error of the MLC positions were <1 mm. The GPR was within the range of 98%-99.7% and was similar in both types of VMAT delivery. In general, the DD was <5 calibration units in both full arcs. A similar DD distribution was found for continuous arc and segmented arcs sums. Exceedingly high DD were not observed in any of the arc segment delivery schemes. The LINAC performance was acceptable regarding the execution of the VMAT QA plan. The segmental analysis proposed in this study is expected to be useful for the prediction of the delivery of the VMAT in relation to the gantry angle. We thus recommend the use of segmental analysis of VMAT as part of the regular QA

[en] The main purpose of a research reactor is pool type research reactor is widely designed in consideration of the heat removal of the core, reactor operation and accessibility. Reactor structure assembly is generally placed at the pool bottom. Primary cooling system (PCS) circulates the coolant from the reactor core to the heat exchanger. Therefore the heat generated from the reactor core is removed continuously. PCS is designed based on the required thermal design flow rate of the reactor core assembly and the operation characteristics of equipment and measuring instruments. Primary coolant is dumped into the pool and goes to the reactor core through the flow guide structure. The fission heat generated from the fuel assembly is transferred to the primary coolant, and then heated primary coolant goes to the PCS equipment room in order to remove the heat by the heat exchanger. The PCS inlet pipe is connected to the outlet nozzle of the reactor structure assembly. ARHSR is designed based on the required flow rate and system constraints. And, centrifugal pump of Case 1 with a non-dimensional specific speed of 1.45 and specific diameter of 2.55 is chosen as the preliminary design of the ARHRS pump based on the system operation

[en] A decay tank shall be designed to provide enough flow residence time to ensure that the N-16 activity decreases before the coolant leaves the decay tank's shielding room. However, when a proper criterion for the flow residence time in a decay tank is not presented, the tank would be oversized/undersized. In this paper, design evaluation for a decay tank is performed by investigating the effect of the fluid distribution along the residence time on the total dose rate and the required minimum flow residence time. The evaluation is also carried out to resize the predesigned decay tank. (author)