Cheul Muu Sim

Characteristics of the IR Neutron Beam in Hanaro and the Recent Development for its Use in Dynamic Neutron Radiography

In HANARO, a BNCT facility was built at its IR beam port which can be used for neutron radiography as well. The values of important parameters for neutron radiography such as neutron flux, the L/D ratio and the effective energy of IR beam were obtained. The neutron flux was estimated theoretically by using an MCNP computer code simulation and was also obtained by using gold wire activation method. The L/D ratio was obtained by using the geometrical information for IR beam port as well as by using the Kobayashi’s L/D device. The effective energy was measured by using the Kobayashi’s BQI 1001. These evaluation of beam characteristics shows that the BNCT facility of HANARO is excellent for the dynamic neutron radiography. Introduction The dynamic neutron radiography is a powerful tool for fluid flow visualization as well as the multi-phase flow research[1,2,3]. This technique can be used to investigate the detail behavior of neutron-opaque fluid in metallic enclosure. HANARO is an open pool type research reactor and its design power is 30 MW. It is operated by KAERI(Korea Atomic Energy Research Institute) and a BNCT(Boron Neutron capture Therapy) facility using the IR beam port has been installed. In the development of this facility, it was recognized that this facility could be well suited for dynamic neutron radiography considering its beam characteristics[3]. In this paper, the IR beam characteristics obtained from the code simulations and experiments were given. In addition, the descriptions were made for the recent installation of accessories and a measure to achieve a higher L/D ratio in the BNCT facility. IR Beam Port and BNCT Facility in HANARO HANARO has 7 beam tubes and their arrangement is shown in Fig. 1. The IR beam tube was the only option for the BNCT at HANARO because a BNCT facility was not considered at the design stage of the reactor and any modification of the biological concrete shield was impossible[4]. The details for arrangement of shutter, filter and collimator are in Fig. 2 and the geometric data for the region from the beam nose to an imaging device position are shown in Fig. 3. The beam tube nose made from Zr-4 is located at the position of the peak thermal neutron in D2O reflector region. Considering that Zr-4 is relatively neutron-transparent, the opening edge of beam tube at the reactor vessel boundary is considered as the diaphragm[5]. A long water cylinder plays the role of beam shutter. By hydraulically moving in/out the water in the water cylinder, it plays the role of the beam shutter. A radiation filter for BNCT should remove fast neutrons and gammas but pass more thermal neutrons. A feasibility study on the candidate materials for the filter was performed through computer simulation and the silicon single crystal was chosen for filtering fast neutrons. Its cross section is high for the fast neutron Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 1343-1348 doi:10.4028/www.scientific.net/KEM.270-273.1343

Scientific Review: Neutron Radiography at HANARO

Neutron radiography is rapidly becoming one of the essential tools for a non-destructive test. Its great advantage, when compared to X-rays, lies in the fact that the neighboring elements in the periodic table, such as boron and carbon, or cadmium and tin, can be distinguished easily by neutron radiography. Another advantage of neutron radiography is that several light elements such as hydrogen and boron, which are transparent to X-rays, are highly neutron absorbent and their trace in samples can be detected without much difficulty. In addition, heavy materials, such as lead, bismuth, and steel, are relatively opaque to X-rays but very transparent to neutrons [1].Neutron radiography is rapidly becoming one of the essential tools for a non-destructive test. Its great advantage, when compared to X-rays, lies in the fact that the neighboring elements in the periodic table, such as boron and carbon, or cadmium and tin, can be distinguished easily by neutron radiography. Another advantage of neutron radiography is that several light elements such as hydrogen and boron, which are transparent to X-rays, are highly neutron absorbent and their trace in samples can be detected without much difficulty. In addition, heavy materials, such as lead, bismuth, and steel, are relatively opaque to X-rays but very transparent to neutrons [1].

Applied Phase-Contrast Radiography with Polychromatic Thermal Neutrons

Instead of conventional radiography the phase-contrast imaging visualizes not only the beam absorption but also the phase shifts induced by the sample at the propagation of a coherent radiation through it. The strong phase changes on the borders between two media can be observed as sharp intensity variations on the radiography image. So the phase-contrast method is an edgeenhancement method which allows to visualize very fine structures where the conventional radiography provides unsatisfactory results.

Design of the cold neutron radiography facility at HANARO

The radiography imaging with cold neutrons is being planned at the research reactor, HANARO, at South Korea. Cold neutrons allow a high sensitivity to light elements and organic materials and easier transmission through metals and heavy elements. Also, it has potential for energy-selective imaging, micro-tomography, phase-contrast radiography, neutron polarized imaging, and dynamic imaging. Conceptual design and simulation have been performed by varying several parameters. The planed neutron radiography facility at HANARO will be competitive to the best nowadays facilities not only in its performance but also its convenience for users

A Study for Imaging of Scattered Radiation Sources Using a Pinhole Camera

The basic performances of scattered X-ray and neutrons are studied for various materials. The results from analytical evaluation of scattered radiations are compared with the experimental results. Observed signal intensities for the scattered radiation from the measurement using a pinhole camera are compared with theoretical calculations by using the relevant parameters. Some possibilities for the applicable fields are also discussed for our future studies. Introduction Radiography is usually an imaging technique to see the residue of direct transmitted radiations after radiation disappears by absorption in material or scattering out from objects, etc. On the contrary, scattered rays should also carry out some information of the object itself. It may be challenging study to know internal structure using scattered radiation as another tool. But, what information can be extracted from the scattered rays is also not always well known. And also, how to make use of such data is also not clear to date. Then, analyses of basic feature of scattered radiations may be valuable itself. In this study, scattered intensities are estimated under a geometrical setup for almost all elements for neutrons and X-rays. Using the results, the degree of scattered intensity for individual materials are discussed in conjunction with type of radiation and its energy. The results are compared with experiments. In our previous study [1], a pinhole camera was realized and applied to measure scattered neutrons and X-rays. The pinhole camera is applied for scattered X-ray intensity measurements for various materials as well as scattered X-ray imaging. The utility of the pinhole camera is also extended for other fields such as a neutron source intensity profile measurement in this study. Imaging of Scattered Radiation Intensity Estimation of Scattered Radiation. An outline of imaging system measuring scattered radiation image using a simplified object is as follows: (1) A flat plate composed of a homogeneous material is assumed. (2) No multiple scatter is assumed. (3a) For simplicity, slow neutrons are assumed and mass of colliding material is assumed to be usually larger than that of neutron. Then, only elastic collision is assumed in this case and its energy is also assumed to be essentially invariant before and after collision. (3b) Similarly, near the Thomson scatter or a low energy Compton scatter can be considered in the low energy X-ray region and then also energy change is negligibly small or does not change. Then, it can be assumed that cross sections does not practically change before and after the scattering by (3a) and (3b). Under these simplifications, the intensity of scattered radiation is evaluated for the following Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 1392-1399 doi:10.4028/www.scientific.net/KEM.270-273.1392

Requirements of Neutron Tomography Standardization for Industrial Application

Neutron Tomography is a radiographic method that provides an ideal examination technique whenever the primary goal is to locate and size planar and volumetric detail in the three dimensions. As neutrons delivers information complementary to those gained with neutrons-nearly all metals can be easily penetrated, while even small amounts of hydrogen and thus of plastics and lubricants can be detected within even thick layers of metal. The standardization is intended to satisfy the need for consistent set of NT performance parameters definitions, including how these performance parameters relate to NT system specification. Requirements standardization covering specific items which are application or performance related, or both example include: beam quality measurement, system configuration, equipment qualification, interpretation of results, and personnel qualifications. Initially, NT examination system performance parameters must be determined and monitored regularly to ensure beam quality and consistent results. Performance measurements involve the use of test phantom of simulated test objects containing actual or simulated features that must be reliably detected or measured. Therefore, in order to do and beam quality perform measurements, two test phantoms of NT are designed referring to X-ray CT.

Ultrasonic Identification of the Structural Changes due to the Impact Testing of a Charpy Specimen Used for the Reactor Pressure Vessel Materials Testing

Ultrasonic analysis using the transit time measurement and non-linearity measurement through a relative attenuation change at the third harmonic frequency for the broken Charpy impact specimens has been performed in order to understand the metallurgical characteristics of the specimen after impact testing. Analytical work simulating a real impact testing using a finite element method (FEM) was also performed in parallel with the real ultrasonic experiment. The results showed that a longer transit time was observed near the broken area and abruptly died away from the center for the base and weld specimen, although the non-linearity behavior was not completely matched with the transit time measurement and this can be correlated with the large stresses obtained from the FEM analysis of the specimen. Introduction A nuclear reactor pressure vessel experiences material damage during operation by various loads such as high pressure and temperature including radiation embrittlement due to neutron irradiation. The damage including cracks can be detected by various nondestructive testing techniques under an in-service inspection (ISI) program and then repaired, and also monitored within an allowable size during the life of the plant, if the crack does not endanger the safety of the structure. However, the damage phenomena caused by neutron irradiation differs from the visible crack, since it involves voids and interstitial formation, which are microscopic in nature. Therefore the material damage called radiation embrittlement caused by neutron irradiation has to be continuously monitored by specific means other than ISI. One of these is called materials surveillance testing and is used to evaluate the degree of degradation of a reactor vessel by measuring the change of the nil-ductility transition temperature through mechanical Charpy impact testing [1]. Although more than 12 specimens for the base and weld as well as heat affected zone metal respectively are required to produce full curves encompassing lower temperatures to the operating temperatures by the regulations, insertion of sufficient number of mechanical test specimens is needed to accurately evaluate the embrittlement effect related to reactor operation, but it is inadequate due to the space limitation. Therefore, a limited number of specimens are only available realistically during construction and thus ample information is not always available for maintaining the integrity and making decisions for its life management. Broken Charpy specimens, which are assumed to be metallugically, the same as unbroken specimens are sometimes reconstituted for more tests in order to solve this problem, although structural changes of the material might have already occurred realistically [2]. Analytical work using a finite element method (FEM), which has been widely used to calculate the displacements and stresses inside the structures depending on the various applied loads was tried in order to understand the characteristics of the specimen’s inside due to impact testing, since these values calculated at certain points can be used to predict the areas and locations where they exceed the allowable stress level which may lead to material deformation or failure. Ultrasonic measurement as one of the nondestructive evaluation methods can be a useful tool to measure the material properties, although it has been widely used for crack detection in structures [3-4] and from Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 328-333 doi:10.4028/www.scientific.net/KEM.270-273.328

Application of Neutron Radiography for Researches on Hanaro

The HANARO operated by KAERI(Korea Atomic Energy Research Institute) has two neutron radiography facilities which are called as the Neutron Radiography Facility(NRF) and the Boron Neutron Capture Therapy(BNCT) facility, respectively. For the researches on HANARO, the NRF was used to find a weld defect in the irradiation rig made from Al for NTD in HANARO. Also, the neutron radiography inspection at the NRF was very useful to find the root causes of a defect in the HANARO fuel. As for the use of the BNCT facility for dynamic neutron radiography, a calibration curve showing the relationship between the extent of the neutron attenuation and the thickness of the liquid in the channel is important and this curve was obtained experimentally and from a computer simulation. Introduction HANARO is an open-tank-in-pool type research reactor operated by KAERI(Korea Atomic Energy Research Institute). Its initial criticality was achieved in 1995 and it is now operating at 24 MW. Among the neutron beam utilization facilities in HANARO, the NRF and the BNCT facility can be used for neutron radiography and they were built in 1997 and in 2001, respectively. The NRF[1] is mainly used for static neutron radiography and its characteristics enable us to obtain very sharp neutron radiographic images. The BNCT facility[2] is being used mainly for dynamic neutron radiography considering that the neutron flux at this beam facility is very high. Many users from private companies and universities are using the NRF and it has been a useful facility for the researches related to HANARO as well. It was used to find the weld defects in the irradiation rig made from Al for the neutron transmutation doping(NTD) in HANARO. Also, the neutron radiography technique was very useful to find the root causes for a defect problem in the HANARO fuel. As for the dynamic neutron radiography using the BNCT facility, a calibration curve showing the relationship between the extent of the neutron attenuation and the thickness of the liquid in the channel is important and this curve was obtained from experiments and a computer simulation. This paper gives some details on the use of neutron radiography in the researches related to HANARO. Present Status of HANARO[3] A bird-eye view of HANARO is shown in Fig. 1. After the power test of HANARO finished in 1996, a two-week operation and one-week shutdown was the basic operation mode. From the beginning of 1998, the operation mode was changed to a weekly operation – at least three operation days every week, for the stable supply of medical RI’s. The weekly operation minimized the unavailability of the reactor for the weekly RI supply. Annual operation was about 160 days during 1998-2001, which indicates that the reactor was operated almost every week except the periods for overhaul inspections. The reactor power was gradually increased to meet the increasing reactor demand. From the middle of 2002, the operation mode was changed again to a two-week operation and one-week shutdown so as to satisfy the rapidly increasing demand. Thereby, the reactor availability reached about 210 days in 2002. Very recently, we changed the operation mode to an 18-day operation and 10-day shutdown. It is almost equivalent to a three-week operation and one-week shutdown for the majority of the reactor Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 1337-1342 doi:10.4028/www.scientific.net/KEM.270-273.1337

Towards the Visualization of Fuel Cavitation in a Nozzle of a Diesel Engine by Neutron Radiography

Preliminary study on the visualization of fuel cavitation in a nozzle of a Diesel engine by neutron radiography was presented. Various real metallic nozzles of the Diesel engines filled with fuel were visualized by neutron radiography. The fuel and the gas bubbles simulating the cavitation were well visualized. The multiplex exposures method by using a chopper with opening the electrical shutter of a CCD camera was carried out for the visualization of cavitation in a fuel nozzle of a Diesel Engine. Introduction It is supposed that the cavitation occurs inside the nozzle of a Diesel engine. The cavitation affects much on the fuel injection. The visualization of fuel cavitation has been required by the researchers of the Diesel engines. No visualization inside the nozzle of the Diesel engine has been reported. Neutron radiography is suitable for visualizing the fuel behaviors inside the metallic nozzle. Now the gasoline engine is used for many cars. It is said that it will be replaced by the fuel battery or the battery cars except special cars like sports cars in future since the gasoline engines need high quality oil and generate rather much CO2 and CO due to low fuel efficiency. While, it will have been used the Diesel engine for big trucks. Now, the fuel of the Diesel engine is light oil. Biological oils and recycle oils will be used for the Diesel engines in future. As the merits of the Diesel engine, the fuel efficiency is good. The amounts of CO and CO2 are small. The torque is high. Various fuels can be used. As the demerits, the Diesel engine exhausts a lot of NOx and PM (particles of materials). NOx and PM cause serious environmental problems. Therefore, improvement of the fuel injection in Diesel engine is an important engineering project. Cavitation is often called cold boiling. Boiling occurs due to the temperature increase up to the saturation temperature. While, cavitation occurs due to pressure decrease below the saturation pressure. In the fuel nozzle of the Diesel engine, the high pressure fuel (around several hundreds atmospheric pressure) is injected into the engine (around several tens atmospheric pressure). Rapid pressure decrease in the nozzle causes the cavitation and it may affect much on the fuel supply to the engine. Fig.1 shows the inside of the nozzle when it is open and close. The fuel is filled in the hatched area. This needle moves up and down with a revolution numbers of the engine from 600 rpm to 6000 rpm that is from 10ms to 100ms in period. Each area is called the nozzle chamber, the sac chamber and the nozzle hole as shown in the left figure. The conditions of the fuel outside the nozzle have been studied well by optical methods [1], but no one observed the conditions of the fuel Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 1349-1355 doi:10.4028/www.scientific.net/KEM.270-273.1349

Assessment of the Uncertainty and the Proficiency Test for Accrediting KOLAS of ISO 17025 for a Neutron Radiography Facility

KOLAS(Korea of Lab Accreditation Scheme) is the charter member of ILAS (International Lab Accreditation Scheme) and APLAS( Asia Pacific Lab Accreditation Scheme), which originates from ISO 17025. KATS (Korea Agent of Technology Standard) governs the KOLAS. The KOLAS describes the basis of satisfying those issues related to a quality assurance and management system. The requirements specify an organization, the accommodation and environmental conditions, an uncertainty in the measurement and an inter-laboratory comparison or proficiency test program. The evaluation process of the requirements of certifying KOLAS for HANARO NRF has been proceeded by a neutron radiography laboratory. NRT Level II course of SNT-TC-1A II is opened, with 20 persons attending for certification. An inter-laboratory comparison or proficiency test program is conducted through with Kyoto University in accordance with ASTM Method for Determining the Imaging Quality in Direct Thermal Neutron Radiographic Testing (E545-91). In order to determine the uncertainty, dimensional measurements for the calibration fuel pin of the RISO using a profile project is performed with the ASTM Practice for Thermal Neutron Radiography of Materials (E748-95) Introduction A neutron radiography facility(NRF) for non-destructive testing was installed at the NR port, one of the eight tangential beam ports of HANARO, a 30MW high flux research reactor. Neutron radiography was carried out at the research reactor TRIGA MARK-III, 2MW in the early 1980s. It was developed in compliance with the nuclear fuel development program in KAERI for one of the post-irradiated fuel test methods. In a variety of inspections in the hot-cell laboratory, the fuel soundness and dimensional assessment of fuel elements and tubes were tested. As for the nonnuclear applications, many diverse tests and trials on explosives, detonators, metallic molds corrosions detection and archeological objects, were conducted. As the industry in Korea is requiring more advanced technologies to be developed, neutron radiography techniques are applied and expanded for a variety of industries. Among the recent results in this trend, micro defect finding in turbine blades, tests of soldering and the alignment of an optical microchip, as well as the test of the lithium-ion density of the cellular phone batteries and archeological objects have been conducted. As part of the quality assurance in these of inspections, KAERI’s neutron radiography laboratory has prepared the evaluation process for the accrediting in KOLAS[1]. Status of HANARO NRF The in-pile collimator is a divergent type. In order to avoid gamma-ray and fast neutron contamination, a collimator beam tube was inserted at a direction tangential to the reactor core. Its neutron beam inlet, having an aperture hole of a diameter of 25mm, is mounted by three 10mm thick sheets of sintered boron carbide(B4C) and inserted between two thin aluminum plates. The inside of the whole beam channel is lined with boron rubber in order to prevent the neutron beam reflection. A Collimator beam tube was designed by the consideration of two important factors such Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 1382-1386 doi:10.4028/www.scientific.net/KEM.270-273.1382