[en] The purpose of this paper is to discuss the recent circumstances in Indonesia concerning nuclear energy program and try to anticipate the challenges and the future trend on the application of nuclear power for electricity generation. It is indispensable for Indonesia with regard to development of industries and improvement of the quality of life to establish sufficient and stable electric power supply. A national energy policy has been adopted, in its way to secure the continuity of energy supply at affordable price; to enhance the people's quality of life, and to reserve an adequate supply of oil and gas as important sources to fund national development program. It is expected that nuclear energy will reduce the dependence on a single type of fuel, economize energy utilization, as well as to support environmental program by applying clean-energy technology. (author)

[en] Reduced-moderation natural circulation BWR has been promoted to solve the recent challenges in BWR nuclear power technology problems as one of advanced small and medium-sized reactors equipped with the passive safety features in conformity with the natural law. However, the elimination of recirculation pumps and a high-density core due to the increase of conversion ratio could cause various thermo-hydraulic instabilities especially during the start-up stage. The occurrences of the thermo-hydraulic instabilities are not desirable and it is one of the main challenges in establishing reduced-moderation natural circulation BWR as a commercial reactor. The purpose of this present study is to experimentally investigate the driving mechanism of the thermo-hydraulic instabilities and the effect of system pressure on the unstable flow patterns. Hence, as the fundamental research for this study, a natural circulation loop that carries boiling fluid with parallel boiling channel has been constructed. Channel gap that has been set at 2 mm in order to simulate reduced-moderation reactor core. Pressure ranges of 0.1 up to 0.7 MPa, input heat flux range of 0 ou to 577 kW/m², and inlet subcooling temperatures of 5, 10, and 15 K respectively, are imposed in the experiments. This experiment clarifies that changes in unstable flow patterns with increase in heat flux can be classified into two in response to system pressure range. In case of atmospheric pressure, unstable flow patters has been classified in beyond order, (1) in-phase geysering, (2) transition oscillation combined with both features of in-phase geysering and natural circulation oscillation, (3) natural circulation oscillation induced by hydrostatic head fluctuation, (4) density wave oscillation, and finally (5) stable boiling two-phase flow. On the other hand, in the system pressure range from 0.2 to 0.7 MPa, unstable patters have been dramatically changed in the following order (1) out-of-phase geysering, (2) density wave oscillation and lastly (3) stable boiling two-phase flow. Transport mechanism of the thermo-hydraulic instabilities and changes in the flow patterns with increment in heat flux are almost equal to the results obtained in the previous natural circulation loop equipped with 5 mm channel gap, except for in-phase geysering. Considering in-phase geysering, it is one of new kind of the insatiabilities since it had never been observed in the loop with wider channel gap. This instability will be explained in this paper on the transport mechanism in detail. (author)

[en] Natural circulation BWR actively equipped with passive safety features has been promoted to solve the recent challenges in BWR nuclear power and safety technology. With regard to startup stage, various thermo-hydraulic instabilities might be induced due to an elimination of re-circulation pumps. A lot of studies have been made on the instabilities in evaporated system as well as in a reactor. In the instabilities, geysering accompanied with flow reversal phenomena has been investigated in a vertical closed loop, U-shaped closed loop, twin parallel channels, and so on. However, in twin parallel study the effect of non-heated length on geysering has not been sufficiently clarified. The objective of this research is to experimentally investigate the thermo-hydraulic instabilities, particular in geysering, with a natural circulation loop consisting of parallel boiling channels and the single connection channel, which simulates the basic flow around the reactor core in the system pressure range from atmospheric to 0.7 MPa. The parallel boiling channels are consisted of heated and non-heated section. The heated section forms annulus and heated from the inner wall. The input heat flux range of 0 up to 580 kW/m², and inlet subcooling temperatures of 5, 10, and 15 K respectively, are imposed in the experiments. In the parallel channels with non-heated risers, three types of thermo-hydraulic instabilities were detected in the following sequence, geysering, natural circulation oscillation, and density wave oscillation. Especially in geysering, it is induced due to rapid condensation in the non-heated risers and it is not be suppressed even at 0.7 MPa though it has a tendency to be suppressed with an increase in the system pressure. On the other hand, in the parallel channels without non-heated risers, sinusoidal oscillation similar to natural circulation oscillation has been detected, and geysering had never observed. The new findings are that the sinusoidal oscillation is induced because of the hydrostatic head fluctuation in the connection channel, where the flow regime is constantly slug flow. The oscillating period is well correlated with the sum of delay time for boiling and passing time of slug bubbles in the connection channel. From the facts described above, it is found that non-heated region in a channel box should be as shorter as possible to prevent geysering from occurring, and sinusoidal oscillation similar to natural circulation oscillation is induced in any configuration of parallel channels. (authors)

[en] The IAEA has a project to help coordinate Member State efforts in the development and deployment of small modular reactor (SMR) technology. This project aims simultaneously to facilitate SMR technology developers and potential SMR users, particularly States embarking on a nuclear power programme, in identifying key enabling technologies and enhancing capacity building by resolving issues relevant to deployment, including nuclear reactor safety. The accident at the Fukushima Daiichi nuclear power plant was caused by an unprecedented combination of natural events: a strong earthquake, beyond the design basis, followed by a series of tsunamis of heights exceeding the design basis tsunami. Consequently, all the operating nuclear power plants and advanced reactors under development, including SMRs, have been incorporating lessons learned from the accident to assure and enhance the performance of the engineered safety features in coping with such external events. This paper presents technology developers and users with common considerations, approaches and measures for enhancing the defence in depth and operability of water cooled SMR design concepts to cope with extreme natural hazards. Indicative requirements to prevent such an accident from recurring are also provided. At first, a review of engineered safety feature design of SMRs is provided, covering the trip and shutdown system, residual heat removal system, safety injection system, containment system and severe accident mitigation features. Afterwards, countermeasures to address the lessons learned from the Fukushima Daiichi accident will be discussed from the viewpoints of design and siting, on-site and off-site emergency preparedness and responses, and nuclear safety infrastructures. It is concluded that water cooled SMR designs have variations in safety system designs that may come from the reactor attributes such as design and safety characteristics, power level, and type of safety system (active, passive or hybrid of active and passive) to cope with accidents. They also have the potential to duly adapt to and cope with a variety of extreme natural hazards (e.g. simultaneous and multiple external hazards). The study suggests that the IAEA should develop relevant safety standards to incorporate SMR specific design features and special condition, as the current safety standards are applicable primarily for land based stationary nuclear power plants with water cooled reactors designed for electricity generation. The paper reports Member States accomplishment in discussion design safety considerations for water-cooled SMRs incorporating lessons learned from the Fukushima Daiichi accident published in 2016 as IAEA-TECDOC-1785. (author)