DESIGN OF SMALL ABSORBER SPHERE SHUTDOWN SYSTEM FOR INDONESIA EXPERIMENTAL POWER REACTOR- REAKTOR DAYA EKSPERIMENTAL

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1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 12, December 2018, pp , Article ID: IJMET_09_12_057 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed DESIGN OF SMALL ABSORBER SPHERE SHUTDOWN SYSTEM FOR INDONESIA EXPERIMENTAL POWER REACTOR- REAKTOR DAYA EKSPERIMENTAL Dedy Priambodo Centre for Nuclear Energy System, BATAN Jalan Kuningan Barat Raya, Mampang Prapatan, Jakarta 12710, Indonesia Marliyadi Pancoko Centre for Nuclear Facility Engineering, BATAN Puspiptek Serpong Gedung 71, Setu, Tangerang Selatan 15310, Indonesia Topan Setiadipura Centre for Nuclear Technology and Safety, BATAN Puspiptek Serpong Gedung 80, Setu, Tangerang Selatan 15310, Indonesia ABSTRACT The RDE Small Absorber Sphere Shutdown System has been designed. This paper briefly introduces the main design concept and function of the RDE s Small Sphere Absorber Shutdown System. Key words: RDE, SAS, element, pneumatic, shutdown. Cite this Article: Dedy Priambodo, Marliyadi Pancoko, Topan Setiadipura, Design of Small Absorber Sphere Shutdown System for Indonesia Ekperimental Power Reactor- Reaktor Daya Experimental, International Journal of Mechanical Engineering and Technology 9(12), 2018, pp INTRODUCTION BATAN has been proposing to build the 10 MW Experimental High Temperature Gas-cooled Reactor (RDE-Reaktor Daya Eksperimental) for promoting the nuclear energy development plan, increasing public acceptance on Nuclear Energy National Program, proofing the safety level of the most advanced reactor technology, owning the newest reactor technology and pursuing national capabilities on nuclear power industries [1] [3]. In the RDE, the control rod system is adopted not only as power regulating control system; it is also adopted as the first shutdown system. At accident conditions, if the control rod system cannot be operated because of failures such as the rod getting stuck, a small absorber sphere system (SAS), are designed for the second shutdown system. SAS will immediately be put into action to shut editor@iaeme.com

2 Design of Small Absorber Sphere Shutdown System for Indonesia Experimental Power Reactor- Reaktor Daya Ekperimental down the RDE, and the reactor finally reaches cold shutdown. SAS maintains the reactor subcritical with no time limitations in the process of the reactor cooldown. During power operation the SAS element are stored in special hoppers/storage vessel arranged above the reactor core. Absorber balls fall into channels by gravity at the opening of the hopper/storage vessel gates. The gates are opened when their drives are de-energized, either automatically or via a shutoff button. Seven channels for SAS are arranged inside wide annular gap thus formed between side reflector and active core barrel. The SAS elements are accommodated by slotted holes in order to achieve distribution over a large area around the core; these holes extend below the top of the core bottom and continue to the bottom plate. Each channel is filled with SAS element from a separate hopper/storage vessel thus eliminating common cause failure of more than one channel (gate jamming). The SAS of RDE has the following functions: To store the SAS elements and to assure shutdown on demand by dropping the shutdown elements into the slotted holes of the side reflector by manual actuation, To remove the SAS elements from the columns of the side reflector in measured quantities by pneumatic push and to return them to the storage vessels above the top thermal shield. The small absorber sphere system is a unique system that employed in pebble bed high temperature reactor. It was first introduced by Siemens/Interatom in HTR-Module design. The system consists of 18 columns of small absorber balls (KLAK) in the side reflector. If the system must be used the small absorber sphere (10 mm diameter, graphite with 10 % B 4 C) fall under gravity into the borings in the side reflector. At the bottom there are closures for each position which can be opened to be able to remove the small absorber balls pneumatically back to the storage vessel. The components for transporting the balls are arranged outside the reactor pressure vessel under this component. The transport pipes are inside the reactor pressure vessel between the core barrel and the ceramic structure. The SAS system on HTR Module also uses the fail-safe principle: in case of loss of electrical power the storage containers are opened and the balls fall into the borings [4], [5]. The RDE SAS system has been designed and derived from the HTR-Module design, the information of HTR-10 in China and expert opinion from the IAEA Technical Cooperation Program and applied simplification in its design. 2. RESULT AND DISCUSSION 2.1. Design The SAS system is provided for cold and long-term shutdown. The SAS elements are stored above the top thermal shield and fall under gravity into reflector columns (slotted holes) on demand. This SAS system is actuated when operational residual heat removal by the main heat transfer system is initiated due to failure of main control and shutdown system of reactor. The system consists of 7 mutually independent units. The only shared component is a carrier gas blower for returning the shutdown elements from the slotted holes of the side reflector to the storage vessels. Helium is specially use as carrier gas for the SAS system of RDE. The SAS system is used for long-term shutdown and to compensate for slow reactivity changes (compensation for lack of xenon poisoning on start-up or, in rare cases, on load change e.g. long-term operation on part load of 50% or lower). Main components necessary for secondary shutdown are: Small ball shutdown elements, Small ball shutdown element storage vessels located in the primary system above the side reflector on the top thermal shield, editor@iaeme.com

3 Dedy Priambodo, Marliyadi Pancoko, Topan Setiadipura Vessel closure with closure solenoid, including inductive limit position indicator, Reflector columns, the slotted holes of the side reflector Pneumatic conveying system. The construction and arrangement of the overall system is apparent from the Block flow diagram in Figure 1, Figure 1. Block Flow Diagram of SAS System for RDE 1. Solenoid & inductive limit position indicator for vessel closure; 2. Level Sensor; 3. Separator; 4. SAS Element Storage vessel; 5. SAS Element; 6. Vessel closure; 7. Slotted hole; 8. Feeder; 9. Elevator/feeding line; 10. Helium gas circulation line; 11. Blower SAS Element The small absorber spheres, then called SAS element are made from boron carbide ((B 4 C) in the graphite as base material. The SAS element specification are shown in Tabel 1 Tabel 1. Specification of SAS Element for RDE Diameter, mm 5 Material Density, kg/m 3 ± 2,000 Total number of SAS elements in the SAS system 1,890,000 B 4 C in graphite matrix (25 % B 4 C by volume) editor@iaeme.com

4 Design of Small Absorber Sphere Shutdown System for Indonesia Experimental Power Reactor- Reaktor Daya Ekperimental The SAS element is 5 mm in diameter. It consists of a graphite shell and an internal absorber zone. As the absorber material, natural boron carbide (B 4 C) is used. In the standby mode, SAS elements are in a SAS Element Storage Vessel that is underneath the reactor closure head. 0 The SAS elements are accommodated by slotted holes in order to achieve distribution over a large area around the core; these holes extend below the top of the core bottom and continue to the bottom plate. The lower region is during reactor operation filled with small shutdown elements for neutron shielding Separator and SAS Element Storage Vessel The separator of the SAS element located at the above of the SAS Element storage vessel. Through separator, the SAS element drop into the lower part of the SAS element storage vessel, while the carrier gas returns to the inlet of the gas blower. The separator is connected to a blower through a pipe-valve system of pneumatic conveying. the SAS Element storage vessel is designed for SAS Element pile. There is a vessel closure at the lower part of the storage vessel, which is normally closed and hold the SAS element in the vessel for the normal condition. All the SAS element are stored in the lower part of the ball storage vessels. Level indicator is installed to measure the position of SAS in the ball storage vessel. From the HTR10 experience, the level indicator of storage vessel was designed on the base of the property of electric conductivity or by hanging vertically two copper electrodes inside the storage vessel; the two upper ends of the electrodes are connected to a power supply, while the lower ends of the electrodes are in open status. When the storage vessel is filled by SAS element, the electrical circuit is closed and gives an full signal to the control room. When the SAS system activated; vessel closure is opened; all SAS element will drop out from the vessel, the two electrodes are not electrically connected by small absorber balls, so the electrical circuit is still in open state and gives an empty signal [6] Slotted Hole The SAS elements are accommodated by slotted holes in order to achieve distribution over a large area around the core; these holes extend below the top of the core bottom and continue to the bottom plate. The lower region is during reactor operation filled with small shutdown elements for neutron shielding. The Slotted hole size of cross-sections, mm editor@iaeme.com

5 Dedy Priambodo, Marliyadi Pancoko, Topan Setiadipura 2.6. Feeder SAS element feeder is a component of absorber sphere shutdown system and plays an important role during pneumatic conveying. SAS element are entrained, fluidized and pushed by carrier gas in feeder and gas-solid phase flow is formed for pneumatic conveying. Feeder integrated into the metallic core support structure, including connections for shutdown element feedlines, and carrier gas. 3. SMALL ADSOBER SPHERE SYSTEM OPERATION The closure of the storage vessel is of a type which allows the discharge of less than full quantities without causing damage to the SAS elements. Most of the weight of the SAS element fill is taken by the stationary disk. The upper portion of the ring around this disk constitutes the outer support of the pile and thus prevents the elements from rolling out. The ring is held in this closed position by a rod along the vessel axis which is connected to a solenoid at its upper end. Power to this solenoid is deenergized on demand, allowing the ring to fall to its lower position under gravity along with the connecting rod and the solenoid lift armature. Since the ring now no longer supports the pile, the SAS elements fall out of the vessel. SAS elements move under gravity from the storage vessel to the slotted hole/channel in the side reflector of the reactor core. When the SAS element filled the slotted channel, reactor will be shutdown. The information on the complete unloading of the storage vessel is provided by the level sensor located in the vessel. Cross sections for shutdown element passage are dimensioned to prevent plugging. For reasons of plant availability, the solenoid has uninterruptible emergency power backup. A close loop pneumatic conveying system is used to return the RDE SAS elements in controlled quantities from the slotted holes of the side reflector to the storage vessels. The SAS elements are drawn from feeder integrated into the metallic core support structure. The carrier gas is helium at cold-gas temperature. When the blower is operated, the entire gas flow is passed through the SAS element fill to the elevator tube with the result that the gas velocity at the inlet is above the downward velocity of the shutdown elements. The absorber balls are conveyed. The SAS elements reach the storage vessel by way of a elevator tube located in the annular gap between the core barrel and side reflector. They are separated from the flow of carrier gas in a cyclone in the storage vessel. A level indicator detects the level in the vessel and is an indirect measure of the height of the stack of shutdown elements in the side reflector. The carrier gas passes to the carrier gas valve in the valve bank at the RPV nozzle by way of a tube at the top of the storage vessel, which also runs through the annular gap, and then to a dust separator and a blower by way of a plenum in the valve bank shared by seven units and then back blower. On the operator s command, the SAS element are discharged from the slotted channels sequentially (in step-by-step mode) with time intervals between the steps. The storage vessels, including closures, are accessible for maintenance operations when the reactor is shut down, the primary system depressurized, and the reactor pressure vessel opened. To prevent air from entering the core, the vessels are mounted on the top thermal shield with leak tight seals and form an air-tight envelope with the core barrel, top thermal shield and other superstructures on the top thermal shield. A gate valve between the storage vessel and the thermal shield maintains airtightness when the storage vessel is opened or removed. 4. CONCLUSIONS editor@iaeme.com

6 Design of Small Absorber Sphere Shutdown System for Indonesia Experimental Power Reactor- Reaktor Daya Ekperimental Small absorber sphere shutdown system for secondary shutdown system of Indonesia Experimental Power Reactor has been designed. It consists of Small ball shutdown elements, storage vessels, Vessel closure, Reflector columns, the slotted holes of the side reflector and close loop pneumatic conveying system. The SAS element is 5 mm in diameter of 25% volume B4C in graphite matrix. The Slotted hole size of cross-sections, mm. ACKNOWLEDGMENT This research is supported by INSINAS Program of Kemenristekdikti the year REFERENCES [1] D. Priambodo, E. Dewita, and I. D. Irianto, Analisis Energi dan Eksergi Pada Sistem HTR-10 Siklus Turbin Uap, J. Pengemb. Energi Nukl., vol. 17, no. JUNE, pp , [2] M. Subekti, S. Bakhri, and G. R. Sunaryo, The Simulator Development for RDE Reactor, J. Phys. Conf. Ser., vol. 962, p , Feb [3] Sriyono, R. Kusmastuti, S. Bakhri, and G. R. Sunaryo, Analysis of helium purification system capability during water ingress accident in RDE, J. Phys. Conf. Ser., vol. 962, p , Feb [4] G. H. Lohnert, Technical design features and essential safety-related properties of the HTR-module, Nucl. Eng. Des., [5] R. H. Lohnert GH, The modular HTR a new design of high-temperature pebble-bed reactor, Nucl. Energy;, vol. 22, pp , [6] H. Z. Zhou, Z. Y. Huang, and X. Z. Diao, Design and verification test of the small absorber ball system of the HTR-10, Nucl. Eng. Des., vol. 218, no. 1 3, pp , editor@iaeme.com