ABSTRAK Program konversi reaktor TRIGA 2000 Bandung dari bahan bakar silinder menjadi bahan bakar pelat perlu perancangan sistem pendingin reaktor yang baru. Perancangan sistem pendingin reaktor yang baru tersebut diusahakan tidak banyak mengalami perubahan dari sistem pendingin reaktor yang telah ada, mengingat ruang dan tempatnya tidak mungkin diubah. Oleh karena itu perlu dilakukan analisis untuk memilih routing perpipaan sistem pendingin reaktor TRIGA pelat yang dapat memenuhi persyaratan pendinginan sistem yang sesuai dengan kondisi ruang dan tempat yang telah ada. Mengingat batasan ruang yang ada maka ada 4 (empat) kemungkinan bentuk routing yang bisa dirancang. Dari keempat kemungkinan routing tersebut kemudian dilakukan analisis waktu tempuh partikel N-16 yang memancarkan radiasi gamma (γ) dari teras ke permukaan tangki reaktor. Penelitian dilakukan dengan mengasumsikan rapat massa(ρ) fluida pendingin konstan (fluida inkompresibel), seluruh N-16 yang dihasilkan dalam teras reaktor terangkut ke permukaan tangki reaktor. Hasilnya menunjukkan bahwa routing alternatif 3 adalah yang paling optimum, karena waktu tempuhnya mendekati 5 (lima) kali waktu paruh N16 (36,7047 detik), sehingga aktivitasnya turun dari 100% menjadi 3%nya (A/A0 = 0,0317) dan panjang pipanya masih cukup untuk dimasukkan ke dalam ruang sistem pendingin reaktor yang tersedia. Kata kunci: Routing, perpipaan, aktivitas N-16, waktu paruh, reaktor TRIGA pelat. ABSTRACT The conversion program in 2000 Bandung TRIGA reactor fuel from the cylinder into fuel plates needs a new reactor cooling system design. The design of the new reactor cooling system are devised in such away to not much changed from the existing reactor cooling system, regarding its space and location have no possibility to change. Therefore, pipe routing analysis is required to select the plate type TRIGA reactor cooling system, to meet the cooling requirements of the system, attempted to match with the existing space and location. According to the availability of the existing space, four (4) possibilities of pipe routing can be designed. From the four possibilities of pipe routing, then analyze the travel time of particles N-16, which emits gamma radiation from the core to the surface of the reactor tank. Analysis was performed by assuming a constant cooling fluid density (ρ) (incompressible fluid), the entire N-16 generated in the reactor core is transported to the surface of the reactor tank. The results show that the third alternative pipe routing is the most optimum, due to its approaching transport time is five (5) times the half-life of N-16 (36.7047 sec), so that its activities decreases from 100% to 3% (A/A0 = 0.0317) and the pipe length is still enough to put in the available space reactor cooling system. Keywords: Pipes, routing, N-16 activities, half-life , TRIGA reactor plate type.
In 2015, research activities to modify TRIGA 2000 Reactor Bandung fuel element from cylindrical to plate-type have been initiated. By using plate-type fuel elements, core cooling process will be altered due to different generated heat distribution. The direction of cooling flow is changed from bottom-to-top natural convection to top-to-bottom forced convection. This change of flow direction requires adjustment on the cooling piping system, in order to produce simple, economical, and safe piping route. This paper will discuss the design of suitable piping routing based on pipe stress and N-16 radioactivity. The design process was carried out in several stages which include thermal-hydraulic data of reactor core to determine the process variables, followed by modeling various pipeline routes. Based on available space and ease of manufacture, four possible alternative routings were determined. Four routings were produced and analyzed to minimize the amount of N-16 radioactivity on the surface of the reactor tank, prolonging the cooling fluid travel time to reach at least five times of N-16 half-life. Subsequent pipe stress analysis using CAESAR II software was conducted to ensure that the piping system will be able to withstand various loads such as working fluid load, pipe weight, along with working temperature and pressure. The results showed that the occurred stresses were still below the safety limit as required in ASME B31.1 Code, indicated that the designed and selected pipeline routing of primary cooling system in the Plate-type Converted TRIGA 2000 Reactor Bandung has met the safety standards.
The conversion program of the 2 MW TRIGA reactor in Bandung consisted of the replacement of cylindrical fuel (produced by General Atomic) with plate fuel (produced by BATAN). The replacement led into the change of core cooling process from upward natural convection type to downward forced convection type, and resulted in different thermohydraulic safety criteria, such as critical heat flux (CHF) limit, boiling limit, and cooling fluid flow stability. In this paper, a thermohydraulic safety analysis of the converted TRIGA reactor is presented by considering the Dynamic Nucleate Boiling Ratio (DNBR) criterion, Onset Nucleate Boiling Ratio (ONBR) limit, and cooling fluid flow stability at various cooling fluid flow rate.The numerical analyses were performed using the HEATHYD program on the hottest channels of reactor core.The combination of heat transfer and fluid flow analysis were conducted for reactor operation at 2 MW with 20 fuel element bundles and four control rod bundles. Incoming fluid flow to the cooling channel was fixed at 44.5 °C temperature and 1.9970 bar pressure, and its flow rate was varied from 1.25 to 3.5 m 3 /h. By inputting these values, as well as the total power of fuel elements per bundle, the wall temperature distribution of the plate fuel element, cooling fluid temperature distribution, and pressure losses in the channels were obtained for the analysis of CHF limit, boiling limit, and flow stability. It was shown that no boiling occurred for the cooling fluid flow rate range of 2.4 to 3.5 m 3 /h, and even at the cooling fluid flow rate of 1.25 m 3 /h where some bubbles occurred, the DNBR was higher than the critical limit (more than 23) while the flow stability criterion in some channels were slightly less than 1 (unstable). At the cooling fluid flow rate of 1.4 m 3 /h, however, the flow became stable in all channel. The results showed that even though some bubbles start to occur, the plate-fueltype 2 MW TRIGA reactor can safely operate in the terms of CHF limit and flow stability.
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