Design study of Pb-Bi cooled fast reactors with natural uranium as fuel cycle input using special radial shuffling strategy has been performed. The reactors utilizes UN-PUN as fuel, Eutectic Pb-Bi as coolant, and can be operated without refueling for 10 years in each batch. Reactor design optimization is performed to utilize natural uranium as fuel cycle input. This reactor subdivided into 6 regions with equal volume in radial directions. The natural uranium is initially put in region 1, and after one cycle of 10 years of burn-up it is shifted to region 2 and the region 1 is filled by fresh natural uranium fuel. This concept is basically applied to all regions. The calculation has been done by using SRAC-Citation system code and JENDL-3.2 library. The effective multiplication factor change increases monotonously during 10 years reactor operation time. There is significant power distribution change in the central part of the core during the BOC and the EOC. It is larger than that in the case of modified CANDLE case which use axial direction burning region move. The burnup level of fuel is slowly grows during the first 15 years but then grow fastly in the rest of burnup history. This pattern is a little bit different from the case of modified CANDLE burnup scheme in Axial direction in which the slow growing burnup period is relatively longer almost half of the burnup history.
Burn up analysis of gas cooled fast reactor (GCFR) with natural uranium fuel has been done. Burn up modification used in order to make reactor can be operated with natural uranium without enrichment. The reactor core subdivided into 10 regions with the same volume in radial directions. Optimization evaluated by burning natural uranium for 100 years and put each of its burn up result per year in reactor with certain configuration. After 10 years burn up period, fuel from first region was shuffling radially to second region and so on fuel from 9th shuffling to 10th and then fuel from 10th was carried out from reactor core and fresh uranium input to the first region. Calculation has been done by using SRAC system code with JENDL-32 as library, with cylindrical two dimensional R-Z core models. Shuffling method was used in order to make reactor can be operated using natural uranium. . This natural uranium initially being burned by guessed power level of burn up. The height and diameter core are 350 cm and 240 cm respectively. The volume fraction for this design is 65% fuel, 10% cladding and 25% coolant; with output power 700 MWTh. The result show that reactor demonstrated excellent performance with effective multiplication factor 1,055
Telah dilakukan analisis neutronik pada Gas Cooled Fast Reactor (GCFR) dengan variasi umur teras dan daya reaktor. Reaktor ini menggunakan uranium alam sebagai bahan bakar dan helium sebagai pendingin. Parameter neutronik yang diamati meliputi faktor multiplikasi (keff) dan densitas bahan bakar. Pengaturan bahan bakar menggunakan strategi shuffling pada model teras silinder dua dimensi R-Z.Teras dibagi menjadi 10 region. Setiap 10 tahun bahan bakar yang ada pada masing-masing region di shuffling ke region berikutnya. Bahan bakar di region 10 dikeluarkan sedangkan pada region 1 akan diisi dengan bahan bakar baru. Penelitian ini dilakukan dengan 3 variasi umur teras dan 3 variasi daya reaktor. Perhitungan menggunakan kode SRAC dengan JENDL-32 sebagai data library. Hasil perhitungan menunjukkan bahwa reaktor dapat dioperasikan hingga 100 tahun pada daya 500 MWTh karena neutron yang berada dalam teras reaktor dapat mempertahankan kekritisannya selama reaktor beroperasi. Semakin lama umur teras maka nilai densitas 235U dan 238U semakin berkurang dan nilai densitas 239Pu semakin bertambah. Semakin tinggi daya yang digunakan maka densitas bahan bakar yang tersisa di akhir periode burn up lebih rendah. Kata kunci : Burn up, faktor multiplikasi, GCFR, shuffling, uranium alam
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