PERFORMA NEUTRONIK BAHAN BAKAR LiF-BeF2-ThF4-UF4 PADA SMALL MOBILE-MOLTEN SALT REACTOR

Abstract

Telah dilakukan analisis terhadap performa neutronik bahan bakar garam lebur LiF-BeF₂-ThF₄-UF₄ pada Small Mobile-Molten Salt Reactor (SM-MSR). Penyesuaian konfigurasi teras dan temperatur operasi harus dilakukan untuk penggunaan bahan bakar baru tersebut agar mencapai k_eff > 1 dan CR (conversion ratio) > 1 pada fraksi 0,5% ²³³U, 20% ²³²Th, 28% Li, 51,5% Be. Setelah didapat nilai k_eff ≈ 1 dan CR ≈ 1, dilakukan analisis pengaruh perubahan Th terhadap Be dan Be terhadap Li yang terlihat dalam perubahan parameter keff dan CR. Setelah itu fraksi ²³³U divariasi antara 0,5–0,46% untuk memperoleh k_eff > 1 dan CR > 1. Dalam perhitungan koefisien reaktifitas temperatur (α_T), temperatur teras dinaikkan sebesar +25K dan +50K., dan untuk koefisien reaktifitas void (α_V), densitas bahan bakar dikurangi hingga 90%. Hasil perhitungan menunjukkan bahwa pengurangan Th terhadap Be menyebabkan penurunan nilai CR dan naiknya keff akibat berkurangnya material fertil. Sebaliknya penambahan Be terhadap Li mengakibatkan terjadi kenaikan nilai k_eff dan menurunkan CR, akibat laju serapan Li lebih besar dari Be. Pada 5 (lima) fraksi ²³³U dalam rentang 0,5–0,49%, hasil perhitungan k_eff dan CR masing-masing bervariasi dalam rentang 1,00001 - 1,00327 dan 1,00016 - 1,00731. Untuk faktor puncak daya (PPF), hasil perhitungan memberikan nilai dalam rentang 2,4311 -2,4714. Sedangkan untuk parameter keselamatan, koefisien reaktivitas temperatur (α_T) dan reaktivitas void (α_V) masingmasing bernilai negatif dalam rentang 4,972×10^-5 - 5,909×10^-5 dan 2,596×10^-2- 2,8287×10^-2 ∆k/k/K. Dapat disimpulkan bahwa teras SM-MSR memberikan nilai negatif di kedua koefisien reaktivitas tersebut untuk setiap fraksi,, sehingga memenuhi kriteria keselamatan dan keselamatan melekat.

Kata kunci: SM-MSR (small mobile-molten salt reactor), bahan bakar LiF-BeF₂-ThF₄-UF₄, keselamatan melekat, koefisien reaktivitas temperatur, koefisien reaktivitas void

The analysis of neutronic performance has been carried out for the molten salt fuel LiF-BeF₂-ThF₄-UF₄ on a Small Mobile-Molten Salt Reactor (SM-SMR). The core configurations and operating temperature should be adjusted in using the new fuel in order to get the calculated keff and CR (conversion ratio) are > 1 in the fraction of 0.5% ²³³U, 20% ²³²Th, 28% Li, 51.5% Be. After obtained that keff and CR close to 1, then the analysis of changes in the Th to Be and Be to Li are carried out, it indicates the changes of keff and CR. Then the ²³³U fraction is varied between 0.5–0.46% to obtain the condition k_eff > 1 and CR > 1. To determine the temperature coefficient of reactivity (α_T),the temperature of core is changed about +25K dan +50K. To determine the void reactivity coefficient (α_V), fuel density is reduced to 90%. The result shows that the reduction of Th causes the decrease of CR and increase of keff due to the number fertile material is less. The addition of Be to Li will make the keff is increase and the CR is decrease, because the macroscopic absorption cross section of Li is greater than Be. From the five ²³³U composition in the ranges 0.5–0.46%, the calculated k_eff and CR varies in the range of 1.00001 – 1.00327 and 1.00016 – 1.00731, respectively. For power peaking factor (PPF), the calculation results give the value in the range of 2.4311 - 2.4714. However, for the safety parameters, the negative temperature reactivity coefficient (α_T) and negative void reactivity CR (α_V) in the range of 4.972×10^-5 – 5.909×10^-5 and 2.596×10^-2 - 2,8287×10^-2 ∆k/k/K, respectively. It can be concluded that the SM-MSR core has negative value for those reactivity for all fractions, so the core fulfill the safety criteria and inherent safety.

Keywords: small mobile molten salt reactor (SM-MSR), LiF-BeF₂-ThF₄-UF₄ fuel, inherent safety, temperature coefficient reactivity, void coefficient reactivity.