ANALISIS PERHITUNGAN KOEFISIEN REAKTIVITAS DOPPLER PARTIKEL TRISO REAKTOR TEMPERATUR TINGGI

ABSTRAK

ANALISIS PERHITUNGAN KOEFISIEN REAKTIVITAS DOPPLER PARTIKEL TRISO REAKTOR TEMPERATUR TINGGI. Salah satu aspek keselamatan melekat HTR didasarkan pada koefisien reaktivitas temperatur bahan bakar dan moderator yang negatif. Koefisien temperatur bahan bakar dikenal dengan sebutan koefisien reaktivitas Doppler. Makalah ini mendiskusikan perhitungan koefisien reaktivitas Doppler partikel TRISO dalam matriks grafit dengan program transport Monte Carlo MCNP5 dan pustaka tampang lintang energi kontinu ENDF/B-VII. Partikel TRISO dimodelkan dengan kisi BCC dimana kernel dan keempat lapisan coating disimulasikan secara eksplisit. Serangkaian perhitungan dikerjakan dengan fraksi packing TRISO yang berbeda dan temperatur kernel, TF, yang berbeda pula. Temperatur matriks grafit, TM, dijaga konstan pada 1200K. Hasil perhitungan memperlihatkan semakin tinggi temperatur bahan bakar, semakin rendah nilai kritikalitas (k) partikel TRISO. Dengan bertambahnya temperatur bahan bakar, reaktivitas partikel TRISO menurun untuk seluruh fraksi packing TRISO yang dipertimbangkan. Hasil perhitungan juga memperlihatkan koefisien reaktivitas Doppler menurun dengan naiknya temperatur bahan bakar dan meningkat dengan bertambahnya fraksi packing TRISO. Dapat disimpulkan bahwa, pemilihan fraksi packing TRISO dan temperatur operasi merupakan opsi penting dalam analisis desain keselamatan melekat reaktor temperatur tinggi.

Kata kunci: koefisien reaktivitas Doppler, partikel TRISO, BCC, MCNP5, ENDF/B-VII

ABSTRACT

ANALYSIS ON THE CALCULATION OF DOPPLER REACTIVITY COEFFISIENT FOR TRISO PARTICLE OF HIGH TEMPERATURE REACTOR. One of HTR inherent safety aspects is based on the negative fuel and moderator temperature reactivity coefficients. Fuel temperature coefficient is known as the Doppler reactivity coefficient. This paper discusses the calculation of the Doppler reactivity coefficient for TRISO particles in graphite matrix with MCNP5 Monte Carlo transport code and ENDF/B-VII continuous energy cross section library. TRISO particles are modeled as BCC lattice where the kernel and four coating layers are simulated explicitly. A series of calculations were done with different TRISO packing fraction and different temperature of the kernel, TF. Temperature graphite matrix, TM, is kept constant at 1200K. The calculation results show the higher the fuel temperature, the lower value of TRISO particles criticality (k). The increasing temperature of fuel, TRISO particle reactivity decreases for all considered TRISO packing fraction. The calculation results show also the Doppler reactivity coefficient decreases with rising of fuel temperature and increases with increasing of TRISO packing fraction. It can be concluded that the choice of TRISO packing fraction and operational temperature are important option in inherent safety design analysis of high temperature reactor.

Keywords: Doppler reactivity coefficient, TRISO particle, BCC, MCNP5, ENDF/B-VI