ANALYSIS ON THE ADEQUACY LEVEL OF DEFENCE IN DEPTH FOR THE MODULAR HTGR

ABSTRACT
ANALYSIS ON THE ADEQUACY LEVEL OF DEFENCE IN DEPTH FOR THE MODULAR
HTGR. The modular HTGR is the nuclear reactor that is used to produce electricity and heat
process for industrial. The reactor has safety characterization that is enough robust.
Nevertheless, safety analysis for this reactor is still needed. Safety objective is to protect
human and environment from ionization radiation hazard which is implemented within
defence in depth concept (DiD) that it consists of five levels. This concept applies the
fundamental safety function for each level that is to control reactivity, to remove heat and to
confine radioactive materials. Therefore, the safety level of nuclear installation can be
evaluated based on the adequacy level of DiD. The objective of this research is to determine
the adequacy level of DiD concept on the modular HTGR. Analysis is carried out by
constructing fault tree which failure of the DiD is as top event. The probability of top event is
to multiply the probability for each level of DiD. Furthermore, each level of the DiD is
analyzed by assessing each the fundamental safety function. So that, each fault tree of DiD
consist of three intermediate event. The adequacy level of DiD is determined based on
complement of failure probability of DiD. Meanwhile, the probability of event is determined
based on possibility event from all level of DiD. The analysis results show that the failure
probability of each level for DiD is between 10-5 and 10-3, so that the adequacy level of DiD is
about 99 %. Based on this analysis, it can be concluded that the modular HTGR has highly
safety level, because the design has inherent safety features which is enough robust.
Keywords: modular HTGR, defence in depth (DiD), fundamental safety function, fault tree
analysis.
ABSTRAK
ANALISIS TINGKAT KECUKUPAN PERTAHAN BERLAPIS PADA MODULAR HTGR.
Modular HTGR merupakan reaktor nuklir yang dapat digunakan untuk menghasilkan listrik
dan panas proses untuk industri. Reaktor ini mempunyai karakteristik keselamatan yang
cukup ketat, namun demikian tetap perlu dilakukan analisis keselamtan. Tujuan keselamatan
adalah untuk melindungi manusia dan lingkungan dari bahaya radiasi yaitu dengan
menerapkan konsep pertahanan berlapis (Defence in Depth, DiD) yang terdiri atas 5 level.
Konsep ini menerapkan fungsi keselamatan dasar untuk setiap level yaitu mengendalikan
reaktivitas, memindahkan panas dan mengungkung bahan radioaktif. Maka dari itu, tingkat
keselamatan instalasi nuklir dapat dinilai berdasarkan tingkat kecukupan DiD. Tujuan dari
penelitian ini adalah menentukan tingkat kecukupan DiD pada modular HTGR. Analisis
dilakukan dengan menyusun pohon kegagalan dengan kegagalan DiD sebagai kejadian
puncak serta probabilitas gagalnya merupakan perkalian dari probabilitas kegagalan setiap
level DiD. Selanjutnya dianalisis setiap level dengan mengkaji setiap fungsi keselamatan
dasar, sehingga setiap pohon kegagalan DiD terdiri atas 3 (tiga) kejadian menengah.
Tingkat kecukupan DiD ditentukan berdasarkan komplemen dari probabilitas kegagalan DiD.
Probabilitas gagal setiap kejadian ditentukan berdasarkan kemungkinan semua kejadian dari
semua level DiD. Analisis menunjukkan bahwa probabilitas gagal setiap level pertahanan
berlapis antara 10-5 sampai 10-3, sehingga didapatkan tingkat kecukupan DiD sekitar 99 %.
Berdasarkan analisis dapat disimpulkan bahwa modular HTGR mempunyai tingkat
keselamatan yang cukup tinggi karena mempunyai fitur keselamatan melekat yang cukup
ketat.
Kata kunci: modular HTGR, pertahanan berlapis (DiD), fungsi keselamatan dasar, analisis
pohon kegagalan.