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"ABSTRAKStruktur pengungkung reaktor nuklir yang berfungsi sebagai proteksi terhadap aksi lingkungan serta penahan gaya gempa merupakan struktur utama dengan faktor keutamaan tinggi. Penelitian ini bertujuan untuk memastikan kemampuan serta daya tahan struktur pengungkung reaktor nuklir terhadap gempa serta memperkirakan dampak penyebaran kontaminasi radiasi ke lingkungan pasca-kecelakaan. Gempa Pariaman, Padang digunakan sebagai input gempa dengan diskalakan pada gempa rencana periode ulang 10.000 tahun.Hasil penelitian menunjukkan struktur reaktor merupakan struktur sangat kaku dengan drift sangat kecil. Kondisi inelastis struktur tertutup baru terjadi ketika ditingkatkan hingga 2 kali. Struktur tertutup serta struktur terbuka yang diperkuat dengan kolom mampu bertahan hingga 1,5 kali gempa rencana sebelum melampaui tegangan ijinnya. Alur paparan penyebaran kontaminasi dapat melalui tanah (Groundshine), atmosfer (Cloudshine), hirupan (inhalation), kontaminasi makanan (ingestion) hingga aliran air (Aquatic Pathway).

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ABSTRACT

Nuclear reactor containment structure that serves as protection against environmental action and retaining the force of the earthquake is the main structure that highly safety factor. This study aims to ensure the capability and durability of a nuclear reactor containment structure against earthquakes and estimates the impact of the spread of radiation contamination into the environment. Earthquake Pariaman, Padang is used as input to the scaled earthquake with return period of 10,000 years.

The results showed the reactor structure is very rigid structure with very little drift. The inelastic behavior of enclosed structure occurs when earthquake increased by 2 times. Structures closed or open structures with columns can last up to 1.5 times before the earthquake exceeded the stress limit. Chronology of exposure spread of contamination can be Groundshine, atmosphere (Cloudshine), inhalation, contamination of food (ingestion), or to the flow of water (Aquatic Pathway)."

"The nuclear reactor is a source of primary radiation. Safety in the operation of thereactor protection system is implemented by the scram action. However scramwhich often happened is the failure of the operation and poses other risks. Thepurpose of this study is to determine the trigger and the reasons for scram withanalytic descriptive method through interviews, observation and documentreview, combined with the preparation of fault tree analysis. The obtained resultsshow that trigger of scram are, the neutron flux density is too high, too fastoperation period, unbalanced load, and the occurrence of positive transientreactivity. While the basic causes of the scram incident are, too fast control rod,irradiation sample composition, corrosion, weakening of the power supplydetector, emptying of the beam tube, and unbalanced neutron flux. Then scram asanticipation of the accident is also the feedback of operating experience forupdating on safety assessment so that failure of the operation can be minimized.Keywords The safe operation of nuclear reactor, reactor protection system, cause of theincident, suddenly shutdown of reactor.

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Reaktor nuklir merupakan sumber radiasi primer. Keselamatan dalampengoperasian reaktor diterapkan oleh sistem proteksi dengan tindakan scram.Namun scram yang sering terjadi merupakan kegagalan operasi dan menimbulkanrisiko lain. Tujuan dari penelitian ini adalah untuk mengetahui pemicu danpenyebab dasar terjadinya scram dengan metode deskriptif analitik melaluiwawancara, observasi, dan telaah dokumen yang dipadukan dengan penyusunanfault tree analysis. Maka diperoleh hasil bahwa pemicu timbulnya scram, yaitukerapatan fluks neutron terlalu tinggi, periode pengoperasian terlalu cepat,pembebanan atau daya di teras tidak merata, dan terjadinya transien reaktivitaspositif. Sedangkan penyebab dasar kejadian scram, yaitu kenaikan batang kendaliterlalu cepat, kesalahan komposisi sampel iradiasi, korosi, pelemahan catu dayadetektor, pengosongan tabung berkas, dan fluks neutron tidak merata. Maka scramsebagai antisipasi kecelakaan juga menjadi umpan balik pengalaman operasiuntuk rekomendasi pemutakhiran penilaian keselamatan sehingga kegagalanoperasi dapat diminimalisir.Kata kunci:Keselamatan operasi reaktor nuklir, Sistem proteksi reaktor, Penyebab kejadian,Scram reaktor."

"The Fukushima accident resulted in the melting of the reactor core due to loss of supply of coolant when the reactor stopped from operating conditions. The earthquake and tsunami caused loss of electricity due to the flooding that occurred in the reactor. The absence of the coolant supply after reactor shutdown resulted in heat accumulation, causing the temperature of the fuel to rise beyond its melting point. In the early stages of the accident, operator could not determine the severity of the accident and the percentage of the reactor core damaged. The available data was based on the radiation exposure in the environment that was reported by the authorities. The aim of this paper is to determine the severity of the conditions in the reactor core based on the radiation doses measured in the environment. The method is performed by backward counting based on the measuring radiation exposure and radionuclides releases source term. The calculation was performed by using the PC-COSYMA code. The results showed that the core damage fraction at Dai-ichi Unit 1 was 70%, and the resulting individual effective dose in the exclusion area is 401 mSv, while the core damage fraction at Unit 2 was 30%, and the resulting individual effective dose was 99.1 mSv, while for Unit 3, the core damage fraction was 25% for an individual effective dose of 92.2 mSv. The differences between the results of the calculation for estimation of core damage proposed in this paper with the previously reported results is probably caused by the applied model for assessment, differences in postulations and assumptions, and the incompleteness of the input data. This difference could be reduced by performing calculations and simulations for more varied assumptions and postulations."