EVALUATION OF NEUTRON SHIELDING PERFORMANCE OF CD-SS 316L AS A CANDIDATE ALLOY FOR DRY CASK OF RESEARCH REACTOR SPENT FUEL Development of dry casks is necessary to support the national strategy for management of spent fuels. One of the requirements for the dry cask is shielding performance for neutron emitted by the spent fuels to be stored in the dry cask. The objectives of this study are to determine the emitted neutrons by the spent fuel generated from GAS research reactor and to evaluate the neutron shielding performance of Cd-SS316L alloy as a candidate material to be used in dry cask for the spent fuels. The former was carried out using Origen 2.1 software, while the latter using MCNP5. The result shows that the emitted neutrons by a spent fuel after 5 years discharged from GAS research reactor were 2.81×103 and 3.32×106 n/s for reactor core power of 15 and 30 MW, respectively. Addition of Cd improves the neutron shielding performance of SS 316L. The evaluation of neutron shielding performance of SS 316L with addition of Cd which is the candidate material for dry cask of the spent fuels from the GAS research reactor can be evaluated using Origen 2.1 software for neutron emission, while the neutron shielding performance was evaluated by the simulation using MNCP 5 software. This study shows the Cd-SS 316L alloy can be used for further study to develop the dry cask design for the GAS research reactor.Key words: Neutron shielding, cadmium, stainless steel, spent fuel.
A key issue contributing to the success of NPP technology is the safe handling of radioactive waste, particularly spent nuclear fuel. According to the IAEA safety standard, the spent fuel must be stored in interim wet storage for several years so the radiation and the decay heat of the spent fuel will decrease to the safe limit values, after which the spent fuel can be moved to dry storage. In this study, we performed a theoretical analysis of heat removal by natural convection airflow in spent nuclear fuel dry storage. The temperature difference between the air inside and outside dry storage produces an air density difference. The air density difference causes a pressure difference, which then generates natural airflow. The result of the theoretical analysis was validated with simulation software and experimental investigation using a reduced-scale dry storage prototype. The dry storage prototype consisted of a dry cask body and two canisters stacked to store materials testing reactor (MTR) spent fuel, which generates decay heat. The cask body had four air inlet vents on the bottom and four air outlet vents at the top. To simulate the decay heat from the spent fuel in the two canisters, the canisters were wrapped with an electric wire heater that was connected to a voltage regulator to adjust the heat power. The theoretical analysis results of this study are relatively consistent with the experimental results, with the mean relative deviation (MRD) values for the prediction of air velocity, the heat rate using natural airflow, and the heat rate using the thermal resistance network equation are +0.76, −23.69, and −29.54%, respectively.
Reaktor Daya Non-Komersial (RDNK) with a 10 MW thermal power has been proposed as one of the technology options for the first nuclear power plant program in Indonesia. The reactor is a High Temperature Gas-Cooled Reactor-type with spherical fuel elements called pebbles. To support this program, it is necessary to prepare dry cask to safely store the spent pebble fuels that will be generated by the RDNK. The dry cask design has been proposed based on the Castor THTR/AVR but modified with air gaps to facilitate decay heat removal. The objective of this study is to evaluate criticality safety through keff value of the proposed dry cask design for the RDNK spent fuel. The keff values were calculated using MCNP5 program for the dry cask with 25, 50, 75, and 100% of canister capacity. The values were calculated for dry casks with and without air gaps in normal, submerged, tumbled, and both tumbled and submerged conditions. The results of calculated keff values for the dry cask with air gaps at 100% of canister capacity from the former to the latter conditions were 0.127, 0.539, 0.123, and 0.539, respectively. These keff values were smaller than the criticality threshold value of 0.95. Therefore, it can be concluded that the dry cask with air gaps design comply the criticality safety criteria in the aforementioned conditions.
ABSTRAK ANALISIS SUB-KRITIKALITAS RAK BAHAN BAKAR NUKLIR BEKAS RSG-GAS MENGGUNAKAN ALUMINIUM.Penggunaan stainless steel sebagai material rak penyimpanan bahan bakar nuklir bekas (BBNB) di fasilitas Kanal Hubung -Instalasi Penyimpanan Sementara Bahan Bakar Bekas (KH-IPSB3) berpotensi menyebabkan terjadinya korosi galvanik pada BBNB sehingga penggantian material rak penyimpanan BBNB perlu dipertimbangkan. Potensi korosi galvanik terjadi karena aluminium sebagai material utama kelongsong Bahan Bakar Nuklir (BBN) Reaktor Serba Guna -G. A. Siwabessy (reaktor RSG-GAS) berinteraksi dengan stainless steel sebagai material rak penyimpan BBNB. Aluminium dapat digunakan sebagai material alternatif rak penyimpanan BBNB untuk mengurangi efek korosi galvanik. Penelitian ini bertujuan untuk mengkaji kritikalitas rak penyimpanan BBNB dengan material aluminium. Jaminan kritikalitas diperlukan untuk menjaga keselamatan fasilitas KH-IPSB3. Rak penyimpanan aluminium yang optimum dikaji dengan melakukan simulasi ukuran pitch dan menghitung laju serapan neutron pada kondisi normal (tidak terjadi kecelakaan). Perhitungan nilai kritikalitas (keff) dilakukan menggunakan program Monte Carlo N-Particle versi 6 (MCNP6). Model yang digunakan adalah model 3-dimensi satu rak utuh yang terisi penuh dengan BBNB di dalam kolam penyimpanan. Hasil perhitungan pada ukuran pitch 127 mm menunjukkan bahwa nilai keff rak penyimpanan BBNB dengan material aluminium (keff = 0,7709) lebih besar 13,20% dibandingkan material stainless steel (keff = 0,6810). Nilai keff rak penyimpanan BBNB dengan material aluminium pada ukuran tersebut masih berada dalam rentang yang disyaratkan yaitu keff kurang dari 0,95. Nilai keff dipengaruhi oleh ukuran pitch, dimana dengan berkurangnya ukuran pitch 1 mm dapat meningkatkan nilai keff sebesar 14,24%. Nilai laju serapan neutron juga mempengaruhi nilai keff, di mana laju serap neutron rak penyimpanan dengan material aluminium lebih kecil dibandingkan material stainless steel. Hasil simulasi menunjukkan bahwa rak penyimpanan dengan material aluminium memenuhi aspek keselamatan untuk digunakan sebagai rak penyimpanan BBNB di KH-IPSB3 karena mempunyai nilai keff<0,95 pada ukuran pitch lebih dari 112 mm (keff = 0,9196).Kata kunci: Sub-kritikalitas, penyimpanan BBNB, rak aluminium.
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