Model distribusi spasial raionuklida pada kecelakaan PLTN (Simulasi di PLTN Muria)

Abstract

PLTN has a disadvantage that can cause a contamination to the environment widely when a serious accident occurred. The aforementioned accident would caused a leakage to the reactor, and this would caused a dispersion of the radionuclide resulted from the fission reaction into the environment, then into the air, and finally would deposited on the surface of the land by rain. The model of spacial distribution of radionuclide is needed to predict the pattern of radionuclide dissemination. This research was intended to map the distribution of radionuclide in the area of study caused by the accident that might occur at PLTN. The method used in mapping the radionuclide spacial distribution is initiated by the assumption that serious damages have occurred at type PWR reactor which is unable to stop the distribution of the radionuclide into the environment. Modeling of spacial distribution of radionuclide was done by using ArcGis 9.3 software, with radial basis function (RBF) method to study the impacted area that consist of 260 country sides which include regency of Jepara, Demak, Kudus, and Pati. Spacial modeling was done by distributing the calculated data on the surface coordinate of studied area at 360O direction using 16 points of compass started from the distance of the source at 200 m up to 35000 m. The selection on the inventory at PWR reactor resulted in two important elements, and they are Cs-137 and I-131. Distribution area of radionuclide on the land surface will depend on the differences of land surface area and the vegetation. Seven days after the accident at PLTN, the radionuclide of Cs-137 and I-131 will be distributed more on land surface (69.979%) than on the vegetation surface (30.021%). After one month, radionuclide will be distributed more on the vegetation surface (40.749% of area) than on the land surface (22.999% of area), and similar conclusions are also true after 2, 3, and 4 months of accident at PLTN. Radionuclide experiences degradation due to distribution and adsorption on the non-vegetated land, and adsorption on the vegetated land with distribution rate value of radionuclide I-131 on the land surface is 1.884E-01/day. This value is higher than the degradation rate value of radionuclide Cs-137 at 1.013E-01/day. Model of spacial distribution of radionuclide Cs-137 and I-131 on the land surface of the area of study within the radius of 35 km from the source shows that seven days after the accident at PLTN, the PAZ (Precautionary action zone) zone is located on all of the area of study within radius of 35 km. That means that the radionuclide will be found on the 260 country sides. One month after the accident, the PAZ zone will be at 154 country sides which are located within the radius of 28.94 km from the source of accident. The areal of PAZ zone will keep decreasing after two, three, and four months of accident, and these areas will become the UPZ zones (Urgent Protective Action Planning Zone). Four months after the accident, the UPZ zones will be within the radius of 5.7 km, while the PAZ zone is located within the radius of 2.47 km. The PAZ zone will include the W001 country side. Prediction on the areal distribution of Cs-137 using arcGis 9.2 resulted in the formation of maps for distribution model of radionuclide on an accident at PLTN in the year of 2010, 2020, 2025, and 2030, to give the areal distribution of radionuclide that is acceptable and is not different significantly.

PLTN memiliki kelebihan dalam hal keefisienan menghasilkan energi listrik, sekaligus memiliki kekurangan yang dapat mencemari lingkungan secara luas apabila PLTN mengalami kecelakaan parah. Kecelakaan yang dimaksud akan menyebabkan kebocoran reaktor yang mendispersikan radionuklida hasil fissi ke lingkungan, terdispersi ke udara, terdeposisi oleh hujan dan sampai pada permukaan darat. Model distribusi spasial radionuklida diperlukan untuk memprediksi pola sebaran radionuklida jika terjadi kecelakaan parah yang memberi gambaran perpindahan radionuklida ke lingkungan. Penelitian dimaksudkan untuk mempetakan distribusi radionuklida di lingkungan wilayah studi yang ditimbulkan oleh kecelakaan PLTN yang mungkin terjadi dengan tujuan: (1) untuk mengetahui faktor kondisi lingkungan wilayah studi, jarak dan waktu terhadap distibusi setiap jenis radionuklida; (2) untuk mengetahui pola distribusi radionuklida di lingkungan dengan bantuan perangkat lunak “GIS” dari waktu ke waktu; (3) untuk dapat menentukan zonasi kedaruratan apabila kecelakan nuklir terjadi di wilayah studi; (4) untuk dapat memprediksi luasan distribusi radionuklida dari kecelakaan PLTN Muria di masa depan. Metoda dalam mempetakan distribusi radionuklida secara spasial pada kecelakaan PLTN Muria diawali dengan asumsi telah terjadi kerusakan parah reaktor jenis PWR pada materi pelindung berlapis bahan bakar urarium sehingga tidak mampu menahan radionuklida terdistribusi ke luar lingkungan dan diasumsikan sumber radionuklida dapat ditangani dalam waktu 7 hari. Densitas radionuklida yang mencapai lingkungan, dihitung dari sumber inventory reaktor dengan memperhatikan factor kondisi lingkungan wilayah studi. Radionuklida yang mencapai permukaan darat dihitung dengan memperhatikan faktor deposisi, serapan tanah, dan serapan akar vegetasi. Pemodelan distribusi spasial radionuklida dilakukan dengan menggunakan perangkat lunak ArcGis 9.3, metoda radial basis function (RBF) teprhadap wilayah studi yang terdiri dari 260 wilayah desa dalam 22 kecamatan di 4 kabupaten meliputi kabupaten Jepara, Demak, Kudus dan Pati. Pemodelan spasial dilakukan dengan cara mendistribusikan data hasil perhitungan pada koordinat permukaan wilayah studi pada arah 360o menggunakan 16 arah mata angin dari jarak sumber mulai radius 200 m sampai dengan 35000 m.