STUDI EKSPERIMENTAL COUNTER CURRENT FLOW LIMITATION (CCFL) DENGAN METODE ANALISIS SINYAL FLUKTUASI TEKANAN DAN VISUALISASI PADA GEOMETRI HOTLEG PWR SKALA 1:30 L/D 22 I/D 3,8

YUSUF RAHMAN, Prof. Dr. Ir. Indarto, DEA.

2020 | Skripsi | S1 TEKNIK MESIN

Pada kasus loss of coolant accident (LOCA) di pembangkit tenaga nuklir jenis pressurized water reactor (PWR), terjadi penurunan tekanan pada sirkuit primer akibat kebocoran, sehingga fluida cair yang berada di dalam sirkuit secara perlahan berubah fase menjadi uap. LOCA diinisiasi oleh terjadinya fenomena flooding, yaitu fenomena saat uap dari reaktor dan kondensat dari steam generator (SG) yang semula mengalir saling berlawanan arah, berubah menjadi aliran searah menuju SG. Fenomena ini sangat dihindari karena dapat menggagalkan proses pendinginan pada reaktor. Oleh sebab itu, penelitian mengenai flooding perlu dilakukan, mengingat dampaknya yang dapat membahayakan keselamatan operasi pembangkit. Penelitian ini dilakukan dengan menginstalasi simulator PWR yang mengikuti desain simulator Upper Plenum Test Facility (UPTF) dengan konfigurasi hotleg terdiri dari saluran horizontal, belokan dan miring (riser). Ukuran geometri hotleg menggunakan skala 1:30 dari ukuran simulator UPTF yang memiliki perbandingan L/D = 22 dan I/D = 3,8. Simulator hotleg memiliki diameter dalam pipa 25,4 mm, panjang pipa horizontal 560 mm dan panjang pipa miring 98 mm dengan kemiringan sebesar 50 derajat. Data dalam bentuk sinyal beda tekanan dan visual diambil menggunakan differential pressure transducer dan kamera handphone (tidak dapat menggunakan video kamera khusus karena sedang bermasalah dan membutuhkan waktu yang lama untuk perbaikan) dengan pengaturan high speed recording. Kemudian, dilakukan analisis distribusi tekanan pada saat terjadinya flooding menggunakan metode probability density function (PDF) dan power spectral density (PSD) berdasarkan data sinyal, dan mengidentifikasi fenomena-fenomena yang muncul pada aliran saat terjadinya flooding berdasarkan data visual. Berdasarkan analisis sinyal PDF dan PSD, peningkatan kecepatan superfisial air dan udara saat terjadi flooding sangat berpengaruh terhadap distribusi sinyal fluktuasi tekanan beserta frekuensinya. Selain itu, berdasarkan pengamatan menggunakan kamera, onset of flooding diawali dengan pembentukan small roll wave dan large roll wave. Sesaat sebelum onset of flooding, pada kecepatan superfisial air rendah dan sedang, fenomena hydraulic jump muncul di sepanjang pipa horizontal, sedangkan pada kecepatan superfisial air tinggi tidak terdapat fenomena hydraulic jump. Karena terdapat perbedaan karakteristik tersebut, pada penelitian ini mekanisme flooding terbagi menjadi tiga wilayah.

In the case of loss of coolant accident (LOCA) on pressurized water reactor (PWR) nuclear plant, the leakage in primary circuit makes pressure drop and it leads to vaporize the liquid phase gradually. LOCA is preceded by flooding phenomenon, which is happened when water vapor from reactor and condensate from steam generator initially flow in counter-current condition, then turned into cocurrent (condensate carried away by vapor) flow that flowing toward steam generator. This phenomenon is strictly avoided because it can cause failure in the cooling process in reactor. Hence, the various study on flooding phenomenon needs to be conducted, considering the impact that could endanger the safety of plant operation. The study was conducted by installing a PWR simulator which follows Upper Plenum Test Facility (UPTF) design with a hotleg configuration which consist of horizontal, bend and riser parts. The hotleg geometry uses scale of 1:30 of the actual geometry UPTF size with ratio L/D = 22 and I/D = 3.8. The hotleg simulator has an inner pipe diameter of 25.4 mm, a horizontal pipe length of 560 mm and an inclined pipe length of 98 mm with a slope of 50 derajat. The data which in form of pressure difference signals and visuals are captured by a differential pressure transducer and a handphone (unable to use the dedicated high-speed video camera because it's damaged and require a lot of time to repair) with high-speed recording settings. Thereafter, the pressure distribution was analyzed by probability density function (PDF) and power spectral density (PSD) methods based on signal data and identify the phenomena that appear inside hotleg when flooding occur based on visual data. Based on signal analysis of PDF and PSD, increasing superficial velocity of water and air during flooding greatly affects the distribution of pressure fluctuation signal and its frequency. Furthermore, from the observation using camera, the onset of flooding begins with the formation of small roll wave and large roll wave. Shortly before onset of flooding, at low and medium superficial water velocities, the hydraulic jump occurs along the horizontal pipe and at high superficial velocity there is no hydraulic jump appeared. Due to these difference in characteristics, in this study the flooding mechanism is divided into three regions.

Kata Kunci : aliran dua fase, onset of flooding, power spectral density, probability density function, visualisasi, mekanisme flooding, kurva flooding.