Saya Lee

Reactor Cavity Cooling System Facility Shakedown and RELAP5-3D Model Validation

A small scale water-cooled experimental facility was built in order to study the complex thermohydraulic phenomena taking place in the Reactor Cavity Cooling System (RCCS) during the normal operation (steady-state case) an during accident scenario when forced convection is lost. The facility represents a portion of the reactor vessel with nine stainless steel coolant risers. The pipes are connected via cold and hot manifolds to a water tank located on top of the cavity. Due to the complexity of the expected thermal hydraulic phenomena, a RELAP5-3D input deck was prepared in order to predict the main thermohydraulic parameters, mainly coolant flow rate and temperatures. During the facility shakedown, the coolant flow was constantly monitored in order to observe the natural circulation startup phase and some interesting features of the coolant behavior were observed. The comparison of the preliminary experimental results from a test run with the prediction of the RELAP5-3D simulations helped validating the assumptions and simplifications adopted in the model for future simulations of steady-state and transients, and confirmed the potentiality of the system code for analysis of such systems. In the present paperwork, a detailed description of the experimental facility and the RELAP5-3D model are provided. Preliminary experimental results from different test runs are described and compared with the RELAP5-3D simulation results.Copyright

Head Loss Through Fibrous Beds Generated on Different Types of Containment Sump Strainers

During a Loss of Coolant Accident (LOCA), the high energy jet from the break may impinge on surrounding surfaces and materials, producing a relatively large amount of fibrous debris (mostly insulation materials). The debris may be transported through the reactor containment and reach the sump strainers. Accumulation of such debris on the strainers’ surface can cause a loss of Net Positive Suction Head (NPSH) and negatively affect the Emergency Core Cooling System (ECCS) capabilities. The U.S. Nuclear Regulatory Commission (U.S.NRC) initiated the Generic Safety Issue (GSI) 191 to understand the physical phenomena involved in this type of event, and help develop the tools to prove the safety and reliability of the existing Light Water Reactors (LWR) under these conditions. Some nuclear power plants have already adopted countermeasures in an attempt to limit the effect of the debris accumulation on the ECCS performance, by replacing or modifying the existing strainer configurations. In this paper, two different strainer designs have been considered and sensitivity analysis was conducted to study the effect of the approach velocity on the pressure drop at the strainer caused by the debris accumulation. The development of the fibrous beds was visually recorded in order to correlate the head loss, the approach velocity, and the thickness of the fibrous bed. The experimental results were compared to semi-empirical models and theoretical models proposed by previous researchers.Copyright