This paper aims at illustrating a number of methods for stabilizing pressure solution and improving surface curvature calculation for the simulation using the moving particle semi-implicit (MPS) method. The unphysical numerical oscillation of pressure originated from the original MPS method can be suppressed by adjusting the collision coefficient in the collision model and using a specific weight function for avoiding the occurrence of excessive pressure value when particles get closer. The pressure gradient solver and the poison pressure equations (PPE) are also modified by implementing a mixed source term of velocity divergence and a corrective matrix, respectively. In addition to the pressure field, the surface tension force is essential for correctly deforming the fluid interface between different phases. The curvature calculation is improved with high accuracy by utilizing a contoured continuum surface model where a new scheme for computing the partial derivatives of the mollified color function is proposed. The Gaussian function for smoothing the color function is specified to ensure a better coincidence of the local contour of mollified color values with the interface. Compared to the original MPS method, both modifications and extensions for the pressure and curvature solver can generate more stable and accurate results, which are presented by a few numerical examples, including the hydrostatic pressure, dam break and bubble rising models.

The paper will describe the following analysis of Loviisa plant’s spent fuel pools. As a consequence of stress tests for the existing NPP’s in Finland after the experiences gathered from the Tohoku -Taheiyou-Oki event in Japan in March of this year Fortum Power and Heat Oy (Fortum) has initiated the following analyses of the Loviisa power plant’s refueling pools and spent fuel intermediate storage pools for the combined cooling loss and the earthquake loads. The following loads will be analyzed: 1) The spent fuel pool and refueling pools water temperature is 100 degrees Celsius. The heat load duration is undetermined; 2) The earthquake ground motion applied simultaneously with the thermal load is defined as follows: (ground motion response spectrum is defined in Guide YVL 2.6), the maximum horizontal acceleration is assumed to be 0.1g, 0.2g, 0.3g and 0.4g, respectively; 3) Own weight; 4) The pool of water, hydrostatic pressure load plus the sloshing load because of earthquake motion. Te analysis is aimed to demonstrate the structural integrity and leak-tightness of the pools under the effect of above loads. The analysis is nonlinear taking into account the cracking of the concrete. As a result of the analysis the maximum strains will be determined in the pool stainless steel liner as well in the pool concrete walls.

The interest in using polyethylene pipe in Class 3 safety water systems in nuclear power plants has grown tremendously in the last few years. PE pipe brings a host of benefits to the application in the form of long-term performance and reliability due to not being prone to corrosion and tuberculation. As the work continues through various ASME committees to develop the appropriate code language for the design and use of PE pipe, it is clear that plastics are not evaluated the same way metallic components would be in similar applications. However, the nature of the failure (i.e. ductile or brittle) is important for both. This paper will give an overview of the methodology used to establish the long-term hydrostatic strength of polyethylene compounds, and how that strength is used for engineering design in a safe a reliable manner. The strength of a polyethylene compound, being a thermoplastic, cannot be determined from a short-term tensile strength test, as with most metals. As such, testing and evaluation methodologies have been developed which take into account the viscoelastic creep response of thermoplastics, as well as potential changes in failure mode, in order to forecast the long-term hydrostatic strength of these materials so they can be safely used in a pressure pipe application. Since PE was first used in a piping application in the late 1950s, PE has continued to evolve as have the methodologies used to evaluate its strength against stresses induced by hydrostatic pressure. The common method for evaluation relies on putting specimens under multiple continuous, steady-state stress levels until failure. These data points are then used in a log-log linear regression evaluation. This regression equation is then extrapolated to a point sufficiently further out in time to where a long-term strength can be established. It has been clearly established that over a temperature range that the stress rupture behavior of PE follows an Arrhenius, or rate process, relationship between temperature and strength. By testing at elevated temperatures it can be “validated” that the extrapolation remains linear and ductile beyond the actual test data. This and other criteria established by ASTM D 2837 and the Plastics Pipe Institute’s Hydrostatic Stress Board allow for establishing an appropriate maximum working stress that will assure a very long design life.