INTRODUCTION

The pump assemblies used in nuclear power plant applications need to be evaluated for design parameters as well as seismic qualifications in order to ensure their reliability considering the criticality of their applications.  The design guidelines for these components are provided in subsections NB, NC, ND & NF of ASME BPVC Sec. III. These sections are described based on the criticality of the components with NB subsection having guidelines for most critical components as likewise the other subsections with reduced criticality. The design is evaluated for various loading combinations described as Level-A through Level-D. This loading also includes seismic loading which corresponds to seismic response at the pump installation site.

Renowned Pump Manufacturer from India approached ANALYZER to seek assistance in evaluating the design of their newly developed pump assembly for its reliability being a nuclear power plant product.

FEA WORKFLOW

• Creation of 3D CAD model for pump assembly. Sometimes the model is provided by the client itself.
• Creation of FEA model using a preprocessing tool – Hypermesh. Here modeling different connections such as bearings with shaft & casing is a great challenge. Two models are created as one for foundation load calculations & the other is for full model stress evaluation.
• The FEA model is analyzed in order to calculate loading for foundation bolts as they are the main load taking members.
• The complete model of the pump assembly is analyzed for load combinations – Level-A through Level-D.
• The assembly is also evaluated for close gap clearances in severe operating conditions.
• Report the results for the client’s reference.

CHALLENGES

• Capturing the Mass of various components of the pump assembly in foundation load calculations
• Bearing modeling in FEA
• Coupling modeling in FEA
• Bolt load extraction from FEA
• Seismic analyses of a pump assembly

THE SOLUTION

The FEA model is prepared for complete pump assembly. In order to avoid complexities, bearings & coupling is modeled in a much simpler way in FEA. The first model is solved in order to extract the foundation loading & complete assembly is solved for various load combinations.

The results showed that the foundation loads are much below the allowable limits. The stresses for various load combinations are within the allowable limit. The assembly is also evaluated for close clearances between mating parts & is predicted to be working fine under severe operating conditions also. Thus the pump design was predicted to be safe even in severe operating conditions during its service life.

BENEFITS

• Pump assemblies are evaluated in a more accurate way than conventional analytical methods.
• The pump assemblies from an idle plant can be used for a working plant by evaluating it for site seismic conditions.
• Evaluation against close clearances would ensure the severe condition operational reliability of pump assembly.