Design of Nuclear Safety-Related Underground Diesel Fuel Oil Storage Tanks

Diesel fuel oil storage tanks are critical components for safety of nuclear power plants. Proper functioning of the emergency diesel generators during an earthquake depends on the fuel oil supplied from the storage tank. Failure of the tank, nozzles or fuel pipes can result in contamination and/or leakage of the fuel. The allowable stress limits and design charts for above ground tanks, which are provided in the ASME Boiler and Pressure Vessel Code for a pressure vessel, are occasionally adopted in the design of underground tanks. However, the analytical methodology for evaluation of stresses in the buried tanks requires detailed analysis different from that for a typical pressure vessel. Soil-structure and fluid-structure interaction effects need to be considered in the analysis for simulation of the actual static and seismic loads. Therefore, advanced simulation techniques and finite element analysis tools have been used by several researchers to evaluate buried tanks. Simple, but acceptably accurate techniques for comprehensive evaluation of underground storage tanks have not been established. This study presents simplified evaluation techniques for a diesel fuel storage tank using fundamental concepts. The diesel fuel oil storage tanks considered here are cylindrical and oriented with their axes in the horizontal direction. The static overburden and seismic pressures cause ovaling of the tank and generate significant bending stresses, which are not addressed in the pressure vessel design approach. The simplified tank evaluation proposed here includes the ovaling effect under static overburden, seismic and sloshing loads. Earthquake induced stresses in hoop and longitudinal directions are calculated using the free field approach and the classical Housner Method is employed in the sloshing analysis. Allowable stress and buckling of the tank wall are checked against corresponding criteria.