Nuclear Plant Structures: Resistance to Aircraft Impact
Authors: Nickell Robert E. 
Published: October 2008

Reinforced concrete structures at nuclear power plants in the United States, in particular containment structures, are designed to be extremely robust and rugged. The ruggedness and robustness of containment structures can be attributed to their design basis, which includes pressure and thermal loads from severe reactor and primary coolant circuit accident events. In addition, the inherent structural integrity of these structures is demonstrated by the degree of protection provided against severe natural phenomena, such as earthquake loads, tornado missiles, floods, and fires. To some extent, the design basis also requires an evaluation of the potential for an aircraft impact accident, depending upon proximity of the plant to airports and the potential frequency of take-off and landing accident occurrence. In order to evaluate potential damage to nuclear power plant concrete structures and other hardened concrete structures from accidental or intentional aircraft impact, some analytical and experimental simulations have been carried out over the past two or three decades. The most recent effort was carried out for the U.S. nuclear power industry by EPRI, at the request of the Nuclear Energy Institute (NEI). The EPRI contractors were ABS Consulting of Irvine, California; Anatech Corporation of San Diego, California; and ERIN Engineering and Research, Inc. of Walnut Creek, California. The early phases of the effort were concerned only with nuclear power plant structures that house nuclear fuel, such as PWR and BWR containment structures, PWR and BWR spent fuel storage pools, dry spent fuel storage systems, and spent fuel transportation casks. A classified final report on these early phases was completed in February 2003 and the results have been reported to the U. S. Nuclear Regulatory Commission (NRC). This presentation is based upon the portion of the results that have been released publicly by NEI. The reference aircraft chosen for the analyses is a Boeing 767-400 traveling at a velocity of 350 miles per hour. The maximum takeoff weight for this aircraft is approximately 450,000 pounds, which includes 23,980 gallons of fuel. It has a wingspan of 170 feet, an overall length of 201 feet, a fuselage diameter of 16.5 feet, and two engines weighing 9,500 pounds each. Three representative containment designs were analyzed: (1) reinforced concrete with a ferritic steel liner, (2) post-tensioned concrete with a ferritic steel liner, and (3) free-standing steel surrounded by a reinforced concrete shield building. All containment designs in the United States were represented by one of these three designs. Two spent fuel storage pools were analyzed, one representing typical PWR pools and the other representing typical BWR pools. Both have stainless steel liners. Three representative dry spent fuel storage systems were analyzed: (1) a vertical concrete storage cask encased in steel; (2) a vertical metal storage cask; and (3) a horizontal concrete storage module. Finally, a metal transport cask tied down on a rail car was analyzed. In all containment cases analyzed, no breach of the containment boundary was found, even though substantial damage to the concrete and deformation of the metallic shell or liner was observed. Similarly, the stainless steel pool liners ensure that, although localized crushing and cracking of the concrete walls is observed, no pool cooling water is lost. For the vertical concrete cask, the stainless steel canister housing the spent fuel assemblies is not breached although there was crushing and cracking of the concrete enclosure at the area of impact. For the vertical metal cask, the cask is dented, but not breached. Similarly, although the damage to the horizontal concrete storage module is substantial, there is no breach of the enclosed canister. The analysis of the transport cask showed that the cask body withstands the impact from the direct engine strike without breaching. The forces on the container are comparable to the forces associated with the impact design basis for these casks.