After the 2011 Japan earthquake and tsunami caused significant damage at Fukushima Daiichi, the Nuclear Regulatory Commission required all US nuclear power plants to have a mitigation strategy for beyond design basis events. Industry-developed response plans, called “FLEX” strategies, deployed new, portable equipment such as diesel generators and cooling pumps. As this new equipment needs to be available after a natural disaster, storage in protected locations is required. Many nuclear plants have recently constructed new storage buildings, or FLEX buildings, as part of their post-Fukushima strategy.

The equipment door is a critical component of a FLEX building. Large enough to drive a semi-trailer truck through, it is required to protect the equipment in case of an earthquake, flood, tornado and also may need to be capable of opening within a few minutes in order to respond during an emergency. The equipment door presented in this paper serves these purposes very effectively. The composite section of the door is capable of shielding the structure from penetration as well as overall dynamic response from tornado missile impact. The door travels on an overhead rail which, being indoors and above the opening, provides reliable door movement in case of snow or ice during winters or in case of debris from wind or tornado. Latches capable of withstanding tornado missile impact forces also restrain the door in case of wind or seismic forces. The door is opened by means of motorized trollies and is also equipped with a backup opening device by means of an air winch in case of a power loss.

The door and the latches that restrain the door from impact are analyzed using ANSYS finite element software. A limit state analysis is performed that identifies the sequence of yield limit states for the components of the door and the door latch as the loading progresses. The analysis continues until the ductility limit state for the latch is reached. Redistribution of stresses within the components of the latch is observed during the analysis. A modal analysis and a direct integration time history analysis is also performed to capture the dynamic response due to impact loading.

Overall, this paper presents a highly robust and reliable design for a FLEX building equipment door that is capable of protecting the contents of the building during a natural disaster and remaining operational during the response after an emergency.

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