On March 11, 2011, a large earthquake with an epicenter a few miles off the northeastern shores of Japan spawned a tsunami that inundated the Fukushima Daiichi nuclear plant. The earthquake disconnected the plant from the offsite power grid. The tsunami disabled the onsite emergency diesel generators. Deprived of electricity for emergency systems, the reactor cores for Units 1, 2 and 3 overheated and melted down.
On March 12, 2012, the Nuclear Regulatory Committee (NRC) ordered owners of US nuclear power plants to develop and implement mitigation strategies to reduce the vulnerabilities of their facilities to extreme earthquakes and floods. While the specific measures varied from plant to plant, the mitigating strategies generally involved portable pumps, portable generators, cables, hoses, and hauling equipment (called FLEX equipment) and associated procedures for workers to use should permanently installed equipment become disabled.
While the NRC’s order and the industry’s FLEX equipment were intended to reduce vulnerabilities to hazards over and above those deemed credible when the nuclear plants were designed and licensed, Dominion Energy has figured out how to use the new equipment to lessen old risks at its Surry nuclear plant, thus reaping a nuclear safety dividend from its Fukushima investment.