An air tunnel at a degrading Savannah River Site nuclear materials processing facility should be able to withstand an earthquake, according to a detailed analysis for the Department of Energy, despite concerns raised two years ago by a federal safety board.
Savannah River Nuclear Solutions (SRNS), management and operations contractor for the 310-square-mile DOE facility in South Carolina, drafted the nonlinear analysis for H Canyon, which processes highly enriched uranium and other nuclear materials to reduce the threat of weapons production. The analysis is a complex structural calculation of the air tunnel’s capabilities to withstand various hazards, including an earthquake. It was completed in late June and is being reviewed by SRNS and Energy Department officials, with a final calculation due in September.
The contractor, with input from DOE, determined the air tunnel should handle a “design basis earthquake,” meaning the tunnel would remain functional following a seismic event. Design basis details the parameters for a building code to ensure it is safe and sturdy enough to withstand various situations.
The calculation is based on Energy Department standards for nonreactor nuclear facilities such as H Canyon. The standards are approved by the federal agency with input from the U.S. Nuclear Regulatory Commission (NRC) and include several criteria, such as meteorological monitoring, the distance between the site and potentially impacted people off-site, and the possible releases of airborne materials to the environment. Studying these factors helped SRNS form a calculation and reach its conclusion on the tunnel.
H Canyon has been a concern for years. The facility began operations in 1955 and is suffering degradation in various areas, including its roofing.
The tunnel is a concrete ventilation duct that is 20 inches thick. It connects H Canyon to its air ventilation system. In a June 2017 report, the Defense Nuclear Facilities Safety Board (DNFSB) cited degradation of the tunnel wall and questioned its ability to withstand an earthquake.
Five months after the DNFSB report, the Energy Department approved a justification for continued operations of the entire H Canyon. That allowed work to continue there while regulators considered ways to buffer safety measures in the tunnel and beyond by updating the facility’s documented safety analysis. The document evaluates potential hazards during design, construction, operation, and eventual cleanup.
One intended safety measure was consideration of measures to prevent earthquake impacts, versus the current method of mitigating impacts after an earthquake. But SRNS concluded the canyon tunnel should remain functional and safe during a seismic event.
In addition to the calculation, the contractor studies the durability of the tunnel by using a remote-control vehicle with a camera for inspections. Savannah River workers found it has only experienced only 2 inches of corrosion in more than six decades of service.
That means the degradation is not presently a significant concern, said SRS spokesman Monte Volk. “If the calculation does not change under review and comment resolution, the conservative controls put in place in 2017 in response to questions about the ability of the air tunnel to withstand a design basis earthquake could be removed,” Volk said via email.
