The Defense Nuclear Facilities Safety Board (DNFSB) was not moved by a Department of Energy statement this week that plutonium stored in the Nevada National Security Site’s Device Assembly Facility is safe from earthquakes that might cause high explosives to detonate in the facility and spew plutonium into the air beyond the site’s borders.
“The facility continues to operate without accounting for the increase in seismic hazard and without evaluating whether the credited structures, systems and components can perform their safety function during and after a seismic event,” DNFSB Chairman Bruce Hamilton wrote in a March 21 letter to Energy Secretary Rick Perry.
A DNFSB spokesperson said Thursday that the board “stands by” the letter, despite DOE’s National Nuclear Security Administration’s (NNSA) saying that the accident DNFSB worries about is only conceivable during a high-yield, underground nuclear-explosive test at the site. That has not been done at the former Nevada Test Site since the early 1990s, and currently is not authorized, an NNSA spokesperson wrote in a statement.
A full-up nuclear-explosive test could in theory cause an earthquake so strong that it upsets conventional explosives “in close proximity with large quantities of nuclear material” and causes a plutonium-spreading explosion, the NNSA spokesperson wrote.
A high-yield test device, like those once put together at the Device Assembly building in the days of full-yield nuclear testing in Nevada, would fit that bill. However, since the NNSA now assembles only much smaller devices for subcritical plutonium experiments, “the worst case radiation dose … is significantly less than established dose limits for the public and are far less than that those reported by the DNFSB,” the NNSA spokesperson stated.
In its letter, DNFSB cited data from the Device Assembly Facility’s current documented safety analysis that said a worst-case explosion caused by an earthquake “could result in 22 rem total effective dose to the public.”
Then there is the matter of the half metric ton of weapon-usable plutonium the NNSA shipped to the Device Assembly Facility sometime before November 2018. Lawmakers from Nevada have repeatedly railed at DOE to remove that material from the testing site’s interior. DOE has said it will only to do when Los Alamos National Lab is ready to process the material into plutonium pits for future warhead refurbishments.
And, the DOE branch said, the plutonium in the Device Assembly Building “would not be adversely impacted by a seismic event” because it “is staged in a secure building that prohibits the introduction of high explosives and ensures adequate protection from external explosive events.”
The NNSA and Nevada site management contractor Mission Support and Test Services could address Hamilton’s concerns in a new Documented Safety Analysis for the Device Assembly Facility: a document that identifies potential hazards at the facility and which Hamilton expects the agency to finish this summer, according to his letter.
“We are pleased that the Department is taking some action,” the DNFSB spokesperson wrote Thursday.
On Monday, Nevada’s congressional delegation seized on the DNFSB letter, and other things, as evidence that Congress should legally bar the NNSA from sending more plutonium to the state.
The NNSA shipped the half metric-ton of plutonium to Nevada because a federal court in South Carolina ordered the agency to move 1 metric ton of plutonium out of that state by Jan. 1, 2020. The half-ton of plutonium that did not go to Nevada will be shipped to the Pantex Plant in Amarillo, Texas, if it has not been already.
In a filing Tuesday with the U.S. District Court for Nevada, where the Silver State sued the NNSA over last year’s plutonium shipment, attorneys for South Carolina said the half-ton of plutonium not already moved to Nevada was still at the Savannah River Site. An attorney for South Carolina declined to say how the state knew where the plutonium was.
The NNSA declined to comment about the location of the half-ton of plutonium bound for Pantex, citing operational security. The agency has said in court that it will ship no more of the 1 ton of plutonium ordered out of South Carolina to Nevada.
Editor’s note, April 8, 2019, 9:55 a.m. Eastern. The story was corrected to show that DNFSB’s concerns were unrelated to the half metric ton of weapon-usable plutonium shipped to the Nevada National Security Site in 2018.
