Near Miss at a Nuclear Material Production and Storage Facility
A potentially explosive situation was reported by safety inspectors at a nuclear waste tank. The waste slurry had formed a thick crust which was trapping hydrogen being continuously generated underneath. The tank has uncertain chemistry and contents.According to the New Scientist article (see references) four million litres of waste "have been behaving mysteriously inside the underground storage tank. Every few months the tank burps releasing a burst of hydrogen and nitrous oxide."Calculation estimated a potential for an explosion equivalent to 230 kilos of TNT. Up to 66 tanks at Hanford are believed to be leaking, 22 are accumulating hydrogen and a further 22 are potentially explosive.Researchers have measured concentrations of 4 per cent hydrogen at the exhaust stack of the tank when the crust breaks, which may imply very high hydrogen concentration under the crust.
Event Date
October 1, 1990
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Cause Comments
Radiation in the waste caused the remaining water to break down, producing hydrogen by radiolysis. But the waste slurry had formed a thick crust trapping the hydrogen continuously generated underneath. Additional hydrogen and nitrous oxide results from the breakdown of organic chemicals that were added to the waste. But a thick, hard crust has formed on the surface of the slurry which traps the gases. Periodically, the crust breaks and collapses, releasing the gases.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
Nuclear waste tank
Storage/Process Medium
Location Type
Location description
Industrial Area
Pre-event Summary
According to the New Scientist article (see references) efforts were made in the 1970s to reduce the volume of nuclear waste. In one tank liquid waste was concentrated into a thick slurry by evaporating off water and adding chemicals that caused other liquids to form solid crystals. The slurry is about the consistency of peanut butter.
Number of Fatalities
3
Currency
Lessons Learned
Lessons Learned
According to the New Scientist report (see references), various methods were tried to prevent hydrogen from building up under the crust. "From 1983 to 1986, crust was broken up by jets of water, but the operation added too much additional water to the tank. Later, pressurised air was used in the same way. A review in 1989 concluded that neither technique worked well, and often made the problem worse. "A historical summary of the plant operation can be found in Gephard 2010 (see reference). However, the report does not report specifically the hydrogen case. That many years later the radiolysis problem was not yet completely solved can be deduced from a RT news report of 2013, which similar explosion potential from hydrogen generated at the walls, especially those with double wall. This source quotes the DOE, stating that all affected areas "...are actively ventilated, which means they have blowers and fans to prevent hydrogen gas build-up....These ventilation systems are monitored to ensure they are operating as intended".
Event Nature
Emergency Action
Near miss, but the source do not report solutions which eliminated completely the problem.
Release Type
Release Substance
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
NewScientist Newsletter, 6 October 1990,
https://www.newscientist.com/article/mg12817373-500-technology-pressure…
(accessed October 2020)
RT news of 3 Apr, 2013,
https://www.rt.com/usa/hanford-nuclear-waste-tanks-288/ ,
(accessed October 2020)