Sandia LabNews

Explosive Destruction System completes major milestone at Pine Bluff Arsenal

SandiaÕs Explosive Destruction SYSTEM is designed to be transportable to remote locations to destroy aging munitions.
SandiaÕs Explosive Destruction SYSTEM is designed to be transportable to remote locations to destroy aging munitions.

In April, Sandia’s Explosive Destruction System (EDS) was used in the completion of a major milestone at the US Army’s Pine Bluff Arsenal in Arkansas — destroying the largest inventory of recovered chemical warfare materiel to date, more than 1,200 munitions that included 450 German Traktor rockets.

With this milestone, the Army completed its mission to destroy all nonstockpile materiel declared when the United States entered into the 1993 Chemical Weapons Convention, an international treaty mandating the destruction of chemical warfare agents and munitions.

Sandia’s Explosive Destruction System is designed to be transportable to remote locations to destroy aging munitions..

 “This goes far beyond the original purpose of EDS,” says Brent Haroldsen (8123). “EDS was created to destroy small numbers of chemical munitions at the recovery site. But because it is robust and flexible, it was the right tool for this job.”

Sandia designed EDS for the Army after construction workers in 1993 unearthed an explosively configured chemical munition in Spring Valley, an upscale neighborhood of Washington, D.C., that during World War I was a chemical weapons research site. The public location prevented the Army from destroying the munition by open detonation. An Army survey identified more than 100 possible sites for buried munitions across the country, indicating an even greater need for a safe and environmentally sound method to destroy munitions.

‘Basic high school chemistry’

The core of EDS is a leak-tight vessel in which munitions are placed. An explosive shaped charge opens the munition’s metal shell, exposing the chemical agent and burster, a small explosive that disperses the agent. The burster explodes or deflagrates safely inside the EDS vessel. A reagent is then pumped into the chamber to neutralize the chemical agent. The chamber is heated and turned to mix the chemicals and facilitate the reaction.

“It’s basic high school chemistry,” says John Didlake (8136). “Heat and mix.”

The entire process takes two days, as heating thousands of pounds of steel takes time. “EDS was never designed to be fast,” says Brent. “Pine Bluff was a shift in perspective.”

Army had planned to build a facility

The Army originally planned to build a fixed facility to dispose of the Pine Bluff nonstockpile arsenal, but the plan ran into technical problems because of the varied condition of nonstockpile munitions. “With stockpile weapons, you are dealing with an arsenal that is mostly uniform. They’ve been stored in reasonable condition, and you know what is inside,” says John. “Recovered munitions have been lying underground for 70 or 80 years, so they are in varying degrees of decay. Some munitions are encircled by tree roots, while others have been in the ocean and are covered with sea scum. Many of these munitions were experimental; however, each one is a special case and is not suited for a production-type facility.”

After considering different options, the Army proposed using two large EDS systems running simultaneously with a smaller system in reserve. First, however, Sandia had to increase the throughput of EDS to meet the Army’s requirement of destroying six rounds every two days. Originally, EDS was intended to treat one munition at a time, but with changes in the configuration of the shaped charges and fragment suppression system, the capacity was increased. Testing at the Defense Science and Technology Laboratory in Porton Down, England, in 2003 showed that the larger EDS could destroy three smaller munitions at once. Further explosive testing by the Explosive and Firing Systems group (5434) demonstrated that the larger EDS had the capacity for six munitions and the smaller EDS could handle three.

The biggest challenge at Pine Bluff was destroying approximately 450 German Traktor rockets containing a variety of different chemical agents that had been stored at the site for 60 or more years. Because they were foreign rounds, some of the chemical agents were different from what is found in US rounds. A particular challenge for the Army was developing a reagent for lewisite, an arsenic-based chemical agent.

The German Traktor rockets at Pine Bluff were in poor condition and the contents were not well-characterized. In the 1950s, after the Army had finished research on the German Traktor Rockets, an unsuccessful attempt was made to destroy them using the traditional method — placing the munitions in a pit with jet fuel and lighting them on fire.  “German Traktor rockets have the propellant at the front and the warhead at the back, hence the name Traktor, because the propellant pulls rather than pushes,” John explains. “Consequently they did not behave as expected. Rockets were ejected from the pit and scattered around the site.”

Many were damaged and had to be placed in secondary containers. While the bursters on some of the munitions were destroyed, others still had complete or partial bursters, and in some cases the burster wells were filled with mud and debris, making it difficult to determine if there was a burster. “The amount of explosives determines the quantity of munitions that can be treated in each batch, so we were dealing with many different scenarios,” Brent says.

A special challenge

About 50 German Traktor rockets still had propellant in the motors. These rockets, which were the last to be processed, presented a special challenge.

“The Army’s original plan was to cut off the motors from the rockets and treat just the warheads in EDS,” explains Brent. “But as the time to begin processing them drew near, the base commander became concerned that the propellant could be contaminated with the chemical agent. He insisted that the motors be processed with the warheads.”

With both the propellant and the burster, those German Traktor rockets contained nearly 17 pounds of energetic material — more than three times the 4.8 pound approved rating of the EDS explosive containment vessel.

In September 2008, Sandia began an intense six-month program to demonstrate that EDS could safely destroy a German Traktor rocket with propellant. The first step was to demonstrate that a properly chosen shaped charge could open the rocket motor without causing the propellant to detonate. This was difficult because the propellant used in the German Traktor rockets is no longer available and the condition of the explosive after 60 years was not known. Sandia’s explosives engineers used their understanding of the physics and chemistry of propellants to select a suitable surrogate for testing that would be more sensitive than the actual propellant.

The next step was to demonstrate that even if the propellant detonated, the vessel would still contain the detonation. In Albuquerque, researchers performed destructive tests on the original EDS vessel using 15 pounds of TNT, the equivalent of more than 45 pounds in the larger EDS. The vessel deformed substantially, as was expected, but the test allowed the researchers to quantify the failure mechanisms. The test results were supported with extensive computer modeling.

Containing the explosion

Next, they took one of the larger EDS vessels out of service at Pine Bluff and tested it with the equivalent of a German Traktor rocket with full propellant, 17 pounds, and an overtest with 21 pounds of explosive. “The Army was willing to accept that the vessel could be damaged and no longer usable as long as it contained the worst-case explosion,” Brent says. “We demonstrated that the explosion would be contained and the EDS would be able to complete the operation. We also showed that the failure mechanism for the vessel is not catastrophic but a leak that would stay within the vapor containment structure. So there were three levels of defense.”

At Pine Bluff, the second and third levels of defense were never employed, as the EDS destroyed the last 57 German Traktor rockets without a single one detonating.

 “With large detonations, we were also concerned with protecting the vessel from high-velocity fragments,” says Brent. The traditional EDS fragment suppression system of two large steel half cylinders placed around the munition would not be sufficient.

Fortunately, Sandia researchers already were developing an improved fragment suppression system. “For each type of weapon, you needed a different fragment suppression system, so it became logistically difficult,” says Brent. “We were looking for something more universal.”

Double layer of steel rods

They came up with a new design consisting of a staggered double layer of steel rods lining the vessel walls that block any line of sight to the vessel walls. The rods are easier to fabricate and handle, and reusable, unlike the half cylinders that can only be used once, resulting in a solid waste reduction of up to 80 percent. The new design also protected the vessel from much larger detonations.

The timing of the advanced fragment suppression system was fortuitous for Pine Bluff. Without it, Brent says EDS never could have handled the challenge of the German Traktor rockets with propellant in the motor.

Since completion of operations at Pine Bluff, the EDS has returned to its original mission of destroying small amounts of munitions at sites such as Camp Sibert in Alabama and Spring Valley in Washington, D.C. Sandia is now developing ways to speed up the EDS. One idea is to inject steam into the vessel to accelerate the heating process. Another tactic would use a MicroChemLab-based device to continuously monitor the liquid inside the vessel, rather than taking a sample at the end of the operation and sending it to a lab for analysis.

 “We’re not really sure what the future holds, as Pine Bluff was the last large repository of nonstockpile munitions,” says Brent. “There are plenty of potential applications, like stockpile weapons with leakage issues or munitions sitting on the ocean floor in coastal waters. We don’t know how EDS would tie into these problems, but its flexibility makes it an obvious choice.”