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2 Occurrences and Origins of Anomalies OVERVIEW OF ORIGINS OF ANOMALIES The Army is progressing with CSDP demilitariza- t~on activities with the goal of completing disposal activities by 2012 in accordance with an extended dead- line provided for by the Chemical Weapons Conven- tion. The U.S. unitary chemical agent and munitions stockpile contains a variety of agent storage containers and weapons types, some of which are configured with bursters, fuzes, and/or propellant charges. Figure 2-1 shows the locations of the eight stockpile storage sites in the continental United States. Munitions in the stockpile were last manufactured in 1968, and some are now almost 60 years old. Con- cerns about the potential consequences of leakages and accidents involving degrading stockpile munitions and containers pending their disposal have been reinforced by continuing observations of deterioration, corrosion, and, occasionally, leaks. Leakages have been most fre- quently encountered in GB M55 rockets, as noted in a report issued by the Government Accounting Office (GAO) in December 1994 (see Box 2-1 for the relevant excerpt). Leaks have continued to occur, with a total of 4,789 leakers reported from 1973 through June 2002 out of more than 3 million munitions (Studdert, 2002~. iThe small portion of the stockpile that originally existed at Johnston Atoll in the Pacific Ocean has been destroyed, and JACADS is undergoing final closure operations. s A number of chemical and mechanical anomalies have frequently led to leaks or have otherwise pre- sented difficulties during operations at baseline incin- eration system disposal facilities (Denison et al., 2002; Thomas, 2002a): · gelled agent (GB) · crystallized agent (GB) · sludged agent (HD) · randomly occurring heavy metals, which create problems in meeting stack emission limits during processing · foaming mustard agent · internal pressurization of munitions from hydro- gen gas generation · various mechanical anomalies such as fabrication discontinuities (cracks and scratches) and unex- pected obstacles to disassembly (such as diffi- culty in loosening screw threads) A promising approach for developing a predictive method to help assess the formation and future fre- quency of leaks is to combine an understanding of the chemistry of agent manufacture and degradation processes (including those associated with stabiliz- ers added to the agents) with a statistical analysis of data accumulated to date on stockpile leaks. This chapter discusses the stockpile in terms of what is known about the original manufacturing processes,
6 EFFECTS OF DEGRADED AGENT AND MUNITIONS ANOMALIES ON CHEMICAL STOCKPILE DISPOSAL OPERATIONS Um villa Chemical ~ ZJ TO ~ - HD -P°TC ~ ~ f:' = ~ ~ ~ 1 1 1 ~ _ ~ De:~3ret ChDmical ~ ,~ In_ GB - C9 P' R. B. TC VX-P,R,M'ST GA-TC (44.5°/0) - \: /7 ~ L Pueblo Chemical / Depot / MD-C, P HT-C (8.5%) GA, GB, VX, H. HD, HT = Chemical agent TC = Ton container B = Bombs R = Rockets C = Cartridges M = Mines P = Projectiles ST = Spray tanks Newpori Chemical Depot VX -TC (4.2%) Edgewood Chemical Activity HD -TC (5.3%) Blue Grass Chemical ACtMtY HD- P GB- P. R VX - P. R (1.7%) ~ \- Chemical ACtM1Y MD-C, PITC HT - C GB- C, P. R FIGURE 2-1 Location and size (percentage of original stockpile) of eight continental U.S. storage sites. Source: OTA (1992~. the chemistry of the agents, the configurations of mu- nitions containing agents, and applicable corrosion mechanisms. DESCRIPTION OF MUNITIONS AND CONTAINERS A detailed description of the original stockpile is given in Chemical Stockpile Disposal Program Final Programmatic Environmental Impact Statement (FPEIS) (U.S. Army, 1988a) and can also be found in the NRC report Disposal of Chemical Munitions and Agents (NRC, 1984~. Both reports and a later NRC re- port, Recommendations for the Disposal of Chemical Agents and Munitions, address earlier expressions of concern about the potential impacts of a degrading stockpile on disposal operations (NRC, 1994a). As noted in Chapter 1, the stockpile contains three main agent types: · GB (sarin),2 a fairly volatile (2.9 mm Hg at 25°C), 2Methylphosphonofluoridate isopropyl ester. highly toxic (LD50= 24 mg/kg) nerve agent (NRC, 1993, 1997a) VX,3 a much less volatile (0.001 mm Hg at 25°C) but more toxic (LD50= 0.14 mg/kg) nerve agent (NRC, 1993, 1997a) H,4 HD,5 and HT6 (sulfur mustards), blister agents with moderate volatility (vapor pressures 0.08 to 0.11 mm Hg at 25°C) and moderate toxic- ity (LD50= 100 mglkg) (Munro et al., 1994; NRC, 1997a). The stockpile also included some nerve agent GA (tabun),7 which is similar to GB. However, all GA was stored at DCD in Utah and has been destroyed along with all of the GB that was stored there. A small amount 3a nerve agent, O-ethyl S-~2-diisopropylaminoethyl) methyl- phosphonothiolate. 4Bis(2-chloroethyl) sulfide. Distilled H. 660 percent HD and 40 percent T. which is bis[2~2-chloro- ethylthiojethyl] ether. 7Ethyl-N,N-dimethylpho sphoramidocyanidate.
OCCURRENCES AND ORIGINS OF ANOMALIES of lewisite,8 an organic arsenical blister agent, remains in the stockpile. A variety of containers and munitions compose the chemical stockpile, some of which are depicted in ~Dichloro(2-chlorovinyl~arsine. 7 Figure 2-2. Containers include bombs that are stored without explosives, aerial spray tanks, and bulk stor- age tanks known as ton containers. Munitions include land mines, M55 rockets, artillery projectiles, and mor- tar projectiles. Munitions typically contain some com- bination of fuze, booster, burster, and propellant col- lectively referred to as "energetics." Table 2-1 indicates which munitions incorporate energetics. The fuze is a small, highly sensitive ex- plosive charge that initiates an explosive chain by detonating a booster. The booster is a medium-size charge that can be detonated by the fuze and is large enough to detonate a much larger burster charge. The burster charge is large enough to rupture the muni- tion and to disperse the agent contained within. The M55 rocket also incorporates a section of solid rocket propellant. Dunnage refers to munition pack- ing materials, which also may be destroyed by com- bustion. Most of the munitions in the stockpile have been stored inside igloos that provide protection from the elements. The enclosed space of the igloo facilitates the monitoring performed to detect leaks and limits the quantities of agents and energetics that are likely to be involved in any single accident. Some bulk ton con- tainers had been stored outdoors but were more recently moved into enclosed shelters to enhance their security. When leaking items are found, they are overpacked (placed inside another container and sealed) and re- turned to storage. Some leakers have been overpacked several times. Problems with degraded items in the stockpile affect the safety of workers engaged in the maintenance of the stockpile and the transport of stockpile items from storage areas as well as that of workers involved in disposal operations. For example, workers in protec- tive clothing perform the overpacking procedure and also decontaminate any area that has been affected by a leak. In general, hazards to workers may arise from conditions such as the following: agent leakage · potential ignition of energetics by a spurious elec- tric discharge instabilities of stabilizers used in energetics- especially the stabilizer in the M55 rocket propellant interactions between agent, energetics, and/or structural materials undetected manufacturing flaws
8 EFFECTS OF DEGRADED A GENT AND MUNITIONS ANOMALIES ON CHEMICAL STOCKPILE DISPOSAL OPERATIONS (a) Fumed Fins ~ Rocket Motor f Cavity Douglass Shipping and Fire - at" ~°' Aluminum ~ -.' (at each End)~ ~ / / / / / ~ Agent Fill IBonnet r valve | ~ Eduction Tube (C) ~ 1~117f Agent Fill ~ FIGURE 2-2 (a) MSS rocket; (b) 105-mm projectile; (c) ton container. Source: U.S. Army (2002a).
OCCURRENCES AND ORIGINS OF ANOMALIES TABLE 2-1 Composition of Munitions in the U.S. Chemical Stockpile Munition Type Agent Fuze Burster Propellant Dunnage MSS 115-mm rocketsa GB, VX Yes Yes Yes Yes M23 land mines VX Yesb Yes No Yes 4.2-inch mortars Mustard Yes Yes Yes Yes 105-mm projectiles GB, mustard yesc yesc No Yes 155-mm projectiles GB, VX, mustard No YesC No Yes 8-inch projectiles GB, VX No Yes No Yes Bombs (500-750 lb) GB No No No Yes Weteye bombs GB No No No No Spray tanks VX No No No No Ton containers GB, VX, GA,4 No No No No mustard, lewisitee aMSS rockets are processed in individual fiberglass shipping containers. bFuzes and land mines are stored together but not assembled. CSome projectiles have not been put into explosive configuration. dGA (tabun), or ethyl-N,N-dimethyl phosphoramidocyanidate, is a nerve agent. eLewisite, or dichloro(2-chlorovinyl) arsine, is a volatile arsenic-based blister agent. Source: U.S. Army (1988a). Chapter 4 describes some specific risks to work- ers that have been encountered during disposal op- erations. MANUFACTURING PROCESS ORIGINS OF ANOMALIES The manufacture of the agents in the stockpile and munition components took place at several locations over a long period of time. This section provides a brief over- view of how manufacturing processes and specifications have contributed to anomalous items in the stockpile. Agent Characteristics GB GB was manufactured at Rocky Mountain Arsenal (RMA) from 1953 to 1957 and stored by manufactur- ing lot in bulk tanks before being loaded into muni- tions or, in the 1960s, into the current storage contain- ers. The purity of GB agent was originally specified at 92 percent, and tributylamine ETBA, (C4Hg)3N] was used as the stabilizer (U.S. Army, 1986a). During the first 2 years of GB production, between 1953 and 1955, the Army produced GB by a two-step distillation pro- cess that met the 92 percent purity specification. How- ever, from 1955 to 1957, the Army eliminated the sec- 9 ond distillation step, which reduced agent purity to about 88 percent. Each batch of GB manufactured in 1953-1957 at the RMA was assigned an agent lot number. Differences in the production methods and the subsequent treatment of these lots are documented in Army records. In the 1960s, the bulk agent was loaded into a variety of con- tainers and munitions that are identified by a munitions lot number. Thus, each item in the stockpile is identi- fied by both an agent lot number and a munitions lot number. Since the decomposition products of GB were known to be acidic, stabilizers were added to scavenge acidic decomposition products and water as they formed. There are currently four main subtypes of GB agent: PRO, PR-RS, RO-RS, and RD-RS. These subtypes arise from combinations of the following designations, because agents of different initial purity were treated in different ways: PRO (preroundout agent) was manufactured from 1953 to 1955 to meet a 92 percent purity specification. TBA was added as a stabilizer. Subsequent testing of these stored agent lots showed purities ranging from 81 to 94 percent, indicating a widely varying degree of decom- position (U.S. Army, 1985~. The TBA was mostly in the form of (C4Hg)3NH+F-, possibly
10 EFFECTS OF DEGRADED A GENT AND MUNITIONS ANOMALIES ON CHEMICAL STOCKPILE DISPOSAL OPERATIONS indicating the formation of HF. Varying amounts of diisopropyl methyl phosphonate (DIMP) and methylphosphonofluoridic acid (MPFA) were also found in the agent: 2 to 6 percent by weight DIMP and 2.7 to 10 percent by weight MPFA. RO (roundout agent) was manufactured from 1955 to 1957 to meet a modified purity goal of 88 percent. The Army continued to test the agent lots over the next few years and found that the RO lots were showing significant acidity. Since some of the agent was intended for use in aluminum M55 rockets, there was concern that acidity would cause corrosion problems. For this reason, over the next 6 years, some RO lots were redistilled to im- prove purity. RD (redistilled RO). In addition to the redistil- lation of some RO lots, the TEA stabilizer was replaced by DICDI (diisopropylcarbodiimide) to reduce the acidity problems and allow the placement of GB into aluminum casings. RS. Lots restabilized with DICDI were des~g- nated by the addition of RS to the basic agent category. M55 rockets were loaded with GB from various agent lots during the 1960s. . . . VX Nerve Agent VX was originally manufactured from 1961 to 1968 at Newport, Indiana. It was 92 to 95 percent pure and had approximately 2 percent added stabilizer (usually DICDI, less frequently dicyclohexyl carbodiimide). When the agent fills were sampled in 1975, the VX content had decreased by 2 to 7 percent, and in some of the lots, about half the DICDI stabilizer had decom- posed (U.S. Army, 1995a). Unlike GB, the VX was never redistilled or restabilized. The fact that a large fraction of the stabilizer had decomposed within 15 years of manufacture and that the VX has not been re- distilled or restabilized suggests that little stabilizer may remain after the 28 additional years that have elapsed since 1975. Mustard Agent Mustard agent was produced at RMA from 1942 to 1945 by the Levinstein process. This produced the form of mustard that is designated H along with sulfur, which was removed by washing. From 1945 to 1946, most of this product was then vacuum-distilled at RMA to pro- duce HD. HD was also manufactured at Aberdeen Proving Ground, in Maryland, using a 500-gallon vacuum distillation still and five vertical reflux con- densers. The initial HD content of mustard agent manu- factured circa 1945 was reported to be 94 percent, with less than 0.005 percent (50 ppm) HC1 content. When sampled in 1982, the HD content had decreased to be- tween 50 and 89 percent, with most analyses indicating less than 85 percent. The agent fills also contained ap- proximately 0.2 percent Fe++ ion, indicating partial dis- solution of the steel container material by acidic impu- rities or by HC1 that came from hydrolysis of the agent (U.S. Army, 1995a). Munition Assembly, Quality Control, and Component Compatibility In the 1960s, when the bulk agents were introduced into the various stockpile munitions and containers, the specification and manufacturing procedures for the assembly of munitions was controlled to a level of quality that ensured the requisite functionality and a reasonably stable storage life. These specifications covered agent purity, energetics type and configura- tion, and component metal parts, along with assembly sequences and joining and sealing procedures. Ranges of acceptable variability in properties were also pro- vided. Agent and munitions lots were systematically identified by type and numbered to allow future trace- ability. However, the possibility that disassembly and deactivation might be necessary at a future date was not considered in the design of the munitions. More- over, when these munitions were manufactured 30 to 60 years ago, chemical analysis and mechanical as- sembly techniques were less sophisticated than they are now, making it possible for anomalies to have been introduced into the munitions during the initial manufacturing. Some anomalies were discovered early in the disposal program for example, the brass valves and plugs that were used on GB ton containers were found to have been attacked by the acidic products of GB decomposition, which leached the zinc from the brass alloy in the plug material. These fittings were subsequently replaced with steel fittings on all the ton containers. One common type of anomaly munitions contain- ing either GB or mustard agent that has gelled has con- sequences for the conduct of disposal operations. This phenomenon occurs with age. In the case of GB, gelling
OCCURRENCES AND ORIGINS OF ANOMALIES is probably related to reactions between GB degradation products and aluminum. For mustard agent, sludging is associated with the formation of dithianium ion. Another anomaly that became apparent during the disposal of mustard munitions, specifically projectiles, has been at- tributed to impurities that may lead to a slow, gas-pro- ducing reaction. During demilitarization operations at JACADS, some projectiles with mustard agent foamed when the burster well was extracted; this was due to the buildup of internal pressure. A more pressing concern in terms of the risks asso- ciated with continued storage of the stockpile is the stability of the M28 propellant used in M55 rockets. This propellant includes nitrocellulose, which is un- stable, decays exothermically, and is autocatalyzed by its own acidic nitrate products. During manufacture, a stabilizer that reacts with the acidic nitrate products to prevent autocatalysis was added, although nitrocel- lulose decay itself is not inhibited. M55 rockets were manufactured from 1959 to 1965, with stabilizer con- tent averaging about 1.8 percent (U.S. Army, 1985~. Initial stabilizer decays continuously over time. The Army has set a level of 0.5 percent stabilizer as the "increased surveillance threshold" and has observed autoignition at levels of 0.2 percent under controlled conditions (NRC, 1994a). Sampling of stabilizer lev- els over time has not shown variability beyond what might be expected from degradation alone. In 1985, 393 M55 rockets were randomly selected from 478,000 rockets in the stockpile, and stabilizer levels were found to be between 1.6 and 2.2 percent. Since the precise starting concentrations for individual lots were unknown (there was considerable variability around the 1.8 percent initial nominal concentra- tion),9 rates of degradation could not be inferred 9According to the 1985 study by the Army Materiel Systems Analysis Activity, the first evaluation of M28 propellant stockpiled since production, the original stabilizer content at the time of manu- facture ranged from 1.57 to 2.17 percent of total weight (U.S. Army, 1985~. In that study, lots stored at Johnston Island had an average stabilizer content of 1.63 percent (95 percent confidence interval of 1.60 to 1.66 percent). These lots exhibited the largest stabilizer loss of all locations. Four lots produced in 1960 and stored at Pine Bluff had low original stabilizer content (1.62 percent), and the report noted the current assay average was 1.45 percent (95 percent confi- dence interval of 1.45 to 1.53 percent) [sic]. The remaining lot seg- ments for all locations (except Johnston Island) were found to be homogeneous. The average stabilizer for these lots was 1.76 per- cent (95 percent confidence interval of 1.75 to 1.77 percent). 11 (OTA, 1992~. Similarly, too little stabilizer might have been added during manufacture in some cases. The degradation of M28 propellant is discussed in more detail later in this chapter. Another problem is the corrosive effect of GB agent degradation products on the aluminum of which M55 rockets are constructed. This corrosion has been re- sponsible for the majority of leakage problems with these rockets. Aluminum was used in these rockets to achieve certain aerodynamic characteristics. Among the manufacturing flaws that might acceler- ate corrosion in chemical munitions and containers are (1) the use of dissimilar metals for junctions, leading to electrochemical reactions, and (2) the improper clean- ing of welded parts. However, subsequent observations of leakage sources suggest that these are not important causes of corrosion problems. While anomalies that arose during manufacturing and initial filling can present unique operational issues during disposal, the long history of storage to date sug- gests that most manufacturing causes have already been identified from an examination of stockpile items that have leaked. For example, lead, cadmium, and mer- cury are occasionally identified in ton containers that were reused by the Army, and it is possible that these heavy metals were residual contaminants, even though the containers were presumably cleaned before refill- ing. In munitions, the presence of lead may have come from lead-based solder, lead compounds in energetic materials, or lead components in fuze assemblies. The presence of mercury, which has been found in ton con- tainers, may be the result of pressure gauge breakage and splashback during filling operations or residual contamination. DETERIORATION PROCESSES FOR AGENTS Surveillance of Agent Deterioration As noted above, the chemical agents stored in the U.S. stockpile were originally manufactured 30 to 60 years ago. The purity of the agent contained in various muni- tions and bulk containers was sporadically checked dur- ing the 1960s and 1970s (U.S. Army, 1985, 1995a). Fol- lowing recommendations from a blue ribbon panel convened in March 1983 to review the chemical retalia- tory surveillance and sampling program, the Surveil- lance Program for Lethal Chemical Agents and Muni- tions (SUPLECAM) was established for purposes that included the following (U.S. Army, 1988b):
12 EFFECTS OF DEGRADED AGENT AND MUNITIONS ANOMALIES ON CHEMICAL STOCKPILE DISPOSAL OPERATIONS · determining the rate of agent decomposition . ~7 ~7 1 gaining an improved understanding of the mecha- nisms of decomposition and stabilization of agents, specifically GB and VX. The SUPLECAM studies, carried out by the U.S. Army Chemical Research, Development, and Engi- neering Center (CRDEC), developed a substantial quantity of data on degradation kinetics and mecha- nisms for GB and VX. This blue ribbon panel offered recommendations on seven items: 1. Are surveillance plans and procedures good enough to determine the current condition of the stockpile? 2. How can the surveillance plans be improved? 3. What further tests or analyses can be performed to provide useful information? 4. Is field testing necessary or desirable? 5. What will be the condition of the munitions by 1990? (The assumption then was that binary muni- tions would be available and the existing stockpile would be available for demilitarization.) 6. What additional data analysis or studies are needed to improve predictions about the condi- tion of these munitions? 7. Can anything be done to prolong the life of the stockpile? The panel recommended the immediate funding of SUPLECAM "to study VX decomposition as a func- tion of time, temperature, inhibitors, and impurities" (U.S. Army, 1988b). Accelerated aging tests were con- ducted with and without inhibitors. Also, viscosity measurements were taken on pure and partially decom- posed agent to determine if thickening or precipitation of the agent had occurred (U.S. Army, 1988b). This work led to intrusive sampling to obtain the necessary VX samples from the stockpile. The samples were stored in glass containers and sent back to the Army' s Edgewood, Maryland, facilities for kinetic and mecha- nistic studies. An important finding was that the DICDI inhibitor decomposes in the presence of water to form urea crystals but does not readily decompose in the absence of water. The SUPLECAM program extended through the 1980s, but similar sampling efforts have not been conducted since that time. Mechanisms and Products of Agent Deterioration Over time, mustard and nerve agents can undergo chemical decomposition. In this section, the mecha- nisms and products of such decomposition are dis- cussed in greater detail. Table 2-2 shows the products resulting from the degradation of nerve and mustard agents. Details of the decomposition pathways for in- dividual agents have been discussed extensively (Munro et al., 1999; NRC, 2001a) and are summarized below. GB Three pathways, shown below, have been identified for the degradation of GB in storage (U.S Army, 1986b, 1988c, 1999a). GB can reversibly form DIMP and DF (Pathway I). The P CH3 bond is the most resistant to TABLE 2-2 Expected Products from Chemical Agent Decomposition Due to Age Agent Decomposition Products VX GB Mustard (HD) Thiolamine; ethylmethylphosphonic acid; ethanol; bis(2-diisopropylaminoethyl) thioether; bis(2- diisopropylaminoethyl) disulfide; o,o'-diethylmethyl phosphonolate; o,o'-diethylmethyl phosphonothiolate; diisopropylaminoethyl mercaptan; o,S-diethyl methyl phosphonothiolate; diisopropylaminoethylethyl sulfide; o,S-diethyl methyl phosphonate; N,N'-diisopropylamino ethyl methyl phosphonate; S-ethyl, S- diisopropyl amino ethyl methyl phosphonothiolate; o-ethyl, S-diisopropyl amino ethyl methyl phosphonothiolate; S'-diisopropyl amino ethyl methyl phosphonothiolate; diisopropylamine HF; isopropyl methylphosphonic acid (IMP); isopropanol; propene; methyl phosphono fluoridate; diisopropyl methyl phosphonate (DIMP); methylphosphonic acid (MPA) HC1; H2S; ethylene; ethylene dichloride; vinyl chloride; 2,2'-dichlorodiethyl disulfide Source: U.S. Army (1988a).
OCCURRENCES AND ORIGINS OF ANOMALIES hydrolysis. The P F bond is hydrolyzed (Pathway III) more rapidly than the P OC3H7 bond (Pathway II). (I) Reversible disproportionation of GB to form diisopropyl methyl phosphonate (DIMP): O O O 2 CH3P F < > CH3P OC3H7 + CH3P F OC3H7 OC3H7 F GB DIMP DF (II) Acid-catalyzed hydrolysis to form methyl phospho- nofluoridic acid (MPFA): O H+ O CH3P F > CH3P F + C3H6 (g) OC3H7 OH GB MPFA (III) Neutral hydrolysis to form isopropyl methyl phosphoric acid (IMPA): 1I H2O 11 CH3P F > CH3P OH + HF 1 1 OC3H7 OC3H7 GB IMPA The DIMP product of the disproportionation reac- tion can be further hydrolyzed to form IMPA, which can undergo a slow further hydrolysis to form methyl phosphoric acid (MPA): 1I H+ 11 CH3P OC3H7 > CH3P OH + C3H6 (g) OC3H7 OC3H7 DIMP IMPA 1I H+ 11 CH3P OH > CH3P OH + C3H6 (g) OC3H7 OH IMPA MPA MPFA, IMPA, and MPA are all acidic and thus may be expected to further accelerate GB decomposi- tion by the autocatalytic process described below. In experiments in which small amounts of these com- pounds were added to GB, the acceleration effect was in the order MPA > IMP ~ MPFA ~ water. In the presence of ferrous metals such as those used in many munitions, and if not inactivated by a stabilizer com- pound, these acidic compounds would be expected to react at the inner metal surface of the munition to lib- erate hydrogen: Steel + 2 HA > Fe++ + 2 A- + H2 (9) where HA is an acidic compound. Aluminum will react with the HF produced in Pathway III (above) to form A1F3 and liberate hydrogen gas: Aluminum + 3 HF ~ A1F3 + 3/2 H2 The A1F3 can complex with additional fluoride ion to form A1F4- or the highly stable A1F63- anion. Two factors that could affect GB decomposition rates need to be considered: autocatalytic processes and rate acceleration at higher temperatures. Since the prod- ucts of GB decomposition are themselves acidic and several of the decomposition pathways noted above are acid-catalyzed, it is possible that the decomposition process could proceed by an autocatalytic mechanism once the added stabilizer has been exhausted (Munro et al., 1999). One characteristic of an autocatalytic pro- cess is a lengthy induction period during which little or no reaction occurs, followed by a sudden rapid increase in the overall reaction rate (Steinfeld et al., 1999) (see Figure 2-3). An autocatalysis rate law for GB decom- position has been suggested: [GB] = [GB] jnjtja, (ks + ku [GB]initial ) t ku [GB]initia' + ks exp{(ks + ku [GB]initial )(t - tI )} where EGB]initial is the concentration at time tI, when all of the stabilizer is consumed, and [GB]t is the concen- tration of GB remaining at time t. The GB loss rate coefficients are ks and ku, in the presence and absence of stabilizer, respectively (U.S. Army, 1985, 1986a). On the basis of very limited data, it has been suggested that loss of GB could begin to accelerate at t 2 30 years (U.S Army, 1986a). Many reaction rates increase at higher temperatures according to the Arrhenius rate law (Steinfeld et al., 1999) k(l) = A exp (-Eac,/RT)
14 o AL o o . _ cat o FIGURE 2-3 Autocatalysis rate profile, product concen- tration versus time; t* is the inflection time, i.e., the time at which product formation occurs most rapidly. Source: Adapted from Steinfeld et al. (19991. where A is a preexponential factor, Earl is the activa- tion energy, R is the gas constant, and T is the tempera- ture in kelvins (°C + 273.16~. Measurements at elevated temperatures give Arrhenius activation energies for Pathways I and II above as 28.3 kcal/mole and 25.4 kcal/mole, respectively (U.S. Army, 1999a). Analysis of SUPLECAM results on overall decomposition rates suggests an effective activation energy of 31 kcal/mole, which is within 20 percent of an earlier result reported in the United Kingdom (U.S. Army, 1999a) but based on only two data points. While Arrhenius behavior would suggest an accelerated decomposition rate for GB at higher temperatures, the data presented in Chap- ter 3 do not show any clear dependence of munition leak rate on ambient temperature. As previously noted, all of the GB that was stored on Johnston Island and at DCD has been destroyed at JACADS and TOCDF, respectively. Gelling of the agent was encountered in about 12 percent of the GB munitions in the DCD stockpile (EG&G, 2002~. GB gelling had previously been encountered in only a few 155-mm GB-filled projectiles during processing at JACADS. The degree of gelling ranges from increased viscosity that slows the draining process to a semisolid state or to a crystallized state, either of which makes it impossible to drain agent after the agent cavity of the rocket has been punched open. EFFECTS OF DEGRADED AGENT AND MUNITIONS ANOMALIES ON CHEMICAL STOCKPILE DISPOSAL OPERATIONS Gel formation has been attributed to the formation of aluminum phosphonate complexes.l° The A13+ ions, formed during the acidic corrosion of aluminum muni- tion parts, can react with the IMPA- ions formed in Pathway III to form a trig-isopropyl methyl phospho- natoaluminate complex: o 3CH3P O + Al3+ ~ Al[OP(0)CH3OCH(CH3)2]3 OC3H7 GB which has the following suggested structure: H3C,..., Ol','n'\~ H3C\ `\\\'o BALI j (CH3)2 CHO (CH3)2 CHO The complexes, which are mostly viscous liquids, can form either a solid that is sparingly soluble in GB or oligomeric or polymeric phosphorus compounds.l2 Complexes can also form as a result of reaction with nickel or copper ions produced from the corrosion of other metal parts, such as brass fittings. Another mechanism that has been suggested for the formation of crystalline solids in stored GB is the for- mation of 1,3-diisopropyl urea when DICDI (the stabi- lizer added to -RS lots) reacts with water in the pres- ence of acid.l3 Cl H3 Cl H3 H+ 1 3H 11 H 1 3 HC N = C=N CH + H:,O > HC N C N CH CH3 CH3 1 - 1 1 CH3 CH3 diisopropyl carbodiimide (DICDI) 1,3-diisopropyl urea 10Yu-Chu Yang, Chief Scientist PMACWA, personal communica- tion to the committee on June 27, 2003. Also see Wagner et al. (2001). 1lYu-Chu Yang, Chief Scientist PMACWA, personal communica- tion to the committee on June 27, 2003. Also see Wagner et al. (2001). 12Yu-Chu Yang, Chief Scientist PMACWA, personal communica- tion to the committee on June 27, 2003. 13Yu-Chu Yang, Chief Scientist PMACWA, personal communica- tion to the committee June 27, 2003. See also U.S. Army (2002b).
OCCURRENCES AND ORIGINS OF ANOMALIES This hypothesis is supported by the fact that urea crys- tals were observed during the filling of rockets and pro- jectiles when GB agent RS lots were used (U.S. Army, 2002b). VX Nerve Agent Hydrolysis of VX agent occurs by cleavage of the P S bond under acidic or alkaline conditions or by cleavage of the P ethoxy bond under near-neutral conditions (Munro et al., 1999; NRC, 2001a): /CH(CH3~2 ~~ HS-CH2CH2-N + C2H5O-P-OH CH(CH3~2 C ~ 3 ,~` diisopropyl ethyl ethyl methyl- ~,~ mercaptoamine phosphoric acid O /CH(CH3~2 C2HsO- P-SCH2CH2-N ~ H3 \ CH(CH3~2 Agent VX ~~ ~~ CH(CH3~2 to HO-~-SCH2CH2-N + C2H5OH CH3 CH(CH3~2 S-~2-diisopropylaminoethyI) ethanol methyl phosphonothioate (EA-21 92) The latter pathway yields the toxic degradation prod- uct EA-2192. Other reaction products are listed in Table 2-2. Since the electron-donating tertiary amine group present in VX makes this agent a Lewis base, the hydrolysis rates are slow (Wojciechowski and Goetz, 2002~. As a consequence, VX is expected to have a long storage lifetime, with little or no acidic attack on steel containers and little or no bimetallic electrochemi- cal reaction at metal junctions. But since VX is a highly toxic material, these assumptions may need to be veri- fied, as a precaution. Note that at least one of the de- composition products above (ethyl methylphosphonic acid) is acidic. An Arrhenius activation energy of 23 kcal/mole has been estimated for VX decomposition (Evans, 1999~. 15
16 EFFECTS OF DEGRADED AGENT AND MUNITIONS ANOMALIES ON CHEMICAL STOCKPILE DISPOSAL OPE^TIONS Mustard Agent Mustard agent H (bis-2-chloroethyl sulfide) under- goes the complex sequence of hydrolysis reactions Cl-CH2-CH2-S-CH2-CH2-CI Suffur mustard (HD) 1 H2O r -Cl- +yCH2 Cl-CH2-CH2-S\ CH 2 sulfonium ion thiodiglycol r H2O > S; / CH2-CH2-S-(CH2-CH2-OH)2 \ CH2-CH2-CI sulfur mustard- thiodiglycol aggregate ~ thiodiglycol /~ J~-CI- / / H2O CH2-CH2-S-(CH2-CH2-OH)2 CH2-CH2-S-(CH2-CH2-OH)2 sulfur mustard-thiodiglycol- thiodiglycol aggregate shown below (Bizzigotti et al., 1998; Munro et al., 1994; NRC, 2001a). / CH2-CH2-CI H2O S / CH2-CH2-OH 'CH2-CH2{)H hemimustarcl \ CH2-CH2-OH thiodiglycol thiodiglycol ~ H2O -CI- ~ H2O S / CH2-CH2-S-(CH2-CH2-oH)2 \ CH2-CH2-OH hemimustard- thiodiglycol aggregate
OCCURRENCES AND ORIGINS OF ANOMALIES A further degradation mechanism is responsible for the formation of the solid or semisolid residues ("heels") that are present at 20-30 percent of the total volume of HD in stored ton containers. Recent tests on mustard-filled projectiles stored at DCD found that up to 70 percent of the agent fill was present as heels (Novad, 2003~. The main constituents of these heels have been identified as a cyclic six-membered ring sul- fonium ion, S-~2-chloroethyl)- 1,4-dithianium chloride, entrained HD, and dissolved iron (Yang et al., 1997~. The mechanism responsible for the formation of the dithianium ion is as follows: 2/~1 - H rich \= HI - H AH = - H AH =+/ - H AH - 1\ ` - ~ 2 - 2)~ > ~ ~ 2 - 2~ - 2 - 2~ ` - 2 - 2 - )2 Cl- CICH2CH2SCH2CH2SCH2CH2CI + C2H4CI2 S/:S Cl The dithianium ion has been identified and charac- terized by 13C cross polarization magic angle spinning nuclear magnetic resonance and by liquid chromatog- raphy/electrospray mass spectrometry (Rohrbaugh and Yang, 1997; Wagner and Yang, 1999~. Both the hy- drolysis and heel-forming reactions can lead to corro- sion of the steel container materials as well as the brass valves and fittings that were used originally in the bulk (ton) containers. Hydrochloric acid reacts with iron to produce ferrous chloride and liberate hydrogen gas; the latter is responsible for the frothing ("champagning") encountered when some mustard rounds are opened. Thiouronium salts absorbed on steel surfaces can also lead to corrosion via a dehydrohalogenation-like mechanism, giving Fe++ ion, vinyl chloride, dithiane, and hydrogen. All of these products of mustard decom- position have been observed during sampling and analysis programs conducted by the Army, including SUPLECAM. In recent tests, mustard-filled projectiles stored at DCD were opened and drained at CAMDS in prepara- tion for agent destruction at PUCDF. It was found that i4"Champagning" is sometimes used by the Army to describe this reaction and its manifestation during projectile opening operations. 17 in many cases only 3 to 4 lb of the 11 lb of agent fill could be drained; the rest of the material remained so- lidified in the munition casing (Novad, 2003~. DETERIORATION PROCESSES FOR ENERGETIC MATERIALS At the time this report was prepared, the chemical stockpile included 367,000 M55 rockets (276,000 GB; 91,000 VX), each filled with 10.7 lb of GB or 10.1 lb of VX, respectively. To date, more than 80,000 M55 rockets have been destroyed in the campaigns at JACADS and TOCDF. Since these rockets were manufactured in the early to mid-1960s, the average age of the remaining rockets is now about 40 years. Deterioration of energetic materials has been recog- nized as a potential source of autoignition in these rockets. A series of studies and reports has investi- gated this issue (e.g., GAO, 1994; NRC, 1994b; U.S. Army, 1988d,1994~. More recently, a comprehensive and substantive evaluation of the autoignition poten- tial, drawing on past theoretical and empirical stud- ies, concluded that risk of autoignition is small com- pared with risk of ignition from external sources such as lightning strikes (U.S. Army, 2002c). See Table 4-3 for details. Nevertheless, because GB M55 rockets have been identified as posing increased risk and because of the uncertainties inherent in the risk estimates, the Army's decision to expedite their destruction early in the disposal schedule for each site is certainly pru- dent. Although M55 rockets containing VX are less likely to autoignite than those containing GB, the dis- posal of rockets in general remains a priority. OBSERVED LEAK FACTORS AND OCCURRENCES BY MUNITION TYPE A memorandum dated April 10, 1996, from Donald E. Brooke summarizing postmortem investigations conducted on chemical munitions was used as a frame- work for the information on leakers and factors con- tributing to such occurrences that is presented in Ap- pendix B (U.S. Army, 1996b). SUMMARY This chapter, with Appendixes A and B. provides a fairly detailed description of the degradation processes affecting chemical agents and (to a lesser degree) pro-
18 EFFECTS OF DEGRADED A GENT AND MUNITIONS ANOMALIES ON CHEMICAL STOCKPILE DISPOSAL OPERATIONS pellants in stored munitions. While stabilizers were added to GB and VX at the time of manufacture to retard decomposition, these stabilizers have degraded over time. The resulting acidic decomposition prod- ucts may corrode metal containment vessels, leading to agent leakage (particularly for GB ). The decompo- sition mechanism is such that agent degradation may be expected to accelerate at elevated temperatures and longer storage times; these hypotheses are explored in Chapter 3. Additional anomalies were identified that may af- fect subsequent processing of munitions in demilitari- zation activities. These include mechanical defects, improperly assembled munitions, gelling or solidifica- tion of agent fills, pressurization, and contamination by substances such as lead or mercury. The processing consequences of these anomalies are explored further in Chapter 4.
