UNITED STATES 

NUCLEAR REGULATORY COMMISSION 

OFFICE OF FEDERAL AND STATE MATERIALS 

AND ENVIRONMENTAL MANAGEMENT PROGRAMS 

WASHINGTON, D.C. 20555 

March 4, 2014 

NRC INFORMATION NOTICE 1999-03, REV. 1: EXOTHERMIC REACTIONS INVOLVING 

 DRIED URANIUM OXIDE POWDER 

 (YELLOWCAKE) 

ADDRESSEES 

All operating uranium recovery facilities that produce uranium oxide powder (yellowcake). All 

Agreement States with the authority to regulate uranium mills (i.e., Utah, Colorado, Texas, Ohio, 

Illinois, and Washington). 

PURPOSE 

The U.S. Nuclear Regulatory Commission (NRC) is issuing this Information Notice (IN) to alert 

licensees to recent events involving pressurized drums of dried uranium oxide powder 

(yellowcake). This IN is a revision to IN 99-03 which previously discussed industry experience 

with pressurized 208-liter (55-gallon) metal drums (hereafter referred to as drums) and related 

exothermic reactions involving yellowcake material. It is expected that recipients will review this 

information for applicability to their licensed activities and consider actions, as appropriate, to 

avoid similar problems. However, suggestions contained in this IN are not NRC requirements; 

therefore, no specific action or written response is required. 

DESCRIPTION OF CIRCUMSTANCES 

The NRC is aware of at least nine different sites that have encountered problems with 

pressurized drums. A brief description of two events is provided below. Both events resulted in 

uptakes of uranium by workers, and both have similar root causes. 

In 2006 at a conventional mill, a worker attempted to open a drum filled with yellowcake that 

exhibited bulging. Unbeknownst to the worker, the sealed drum was pressurized. The pressure 

was apparently caused by the generation of oxygen gas within the drum from the decomposition 

of hydrogen peroxide precipitated yellowcake product. When the drum sealing bolt was 

loosened, the pressure in the drum caused the lid to blow off the drum and strike the worker. 

The worker received an uptake of uranium, although the uptake was less than regulatory limits. 

Records indicate that the drum lid had remained unsealed for three hours after the drum had 

been filled with yellowcake product, as required by site procedures. 

ML14028A175
IN 1999-03, Rev. 1 

Page 2 of 5

The facility operator conducted an investigation and identified the root cause as less than 

adequate procedures. The facility operator concluded that the product did not completely cool, 

or off-gas, within the three-hour time interval. Corrective actions included revising the 

applicable procedure to extend the drum sealing interval from three to four hours and providing 

additional training to site workers. 

The second incident occurred in 2012 at a uranium refinery in Canada while workers were 

opening a drum of yellowcake supplied by an in-situ uranium recovery facility. When a refinery 

worker loosened the ring clamp on the drum lid, the pressure in the drum (produced by an 

unexpected build-up of oxygen gas) caused the lid to buckle. The escaping gas ejected 

approximately 20 kilograms (44 pounds) of dried, powder-like yellowcake material from the 

drum. The incident resulted in three refinery workers receiving uptakes of uranium. The 

refinery operator subsequently identified several other drums, supplied by the same uranium 

recovery facility, which also showed signs of internal pressurization. The uranium recovery 

facility operator conducted an investigation to determine the causes of the pressure buildup in 

the drums. The facility operator concluded that the drums became pressurized due to: 

(1) inadequate cooling and venting of the dried yellowcake product prior to sealing the drum lid; 

and (2) inadequate drying of the yellowcake product (i.e., inadequate dryer residence time). 

The NRC later determined that inadequate procedures were contributing causes of the event. 

BACKGROUND 

The NRC issued IN 99-03 on January 29, 1999, to alert licensees to incidents involving 

exothermic reactions that occurred after packaging hydrogen peroxide precipitated yellowcake 

powder into drums. The original IN discussed two types of exothermic reactions—oxygen 

generation as a byproduct of the drying process and hydrocarbon contaminants reacting with 

the yellowcake product. At that time, industry took corrective actions which included leaving the 

drums unsealed for a minimum of three hours and preventing oil and grease from being 

introduced into the precipitation and drying circuits. 

Since 1999, the uranium recovery industry has experienced several more pressurized drum 

events. Because these events continued to occur, the causes may not be well understood by 

the industry. Further, past actions taken by industry to prevent pressurized drums may not have 

been fully effective. 

The IN 99-03 also advised facility operators about exothermic reactions of yellowcake with 

organic materials. These reactions can cause spontaneous combustion of flammable materials 

such as oil that may enter the process circuit. Refer to Enclosure 1 for an expanded discussion 

of this hazard. 

DISCUSSION 

In both the 2006 and 2012 instances, the fundamental cause of the pressurized drums was 

attributed to the build-up of oxygen gas in sealed containers. The oxygen gas apparently 

originated from the decomposition of residual uranyl peroxide hydrates or hydrogen peroxide in 

the dried yellowcake product. Both incidents indicate that the drum lids may have been sealed 

onto the drums prior to the completion of the uranyl peroxide hydrate decomposition process. 

Both sites used a minimum three-hour time delay as mentioned in IN 99-03; however, this time 

delay must have been insufficient based on site-specific operational parameters. 
IN 1999-03, Rev. 1 

Page 3 of 5

In early 2013, the NRC established a working group to: (1) review the generic implications of the 

most recent pressurized drum incident including the reasons why drums continue to become 

pressurized; (2) identify industry experience with pressurized drums; and (3) ascertain whether 

there were any related trends across the industry. The working group consisted of NRC staff, 

industry representatives, and subject-matter experts. The NRC used the findings of the working 

group, as well as information solicited from 14 current and former uranium recovery facilities, in 

the development of this revision to IN 99-03. As part of the revision process, the NRC is also 

correcting some of the chemical nomenclature used to describe the thermal decomposition 

process provided in the original IN. More importantly, as a result of industry experience gained 

since the NRC issued IN 99-03, this revised IN recognizes a broader range of relevant factors 

that could result in pressurized drums. 

The working group developed a questionnaire that was submitted to various national and 

international companies having direct experience processing or handling yellowcake. The 

working group received 14 responses from various entities. The responses were subdivided 

into two basic categories—sites using ammonia precipitation circuits and sites using hydrogen 

peroxide precipitation circuits. The survey responses provided the working group with detailed 

information about dryer and packaging operations at each site as well as industry experience 

with pressurized drums. If the facilities had experienced pressurized drum problems, the survey 

asked the respondents to explain the possible causes for the pressurizations. As discussed in 

Enclosure 1, sites using the ammonia precipitation process with high-temperature calciners 

have not experienced pressurized drums. Only sites using the hydrogen peroxide precipitation 

circuits have experienced pressurized drums. Enclosure 3 provides a matrix of the operating 

parameters for the 11 sites using hydrogen peroxide precipitation circuits and the suspect 

causes of past drum pressurizations. 

 

The working group concluded that many drum pressurizations were apparently caused by 

changes in the chemical composition of the yellowcake product after it had been placed into a 

sealed container. The level of pressurization appears to be related to the cooling and venting 

time of the product prior to sealing of the drum. The working group determined that the 

minimum required cooling and venting time for recently dried yellowcake in an unsealed drum 

depends on the type of dryer, drying temperature, residence time (time product remains in 

dryer), hold-up time (time interval between completion of drying cycle and when product is 

placed into drum), dryer feed rate, and product moisture content. These various operational 

parameters may ultimately contribute to oxygen gas buildup in yellowcake drums. 

As noted earlier, multiple operators reported that they had experienced pressurized drum 

problems, but the specific chemical reactions causing the pressurizations were not always clear. 

In their survey responses, facility operators provided two general corrective actions to address 

the pressurized drum issue—increasing the cooling/venting time before the lid is sealed onto the 

drum and conducting visual inspections of the drums for signs of pressurization prior to 

shipment. These operators found that increasing the cooling and venting time before sealing 

the drums and inspecting the drums before shipment appear to have resolved the problem. A 

range of cooling and venting times was reported, from 4 to 24 hours (see Enclosure 3). In 

several instances, facility operators chose to extend the cooling and venting times in response 

to past experiences with pressurized drums. Each facility operator should evaluate their 

operations and decide how to implement site-specific corrective actions as necessary to prevent 

pressurized drums.
IN 1999-03, Rev. 1 

Page 4 of 5

The working group found that many operators did not measure their product temperature 

directly, and that discrepancies existed between the maximum dryer temperature and the 

chemical composition of their final product. It is product temperature, not dryer temperature, 

which ultimately drives the thermal decomposition process. The working group concluded that, 

for typical U.S. facilities utilizing hydrogen peroxide precipitation and drying temperatures below 

800 degrees Celsius (°C) [1472 degrees Fahrenheit (°F)], a cooling and venting period of 12 to 

24 hours appears sufficient to prevent oxygen gas buildup in yellowcake drums. Above dryer 

temperatures of approximately 800 °C (1472 °F), it is expected that the uranyl peroxide product 

will be converted to UO3 (uranium trioxide) product. Oxygen production is not expected to occur 

after the uranyl peroxide product has been completely converted to UO3 product. For dryers 

operating below 800 °C (1472 °F), shorter periods of yellowcake cooling and venting prior to 

securing the drum lid may be ineffective to prevent oxygen buildup in sealed drums. 

CONCLUSION 

Based on its working group findings and questionnaire responses, NRC concludes that: 

 The most likely cause for the drum pressurization events was attributed to continued 

decomposition of dried uranium product and the production of oxygen after the drums have 

been filled and sealed. 

 For facilities utilizing hydrogen peroxide precipitation and drying temperatures below 800°C 

(1472°F), a cooling and venting period of at least 12 hours appears to be necessary to 

prevent oxygen gas build-up in yellowcake drums. Shorter periods may be ineffective. 

Many operators have elected to implement a cooling and venting time of 24 hours. 

 To prevent drum pressurizations, facility operators have implemented two basic corrective 

actions—increasing the cooling/venting time before the lid is sealed and conducting visual 

inspections of the drums for signs of pressurization prior to shipment. 

 Facility operators should evaluate the potential for organic-based exothermic reactions, as 

discussed in Enclosure 1. Facility operators should develop protocols to minimize the 

potential for organics, including oils and greases, to enter into yellowcake process circuits. 

 In addition to being industrial and radiological hazards to workers, shipments of uranium 

yellowcake in packages with internal pressures that reduce the effectiveness of the 

packages are prohibited by U.S. Department of Transportation regulations. Enclosure 1 

provides additional information about these regulations. 
IN 1999-03, Rev. 1 

Page 5 of 5

CONTACT 

This information notice requires no specific action or written response. If you have any 

questions about the information in this notice, please contact one of the technical contacts listed 

below. 

 /RA Aby Mohseni for/ 

Larry W. Camper, Director 

Division of Waste Management 

 and Environmental Protection 

Office of Federal and State Materials 

 and Environmental Management Programs 

Contacts: Robert Evans, Region IV 

 (817) 200-1234 

 Robert.Evans@nrc.gov 

 Ronald Burrows, FSME 

 (301) 415-6443 

 Ronald.Burrows@nrc.gov 

 Thomas McLaughlin, FSME 

 (301) 415-5869 

 Thomas.Mclaughlin@nrc.gov 

Enclosures: 

1. Detailed Technical Discussion 

2. Bibliography 

3. Survey Results for Facilities Using Hydrogen Peroxide Precipitation 

4. FSME Recently Issued Generic Communications 
IN 1999-03, Rev. 1 

Page 5 of 5

CONTACT 

This information notice requires no specific action or written response. If you have any 

questions about the information in this notice, please contact one of the technical contacts listed 

below. 

 /RA Aby Mohseni for/ 

 Larry W. Camper, Director 

Division of Waste Management 

 and Environmental Protection 

Office of Federal and State Materials 

 and Environmental Management Programs 

Contacts: Robert Evans, Region IV 

 (817) 200-1234 

 Robert.Evans@nrc.gov 

 Ronald Burrows, FSME 

 (301) 415-6443 

 Ronald.Burrows@nrc.gov 

Thomas McLaughlin, FSME 

 (301) 415-5869 

 Thomas.Mclaughlin@nrc.gov 

Enclosures: 

1. Detailed Technical Discussion 

2. Bibliography 

3. Survey Results for Facilities Using Hydrogen Peroxide Precipitation 

4. FSME Recently Issued Generic Communications 

ML14028A175 

RIV:DNMS/RSFS C:DNMS/RSFS DD:DNMS D:DNMS 

RJEvans DBSpitzberg VHCampbell AVegal 

/RA/ Via email Via email Via email 

10/24/13 11/06/13 01/02/14 12/31/13 

FSME:DMSSA FSME:DWMEP DWMEP/DURLD C:DWMEP/DURLD 

ARMcIntosh RABurrows TGMcLaughlin BvonTill 

Via email Via email Via email Via email 

10/24/13 10/28/13 10/28/13 10/29/13 

NSIR FSME:DMSSA FSME:DILR OGC/GCLR/RMR 

CGrigsby DWhite JCai TLStokes 

Via email Via email Via email Via email 

10/28/13 10/24/13 11/05/13 12/17/13 

OE/EB NMSS DD:DWMEP/DURLD D: MSSA 

TMarenchin HJGonzalez DPersinko JMoses for 

LDudes 

Via email Via email /RA/ /RA/ 

11/14/13 11/08/13 01/24/14 02/28/14 

D:DWMEP 

AMohseni for 

 LWCamper 

/RA/ 

03/04/14 

OFFICIAL RECORD COPY 
IN 1999-03, Rev. 1 

Enclosure 1 

Page 1 of 7

Detailed Technical Discussion 

At least nine uranium recovery facilities have experienced pressurized drum events. The 

reasons for these pressurization events varied from facility to facility (see Enclosure 3 for a 

complete list of suspected causes for the drum pressurizations). The actual causes of previous 

drum pressurization events are still in question. The causes may include the decomposition of 

free hydrogen peroxide (H2O2) carried over with the dried yellowcake, decomposition of uranyl 

peroxide product, production of steam from residual water, reaction of uranium compounds with 

inorganics, or perhaps a combination of these causes. In addition, a reliable and accurate 

chemical test for free hydrogen peroxide in yellowcake has not been validated which would 

allow facilities to precisely determine the actual causes for these types of incidents. 

The NRC’s working group identified several topics that are discussed in detail below. The 

working group’s findings are based on the information that was identified or made available to 

the group, in part, through uranium recovery facility responses to surveys. Two of the 14 

surveys were conducted for sites that are no longer in service, meaning that some of the 

information presented in the survey may be based on individual recollections versus formal 

documentation. 

Precipitation with Ammonia and Use of a Calciner to Dry Yellowcake

Three facility operators out of 14 reported using ammonia precipitation instead of hydrogen 

peroxide precipitation. These operators also dried their precipitated product at high 

temperatures in a calciner. There was no evidence that the ammonia precipitation process, in 

combination with a calciner, had ever resulted in pressurized drums. Therefore, these types of 

facilities are excluded from the current discussion about H2O2 precipitated product. 

The Chemistry of Hydrogen Peroxide Precipitated Yellowcake

Facilities using the hydrogen peroxide precipitation process may create pressurized drums if 

their operational processes are not appropriately controlled. The chemical product of 

precipitation depends on the temperature of the solution undergoing precipitation. Based on the 

survey results, hydrogen peroxide precipitation typically occurs under ambient conditions. At 

temperatures below 50°C (122°F), the precipitate is generally of the form UO4 • 4H2O (uranyl 

peroxide tetrahydrate). The final desired product is UO4 • 2H2O (uranyl peroxide dihydrate). 

Converting the tetrahydrate form (UO4 • 4H2O) of uranyl peroxide to the desired dihydrate form 

(UO4 • 2H2O) occurs quickly under typical drying conditions. For example, laboratory samples 

of UO4 • 4H2O will dehydrate to UO4 • 2H2O in about one hour when dried at 100°C (212°F) 

(product temperature, not dryer temperature). Typical maximum dryer temperatures at facilities 

using hydrogen peroxide precipitation range from 130°C (266°F) to 649°C (1200°F), with most 

facilities operating well below 300°C (572°F). Of course, laboratory studies do not take into 

account industrial scale production issues such as difficulty in ensuring uniform drying 

temperature of the product and desired moisture content. The composition of the final product 

will depend on a variety of drying conditions including dryer temperature, heating time, heating 

rate, feed rate, product temperature, water content, hydrogen peroxide content, pressure, etc. 

As a result of all of these variables affecting the final product, it is likely that other chemical 

species are forming. The compound UO4 • 2H2O does not undergo dehydration like UO4 • 
IN 1999-03, Rev. 1 

Enclosure 1 

Page 2 of 7

4H2O, but rather loses oxygen and water simultaneously (i.e., it decomposes to another 

compound). Uranium trioxide (UO3) will form at around 500°C (932°F) (product temperature), 

so for most facilities this reaction is not expected to occur. However, a range of uranium 

compounds between UO4 • 2H2O and UO3, are likely to form under current typical drying 

temperatures and drying times. As a group, these intermediate compounds are referred to as 

amorphous UOX, where (3≤x≤3.5). While UO4 • 2H2O is considered the most stable form of 

uranyl peroxide, amorphous UOX is considered unstable with respect to the decomposition to 

UO3 even at room temperature. Table 1 demonstrates one example of dryer temperature 

versus product formation. 

Table 1 

Drying Temperature and product composition: Phases identified in hydrogen peroxide 

precipitated yellowcake dryer product by X-ray diffractometry1 

Sample 

ID 

Dryer 

Discharge 

Temperature 

(°C) 

UO4·2H2O Amorphous

UOx

UO3 U3O8

001 as-is X 

015 125 X 

002 131 X 

022 145 X 

016 150 X 

003 175 X 

017 175 X 

004 225 Trace X 

005 275 X 

006 325 X 

018 375 X 

019 400 X 

008 425 X 

020 425 X 

021 450 X 

023 475 X 

010 525 X 4.30% 

011 575 X 

012 625 X 

014 769 X 

1

empty cells indicate not detected 

In addition, amorphous UOX has been reported to react with free water to liberate oxygen gas. 

It is not clear whether this is a reaction resulting in UO3, or some other type of reaction. 

Experiments to date have demonstrated this effect by mixing relatively large amounts of water 

with amorphous UOX. Figure 1 demonstrates this phenomenon. It is unknown what effect 

residual moisture at levels typical of uranium recovery facilities has on amorphous UOX. It has 

also been found that neither UO4 • 2H2O nor UO3 react with water in this manner. 
IN 1999-03, Rev. 1 

Enclosure 1 

Page 3 of 7

Figure 1 

Product chemistry: Dried hydrogen peroxide precipitated yellowcake reactivity with water 

 

Addition of Excess Hydrogen Peroxide During Precipitation Process

A stoichiometric excess of hydrogen peroxide is required to optimize precipitation of uranyl 

peroxide yellow cake. The degree of excess is determined by the composition of the uranium 

bearing solution (feed stock for precipitation). Molybdenum, vanadium, and other reactive 

metals contained in the feed stock react with hydrogen peroxide to form soluble complexes. In 

addition, some fraction of hydrogen peroxide may decompose during the precipitation process. 

Facility operators should be aware that some of this excess hydrogen peroxide may be carried 

over into the drying process. The working group understands that an effective drying cycle 

should eliminate this excess hydrogen peroxide. 

Stability of Hydrogen Peroxide in the Presence of Uranyl Peroxide Solids

Precipitation of dissolved uranium by the addition of hydrogen peroxide is a well-known and 

common process within the uranium recovery industry. It has been demonstrated that this 

precipitation process is a reversible chemical reaction. One consequence is that an excess of 

dissolved hydrogen peroxide must be maintained in solution to drive the precipitation reaction to 

completion and, hence, to minimize dissolved uranium losses in resulting waste streams. The 

use of excess hydrogen peroxide is a common practice in the uranium industry where the 

maintenance of low uranium tails in the precipitation process is desired. The filtrate fluids 

associated with the resulting uranyl peroxide slurry must also contain a modest but finite 

concentration of dissolved hydrogen peroxide to avoid dissolution of uranyl peroxide solids. As 

a result, moist uranyl peroxide slurries entering any drying equipment may contain a small but 

finite concentration of dissolved hydrogen peroxide. 
IN 1999-03, Rev. 1 

Enclosure 1 

Page 4 of 7

Industrial hydrogen peroxide solutions are relatively stable as long as they are properly stored at 

moderate temperatures, maintained at a pH below 5, and do not come into contact with 

impurities, especially metals. Uranyl peroxide solids are typically precipitated at low pH (2-4) 

under ambient conditions in the presence of small amounts of excess hydrogen peroxide. The 

resulting slurries are usually pressed and washed at ambient conditions in a filter press 

operation to remove soluble filtrate impurities from the filter cake. The acidity of the wet cake 

will likely remain low keeping any residual free hydrogen peroxide relatively stable. This free 

hydrogen peroxide will, however, begin to decompose over time to oxygen gas and water as it 

remains in contact with the uranyl peroxide solids. The rate of this decomposition is unknown 

and, if a test were to be performed to measure residual free hydrogen peroxide, it would have to 

be performed on fresh uranyl peroxide solids to minimize the subsequent decomposition of 

hydrogen peroxide. This may explain why it has been difficult to measure free hydrogen 

peroxide in filter cake samples as the time to perform the tests might be too long for the 

hydrogen peroxide to remain stable and not decompose. 

The other condition under which hydrogen peroxide can decompose is elevated temperature. 

Hydrogen peroxide will slowly decompose at room temperature. The rate of decomposition will 

increase as temperature increases. If any free hydrogen peroxide enters the dryer it will likely 

decompose as the temperature of the uranyl solids increases. However, if the free hydrogen 

peroxide fails to instantly decompose upon entry into the drying chamber, the residual hydrogen 

peroxide may be captured in the uranyl peroxide crystalline structure during the drying process. 

Facility operators should try to minimize the amount of residual free hydrogen peroxide in the 

product prior to the drying process. 

Drying Temperature of Uranyl Peroxide in Rotary Vacuum Dryers

While different dryer types and precipitation processes are utilized in the industry, the majority of 

facility operators uses hydrogen peroxide precipitation and employs some type of rotary vacuum 

dryer that operates at a relatively low temperature. These systems are typically batch 

operations with ambient temperature yellowcake slurry introduced into a pre-heated chamber at 

atmospheric pressure. The chamber is then sealed and depressurized. The sub-atmospheric 

pressure within the chamber (i.e., the vacuum) does not remain constant during the drying 

cycle. Rather, the pressure continuously decreases as water vapor is liberated and evacuated 

from the chamber via the vacuum pump circuit. The vapor capacity of the vacuum pump limits 

the operational vacuum (pressure) within the chamber. During the period in which boiling of 

free moisture is the principle process within the drying chamber, the temperature of the 

yellowcake solids is tied to the boiling point of water at that pressure. Near the end of the drying 

cycle, sufficient free moisture has been removed and the pressure within the chamber 

decreases and approaches a steady state. As this condition is reached, the yellowcake 

temperature rapidly rises toward the temperature of the heating surfaces within the drying 

chamber. Essentially, there are two phases to the batch vacuum drying cycle. The first is 

controlled by the temperature-pressure relationship of boiling water and the capacity of the 

vacuum pump to remove water vapor. In the second phase, the vacuum pump vapor capacity 

is no longer limiting and the temperature of the solids is controlled by heat transfer between the 

vessel surfaces and the yellowcake solids. 

Regardless of the temperature of the dryer, there is still a minimum time necessary where 

moisture is driven off before the yellowcake is heated to above 100°C (212°F), the point where 

UO4 • 2H2O starts to be created. Continued heating of the product can therefore lead to 
IN 1999-03, Rev. 1 

Enclosure 1 

Page 5 of 7

conversion to hydrated UO4 (uranyl peroxide); however, there is likely limited time for conversion 

of UO4 to UO3 (uranium trioxide). As such, any remaining UO4 that does not convert to the 

more stable UO3 could lead to drum pressurization. Therefore, it is important for facility 

operators to control the drying process parameters, including temperature, to control product 

chemistry. 

Potential Reactions for Uranyl Peroxide Yellowcake in the Presence of Organic Matter

Five of 11 respondents that used hydrogen peroxide (H2O2) precipitation process reported that 

they have experienced exothermic reactions in yellowcake due to organic contamination, and 

five of 11 reported that they pay special attention to hydrocarbon contamination. 

The reaction of H2O2 with organics is a well-known but complex reaction. When H2O2 is in the 

presence of most organic matter, the hydrogen peroxide can react with the organic to form 

organic peroxide compounds which are usually unstable or can cause the organic to be 

oxidized, i.e., “chemically burned.” When organic peroxide compounds are formed they have 

been known to detonate, i.e., cause spontaneous combustion or cause oxidation reactions to 

occur. These latter reactions result in the evolution of heat (from the “burning” of the organics) 

and the evolution of CO2 (carbon dioxide), CO (carbon monoxide), and H2O (water) depending 

upon the completion of the reaction. When hydrogen peroxide reacts in this way with organics 

there is always a signature gas evolution which will be indicative of the reaction taking place. 

Under certain conditions of temperature, metal catalysts, and reactant concentrations, organics 

can react with the hydrogen peroxide. This interaction results in a complex, multi-step reaction 

which typically forms many intermediate hydroxyl radicals as the oxidation reaction is on-going. 

This process can be simplified as follows: 

 H2O2 + Organics (CxHy) →A →B →C.... →CO2 + CO + H2O + Heat 

Where A, B, C, etc. are the intermediate compounds that form prior to full oxidation (compounds 

that contain OOH- or OH- radicals). The end result of this chain of reactions is that the organic is 

“chemically burned” and the signature off-gases of this reaction are CO2 + CO + H2O plus heat. 

When these intermediate compounds form, they combine unstably bound oxygen together with 

hydrogen and carbon in the same molecule, and these organic peroxides can ignite easily and 

burn rapidly and intensely. When organic peroxide begins to decompose, the heat produced by 

its decomposition may not dissipate as quickly as it is generated which can result in increasing 

temperatures which further intensifies the rate of exothermic decomposition. This can create a 

dangerous situation known as a self-accelerating decomposition. 

When wet yellowcake is introduced into a dryer system it is important that the product not 

contain organic matter as the reactions of any residual H2O2 or decomposed uranyl peroxide 

hydrate can occur. For trace amounts of organics, this will likely not be an issue as the dryer 

can dissipate any heat that is formed by these reactions, or the organic will be driven off by the 

heat of the drying operation. If, however, larger amounts of organics were to be introduced into 

the dryer, a self-accelerating reaction can occur where the heat cannot be dissipated, high 

temperatures are generated, and a violent reaction is possible. This has occurred in some dryer 

facilities when there was a mechanical failure in the dryer which caused large quantities of 

organics such as oil to be introduced into the dried yellowcake at elevated temperatures. 
IN 1999-03, Rev. 1 

Enclosure 1 

Page 6 of 7

If the yellowcake is dried at high temperatures as in a calciner, the problem of organic reactions 

is less likely since the higher temperatures encountered in the dryer will drive off the volatile 

organics and decompose any organic peroxides that might have been formed. In a low 

temperature dryer, some organics can remain with the dried uranyl peroxide hydrates and 

become unstable in the dryer or when removed from the dryer. This could have consequences 

for drummed material as the decomposition of any organic peroxide can generate heat plus 

CO2, CO, and H2O. The consequence of this could be the slow generation of combustion gases 

(for small amounts of organics) or a more violent reaction if large amounts of organic peroxides 

begin to decompose and generate heat which can cause a self-accelerating reaction to occur. 

In summary, facility operators should be aware that organic reactions are possible with 

yellowcake product, and operators should try to locate and eliminate potential sources of 

organic matter from entering into the precipitation and drying circuits. 

Packaging (Drumming) of Yellowcake

Dried yellowcake is almost exclusively stored and shipped in 208-liter (55 gallon) steel drums. 

In the U.S., the drums must meet U.S. Department of Transportation specifications if the facility 

operator plans to ship yellowcake material in the drums. Facilities use new drums, 

reconditioned (used) drums, or a combination of both, depending on drum availability and/or 

cost. It is critical that operators ensure that drums used to ship yellowcake do not have any 

organic material (such as oil or grease) in them. Employees must be trained and informed 

about the serious complications of organic material in drums to ensure that drums used for 

shipment are received from the suppliers in acceptable condition and the facility does not 

inadvertently use such drums for another purpose that could result in organic material 

contamination prior to filling with yellowcake. 

Information Notice 99-03 cautioned that new drums and lids could be a potential causal factor in 

drum pressurization incidents due to the tighter seal of such drums compared to reconditioned 

drums and lids. The tighter seal could prevent the off gassing from escaping the drum, thereby 

leading to pressurization. Although this condition is still possible with new drums or 

reconditioned drums that happen to have better seals, the working group believes that 

appropriate controls, such as adequate cooling and venting times, will prevent any significant 

potential for gas build up and drum pressurization. 

To limit the potential of shipping a drum of yellowcake that has been pressurized due to an 

unexpected cause, including a human factor, it is strongly suggested that operators include as 

part of their final pre-shipment inspection a procedure to check each drum for pressurization. 

This can be accomplished by a visual inspection of drum lids and a physical check by pushing 

on the lid and checking for deflection and/or tapping the lid with a rubber mallet to assess 

deflection and the tone resulting from the tapping. Any drums suspected of pressurization 

should be returned to the drumming area and carefully depressurized and opened to confirm 

conditions and causes, if appropriate. Operators should also develop controls to manage the 

risk of the addition of excess free moisture/water to open drums of product. The working group 

is aware that one study indicated that pressure is generated from the addition of water into 

amorphous product. For example, operators should avoid spraying unsealed drums with water 

to avoid the possibility of adding free water to the dried product. 
IN 1999-03, Rev. 1 

Enclosure 1 

Page 7 of 7

Shipment of Pressurized Drums

A facility operator who ships pressurized drums may be in violation of U.S. Department of 

Transportation regulations. In particular, the shipment of pressurized drums may violate 

regulations 49 CFR 173.24(b)(3) and 49 CFR 173.475(a). Regulation 173.24(b)(3) states that 

there will be no mixture of gases or vapors in the package which could, through any credible 

spontaneous increase of heat or pressure, significantly reduce the effectiveness of the 

packaging. Regulation 173.475(a) states that, before each shipment of any Class 7 

(radioactive) materials package, the offeror (the facility operator who offers the drum for 

shipment) must ensure, by examination or appropriate tests, that the packaging is proper for the 

contents to be shipped. Based on these two regulations, a standard metal drum may not be the 

proper package for pressurized uranium product because the pressurization reduces the 

effectiveness of the packaging. Further, the packaging process may be inadequate if it allows 

gases and vapors to increase the internal pressure of the package (the drum), resulting in rapid 

and uncontrolled depressurization when the package is opened. 

Facility operators should also be aware of regulation 49 CFR 173.22(a)(4). This regulation 

requires persons who offer hazardous material for transportation to comply with the 

manufacturers’ instructions for packaging. This regulation applies to drums that have been 

certified by the Department of Transportation and marked or stenciled accordingly. Many drum 

manufacturers provide specific instructions for proper closure of the drum, including a 

requirement to torque the drum seals. Facility operators should be aware of any specific 

closure instructions provided by the manufacturer or distributer of their certified drums, if these 

drums are used to transport yellowcake material. 

Suggestions for the Uranium Recovery Industry

The working group suggests that the information presented in this IN be supplemented by the 

uranium recovery industry. The working group suggests that the industry consider expanding 

the information by determining the chemical species of their product, product temperature 

versus holding time prior to sealing, impact of excess hydrogen peroxide on the decomposition 

process, rate of moisture reduction in the dryer, optimum drying parameters (feed rate, 

temperature, and residence time), and development of procedures and training program to alert 

workers of the potential risks. For example, facility workers should be made aware that drying is 

a dynamic process and the change of any process parameter, such as feed rate or dryer 

temperature, may result in a product that is incompletely dried. Facility operators should use 

this information to establish site-specific parameters to assure that drum pressurizations do not 

occur. 

Facility operators should consider establishing procedures or other protocols to identify and 

manage pressurized drums. These procedures should include inspections of the drums for both 

pressurization and integrity prior to transport. This inspection should be complete even if the 

drum is stored for an extended period of time prior to actual shipment. Finally, the receiver of 

shipped drums should also inspect drums for pressurization upon receipt and before opening a 

sealed drum. 
IN 1999-03, Rev. 1 

Enclosure 2 

Page 1 of 2

Bibliography

Boggs, J. E., & El-Chehabi, M. (1957). The thermal decomposition of uranium peroxide, UO4 • 

2H2O. Journal of the American Chemical Society, 79(16), 4258-4260. 

Brady, L. J., Susano, C. D., & Lawson, C. E. (1948). Chemical and physical properties of 

uranium peroxide. Report AECD-2366. Oak Ridge, TN: U.S. Atomic Energy 

Commission, Technical Information Branch. 

Cordfunke, E. H. P. (1961). α-UO3: Its preparation and thermal stability. Journal of Inorganic 

and Nuclear Chemistry 23(3-4), 23, 285-286. 

Cordfunke, E. H. P., & Aling, P. (1963). Thermal decomposition of hydrated uranium peroxides. 

Journal of the Royal Netherlands Chemical Society, 82, 257-263. 

Cordfunke, E. H. P., & Van Der Giessen, A. A. (1963). Pseudomorphic decomposition of 

uranium peroxide into UO3. Journal of Inorganic and Nuclear Chemistry 25(5), 553-554. 

El-Chehabi, M. (1957). Decomposition of uranium peroxide. (Master’s Thesis). The University 

of Texas. 

Gayer, K. H., & Thompson, L. C. (1958). The solubility of uranium peroxide in acidic and basic 

media at 25 °C. Canadian Journal of Chemistry 36(12), 1649-1652. 

Gupta, C. K., & Singh, H. (2003). Uranium resource processing: Secondary resources. Berlin: 

Springer-Verlag. 

Harrington, C. D., & Ruehle, A. E. (Eds.). (1959). Uranium production technology. Princeton, 

N.J.:Van Nostrand. 

Hausen, D. M. (1998). Characterizing and classifying uranium yellow cakes: A background. 

JOM 50(12), 45-47. 

Katz, J. J., & Rabinowitch, E. (1951). The chemistry of uranium: The element, its binary and 

related compounds (Part I). New York, NY: McGraw-Hill Book Company, Inc. 

Leininger, R. F., Hunt, J. P., & Koshland, D. E. (1958). Composition and thermal decomposition 

of uranyl peroxide (Paper 69). Chemistry of uranium: Collected papers, TID-5290, 

Book 2 (704-721). Oak Ridge, TN: U.S. Atomic Energy Commission Technical 

Information Service Extension 

Merritt, R.C. (1971). The extractive metallurgy of uranium. Golden, CO: Colorado School of 

Mines Research Institute. 

Metzger, R., et al. (1997). Solubility characterization of airborne uranium from an in-situ 

uranium processing plant. Health Physics 72(3), 418-422. 

Moore, R. L., & Watts Jr., R. A. (1952). Production of UO3 by calcination of uranyl peroxide, 

Document No. HW-26531. Richland, WA: Hanford Works. 
IN 1999-03, Rev. 1 

Enclosure 2 

Page 2 of 2

 

Patton, F. S. (1963). Enriched uranium processing. New York, NY: Macmillan Co. 

Rich, R. L. (2007). Inorganic reactions in water. Berlin: Springer-Verlag. 

Rodgers, C., & Dyck, B. (2012). Uranium peroxide precipitate drying temperature relationships. 

CIM Journal 3(3), 149-156. 

Sato, T. (1961). Uranium peroxide hydrates. Die Naturwissenschaften 48(21), 668. 

Sato, T. (1963). Preparation of uranium peroxide hydrates. Journal of Applied Chemistry 13(8), 

361-365. 

Sato, T. (1976). Thermal decomposition of uranium peroxide hydrates. Journal of Applied 

Chemistry and Biotechnology 26(4), 207-213. 

Silverman, L. & Sallach, R. A. (1961). Two uranyl peroxides. Journal of Physical Chemistry 

65(2), 370-371. 

Thein, S. M., & Bereolos, P. J. (2000). Thermal stabilization of 233UO2, 233UO3, and 233U3O8, 

Report ORNL/TM-2000/82. Oak Ridge, TN: Oak Ridge National Laboratory. 

Walenta, K. (1974). On studtite and its composition. American Mineralogist 59, 166-171. 

The data for Table 1 comes from “Laboratory Characterization of Dryer Test Products,” Cameco 

Corporation, Gerhard Heinrich, John Krause, Mike Murchie, November 2009. 

The data for Figure 1 comes from “Laboratory Characterization of Dryer Test Products,” 

Cameco Corporation, Gerhard Heinrich, John Krause, Mike Murchie, November, 2009 but was 

adapted and updated for a presentation to the CNSC: “Rabbit Lake UOC Drying Process,” 

Cameco Corporation, Kirk Lamont, November 2012.
IN 1999-03, Rev. 1 

Enclosure 3 

Page 1 of 1

Survey Results for Facilities Using Hydrogen Peroxide Precipitation 

Time in Dryer 

(hours) 

Dryer 

Temp (oC) 

Yellowcake Temp 

(oC) When 

Barreled 

Cooling and 

Venting 

Time (hours)* 

Percent (%) 

Moisture in Dried 

Yellowcake 

Have You Experienced 

Any Drum 

Pressurizations? 

Suspected Causes of 

Drum Pressurizations 

12-16 232 Not measured >12 0 – 1.5 

Limit of 2 

No 

18-20 164 130 24-72 <1 Yes Decay of residual H O2 236-48 160 160 24 <1 Yes Not determined 21-22 163 138 24 1-8, 

Typically 

3-5 

Yes Moisture vaporizing 

(steam) 

6 130 <80 Described as 

“minimal” 

<2 No 

16-20 235 Not measured >12 0.5-1.5 

Limit of 2 

Yes Decay of H O2 2 and 

sealing drums too soon

4.5-6 649 66 Previously 3, 

changed to 24

1-4 Yes Cooling time and drying 

time too short 

6 371 < 371 4 “no moisture” Yes Decay of H O2 2

Unknown Not given Unknown “a number of 

hours” 

Not measured Yes Excess H O2 2 added 

during precipitation 

20-30 150 <90 12 1-4 w/w Yes Hot yellowcake added 

to moist drum 

1.5 245 80 >3 0.5-2.0 Yes Unknown 

* Cooling and venting times are current times, or the most recent times for facilities that are no longer in operation. Several sites increased their 

cooling and venting times in response to previous pressurized drum events or in response to IN 1999-03.
IN 1999-03, Rev. 1 

Enclosure 4 

Page 1 of 2 

List of Recently Issued Office of Federal and State Materials 

and Environmental Management Programs Generic Communications 

Date GC No. Subject Addressees 

11/15/2013 IN-2013-22 Recent Licensing 

Submittals Containing 

Personally Identifiable 

Information 

All materials licensees, certificate 

holders, applicants, and other 

entities subject to regulation by the 

U.S. Nuclear Regulatory 

Commission for the use of source, 

byproduct, and special nuclear 

material. All Radiation Control 

Program Directors and State 

Liaison Officers. 

10/17/2013 RIS-2013-17 Resuming Normal 

Interactions Between the 

NRC and NRC 

Stakeholders Following an 

Agency Shutdown 

All U.S. Nuclear Regulatory 

Commission (NRC) licensees, 

certificate holders, permit holders, 

and applicants; all Agreement and 

Non-Agreement States, and State 

Liaison Officers; and other 

interested stakeholders. 

10/09/2013 RIS-2013-16, 

Supp. 1 

Interactions Between the 

NRC and NRC 

Stakeholders During a 

Lapse of Agency 

Appropriations 

All U.S. Nuclear Regulatory 

Commission (NRC) licensees, 

certificate holders, permit holders, 

and applicants; all Agreement and 

Non-Agreement States, and State 

Liaison Officers; and other 

interested stakeholders. 

10/01/2013 RIS-2013-16 Interactions Between the 

NRC and NRC 

Stakeholders During a 

Lapse of Agency 

Appropriations 

All U.S. Nuclear Regulatory 

Commission (NRC) licensees, 

certificate holders, permit holders, 

and applicants; all Agreement and 

Non-Agreement States, and State 

Liaison Officers; and other 

interested stakeholders. 

09/16/2013 IA-03-02 Criteria for Reporting 

Cybersecurity Incidents 

All Radiation Control Program 

Directors and State Liaison 

Officers. All Increased Controls 

(IC) materials licensees. All 

licensees possessing Category 2 

and higher materials. 
IN 1999-03, Rev. 1 

Enclosure 4 

Page 2 of 2 

List of Recently Issued Office of Federal and State Materials 

and Environmental Management Programs Generic Communications

Date GC No. Subject Addressees 

09/11/2013 RIS-2013-14 Reporting Transactions 

Involving Temporary 

Jobsites to the National 

Source Tracking System 

All industrial radiography and well 

logging licensees, and all Radiation 

Control Program Directors and 

State Liaison Officers 

Note: This list contains the six most recently issued generic communications, issued by the 

Office of Federal and State Materials and Environmental Management Programs. A full listing 

of all generic communications may be viewed at the NRC public Web site at the following 

address: http://www.nrc.gov/reading-rm/doc-collections/gen-comm/index.html