re: question on 1969 Rocky Flats fire

[rurban@jason.com]

Jaro asked about the amount of plutonium involved in the fire (two tons ??) as well as any credible reference sources which may be consulted for further details of the event....see below snips with sources listed, followed by DOE Case Study statement.



"Some scrap Plutonium had been stored improperly in uncovered cans under a glovebox in building 776-777 at Rocky Flats. That morning, a Sunday, it did what plutonium has a nasty habit of doing: it ignited spontaneously, and set fire to the glovebox itself."

Combustible oily rags contaminated with plutonium were near the area where the fire started and have been implicated as the root cause of the fire. That fire caused spontaneous combustion of a plutonium briquette that was stored nearby. ...Plutonium metal briquettes were produced from scrap metal in an area adjacent to the production glovebox line and were stored in open cans in a shielded chest in the production area.(A)



""Glovebox" here gives a misleading impression of size; it was no mere box but a large chamber, constructed of nearly six hundred tons of combustible material, radiation shielding included."

The plutonium storage glovebox and other gloveboxes contained tons of flammable Benelex and Plexiglas.[1] Benelex, composed of wood fiber and plastic, was used to shield against neutron radiation. Plexiglas was used for shielding and glovebox window material. (A)



"The heat detectors installed to give an alarm in such an eventuality had - with stupefying lack of foresight - been positioned outside and under the glovebox, so that they were insulated from the heat until the fire was blazing out of control. When the detectors did finally sound the alarm at 2.27 pm, the smoke was so thick that the arriving fire-fighters could barely find their way to the fire."

Heat sensors for the storage cabinet did not function as designed because a large amount of shielding had been added, which effectively disabled them.  (A) 



"The smoke, of course, included an impressive concentration of plutonium oxide; among the materials consumed in the blaze was some $20 million worth of plutonium. At $10,000/Kg this works out at about 2000Kg - two tons of a material of which a microgram is likely to be toxic!"

The central estimate of the plutonium release to the atmosphere from the fire is ~20 mCi (~300 mg).... All measured releases amount to less than 3 mg of plutonium. (A)   

Total releases were estimated to range from 0.14 to 0.9 g of plutonium  (B)



"For the fire-fighters the immediate problem was the possibility of criticality, if they used water on the fire. Because of its effectiveness as a moderator water is strongly contra-indicated for such occasions. But the fire-fighters used up their carbon dioxide within ten minuets, and had nonetheless to resort to water. It took them four hours to bring the fire under control, and some trouble spots burned throughout the night."

At 2:27 p.m. in the afternoon of 11 May 1969 (Mother’s Day), an alarm from Buildings 776-777 was received at the Rocky Flats fire station....Using experience gained fighting the 1957 fire, the captain directed that water be used to fight the fire....The fire was considered to be extinguished by 8 p.m., and a fire watch was established at that time. Several small fires recurred during the night and the following morning.  (A)



"When eventually, some days later, investigators with breathing apparatus could survey the radioactive ruins, they assessed the damage at $45million-plus the $20 million-worth of plutonium."

Based on an October 7, 1957, fire report, the total book inventory of weapon-grade plutonium located in the area of the September 11, 1957, fire in room 180, building 71 (Chemical Reprocessing and Fabrication building) was 42.3 kilograms. There had been 14.3 kilograms in material transferred out but not yet recorded in the accountability system and in material whose exact amount and location was not known. Therefore, the total book inventory in room 180 at the time of the fire was, as accurately as possible, 28.0 kilograms. A study of inventory differences dated January 6, 1964, looked at the inventory in building 71 at the time of the fire and the amount removed, recovered, and in measured discards and concluded that the amount of inventory difference represented a decrease in "book inventory" of 6.0 kilograms as a result of the fire.  (C)  

The total "book inventory" of the weapon-grade plutonium involved in the May 11, 1969, fire in buildings 776 and 777 (Plutonium Fabrication and Assembly buildings) was 3557 kilograms. The measured amount, "physical inventory," of plutonium recovered from material removed from buildings 776 and 777 after the fire was 3651 kilograms. The measured amount of plutonium in the debris generated as a result of the fire and sent to waste was 10 kilograms. Thus, an inventory difference of 104 kilograms MORE material was removed from the fire than the book inventory indicated.  (C) note Plutonium inventory in the buildings involved in the fires at the Rocky Flats Plant was in different forms, including metals, compounds, holdup, and scrap. After the fire, plutonium was measured by "physical inventory." Most was recovered, including that in holdup; this explains how it was possible to recover more plutonium than was in the "book inventory." "Holdup" is material that has adhered to glove

boxes, ducts, etc., over the years. While the majority of holdup in the complex is booked based upon measurements or engineering estimates, the uncertainty of these values is high. Verification of these values or the establishment of more accurate values cannot be achieved until large- scale dismantlement or recovery.  (C)



Sources



A:  http://www.racteam.com/Experience/Publications/RF_1969_Fire_Source_Term.htm



B:  http://www.racteam.com/Experience/Publications/RF_1969_Fire_Risk.htm



C:  http://www.osti.gov/html/osti/opennet/document/press/pc24.html



ACCIDENT CASE STUDIES



On May 11, 1969, Rocky Flats Plant experienced the worst accident in plant history, a major fire in the 776-777 building, initially caused by pyrophoric plutonium scrap. One of the costliest industrial fires of all time damages were estimated at between $26 to $50 million dollars this accident was intensified and confounded by a number of operational errors. 

The fire at 2:27 p.m. Sunday was reportedly caused by spontaneous ignition of a 1.5-kg briquette of plutonium alloy scrap contained in a metal can. This scrap was believed to have been oily and coated with residual CCl{sub 4} (carbon tetrachloride). Once ignited, the fire spread through several hundred interconnected gloveboxes in the two connected buildings. 

The fire started in the west end of the north line, progressed eastward, crossed over to the south line through the interconnecting boxes, and spread through the south line. The fire spread through the machining boxes at the east end of 776 and into the inspection boxes in 777. Damage was extensive. Both Benelex, a combustible neutron shielding material added to the gloveboxes, and the combustible Plexiglas glove box windows contributed to rapid spread of the fire. 

The main fire lasted about 4 hours, with minor flareups occurring through the next night. After futile attempts to control the fire with conventional procedures, the firemen finally resorted to the unorthodox procedure of applying water to bring the fire under control. This was the first time in history that water had been used to fight a plutonium fire. Despite attendant criticality dangers, the use of water was successful in controlling the fire. 

The interiors of the two extremely large, high-bay buildings were grossly contaminated. An extensive, long-term cleanup effort was necessary for decontamination. Limited production was restarted about 6 months later in a temporary production line constructed in an adjacent building. 

As damaging as the fire was, the water use prevented breaching of the outer walls and ceiling of 776 and 777, thus preventing a major release of plutonium to the environment. The small amount of plutonium released almost entirely contained on plantsite was about 0.0002 curies. Slightly contaminated external areas were subsequently cleaned up. 

Fortunately, the fire caused no direct deaths. However, one fireman received significant plutonium lung burdens, and other firemen and personnel incurred smaller radiation inhalations and exposures while fighting the fire and later cleaning up heavily contaminated areas. 

Immediately prior to the fire, personnel levels were significantly cut with no real decrease in work load or production demands. Strict attention to plutonium chip handling no longer seemed to have been a top priority. 



The many lessons learned from this 1969 fire include the following: 

-Plutonium pyrophoricity is unpredictable as to when it may occur. 

-Combustible materials such as Benelex and Plexiglas must be kept to a minimum in process buildings. 

-Uncleaned and uncanned briquettes cannot be left unprotected and unattended on off- shifts. 

-Buildings 776-777 were essentially one large room with interconnected glovebox trains with basically no fire breaks or fire walls. This setup allowed for rapid, large-area spread of fire and radioactive contamination. 



These lessons learned from the 1969 fire have led to a number of current-day, continuing safety improvements including the following equipment modifications and procedural revisions: 

-A central, computerized alarm system has been installed. 

-A sprinkler/water system has been put in place. 

-Gloveboxes with inert atmospheres, heat detectors, and minimal Benelex and Plexiglas shielding are used. 

-Water-filled double walls have been constructed. 

-Firewater dams on doors are in place. 

-Removal of flammable material from gloveboxes is done regularly. 

-Briquettes are stored in metal containers with tight lids. 

-Containers are placed on metal racks with heat detectors. 

-Canning of briquettes is done in an inert atmosphere or vacuum for unattended (overnight or longer) storage.  

 http://tis.eh.doe.gov/techstds/standard/hdbk1081/hbk1081f.html#ZZ39



I love learning new things, I had been unaware of this and the preceding 1957 fire event, thanks for the inquiry.

Rick Urban

Yuma, AZ



All comments are mine alone, and represent no one but me.



Richard Urban

Yuma, AZ