United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 90-70: Pump Explosions Involving Ammonium Nitrate

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
              OFFICE OF NUCLEAR MATERIAL SAFETY AND SAFEGUARDS
                           WASHINGTON, D.C.  20555

                              November 6, 1990


Information Notice No. 90-70:  PUMP EXPLOSIONS INVOLVING AMMONIUM 
                                   NITRATE 


Addressees: 

All uranium fuel fabrication and conversion facilities. 

Purpose: 

This Information Notice is being issued to inform uranium fuel fabrication 
and conversion facilities of an explosion potential associated with the 
pumping of solutions containing ammonium nitrate.  There also could be this 
risk in the pumping of other solutions in which the chemical characteristics 
of the solute are similar to those of ammonium nitrate (described below).  
It is suggested that recipients review the information here and consider 
actions, if appropriate, to preclude possible pump explosion potential.  
However, suggestions contained in this Information Notice do not constitute 
U.S. Nuclear Regulatory Commission (NRC) requirements; therefore, no 
specific action or written response is required. 

Description of Circumstances: 

On December 7, 1988, at a fuel fabrication facility, an incident occurred in 
which a pump servicing a uranyl nitrate system exploded; on April 29, 1990, 
at another fuel fabrication facility, a pump associated with an ammonium 
diurinate (ADU) system exploded.  The following was common to both 
incidents: 

     1.   The pumps were left on for a lengthy period of time (e.g., 40 
          hours), without the solutions containing ammonium nitrate being 
          able to leave the pumps.  Thus, these "dead-headed" pumps, over a 
          period of time, boiled off the majority of the water in the 
          solution thereby concen-trating the amount of ammonium nitrate, 
          and a rapid thermal decomposition resulted.  Investigations of 
          these incidents have determined that dryness is not a necessary 
          condition for ammonium nitrate to explode.  A concentrated 
          solution, together with activation energy provided by the 
          overheated pump, may be sufficient.  

     2.   The explosive substance was determined to be ammonium nitrate.

The "dead-heading" of the pumps was caused in one case by a closed valve, 
and in the other case, by the clogging of a flow-restricting orifice with 
accumulated solids.  The explosions have been formally characterized as a 
"rapid thermal decomposition," i.e., no ignition or detonation occurred.  
The pump housings were blown apart with sufficient force to break the bolts 
that held them 


9010310117 
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                                                            IN 90-70 
                                                            November 6, 1990
                                                            Page 2 of 3 


together.  In one case, the suction half of the pump became a projectile, 
struck a steel pipe, bent it 15 degrees, and then skidded for another 16 
feet before coming to rest.  In the other case, an individual who was in the 
affected area received a minor laceration requiring first aid.  An analysis 
of the individual's exposure determined that no significant exposure 
resulted. 

Discussion: 

The events described in this Information Notice emphasize the need for 
uranium processing facilities to identify potentially explosive compounds 
and mixtures, be aware of where they are located or where they can 
accumulate or form, and take preventive measures to preclude the conditions 
that could cause an explosion to occur. 

For the incidents just discussed, some of the corrective actions taken or 
considered consisted of the following: 

     o    Use of temperature sensor shut-off devices with pumps.

     o    Implementation of strong administrative control (i.e., independent 
          verification sign-off), regarding correct valve positions.

     o    Evaluation of other systems in the plant for similar problems, 
          i.e., presence of, or potential for, formation of ammonium 
          nitrate, together with activation energy sources.

     o    Use of "dead-man" switches in automatic or semi-automatic 
          operations, instead of normal manual switches, to prevent 
          personnel from overriding pump operations.

     o    Use of a water rinse between operations involving nitric acid and 
          ammonium hydroxide, to preclude the formation of ammonium nitrate.

     o    Evaluation of vent and scrubber systems, since various materials 
          pass through them.

     o    Interlocking pumps with tank-level indicators to shut pumps off at 
          a low level, in order to prevent a concentrating condition.

     o    Removal of unnecessary discharge valves to prevent "dead-heading."

     o    Implementation of a valve tagging system.

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                                                            IN 90-70 
                                                            November 6, 1990
                                                            Page 3 of 3 


No specific action or written response is required by this Information 
Notice.  If you have any questions, please contact the technical contacts 
listed below or the Regional Administrator of the appropriate regional 
office. 




                              Richard E. Cunningham, Director
                              Division of Industrial and 
                                Medical Nuclear Safety
                              Office of Nuclear Material Safety 
                                and Safeguards 

Technical Contacts:  Edward McAlpine, Region II
                     (404) 331-5547

                     George H. Bidinger, NMSS
                     (301) 492-0683

Attachments:
1.   List of Recently Issued
       NMSS Information Notices
2.   List of Recently Issued
       NRC Information Notices
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