Information Notice No. 90-70: Pump Explosions Involving Ammonium Nitrate
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
All uranium fuel fabrication and conversion facilities.
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
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
November 6, 1990
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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
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.
November 6, 1990
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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
Richard E. Cunningham, Director
Division of Industrial and
Medical Nuclear Safety
Office of Nuclear Material Safety
Technical Contacts: Edward McAlpine, Region II
George H. Bidinger, NMSS
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