Contribution of Ammonia and Defoamers to Lower Flammability Limit in SRS High Level Waste Page: 2 of 7

                                
The High Level Waste Tank Farms store and process high-level liquid wastes from a number of sources
including F- and H-Canyon, Receiving Basin for Offsite Fuels (RBOF), the 299-H Decontamination
Facility and the Defense Waste Processing Facility (DWPF). These wastes are made alkaline prior to
transfer to the Tank Farm and are subject to acceptance based on their composition. These wastes may
contain minor concentrations of organic and other potentially flammable compounds. The Authorization
Basis for the Tank Farms identifies several controls to prevent unwarranted, adverse chemical reactions.
However, current analysis of the accident scenarios does not evaluate the impact of the presence of organic
compounds. A Potential Inadequacy in the Safety Analysis (PISA) has been declared regarding the issue of
organic compounds in the waste.2 Processing vessels of concern include the pump tanks (PT), waste tanks,
(WT), and evaporators. Ammonia and defoamers were previously evaluated, and it was concluded that
defoamers were not a problem and that ammonia was sufficiently controlled by current means.3,4 However,
additional studies were recommended. This report documents further analysis of the flammability aspects of
ammonia and siloxane defoamers.
Discussion
Allowable Ammonia Concentration
M. E. Jamison, concluded the following about ammonia receipts to the Tank Farm.4
Historically, the F and H canyons have sent bulk waste transfers containing ammonia from
performing Process Vessel Vent (PVV) flushes and from reactor assembly dissolving. In 1976
the canyons changed their processing flowsheet to reduce the amount of ammonia generated by
destroying hydrazine and sulfamate with nitrite. This change resulted in a 94% reduction in the
ammonia sent to the tank farms. Recent PVV flushes sent to the tank farm have been safely
received by limiting the ammonia to 10% of the LFL under equilibrium conditions (i.e., 0.127
wt.% ammonia at 70 C).
The DWPF recycle water, during sludge only operations, sends trace concentrations of
ammonia to the tank farm. However, after coupled operations commence [should a
tetraphenylborate process be used] the ammonia concentration in the DWPF recycle will
increase. The DWPF WCP (Waste Compliance Plan) for couple operations will address the
10% CLFL (composite lower flammability limit) ammonia requirement prior to receipt.
3.2.1 Required Controls to Safely Receive Ammonia
To ensure a CLFL is not reached, influent transfers must be limited to <25% of CLFL under
liquid-vapor equilibrium. A more restrictive 10% LFL requirement will be implemented in the
Tank Farm Waste Acceptance Criteria (WAC) to reduce the industrial hygiene risk and to
allow other flammable constituents to be present while maintaining a CLFL below 25%.
The Tank Farm WAC5 has been revised to control ammonia in transfers to the Tank farm as
recommended.4
Control of the ammonia concentration so that it will only contribute 10% of CLFL in organic tanks and
<=5% of CLFL in non-organic tanks should assure that ammonia does not become an LFL concern. In a
caustic environment, ammonia will exist largely in the free ammonia form (as opposed to the ammonium
form) and will tend to vaporize and be flushed from waste tanks by the ventilation system. Therefore with
these controls in place, the maximum amount of ammonia that would be expected is right after a transfer
that is high in ammonia. Since there are controls on the initial concentration of ammonia (and ammonium)