Metal Dissolution - h3010v20174

DOE-HDBK-3010-94

Appendix B; Plutonium Recovery Facility

concentration to the range of 5 - 7 g/l. A schematic of this system is presented as

Figure B.7.

2.2.2.2.3

M etal D issolu tion

Recycle metal dissolved in the H-Plant is received in a ready-to-process form. This

metal contains an impurity whose dissolution is not desired. The metal dissolution

process is designed to dissolve all of the plutonium metal while leaving behind an

intact residue that is removed for shipment elsewhere. A schematic of this process is

presented as Figure B.8. The metal is placed in a small 7-liter spray chamber and the

lid on the system is locked. Then, 14% sulfamic acid is added to the 40-liter slab

vessel below the spray chamber. Plutonium metal will dissolve in sulfamic acid in the

temperature range of approximately 70 F to 195 F. However, a plutonium hydride

sludge will form at temperatures below about 120 F, and accelerated dissolution of

the impurity will occur at temperatures above 160 F. These two points effectively

define the desired operating range. The steam flow control valve on the heat

exchanger inlet line is controlled by a temperature sensor on the slab tank. Based on

both the flowrate of the dissolving solution and the steam pressure, the valve is fully

open at a temperature of 70 F and completely shut at a temperature of 125 F.

The dissolution reaction is exothermic and can accelerate above the desired upper

temperature limit if temperature is not adequately controlled. It also produces

hydrogen gas as a byproduct, and the production rate will increase with increasing

temperature. This is more of a problem at the start of the reaction when sulfamic acid

concentration is at its peak. In any case, the solution temperature must be controlled,

and a potentially dangerous byproduct must be handled safely.

The basic operation of the system is a simple acid spray loop, where acid is

transferred from the slab vessel by a small centrifugal pump and passes through a

steam heat exchanger and an in-line cartridge filter before it is sprayed onto the metal.

This liquid drains out of the spray chamber through an always open overflow line into

the slab vessel. The 7-liter spray chamber has an always open vent line to the vessel

vent system and a fail high temperature detector. A hydrogen detector samples the

offgas to the vessel vent system, and a flame arrester is provided in the vent line

before it exits the glovebox. The temperature detector provides signals to a high-

temperature alarm if the temperature of the spray chamber outlet overflow exceeds

148 F and an interlock turns off the centrifugal pump if temperature exceeds 155 F.

If hydrogen offgas concentration exceeds 2.5% (lower flammability

limit in air is 4.0%), the pump is also automatically turned off. Without additional

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