High Volume Electrolytic Purification of Salt Water Contaminated Radioactive Waste Water Streams

The individual processes described in this article, while not currently used in the processing of radioactive waste water, are standard chemical and industrial processes in long use for other reasons. The designer of this process, as applied here, is Walter L. Johnson.
Fundamental process
Electrolysis of water , producing pure H2 (some Tritium) and O2/Cl2 , and leaving a highly concentrated radioactive mixture.
Fukushima
It is highly likely that never in history has it been necessary to process millions of gallons of seawater contaminated radioactive water. Traditional methods of water purification - filters, resin columns, and boiling - may not be effective or practical in this case due to the extreme nature of the situation and in particular the high salt content of the water. Another method is necessary that both purifies the water and handles the salt content without degrading the process itself. The method described here is not restricted in any serious or unmanageable way by the presence of salt. Electrolysis rate is affected by the NaCl in solution but the quality of the purification and volume reduction is not. The ultimate reduction factor is limited only by the solubility of the NaOH produced from the salt, the radiation levels resulting from the concentration of radioactive constituents, and the restrictions imposed to prevent any potential inadvertent criticality from Uranium and Plutonium contamination. It is likely that the limiting factor will vary depending on the water source and particular contamination and should be determined by testing the water source before commencing volume reduction along with monitoring during volume reduction.
Advantages in the Fukushima context over other methods -
1. Can handle any contaminant expected without degradation of the process.
2. No filters or resin columns required so nothing to clog up or require periodic replacement.
3. Much higher reduction factor for seawater (about 46.5) than boiling (about 10.86, based on the water being
boiled down to about chemical saturation, drained, and solidified), because the process converts NaCl to
the much more soluble NaOH .
4. At the end of the process, the liquid remaining is manageable without stopping the process for extended periods.
5. The gases produced are easily filtered.
6. The O2 and Cl2 produced can with proper precautions be vented to the atmosphere.
7. The H2 can be burned and reused in the reactor or vented to the atmosphere if Tritium levels are low enough.
8. Industrial equipment is available that would probably be relatively easily modifiable for this purpose or at least
provide a starting point.
9. Because of the nature of the process, individual electrolytic cells are probably small enough to reduce the risk of
inadvertent criticality.
Disadvantages -
1. Higher power is required than for other methods.
2. Non-standard process and would require testing and approval.
3. Perhaps could not be done in time to be useful in the case of Fukushima.
Theoretical maximum volume reduction factor
For pure seawater the factor is approximately 46.5 and is based on the water being pure seawater at 33000 ppm NaCl, the NaCl being converted to NaOH at the end of the process and the solubility of NaOH in water leaving rapidly increasing concentrations of whatever was in the water. Water is continuously added to the chamber until contaminant concentration (measured by conductivity) or radiation levels dictate that the remaining mixture be drained out of the chamber.
Monitoring
Temperature, conductivity, and explosive gas levels are continuously monitored in the chamber. Continuous Cl2 and explosive gas measurements are taken everywhere. Gamma and neutron radiation levels are monitored everywhere. Airborne contamination levels are monitored everywhere and especially downstream of all HEPA filters. HEPA filters are changed whenever dictated by radiation levels or downstream airborne radioactivity.
Equipment
Standard industrial electrolytic H2 production units could probably be relatively easily modified and used for this process, and are already designed to do most of the non radioactivity related things in this article. These units are designed specifically for sustained untended operations. Other portions of this process, such as the stabilization by concrete, radiation monitoring, and liquification of Cl2 are standard processes used in handling radioactive waste and Cl2. The only other unusual equipment is whatever might be used to burn H2 if necessary.
Heat
Significant heat is produced by this process, so some means of cooling the chamber and condensing the water from the H2 burning process may be required.
Radiation
When this process is used, extremely high and possibly lethal radiation levels could be produced close to the system. Shielding, chamber size, batch size, and management of personnel access should be used to minimize exposures and exposure rates. Controls should be engineered into the system such that personnel could operate the equipment and manage the process from a distance with minimal personnel involvement.
Airborne radioactivity
This process should be engineered to result in no additional releases of airborne activity. If such a release is detected, operations should be stopped and the cause investigated and fixed.
Explosive mixture control
Argon or Nitrogen could be used to inert the chamber prior to use and when not collecting the separated gases in order to avoid an explosive mixture. Continuous measurement of accumulated gases with purging as necessary along with design of the chamber to preclude gas accumulation will prevent dangerous H2 and O2 mixtures in the chamber. Any gases vented from the chamber are passed though HEPA filters.
Disposition of gases
A determination should be made of the amount of Tritium there is in the waste water to be processed using this method in order to determine what to do with the H2 produced from the rig. The O2/Cl2 can be vented to the atmosphere away from personnel and the rig as it will not be radioactive at all unless the Cl2 experienced a neutron flux in the reactor. Disposial options exist for Cl2, including disposal by pressurization, liquification, and storage or some other standard method. The volume of this material will be very small relative to the large amount of water processed and more easily shielded, handled, transported, and stored using standard methods. Disposal could be by burial locally at the site or at some other facility similar to the Idaho National Engineering Laboratory.
Inadvertent criticality
It is likely in the case of Fukushima that due to core damage and leakage from containment that there could be some Uranium or Plutonium present in the waste water, so precautions should be taken to prevent inadvertent criticality. Periodic sampling and isotopic analysis prior to processing of the waste water, continuous neutron surveys of the rig, inlet, and outlet piping, along with boron poisoning of the liquid in the chamber should suffice in this regard. Sampling and isotopic analysis of the concentrated mixture along with monitoring the concrete blocks would be appropriate as well to ensure that there is no risk of inadvertent criticality in the concrete blocks produced from this process. This process should be engineered such that based on concentrations of Uranium and Plutonium in the liquid to be processed, criteria be established to ensure batch size and Uranium/Plutonium concentrations do not provide for a critical mass under any conceivable geometries encountered normally or by an accident during the process.
Capacity
Power requirements are significant. Standard industrial H2 production equipment . 100,000 liters of water can make about 400,000 kg of concrete or about 174 cubic meters of concrete . That would be equivalent to a slab one meter tall, 10 meters wide and 17.4 meters long. So 100 million gallons of waste water could be reduced to a block one meter tall, 100 meters wide, and about 174 meters long - hardly unmanageable. Radiation levels may be more limiting in the case of Fukushima than theoretical reductions in gross volume. Automation should be used as much as possible so that radiation levels are less limiting.

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