Philip Steiner and Clint Miller
Pacific Gas and Electric
ABSTRACT
This paper will discuss the on site treatment of two mixed waste streams at Diablo Canyon Power Plant. Twenty five drums of freon dry cleaner still bottoms were treated by distillation. This resulted in seven drums of non-radioactive freon which were sold for reuse and eighteen drums of radioactive still bottoms. The still bottom drums were sent off site for incineration. Due to the reduced content of freon in the still bottoms the cost of the incineration service was reduced. On site treatment of this material enabled freon to be recycled, decreased the volume of mixed waste to be shipped for off site treatment and reduced the cost of this treatment.
Micro encapsulation of radioactive resin contaminated with chromates using a polymer binder will also be discussed. Treatability studies indicated that cement encapsulated resin would not pass a TCLP test. Vinyl Ester Styrene micro encapsulation of the resin did pass the TCLP test, rendering the material non hazardous for heavy metals. This product has been approved for disposal at the Barnwell, SC burial site as a radioactive waste. This on-site treatment enabled the disposal of this resin while other treatment methods are still awaiting approval.
DISCUSSION
The disposition of two mixed waste streams from the Diablo Canyon Power Plant was aided by on site treatment. Legacy wastes from on site laundry dry cleaning operation are a major source of commercial mixed waste. Removal of chromate corrosion inhibitor from the component cooling water system at Diablo Canyon also resulted in the generation of mixed waste.
Dry Cleaner Still Bottoms
At Diablo Canyon dry cleaners were used to launder protective clothing for many years. The use of launderable garments greatly reduced the generation of solid radwaste. Prior to the regulatory creation of the mixed waste definition, waste still bottoms and filters from dry cleaners were disposed of as low level radwaste. Such wastes generated since 1989 were by definition mixed waste.
Dry cleaning operations ceased at Diablo Canyon in 1992. The dry cleaners were drained, removed from the laundry facility, decontaminated by off site services and any residuals disposed of as radwaste. The operation of the dry cleaners to support plant operation after the creation of the mixed waste definition resulted in the generation of 29 drums of still bottoms. Four of thesedrums had been adsorbed as was the past practice for disposal as radwaste. These drums were rendered a non incinerable and solid mixed waste. The remaining drums were stored as liquids in the hope that an incinerator might some day be licensed to treat this material.
Analysis of this waste stream was conducted to determine the chemical hazard of the waste and assist in waste profiling for future treatment. This analysis indicated that a high content of the dry cleaner solvent Freon-113 was in the still bottoms. About a third of the liquid still bottom waste volume in storage was Freon-113.
Diversified Scientific Services, Inc (DSSI) of Kingston, Tn had obtained a license to treat certain liquid mixed waste by incineration with energy recovery in 1989. In 1991, this license was expanded to cover the treatment of freon and other listed solvents. A few utilities shipped their still bottom waste to DSSI directly in 1991 for destruction. In November of 1991, DSSI was acquired by Chemical Waste Management. A series of physical improvements to the facility, completion of an EPA compliance burn and reduction of waste inventory prevented DSSI from receiving any additional waste from 1992 through much of 1994.
During this waiting period, Diablo Canyon considered the possibility of treating the still bottoms on site using a standard distillation unit. The cost of mixed waste treatment at DSSI increased dramatically as the content of listed solvents increased. By removing the freon solvent from the waste, the unit cost as well as the volume of waste could be reduced. In addition, the recovered freon could be reused for beneficial purposes.
In March of 1994, Diablo Canyon submitted a revision to our existing RCRA Part B permit. This revision included the use of several mixed waste treatment techniques and some changes to the mixed waste storage locations. In September of 1994, we informed the State of California of our intent to conduct a treatability study to distill the still bottom waste and recover the freon solvent.
This test was conducted on a single drum of waste from December 1994 through January 1995. The distillation unit used could hold about 20 gallons of liquid. The unit was self contained with the exception of a poly bottle to collect the distillate and a drum of water to provide cooling. Waste was processed in a batch mode. About one third of the drum was recovered as pure freon solvent. In March of 1995, we reported the results to the State of California. The treatability test proved that the freon could be recovered. Both gamma and tritium analysis of the distillate proved that the recovered freon was not radioactive.
The still bottom waste in storage at Diablo Canyon could not be treated until the revised Part B permit was issued. This did not occur until over a year later in June of 1996. Starting in July of 1996, the remaining twenty four drums of liquid still bottom waste in storage was treated by distillation on site using the same unit. Seven drums of freon ( 350 gallons) were recovered by this treatment. The freon was sold for $21/gallon to provide revenue of $7,428.
Eighteen drums (945 gallons) of residual still bottom waste remained after treatment. The freon content for 10 of these drums was less than 3% while the content for the other eight drums was less than 11%. These drums were shipped to DSSI in August of 1996. Confidentiality agreements do not permit us to reveal the treatment dollar savings obtained. The average unit costs for treatment were reduced by 46% by having reduced the freon content of the waste.
On site treatment of dry cleaner still bottoms resulted in the recovery of freon for profitable resale. The volume of still bottom waste was reduced by 27% and the unit treatment cost to destroy the waste was reduced by 46%. It took seven years to implement a disposal method for still bottoms. The actual time to perform the treatability study and process the waste on site was less than three months.
Based on this successful experience, on site distillation treatment of other mixed waste streams might be possible. Treatability studies for the distillation of solvent soaked rags and dry cleaner filters using a special still are under consideration.
Chromated Resin
The component cooling water system at Diablo Canyon originally used chromate as a corrosion inhibitor. Chromates were replaced with molybdates in 1991. The removal of chromate corrosion inhibitor from component cooling water was accomplished by using ion exchange resin. About 32 ft3 of anion resin was expended in the removal of chromate from the system. Unfortunately, this resin was found to be slightly contaminated with radioactive cobalt and chrome. A sample of the resin was sent off site for hazardous waste analysis. The resin failed the Toxicity Concentration Leaching Procedure (TCLP) for chromium.
In 1991, we informed the State of California of our intent to conduct a treatability study to solidify the chromated resin in cement. A small sample of resin was solidified with cement under the SEG process control program and sent off site for a TCLP analysis. This test also failed. The TCLP protocol requires that any waste must pass through a screen prior to leach testing. The cement monolith was ground to enable passage through the screen. It is assumed that the grinding exposed the surface of enough resin beads for the material to fail the leach test.
Diablo Canyon had a contract in place with Diversified Technologies through SEG to solidify spent resin using polymer solidification. At that time Diversified offered two methods of polymer solidification using vinyl ester styrene. Both methods had been approved by the NRC as a means to stabilize radioactive spent resin. One method was the insitu process. This method required no mixing of the waste and binder which provided high waste loadings. This method could require chemical pretreatment of the resin, however, to ensure that the binder would properly solidify. The other method was the original DOW solidification process which requires high shear mixing. This method can only produce a waste loading of about 65% for resin but, does not require any chemical pretreatment of the resin.
In March of 1993, Diablo Canyon informed the State of California of our intent to perform a treatability study on the chromated resin using polymer solidification. In March of 1994 samples of the chromated resin were obtained and polymer solidifications were conducted. Test of the insitu process determined that chemical pretreatment was required. This was undesirable sincethe treatment resulted in putting the chromate back into a liquid solution. The mixing process was able to solidify the resin without any pretreatment. In order to pass the TCLP test, we wanted to avoid grinding the product and exposing the surface of resin beads. The mold used to cure the micro encapsulated waste produced tubular monoliths or "French fries". These strips can pass through the required TCLP screen size without any need for grinding. The polymer solidified resin was tested and passed TCLP in 1994. The solidification of this resin by polymer rendered the waste non-hazardous for chromium.
In March of 1995, we reported the results of the treatability study to the State of California. The Barnwell disposal site was closed to Diablo Canyon from mid 1994 to mid 1995. When news that Barnwell would reopen came, we submitted a request for approval to dispose of this resin, solidified in polymer, as a radioactive waste to the State of South Carolina in June of 1995. The State of South Carolina approved this request in July of 1995. No full scale solidification of the spent resin could be conducted at Diablo Canyon until our revised Part B permit was issued. This did not occur until one year later in June of 1996.
In September of 1996, work began to solidify the chromated resin in storage at Diablo Canyon. Diversified Technologies was contracted to solidify the resin using the DOW process. High shear mixing was accomplished using a 5 gallon pail mixer. Larger mixers are available but, mobilization and rental cost of such units was not justified for the small waste volume.
Resin and binder were added to the 5 gallon pail and thoroughly mixed. The mixture was manually poured into a drum and the exotherm of the billet was monitored with a thermocouple. This process was repeated until all of the resin was solidified. Seven drums of solidified resin were produced in the end containing 87 billets of pre mixed waste. The individual layers in each drum do bond together due to the exotherm of the binder. It required 100 hours for a vendor technician and a utility helper to solidify the resin using this process.
The cost to solidify this resin including binder, equipment rental, transportation and vendor labor was $17,900. These drums were shipped to Barnwell, SC on October 17, 1996 using a dromedary van. The waste was disposed of in October at Barnwell prior to the price increases. The shipment of these seven drums cost $4,630 and the disposal cost was $17,647. It required five years to implement a disposal method for this waste. The actual time to perform a treatability study and process the waste was less than one month. The total cost to dispose of this waste was $1,256/ft3.
Based on this successful experience, a polymer encapsulation treatability study is underway on grit from a tool cleaner. The grit is contaminated with lead. The high shear mixing process must be used on this waste due to its small granular size.
CONCLUSION
On site treatment at Diablo Canyon assisted in the disposition of two mixed waste streams. The treatment processes used were well known and there was no waiting period for development of any new technology. The time required to test the treatment methods and perform the actual waste treatment was less than three months for each waste stream. The actual time period required to disposition the wastes took from five to seven years. Mixed waste disposal remains a regulatory problem not a technical problem. Years of effort must be expended to submit, wait and obtain the proper permits.
The long lead time to obtain permits and approvals stifles innovation and more efficient processes. Diversified Technologies now offers an advanced polymer solidification process for bead resin which does not require mixing or chemical pre-treatment and reduces the final waste volume by nearly 40%. Unfortunately, this more efficient process could not be used at Diablo Canyon because submittals and approvals were already in the mill for the DOW process.
Based on the successful use of encapsulation and distillation at Diablo Canyon, on site treatment of other mixed waste streams is under consideration.