China Guangdong Nuclear Power Company (CGNPC) decided to improve the design-basis evaporative waste processing system of the CPR-1000 PWR reactor planned for Yangjiang NPP in Guangdong Province. EnergySolutions subsequently won the international tender to provide liquid waste processing systems that could achieve project discharges of 37Bq/L.

The bulk of the constituents in liquid radioactive waste (LRW) streams are dissolved minerals, organic compounds and particulates. A large percentage of these are efficiently removed by utilizing standard filtration and ion exchange processes.

EnergySolutions’ system starts with the Advanced Liquid Processing System, a portable system operating at 17 NPPs in the USA that is capable of removing ionic impurities and suspended particulate from LRW through ion exchange, chemical pretreatment and deep bed filtration.

Small particulate and colloids too fine to be removed by EQUA*FLEX vessels are removed by utilizing EnergySolutions’ Advanced Injection Method chemical injection system. This is accomplished by the injection of polymer into the feed stream which agglomerates the colloidal particles making them easily removed by down-stream filtration mechanisms.

In addition, the system separates the higher- and lower-conductivity feed streams and directs them to individual treatment trains. This is important because experience in operating US PWRs has shown that uniformity of chemical speciation in the feed is critical in ensuring optimal ion exchange kinetics and capacities. By separating high- and low-conductivity streams and treating them using separate trains, high performance is assured.

Second, the system applies proprietary ion-selective media for removal of targeted species, including Sb-125, Ag-110 and Ni-63.

The majority of the radionuclides that make up the 500GBq of radioactivity in the feed stream are removed by the AIM system. Subsequently the granular activated charcoal beds are discharged to high integrity containers (HICs) for disposal. The AIM pretreatment allows the ion exchange media to operate free from challenging colloidal material. Without this AIM pretreatment, ion exchange systems often suffer breakthrough of radionuclides long before operating capacity is realized, because of the passage of colloidal species. Co-58 and Ag-110 are two species that typically present as colloids and are seen in effluents if not removed by AIM.

Final polishing by Thermex reverse osmosis was proposed for Yangjiang to ensure against any failure of the upstream systems, and also to establish the capability to remove organic contaminants, or indeed any other species likely to present an environmental impact in the future.

Polishing of pure streams by reverse osmosis is especially effective for polishing pure water post-ion exchange by molecular rejection of tramp radionuclides. Because the water is purified first by ALPS, salt rejection from the membrane is minimal. The rejected salt in fact dilutes the process feeds to ALPS when it is returned to the treatment feed system. Thermex systems (there are a total of five in operation) typically process approximately 190,000m3 of effluent annually. As a final polishing step, the Thermex system ensures the removal of species such as Sb-125, Ag-110m and Co-58.

Spent ion exchange media from the liquid waste system will employ the EnergySolutions self engaging dewatering system, which is also used in the USA. In the system, a vacuum pump removes water through EnergySolutions’ proprietary liner filtering system. It is the basis of regulatory compliance for disposal of the waste form in a cask.

In China, waste from its planned civil nuclear power programme is being considered now. EnergySolutions’ involvement is coming at the very start of the new-build process. China’s forward-looking approach can and will be replicated elsewhere.

Author Info:

Tim Milner is technology development director of nuclear waste management services company EnergySolutions, which has operations North America, Europe and Asia.

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