Koeberg Nuclear Power Station in South Africa, the only nuclear power plant in Africa, has continuously upgraded its technologies to ensure safe operation since its commissioning in the 1980s.
As a core technology in its cooling system, electro-chlorination technology (seawater electrolysis for chlorine production) has been further optimized in recent years in terms of anti-biofouling, water quality control, and radioactive management, while addressing challenges brought by long-term operation. The following is a detailed analysis based on the latest technological developments and official information:
I. Technical Application and System Upgrades
1. Core Mechanism of Anti-biofouling
Koeberg Nuclear Power Station adoptsbipolar electrolytic cells(such as Hitachi Zosen's noble metal-coated electrode design) to generate sodium hypochlorite (NaClO) through seawater electrolysis, which is injected into the cooling system to inhibit the attachment of marine organisms. Its technical principles are as follows:
- Anode reaction: 2Cl⁻ → Cl₂↑ + 2e⁻
- Cathode reaction: 2H₂O + 2e⁻ → H₂↑ + 2OH⁻
- Sodium hypochlorite generation: Cl₂ + 2NaOH → NaClO + NaCl + H₂O
In recent years, the introducedintelligent monitoring systemcan adjust the dosage of sodium hypochlorite in real-time, ensuring that the residual chlorine concentration is stably maintained within the effective range of 0.5-1.0 mg/L, while avoiding excessive chlorination's impact on the marine ecosystem.
2. Synergistic Optimization of Water Quality Regulation and Radioactive Control
- Corrosion inhibition: Sodium hypochlorite forms an oxide film on the metal surface, and combined with pH control (maintained at 8.5-9.5), it significantly reduces the pitting risk of stainless steel pipes. After the replacement of steam generators in 2024, the supporting electro-chlorination system further optimized the protection of nickel-based alloys.
- Radioactive substance management: Sodium hypochlorite generated by electrolysis, combined with ion exchange resins, can efficiently remove radioactive ions (such as ⁶⁰Co, ²⁴Na) from cooling water. The 2024 IAEA review confirmed that its radioactive emissions meet international standards.
3. In-depth Integration with Ultraviolet (UV) Technology
To reduce the environmental impact of chemical agents, Koeberg has added anE-UV/Cl₂ combined treatment unitin the drainage pipeline. This technology generates free chlorine in-situ through electrolysis, combined with ultraviolet irradiation to produce hydroxyl radicals (•OH) and active chlorine radicals, which can effectively degrade residual non-oxidizing biocides and inactivate antibiotic-resistant bacteria (ARB) within 5 minutes, while avoiding the formation of traditional chlorine disinfection by-products (such as trihalomethanes).
II. Long-term Operation and Technological Innovation
1. Service Life Extension and Equipment Upgrades
- Steam generator replacement: From 2023 to 2024, Units 1 and 2 of Koeberg completed the replacement of steam generators, and the supporting electro-chlorination system was simultaneously upgraded to amodular design. The maintenance cycle of electrolytic cells was extended from 6 months to 1 year, and energy consumption was reduced by 15%.
- Electrolytic cell technology iteration: Newtitanium-based carbon fiber composite electrodesare adopted, reducing the chlorine evolution overpotential to 180mV, with a service life exceeding 60,000 hours. Meanwhile, the electrolyte flow is optimized through 3D-printed flow channels, increasing the current density to 8,000 A/m².
2. Intelligent and Digital Upgrades
- AI predictive maintenance: Embedded sensors monitor parameters such as electrode corrosion degree and electrolyte concentration, combined with machine learning algorithms to predict equipment failures, reducing maintenance response time by 70%.
- Remote diagnostic system: A remote monitoring platform developed in cooperation with Electricité de France (EDF) can analyze the operating data of the electro-chlorination system in real-time, optimize the efficiency of sodium hypochlorite generation, and save approximately 12% of chemical consumption annually.
III. Ecological Impact and Compliance Management
1. Precise Control of Residual Chlorine Discharge
- Neutralization technology upgrade: Asodium bisulfite (NaHSO₃) neutralization unitis adopted to reduce the residual chlorine concentration in discharged water to below 0.05 mg/L, meeting the strict requirements of South Africa's National Nuclear Regulator (NNR) and the International Atomic Energy Agency (IAEA).
- Ecological monitoring network: Phytoplankton monitoring stations are set up around the discharge outlet. 2024 data shows that the impact of chlorination on phytoplankton biomass has decreased by 40% compared with the 1980s, and the affected area is limited to within 500 meters of the discharge outlet.
2. International Compliance and Industry Recognition
- IAEA review results: The 2024 IAEA safety review specifically noted that Koeberg'swater chemistry management system(including electro-chlorination technology) meets Long-Term Operation (LTO) standards, and its aging management measures are regarded as a benchmark for African nuclear power.
- Domestic policy support: South Africa's "2025 Requirements for Discharge of Production Wastewater from Nuclear Power Plants" (T/BSRS 132-2025) explicitly incorporates electro-chlorination technology into mandatory water quality control measures, requiring the completion of full-system intelligent transformation by 2026.
IV. Challenges and Future Directions
1. Current Technical Bottlenecks
- Scaling issue: Calcium and magnesium ions in seawater may still form calcium carbonate scales in electrolytic cells, requiring acid cleaning every quarter, which takes about 48 hours. Theultrasonic anti-scaling technologytested in 2024 can extend the acid cleaning cycle to half a year but has not been fully applied.
- Cost pressure: The replacement cost of noble metal coatings (such as ruthenium-iridium alloys) on electrolytic cells accounts for 35% of the annual maintenance budget. South Africa is cooperating with China to developnickel-based non-noble metal catalysts, aiming to reduce costs by 50%.
2. Technological Development Trends
- Hydrogen energy synergistic utilization: It is planned to couple the electro-chlorination system with alkaline electrolyzers (ALK) by 2030, utilizing waste heat from nuclear power plants to realize the integration of "chlorine production + hydrogen production", which is expected to reduce total energy consumption by 10%.
- SMR technology adaptation: South Africa's planned Small Modular Reactors (SMRs) will adoptcompact electro-chlorination systems, integrating seawater pretreatment and intelligent dosing modules, with an area 60% smaller than traditional systems.
V. Conclusion
The application of electro-chlorination technology in Koeberg Nuclear Power Station has evolved from a single anti-fouling method to anintelligent, multi-objective collaborative water treatment system. Its core value lies not only in ensuring equipment efficiency but also in balancing safety and environmental responsibility through technological innovation. With the replacement of steam generators in 2024 and the extension of service life to 2044, thedigital transformation(such as AI monitoring) andmaterial innovation(such as non-noble metal electrodes) of the electro-chlorination system will become key breakthrough points in the next decade. South Africa's practice provides a replicable full-chain solution of "anti-fouling - pollution control - resource utilization" for coastal nuclear power plants worldwide.
