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Nuclear Safety

Daya Bay maintains a world class safety record since its operation in 1994. It ranks at high level in the World Association of Nuclear Operators (WANO) performance indices. The WANO, covers over 400 commercial nuclear power reactors.


Daya Bay is equipped with two pressurised water reactors with proven records. They have three leak-tight barriers to ensure against radioactive releases:


Fuel cladding



The cladding encloses the radioactive material produced during nuclear fission and prevents it from escaping.


Reactor pressure vessel


Its 200mm-thick steel wall keeps cooling water containing a minute amount of radioactive material within the primary coolant circuit.



Containment building



A 900mm-thick pre-stressed concrete structure with a 6mm-thick steel interior lining houses the reactor pressure vessel. The containment building can withstand the impact of a large commercial aircraft.

Daya Bay has established contingency plan to cater for different levels of emergency, with appropriate level of response.  Emergency response organisation and communication mechanism are in place to facilitate the emergency response and communication  in the unlikely event of a nuclear accident. Besides, Daya Bay regularly provides training and holds emergency exercises within the site and jointly with Guangdong authorities:


  • Regular emergency exercises are conducted by individual work teams on regular basis.
  • Comprehensive exercises at the power station operator (2-3 times per year).


Emergency exercises for the mainland government departments in collaboration with the operator  (once every 5 years as a minimum).

  • Daya Bay provides a RMB300 million third party compensation according to regulatory requirement for any single nuclear accident.

  • The PRC Government will provide a maximum financial compensation of RMB 800 million for claims exceeding the upper limit responsible by the operator. 

  • Any compensation beyond the aforesaid limits will be further assessed and decided by the State Council of the PRC Government. Such arrangement is in line with the principles of international agreements.

After the Fukushima accident, the Chinese government conducted a nation-wide comprehensive safety review on all operating nuclear power stations and those under construction. Safety Review confirmed that Daya Bay meets national safety standard and the latest world practices. Improvements were requested to further enhance safety to match world upgrades.


All works were completed by the end of 2013 meeting following requirements:



  • Plant improvements against earthquake and flooding 
  • Refinement of safety analysis 
  • Emergency preparedness and co-ordination 
  • Public communication and disclosure

  •  Daya Bay conducts ongoing safety assessment at both the construction stage as well as during operation. Assessment reports are submitted to the National Nuclear Safety Administration for review.
  •  Daya Bay participates in the annual benchmarking exercise organised by EDF (Electricite de France). The exercise benchmarks 9 key operational areas (including safe operation performance) among a total of 65 PWR (i.e. Pressurised Water Reactor) units from France, China, United Kingdom and South Africa.
  • Following the practices of WANO,  Daya Bay actively participates in the WANO voluntary peer review regularly to benchmark and compare its performance against the international nuclear community; to identify areas of improvement; and learn the best practices from WANO members.

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Radiation and Daily Life

Daya Bay has a comprehensive environmental monitoring programme to protect the health of its staff and the general public.


  • Daya Bay has a long-term commitment to environmental management. It has held the ISO 14001 accreditation since 1999 and is the first nuclear power station and the first electric utility in the Mainland to attain the accreditation. 
  • Over the years, regular monitoring has indicated that the effect of radioactive releases on the environment is low if not negligible. ·
  • Strict operation control at Daya Bay has kept its resulting radiation dosage to the nearby public to about a thousandth of the regulation limits of less than 0.25 millisieverts. (HK typical annual radiation dosage of about 3 millisieverts) 

    The Hong Kong Observatory continuously monitors the Hong Kong ambient gamma radiation level throughout 12 field stations. In case of any significant increases in the level, a quick assessment with additional mobile measurements would be reported to emergency response centre.

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Power Station Operation

The spent fuel assemblies can be delivered for backend management of fuel cycle after 8 years storage in spent fuel pool. The backend service provider is required to reprocess the spent fuel in accordance with national policy similar to certain European countries and Japan. 

In the highly unlikely case of power interruption from Daya Bay, CLP can immediately bring in backup capacity and customers would not be affected. The backup arrangements include:


  • making use of CLP's reserve capacity; 
  • drawing on power supply from the pumped storage power station at Conghua in Guangdong province; 
  • use of backup supply from the Penny's Bay power station; 
  • calling on emergency supply from the HK Electric ; and 
  • making use of margin available in the frequency of the transmission system

In September 2009, the power supply contract has been extended for an additional term of 20 years up to 2034. In order to secure additional clean and cost-competitive energy for Hong Kong, Daya Bay has increased its electricity supply to Hong Kong from 70% to around 80% of its output for late-2014 to 2023. Hong Kong can enjoy not only the continued supply from a reliable and secure source, but also clean power which gives no emissions.

Background Information

The use of a three leak-tight barriers design is a common international practice for modern nuclear power stations.


  • In the Pressurised Water Reactor, the metallic cladding protecting fuel assemblies are installed inside a 200-millimetre thick steel casing to form the reactor core. 
  • The reactor cooling water takes heat out from the fuel assemblies and circulates in the completely sealed metallic pipes. 
  • All are isolated from the external environment by a 900 centimetre thick reinforced concrete containment, thus preventing any impact to the public.


For the impact of imperfect fuel rod sealing:


  • Any presence of radioactive iodine and noble gases may be measured in the reactor cooling water which is completely confined in pipes and containment. 
  • These gases will be filtrated in a dedicated system and will not lead any change in the radioactivity measured inside and outside the concrete containment building. 
  • The 5 on-site radiation monitoring stations within 1 km from the nuclear power station continuously monitor the nearby environment to ensure no abnormal level of radiation at Daya Bay.

For those non-emergency LOEs, The Daya Bay Nuclear Power Operations and Management Company (DNMC) and HKNIC will inform the public through their websites within 2 working days or 72 hours after the event is identified and confirmed by DNMC. Information released will include an event summary, a provisional classification and a preliminary appraisal on its impact to the environment and public safety. For those events requiring an emergency response, actions will be taken by the Guangdong and HKSAR governments according to an established emergency response mechanism. Please refer to the following organization chart for the information flow. Relevant information is also available on the HKSAR Government website at http://www.dbcp.gov.hk/eng/info/index.html

Organization chart for information flow

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Nuclear Basic

Tritium is a by-product generated in the nuclear power production process and the release of tritium is a normal operating procedure for nuclear power stations adopting the Pressurized Water Reactor technology.


Handling of Tritium Discharges


There is a purification system for the nuclear power reactor in which the radionuclides carried in the reactor cooling water are extracted by filtration or electrolytic processes to control its level of radioactivity. Residuals of the extraction process, including tritium found in the water bearing the radionuclides, are collected and stored until their radioactivity has decreased to an acceptable level and are subsequently released in a controlled process either in gaseous or liquid form to the environment.


The impact of Radiological Releases on the Environment


Tritium has a weak radioactivity and it does not accumulate in human tissue or organs and is excreted normally after being ingested into the human body. Its overall health impact compared to other radionuclides is therefore low. As tritium has a far lower health impact than other radionuclides, typically higher regulatory limits for liquid radiological releases are prescribed for tritium than other radionuclides at the nuclear power station site. These limits are in line with those being adopted for the nuclear power stations in France. According to relevant national regulations, the annual radiation dosage to people in the vicinity of a nuclear power station site should not exceed 0.25 millisieverts (mSv) per person per annum (about one tenth of typical background radiation dosage received by a Hong Kong resident in a year).


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The two Nuclear Power Stations are of completely different design, in terms of the reactor type, the moderator, the time needed for the control rods to stop the chain reaction during an emergency shutdown and the structure of the containment building.


  Chernobyl Daya Bay
Reactor Type  Russian water-cooled graphite-moderated boiling water reactor  Pressurised water reactor
Moderator Graphite: Inflammable Water: non-flammable
Time for control rods to completely stop the chain reaction during emergency shutdown 15 seconds Less than 2 seconds
Containment building to stop release of radioactivity None 90cm thick pre-stressed concrete lined with 6mm steel

In conclusion, given the differences in design, an accident similar to that at the Chernobyl nuclear power station in 1986 could not happen at Daya Bay.

Daya Bay has a design life of 40 years and it is extendable depending on reactor operation and maintenance conditions.


The nuclear station will be withdrawn from operation and decommissioned at the end of its life. Decommissioning will involve: removing the nuclear fuel from the reactor for storage and subsequent reprocessing, dismantling the conventional island and other conventional facilities, decontaminating the radioactive areas which includes facilities in the containment building and the fuel building to an allowable level after which it would be dismantled and its radioactive components disposed of as intermediate level waste. Following dismantling of the reactor, the site would be returned for other use. The cost for station decommissioning is included as part of the operating cost of the power station.