HKNIC - FAQ on Daya Bay
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FAQ on Daya Bay
  1. How is nuclear safety being assured at Daya Bay?
  2. Will there be radiation effects caused by Daya Bay on the public and the environment?
  3. What are the contingency measures for Daya Bay in case of an accident?
  4. How does Daya Bay compare to Chernobyl?
  5. How does Daya Bay handle its spent fuel?
  6. What is planned for Daya Bay at the end of its life?
  7. What happens if there is an interruption of power supply from Daya Bay to Hong Kong?
  8. What is the arrangement for the supply of nuclear power to Hong Kong from Daya Bay beyond the current contract?
  9. Concerning the operational matter related to the imperfect fuel rod sealing at Unit 2 reported in May 2010, what is the impact on plant operation and the environment?
  10. Why is Tritium being produced in the nuclear power production process? Does the release of Tritium constitute any impact to the external environment and public health?
  11. In the event of a serious nuclear accident at Daya Bay Nuclear Power Station, is there any compensation for the public being affected?
  12. What is the notification mechanism of non-emergency Licensing Operation Events (LOEs) and emergency events at Daya Bay Nuclear Power Station?
  13. What is the progress of the nation-wide safety review on mainland nuclear power plants? What are the major areas covered in the review?
  14. What safety assessment and emergency preparedness have been carried out at the Daya Bay Nuclear Power Station?


1. How is nuclear safety being assured at Daya Bay?
  Daya Bay has provided electricity reliably to Hong Kong and Guangdong province while maintaining a world class safety record since its operation began in 1994. It ranks in the median or top quartile levels in the performance indices of the World Association of Nuclear Operators, representing an excellent record of plant reliability, performance and safety. Membership of the association covers the operators of all the world's some 400 commercial nuclear power reactors.
 
Daya Bay is equipped with two 984 MW pressurised water reactors, the most widely used type of reactor in the world with a proven record of safe operation. The reactors have three barriers to ensure against radioactive releases:
 
  • Fuel cladding -
    the uranium fuel is sealed in the metallic cladding of the fuel rods which make up the fuel assemblies
  • Reactor pressure vessel -
    its 20 centimetre thick steel wall and the primary circuit piping, sealing the cooling water for the reactor
  • Containment building -
    a 90 centimetre thick pre-stressed reinforced concrete wall with a 6 millimetre thick inner steel lining
The plant is operated by qualified operators, using well-established safety practices and procedures. Safety is ensured by continuous monitoring by China's national nuclear regulator, the National Nuclear Safety Administration, based on national regulations that are in line with international guidelines and practices.
2. Will there be radiation effects caused by Daya Bay on the public and the environment?
 
Daya Bay has a comprehensive environmental monitoring programme to protect the health of its staff and the general public. Regular checks over the years have indicated that there has been no excessive or undue release of radioactivity and the effect of radioactive releases on the environment is low if not negligible. Regulations in China require radioactivity releases to be strictly controlled so that the annual radiation dosages to people in the vicinity of a nuclear installation do not increased by more than 0.25 millisieverts. Strict operation control at Daya Bay has kept its resulting radiation dosage to the nearby public to about a thousandth of the limiting figure. In comparison, the Hong Kong public receives a typical radiation dosage of about 3 millisieverts a year from all sources in the environment, with about 40% of the total dosage of this coming from radioactive gases released into the air from the earth and building materials, 30% from direct radiation from rocks and soil, 10% from food and drink, 5% from radiation from space and 15% from man-made sources or our activities, mainly from X-ray examinations, but with a small quantity from air travel, and using television and other electronic devices.
Daya Bay's long-term commitment to proper environmental management is demonstrated by its ISO 14001 accreditation since 1999. It was the first nuclear power station and the first electric utility in the Mainland to attain such accreditation.
The Hong Kong Observatory has 12 radiation monitoring stations to assess the local background radiation and monitor changes of radiation levels round the clock. These stations have reported no increase in the level of radiation since the commercial operation of Daya Bay.
Any significant increases in the radiation level at or around the station or in Hong Kong will trigger a quick assessment of the situation and of any requirement for additional measurements or monitoring.
3. What are the contingency measures for Daya Bay in case of an accident?
 
Daya Bay has established procedures for handling emergencies in accordance with international practice. In the unlikely event of an emergency, the power station operators would promptly inform various national and provincial authorities, including the emergency response organisation in Guangdong, which, when making an emergency declaration, would simultaneously notify its counterpart in Hong Kong.
In accordance with their obligation under the International Atomic Energy Agency Convention on Early Notification of a Nuclear Accident, the Chinese authorities would immediately inform the Agency and neighbouring states of the accident.
Daya Bay regularly holds exercises and drills and joint exercises with Guangdong authorities.
According to international practice, in case of a serious accident at a pressurised water reactor, only those people within a 5 kilometre zone need be evacuated, while sheltering is required only within a 10 kilometre zone. These practices imply that Hong Kong does not need to plan for evacuation or sheltering. The northeast coast of Hong Kong is about 24 kilometres away, while Tsim Sha Tsui is 50 kilometres away.
Although the chance of a serious nuclear accident at Daya Bay is very remote, the Hong Kong Government has in place a comprehensive contingency plan to cover such an eventuality
  • The Hong Kong Observatory maintains a radiation monitoring network of 10 field stations in Hong Kong to monitor ambient gamma radiation levels throughout the territory
  • Citizens would be informed and notified of any necessary actions
  • If necessary, vessels in Mirs Bay would be asked to leave the area, and residents and visitors of Ping Chau would be relocated to safe areas
  • People entering Hong Kong from the Mainland would be scanned for radioactivity at the border, and would be decontaminated if necessary
  • Water and food from the Mainland and within Hong Kong would be monitored and would not be released for consumption if found affected
4. How does Daya Bay compare to Chernobyl?
  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 90 cm thick pre-stressed concrete lined with 6 mm 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.
5. How does Daya Bay handle its spent fuel?
 
After being loaded into the reactor for power generation, nuclear fuel will be consumed over three to four-and-a-half years, when it becomes spent fuel.
Under an agreement, the Guangdong Nuclear Power Joint Venture Co., Ltd. transfers the spent fuel to a national service provider, which is required to reprocess it in accordance with national policy similar to certain European countries and Japan. The operation of the service provider is supervised by the National Nuclear Safety Administration and its environmental impact is supervised by the Ministry of Environmental Protection .
6. What is planned for Daya Bay at the end of its life?
 
Daya Bay has an expected life span of at least 40 years, after which the station will be withdrawn from operation and decommissioned.
Decommissioning will involve:
  • removing the nuclear fuel from the reactor for storage and subsequent reprocessing
  • dismantling the conventional island and other conventional facilities
  • leaving the reactor building and its contents unused for several decades to about a century to allow levels of radioactivity to fall, 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
7. What happens if there is an interruption of power supply from Daya Bay to Hong Kong?
 
At present, 70% of Daya Bay's output is delivered to Hong Kong to serve one third of CLP Power's electricity needs. A total loss of supply is highly unlikely. The two reactors are capable of independent operation and the station has never encountered a simultaneous supply loss from the two units. In addition, power from Daya Bay can be delivered to Hong Kong along several transmission lines taking different geographical routes. A simultaneous disruption of all these routes is very unlikely.
In the case of a disruption of supply from Daya Bay, either because of a planned outage or an unplanned shutdown, 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 Hongkong Electric Company
  • making use of margin available in the frequency of the transmission system
8. What is the arrangement for the supply of nuclear power to Hong Kong from Daya Bay beyond the current contract?
 
The current supply contract, with which HK receives 70% of the nuclear electricity supply generated from Daya Bay, has a term up to May 2014. In September 2009, the contract has been extended for an additional term of 20 years up to 2034, enabling Hong Kong to enjoy not only the continued supply from a reliable and secure source but also clean power which gives no emissions.
9. Concerning the operational matter related to the imperfect fuel rod sealing at Unit 2 reported in May 2010, what is the impact on plant operation and the environment?


Background Information

 
In the Pressurised Water Reactor at Daya Bay, the uranium fuel is sealed in the metallic cladding of the fuel rods which make up the fuel assemblies.
The fuel assemblies are in direct contact and cooled by the reactor cooling water.
The reactor cooling water is enclosed completely by another two layers of containment and isolated from the external environment, thus preventing any impact to the public.
The use of a three-layer containment design, comprising the fuel rod, a 200-millimetre steel casing and a 0.9-metre thick reinforced concrete structure, is a common international practice for modern nuclear power stations.
Daya Bay has a comprehensive environmental monitoring programme, and regular checks over the years have indicated that there has been no undue release of radioactivity that has an adverse effect on health or the environment.


The operational matter

 
In May, the operators noticed through regular measurements the presence of radioactive iodine and noble gases in the Unit 2 reactor cooling water.  Preliminary assessment indicates the presence of imperfect sealing at a fuel rod.
The amount of these radioactive substances is low and has remained steady, at well within one-tenth of the allowable design operating limit.  This has no effect at all on the operation of Daya Bay.
At such an amount, the situation did not even constitute a Below Scale, or Level 0, Licensing Operational Event.


The significance

 
The radioactive substance is confined in the reactor cooling water.  There is no resulting change in the radioactivity measured inside and outside the concrete containment building.
As there was no radioactive release to the environment, there is no impact on public health and safety.
Daya Bay has 5 on-site radiation monitoring stations within 1 km from the nuclear power station.  The data shows normal fluctuations about a steady background levels and is comparable to earlier months.  The other 5 radiation monitoring stations located further away also show no abnormal level of radiation.
10. Why is Tritium being produced in the nuclear power production process? Does the release of Tritium constitute any impact to the external environment and public health?


Tritium is a nuclide of hydrogen, which is produced naturally when cosmic rays impact hydrogen molecules in the atmosphere. It is used in exit signs and luminous watch dials.

Tritium is also 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. Indeed, nuclear power stations deploying the same technology around the world adopt the same practice.

During the process of nuclear power production, reactions of certain chemicals will yield tritium. For example, it is necessary to add boric acid to the reactor cooling water to manage the rate of nuclear fission in the reactor, and its boron will combine with the neutron released in the nuclear fission process to form tritium.


Handling of Tritium Discharges

Most of the tritium generated (both in gaseous and liquid form) during nuclear power production is totally enclosed in the primary cooling water system, and therefore will not accumulate in the reactor. Tritium will be collected and tested before disposing according to the laid down procedures stipulated by the PRC government and the power station. Given the very low radioactivity level of tritium and the small amount of tritium release, continuous environmental monitoring shows no adverse impact from its release on station staff and the surrounding environment. The release of tritium is a normal operating procedure for nuclear power stations adopting the Pressurized Water Reactor technology around the world.


The impact of Radiological Releases on the Environment

The total annual radiological release from Daya Bay (including the gaseous and liquid releases of tritium) is prescribed in the stringent regulations set out by the State. 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 that a Hong Kong resident receives in a year). The effect of the total annual radiological release should also conform to this annual limit. The set limit is similar to that of other overseas nuclear power stations adopting the same technology.

Daya Bay has strictly complied with the statutory requirements, and conducted regular monitoring and data analysis on air and water samples collected from nearby area. According to the data collected of seawater samples, the levels of tritium released have been low and stable, which is also well within the annual limit set out by the State. The concentration of tritium in the water sample is about 5 Bq/litre, which is far below the 10,000 Bq/litre limit set by World Health Organization for drinking water.

The total annual radiological release (including the gaseous and liquid releases of Tritium) from Daya Bay is within one-thousandth of the annual release limit. The impact of these releases in a year is less than that of the radiation from a half-hour of travel on commercial flight, and should have almost no effect on the nearby environment or the health of the nearby individuals.

The Health Bureau of Shenzhen Municipality published a "Study Report on the Health Assessment of Residents Living in the Vicinity of Daya Bay and Lingao Nuclear Power Stations" in October 2008. The study covered specific studies and continuous monitoring of the health of the nearby residents and radioactivity in the surrounding environment of the two power stations. It included assessments with period spanning site selection, commissioning and commercial operation, and confirmed that the operation of Daya Bay had no adverse effect on the surrounding environment and the health of the nearby public.
 

11. In the event of a serious nuclear accident at Daya Bay Nuclear Power Station, is there any compensation for the public being affected?
 

According to China's current laws and regulations, for any single nuclear accident happened at Daya Bay which leads to third party claims, the operator of the power station shall be liable for a maximum compensation amount of RMB300 million. The operator should have adequate insurance coverage to meet this liability. The PRC Government will provide a maximum ex-gratia payment 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.

According to international conventions (including the Paris and Vienna Conventions) on compensation due to a nuclear accident, the liability of nuclear accident is channelled exclusively to the operator of a nuclear installation and all claims should be made in the country in which the accident occurred.

For details of the relevant laws and regulations in China, please refer to the following webpage :
http://www.gov.cn/gongbao/content/2007/content_711045.htm (Chinese only)
 
12. What is the notification mechanism of non-emergency Licensing Operation Events (LOEs) and emergency events at Daya Bay Nuclear Power Station?
 

Starting from 11 January 2011, the Daya Bay Nuclear Power Operations and Management Company (DNMC) and HKNIC have announced a new notification mechanism for non-emergency Licensing Operational Events (LOEs) at the Daya Bay Nuclear Power Station. Both companies will inform the public of a non-emergency LOE through their websites within 2 working days 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. HKNIC will, at the same time, inform the Security Bureau and the Environment Bureau of the HKSAR government.

For those events which require emergency response, actions will be taken by the Guangdong and HKSAR governments and their related departments according to the established emergency response mechanism based on a cooperative agreement on emergency response for Daya Bay. 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.htm
 
Organization chart for information flow
Organization chart for information flow
13. What is the progress of the nation-wide safety review on mainland nuclear power plants? What are the major areas covered in the review?
 

After the Fukushima incident, the China State Council has ordered the Ministry of Environmental Protection and the National Nuclear Safety Administration (NNSA) to conduct a nation-wide comprehensive safety review on all operating nuclear power stations and those under construction. Safety inspections and review on the Daya Bay Nuclear Power Station was conducted in April 2011. Areas covered by the safety review include the robustness in site selection, plans and abilities for seismic and flood protection, prevention of incidents caused by multiple extreme natural events and remedial measures, robustness of the preventive and remedial measures of severe accidents, and effectiveness of environmental monitoring system and contingency system.

The Daya Bay Nuclear Power Station will strictly observe the improvement measures put forward by the government after the comprehensive nuclear safety review, including safety enhancement measures for withstanding extreme multiple natural disasters and strengthening capability for emergency preparedness. For more detailed information regarding the national comprehensive nuclear safety review, please refer to the relevant website of NNSA :
http://www.mep.gov.cn/ztbd/rdzl/dzhaq/ (Chinese only)
 
14. What safety assessment and emergency preparedness have been carried out at the Daya Bay Nuclear Power Station?
 

Daya Bay Nuclear Power Station has conducted 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 and monitoring. Meanwhile, Daya Bay has also participated 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 (ie Pressurised Water Reactor) units from France, China, United Kingdom and South Africa. In 2011, Daya Bay achieved 6 out of the 9 key areas at top quartile performance (including Safe Operation, Capacity Factor, Industrial Safety, Chemistry Performance, Unplanned Reactor Shutdown etc), with the remaining 3 achieved above average performance.

The scope of the emergency preparedness of Daya Bay covers all related operational units within the power station. Other external units relate to emergency response and staff of the contractors will also be involved on a need basis. The power station will usually hold comprehensive emergency drills 2 to 3 times per year, and conduct regular (around 15 to 20 times per year) emergency preparedness trainings for individual operational units, in order to maintain staff's vigilance and capability for emergency response.