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How Safe is Nuclear Energy?
I. The Global Energy Situation
1. What is the situation regarding nuclear power reactors in the world?
A1. Short Answer:
More than 50 years have passed since the operation of the first nuclear power plant
in 1954, and during this time nuclear power has become a well-established, mature
technology. At the end of 2005, there were 443 civilian nuclear power reactors
operating in 31 countries around the world. However the pace of constructing new
nuclear plants has been slowed down in the past few decades - 26 reactors are in
different stages of construction in 11 countries, most of them in Asia (Japan, China,
Republic of Korea, Democratic Republic of Korea and India). Twenty-two of the last
31 reactors to be connected to the grid are also in the Far East and South Asia. By
contrast, in Western Europe and North America, nuclear construction has been a
frozen playing field - the last plant to be completed being Civaux-2 in France in 1999.
However, site preparation began in Finland for the 1600 MW(e) Olkiluoto-3 plant.
Explanation:
Nuclear energy supplies 16% of all electricity generated in the world. This
percentage has been roughly stable since 1986, indicating that nuclear power has
now grown at the same rate as total global electricity for 17 years.
According to the IAEA Power Reactor Information System (PRIS), in four countries
(Lithuania, France, Slovakia, and Belgium), nuclear energy represents more than
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50% of the installed capacity. In other 4 countries (Sweden, Ukraine, Slovenia and
Republic of Korea), it represents more than 40% of the electric capacity.
There are 121 nuclear power plants in North America, most of them in the United
States (104). Before the recent EU expansion nuclear energy was already the
largest single source of electric energy in the European Community, ahead of coal
and gas. In the newly expanded EU, 13 out of 25 countries operate 153 nuclear
power reactors to generate electricity. In Latin America there are two operating
plants in each of Argentina, Brazil and Mexico and one under construction in
Argentina. There are two operating plants in South Africa.
Capacity is greatest in Japan, with 54 reactors in operation and two under
construction. In the Republic of Korea, with 19 reactors in operation and one under
construction, 40% of total electricity came from nuclear power in 2003. Elsewhere in
Asia, nuclear power’s absolute and relative contributions are smaller, but China and
India in particular plan significant expansion. India, with 14 operating reactors, gets
only 3.3% of its electricity from nuclear power. But nine more reactors are under
construction, including the 500 MW(e) prototype fast breeder reactor at Kalpakkam,
and India’s goal is, by 2050, to supply 25% of its electricity from nuclear power.
China, now with nine operating reactors, two under construction and but 2.2% of its
electricity from nuclear power, plans expansion to 32-40 GW(e) by 2020 for 4-5% of
the electricity supply. In 2004 China’s State Council formally approved at least 7
GW(e) of new capacity beyond that already under construction.
The majority of operating units (82%) are of the Light Water Reactor (LWR) type,
61% of those being of the Pressurized Water Reactor (PWR) type, and 21% being of
the Boiling Water Reactor (BWR) type. Pressurized Heavy Water reactors (PHWR or
CANDU) represent about 9% of the total. Different types of gas-cooled reactors
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represent 5%, while Light-water-cooled Graphite-moderated, water (RBMK)
represent about 4% of the total amount.
Nuclear expansion, as well as near-term and long-term growth prospects, is
centered in Asia. Nineteen out of 25 new plants will be located either in China, the
Republic of Korea, Japan or India. Twenty-one of the last 30 reactors to have been
connected to the grid are in the Far East and South Asia.
Given the limited amount of new construction, much of the increase in nuclear
generating capacity over the past decade has been credited to increased availability
- a change tied directly to improvements in global safety performance.
2. What is the contribution of nuclear energy to mitigating the problems
associated with greenhouse gas emissions and consequent global warming?
A2. Short Answer:
Nuclear power plants emit virtually no greenhouse gases. The complete nuclear
power chain, from uranium mining to waste disposal, including reactor and facilities
construction, emits only 2-6 grams of carbon per kilowatt-hour. Therefore, the
operation of the world’s nuclear power reactors avoids the release of roughly 600
million tones of carbon, should the same energy have be generated by a
proportionate mix of non-nuclear sources.
Explanation:
Studies have shown that, when the whole chain from mining to waste disposal is
considered, nuclear power produces only 2-6 grams of carbon pre kilowatt-hour. This
is about the same as wind or solar power, and less than 1% of the amount produced
by coal, oil or even natural gas.
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The 600 million tones of carbon avoided by the operation of the world’s 443 nuclear
power reactors is approximately twice the total amount to be avoided by the Kyoto
Protocol in 2010.
Both nuclear and other renewable sources of energy, such as wind, solar and
geothermal plants could play a major role, as the reduction of carbon emissions
becomes a higher priority. The problem is that no “renewable” source has been
demonstrated to have the capacity to provide the “base-load” amounts of power
needed to replace large fossil fuel plants. Wind power, for example, may be an
excellent choice for sparsely populated rural economies, particularly if they lack
modern electrical infrastructure; on the other hand, it seems unlikely that wind power
will be able to support the electricity needs of tomorrow’s mega-cities.
3. How has privatisation and the opening of electricity markets affected the
safety of the nuclear power plants?
A3. Short Answer:
Privatisation has had a major impact on the electric power industry, and as such, the
nuclear power industry in many countries. But the impact has been mainly on
commercialisation and tariffs. The impact on plant safety has been minor, since no
significant changes in regulatory requirements have occurred due to privatisation,
and whoever owns and operates a nuclear power plant still has the ultimate
responsibility for its safety.
Explanation:
The main impact of privatisation has been in the commercialization of the produced
electric power. Of course, in a privatised environment operational costs are an
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important factor and efforts to cut costs become an ever important priority. However,
a “safe plant is also a reliable plant”. This can be demonstrated by the examination
of the list of “plant performance indicators” which are, in large part, common to the
list of “safety indicators”.
The examination of both performance indicators and safety indicators in most plants
shows that privatisation has not adversely affect plant safety. Even in exceptional
cases, such as in Canada, where strong cost cutting measures have led to
deterioration of plant performance to the point where several reactors have been
temporarily shutdown, the regulatory body cited no safety reasons for ordering the
plants to shutdown.
Since the accident at Chernobyl in 1986, the IAEA has established networks to
conduct peer reviews, compare safety practices, and exchange vital operating
information to improve safety performance. A more systematic analysis of risk was
used to ensure that changes made were in areas that would bring the greatest safety
return. Although the focus of this international effort was on improving safety, the
secondary benefit has been a steady increase in nuclear plant availability and
productivity. In 1990, nuclear plants on average were generating electricity 71% of
the time. That figure had risen to 81% - an improvement in productivity equal to
adding more than 34 new 1000 megawatt nuclear plants - all at relatively minimal
cost.
The result is that existing well-run nuclear power plants have become increasingly
valuable assets. Although the front-loaded cost structure of a nuclear plant is high,
the operating costs have become relatively low and stable. While these
improvements to safety and economics have not been well publicized - and have not
yet had a significant impact on the public’s opinion of nuclear power - they have not
escaped the notice of investors. They have been a strong factor in decisions to
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extend the licences of existing plants - for example, in the United States, where 19
plants have received 20 year licence extensions in the past 5 years. Regulatory
bodies in countries where privatisation has taken place must continue to carefully
monitor plant safety performance to ensure that cost reductions do not compromise
the levels of safety.
4. A burdensome regulatory process could be difficult to maintain in a
competitive business environment. How is this new environment affected the
regulatory requirements? What is the impact on plant safety? Are utilities and
operators pressing to lessen regulatory requirements? How can safety and
competitiveness be balanced?
A4. Short Answer:
Safety requirements have not been changed due to deregulation of the electric
power market. The safety requirements and standards remain the same. And
regulatory bodies have not, and will not, be willing to lessen them due to economic
reasons. The utilities, on the other hand, now have additional requirements for
competitiveness. These however must not compromise safety requirements. This is
usually stated in the utilities safety policy statements. Read more…
Explanation:
Competitiveness is one of the key objectives of utilities in a deregulated electric
power market. However, it is widely recognized that a well run, safe plant is also an
economic, and thus a competitive, plant. The costs associated with unplanned or
regulatory imposed outages can quickly exceed those associated with maintaining a
safely built and safely operated facility.
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The strategy of the industry is to demonstrate a good safety record and maintain
high operational performance, and reduce the risks associated with insurance and
liabilities. Optimisation of maintenance programs, based on predictive maintenance,
instead of repair maintenance, has also contributed to high plant availability and
therefore good safety and economic performance.
Lessons learned from recent events have demonstrated that operating a plant in an
unsafe condition can be most costly in the long range.
II. Safety of Nuclear Installations
5. Several countries around the world are building new nuclear power reactors.
Is there some system to ensure that they all live up to a common, satisfactory
level of safety?
A5. Short Answer:
Yes, a global safety regime has been instituted by the international community after
the accident at Chernobyl to promote a common level of safety throughout the world.
This “regime” includes binding safety conventions, internationally accepted safety
standards, and a peer review system to promote compliance and assist countries in
improving safety whenever necessary.
Explanation:
Nuclear safety has been always a matter of international concern. In the early 1970s,
the IAEA developed a series of 5 Codes of Practice and 50 Safety Guides which
were applied and/or adapted as regulation by developing countries entering into the
nuclear power arena. Later, after the accident at Three Mile Island in 1979, the 5
Codes were revised as a set of international standards for all countries.
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But it was after the accident at Chernobyl that a truly “international nuclear safety
regime” was fully developed. This “regime” is based on:
1. Binding international conventions;
2. Internationally accepted safety standards; and
3. An extensive system of peer reviews.
Two conventions, one on the Early Notification of a Nuclear Accident and a second
on Assistance in the Case of a Nuclear Accident or Radiological Emergency were
developed just a few months after the Chernobyl accident. A Convention on Nuclear
Safety was developed later, requiring the parties to: 1) report every 3 years on the
safety status of their nuclear power plants according to detailed guidelines; 2)
identify any known deficiencies; and 3) take the necessary actions to eliminate them.
These reports are critically reviewed among the parties of the Convention and
general recommendations are derived at a periodic review meeting every 3 years.
Later, a similar Joint Convention on the Safety Management of Spent Nuclear Fuel
and Nuclear Waste was developed with a similar reporting mechanism.
IAEA safety standards are periodically revised and updated to reflect the state of the
art in nuclear safety, and to include new areas, such as the nuclear fuel cycle;
modern techniques, such as human-machine interaction and assessment of the
probability of occurrence of certain postulated accidents. These standards are now
accepted worldwide, and, although not obligatory, have been adopted by several
countries on a voluntary basis, and are used as the basis of national regulations in
numerous other member States.
Evaluation of the safety status of nuclear programs is the third tier of the global
safety regime. Operational safety reviews are been conducted by the WANO (World
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Association of Nuclear Operators) at almost every plant worldwide, and these
services are scheduled to be repeated every 3 years. Additional plant reviews are
conducted by the IAEA Operational Safety Review Teams (OSART), which are
made up of experts from countries around the world. From a slightly different
perspective, reviews of the national regulatory bodies, including their legal
infrastructure and safety assessment activities, are carried out by the International
Regulatory Review Team (IRRT) of the IAEA.
Altogether, these reviews confirm and keep current the information provided to the
Conventions. They also provide assurance that an acceptable level of safety has
been and continues to be achieved throughout the nuclear industry.
6. Three Mile Island and Chernobyl were major nuclear disasters affecting
thousands of people and contaminating large areas. Why haven’t plants of that
type been shut down?
A6. Short answer:
Three Mile Island (Pennsylvania, USA) was a severe accident that occurred in 1979.
The accident destroyed the power-producing core of the light water power reactor
but led to no release of radioactivity to the environment and no personal injuries or
contamination. The Chernobyl (Ukraine) accident, which occurred in 1986, was
indeed the most devastating in the history of nuclear power. It resulted in 28
radiation-induced fatalities within few months after the accident, evacuation of
hundreds of thousands of people and contamination of vast territories of Russia,
Belarus and Ukraine. In both cases, the lessons learned from the accident were
applied almost immediately by the world nuclear industry to modify similar plants, to
improve personnel training and to improve operational management with the
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objective of avoid the repetition of similar a accident. These important steps led to
considerable improvements in plant safety worldwide.
Explanation:
The accident at the American pressurized water reactor (PWR) at Three Mile Island
was a loss of coolant due to a combination of design deficiencies and operators
errors, leading to the uncovering and partial meltdown of the reactor core. The
containment building around the reactor kept all of the contaminated water and any
radioactive material confined to the plant. The only exception was the release of a
minimal amount of radioactive gas released as a pressure control mechanism. This
release had no significant impact on the environment, the plant personnel or the
public.
The reaction from the nuclear industry and national regulators was a comprehensive
investigation of the accident and its causes. This, in turn, led to several key design
modifications to improve the safety of plants of the same type. The lessons learned
from the TMI accident also resulted in significant changes to the overall approach to
nuclear safety throughout the world, including new developments in the area of
human factor engineering. It also led to the creation of the Institute of Nuclear Power
Operation (INPO).
The Chernobyl accident occurred in a completely different type of reactor (Light
water-cooled Graphite-moderated Reactor, RBMK), used only in the former Soviet
Union. Acute radiation syndrome was diagnosed and confirmed for 134 persons (fire
fighters and recovery operation workers). Among them, 28 persons died in 1986 due
to acute radiation syndrome, and 17 died in 1987-2004 from various causes, not all
linked to radiation. No cases of acute radiation syndrome have been recorded
among the general population. About 600,000 persons have been recognised as
liquidators (recovery operation workers). It was assessed that the average effective
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dose from external gamma radiation to recovery operation workers in the years
1986-1987 was on the order of 100 miliSieverts. In addition, 10 % of the 116,000
people that were evacuated from the “exclusion zone” may have received doses
greater than 50mSv but fewer than 5% received more than 100 mSv. More than 18
years after the accident, the confirmed detectable radiation-induced human health
effect of the accident has been a sharp increase of thyroid cancer among exposed
children from the affected area. Since the accident, the number of patients having
thyroid cancer (who were children and adolescents in 1986) reached 4 000 in
Belarus, Russia and Ukraine. Since thyroid cancer can generally be successfully
treated, only dozen patients among the diagnosed are known to have died from this
cause.
The reaction from the nuclear industry to the Chernobyl accident was the wide
recognition that “an accident anywhere is an accident everywhere.” An immediate
international effort was launched to develop a truly “international nuclear safety
regime” composed of binding safety conventions, internationally accepted safety
standards and a peer review system to verify the safety level of all plants.
The reaction of utilities operating nuclear plants was the creation of the World
Association of Nuclear Operators (WANO), in order to maximise the safety and
reliability of the operation of nuclear power plants by exchanging information and
encouraging communication, comparison and emulation amongst its members.
Several international initiatives have been conducted subsequently to improve the
safety of Chernobyl-type reactors (RBMK). These have included hardware
modifications, improved plant maintenance and in-service inspections, based on
additional safety analysis, and the promulgation of a committed safety culture among
the operators. The IAEA conducted a project on the safety of RBMK type reactors
involving a complete review of plant design and operational aspects. The initiative
resulted in a list of plant improvements that were implemented with international
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support from the European Community, European Bank for Reconstruction and
Development (EBRD) and the World Bank. The other 3 reactors at the Chernobyl
site were all later shut down. Both the International Atomic Energy Agency (IAEA)
and the World Association of Nuclear Operators (WANO) have introduced periodic
peer reviews of nuclear plants, worldwide, to assure that they are operated
according to best international practices.
7. The Chernobyl accident in 1986 was the world’s worst nuclear accident. It
killed dozens of people and contaminated a very large area around the plants.
What is the risk that such accidents will happen again elsewhere?
A7. Short answer:
The risk of a new accident of the same type of Chernobyl has been greatly reduced
due to international and national efforts to improve substantially the safety of these
plants. Read more…
Explanation:
The accident at Chernobyl was caused by a combination of design deficiencies and
operator errors. Immediately after the Chernobyl accident, nuclear authorities of the
former Soviet Union undertook several measures to avoid the repetition of a similar
accident. These involved modifications to the reactor design and associated safety
systems, as well as administrative measures to ensure proper actions by operators.
As a follow up, an Extra-Budgetary Project for the safety of RBMK Nuclear Power
Plants was carried out by the IAEA during 1990-1997 with broad international
support. This project carried out a comprehensive review of the design and operation
of RBMK type plants and identified the main safety issues. Then, support from the
international community was provided to improve the safety conditions at the RBMK
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reactors. At the conclusion of the Project, technical experts and scientists concluded
that the likelihood of a similar accident was very low, could be discarded, although
further safety improvements were encouraged.
Such improvements have continued in recent years. The National Reports of Russia
and Lithuania (in Ukraine the 3 remaining RBMKs at Chernobyl have been
shutdown) presented in the recent review meetings of the Convention on Nuclear
Safety have demonstrated a significant upgrading of the level of safety of this type of
plants. This has also been demonstrated by the reduction in the number of reported
abnormal events as well by other safety indicators such as plant availability and dose
reduction.
8. More than 15 potentially dangerous RBMK reactors are still operating in
Russia and Lithuania. What has been done to alter their design and operation
to prevent similar nuclear disasters? What specific measures have been taken
to ensure their safety?
A8. Short Answer:
After the Chernobyl accident, there was broad agreement that the original design of
the RBMK reactor core and its shutdown system had severe deficiencies.
Modifications carried on RBMK reactors between 1987 and 1991 addressed the
most serious problems in these areas. Modifications introduced later, with the
assistance of the international community, aimed at further improving overall safety
to an (internationally) acceptable level. Some additional modifications are still
underway in order to achieve even higher safety levels, as required by the
Convention on Nuclear Safety. Read more…
To view reactors by type, see IAEA data. (Note: RBMKs are listed as LWGR types).
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Explanation:
The immediate actions to avoid the repetition of the Chernobyl accident were carried
out by the former Soviet Union itself. Later, in 1992, upon request of the former
Soviet Union and later of Russia, the IAEA started a program on the safety of RBMKtype reactors which included a wide range of activities including review and
assessment of the Smolensk and Ignalina plants that served as references for the
program. Support from the international community, including EU, EBRD and
WANO, were essential to the success of that five-year program.
At the conclusion of the IAEA program, it was generally agreed that results of the
international assistance have increased the confidence that the known shortcomings
and the requisite safety improvements of RBMK reactors have been identified and
addressed. This includes both design and operational considerations. The plant
specific status of the implementation of safety improvements have been reported in
the National Reports to the Convention on Nuclear Safety. This demonstrates an
ever increasing level of safety, which supports continuity of operation of these
reactors, (except for the three additional units at Chernobyl, which have been shut
down).
9. What kind of safety assessment has the IAEA performed to assess the
safety of WWER and RBMK reactors?
A9. Short Answer:
In 1990, the IAEA launched an international project on the safety of WWER 440/230.
Later this project was expanded to include all WWER and RBMK - type reactors.
This project evaluated the safety of the design and sponsored expert safety visits to
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the power plants to identify safety deficiencies and to make recommendations on
how to solve them. The project grouped the deficiencies into so called “safety
issues,” prioritised them and monitored their solutions through assistance provided
by the EU, the World Bank, EBRD and bilateral agreements.
The project concluded in 1998 with the resolution of the main safety issues. But the
enhancement of safety at WWER and RBMK reactors continues, with many of the
additional low priority issues now being resolved as a result of follow-up assistance
provided by the IAEA through its technical cooperation program.
Explanation:
The IAEA project on the Safety of WWER and RBMK Nuclear Power Plants was a
major scientific and technical undertaking of IAEA, carried out with support of several
Member Sates during the period of 1990 - 1998. Dozens of expert safety missions
were conducted inside the plants, and 20 technical studies were conducted by the
IAEA involving dozens of outside experts provided cost free by member States.
The final project report (IAEA-EBP-WWER-15) described and ranked all of the key
safety issues, identified the issues that remained to be solved at that time, presented
an overview of the remaining work to be done and specified the relevant IAEA
assistance which was planned. The results and recommendations of the Project
were intended only to assist the national decision makers who have the sole
responsibility for the regulation and safe operation of their nuclear power plants.
Progress in the implementation of these additional safety improvements is further
documented in the final report of the 2nd Review Meeting of the Convention of
Nuclear Safety, where it is recognized the good progress achieved by all these
plants to increase their level of safety.
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10. What kind of evaluation have the IAEA and other organizations conducted
in plants that combine Eastern and Western technologies, such as Temelin in
the Czech Republic?
A10. Short Answer:
The IAEA has been providing assistance in the safety evaluation of the Temelin
nuclear plant since 1990. Indeed, it was the IAEA Temelin Design Review Mission,
carried out in 1990, that prompted the decision to change the plant’s fuel design and
instrumentation and control systems, which was provided by an America company.
Additional IAEA assistance has been subsequently provided in the evaluation of
safety issues and their solutions, and in the review of Probabilistic Safety
Assessment (PSA), Quality Assurance (QA), and the application of Leak Before
Break (LBB) concept. Fire protection and Operational Safety (OSART) missions
have also been conducted at the Temelin plant.
Explanation:
Several international safety missions have been conducted at Temelin by the IAEA
and other organizations. The initial missions focused on the design, but later they
concentrated on the compatibility of Western technology with the original Russian
design.
The most recent assessments were conducted by GRS - Germany, through a
bilateral agreement, by the association of Western regulatory bodies (WENRA), and
by the Atomic Question Group (AGQ) in relation to the acceptance of Czech
Republic in the EU.
All of these recent assessments concluded that the design and operational safety of
Temelin is in compliance with national requirements and international practices.
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The work of the Czech regulatory body (SUJB) in licensing and controlling Temelin
was also independently evaluated by two International Regulatory Review Team
(IRRT) missions of the IAEA in January 2000 and June 2001, with positive results.
11. Many nuclear power plants are reaching the end of their operational
lifetimes. But many operators are getting extensions of their operating
licenses. Isn’t this dangerous since the plants are too old?
A11. Short Answer:
The decision to extend the life of a nuclear power plant beyond the original
“estimated life” is taken only after a careful evaluation of all safety implications,
especially the actual condition of key components, such as the reactor vessel, (the
steel vessel containing the reactor core) and its anticipated condition at the end of
the extended life. Usually such extensions are accompanied by comprehensive
upgrading of plant safety conditions, including replacement of obsolete components
and the addition of new safety system and components according to the new
standards and developments of technology.
Explanation:
The estimated “life time” for a nuclear power plant arises mainly from two
requirements: 1) from the commercial point of view, one needs to estimate the period
of operation in order to depreciate the capital cost and calculate tariffs; 2) from the
technical viewpoint, one has to estimate the life time of the limiting component which
cannot be easily replaced by maintenance, usually the reactor vessel.
Not all countries establish a fixed “life time” period for nuclear power plants at the
initial licensing. Normally, however, the condition of all plant components are
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constantly monitored, and obsolete or worn out components are replaced during
routine maintenance, as required. Since the “life” of components is estimated at the
beginning using conservative operational conditions, the actual life may be longer
than the initial estimate, thereby permitting the extension of plant life without
compromising safety.
On the other hand, operating experience may show deterioration of components
faster than estimates due to previously unknown phenomena. But modern
technology has permitted the replacement of components which were planned to last
for the “life of the plant”, as is typical the case of steam generators and reactor
vessel heads of PWR. Even the radiation damage, which limits the life of reactor
vessel can be overcome in some cases by the modern on-site “annealing” process.
At the end, the decision to extend the life of a plant is a commercial one, which
balances the cost of the effort to refurbish the plant to maintain its safety, and the
economic benefits of the additional electricity to be generated. This same balance
has sometimes led to early plant retirements, showing that the nuclear industry is
conscious of its responsibility for safety.
12. The safe operation of any complicated equipment depends a lot on the
people and how well they are trained. But levels of technical education and
work discipline are low in some countries with nuclear plants. Is anything
being done to upgrade the quality of personnel to ensure better safety?
A12. Short Answer:
New standards of qualification and training of operators have been developed with a
recognition of the importance of the human factor in nuclear safety. The Systematic
Approach to Training (SAT) has been used to ensure adequate training of plant
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operators across the nuclear industry. The creation of the World Association of
Nuclear Operators (WANO) has contributed to the dissemination of this
methodology, and WANO peer reviews have been used to demonstrate adequate
levels of training, and to propose further improvements when necessary.
Staff training and qualifications is also an inherent module in IAEA nuclear plant
safety review missions; additionally, training plant staff is a significant part of the
safety assistance provided under the Agency’s technical cooperation programme.
Explanation:
The nuclear industry has always recognised the importance of the human factor in
ensuring safety. Comprehensive training programs, including the use of plant
simulators, have been part of nuclear industry from its inception.
But it was after the accident at Three Mile Island that the new discipline of “human
factor engineering” (or man-machine interaction) was thoroughly developed.
Additional requirements for the number of operators in the control room were
established. The qualification and training of the operators were enhanced. The
design of all control rooms were reviewed from the ergonomic point of view, and
many modifications were introduced in order to assist the operators in the diagnosis
of plant conditions, especially during emergency situations. Plant procedures were
reviewed and revised in order to present the information in a more “operator friendly”
way. The use of plant specific simulators, with greater simulation capabilities has
been greatly extended.
The monitoring and evaluation of events caused by operator errors has been further
developed and refined. These evaluations have demonstrated that, although still an
important factor, operator errors have been consistently decreasing at most of
nuclear plants around the world.
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13. Power blackouts affected major cities in the USA, Canada and Europe in
2003. What has been the impact of these events on the operation of nuclear
plants? Is their safe operation still ensured?
A13. Short Answer:
Most nuclear power plants are designed to remain in operation even if they are not
connected to the larger electrical grid. All nuclear power plants are equipped with
multiple redundant emergency power supply (diesel generators) which can go into
operation in few seconds in case of a total failure of power supply. In the meantime,
redundant battery sets provide essential power to the instrumentation and controls
that monitor plant status and activate the emergency power supply. The diesel
generators sets are provided with independent fuel tanks and reserve fuel adequate
for several days operation. In addition, administrative arrangements are in place for
refilling these tanks in the improbable case of extended periods without reestablishing connection to the electric power grid.
Explanation:
The loss of external power supply is a “design basis accident” considered in all
nuclear power plants. Multiple redundant emergency diesel generators are usually
provided to cope with these events. This emergency power is used to operate the
safety equipment necessary to maintain the cooling of the reactor core and other
essential plant safety functions.
Calculations of the probability of occurrence of certain postulated accidents
recognize that there is a remote probability that all diesel generators could fail due to
a “common mode failure” (a common deficiency in the design or a common error in
the maintenance of all units). This has led some plants to add a direct connection to
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a reliable alternate source (e.g., nearby hydro plants) or to use a “diverse” type of
emergency, such as an electric generator driven by a small gas turbine.
14. Some nuclear power plants are built on sites subject to natural phenomena
such as earthquakes or tornados, which can pose a risk for any installation.
What has been done to ensure the safety of these plants?
A14. Short answer:
Nuclear power plants are designed against natural phenomena according to detailed
studies performed at the time of the selection of the site for the construction. These
studies define the maximum threatening phenomena expected at the site, and
include “design basis earthquakes, floods, etc.” Sites are constantly under reevaluation during the entire life of the plant. Phenomena such as earthquakes are
constantly monitored, and in the event that a lower level earthquake - the so called
safe shutdown earthquake - occurs, the plant is shut down and a detailed
investigation is carried out.
Explanation:
The pursuit of a nuclear project is only authorised after detailed studies are
conducted to identify all important potential physical threats to a site. These include
maximum meteorological conditions such as rain, wind, flood levels, and extreme
natural phenomena such as tornados, earthquakes, hurricanes and tsunamis. Past
data, as well as detailed analytical models, are used to define design basis
parameters for the specific site.
The construction of the plant takes into account all these parameter when designing,
fabricating and installing main components and essential safety equipment.
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Site parameters are constantly re-evaluated and, in case of new information, design
modifications can take place, such as the re-enforcement of structures or the
replacement of equipment, as occurred in some WWER plants after a new
earthquake design basis was defined.
Site parameters are constantly monitored and automatic actions or safety
procedures are in place to put the plant in a safe condition if any of the parameters
are exceeded. In certain situations, such as the approach of a hurricane, a
precautionary shutdown may take place.
Extensive experience has shown that this philosophy of conservative design has
been sufficient to cope with all of these types of natural phenomena at all nuclear
power plants.
15. Some nuclear power plants are built on sites close to dangerous
transportation routes or gas and oil pipelines. Others could be damaged by an
airplane crash. Is there a way to protect these plants against such disasters?
A15. Short Answer:
Site studies carried out before the construction of a nuclear power plant identifies all
the potential threats due to human activities around the plant. Explosions of
dangerous goods on nearby routes, in vulnerable pipelines or as a result of airplane
crashes are either taken into account in the design. In some instances, they are
excluded due to the low probability of such occurrences. In some cases, routes are
redirected, pipelines are moved or air-space around the plant is controlled.
Explanation:
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FACT SHEET
During the site selection for a nuclear power plant, all man-induced events which can
be a threat to the plant are identified. Some of these may be decisive in excluding a
given site from further consideration. Some may require remedial action, such as the
re-location of roads, pipelines or air fields.
After identifying such possible events and considering their probability, a set of maninduced events is taken into consideration in the design and construction of the
plant.
Plant buildings are usually designed and constructed to support the shock wave from
a possible explosion of dangerous cargo on a nearby road, should it be relatively
close to the plant. Dangerous ship cargo in a nearby river or sea are also
considered.
Regarding airplane crashes, a detailed study of air routes is carried out, including the
types of planes and the frequency of flights to determine the need for a specific
protection against such events. In cases where an airplane crash is considered in
the design, reinforcement of the containment building is required. In many countries,
a “no fly zone” is established around the nuclear plant sites, where passage of
commercial, military and civil airplanes is prohibited. Also the provision of redundant
emergency systems, such as power supplied by stand-by diesel generators or more
than one control room (spatially separated main and emergency control rooms)
protect the plant from the simultaneous loss of both systems.
16. What is the role of the IAEA in assessing plant safety and investigating
abnormal events in nuclear power plants and other installations?
A16. Short Answer:
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FACT SHEET
The assessment of nuclear power plant safety is the responsibility of national
authorities of each country. The IAEA is only involved in the investigation of
abnormal events or accidents if it is requested by a member State.
The IAEA regular programme puts considerable effort into developing standards for
all safety thematic areas and for all types of nuclear installations (Safety Standards
and Safety Guides). Tools and services to promote the exchange of information on
abnormal events, such as the Incident Report System (IRS) and the Agency peer
review services provide important opportunities to share lessons and learn from
others. The Agency is also promoting self-sustaining networks within and between
Member States based on strategic knowledge management to provide more
opportunities to share safety information.
Explanation:
Assistance to Member Sates in the field of nuclear safety is in the Statutes of the
IAEA. This assistance is always provided upon request of a member State and
delivered as advice to the national authorities. It can be provided to review either
design or operational considerations, or in case of abnormal events, to assist in the
identification of root causes and the sharing of lessons throughout the world nuclear
community.
In some cases, based on the provisions of the Convention for Assistance in Case of
Nuclear or Radiological Accidents, the IAEA has also supported Member States in
evaluating accident conditions, recovery activities and the mitigation of accident
consequences.
Up to now, most of these cases have been related to radiological emergencies
connected with loss of control of radiation sources. In these cases, the Agency has
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FACT SHEET
produced independent evaluation reports with a description of the events and the
conclusions and recommendations related to the lessons learned.
Assistance has also been provided, on numerous occasions, to help with an
independent assessment of events. Examples include events that have taken place
at nuclear power plants in Spain, France and Hungary. In the case of Hungary, at the
request of the Government of Hungary, the IAEA conducted an independent expert
mission at the Hungarian Atomic Energy Authority and the Paks Nuclear Power Plant
to assess the results of the national regulator’s investigation of the 10 April 2003 fuel
cleaning incident at the Paks NPP.
17. If a nuclear power plant does not have containment, how can one be sure
that no radioactive material is released to the environment?
A17. Short Answer:
The containment is an additional safety barrier, included in the design of some
nuclear power plants, but not necessarily in all plant designs. The acceptance of the
design (and therefore, the license to construct) is only completed after the evaluation
of a number of postulated accidents defined for each specific design. The ultimate
goal is ensure that in the worst credible accident for a given design, the radiation
dose to the public will not exceed the established national limits. This has been
determined by some national regulatory authorities to be assured for certain designs
without a containment building.
Explanation:
The authorization process to build a nuclear power plant requires the detailed
analysis of postulated accident scenarios according to the plant design. These form
the “design basis accidents” for a given design. Safety systems are designed to cope
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FACT SHEET
with these accidents, and the analyses must demonstrate, given conservative
assumptions, that the doses to the public will not exceed the established safety
limits.
For certain nuclear plants modular construction in the form of “multiple-channel” is
used. Examples include Gas Cooled Reactors (Magnox and AGR type reactors) and
Light-water-cooled Graphite-moderated Reactors (RBMK). In these cases, it has
been demonstrated that under design basis accidents a containment building is not
required to ensure that safety limits are not exceeded. There exists, however, a
small possibility that an accident “beyond the design basis” may occur, such as was
the case at Chernobyl. Recent evaluations show that in the case of Chernobyl, even
if a containment building has been present, it would not have resisted the large
steam explosion that occurred. Therefore, the current approach is to try to avoid
“beyond design basis accidents,” or better, make their probability so low that they
can be practically excluded.
Nowadays, more detailed safety analyses using probabilistic methods are carried out
to identify possible sequences leading to “beyond design basis accidents”. Additional
measures are now being taken into consideration to cope even with these remote
possibilities.
Additionally,
these
accident
scenarios
are
used
for
planning
emergency
preparedness measures, which could be used for ultimate protection of the
population (through sheltering or evacuation) in the remote possibility of such an
event.
18. What has been done by the IAEA in the case of events involving nuclear
plant safety reported by the press?
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FACT SHEET
A18. Short Answer:
The IAEA’s Incident and Emergency Centre maintains a system of reporting of
events related with nuclear energy, including both operational events at nuclear
power plants and radiological incidents throughout Member States. The reporting
system uses the International Nuclear Event Scale (INES) to convey to the public the
significance of the event. The information is transferred to the INES contact point in
all Member States, and also published on the IAEA website.
Later, more detailed information, the evaluation of the event and the lessons to be
learned, are usually published as an entry in the Incident Reporting System (IRS).
Explanation:
The reporting of significant events - those graded level 2 or more, in the INES scale,
or those attracting media attention - is a commitment of all Member Sates
participating in the INES network. The dissemination of the initial information by the
IAEA is a routine activity.
Through the Incident Reporting System (IRS), operated jointly with the OECD/NEA,
feedback of international operating experience for nuclear power plants proper
reporting and feedback of safety significant events for the international community is
ensured, and its causes and the lessons learned can then be disseminated widely.
The detailed assessment of some events is carried out, depending on their
significance for nuclear safety and their relevance for other organizations in the
nuclear industry. In these cases, an IAEA mission is sometimes sent to the country
to collect specific data, to review the facts and assess the actions taken. A report
containing recommendations to the country - to the operators and/or regulatory body,
depending on the situation - is prepared and presented to the country authorities.
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FACT SHEET
Lessons learned and recommendations to all related nuclear industries are also
contained in the report.
Whenever several events present a common root cause or other commonalities,
larger technical meetings are organized by the IAEA. These aim to produce deeper
analyses, identify broader lessons from the collective series of events, develop
additional guidelines, and possibly initiate new IAEA activities in the related field.
One recent example of this was a Workshop on Nuclear Management and Safety
Culture: Lesson Learned from Recent Events organized in June 2003 to evaluate
events that occurred in 4 power plants in Japan, Germany and the USA.
III. Security of Nuclear Installations
19. Are nuclear power plants and other nuclear facilities vulnerable to terrorist
attacks? Is anything being done to protect them?
A19. Short Answer:
Security has always been a vital consideration in nuclear plant design and operation,
but since the terrorist attacks of 11 September 2001, security at nuclear plants has
become a major focus for governments and concerned international organizations
such as the IAEA. Good progress has been made in ensuring better nuclear security.
While much remains to be done, nuclear installations around the world have
strengthened security forces, added protective barriers, limited access to sensitive
information and taken other measures commensurate with the current security risks.
Explanation:
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FACT SHEET
Recent terrorist attacks in Tanzania, the USA, Saudi Arabia, Indonesia, Spain and
other countries have led to a re-evaluation of security in every industrial sector,
including nuclear power. Nuclear security activities have greatly expanded in scope
and volume. New scenarios of security threats have been identified and the
vulnerabilities are being reduced.
The risks of terror at nuclear power plants have been in the spotlight, but several
features of nuclear power plants that protect them against external events, such as
external explosions or airplane crashes, may also help to protect them against
terrorist attacks.
IV. Radiation Safety, Wastes and Transport
20. The spent fuel and high-level waste from nuclear plants is very dangerous,
but no country has a complete plan for how to permanently deal with this
waste. Shouldn’t this problem be addressed before any new nuclear plants are
built?
A20. Short Answer:
The total amount of civilian high-level nuclear wastes is relatively small. Up to now,
all of these wastes from the decades of operation of the more than 440 nuclear
power plants are completely kept in intermediate repositories. There is a broad
scientific consensus that deep geological disposal, using a system of engineering
and natural barriers to isolate the wastes, is the preferred method for their
permanent disposal.
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FACT SHEET
However, up to now, no such system has been constructed. The technical means for
final disposal of these wastes are readily available, and political factors have been
the principal cause for delays in the implementation of such solutions.
In order to be able to fund the proper dispose of the wastes in the future, the cost of
final disposal is taken into consideration in most countries as part of the cost of the
electricity produced. However, this represents only a small fraction of the total cost.
This approach demonstrates the responsible care being taken with respect to future
generations, since environmental costs are being borne by those who enjoy the
benefits of the operation of the nuclear power plants. Incorporation of external costs
into the price of electricity is a unique feature of the nuclear industry.
Explanation:
There are two types of categories of radioactive wastes: Low and intermediate-level
wastes (L/ILW); and High level wastes (HLW).
Low-level wastes are produced by numerous applications of nuclear activities in
industry, medicine, research, and by nuclear power plants. Disposal of low-level
wastes in near surface or shallow burial is used widely. Intermediate level wastes are
produced by the operation of nuclear power plants. Such wastes may include resins
from water cleanup or solidified chemical sludge as well as pieces of contaminated
equipment. Disposal options are similar to those for low level wastes, but the
radioactive content requires shielding during transportation and handling.
The high level waste arises from the reprocessing of spent fuel from nuclear power
plants or the spent fuel itself in countries where no reprocessing is been carried out.
They are placed in interim storage at plant sites or at reprocessing facilities, before
an eventual final disposal in a geological repository. The liquid high-level wastes
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FACT SHEET
from reprocessing are immobilised in a stable matrix (e.g. borosilicate glass) before
final disposal.
Several countries are evaluating the available options for final disposal. Finland has
already taken a “decision in principle” to construct a geological repository in a site
close to a nuclear power plant. The site is now into detailed evaluation and the
detailed design is under development. Other countries, such as Sweden, France and
United States, are at different stages of this process.
To better comprehend the magnitude of the waste issue one can note that the spent
fuel produced from all the world’s reactors in a year, even without reprocessing,
would fit in a structure the size of a soccer field with a depth of 1.5 m. When the
actual amount of spent nuclear fuel produced globally every year (12 000 tonnes) is
contrasted with the 25 billion tonnes of carbon waste released directly into the
atmosphere every year from fossil fuels, the amount of nuclear waste seems
relatively small.
21. Accidents involving radiation sources used in medicine or industry can
occur in countries without the adequate infrastructure to cope with the
consequences. What is being done to avoid these types of tragedies?
A21. Short Answer:
The IAEA recommends that the appropriate infrastructure, both legal and technical,
should be established in any country dealing with nuclear energy, even if only with
small radiation sources. And the IAEA is assisting many developing countries in
establishing such an infrastructure through its Technical Cooperation Program. In the
event of a radiological emergency, the IAEA is ready to assist, upon request, and
has assisted any country that is in urgent need.
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FACT SHEET
Explanation:
The IAEA has established an Incident and Emergency Centre that receives requests
and coordinates the provision of assistance to Member States in the case of a
nuclear or radiological emergency.
These services have been used several times, in recent years, for events related to
loss of radiation sources, finding of abandoned “orphaned” sources, and
overexposures of individual workers and medical patients.
With the help of organizations and personnel from more developed countries, the
IAEA has been able to coordinate such emergency assistance. This has included
providing support in regaining control of the situation, evaluating the doses to
affected personnel, evaluating the possible measures to be taken and providing
medical treatment, when necessary.
Once an emergency is under control, an IAEA technical report has usually been
prepared both to keep an historic account of the facts and to share the lessons
learned with the international community. The final aim is to avoid similar events in
the future.
22. There is a large volume of radioactive material being transported in Europe
and around the world. What are the risks for the other vehicles and the
population that come close to these materials?
A22. Short Answer:
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FACT SHEET
Experience has demonstrated that the risk involved in the transportation of
radioactive material is very low; much lower than the risks associated with the
transport of other dangerous goods. With more than twenty million shipments made
every year, no major accident has occurred in which radiation was spread to the
environment or posed some risk to the population or the workforce. The few cases of
injuries were due to mechanical factors associated with the accident rather than from
the radioactive nature of the shipment.
Explanation:
Transportation of radioactive materials is only a small fraction (less than 2%) of all
dangerous goods transported every year. And those are already a minor fraction
(less than 0.02%) of all shipments. Since 1961, the IAEA has developed Regulations
for the Safety Transport of Radioactive Materials (Requirements-TS-R-1), which has
been consistently revised and updated (2 year cycle). These regulations have been
adopted, essentially, by all countries and by regional and international transport
organisations. The adoption has been either directly or by reference, and therefore,
became mandatory for all international shipments by rail, air or sea transportation.
These regulations, and the additional associated guidance material developed later,
are based upon two principles: i) they formulate “what” is to be achieved, rather than
“how” it has to be achieved. ii) the burden of safety is put, as far as practicable, upon
the packing that contains the radioactive material by a safe design containing
multiple barriers - and the limitation of the transported quantities, not on the carrier or
their procedures.
The first principle relies on designers, fabricators and users to demonstrate that the
packages satisfy the regulatory standards. The second principle minimises the
contribution to safety by the carrier, but does not remove from the carrier or the
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FACT SHEET
transport workers the responsibility to treat radioactive material consignments with
the requirements of the regulations.
Source: www.iaea.org
For more information contact;
National Nuclear Regulator
Communications & Stakeholder Relations Office
Tel: (+27) 12 674 7100/09
Fax: 0865884450
Email: enquiry@nnr.co.za
Website: www.nnr.co.za
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