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Transcript of Lifetime extension
In 2011, UK energy demand was 353.7 TWh; 62.7 TWh from nuclear .
Government targets to reduce GHG emissions by 34 % by 2020.
Currently cost of electricity from renewable sources expensive in comparison to nuclear.
Currently 10 operating nuclear plants (16 reactors) with 8 of these to close by 2025.
Plans to build 6 new plant – 2 operating by 2020.
Loss of 8 plant equivalent to 50.16 TWh or 8360 onshore wind turbines.
Renewable sources not competitive, generating only 34.4 TWh in 2011 and cost of electricity is high. Should nuclear reactors have predicted lifetimes of should they be allowed extensions? Amiir Asri
Daniel Thompson Safety risks of old reactors In the 1950s, world turned its attention to harnessing the power of nuclear energy in a controlled manner.
It was not until 1970s that detailed analyses and large scale testing of reactors were enforced, ensuing the 1979 melt down of the Three Mile Island reactor.
Overall, extensive studies on nuclear reactors ensured that accidents were avoided: in over 14,500 cumulative reactor years of commercial operation in 32 different countries, only 3 major disasters were recorded for the industry. Questions? Thank you for listening Lifetime extension Plant is taken offline and site dismantled and cleared. Any contaminated waste is sent to waste repository. Site is closed off and any buildings onsite blocked to prevent anyone from getting in. Plant allowed to continue operating. Retrofitted with better equipment. However, plant will eventually be decommissioned. Despite this, if funds are unavailable for decommissioning, this is a favourable option. Reactor facts Average age: 27 years
Usual life time: 40 years (licensed) but can be increased to 60.
Modern reactors (generation III+) more mechanised.
Lifetime extensions applicable to most reactor types: BWR, PWR, PHWR, GCR etc.
In the UK, EdF planning extensions of 7 to 70 years; review of all reactors every 10 years by Office for Nuclear Regulation
In the USA 70% of reactors received licensing for extension. The Three Mile Island accident occurred due to the failing of a relief valve which allowed large amounts of reactor coolant to escape.
This mechanical failure, combined with ambiguous control room indicators, caused a partial nuclear meltdown.
The accident was rated 5 on a 7 step international scale for nuclear accidents.
The age of the reactor at the time of accident was three months. The Chernobyl disaster was ultimately caused by an unexpected power surge which caused the reactor vessel to rupture.
This was followed by a series of steam explosions which caused the graphite moderator of the reactor to be exposed to air and ignite.
The accident was rated 7 on a 7 step international scale.
The age of the reactor at the time of the accident was 30 years. Fukushima accident was caused, ultimately, by a Tsunami, which lead to a series of equipment failures.
The accident was rated 6 on a 7 step international scale.
Age of reactor at the time of accident was 40 years. However Improvements Fukushima, 2012 Three Mile Island, 1979 Chernobyl, 1986 For example 1979 1986 2012 New Reactor are better designed to run under safe operating limits and conditions, as set out as part of the license defined by the Nuclear Regulatory Commission (NRC) in 1986. Old reactors are also operated under this act, however they are not as economical.
The use of Probability Risk Assessment (PRA) technology was increased in all regulatory matters as introduced from 1995. Additionally, the newly built reactors included design features previously not present such as:
1) Standardised design for each type to expedite licensing, reduce capital cost and reduce construction time.
2) Simpler and more rugged design, making them easier to operate and less vulnerable to operational mishaps.
3) Higher availability and longer operating life - typically 60 years,
4) Further reduced possibility of core melt accidents.
5) Substantial grace period, so that following shutdown the plant requires no active intervention for (typically) 72 hours.
6) Resistance to serious damage that would allow radiological release from an aircraft impact.
7) Higher burn-up to use fuel more efficiently, reduce the amount of waste.
8) Greater use of burnable absorbers ("poisons") to extend fuel life. In 1998 NRC made PRA methods to address complex safety issues in newly built reactors to address issues such as:
1) Station Blackouts
2) Anticipated Transients without Scram
3) Pressurised Thermal Shock
These methods were not as effective when applied to older reactors. Fuel Cladding: Old reactors have a greater probability of fuel failures, even with replaced cladding, than new builds.
Heavy steal reactor vessel: Ranges from 9'' to 1 ft thick with primary cooling water system piping – The integrity vessel in old reactors cannot be guaranteed as strongly as in new builds.
Containment building: Heavily reinforced structure of concrete and steel (up to several feet thick) surrounding the reactor. Designed to contain radioactivity that may be released from reactor system in the unlikely event of a serious accident – Design for current reactors uses more accurate analysis of seismic loading, bending moments and additional support. However, new containment's can also be built around old reactors.
Cooling water supply: Safety systems require electricity to operate, hence emergency diesel generators required to provide immediate back-up power – New reactor builds have complex, diverse and multiple networked water supply for safety system to ensure water supply. This assurance is limited in old reactors. Causes of reactor failure Imbalance So what do we do with the old reactors? Pros and cons Decommission
Large amounts of waste produced
Long time scale for building new plant (authorisation, licensing and construction)
Better/advanced technology Extension
Keep existing facilities operating for additional 5-10 years (regulation check period)
Not applicable to all reactors e.g. Magnox
Political Extension v.s. decommissioning How is lifetime extension decided and why? Current situation So which one should we pick? Conclusion Future developments The role of modeling Simulations of fuel element/bundle for different reactor types used to compute temperature, pressure and velocity distribution.
Important as flow regime of coolant can result in hot spots and poor mixing, especially as complex flow phenomena have been observed (experimentally) in rods; patterns not exhibited in pipe flow such as transverse repulsion and large scale vortices.
Used to help design more efficient and resilient equipment. Market for life extension
Not yet an issue in countries building new reactors
Fixed lifetime in some countries (Japan) while others allow for extension.
UK has no set maximum lifetime
In France reactors beyond 40 years can be extended following Court of Audit decision
Economically, extension more feasible than building new reactors and other forms of energy due to capital and timescale for national grid connection. Decisions consists of 3 phases and take into consideration: regulations, environmental, economic, governmental and public concerns
Phase 1: Feasibility and scope based on assessments of structures, facilities, licensing requirements and economics.
Phase 2: Detailed evaluation and license application if found to be feasible.
Phase 3: Implementation. Extension Decommission Operating cost of nuclear plant low compared to capital and decommissioning
Failure rate could increase as it is difficult to track individual equipment and component failure rates.
Many new breed of reactors not yet online, halting building of new reactors and plants. Not all reactors can be extended
Large capital cost (which may not be fully available) and very lengthy time span
Time to build new reactor is 10 years
large carbon footprint for building new plant Complex with many steps and variables to consider Life extension individual and specific as no two reactors are the same
Increase in energy demand which needs to be met
Can extend energy production of plant
Standard practice in USA and France
Older plants and reactors can be made as competitive and efficient as newer designs
Complex process but cheaper and shorter to complete than decommissioning Other options Build a new nuclear plant
Although the cost of operating a Plant Life Extension (PLEX) program is considerably lower than the capital cost of building a new plant, building new reactors have the added benefit of enhanced technological features that may have improved safety, reliability, operability and maintainability. Alternative Sources of Energy
World will need twice as much electricity in 2050 as it does today. Current situation: Most of the world’s electricity comes from coal (40%) and gas (20%) with hydroelectric (16%) and nuclear (13%).In Europe most of new generating capacity being added today is low-carbon wind.To meet objective set by world leaders in Copenhagen in 2009 to limit average increase in global temperatures to 2°C, alternative low-carbon sources need to be looked:HydroWindBiofuelsSolar PowerCoal and gas burned in plants that can capture and store the carbon emissions (CCS) Alternative sources of energy The use of wind power is increasing at an annual rate of 20%, with a worldwide installed capacity of 238,000 megawatts (MW) at the end of 2011, and is widely used in Europe, Asia and the United States.Since 2004, photovoltaics passed wind as the fastest growing energy source, and since 2007 has more than doubled every two years. At the end of 2011 the photovoltaic (PV) capacity was 67,000 MW and PV power stations are popular in Germany and Italy.Solar thermal power stations operate in the USA and Spain, and the largest of these is the 354 MW SEGS power plant in the Mojave Desert.The world’s largest geothermal power installation is the Geysers in California, with a rated capacity of 750 MW. Brazil has one of the largest renewable energy programs in the world, involving production of ethanol fuel from sugarcane, and ethanol now provides 18% of the country’s automotive fuel. Technology developments in the nuclear industry The potential benefits of building new reactors with evolutionary design changes may outweigh the decision to extend lifetime of ageing reactors.Four main quantum leaps that can be made to overcome current nuclear energy challenges:The ultimate nuclear reactor should be intrinsically, with a probability of a core melt equal to zero even in the case of a loss-of-coolant accident.These reactors should generate fewer nuclear wastes than light water reactors, and should serve for recycling and transmuting Generation II,III and III+ wastes. Reactors should be versatile and serve various types of applications, i.e. electricity generation, combined electricity/heat production, hydrogen production or desalination seawater.Some of these reactors should be modular, with a power-per-unit to spread and smooth out the replacement of current nuclear reactors, for industrial and economic reasons. Two categories of nuclear reactor:
Conventional Nuclear Reactors (Generation I and II reactors)
Advanced Nuclear Reactors (Generation III and IV reactors)
Generation I reactor (early prototype of power reactor)
Generation II reactor (most current nuclear power plants)
Generation III reactor (evolutionary improvements of existing designs)
Generation IV reactor (technologies still under development)
Generation III reactors have the following desired features:
Higher availability and longer operating life-typically 60 years
Reduced possibility of core melt accidents
A simpler and more rugged design, making them easier operate and less vulnerable to operation upsets
Higher burn-up to reduce fuel use and the amount of waste; and burnable absorbers (“poisons”) to extend fuel life