www.uic.com.au/nip60.htm
Small Nuclear Power Reactors UIC Nuclear Issues Briefing Paper # 60 April 2004 * There is revival of interest in small and simpler units for generating electricity from nuclear power, and for process heat. As nuclear power generation has become established since the 1950s, the size of reactor units has grown from 60 MWe to more than 1300 MWe, with corresponding economies of scale in operation. At the same time there have been many hundreds of smaller reactors built both for naval use (up to 190 MW thermal) and as neutron sources, yielding enormous expertise in the engineering of deliberately small units. Today, due partly to the high capital cost of large power reactors generating electricity via the steam cycle and partly to consideration of public perception, there is a move to develop smaller units. These may be built independently or as modules in a larger complex, with capacity added incrementally as required. Economies of scale are provided by the numbers produced. There are also moves to develop small units for remote sites. The most prominent modular project is the South African-led consortium developing the Pebble Bed Modular Reactor of 110 MWe. A US-led group is developing another design with 285 MWe modules. Both drive gas turbines directly, using helium as a coolant and operating at very high temperatures. They build on the experience of several innovative reactors in the 1960s and 1970s. Generally, modern small reactors for power generation are expected to have greater simplicity of design, economy of mass production, and reduced siting costs. Many are also designed for a high level of passive or inherent safety in the event of malfunction*. Some engineered systems operate passively, eg pressure relief valves. Inherent or full Passive safety depends only on physical phenomena such as convection, gravity or resistance to high temperatures, not on functioning of engineered components. Some are conceived for areas away from transmission grids and with small loads, others are designed to operate in clusters in competition with large units. US Congress is now funding research on both small modular nuclear power plants (assembled on site from factory-produced modules) and advanced gas-cooled designs (which are modular in the sense that up to ten or more units are progressively built to comprise a major power station). A US DOE report in 2001 considered nine designs which could possibly be deployed by 2010. Already operating in a remote corner of Siberia are four small units at the Bilibino co-generation plant. These four 62 MWt (thermal) units are an unusual graphite-moderated boiling water design with water/steam channels through the moderator. They produce steam for district heating and 11 MWe (net) electricity each. They have performed well since 1976, much more cheaply than fossil fuel alternatives in the Arctic region. There was also an Army program for small reactor development and some successful small reactors from the main national program commenced in the 1950s. One was the Big Rock Point BWR of 67 MWe which operated for 35 years to 1997. Of the following, the KLT-40 is a design with conventional pressure vessel plus external steam generators (PV/loop design). The others mostly have the steam supply system inside the reactor pressure vessel ('integral' PWR design). All have enhanced safety features relative to current PWRs. The Russian KLT-40 is a reactor well proven in icebreakers and now proposed for wider use in desalination and, on barges, for remote area power supply where it produces 30-35 MWe (net) as well as heat. While these are designed to run 3 years between refuelling it is envisaged that they will be operated in pairs to allow for outages, perhaps with on-board refuelling capability and spent fuel storage. At the end of a 12-year operating cycle the whole plant can be taken to a central facility for overhaul and storage of spent fuel. Although the reactor core is normally cooled by forced circulation, the design relies on convection for emergency cooling. Up to 35 MWt can be utilised for desalination in addition to the electrical output. A smaller Russian PWR unit under development is the ABV-6M, with 38 MW thermal, 12 MWe output. It is compact, with integral steam generator and enhanced safety. The whole unit of some 600 tonnes will be factory-produced for ground or barge mounting. The CAREM (advanced small nuclear power plant) being developed by CNEA and INVAP in Argentina is a modular 100 MWt /27 MWe pressurised water reactor with integral steam generators designed to be used for electricity generation (27 MWe or up to 100 MWe) or as a research reactor or for water desalination. CAREM has its entire primary coolant system within the reactor pressure vessel, self-pressurised and relying entirely on convection. It is a mature design which could be deployed within a decade. On a larger scale South Korea's SMART (System-integrated Modular Advanced Reactor) is a 330 MWt pressurised water reactor with integral steam generators and advanced safety features. It is designed for generating electricity (up to 100 MWe) and/or thermal applications such as seawater desalination. The design life is 60 years, with a 3-year refuelling cycle. A one-fifth scale plant (65 MWt) is being constructed, for operation in 2007. The Japan Atomic Energy Research Institute (JAERI) is developing the MRX, a small (50-300 MWt) integral PWR reactor for marine propulsion or local energy supply (30 MWe). Technicatome in France has developed the NP-300 PWR from submarine power plants and aimed it at export markets for power, heat and desalination. It can be built for applications of 100 to 300 MWe or more with up to 500,000 m^3/day desalination. The Chinese NHR-200 is a simple and robust 200 MWt integral PWR used for district heating or desalination. Spent fuel is stored around the core in the pressure vessel. The International Reactor Innovative & Secure (IRIS) is being developed by Westinghouse as an advanced 3rd generation reactor. IRIS-50 is a modular 50 MWe or more pressurised water reactor with integral primary coolant system and circulation by convection. Enrichment is 5% with burnable poison and fuelling interval of 5 years (or longer with higher enrichment).
Liquid Metal cooled Fast Reactors The Encapsulated Nuclear Heat Source (ENHS) is a liquid metal-cooled reactor of 50 MWe being developed by the University of California. The core is in a metal-filled module sitting in a large pool of secondary molten metal coolant which also accommodates the separate and unconnected steam generators. Fuel is a uranium-zirconium alloy with 13% U enrichment (or U-Pu-Zr with 11% Pu) with a 15-year life. After this the module is removed, stored on site until the primary lead (or Pb-Bi) coolant solidifies, and it would then be shipped as a self-contained and shielded item. A new fuelled module would be supplied complete with primary coolant. The ENHS is designed for developing countries but is not yet close to commercialisation. A related project is the secure transportable autonomous reactor for hydrogen production - STAR-H2. It a lead-cooled fast neutron modular reactor with passive safety features. It uses U-transuranic nitride fuel in a cassette which is replaced every 15 years. The reactor heat at 780C is conveyed by a helium circuit to drive a separate thermochemical hydrogen production plant, while lower grade heat is harnessed for desalination (multi-stage flash process). Any commercial electricity generation would be by fuel cells, from the hydrogen. For both these concepts, regional fuel cycle support centres would handle fuel supply and reprocessing, and fresh fuel would be spiked with fission products to deter misuse. Complete burnup of uranium and transuranics is envisaged in STAR-H2, with only fission products being waste. Russia has experimented with several lead-cooled reactor designs, and has used lead-bismuth cooling for 40 years in its submarine reactors. Pb-208 (54% of naturally-occurring lead) is transparent to neutrons. A significant Russian design is the BREST fast neutron reactor, of 300 MWe or more with lead as the primar...
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