Future Nuclear Reactors Options for Future Reactors New Light Water Reactors

1. Future Nuclear Reactors • Options for Future Reactors • New Light Water Reactors • High-Temperature Gas-Cooled Reactors • Liquid-Metal Reactors • Prospects for New Reactors Future Reactors

2. Are Present Reactors Safe Enough? • Three Mile Island, Chernobyl • Immediate response: redundant components → complexity and cost • Concept of inherent or passive safety: immutable physical laws • Inherent →transparently passive; passively stable; transparently passively stable; • Generation III + Generation IV: additional goals – more efficient, less costly. Future Reactors

3. Categories of Future Reactors ABB=Asea Brown Boveri; AECL=Atomic Energy of Canada, Ltd; CE=Combustion Engineering; GA=General Atomics; GE=General Electric; W=Westinghouse. Future Reactors

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7. Characteristic Features • Standardized design: licensing, capital cost, construction time • Simpler more rugged design: easier to operate, less vulnerable to human factor • Higher availability, longer operational life ~ 60 yr • Reduced possibility of core melt accidents • Minimal effect on the environment • Higher burn-up: reduced fuel use and waste • Burnable absorbers: extent fuel life Future Reactors

8. Design Features • Evolutionary LWRs: refined version of the current LWRs • Mid-Sized LWRs: substantial changes, passive safety • Other LWRs: radical changes, international aspect Future Reactors

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10. H = 21 mD = 7 mLife = 60 yrSingle forgingExternal recirculation loops has been eliminatedNo nozzles > 2 inWelds is reduced by 50 % All of the pipings and pipe supports in the primary system have been eliminated → biggest source of occupational exposure has been elim. Future Reactors

11. Cobalt has been eliminated from the design • The steel used in the primary system is made of nuclear grade material (low carbon alloys) which are resistant to integranular stress corrosion cracking • Fine Motion Control Rod Drives (FMCRD) • The Control and Instrumentation (C&I) systems use state of the art digital and fiber optic technologies • Multiplexing and fiber optics have dramatically reduced the amount of cabling in the plant • The entire plant can be controlled from one console • Advanced plant layout • External recirculation system → internal • Simplified active safety system Future Reactors

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13. APR600 Passive safety systems: only natural forces, such as gravity, natural circulation and compressed gas. No pumps, fans, diesels, chillers, or other rotating machinery The passive safety systems include passive safety injection, passive residual heat removal and passive containment cooling. The passive safety systems are significantly simpler. The AP1000 has 50 percent fewer valves, 83 percent less piping, 87 percent less control cable, 35 percent fewer pumps and 50 percent less seismic building volume than a similarly sized conventional plant. These reductions in equipment and bulk quantities lead to major savings in plant costs and construction schedules. Future Reactors

14. Mid-sized Passive Light Water Reactors • The emergency cooling systems are simpler and more passive, relying on large pools of water fed by gravity, rather than on flow sustained by pumps. • Emergency electric power requirements are reduced so that they can be satisfied by batteries rather than emergency diesel generators. • Reactor power densities are reduced. • The designs have been simplified to reduce costs and sources of possible operating or maintenance error. Future Reactors

15. PIUS PIUS could be called a very innovative LWR. The PIUS concept was invented by Kåre Hannerz, who was with ASEA/Atom and then with Asea-Brown-Boveri (ABB-Atom). The term PIUS is an acronym for ”process inherent ultimate safety,” and it is also sometimes referred to as the Secure-P reactor. Future Reactors

16. BUILT-IN SAFETY • The core is submerged into a pool with highly borated water • Primary loop is isolated from the pool by hydraulic locks • The core power output must always be kept at a level to avoid dry-out • Amount of water is enough for 1 week Future Reactors

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18. Very-High-Temperature Reactor (VHTR) Characteristics • He coolant, direct cycle • 1000°C outlet temperature • 600 MWth, nominally based on GT-MHR • Coated particle fuel • Solid graphite block core • High thermal efficiency • Hydrogen production • Passive safety Reactor physics issues • Fuel double heterogeneity • Stochastic behavior of pebble movement (for PBR variant) • Graphite scattering treatment Future Reactors

19. Very-High-Temperature Reactor (VHTR) • VHTR is a grapahite moderated, He-cooled reactor with once-through uranium fuel cycle • High core outlet temperature of 1000 C enables H production or process heat for the petrochem industry • The core could be a prismatic block or a pebble-bed • Can adopt U/Pu fuel cycles and waste minimization • Can produce heat and may incorporate electricity generation Future Reactors

20. Gas-Cooled Fast Reactor (GFR) • Characteristics • He (or SC CO2) coolant, direct cycle gas-turbine • 850°C outlet temperature • 600 MWth/288 MWe • U-TRU ceramic fuel in coated particle, dispersion, or homogeneous form • Block, pebble, plate or pin core geometry • Waste minimization • Efficient electricity generation • Reactor physics issues • Core configuration dependent • Neutron streaming • Data for actinides and fuel matrix candidate materials Future Reactors

21. Gas-Cooled Fast Reactor (GFR) • GFR is a fast-spectrum He-cooled reactor with closed fuel cycle. • High outlet temperature allows delivery of electricity, H, or process heat with high efficiency • Uses direct Brayton cycle gas turbine for high thermal efficiency • Fuel: composite ceramic fuel, or advanced fuel particles • Core - prismatic blocks, pin- or plate based fuel assemblies • Has integrated, on-site spent fuel treatment and refabrication plant Future Reactors

22. Lead-Cooled Fast Reactor (LFR) Characteristics • Pb or Pb/Bi coolant • 550°C to 800°C outlet temperature • U-TRU nitride or Zr-alloy fuel pins on triangular pitch • 120–400 MWe • 15–30 year core life • Core refueled as a cartridge • Distributed energy generation • Transportable core • Passive safety and operational autonomy Reactor physics issues • Data for actinides, Pb, Bi • Spectrum transition at core edge • Reactivity feedback coefficients Future Reactors

23. Lead-Cooled Fast Reactor (LFR) • LFR is a fast-spectrum led or lead/Bi liquid metal-cooled reactor and a closed fuel cycle for efficient conversion of fertile uranium and managements of actinides • Has a full actinide recycle fuel cycle • Fuel is metal or nitride-based, containing fertile uranium and transuranics • Could be made small (50-150 MWe), as a “battery” - a long-life, factory fabricated core - replaceable reactor module, with very long refueling interval (15-20 yrs), good for developing countries. Future Reactors

24. Sodium-Cooled Fast Reactor (SFR) Characteristics • Sodium coolant, 550°C Tout • 150 to 1500 MWe • U-TRU oxide or metal-alloy fuel • Hexagonal assemblies of fuel pins on triangular pitch • Homogenous or heterogeneous core • Consumption of LWR discharge actinides • Efficient fissile material generation Reactor physics issues • Actinide data • Full-core transport effects • Spectral transition at core periphery and beyond • Accurate modeling of expansion feedback Future Reactors

25. Sodium-Cooled Fast Reactor (SFR) • SFR is a fast-spectrum sodium-cooled reactor with a closed fuel cycle for efficient management of actinides and conversion of fertile U. • Useful for management of Pu and other actinides • Could also produce electricity Future Reactors

26. Supercritical-Water-Cooled Reactor (SCWR) Characteristics • Water coolant at supercritical conditions (~25 MPa) • 510°C outlet temperature • 1700 MWe • UO2 fuel, clad with SS or Ni-based alloy • Square (or hex) assemblies with moderator rods • High efficiency, compact plant • Thermal or fast neutron spectrum Reactor physics issues • Similar to BWR’s • Increased heterogeneity • Strong coupling of neutronics and T-H • Neutron streaming Future Reactors

27. Supercritical-Water-Cooled Reactor (SCWR) • SCWR is a high-temperature, high-pressure water-cooled reactor that operates above the thermodynamic critical point of water (374 C, 22.1 Mpa or 705 F, 3208 psia). • The supercritical water coolant enables a thermal efficiency about one-third higher than current LWRs • The fuel is uranium oxide • SCWR is primarily designed for efficient electricity production, with an option for actinide management • Can operate as an open fuel cycle with a thermal spectrum or a as a closed cycle with a fast spectrum and reprocessing facility Future Reactors

28. Molten Salt Reactor (MSR) Characteristics • Molten fluoride salt fuel • 700–800°C outlet temperature • 1000 MWe • Low pressure (<0.5 MPa) • Circulating actinide-bearing fuel • Graphite core structure to channel flow • Actinide consumption • Avoids fuel development and fabrication Reactor physics issues • Evolution of mobile-fuel composition • Modeling of nuclear, thermal, and physio-chemical processes • Delayed neutron precursor loss Future Reactors

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30. Are Present Reactors Safe Enough? General Considerations in Reactor Safety Design Goals The most complex challenge has been to assure that the flow of coolant to the core is maintained under any accident circumstances, so that the decay heat is removed. Attempts to guarantee this have led to the installation of alternative cooling paths and redundant components. For example, several independent diesel generators provide electric power to the pumps should the outside electricity supply fail. A profusion of pipes, valves, and control systems has evolved from the search for greater safety, often introduced by retrofitting an existing reactor. This has added to the complexity and cost of the reactors, and it puts extra burdens upon the operators. Future Reactors

31. Terminology for ”Safe” Reactors The terms ”inherent” and ”passive” are intended to suggest that the safety of the reactor will depend on immutable physical phenomena rather than on the proper performance of individual components or correct actions by reactor operators. In the extreme version of the concept, in a passively safe reactor all operators could become incapacitated and all external electricity and water could be shut off, and the reactor would still turn itself off and gradually cool with no damage. Future Reactors

32. This terminology has been widely used and also widely criticized. The objections have had several strands: • Inherent or passive safety is a matter of degree rather than a totally new departure. A negative temperature coefficient or a negative void coefficient is a passive safety feature, and therefore most existing reactors already have passive safety features. • The terms are misleading because they seem to suggest that an accident would be totally impossible, while in fact one can find circumstances in which any given reactor might fail, if arbitrarily improbable scenarios are permitted. • The terms could appear to have a prejudicial aspect, because they could seem to suggest that existing reactors are not safe. Future Reactors

33. The criticisms have had some force, and to defuse them alternative words have sometimes been suggested. It has has been introduced the term transparently passive as an equivalent to ”inherent” and has also suggested the use of the terms ”passively stable” and the still more comprehensive ”transparently passively stable”. Whatever words are used, however, the concept is clear: it is safer to rely on systems that depend only upon basic physical processes (e.g., gravity or thermal expansion) rather than on the consistent good performance of equipment and operators. Future Reactors

34. Categories of Future Reactors ABB=Asea Brown Boveri; AECL=Atomic Energy of Canada, Ltd; CE=Combustion Engineering; GA=General Atomics; GE=General Electric; W=Westinghouse. Future Reactors

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38. Evolutionary LWRs. These are essentially refined versions of current large light water reactors. Mid-sized passive LWRs. The two reactors listed in the table incorporate substantial changes in the reactor configuration, compared to present LWRs, but the basic principles are the same. The chief differences involve increased use of passive safety features, especially in the system for emergency core cooling. Other LWRs. The two reactors listed in this category represent fairly radical departures from standard designs. The design of reactors is becoming more of an international enterprise than in the past. The original PIUS design was by ABB-Atom, and the SIR reactor was originally a United Kingdom – United States project. Both now involve the same parent company, Asea Brown Boveri (ABB) Future Reactors

39. Advanced non-LWRs. These include an array of diverse designs. The GT-MHR is a recent variant of the high-temperature, gas-cooled reactors being studied by the General Atomics Company. The ALMR is a sodium-cooled, fast neutron reactor. CANDU-3 is an advanced and somewhat smaller version of the heavy water reactors developed in Canada. Of these reactors, the PIUS, GT-MHR, and ALMR reactors have design features that their proponents claim make them inherently safe. It is less common for the proponents of the various other reactors to make equivalently strong claims, although they quote very low accident probabilities and stress passive safety features, especially in the case of the advanced passive LWRs. Future Reactors

40. NEW LIGHT WATER REACTORS Evolutionary Light Water Reactors Two 1315-MWe advanced boiling water reactors (ABWRs) are under construction in Japan, in a collaboration of General Electric, Hitachi, and Toshiba; the reactors are scheduled to go on-line in 1996 and 1997. Four 950-MWe Combustion Engineering System 80 reactors are under construction in South Korea; these are a preliminary and smaller version of the System 80+ under development ABB-CE. Westinghouse is designing an advanced PWR (APWR) in collaboration with Mitsubishi. Although the General Electric ABWR is under construction in Japan, no new reactor has yet received NRC approval for construction in the United States. Future Reactors

41. As implied by the designation ”evolutionary,” the differences between the ABWR and previous BWRs are not striking. On the basis of its probabilistic safety assessment, GE projects a core damage probability of less than 10-6 /RY and a probability for an off-site dose of more than 0.25 Sv of 2x10-9. In addition, the projected construction time is only 48 months and the overall cost well below that of recent LWRs.. France began construction of next-generation 1455-MWe PWRs, the so-called N4 series. Four units were under construction in 1995, and these are scheduled to go into operation in 1996 through 1998. The one new reactor being put into operation in the United Kingdom is the 1188-MWe Sizewell B reactor, a PWR being put into operation in 1995. In addition, there is a joint French – German program to develop a future 1500-MWe ”European Pressurized Water Reactor” (EPR), but the timing of a first order for an EPR is not yet established. Future Reactors

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44. Mid-sized Passive Light Water Reactors General Considerations The ”advanced” or ”innovative” LWRs that are under consideration are smaller and simpler than the current generation of LWRs. In the U.S., two designs have been under development with the support of the DOE and the Electric Power Research Institute (EPRI): the Westinghouse AP600 and the General Electric SBWR. Both reactors are about 600-MWe in size. Future Reactors

45. Special features of this category of reactors are: • The emergency cooling systems are simpler and more passive, relying on large pools of water fed by gravity, rather than on flow sustained by pumps. • Emergency electric power requirements are reduced so that they can be satisfied by batteries rather than emergency diesel generators. • Reactor power densities are reduced. • The designs have been simplified to reduce costs and sources of possible operating or maintenance error. Future Reactors

46. PIUS PIUS could be called a very innovative LWR. The PIUS concept was invented by Kåre Hannerz, who was with ASEA/Atom and then with Asea-Brown-Boveri (ABB-Atom). The term PIUS is an acronym for ”process inherent ultimate safety,” and it is also sometimes referred to as the Secure-P reactor. Future Reactors

47. Important five criteria on nuclear power plants which could make it easier for nuclear power to meet the demands : 1. Good economy at moderate ratings. The 1000 MWe nuclear units now being built can rarely be accommodated in the grid of a developing nation, and a unit of this rating is also sometimes too large in an industrialized country. 2. Minimum of high-technology hardware. This is a fundamental requirement of a developing country in the process of building up its overall technological infrastructure. The availability of foreign currency and credits sets a limit to what can be achieved. 3. Simple, reliable operation. Experienced and skilled technicians are another commodity in short supply, on which the introduction of nuclear power must not make disproportionate demands. Future Reactors

48. 4. Inherent, passive safety. The prevention of large releases of radioactivity must not be dependent on the performance of active, failure-prone systems and components or on operator judgement. Adoption of this principle will lead to: • simple plant design, with few systems and components and a minimal requirement for foreign currency. • simple operation, with a minimum of interference from safety- related considerations. • greater freedom in siting. • virtual elimination of the risk of core melt-down, even under the adverse conditions caused by social unrest. • improved confidence of the general public. • 5. Minimum potential for nuclear weapons proliferation. Future Reactors

49. BUILT-IN SAFETY Two design rules have been established, and these jointly guarantee the integrity of the core and com- pliance with the PIUS principles: A. The core is submerged in water in all situations for an extended period of time following any inci- dent, by providing a sufficient supply of water for submergence even under adverse conditions indepen- dently of the actions of the operat- ing staff. The required time has been set, somewhat arbitrarily, at one week. B. The core power output must always be kept at a level at which the submerging water provides ade- quate cooling (i.e. avoids dry-out conditions). These rules must be satisfied under all conditions, without reliance on any mechanical or electrical equipment or on operator action. Future Reactors

50. The PIUS reactor is a light water reactor in which the reactor core and the primary system are submerged in a pool of cold borated water contained in a large concrete vessel. Typically, this vessel might have a 13-m inside diameter (17-m outside diameter) and a 35-m height. The pool, with a much greater volume than the primary loop, contains cold, highly borated water and has no function during normal operation. However, it is the key to the avoidance of serious consequences in the case of a reactor malfunction. In normal operation, the water in the primary system is isolated from the borated pool by ”very clever hydraulic locks”. These locks are essentially interfaces between the two water supplies, maintained by careful control of the pressure of the water in the primary loop. There is one such lock below the core and one above it. They are normally closed, and there is no interchange between the water in the primary loop and in the pool. Future Reactors