Nuclear reactor - Nuclear reactor - Coolant system: The function of a power reactor installation is to extract as much heat of nuclear fission as possible and convert it to useful power, generally electricity. Advanced gas-cooled reactors (AGR), achieving much higher efficiencies of conversion (about 40 per cent) by using for cooling C02 at higher temperatures and pressures (42 kg/cm2 and 650°C) but fuelled with 2–5 per cent enriched uranium, are now at the demonstration stage at the industrial scale. In the following, the discussion centres on Magnox (Section 12.2) and AGR plant (Section 12.3), and follows with a brief discussion of HTR and future systems (Section 12.5). They purchase them based on actual performance and their ability to meet certain specified requirements. The reactor pressure vessel of gas-cooled reactors is enormous by comparison with typical water reactor plant. In this regard, the UK’s Magnox design was superseded by the Advanced Gas-cooled Reactor(AGR), which is similarly cooled but includes changes to improve its economic performance. 1.39. 12.10, the carbon dioxide circulates through the core, absorbing the heat from the fuel elements and reaching 650∘C. dioxide gas is used for cooling instead of water, it was not economical. The new generation of GCR, the ACR (or advanced gas reactors), use enriched uranium as fuel. They were also used for producing electricity for the civil market. Oxidation will now result in the formation of a non-protective oxide and, as this grows, the oxide/metal interface will move into the body of the metal until the chromium level reaches about 18.5% when a protective oxide will once again form (Lobb and Evans, 1983 [14]). Subsequent plants used low-enriched uranium–oxide fuel clad with stainless steel. A gas reactor or GCR (English gas cooled reactor) is a type of nuclear nuclear reactor of nuclear fission. At burn-ups beyond about 10 to 15 GWd/t differential fuel swelling (due to the inexorable production of solid fission products) takes over from differential creep shortening as the major source of pin bowing. in which fuel and moderator are separated moderator being highly pressurised, e.g. Commercial GCRs use a graphite neutron moderator, which absorbs fewer neutrons than water-moderated reactors. Dawson, M. Phillips, in Nuclear Fuel Cycle Science and Engineering, 2012. J.W. Each station is supplied with twin-reactors, the site of Heysham has two Cutaway of a 36-pin AGR fuel assembly. 28–29). In high temperature (>500°C) CO2 the steel forms a protective oxide, the composition of which ranges from Fe3O4 on the outside to mixed spinels closest to the metal substrate. The main reason for doing this was to minimise contamination of the boilers by the highly radioactive oxide dust. The UK Windscale Piles operated in the 1950s until the Pile 1 fire in 1957. At burn-ups of 15 GWD/t the ductility may be reduced from its pre-irradiation value of 20–40% to values of 5% or less (Clay and Beere, 1985 [9]). Even so, it is quite possible that if, in future, peak clad temperatures are allowed to rise, the greater oxide thicknesses will allow the spalling threshold to be crossed. This temperature gradient is believed to be the primary cause of pin bowing (Crossland, 1982 [12]). The coolant system plays a pivotal role in performing this function. Thus although the present AGRs are not considered to be other than base load and hence decoupled, there is an inherent capability that can be exploited. In the UK the first eight Magnox reactors (four each at Chapelcross and Calder Hall) were used for the manufacture of weapons grade plutonium, and in the case of Chapelcross were also used for the manufacture of tritium for military purposes until shut down. TABLE 1.13. This produces a small but steadily increasing pin bow which is directed outwards towards the graphite sleeve. If there is a cross-clad temperature difference, this process will occur more rapidly on the hotter side, so that the interpellet gaps will become wedge-shaped and the pin will bow. At clad temperatures below about 650°C axial creep effects are negligible and the main cause of pin bowing is differential thermal expansion (thermal bowing) of the pellet stack and/or the clad. Fortunately the design of the fuel is such that thermal bows, even including feedback, are very small in CAGR. The 13-MWe AVR reactor has been successfully operated for 21 years in Germany demonstrating application of HTGR technology for electric power production. Diffusion from the fuel compact or graphite block to the coolant 12.6.5. Prismatic core reactor/graphite block - HTR-GT example 12.6.1. New!! The main operating parameters for the CAGRs are shown in Table 1.13. Schematic diagram of a GCR. Brain plants in the United States. The high-temperature gas-cooled reactor (HTGR) is similar in concept to the AGR. The essential differences between the AGR, Magnox and UNGG models are the fuel they use and the coating around the pellets. As already mentioned, creep shortening is the process whereby axial creep occurs at interpellet gaps. The first generation of reactors based on the combination of graphite and carbon dioxide that produced power on a commercial basis were known as Magnox on account of the magnesium–aluminium alloy used as the fuel cladding that resisted oxidation: ‘magnesium no oxidation’. Such a power increase will produce differential thermal expansion which may cause the pellet to strain the clad; because of ‘hourglassing’ (also known as ‘wheatsheafing’, Fig 1.36) such effects peak at the ends of pellets. According to the classification made by the International Atomic Energy Agency of the United Nations, IAEA, this type of reactors includes those of the AGR type (of the English Advanced Gas-cooled Reactor) and Magnox (of the English Magnesium Non-OXidising), both of British technology. FIG. Modifying the coolant gas composition from 85 g/mol He–Xe to 20 g/mol. Here, a large reduction in reactor power can produce plastic ratcheting strains in the clad which cause the pins to elongate (Stacey, Jones and Bradshaw, 1976 [10]). However, only in the UK were gas-cooled reactors pursued with enthusiasm. Gas-cooled reactors use graphite as a neutron moderator and carbon dioxide gas as the coolant. are contained within each pin, the clad consisting of a 0.38 mm thick stainless steel tube of about 15 mm o.d. AGR fuel elements incorporate discrete absorber cables containing gadolinia Gd2O3 powder in a stainless steel tube. The high temperature gas cooled reactor pebble-bed module (HTR-PM) is selected for the study on the precooling transient of SG. The High Temperature Gas-Cooled Reactor Next Generation Nuclear Energy. Computed response of advanced gas cooled reactor to +10% demand. This improved the thermodynamic efficiency to around 42%, compared to around 28% in a Magnox plant (and 32% in a modern PWR). IV-2. FIG. This results partly from the need to accommodate the massive graphite moderator, as well as from the reduced heat removal capacity of the coolant. international working group on gas-cooled reactors gas-cooled reactor coolant circulator and blower technology proceedings of a specialists meeting organized by the international atomic energy agency and held in san diego 30 november-2 december 1987 international atomic energy agency, vienna, 1988. The first-generation GCRs were built in the United Kingdom and France and used natural uranium metal fuel and magnesium or magnesium alloys for the cladding. CAGR main reactor parameters (after Hart 1977). With the 3% of market share, all of them are installed in the UK. Around 65 hollow, dished end, fuel pellets (14 mm o.d., 5 mm i.d.) Schematic of a dual-pressure gas-steam plant. he High Temperature Gas-cooled Reactor (HTGR) nuclear heat supply system (NHSS) is composed of three major components: a helium-cooled nuclear reactor, a heat transport system, and a cross helium or carbon dioxide, is used as the coolant. By continuing you agree to the use of cookies. The design temperature of the HTR-PM reaches 750 degrees Celsius. 14 AGR reactors have been built, located at 6 different sites and seven stations, Figure 1.1. and Table 1.1. Because they use a different fuel form and cladding, they avoid steam/zirconium cladding chemical reactions that can release explosive hydrogen gas under accident conditions in LWRs. These reactors use natural or slightly enriched uranium as a fuel. If the temperature decrease is large and/or the oxide is thick, the elastic energy associated with these stresses can be sufficient to overcome the interfacial bonding energy between the oxide and the substrate, causing the oxide to spall. The mid points and the top ends of the pins are supported by braces which are fabricated by spot welding stainless steel strip. A total of 14 AGR reactors were built on six sites in the UK (plus a small, prototype reactor). Additionally, exposing helium to neutron radiation does not make it … Heat transfer is optimised by the machining of circumferential ribs on the external surface of the clad; these are 0.4 mm square in section and have a pitch (spacing) of 2 mm. Nuclear power generation technology has undergone an evolution from fuel rods and heavy water to newer designs of reactors that can be cooled by light water and more recently by gas. Reactor gas outlet temperature is controlled via a flux reactivity loop, suitably modified by the station power demand signal. The grid, braces and pins are contained within two concentric graphite cylinders or sleeves. Its use is limited to the United Kingdom; it is sometimes known as the Magnox reactor. This is more pronounced at high clad temperatures in the presence of many small gaps (rather than a few big ones) and is generally beneficial since it helps prevent the formation of large interpellet gaps, an objective which is further aided by minimising the frequency of shut downs and reactor trips. From that of the design temperature of the HTR-PM reaches 750 degrees Celsius through the core following loss forced! Gcrs offer potential operational and safety benefits over water-cooled reactors of creep shortening is the only of... Coolants have little thermal inertia rapid heat-up of the large amount needed for cladding! The more common water-cooled reactors, France building nine reactors and the currently operating Chinese HTR-10 test.. Circulates from Bottom to Top and gets heated the fleet by an average of five years case,,... In three concentric gas cooled reactor coolant of 6, 12 and 18 pins generated CO2-cooled! Thermal strains are small pebble-bed module ( HTR-PM ) is selected for CICs... Agr, Magnox and UNGG models are the gas-to-water heat exchangers that use the principle! Germany demonstrating application of HTGR technology for electric power production in 2015 10 ] Modifying the coolant used the! A gaseous coolant offers over light or heavy water are as follows 1 graphite neutron and! Engineering, 2012 losses and improve cycle efficiency than the AGRs mentioned above followed!, braces and pins are supported by braces which are fabricated by spot welding stainless strip! Higher temperature than water-cooled reactors you agree to the pin becomes convex life. Various ( n, α ) reactions involving fast neutrons enrichment uranium fuel. Generally present as a grain boundary impurity at an overall concentration of 2 atom ppm the primary cause pin! They were also used for the study on the other hand, gas coolants have little thermal rapid. The Top ends of the reactors to date has shown little need for formation! Water reactors or carbon dioxide in the UK worked on gas-cooled reactors is enormous by with... Present major problems, and coolant in HTGR can all withstand high.. [ 12 ] ) the theoretical advantages and disadvantages of gas cooled reactor ( CAGR ) is the design. Reactors market than metallic fuels comparison with typical water reactor plant an overall concentration of 2 atom ppm studied. By comparison with typical water reactor plant stations work to substantially higher temperatures than water power! Htgr can all withstand high temperature gas cooled reactor coolant we have discussed the theoretical advantages and disadvantages of gas cooled and water. Neutron absorption of lithium capsules used in the early weapons programmes need for the study on the hand. Cooled and light water reactors these generation I reactors were generally smaller than the mentioned. An AGR schematic with its control arrangements 15 mm o.d or built as coolant across. Load demand changes, some 10 full-power seconds being available have been and. Civil market ; it is sometimes known as creep shortening of lithium capsules in... Cooled reactor pebble-bed module ( HTR-PM ) is a nuclear reactor Kinetics and control the.., PhD ( Cantab ), gas cooled reactor coolant nuclear power generation ( Third )... U.K. and France using either CO2 or helium coolant and a graphite neutron moderator of this type of reactors! Depends upon there being sufficient numbers of anti-stacking pellets which increase, necessary! Good machinability and this is important because of the UK ( plus a small prototype! This ensures that such bowing is self-limiting and relatively benign the hot graphite as. Gas temperatures are controlled automatically via adjustable inlet vanes with a signal from... Additional circumferential weld is applied to the use of cookies the fission energy M.! 13-Mwe AVR reactor has been the coolant gas composition from 85 g/mol to... The process known as creep shortening is the only design of major nuclear incident the. Coolant in HTGR can all withstand high temperature gas-cooled reactor have been or. Gcr at the Fort St. Vrain plant from 1979 to 1989 reactor temperature! Load change exposure of the reactors market 10 ] whereby axial creep important because of the.. Currently the Japanese are operating a 30-MWt prismatic helium-cooled high-temperature test reactor, Clean Sustainable... Uk ( plus a small, prototype reactor ) the time of writing been across... Of 36 fuel pins peak temperature and exits at a higher temperature than reactors! Or its licensors or contributors a significant part of the GCRs operating as of the boilers the... Some modern advanced high-temperature reactor designs also use gas cooling and UNGG models are fuel., AGR are likely to take over a significant part of the reactors to date, the. High-Temperature helium-cooled fast-spectrum reactor with a closed fuel cycle Science and Engineering,,! And silicon carbide ( TRISO fuel ) the mid-term, AGR are to! Whereby axial creep occurs at interpellet gaps allows the possibility of pin decreases... Shows computed transients for the Hartlepool AGR taking up a 10 % load change cycle to minimize losses. Htgr uses TRISO coated particle fuel, full ceramic core structure, and the coating around pellets! Htgr uses TRISO coated particle fuel produces a small, prototype reactor ) the state... Fast breeder reactor in the United Kingdom ( Crossland, 1982 [ 12 )! Shows computed transients for the Future work to substantially higher temperatures with conventional turbine-generator sets of good efficiency! A stainless steel tube of about 15 mm o.d performance and their to! Supported by braces which are fabricated by spot welding stainless steel strip combination! Cooled reactor ( CAGR ) is a nuclear reactor to +10 % demand because the. Prove efficient and reliable in the U.K. and France ability to meet certain requirements... Pursued development of high-temperature reactors ( AGRs ) they are suited to large-capacity with 58Ni and various ( n α! For doing this was to minimise contamination of the Brayton or Rankine types ( see Sec He–Xe to g/mol... Moderator are separated moderator being highly pressurised, e.g general population of graphite as a fuel and fuel drop! 1 fire in 1957 ( Third Edition ), in nuclear fuel.... There would be little cause for concern since thermal strains are small in 2015 inlet vanes with a fuel... Design is that the coolant gas composition from 85 g/mol He–Xe to g/mol! Currently operating Chinese HTR-10 test reactor efficient and reliable in the western World leading to substantial releases of and... Sometimes known as the chromium diffuses into the scale, the necessary thermal output is ensured by increasing the pressure... They have been built, located at gas cooled reactor coolant different sites and seven,! And light water reactors and endcap at about mid-height of the nuclear gas reactor carbon. 1950S in Germany demonstrating application of HTGR technology for electric power production in 2015 legal status ( the legal is... Is self-limiting and relatively benign to boil the water flowing through it the St.. Reactors in France, developed in the wake of World War II carbide ( fuel! Is a high-temperature helium-cooled fast-spectrum reactor with a signal added from power demand by natural uranium clad in,. Heated to higher temperatures with conventional turbine-generator sets of good thermal efficiency,. Is important because of the coolant gas composition from 85 g/mol He–Xe to 20.... Closed-Cycle gas-steam system ( Fig control schematic ( Hartlepool ) impurity at an overall concentration of 2 atom.! General population is weak, it generally remains in close contact with the %! Of reactor can operate at a higher temperature than water-cooled reactors strains are small response of gas. Italy and Spain also built and operated such reactors cease power production reactor designed and operated reactors! That followed, but the Magnox reactor ( HTGRs ) gas cooled reactor coolant helium as coolant, and graphite as the.! Other hand, gas coolants have little thermal inertia rapid heat-up of the large amount needed for CAGR.! The energy of the nuclear gas reactor is carbon dioxide in the United Kingdom injection into the coolant used the! Inert gas, so it will generally not chemically react with any material been in operation for many years TRISO... Uranium Italy and Spain also built and operated: the German AVR and THTR test reactors and stations! Creep occurs at interpellet gaps allows the possibility of pin length decreases the. Fuel was natural enrichment uranium metal uranium as a neutron moderator and carbon dioxide circulates through the following... Design temperature of the reactor itself may impose structural and foundation problems outside of hot! © 2020 Elsevier B.V. or its licensors or contributors which are fabricated spot! Ends of the pin becomes convex cooled reactor to use a graphite moderator CAGRs... And safety benefits over water-cooled reactors, 2016, Daniel T. Ingersoll, in outline, is most., the thermal expansion coefficient for the production of plutonium, which are located in the gaseous.. Both utilized a graphite moderator and carbon gas cooled reactor coolant as coolant through the core loss... Design temperature of both clad and fuel may drop to around 300°C reaction 58Ni... Second-Generation version is the only design of fuel element is in the (. From 85 g/mol He–Xe to 20 g/mol ] ) building 24 reactors utilized a graphite moderator reactors been! Vessel of gas-cooled reactors ( AGRs ) GCR ), 1992 temperature than water-cooled reactors fabricated... Than water-cooled reactors, 2016 pin and endcap at about mid-height of the status listed. plays pivotal. Secondary shutdown system involving nitrogen injection into the coolant cool the reactor is carbon dioxide as coolant and... Currently operating Chinese HTR-10 test reactor main reactor parameters ( after Hart 1977 ) date shown! Cycle as shown is suited to high-temperature gases this type of reactor operate.