Neutronic Reactors

The only large-scale use of deuterium in industry is as a moderator, in the form of D2O, for nuclear reactors. Because of its favorable slowing-down properties and its small capture cross section for neutrons, deuterium moderation permits the use of uranium containing the natural abundance of uranium-235, thus avoiding an isotope enrichment step in the preparation of reactor fuel. Heavy water-moderated thermal neutron reactors fueled with uranium-233 and surrounded with a natural thorium blanket offer the prospect of successful fuel breeding, ie, production of greater amounts of (by neutron capture in thorium) than are consumed by nuclear fission in the operation of the reactor. The advantages of heavy water-moderated reactors are difficult to assess. 

Other options for eliminating weapons-grade plutonium arc to seal it permanently in solid radioactive waste and dispose of it in waste repositories, and to use the plutonium to fuel fast neutron reactors (without reprocessing the plutonium into a MOX fuel). 

Nuclear and magneto-hydrodynamic electric power generation systems have been produced on a scale which could lead to industrial production, but to-date technical problems, mainly connected with corrosion of the containing materials, has hampered full-scale development. In the case of nuclear power, the proposed fast reactor, which uses fast neutron fission in a small nuclear fuel element, by comparison with fuel rods in thermal neutron reactors, requires a more rapid heat removal than is possible by water cooling, and a liquid sodium-potassium alloy has been used in the development of a near-industrial generator. The fuel container is a vanadium sheath with a niobium outer cladding, since this has a low fast neutron capture cross-section and a low rate of corrosion by the liquid metal coolant. The liquid metal coolant is transported from the fuel to the turbine generating the electric power in stainless steel... 

In fast (neutron) reactors, the fission chain reaction is sustained by fast neutrons, unlike in thermal reactors. Thus, fast reactors require fuel that is relatively rich in fissile material highly enriched uranium (> 20%) or plutonium. As fast neutrons are desired, there is also the need to eliminate neutron moderators hence, certain liquid metals, such as sodium, are used for cooling instead of water. Fast reactors more deliberately use the 238U as well as the fissile 235U isotope used in most reactors. If designed to produce more plutonium than they consume, they are called fast-breeder reactors if they are net consumers of plutonium, they are called burners . 

Large amounts of sodium waste arise from fast neutron reactors (Phenix and Superphenix in France, Dounreay in the UK, Monju in Japan), which are cooled by large amounts of liquid sodium, which is contaminated by 137Cs during its functioning. We shall see that it is possible to remove radioactive cesium after conversion of liquid sodium to sodium hydroxide. 

The Experimental Breeder Reactor EBR-1 was the first power reactor and the first fast neutron reactor. It was put in service in 1951 on the site of Idaho in the United-States and it became the world s first electricity-generating nuclear power plant when it produced sufficient electricity to illuminate four 200-watt light bulbs. 

Fast neutron reactors with a closed fuel cycle to achieve a durable production of electricity while minimising needs of uranium and the burden of long-lived radioactive waste. 

The French Act of 28 June 2006 on a sustainable management of nuclear materials and radioactive waste sets plans for a prototype of fast neutron reactor to proceed in the 2020s with demonstrations of advanced recycling modes that are anticipated in 2012 to offer best prospects of industrial applications. 

During 1962 - 1997 a munber of NSs with lead-bismuth LMC in the primary circuit were in operation in the Russian Navy. Reactors of such NSs developed imder scientific management of the Russian Research Center Institute for Physics and Power Engineering (RRC IPPE, below IPPE), Obninsk, fall into the category of intermediate-neutron reactors [1]. Fuel composition of LMC reactors comprises intermetallic compoimd UBen with enrichment up to 90 % dispersed over beryllium matrix. Some characteristics of such-type NSs are demonstrated in Table 1. 

The lirst-generation NSs were equipped with BM-A -type water-cooled thermal neutron reactors. Today it is very difficult to identify either the type or power production of cores unloaded from the first-generation NSs and stored in Gremikha. 

The fission of one nucleus of produce about 200 MeV of usable energy, to be compared with 4 eV produced by the oxidation of one C atom. During the overall process, a huge amount of heat is produced through a controlled nuclear chain reaction in a critical mass of fissile material. Potential future developments (fission in fast neutron reactors (breeders), also known as fourth generation nuclear, which... 

In thermal-neutron reactors has an important advantage over or Pu in that the number of neutrons produced per thermal neutron absorbed, tj, is higher for than for the other fissile nuclides. Table 6.1 compares the 2200 m/s cross sections and neutron yields in fission of these three nuclides. Thorium has not heretofore been extensively used in nuclear reactors because of the ready avaUabihty of the U in natural or slightly enriched uranium. As natural uranium becomes scarcer and the conservation of neutrons and fissile material becomes more important, it is anticipated that production of U from thorium will become of greater significance. 

We assume that irradiation is carried out by a homogeneous particle flux in a neutron reactor. The minimum amount of an element which can be detected increases with the efficiency of the measuring apparatus the bombarding flux the reaction cross-section ff, the irradiation time (up to saturation activity), the decay constant, X, of the radioactive nuclide formed, and the time from end of bombardment to start of counting, fcooi- y proper selection of t- and the sensitivity for any element can be changed and... 

Liquid sodium has attractive properties for its application as a working fluid in a fast neutron reactor with the ability to breed plutonium fuel by the reaction of ura-nium with the fast neutrons. Sodium does not act as a neutron moderator, its liquid state at atmospheric pressure reaches from 97.8 °C to 892 °C, its heat transfer properties are excellent and its nuclear reactions do not cause a long lasting activation. Sodium is the medium which is able to transfer the energy generated in the high density reactor core better than any other heat transfer fluid... 

Graphite compounds of rubidium and cesium seem to be more stable and to be formed easily. This is of technical importance since the absorption of the fission elements rubidium and cesium by graphite immersed in liquid sodium will be applied to remove them from the sodium coolant of a fast neutron reactor The formation of a lithium compound of this type has never been observed. 

The choice of cladding material for fast reactors is less dependent upon the neutron absorption cross section than for thermal reactors. The essential requirements for these materials are high melting point, retention of satisfactory physical and mechanical properties, a low swelling rate when irradiated by large fluences of fast neutrons, and good corrosion resistance, especially to molten sodium. At present, stainless steel is the preferred fuel cladding material for sodium-cooled fast breeder reactors (LMFBRs). For such reactors, the capture cross section is not as important as for thermal neutron reactors. 

VI. An Outline of Potential Hazards to the Population from Accidents to Sodium-Cooled Fast Neutron Reactors. 

VI. AN OUTLINE OF POTENTIAL HAZARDS TO THE POPULATION FROM ACCIDENTS TO SODIUM-COOLED FAST NEUTRON REACTORS... 

Ibaki, S.et al., 1998, Current Statusofthe Prototype FBRMonju , Workshop on The Future of Fast Neutron Reactor , ENS 1998, Nice, France. 

An organisation has been set out with means for guaranteeing satisfactory processing of experience feedback from the plant, other French and Overseas fast neutron reactors and the PWR plants... 

The role of Group R is to organise expenence feedback from French and foreign fast neutron reactors together with PWR plants... 

The primary sodium pollution incident, which is particularly significant of the prototype nature of the fast neutron reactor at Creys-Malville, led to a long shutdown which justified its classification as a level 2 seriousness incident, although it did not bring into question the safety of the installations... 

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