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Stutensee, Germany

Kessler G.,Jagersteig 4
Power Systems | Year: 2012

Plutonium isotopes, but also the isotopes of minor actinides: mainly neptunium, americium and curium can be fissioned by neutrons in the core of nuclear reactors. They also can be transformed as non-fissile isotopes by neutron capture into fissile nuclides (transmutation). Incineration of 99% of the plutonium, neptunium, americium and curium would decrease the long term radiotoxicity of the high active waste (HLW) such that the radiotoxicity level of natural uranium would be underrun already after about 3 × 104 years. This requires chemical separation of plutonium, neptunium, americium and curium and the fabrication of fuel elements with these actinides. These chemical separation methods and the fuel refabrication methods were already developed by research and development programs and demonstrated in pilot plants or at laboratory scale. The possible incineration rates for the different actinides in different reactor types (light water reactors, liquid metal cooled fast breeder reactors and accelerator driven systems) have been thoroughly investigated. Reactor strategies with light water reactors operating in symbiosis with liquid metal cooled fast breeders or accelerator driven systems are feasible. The different reactor and fuel cycle strategies have different radioactivity loads and different radiotoxicity levels within the different parts of their fuel cycle. Whereas the radiotoxicity can be drastically decreased in the back end of the fuel cycle, the masses of plutonium and minor actinides and their radioactivity and radiotoxicity can be higher during reprocessing and refabrication. Transmutation and destruction of long-lived fission products is only feasible with reasonable efficiency for Iodine-129 and Technetium-99. © Springer-Verlag Berlin Heidelberg 2012. Source


Kessler G.,Jagersteig 4
Power Systems | Year: 2012

The safety design concept of LMFBRs follows the same basic principles (multiple barrier concept and four level safety concept) as they were developed for light water reactors. This holds despite of the fact that LMFBRs have different design characteristics (fast neutron spectrum, liquid metal as coolant, plutonium-uranium fuel). It has been shown that LMFBRs possess a strong negative power coefficient and good control stability. The main design characteristics of control and shut-off systems do not differ much from those of light water reactors. For sodium cooled fast reactors the sodium temperature and sodium void coefficient can become positive above a power output of the core above about 350 MW(th). Therefore, special design provisions are taken for future LMFBR designs, e.g. flat and heterogeneous cores. The excellent cooling and natural convection properties as well as the low system pressure of about 1 bar of liquid metal cooled fast breeder allow the safe decay heat removal by a number of ways. The consequences of sodium fires or sodium water reactions can be prevented or limited by special design provisions. On the other hand, lead and lead-bismuth-eutecticum (LBE) as coolant do not chemically react neither with oxygen of the atmosphere nor with water in failing tubes of a steam generator. Historically the characteristics of homogeneous sodium cooled cores with a positive sodium void coefficient of the early prototype fast breeder reactors have lead to the analysis of core disruptive accidents with the objective to find a basis for the main design requirements of the containment. The discovery of the negative control rod drive line expansion coefficient in the early 1980s, changed this situation and lead to a new safety design which avoids anticipated transients without scram (ATWS) for future LMFBRs. The high boiling points of lead with 1,740°C LBE with 1,670°C offer an advantage with respect to safety concerns compared to sodium as coolant. © Springer-Verlag Berlin Heidelberg 2012. Source


Kessler G.,Jagersteig 4
Power Systems | Year: 2012

Nuclear power generation is currently mainly based on light water reactors, designed as pressurized water reactors and boiling water reactors. These are built by a number of manufacturers in various countries of the world. In this chapter, the standard German PWR of 1,300 MW(e) and the European Pressurized Water Reactor (EPR) will be described. In addition, the chapter deals with the German Standard BWR of 1,280 MW(e) and the newer design SWR-1,000 (KERENA). Gas cooled and graphite moderated commercial reactors with natural uranium were developed in the United Kingdom and in France and built in the 1950s and 1960s (MAGNOX reactors). Advanced gas cooled reactors (AGCRs) with graphite as moderator and carbon dioxide as coolant gas have been built in unit sizes up to 620 MW(e). High temperature gas cooled reactors with gas outlet temperature of 700-740°C use helium as a coolant gas. Their fuel elements have been developed as prismatic or spherical pebble fuel elements. High temperature gas cooled reactors with medium enriched uranium are now designed mainly as small modular reactors for safety reasons. Power reactors with heavy water as the moderator and heavy water or light water as coolant have been developed in Canada, Europe and Japan up to unit sizes of 630 MW(e). The advanced CANDU reactor (ACR) is developed currently to a unit size of up to 1,000 MW(e). Homogeneous core thermal breeders with molten salt and light water breeder reactors together with accelerator driven subcritical reactor cores are still in the design or development phase. © Springer-Verlag Berlin Heidelberg 2012. Source


Kessler G.,Jagersteig 4
Power Systems | Year: 2012

The most important reactor physics characteristics needed for the understanding of the design and operation of nuclear reactors and of their fuel cycle are presented. This comprises the criticality factor, the neutron and temperature distributions in the reactor core and reactivity effects to be controlled by the safety systems. The evolution of the isotopic composition during burnup, i.e., the buildup of fission products and actinides in the reactor fuel, and the importance of conversion and breeding ratios are discussed together with the fuel utilization. Inherent safety characteristics like the negative fuel Doppler coefficient and the negative coolant temperature coefficient are essential for the safe operation and control of nuclear reactors. © Springer-Verlag Berlin Heidelberg 2012. Source


During normal operation of nuclear power plants and facilities of the nuclear fuel cycle small amounts of radioactivity are released into the environment at a monitored and controlled rate. Men may be exposed to external radiation as well as radiation by inhalation and ingestion. Upper limits for the radiation exposure of individuals of the public as well as of employees during their occupational work time have been set by the International Commission on Radiation Protection as well as by state organizations. The nuclear fuel cycle begins with uranium mining and milling where the main effluents are radon and dust particles containing uranium and its decay products. Radioactive effluents are reported for both open pit and underground mining. This is followed by listing the radioactivity release and exposure rate of uranium conversion, enrichment and fuel fabrication facilities. For Pressurized Water Reactors the annual effective dose to the public is well below one micro-Sievert. For Boiling Water reactors the annual effective dose is somewhat higher. However, this is still more than a factor 100 lower than the permissible limit. Release data for radioactive nuclides from the European spent fuel reprocessing and waste treatment centers are collected by the European Commission. The radioactive exposures to the public from these facilities are well below the permissible effective radiation exposures as well. The same result is valid for the plutonium/uranium mixed oxide fuel refabrication plant MELOX in France. © Springer-Verlag Berlin Heidelberg 2012. Source

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