Nuclear reactors passive

Nuclear Reactors. Nuclear power faciUties account for about 20% of the power generated in the United States. Although no new plants are plaimed in the United States, many other countries, particularly those that would otherwise rely heavily on imported fuel, continue to increase their nuclear plant generation capacity. Many industry observers predict that nuclear power may become more attractive in future years as the price of fossil fuels continues to rise and environmental regulations become more stringent. In addition, advanced passive-safety reactor designs may help allay concerns over potential safety issues. 

Metal Cleaning. Citric acid, partially neutralized to - pH 3.5 with ammonia or triethanolamine, is used to clean metal oxides from the water side of steam boilers and nuclear reactors with a two-step single fill operation (104—122). The resulting surface is clean and passivated. This process has a low corrosion rate and is used for both pre-operational mill scale removal and operational cleaning to restore heat-transfer efficiency. 

Forsberg, C. W., and Weinberg, A. (1990). Advanced Reactors, Passive Safety, and Acceptance of Nuclear Energy. Annual Review of Energy 1 h 1.33-1. S2. 

Pressurised water nuclear reactors require metals that will have a high degree of corrosion resistance to pure water at around 300°C. Laboratory testing of materials for this application have included potentiostatic polarisation experiments designed to clarify the active-passive behaviour of alloys as well as to establish corrosion rates. Since pressure vessels are used for this work, it is necessary to provide sealed insulated leads through the autoclave head . 

The silvery, shiny, ductile metal is passivated with an oxide layer. Chemically very similar to and always found with zirconium (like chemical twins, with almost identical ionic radii) the two are difficult to separate. Used in control rods in nuclear reactors (e.g. in nuclear submarines), as it absorbs electrons more effectively than any other element. Also used in special lamps and flash devices. Alloys with niobium and tantalum are used in the construction of chemical plants. Hafnium dioxide is a better insulator than Si02. Hafnium carbide (HfC) has the highest melting point of all solid substances (3890 °C record ). 

FORSBERG, C.W., WEINBERG, A.M., "Advanced Reactors, Passive Safety and Acceptance of Nuclear Energy", (Annual Rev., 1990,15 133-52). 

Small and medium size reactor development has many incentives some are economic others are safety related. The motivation for these developments has included the need to influence public acceptability of nuclear power. The simplicity of reactor designs should improve the transparency of their reactor safety. Another incentive to SMR development has been its suitability for the implementation of new design approaches. Innovative and evolutionary designs with novel features have been implemented in the SMR range. A passive safety approach has so far been the technology of small and medium reactors. Some Member States have been or are interested in SMR developments since TMI and Chernobyl as an answer to utility, as well as public requirements, in particular to saf and public acceptance issues. The economics of nuclear reactors are summarised in y pendix I. SMRs have particular characteristics which can enable them to be economically viable in spite of losing the advantage of the economics of scale. These economic incentives are included in the list below. 

K. Sako, et.al., "Concept of Highly Passive Safe Reactor SPWR, Reactor System Design", Proc. Int. Specialists Meeting on Potential of Small Nuclear Reactors for Future Clean and Safe Energy Sources, Tokyo (1991). 

Determination of uranium in soil samples can be carried out by nondestructive analysis (NDA) methods that do not require separation of uranium (needed for alpha spectrometry or TIMS) or even digestion of the soil for analysis by ICPMS, ICPAES, or some other spectroscopic methods. These NDA methods can be divided into passive techniques that utilize the natural radioactive mission (gamma and x-ray) of the uranium and progeny radionuclides or active methods where neutrons or electromagnetic radiation are used to excite the uranium and the resultant emissions (gamma, x-rays, or neutrons) are monitored. In many cases, sample preparation is simpler for these nondestructive methods but the requiranent of a neutron source (from a nuclear reactor in many cases) or a radioactive source (x-ray or gamma) and relatively complex calibration and data interpretation procedures make the use of these techniques competitive only in some applications. In addition, the detection limits are usually inferior to the mass spectrometric techniques and the isotopic composition is not readily obtainable. 

Wood, C. J., Marble, W. J., Prystuba, M., Hudson, M. J. B., Wilkens, D. L. Experience with zinc injection passivation at BWR plants in the USA. Proc. 5. BNES Conf. Water Chemistry of Nuclear Reactor Systems, Bournemouth, UK, 1989, Vol. 1, p. 111-114... 

The Fixed Bed Nuclear Reactor (FBNR) concept assumes the use pressurized water reactor (PWR) technology, but incorporates hi temperature gas cooled reactor (HTGR) type fuel and the concept of a suspended fixed bed core. Spherical fuel elements are fixed in the suspended core by the flow of water coolant. Any accident signal will cut off the power to the coolant pump causing a stop in the flow. This would make the fuel elements fall out of the reactor core, driven by gravity, and enter a passively cooled fuel chamber where they would reside in a subcritical condition. The Fixed Bed Nuclear Reactor (FBNR) is a simplified version of the fluidized bed nuclear reactor concept [XII-1 to XII-9]. In the FBNR, spherical fuel elements are in a fixed position in the core therefore, there is no concern about the consequences of multiple collisions between them, an issue that may be raised about the fluidized bed concept. Relatively little work has been done for the fixed bed nuclear reactor so far, but the experiences gained from the development of a fluidized bed reactor can facilitate the development of the FBNR. 

XVn-9] KAMBE, M., UOTANI, M., Design and development of fast breeder reactor passive reactivity control systems LEM and LIM, Nuclear Technology, Vol. 122, pp. 179-195 (May 1998). 

XVII-10] KAMBE, M., Fast reactor passive shutdown system LIM, ICONE-7 (Proc. of the 7th Int. Conf on Nuclear Engineering, Tokyo, Japan, April 1999) pp. ICONE-7069. 

XXIX-4] MAHESHWARI, N.K., VUAYAN, P.K., SAHA, D., SINHA, R.K., Passive safety features of Indian innovative nuclear reactors, IAEA-TECDOC-1451, Vienna (May 2005). 

PASSIVE SAFETY FEATURES OF INDIAN INNOVATIVE NUCLEAR REACTORS... 

Among others, the FBNR concept was considered at the IAEA consultancy meeting on Small Reactors without On-site Refuelling in March 2004, attended by experts from 6 IAEA Member States and the comment on FBNR was as follows In particular, the consultancy noted that the innovative approach proposed in the Fixed Bed Nuclear Reactor (FNBR) concept (Federal University of Rio Grande Do Sul, Brazil) relating to hydraulically supported column of spherical fuel elements offers a good potential to serve as a method of passive control of core reactivity. This concept needs to be further developed and polished for its possible implementation in small reactors. ... 

What is meant by passive stability in nuclear reactor design ... 

Enhancement of both nuclear and radiological safety through further development of positive safety properties inherent to fast nuclear reactors and through wide implementation of innovative passive devices and systems for safety functions. 

Passive safety systems based on natural circulation are intended to provide the ultimate heat sink in cases of failure of the normal operation of the reactor cooling system. Because of its critical importance, fundamental understanding of the properties and characteristics of namral-circulation hydrodynamics, thermal responses, and thermodynamics in the complex engineering equipment of nuclear reactor power systems is essential. For the Gen IV systems that are based on natural circulation at normal operating states the properties and characteristics under steady-state conditions must also be well understood. 

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