Loss-of-coolant accidents

Safety. A large inventory of radioactive fission products is present in any reactor fuel where the reactor has been operated for times on the order of months. In steady state, radioactive decay heat amounts to about 5% of fission heat, and continues after a reactor is shut down. If cooling is not provided, decay heat can melt fuel rods, causing release of the contents. Protection against a loss-of-coolant accident (LOCA), eg, a primary coolant pipe break, is required. Power reactors have an emergency core cooling system (ECCS) that comes into play upon initiation of a LOCA. 

Reactor coolant pump (RCP) seal failures that lead to a loss of coolant accident (LOCA)... 

Generic Evaluation of Feedwater Transients and Small Break Loss-of-Coolant Accidents in GE-Designed Operating Plants and Near-Term Operating License Applications, January... 

In April 1982, a data workshop was held to evaluate, discuss, and critique data in order to establish a consensus generic data set for the USNRC-RES National Reliability Evaluation Program (NREP). The data set contains component failure rates and probability estimates for loss of coolant accidents, transients, loss of offsite power events, and human errors that could be applied consistently across the nuclear power industry as screening values for initial identification of dominant accident sequences in PRAs. This data set was used in the development of guidance documents for the performance of PRAs. 

In the following sections, the flow patterns, void fraction and slip ratio, and local phase, velocity, and shear distributions in various flow patterns, along with measuring instruments and available flow models, will be discussed. They will be followed by the pressure drop of two-phase flow in tubes, in rod bundles, and in flow restrictions. The final section deals with the critical flow and unsteady two-phase flow that are essential in reactor loss-of-coolant accident analyses. 

Although these equations were developed from steady-state CHF data, they are also suggested for use in flow depressurization during a loss-of-coolant accident (Slifer and Hench, 1971). 

Bauer, E. G., G. R. Houdayer, and H. M. Sureau, 1978, A Nonequilibrium Axial Flow Model and Application to Loss-of-Coolant Accident, in Proc. Transient Two-Phase Flow CSN1 Specialists Meeting, 1976, Atomic Energy of Canada 7 429-437. (3)... 

Edwards, A. R., and D. J. Mather, 1973, Some U.K. Studies Related to the Loss of Coolant Accident, ANS Topical Meeting on Water Reactor Safety, Salt Lake City, UT. (3)... 

Hoppner, G., 1971, Experimental Study of Phenomena Affecting the Loss of Coolant Accident, Ph.D. thesis, University of California, Berkeley, CA. (6)... 

Oberjohn, W. J., and R. H. Wilson, 1966, The Effect of Non-uniform Axial Flux Shape on the Critical Heat Flux, ASME Paper 66-WA/HT-60, Winter Annual Meeting, ASME, New York. (5) Ogasawara, H. et al., 1973, Cooling Mechanism ofthe Low Pressure Coolant-Injection System of BWR and Other Studies on the Loss-of-Coolant-Accident Phenomena, ANS Topical Meeting Water Reactor Safety, p. 351, Salt Lake City, UT. (4)... 

Slifer, B. C., and J. E. Hench, 1971, Loss of Coolant Accident and Emergency Core Cooling Models for General Electric Boiling Water Reactors, NEDO-10329, General Electric Co., San Jose, CA. (5) Smith, A. M., 1969, Oak Ridge National Lab., Personal communication to J. K. Jones, November. (5)... 

Figure 11-9 Event tree for a loss-of-coolant accident for the reactor of Figure 11-8.

Loss, in lasers, 14 664-666 Loss factor, monitoring, 10 15 Loss-in-weight method, 26 248 Loss-in-weight systems, 26 249 Loss modulus, 20 346 21 722-723 Loss-of-coolant accident (LOCA), 17 577, 582, 595, 596... 

It is highly improbable that a nuclear fission power plant would ever explode like a nuclear bomb, but a loss of coolant accident could result in a melt down condition. In a melt down, a large amount of radiation can be released at ground-level. A nuclear or conventional chemical or steam explosion could disperse much of the radioactive particles into the atmosphere. This is essentially what happened when the Chernobyl gas explosion occurred in the Soviet Union in 1986. 

AP600 Passive Safety System Details, These features reduce operator responsibilities and add an extra margin of safety over contemporary PWR designs. See Fig. 37 on p. 1121. Large volumes of water stored in the containment eliminate the need for operator action to assure make-up water, either for small leaks that may occur during normal operation or for a major loss of coolant accident (LOCA). A passive plant is a system llial assures public safety even if the operators fail to act... 

LWR tests-to-failure had been performed to evaluate accident scenarios involving loss of coolant accident (LOCA) events such as occurred in the Three Mile Island incident. The power burst tests in a 20 MWt PWR have created fuel failures and defined the initiating conditions. The LOCA tests with a 50 MWt... 

Withdrawn from service Reason 1982 loss-of-coolant accident... 

In the event of a malfunction of the reactor or safety related equipment, a condition known as a Loss of Coolant Accident (LOCA) may occur within the Primary Containment Structure. Should this happen, the environment would become dramatically altered in a matter of seconds and result in the escalation of temperature and pressure to dangerous levels. To counteract this condition, large quantities of water with chemical additives are automatically directed onto all surfaces by means of high pressure spray systems. 

Passive safety features for the MHR include ceramic, coated-particle fuel and an annular graphite core with high heat capacity and low power density. Recently, INL has used the ATHENA thermal hydraulic code to model the response of the MHR during loss-of-flow and loss-of-coolant accidents and has confirmed these passivity safety features work to maintain fuel temperatures well below failure thresholds [8]. 

Further studies concerning the stability limit of water at higher pressure and temperature (where this method is expected to be less accurate) with more realistic pressure-profile are in progress. Those data would be particularly important in the safety analysis of power plants (including nuclear ones) where during a so-called LOCA (Loss of Coolant Accident) part of the cooling liquid can reach some degree of metastability due to sudden pressure loss (see e.g. [ ]). 

It is highly unlikely that a nuclear fission power plant would ever explode like a nuclear bomb, but a loss of coolant accident could result in a melt down condition. 

Electric wires and cables used in nuclear power plant are exposed by low dose rate irradiation during the life time of the plant. In addition, loss of coolant accident (LOCA) that is a design basis accident brings about the degradation by heat and radiation on the electric wire and cables. The dose varies from plant to plant. IEEE std.323-1974 (/) estimated the dose 0.5 MGy for the period of the life time and 1.5 MGy for LOCA as one of the example. The standard estimated 40years and one year, for the lifetime of plant and duration of LOCA respectively. 

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