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Void coefficient of reactivity

The effectiveness of delayed neutron detectors for detecting clad failure was tested by operating the reactor with vented fuel SA in the core. The void coefficient of reactivity at various core locations were measured using two special SA fabricated for this purpose. The void coefficient was found to be negative. [Pg.5]

The void coefficient of reactivity could be large enough to result in a positive power coefficient under some conditions... [Pg.17]

The equivalent of 70-80 rods will be kept within the core at all times. This can be compared with the specified operating minimum at Chernobyl of the equivalent of 30 rods in the core and the 6-8 equivalent rods at the time of the accident. This extra provision will greatly reduce the value of the void coefficient of reactivity. [Pg.92]

Benchmark ULOF of Modified BN-800 reactor with near zero sodium void coefficient of reactivity was analysed and results were presented at IAEA Consultancy Meeting of December 1996. Based on this, improvements to the pre-disassembly phase accident calculation codes have been made. [Pg.94]

An anticipated difference between the ATHR and helium-cooled reactors is the coolant void coefficient of reactivity, since the relevant nuclear cross sections for molten salts are larger than those for helium. The void coefficient corresponds to the amount of reactivity that is added or subtracted by complete removal of the coolant. Since initial AHTR calculations indicated that the void coefficient could be positive or negative depending on the precise design of the core, the focus of the physics analysis effort was to characterize this effect more carefully. [Pg.39]

Table 3.1. Void coefficient of reactivity for different salt compositions (initial SNL model)... Table 3.1. Void coefficient of reactivity for different salt compositions (initial SNL model)...
The type of accidents in which the Doppler effect plays a crucial role are those resulting from very high rates of reactivity increase, say l/sec or greater. Normal safety control systems are adequate to cope with accidents resulting from lesser rates of insertion. In the safety studies for the earlier small alloy fuel reactors, the main type of accident leading to the reactivity increase was core meltdown (8), which was in turn considered to result from either coolant failure or some less severe type of reactivity transient. In many of the large breeder reactor concepts of the future, the coolant has a positive void coefficient of reactivity (77, 12a) which could conceivably lead to an autocatalytic expulsion of the coolant and consequently high rates of reactivity increase. [Pg.111]

Self-shutdown of the reactor in emergency conditions due to negative void coefficient of reactivity. [Pg.132]

The thermal absorption of thorium is three times that of Due to this, the deleterious effects of parasitic absorption are less in thorium systems, and one can consider the use of light water coolant. This opens the way to in-core boiling. The reactor then has to be vertical, and then it becomes possible to design for 100% heat removal by natural circulation and passive safety. The possibility of positive void coefficient of reactivity has been countered by the lattice being under moderated with a burnable absorber in the fuel cluster. [Pg.512]

A reactor core of such a large volume has the disadvantage that load and load distribution in the reactor are difTicult to control. Another problem of this reactor type is the positive void coefficient of reactivity which may occur under certain circumstances. With increasing concentration of steam bubbles in the coolant, the absorption of neutrons in the coolant decreases while moderation of the fast neutrons by the graphite moderator remains unchanged. For this reason, an increase in reactor power is not limited by inherent physical properties of the reactor core and, therefore, the reactor load has to be controlled by extensive active measures, i. e. by complicated instrumentation. [Pg.52]

Avoidance of a positive coolant void coefficient of reactivity or... [Pg.82]

Apart from thorium utilization and establishing a slightly negative void coefficient of reactivity, the AHWR incorporates several passive safety features, which include core heat removal through natural circulation of the coolant in the main heat transport system. [Pg.144]

Void Coefficient of Reactivity Reactivity Loss at Full Power Fuel Temperature at Full Power... [Pg.97]

There are two features of contemporary fast reactors which have attracted particular attention on the grounds of safety core disruptive accidents (CDAs) caused by positive reactivity transients which may be exacerbated by the fact that coolant void coefficient of reactivity is under some circumstances positive (if the coolant is sodium) and sodium fires. There is no doubt that there will be continuing work during the coming decade to improve safety in both of these areas. [Pg.539]

The void coefficient of reactivity is an important inherent safety characteristic of reactor core. The calculations performed with continuous energy Monte Carlo code MVP show negative void coefficient of -15% Ak/k (at 40% void, BOL) and temperature coefficient of -2.3E-4% Ak/k/°C for graphite. These coefficients are rated sufficient to secure passive shutdown of the reactor core in accidents. [Pg.409]

It is shown by comparison with experimental data from zero energy assemblies that the interplay of these parameters is well understood and that in particular the coolant void coefficient of reactivity can be predicted accurately. The representation of the complete core of the Winfrith SGHWR is discussed and it is shown that the validity of the techniques used have been experimentally demonstrated. Finally the nuclear design aspects of larger SGHWRs including those designed for operation with natural uranium fuel are reviewed. [Pg.59]

The most important differences between the enriched and natural fuelled reactors stem from the fact that, with the natural system, one no longer has the freedom to choose the fuel/moderator ratios to give a void coefficient of reactivity which is near to zero. Instead, it is substantially positive. This, as a result, alters the control requirements and it is these aspects which are at present receiving intensive study. The problem is not one of searching for a method of control, but one of comparing various methods to Identify a reasonably elegant and inexpensive solution. [Pg.231]

Moderator (and coolant) temperature coefficient of reactivity Moderator void coefficient of reactivity Fuel temperature coefficient of reactivity Effective prompt neutron lifetime Delayed neutron fraction(s)... [Pg.81]

Negative void coefficient of reactivity, low core power density, negative fuel temperature coefficient of reactivity, and low excess reactivity... [Pg.418]

A critical reactor will become either sub- or supercritical when a void is introduced into the core. The magnitude and sign of the reactivity effect due to the void is known as the void coefficient of reactivity, and it is a complex function of core design, void location, and void volume. The void coefficient is an important parameter in the hazards evaluation of a broad class of reactors and also in the operation of certain reactors, such as the boiling water type. [Pg.174]


See other pages where Void coefficient of reactivity is mentioned: [Pg.219]    [Pg.597]    [Pg.14]    [Pg.77]    [Pg.165]    [Pg.325]    [Pg.326]    [Pg.143]    [Pg.143]    [Pg.114]    [Pg.534]    [Pg.116]    [Pg.272]    [Pg.59]    [Pg.343]    [Pg.357]    [Pg.366]    [Pg.59]    [Pg.61]    [Pg.61]    [Pg.104]    [Pg.111]    [Pg.111]    [Pg.61]    [Pg.172]    [Pg.174]   
See also in sourсe #XX -- [ Pg.116 ]




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