Fuel element for steam power plants

 

The invention relates to structures steam-generating power plants high calorific and, first of all, can be used in steam generating plants nuclear fuel (steam-water nuclear reactors). The proposed device for a fuel element rod type used in steam power plants. The proposed fuel element for a steam-generating power plants contains a source of energy (for example, nuclear fuel). The energy source has a periodic structure consisting of alternating zones containing a source of energy, and inactive zones filled with an inert ballast. Period (L) alternating along its length active and inactive zones is in the range L=1-100 effective dimensions of its cross section (diameter). The predominant values are L>(D/)1/2whereeffective coefficient of thermal conductivity of a fuel rod; D is the effective diameter of a fuel rod;- the heat transfer coefficient from the surface of a fuel rod in a boiling fluid. The ratio of the length of the active zone to the length of the inactive zone is the m of ceramic materials (for example, of the oxides of aluminum, titanium, zirconium, silicon or metal (e.g., made of different steels, zirconium). The technical result - the increase in resistance of a fuel rod to local perturbations. 1 C.p. f-crystals, 2 Il.

The invention relates to structures steam-generating power plants high calorific and, first of all, can be used in steam generating plants nuclear fuel (steam-water nuclear reactors).

The object of the invention is a device for a fuel element (hereinafter, the fuel rod) rod type used in steam power plants.

The device of the fuel Rods is the subject of a large number of inventions. The most representative of the number of inventions registered in the last 15 years are presented in the materials of the following patents and presents for examination of applications for inventions: 1. USA patent 4592479, 1986, 2. USA patent 4664882, 1987, 3. USA patent 4783308, 1988, 4. USA patent 5178825, 1993, 5. USA patent 5323434, 1994, 6. USA patent application No 20010003537, Kind Code A1 2001, 7. USA patent application No 20010014135, Kind Code A1, 2001.

The disadvantage of all known structures of the fuel Rods is thermal instability of the mode of operation is Ivate in the disturbed zone of a spontaneous transition from a normal (standard) heat mode of operation of a fuel rod (corresponding to nucleate boiling of the working fluid medium in emergency high temperature state film boiling regime, which then extends along the entire length of a fuel rod. Described a phenomenon known in physics and engineering as "boiling crisis" leads to the destruction of the steam generating installation and is accompanied by major social disaster.

As a prototype of the invention is selected patent, presents under 3 in the above list of analyzed sources of information: USA patent 4783308, 1988, "Boiling water reactor fuel rod" ("Fuel element for steam-water reactor"). Protected by this patent the device (prototype) structurally designed as follows: the fuel element has a tubular, cylindrical shape; a thermal energy source (nuclear fuel in tablet form) is loaded inside the tubular, cylindrical fuel rod along its length uniformly (uniform Assembly stacked on top of each of the pellets of nuclear fuel). The prototype has all the above-mentioned disadvantages of the Fuel elements, namely, the phenomenon of instability of thermal regime of steam with respect to perturbations, randomly appearing on the localized site of such a fuel rod. These local disturbances are the cause of the emergency high-temperature state film boiling regime, emago of the invention is the design of a fuel rod, which would be named disadvantages and which should provide a high level of stability of the normal operation of a fuel rod to thermal perturbations, i.e., a high level of safety steam-generating power plants of large capacity.

Specific tasks, the solution of which is oriented the invention and which provide the benefits of the protected device when compared with the device of the prototype are as follows.

- Localization occurred on the TVEL emergency source of overheating and avoid frontal distribution of the hearth film boiling on the entire length of a fuel rod, leading to disastrous consequences.

- Increase threshold thermal perturbations that can form the emergency source of overheating in the fuel element (i.e., increasing the resistance of a fuel rod to the local perturbation).

- Increase the maximum safe value of thermal power removed from the unit of mass loaded in the TVEL energy source.

Put in the invention of the tasks are implemented as follows.

Proposed fuel element for a steam-generating power plants placed inside energy source (NAPA active zones, containing the energy source, and inactive zones filled with an inert ballast.

In the fuel element for a steam-generating power plants period (L) alternating along its length active and inactive zones selected in the range L= 1 - 100 of effective dimensions of its cross section (diameter), the predominant values are L>(D/)1/2whereeffective coefficient of thermal conductivity of a fuel rod; D is the effective diameter of a fuel rod, [cm] ;- the heat transfer coefficient from the surface of a fuel rod in a boiling liquidIn the fuel element for steam power plants the ratio of the length of the active zone to the length of the inactive zone is selected in the range of 0.1 to 1, with the preferred spacing of 0.5 to 1.

In the fuel element for a steam-generating power plants inactive zone filled with inert ballast from ceramic materials (for example, from oxides of aluminum, titanium, zirconium, silicon or metal (e.g., made of different steels, zirconium).

Example 1. The example design (devices) sallalla, containing inert ballast;
3 - the body of the rod type fuel elements in the form of cylindrical tubes;
L - step periodic structure placed in Fe energy source;
La, Ls - dimensions respectively active and inactive zones in a periodic structure of a fuel rod;
D - diameter of a fuel rod.

Calculations showed that the proposed in this invention, the periodic structure of a fuel rod allows to achieve significant advantages in comparison with the traditional design of a fuel rod, uniformly filled with energy source. The most pronounced advantages achieved if the period of alternation of active and inactive zones selected in the interval L=1-100 effective cross-section of a fuel rod, the predominant values are L>(D/)1/2whereeffective coefficient of thermal conductivity of a fuel rod; D is the effective diameter of fuel element [cm];- the heat transfer coefficient from the surface of a fuel rod in a boiling liquid. The optimal ratio of the size of the active and passive zones lies in the interval La/Ls= 0.1 to 1, the predominant javljaetsja film boiling, formed locally in a single active area of a fuel rod, it is localized ("locked" in this area) and does not extend the entire length of a fuel rod, while on a homogeneous fuel elements with identical capacity of the entire TVEL mode traveling wave goes into alarm state film boiling.

Threshold thermal perturbations that can form the emergency source of overheating in the fuel elements of the proposed design, increases in 1,5-3 times in comparison with similar power TVEL prototype.

For fuel elements of the proposed design is extremely safe thermal power removed from the unit of mass is introduced into the fuel rod power source increases 1.2-2 times.

Example 2.

A direct test of the effectiveness of the invention is carried out on the electrical model of a fuel rod. Model electric heating element made from soldered between themselves and the striped wire fragments, where the active fuel zone was fragments of wires with high resistivity (e.g., made of Pt, alloys of Ni-Cr and Fe-Cr-Al), and an inactive zone was simulated low-resistance wire fragments (for example, made of si or Ag).

Diagram fuel design privatescope power TVEL;
5,6 - instruments for measuring electrical current and voltage on a wire electric heating element "AB" to register dissipated in the fuel rod power.

In the experiments illustrated in Fig.2, was used pair of Pt active area (1), Cu - inactive zone (2). These wire fragments were welded with each other to form a periodic structure, simulating the proposed fuel element.

The diameter of the platinum and copper wires of 0.1 mm, the dimensions of the wire fragments for active and inactive zones were equal and amounted to 3 mm Such a combination of a wire filament was stretched in the vertical direction and immersed in the aquatic environment. Electric power was supplied from a regulated source of electrical power (4), and dissipated on the model integral fuel rod power was measured using a devices, recording the current and voltage (5 and 6). Comparison of the output characteristics of such a model partitioned TVEL was conducted with similar heater, entirely made of platinum wire (FE - prototype).

The experiments were conducted in heated to 95-98oWith the aquatic environment, in order to avoid destruction of the wire model of a fuel rod when it Loket local section of the wire of a fuel rod size 2-3 mm. The fact of occurrence on the fuel rod in-state film boiling regime (emergency) were recorded visually by the appearance of zones, red heat (700-800 C) on a wire heater.

The results confirm the advantages of the proposed fuel element with periodic along its length by placing a source of thermal energy before TVEL prototype with homogeneous (uniform along the entire length) release:
the maximum allowable thermal capacity, which spontaneously occurs abnormally high temperature state film boiling has increased by almost 30%;
the power of a local perturbation initiates emergency film mode, increased by more than 50%.


Claims

1. Fuel element for a steam-generating power plants, enclosing a source of energy (for example, nuclear fuel), characterized in that the energy source has a periodic structure consisting of alternating active areas containing a source of energy, and inactive zones filled with an inert ballast, and the period (L) alternating along its length active and inactive zones selected in the interval L = 1-100 effective it brings alausi element for steam generating power plants under item 1, characterized in that the values of

L > (D/)1/2,

whereeffective coefficient of thermal conductivity of a fuel rod

D is the effective diameter of fuel element [cm];

- the heat transfer coefficient from the surface of a fuel rod in a boiling liquid

 

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