JPS63308599A - Steam exhaust for nuclear reactor - Google Patents

Abstract

PURPOSE:To enable a load due to a bubble pressure pulsation generated when a liquid is discharged to be reduced in a pipeline that is dipped in a coolant and has a number of ejecting nozzles by making the content volume of the ejecting nozzles such that a dimensionless parameter defined by a specific relational expression is not larger than a prescribed value. CONSTITUTION:The distal end portion 13 of a relief bent pipe 12 is dipped in a coolant 4 in a pressure restraining chamber. The inner diameter of the distal end portion 13 is larger than that of a portion upstream of the distal end portion 13. The distal end portion 13 is provided with a plurality of coolant outlets 14. The distal end portion 13 is constructed such that, when the content volume of a region wherein the outlets, namely, ejecting nozzles 14 are formed, the whole area of the nozzles 14 and the length of the wetted perimeter thereof are V, Ah and Zh, respectively, a dimensionless parameter phi defined by phi=(V.Zh)/(4Ah<2>) satisfies 10<2phi<=10<3>. Thus, a conventional dynamic load level at a condensation is reduced, and moreover, an extreme reduction in discharge flow rate can be removed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a steam exhaust system, and particularly to a steam exhaust system for a boiling water nuclear reactor.

[Conventional technology]

FIG. 1 schematically shows a reactor containment vessel of a conventional boiling water reactor. The reactor containment vessel consists of a dry well 2 that houses the reactor pressure vessel 1, a doughnut-shaped pressure suppression chamber (hereinafter referred to as 1-rus) 3, and a vent system pipe line that connects these. is filled with cooling water 4.

As shown in FIG. 2, the vent system consists of a vent pipe 5 and a relief vent pipe 1-6 as steam lines, and the lower portions of these vent pipes 5 and 6 are immersed in cooling water 4. Pens 1 to 5 guide steam in the dry well 2 leaking from the reactor pressure vessel 1 through the pipe breakage into the cooling water 4 in the pressure suppression chamber 3 in the event of a coolant loss accident hypothesizing a reactor pipe breakage. It is something. The relief vent pipe 6 is
The steam in the reactor pressure vessel 1 is transferred to the cooling water 4 in the pressure suppression chamber 3.
It leads inside. Until the air in the relief vent pipe 6 and the high-temperature, high-pressure steam released from the reactor pressure vessel 1 are released into the cooling water 4, the bubbles expand and compress repeatedly, causing transient damage to the torus wall and internal structural materials. Large load (
bubble pressure pulsation) is added. Furthermore, the steam condensation vibration load is
This is caused by steam condensation vibration that occurs over a long period of time at the outlet of the relief vent pipe 6 during the period when steam is released from the relief vent pipe 6 into the cooling water 4 .

[Problem to be solved by the invention]

These loads mentioned above are transmitted to structures such as the relief vent pipe and the pressure suppression chamber, and there is a risk that these structures may be damaged.

SUMMARY OF THE INVENTION An object of the present invention is to provide a steam exhaust device that alleviates the load caused by bubble pressure pulsations during fluid discharge.

[Means to solve the problem]

Means for solving the above-mentioned object is provided in a steam exhaust system for a nuclear reactor that condenses steam generated in a reactor vessel by passing it through a pipe and discharging it into a coolant in a pressure suppression chamber. A large number of jet ports are formed in a portion of the pipe that is submerged in the coolant, and the internal volume of the region where the jet ports are formed is V, the total area of the jet ports is Ah, and the jet ports are This is a steam exhaust device for a nuclear reactor characterized by existing in the range of the following formula (% formula %) when the wetted edge length is Zh.

[Effect]

Of the steam generated in the reactor pressure vessel, the steam to be discharged passes through a pipe and is spouted into the coolant from a number of jet ports, and the spouted steam is condensed by the coolant. As described above, by setting the dimensionless parameter r in the jet nozzle forming region, the dynamic load level during condensation, which is conventional, is reduced, and a significant decrease in the exhaust flow rate is not caused.

〔Example〕

An embodiment of the present invention will be described below using a relief vent pipe 1 as an example.

In FIG. 3, the tip 13 of the relief vent pipe 12 is submerged in the cooling water 4 in the pressure suppression chamber 3.

The inner diameter of the distal end portion 13 is larger than the inner diameter of the portion upstream of the distal end portion 13 . A plurality of coolant outlet ports 14 are installed in the tip portion (hereinafter referred to as the enlarged portion) 13 . Although not shown, the relief vent pipe 12 is connected to the reactor pressure vessel 11 via a relief valve and a main steam pipe. When the relief valve operates, high-pressure steam within the reactor pressure vessel 1 flows into the relief vent pipe 12 and compresses the air originally existing within the relief vent pipe 12. The compressed air becomes high-pressure bubbles 11 (FIG. 5) and is ejected from the coolant outlet 14 into the cooling water 4 of the pressure suppression chamber 3. The present invention actively reduces the pressure inside the relief vent pipe 12 by enlarging the enlarged portion 13 at its tip, and gradually exhausts air by arranging the coolant outlet in the water depth direction.

The load is relieved by the above two effects. The effects of the present invention will be explained in detail using FIGS. 4 and 5, and dimensionless parameters serving as indicators of load relaxation will be derived. Generally, the dynamic pressure P in pool water accompanying the growth of bubbles is proportional to the time derivative of the rate of change in volume of the bubbles.

Pcc VB...
(1) Liquid levels 1-5 are formed within the relief vent pipe 12. As the liquid level 15 falls in the direction of arrow 16,
Since the number of coolant outlet ports 14 increases, the right side of equation (1) is proportional to the rate of increase A of the flow path area of the coolant outlet ports 14. Moreover, the mass flow rate of the coolant is the internal pressure P of the relief vent pipe 12.
1 and proportional to the hydraulic equivalent diameter D h of the coolant outlet 14 . Therefore, VB” PtDhAh・
・12). If the falling speed of the liquid level 15 is constant,
A, h is proportional to the outlet area per unit length.

Therefore Here, n is the number of coolant outlets 14 at the same height, a is the cross-sectional area of one coolant outlet, S is the coolant outlet arrangement pitch in the height direction.

Also, the relief vent pipe internal pressure P1 is inversely proportional to the cross-sectional area of the enlarged portion 13 Plo:AP...(4) Therefore, from equations (1)2 to (4), the dynamic pressure P is A
p If the length of the part where the outlet 5 is located is L, the volume of the enlarged part 13 is v (=APL), and the total Dh of the coolant outlet 14 is Ah
Substituting into the wet edge length Zh of the coolant outlet 14, we get
We get the following equation.

hV The dimensionless parameter ψ is defined by the following equation.

FIG. 6 shows a relative representation of the measured value of the dynamic load with this dimensionless parameter taken as the horizontal axis. It can be seen from this that as the value of T increases, the dynamic load decreases. 1 on the vertical axis
．． 0 is the conventional dynamic load level and the corresponding value of ψ is 100. Therefore, performance superior to the conventional type can be obtained in the range ψ>100. In particular, in the region of r≧300, the dynamic load is significantly reduced. In addition, Fig. 7 shows the relationship between the exhaust system steam flow rate and ψ, but since an increase in T generally corresponds to a decrease in the total area of the coolant outlet 14, the exhaust flow rate This will lead to a decline. However, in the region of ψ≦1000, no significant decrease in exhaust flow rate is observed, and the original function as a relief vent pipe can be fully satisfied.

Therefore, if the relief vent pipe structure is such that ψ exists in the region of 100<'f'≦1000,
The effect is that the function of the relief vent pipe 12 is not impaired and the dynamic load can be reduced.

By the way, as is clear from Equation 1 (7), the means to increase T and alleviate the load of bubble pressure pulsation are as follows: (1) Enlarging the pipe diameter (increasing ■) (2) Increasing the total number of coolant outlet ports Decrease in area (decrease in Ah) (3
) There are three types: decrease in the diameter of the coolant outlet (increase in zh), enlargement of the tip part illustrated in Figure 3 ((1)
) is not the only effective method. On the contrary, it should be noted that even if the pipe diameter is made smaller, a pipe that is effective in reducing the load can be manufactured by increasing the value of r using the above measures (2) and (3).

Moreover, FIG. 7 shows the relationship between the flow rate of exhaust system steam flowing into the relief vent and . An extreme increase in r causes a decrease in the exhaust flow rate. This is particularly dependent on the fact that the total area of the coolant outlet 14 is reduced. This is because among the parameters that constitute r in equation (7), Ah
This is because the effect is squared. There is no significant decrease in flow rate in the range of T≦1-〇〇〇.

〔Effect of the invention〕

As described above, according to the present invention, in a system for exhausting steam generated in a nuclear reactor into the coolant in a pressure suppression chamber, it is possible to reduce the dynamic load that occurs during exhaust without causing a significant decrease in the flow rate of the exhaust system. can be achieved.

[Brief explanation of the drawing]

Fig. 1 is an external view of the reactor containment vessel of a boiling water reactor, Fig. 2 is a sectional view taken along the line 1--1 shown in Fig. 1, and Fig. 3 is a relief which is a preferred embodiment of the present invention. Structural diagram of vent pipe,
Fig. 4 is an explanatory diagram showing the function of the relief vent pipe shown in Fig. 3, Fig. 5 is an enlarged view of the v section of Fig. 4, and Fig. 6 is a characteristic showing the relationship between dimensionless parameters and the magnitude of dynamic load. Figure, 7th
The figure is a characteristic diagram showing the relationship between dimensionless parameters and exhaust system steam flow rate. 1...Reactor pressure vessel, 2...Dry well, 3...
- Pressure suppression chamber, 4... Cooling water, 12... Relief vent pipe, 13... Enlarged part, 14... Coolant discharge port.

Claims (1)

[Scope of Claims] 1. A steam exhaust system for a nuclear reactor that discharges steam generated in a reactor vessel through a pipe into a coolant in a pressure suppression chamber and condenses the steam, wherein the pipe is A large number of jet ports are formed in the part submerged in the coolant, and the internal volume of the region where the jet ports are formed is V, the total area of the jet ports is A_h, and the length of the wet end of the jet ports is Steam exhaust from a nuclear reactor characterized in that ψ, which is determined by the following formula ψ=(V・Z_h)/(4A_h^2), exists in the range of 10^2<ψ≦10^3, where is Z_h. Device.