JPS6223839B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steam exhaust system, and more particularly to a steam exhaust system having a relief vent pipe for a containment vessel of a boiling water nuclear reactor.

FIG. 1 schematically shows a reactor containment vessel of a conventional boiling water reactor. The reactor containment vessel includes a dry well 2 that stores the reactor pressure vessel 1.
It consists of a donut-shaped pressure suppression chamber (hereinafter referred to as a torus) 3, and a vent system connecting these, and the torus 3 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 6, and the lower portions of the vent pipe 5 and the relief vent pipe 6 are immersed in cooling water 4. The vent pipe 5 guides the steam in the dry well 2 into the cooling water 4 in the pressure suppression chamber 3 in the event of a coolant loss accident hypothetically rupturing a reactor pipe. The relief vent pipe 6 guides steam within the reactor pressure vessel 1 into the cooling water 4 within the pressure suppression chamber 3. 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. A large load (bubble pressure pulsation) is applied. Furthermore, the steam condensation vibration load 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 discharged from the relief vent pipe 6 into the cooling water 4 . These loads are transmitted to structures such as relief vent pipes and pressure suppression chambers,
There is a risk of damage to these structures.

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.

The present invention has experimentally confirmed that the pulsating load applied to the pressure suppression chamber when the relief valve is activated is caused by the vibration of high-pressure bubbles released from the relief vent pipe, and the present invention has developed a relief vent pipe as a means to eliminate this. The tip of the bubble is enlarged to promote a decrease in bubble pressure, and dimensionless parameters are constructed from the volume of the enlarged part, the total flow area of the small holes installed on the surface of the enlarged part, and the wetted length of the small holes. It also defines the range of dimensionless parameters that are effective for reducing loads.

An example of the relief vent pipe according to the present invention is shown in FIG. The tip 13 of the relief vent pipe 12 is
It 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 . Tip part (hereinafter referred to as enlarged part) 1
3 is provided with a plurality of coolant outlet ports 14. 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 in the reactor pressure vessel 1 flows into the relief vent pipe 12, and the relief vent pipe 1
Compress the air present in 2. 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. In the present invention, the pressure inside the relief vent pipe 12 is actively reduced by enlarging the enlarged portion 13 at the tip of the relief vent pipe 12, and air is gradually discharged by arranging the coolant outlet 5 in the water depth direction.
The load is relieved by the above two effects. Fourth
The effects of the present invention will be explained in detail with reference to FIG. 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.

P∝V¨B _... (1) A liquid level 15 is formed in the relief vent pipe 12. As the liquid level 15 falls in the direction of the arrow 16, the number of coolant outlets 14 increases, so the right side of equation (1) is the increase rate of the flow path area of the coolant outlets 14 A〓 _h
is proportional to. Also, the mass flow rate of the coolant is proportional to the pressure P ₁ inside the relief vent pipe 12, and the mass flow rate of the coolant is proportional to the pressure P 1 inside the relief vent pipe 12.
It is proportional to the hydraulic equivalent diameter D _h of 4. Therefore, V¨ _B ∝P ₁ D _h A〓 _h ……(2). If the rate of descent of the liquid level 15 is constant, then A〓
_h is proportional to the outlet area per unit length.

Therefore, A〓 _h ∝na/S ……(3) Here, n is the coolant outlet 1 at the same height.
The number a in 4 is the cross-sectional area S of one coolant outlet, which is the pitch of the coolant outlet array in the height direction.

In addition, the relief vent pipe internal pressure P ₁ is the enlarged part 13
P ₁ ∝A ⁻¹ _P ...(4) Therefore, from equations (1) to (4), the dynamic pressure P is P∝naD _h /SA _P ...(5) If the length of the part where the outlet 5 is located is L, then the volume V (=A _P L) of the enlarged part 13 and the total area A _h (=L/S×na) of the coolant outlet 14 are established, and the hydraulic power The equivalent diameter D _h is A _h and the wetted edge length Z _h of the coolant outlet 14.
Using this, D _h (=4A _h /Z _h ) is obtained. Substituting this into equation (5), we get the following equation.

P∝4A _h ² /Z _h V ... (6) The dimensionless parameter is defined by the following formula.

=Z _h V/4A _h ² ...(7) This dimensionless parameter is plotted on the horizontal axis, and the measured values of the dynamic load are relativeized and shown in FIG. It can be seen that as the value increases from now on, the dynamic load decreases. 1.0 on the vertical axis is the conventional dynamic load level, and the corresponding value is 100. Therefore, better performance than the conventional type can be obtained in the range >100. In particular, in the region of ≧300, the dynamic load is significantly reduced. Furthermore, Fig. 7 shows the relationship between the exhaust system steam flow rate and the exhaust system steam flow rate. will be invited. However, in the range of ≦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 the value exists in the range of 100<≦1000, the function of the relief vent pipe 12 is not impaired and the dynamic load can be reduced.

According to the present invention, dynamic loads are reduced without impairing the function of the relief vent pipe.

[Brief explanation of the drawing]

Figure 1 is an external view of the reactor containment vessel of a boiling water reactor, Figure 2 is a cross-sectional view of the torus shown in Figure 1,
Fig. 3 is a structural diagram of a relief vent pipe according to a preferred embodiment of the present invention, Fig. 4 is an explanatory diagram showing the function of the relief vent pipe shown in Fig. 3, and Fig. 5 is a V section of Fig. 4. The enlarged view, FIG. 6 is a characteristic diagram showing the relationship between the dimensionless parameter and the magnitude of the dynamic load, and FIG. 7 is a characteristic diagram showing the relationship between the dimensionless parameter and the 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 section, 14... Coolant discharge port.

Claims (1)

[Scope of Claims] 1. A steam exhaust device having a relief vent pipe connected to a reactor vessel and guiding steam in the reactor vessel into a coolant in a pressure suppression chamber, wherein The cross-sectional area of the first region of the relief vent pipe is made larger than the cross-sectional area of the second region of the relief vent pipe located above the first region of the relief vent pipe. A large number of jet ports are formed in the first region, and when the internal volume of the first region is V, the total area of the jet ports is A _h , and the length of the groove of the jet ports is Z _h , the following A steam exhaust device characterized in that it is determined by the formula = (V・Z _h )/(4A _h ² ) and exists in the range of 10 ² <≦10 ³ .