JP2003329794A - Vent device for top of reactor pressure vessel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vent device for a top of a reactor pressure vessel which enables highly reliable safe operation by effectively and surely preventing accumulation of a non-condensible gas around the top of the reactor pressure vessel. <P>SOLUTION: The vent device 20 for the top of the reactor pressure vessel comprises a head spray system 31 of the reactor pressure vessel for feeding cooling water to a head spray nozzle 36 of the reactor pressure vessel disposed in an upper part of the reactor pressure vessel 22 and a vent system 30 of the reactor pressure vessel for guiding the non-condensible gas produced during operation of a reactor to a main steam pipe. The head spray system 31 of the reactor pressure vessel is provided with a branch vent system 32 branched from a reactor pressure vessel 22 side of a check valve 39 provided on a head spray pipe 38 of the reactor pressure vessel. The branch vent system 32 is provided with a vent branch pipe 40 branched from the head spray pipe 38 of the reactor pressure vessel. The vent branch pipe 40 has a downstream side thereof connected to a vent pipe 33 of the system 30 and an orifice 41 provided halfway of the vent branch pipe 40. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear reactor pressure vessel top vent facility for treating non-condensable gases present in the reactor pressure vessel.

[0002]

2. Description of the Related Art Generally, a boiling water nuclear power plant (hereinafter referred to as a BWR plant) has a reactor pressure vessel (hereinafter referred to as RPV) inside a reactor containment vessel (hereinafter referred to as PCV) 1 as shown in FIG. 2) is stored and this R
A gas treatment facility is provided around the top of PV2. RPV
A reactor core 3 is housed in the reactor 2, while the reactor core 3 is immersed in the reactor cooling water 4. The RPV 2 is divided into a liquid phase part in which the reactor cooling water 4 is stored and a gas phase part 5 above the liquid phase part.

In the reactor cooling water 4 in the RPV 2, hydrogen gas and oxygen gas, which are decomposed and produced from the cooling water 4 by neutron irradiation accompanying the nuclear reaction in the core 3, or, in some cases, a trace amount from the fuel rods are produced. There are leaking non-condensable gases such as radioactive noble gases such as Kr and Xe. For this reason, the gas waste treatment system (not shown) for treating the non-condensable gas is BW.
It is installed in the R plant.

During normal operation of the BWR plant, the non-condensable gas generated in the RPV 2 is guided from the RPV 2 via the main steam pipe 6 connected to the steam turbine T, and is guided to the condenser via the steam turbine T. After that, it is treated in the gaseous waste treatment system provided in this condenser. The main steam pipe 6 has P
Main steam isolation valves 7a and 7b are provided on the upstream side and the downstream side of the CV (reactor containment vessel) 1, respectively.

A reactor pressure vessel vent pipe (hereinafter referred to as RPV vent pipe) 8 is provided on the top of the RPV 2. The RPV vent pipe 8 is connected to the main steam pipe 6 via the motor-operated valve 9 on the upstream side of the main steam isolation valve 7a to form a reactor pressure vessel vent system (hereinafter, RPV vent system) 10. The RPV vent system 10 discharges the non-condensable gas that may accumulate in the RPV 2 from the top of the RPV 2 and joins the main steam passing through the main steam pipe 6.

Furthermore, when the operation of the BWR plant is stopped and the RPV2 is cooled, the RPV in the vapor phase is cooled.
A reactor pressure vessel head spray system (hereinafter referred to as an RPV head spray system) 11 that supplies cooling water to the upper portion of the RPV 2 is provided to cool the gas phase portion 5 in the RPV 2. The RPV head spray pipe 12 of the RPV head spray system 11 is provided with a check valve 13 and reactor containment (PCV) isolation valves 14a and 14b near the inside and outside of the PCV 1, respectively.

When the boiling water reactor is stopped, cooling water is supplied from the RPV head spray pipe 12 through the check valve 13 to the RPV.
2 is sprinkled with water to cool the upper part of the dome in RPV2.

[0008]

The non-condensable gas generated in the RPV 2 during the normal operation of the boiling water reactor is basically a gas discharged from the condenser through the main steam pipe 6 and the steam turbine T. It is transferred to the waste treatment system and treated in this gaseous waste treatment system. The non-condensable gas accumulated in the upper part of the RPV 2 is also discharged into the main steam pipe 6 by the RPV vent system 10,
The design is designed to prevent the accumulation of non-condensable gas above the RPV2.

However, the RP connected to the top of the RPV2
The V head spray system 11 does not take any measures to reliably prevent the accumulation of non-condensable gas. In order to surely prevent the accumulation of non-condensable gas even around the top of the RPV2, it is necessary to prevent the gas accumulation itself in a portion where the non-condensable gas may be accumulated to some extent. This is important for ensuring stable operation and reliable operation.

On the other hand, during normal operation of the boiling water reactor, R
It is known that hydrogen gas and oxygen gas, which are the main components of the non-condensable gas generated in PV2, are accumulated at the rising portion of the pipe. From this point of view as well, it is strongly desired to prevent gas accumulation in the top of the RPV2 where there is a possibility that some non-condensable gas may accumulate, in advance.

The present invention has been made in consideration of the above-mentioned circumstances, and efficiently and reliably prevents the accumulation of non-condensable gas around the top of the reactor pressure vessel, and ensures reliable and stable operation. It is an object of the present invention to provide a reactor pressure vessel top venting device capable of performing the above.

Another object of the present invention is to prevent the non-condensable gas from accumulating around the top of the reactor pressure vessel during normal operation, and to surely prevent the non-condensable gas from being accumulated during operation of the reactor isolation cooling system. It is to provide a venting equipment at the top of a reactor pressure vessel that can sufficiently maintain its function.

Another object of the present invention is to efficiently remove the non-condensable gas from the non-condensable gas accumulation portion where it is difficult to exhaust the non-condensable gas from around the reactor pressure vessel in the conventional reactor pressure vessel vent system. It is an object of the present invention to provide a vent facility at the top of a reactor pressure vessel that effectively and effectively exhausts gas and prevents the accumulation of non-condensable gas.

[0014]

In order to solve the above-mentioned problems, the reactor pressure vessel top venting equipment according to the present invention is, as set forth in claim 1, a reactor pressure vessel above a reactor pressure vessel. In a reactor pressure vessel having a reactor pressure vessel head spray system for supplying cooling water to a head spray nozzle and a reactor pressure vessel vent system for guiding a non-condensable gas generated during a reactor operation to a main steam pipe, The reactor pressure vessel head spray system includes a branch vent system branched from the reactor pressure vessel side of the check valve provided on the reactor pressure vessel head spray pipe, and the branch vent system is a reactor pressure vessel. A vent branch pipe branched from the vessel head spray pipe is provided, and the downstream side of this branch pipe is connected to the reactor pressure vessel vent pipe of the reactor pressure vessel vent system. In the middle of the branch pipe is provided with a orifice.

In order to solve the above-mentioned problems, the venting equipment at the top of the reactor pressure vessel according to the present invention comprises:
As described above, in the branch vent system, an on-off valve that is remotely operated is provided downstream of the orifice of the vent branch pipe.

Further, in order to solve the above-mentioned problems, the venting equipment at the top of the reactor pressure vessel according to the present invention comprises:
As described above, in the reactor pressure vessel head spray system, reactor containment vessel isolation valves are provided inside and outside the reactor containment vessel of the reactor pressure vessel head spray piping, while the reactor pressure vessel head is provided. The spray pipe is configured so as to also serve as the injection pipe of the cooling equipment for reactor isolation.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a reactor pressure vessel top vent facility according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a schematic system diagram showing an embodiment of a reactor pressure vessel top vent facility according to the present invention.

This reactor pressure vessel top vent equipment is generally designated by reference numeral 20, and is a reactor containment vessel (hereinafter referred to as PCV) 2 of a boiling water nuclear power plant (BWR plant).
1 and a reactor pressure vessel (hereinafter referred to as RPV) 22 are installed in a dry well 23.

The BWR plant is a reactor containment vessel (PC
A reactor pressure vessel (RPV) 22 is housed in V) 21 and a reactor core 24 is housed in this RPV 22. The reactor core 24 is immersed in the reactor cooling water 25. A liquid phase portion storing the reactor cooling water 24 is formed in the lower portion of the RPV 22, while a gas phase portion 26 of the RPV 22 is formed above the liquid phase portion.

The reactor cooling water 25 in the RPV 22 is heated and vaporized by receiving neutron irradiation by a nuclear reaction while passing through the core 24. The generated steam is separated into water and water in the RPV 22, dried, and then sent to the steam turbine 28 through the main steam pipe 27 to work in the steam turbine 28.
Drive a generator (not shown). The main steam pipe 27 is provided with main steam isolation valves 29 a and 29 b on the upstream side and the downstream side of the reactor containment vessel 21, respectively. The steam that has worked in the steam turbine 28 and has expanded is condensed in a condenser (not shown) and then passes through the reactor condensate / water supply system to R
It is returned to the PV 22 again.

Further, the reactor pressure vessel top vent equipment 20 provided in the reactor pressure vessel (RPV) 22 of the BWR plant is a reactor pressure vessel (RPV) vent system 30.
And a branch vent system 32 branched from a reactor pressure vessel head spray system (hereinafter referred to as an RPV head spray system) 31.

The RPV vent system 30 is a reactor pressure vessel (RPV) vent pipe 33 connected to the top of the RPV 22.
Have. The RPV vent pipe 33 is connected to an RPV head vent nozzle 34 formed on the top of the RPV 22, and on the other hand, an electric valve 3 which is remotely operated as an on-off valve.
5 are provided. The downstream side of the motor-operated valve 35 is connected to the main steam pipe 27 on the upstream side of the main steam isolation valve 29 a in the reactor containment vessel 21.

The branch vent system 32 also includes a vent branch pipe 40 branched from the check valve 39 downstream side of the reactor pressure vessel (RPV) head spray pipe 38. An orifice 41 is provided in the vent branch pipe 40, and the downstream side of the orifice 41 is the R of the RPV vent system 30.
It is connected to the PV vent pipe 33 on the upstream side of an electrically operated valve 35 as an on-off valve which is remotely operated. Bent branch pipe 40
Is provided at the top of the RPV head spray pipe 38 downstream of the check valve 39. Bent branch pipe 40
The branch portion of is provided at a position as close as possible to the check valve 39.

Further, the RPV head spray system 31 is
The RPV head spray pipe 38 is provided on the top of the RPV 22 and the reactor pressure vessel head spray nozzle (hereinafter,
It is called RPV head spray nozzle. ) 36. The RPV head spray pipe 38 of the RPV head spray system 31 may also serve as the cooling water injection pipe of the reactor isolation cooling facility (hereinafter referred to as RCIC) 43. RCIC43 is RPV2 when the boiling water reactor is shut down.
2 is equipment for cooling the gas phase portion 26 of the RPV 22 by using the cooling water of the cooling system at the time of stop in order to reduce the residual pressure of the upper dome.

On the other hand, the RP of the RPV head spray system 31
The V head spray pipe 38 is provided with a check valve 39 and a reactor containment vessel isolation valve (PCV isolation valve) 44a, 44b on the way. The PCV isolation valves 44a and 44b are installed inside and outside the reactor containment vessel 21, respectively, and are normally closed during the operation of the reactor.

By the way, the RPV vent system 30 and the branch vent system 32 using the RPV head spray system 31 constituting the reactor pressure vessel top vent equipment 20 work in cooperation with each other to non-condensate around the reactor pressure vessel 22. The non-condensable gas is led out from the gas accumulating portion and discharged to the main steam pipe 27.

R is provided on the top of the reactor pressure vessel (RPV) 22.
By providing the PV vent system 30 and the branch vent system 32 using the RPV head spray system 31 and allowing them to cooperate with each other, a portion that may accumulate near the top of the RPV 22 during normal operation of the nuclear power plant. The non-condensable gas such as oxygen gas, hydrogen gas and radioactive noble gas such as Kr and Xe can be smoothly and smoothly discharged to the main steam pipe 27 side, and the non-condensable gas is accumulated around the top of the RPV 22. To prevent this from happening.

Next, the vent equipment 20 at the top of the reactor pressure vessel
The action of will be described.

This reactor pressure vessel top venting equipment 20
Is the main steam isolation valve 2 during normal operation of the BWR plant.
9a, 29b and the motor operated valve 35 are set to the open state,
The PCV isolation valves 44a and 44b are set to the closed state.

When the reactor is operated, hydrogen gas and oxygen gas are decomposed and produced from the radiolysis of the reactor cooling water 25 caused by the nuclear reaction in the core 24, while the fuel rods of the fuel assemblies loaded in the core are sometimes generated. There is a radioactive noble gas such as Kr or Xe that may leak in a smaller amount. These non-condensable gases such as hydrogen gas, oxygen gas, and radioactive noble gas are generated in the RPV 22 during normal operation of the nuclear power plant.

Most of the generated non-condensable gas is RPV2.
2 is mixed with the main steam through the main steam pipe 27, is guided to the steam turbine 28, and is discharged from the steam turbine 28 to a condenser (not shown), and the gas waste attached to this condenser is discharged. A material processing system (not shown) guides and processes.

During normal operation of the BWR plant, the motor-operated valve 35 that is remotely operated is set to the open state.
The PV vent system 30 and the branch vent system 32 are in operation. Therefore, the non-condensable gas in or around the head portion of the RPV 22 passes through the main steam pipe 2 through the RPV vent pipe 33 of the RPV vent system 30 and the vent branch pipe 40 of the branch vent system 32 using the RPV head spray system 31.
A vent channel leading to 7 is formed. Therefore, RP
Non-condensable gas accumulates in the vicinity of the head portion of the V22, for example, in the head portion of the RPV 22, the electric valve 35 upstream side piping portion of the RPV vent system 30, and the check valve 39 downstream side piping portion of the RPV head spray system 31. Can be prevented in advance.

When the BWR plant is shut down,
The electric valve 35 of the RPV vent system 30 is closed, and the PCV isolation valves 44a and 44b are opened. By opening the PCV isolation valves 44a and 44b, a part of the cooling water for the stop cooling system (for example, cooling water in the suppression chamber) is supplied to the RPV 22 through the RPV head spray system 31 and spray-cooled. , The residual pressure of the RPV22 upper dome is lowered.

At this time, the branch vent system 32 is branched from the RPV head spray system 31, but the electric valve 35 of the RPV vent system 30 is closed, and the branch vent system 32 is closed.
Due to the throttling resistance of the orifice 41, it is possible to reliably prevent the cooling water from flowing into the main steam pipe 27 side, and almost the entire amount is effectively supplied into the RPV 22.

RPV by RPV head spray system 31
In order to surely close the motor-operated valve 35 of the RPV vent pipe 33 during head spraying of 22, the motor-operated valve 35 can be closed by an opening permission signal of the PCV isolation valves 44a and 44b.

During normal reactor operation, RCIC43
When the valve operates, the branch vent system 32 for the cooling water immediately after the operation
The transfer resistance to the RPV head spray pipe 38 of the RCIC 43 is prevented by preventing the shift to the maximum by the throttling resistance of the orifice 41.
There is no problem with the cooling water injection function via the.

According to this reactor pressure vessel top vent equipment 20, the non-condensable gas cannot be discharged only by the conventional RPV vent system 30 during the normal operation of the nuclear power plant, and the accumulation of the non-condensable gas cannot be prevented. A non-condensable gas from a part, for example, the check valve 39 downstream side piping part of the RPV head spray system 31 can also be reliably discharged, and gas accumulation in the RPV head spray piping part can be prevented in advance. Moreover, even if the non-condensable gas is prevented from accumulating in the downstream piping of the RPV head spray system 31, the cooling function of the RCIC 43 is not impaired, so that reliable and stable operation can be performed.

FIG. 2 is a schematic system diagram showing a second embodiment of the reactor pressure vessel top vent equipment according to the present invention.

The reactor vent vessel top vent equipment 20A shown in this embodiment has a structure of a branch vent system 45 shown in FIG.
Since it is basically different from the reactor pressure vessel top vent equipment 20 shown in FIG. 3 and other configurations are substantially the same, the same reference numerals are given and description thereof will be omitted.

The branch vent system 45 is provided with a vent branch pipe 46 branched from the downstream side of the check valve 39. The vent branch pipe 46 is provided with an orifice 41 and an electrically operated opening / closing valve in the middle thereof. A valve 47 is provided. The orifice 41 is provided near the branch from the reactor pressure vessel head spray system 31, while the electric valve 47 is provided downstream of the orifice 41 near the orifice 41.

Next, the vent equipment 20 at the top of the reactor pressure vessel
The operation of A will be described.

This reactor pressure vessel top vent equipment 20A
Is the main steam isolation valve 2 during normal operation of the BWR plant.
9a, 29b and the motor-operated valves 35, 47 are set to the open state, and the PCV isolation valves 44a, 44b are set to the closed state.

When the reactor is operated, hydrogen gas and oxygen gas are decomposed and produced by the radiolysis of the reactor cooling water 25 caused by the nuclear reaction in the core 23, while the hydrogen rods and the fuel rods of the fuel assembly loaded in the core may be generated. There is a radioactive noble gas such as Kr or Xe that may leak in a smaller amount. These non-condensable gases such as hydrogen gas, oxygen gas, radioactive noble gas, etc., are generated by the RPV22 during normal operation of the nuclear power plant.
Occurs within.

The generated non-condensable gas is mixed with the main steam from the RPV 22, passes through the main steam pipe 27, and then the steam turbine 28.
On the other hand, it is discharged from the steam turbine 28 to a condenser (not shown) and is guided to a gas waste treatment system (not shown) attached to this condenser for treatment.

During normal operation of the BWR plant, since the electrically operated valves 35 and 47 that are remotely operated are set to the open state, the RPV vent system 30 and the branch vent system 45 are in the operating state. Therefore, the non-condensable gas in and around the head portion of the RPV 22 is R of the RPV vent system 30.
A vent flow path communicating with the main steam pipe 27 is formed through the PV vent pipe 33 and the vent branch pipe 46 of the branch vent system 45 using the RPV head spray system 31. Therefore, in the vicinity of the head portion of the RPV 22, for example, in the head portion of the RPV 22, the electric valve 35 upstream piping portion of the RPV vent system 30, and the check valve 3 of the RPV head spray system 31.
9. It is possible to prevent the non-condensable gas from accumulating in the downstream piping portion before and surely.

When the BWR plant is shut down,
Motorized valve 35 of RPV vent system 30 and branch vent system 4
5 is closed, and the PCV isolation valves 44a, 44 are closed.
b is opened. By opening the PCV isolation valves 44a and 44b, a part of the cooling water in the cooling system during stop (for example, cooling water in the suppression chamber) is supplied into the RPV 22 through the RPV head spray system 31 and spray-cooled. The residual pressure in the upper dome of the RPV22 is reduced.

At this time, the branch vent system 45 is branched from the RPV head spray system 31, but the branch vent system 4
Since the motor-operated valve 47 of No. 5 is closed, it is possible to reliably prevent the cooling water from flowing into the main steam pipe 27 side, and the total amount is RPV.
22 is supplied.

RPV by RPV head spray system 31
In order to surely close the motor-operated valve 47 of the branch vent system 45 and the motor-operated valve 35 of the RPV vent pipe 33 during the head spray of 22, the PCV isolation valve 4 is closed.
It is also possible to use the opening permission signals of 4a and 44b.

Further, when the RPV head spray system 31 operates during normal reactor operation, the transfer of the cooling water to the branch vent system 45 immediately after the operation is prevented by the throttle resistance of the orifice 41 as much as possible, and the branch vent is also provided. The motor-operated valve 47 of the system 45 and the motor-operated valve 35 of the RPV vent system 30 are closed by receiving the automatic closing signal a by the activation of the RPV head spray system 31, and thereby the RPV head spray system (RCIC
43) There is no problem in the cooling water injection function via the RPV head spray pipe 38 of 31.

This reactor pressure vessel top vent equipment 20A
According to this, during the operation of the BWR plant, it is possible to smoothly and smoothly discharge the non-condensable gas around the RPV 22 in a portion that cannot be discharged only by the operation of the conventional RPV vent system 30. It is preferable to provide the branch vent system 45 with the orifice 41 and the motor-operated valve 47 in terms of operation when the reactor is stopped.

Moreover, the venting equipment 2 at the top of the reactor pressure vessel
Even if 0A adopts a structure for discharging the non-condensable gas from the downstream piping of the RPV head spray system 31, the RCIC
Since the cooling function of 43 is not impaired, highly reliable and stable operation can be performed.

Although FIG. 2 shows an example in which the vent branch pipe 46 of the branch vent system 45 is connected to the upstream side of the electric valve 35 of the RPV vent system 30, the vent branch pipe 46 is located downstream of the electric valve 35. It may be connected to the RPV vent pipe 33, or may be directly connected to the main steam pipe 27.

(Other Embodiments) RCIC in normal operation
By closing the electrically operated valve 35 of the RPV vent system 30 and the electrically operated valve 47 of the branch vent system 45 by a remote manual operation after the activation signal of 43, the injection function of the RCIC 43 is further improved.

[0055]

EFFECTS OF THE INVENTION In the reactor pressure vessel top vent equipment according to the present invention, a reactor pressure vessel vent system and a branch vent system utilizing a reactor pressure vessel head spray system are provided to the vicinity of the reactor pressure vessel top. Accumulation of non-condensable gas can be prevented efficiently and reliably, and reliable and stable operation can be performed.

Even when the reactor pressure vessel head spray system is also used as the injection pipe of the reactor isolation cooling system, non-condensable gas is accumulated near the top of the reactor pressure vessel during normal operation of the reactor. By the cooperation of the reactor pressure vessel vent system and the branch vent system, it prevents it in advance and surely, and fully demonstrates the injection cooling function without impairing the injection cooling function during operation of the reactor isolation cooling system, Can be maintained.

Further, the exhaust treatment of the non-condensable gas in the portion which cannot be exhausted by the reactor pressure vessel vent system can be efficiently and effectively performed by the branch vent system, and the non-condensable gas around the top of the reactor pressure vessel can be treated. It is possible to prevent gas from accumulating in advance.

[Brief description of drawings]

FIG. 1 is a schematic system diagram showing an embodiment of a reactor pressure vessel top vent facility according to the present invention.

FIG. 2 is a system diagram showing a second embodiment of a reactor pressure vessel top vent facility according to the present invention.

FIG. 3 is a schematic system diagram of a conventional reactor pressure vessel top vent facility of a nuclear power plant.

[Explanation of symbols]

20 Reactor Pressure Vessel Top Vent Equipment 21 Reactor Containment Vessel (PCV) 22 Reactor Pressure Vessel (RPV) 23 Drywell 24 Reactor Core 25 Reactor Cooling Water (Liquid Phase) 26 Gas Phase (Vapor Phase) 27 Main Steam pipe 28 Steam turbines 29a, 29b Main steam isolation valve 30 Reactor pressure vessel vent system (RPV vent system) 31 Reactor pressure vessel head spray system (RPV head spray system) 32 Branch vent system 33 Reactor pressure vessel vent pipe ( RPV vent pipe) 34 Reactor pressure vessel head vent nozzle (RPV head vent nozzle) 35 Motorized valve (remote control valve) 36 Reactor pressure vessel head spray nozzle (RPV head spray nozzle) 37 Drywell 38 Reactor pressure vessel head spray Piping (RPV head spray piping) 39 Check valve 40 Vent branch arrangement 41 orifice 43 reactor core isolation cooling system (RCIC) 44a, 44b reactor containment isolation valve (PCV isolation valve) 45 branch vent system 46 bent branch pipe 47 the electric valve (remote control valves)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akio Shioiri             8th Shinsugita Town, Isogo Ward, Yokohama City, Kanagawa Prefecture             Ceremony company Toshiba Yokohama office (72) Inventor Richi Kuroda             8th Shinsugita Town, Isogo Ward, Yokohama City, Kanagawa Prefecture             Ceremony company Toshiba Yokohama office

Claims (3)

[Claims] 1. A reactor pressure vessel head spray system for supplying cooling water to a reactor pressure vessel head spray nozzle above a reactor pressure vessel, and an atom for guiding a non-condensable gas generated during reactor operation to a main steam pipe. In a reactor pressure vessel with a reactor pressure vessel vent system, the reactor pressure vessel head spray system is branched from the reactor pressure vessel side of the check valve provided on the reactor pressure vessel head spray pipe. The branch vent system is provided with a vent branch pipe branched from the reactor pressure vessel head spray pipe, and this branch pipe is connected to the reactor pressure vessel vent pipe of the reactor pressure vessel vent system on the downstream side. On the other hand, the vent equipment at the top of the reactor pressure vessel is characterized in that an orifice is provided in the middle of the vent branch pipe. 2. The reactor vent vessel top vent facility according to claim 1, wherein the branch vent system is provided with an on-off valve which is remotely operated downstream of the orifice of the vent branch pipe. 3. The reactor pressure vessel head spray system comprises reactor containment vessel isolation valves inside and outside the reactor containment vessel of the reactor pressure vessel head spray piping, while the reactor pressure vessel head spray system is provided. The reactor pressure vessel top vent equipment according to claim 1, wherein the piping is configured so as to also serve as an injection piping of the reactor isolation cooling equipment.