JPS58218688A - Emergency shutdown system for reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides an atomic system that safely cold-shuts down a nuclear reactor by injecting a neutron absorber with a large neutron absorption capacity into the reactor when control rods cannot be inserted. Concerning emergency shutdown method of furnace.

[Technical Background of the Invention] Conventionally, in nuclear power plants that use light water reactors, if a situation occurs where control rods cannot be inserted into the reactor core, sodium pentaborate (chemical formula: Na
A method has been adopted in which a neutron absorber consisting of an aqueous solution of 2 B+eO+ 6 :10H20) is injected to safely bring the reactor to cold shutdown from rated power operation.

In order to inject this neutron absorber into a nuclear reactor, a neutron absorber injection device 1 as shown in the figure is generally used. This neutron absorber injection device 1 is housed in an auxiliary building 2, which includes a stainless steel storage tank 4 for storing the neutron absorber 3, a test tank 5, an injection pump 6, an injection pump explosion valve 7, and others. The main part is composed of piping 8 and the like necessary for the system.

The operation of the neutron absorber injection device 1 is performed by remote manual operation from the main control room, and the injection pump explosion valve 7
By operating the injection pump 6, neutron absorption J3 is injected from the storage tank 4 into the reactor 9. At this time, the neutron absorber 3 is injected into the reactor 9 through the nozzle 11 at the bottom of the reactor pressure vessel 10 and mixed into the coolant of the reactor 9. Note that 12 is the core of the nuclear reactor 9.

[Problem 1 of Background Art The size of such a neutron absorbent injection device 1 is determined as follows.

First, the minimum boron concentration is excluded by the nuclear meter. This minimum boron concentration is defined as the minimum amount of boron required to bring the reactor 9 into cold shutdown divided by the amount of water in the reactor pressure vessel 10 at normal water level, including the recirculation piping. I can do it. Next, the desired boron concentration is determined from this minimum boron concentration, including allowances for uneven mixing and leakage, and allowances for dilution of reactor residual heat removal system piping, etc. Design 1 Once the m degree of boron is determined, the reactor pressure vessel 10
The required amount of sodium pentaborate to be injected into the furnace is calculated from the amount of water, and the required volume of the storage tank 4 is calculated from this injected amount into the furnace. At that time, the solubility of 1-lium pentaborate varies depending on the temperature, so the design temperature used for the h1 cage is set to a sufficiently low value that can be maintained. Furthermore, the storage tank 4 is controlled by electric heating so that the temperature does not drop below the design temperature. The volume of the stage 81 of the storage tank 4 is determined by including the necessary volume of the storage tank 4 calculated in this way and the allowance for water evaporation and free space.

On the other hand, the boron concentration change rate of the coolant in the reactor 9 is calculated by the nuclear meter, and the time range in which the sodium pentaborate aqueous solution in the storage tank 4 should be injected into the reactor 9 corresponds to this boron concentration change rate h1. This allows the infusion pump 6
The design flow rate of is determined.

The design capacity of the storage tank 4 and the design flow rate of the injection pump 6 determined as described above are considerably large values, and therefore, a neutron absorbent injection device using an aqueous sodium pentaborate solution as a neutron absorbent becomes bulky. .

[Object of the Invention] The present invention has been made to address the above-mentioned problems, and when it is impossible to insert a control rod into the core of a nuclear reactor, an element with a larger neutron absorption cross section than boron is introduced into a pressure vessel housing the core. Provides an emergency shutdown method for a nuclear reactor that enables safe cold shutdown of a nuclear reactor with a smaller injection amount of neutron absorber than conventional methods by injecting a neutron absorber made of an aqueous solution of a compound such as gadolinium nitrate. This is what I am trying to do.

[Summary of the Invention 1 1 In other words, the present invention provides, when control rods cannot be inserted into the core of a nuclear reactor, a neutron absorption system consisting of an aqueous solution of a compound of an element having a larger neutron absorption cross section than boron into a pressure vessel housing the core. This is an emergency shutdown method for a nuclear reactor, characterized by bringing the reactor to cold shutdown by injecting a chemical agent.

Examples of L invention] The details of the present invention will be explained below with reference to one embodiment.

In the unlikely event that a control rod becomes unable to be inserted into the reactor core, trinium (nitric acid), which has a greater neutron absorption effect than the conventional sodium pentaborate aqueous solution, is used as a neutron absorber.
Chemical formula: Gd (NOs)! 1.6.5H20
) An aqueous solution is injected into the reactor 9 from the neutron absorber injection device 1 configured as shown in the drawing by remote control from the main control room, and mixed into the coolant of the reactor 9, allowing the C1 reactor 9 to safely operate at its rated power. From Cold 4- to Warm Shutdown.

Here, a neutron absorber has the ability to absorb neutrons, and the probability that a certain atomic nucleus absorbs neutrons is quantitatively expressed by a quantity called absorption cross section. In other words, this absorption cross section is proportional to the probability of absorbing neutrons, and if the value is doubled, the effect of absorbing neutrons is doubled.

Using this absorption cross section to express the neutron absorption effect of gadolinium nitrate per molecule of sodium pentaWAate, gadolinium nitrate has an absorption effect of 49,000 burns, and sodium pentaborate has an absorption effect of 3,800 burns. In other words, gadolinium nitrate has a neutron absorption capacity approximately 13 times that of sodium pentaIslate on a per molecule basis. Moreover, the molecular density of nitric acid in gadolinium nitrate aqueous solution is the same as or greater than that of helium (pentaboric acid) in sodium pent(2)ate aqueous solution, so gadolinium nitrate aqueous solution has not been used conventionally. It has a neutron absorption capacity more than 13 times greater than pentaboric acid solution.

In addition to the above gadolinium nitrate aqueous solution, an aqueous solution of a compound of zamarium, ]-ropium or cadmium with chlorine or a base can also be used as a neutron absorber. However, the neutron absorption capacity of aqueous solutions of these compounds is greater than conventional sodium pentaborate aqueous solutions, but smaller than gadolinium nitrate aqueous solutions, so gadolinium nitrate aqueous solutions are optimal as neutron absorbers.

In addition, nitrate compounds such as gadolinium nitrate are generally
Since the storage tank 4 is highly corrosive, it is desirable to use a highly corrosion-resistant liner for the inner wall of the storage tank 4 etc. instead of the conventional stainless steel liner, or to form the entire storage tank 4 from ceramics or the like.

[Effects of the Invention] As is clear from the explanations given below, according to the present invention, a neutron absorber is used that has a much greater neutron absorbing effect than the conventional one, so it can be injected into the reactor with only small stones. , the neutron absorber injection device can be significantly downsized.

[Brief explanation of the drawing]

The figure is a piping system diagram of a neutron absorber injection device for injecting a neutron absorber into a nuclear reactor. 1...Neutron absorber injection device 3.
・・・・・・・・・・・・Neutron absorber 4・・・・・・・・・
...... Storage tank 6 ...... Injection pump 7 ...... Injection pump explosion valve 9
......... Nuclear reactor 10... Nuclear pressure vessel 12...
・・・・・・・・・Reactor representative patent attorney Sasu Suyama −

Claims (2)

[Claims] (1) When control rods cannot be inserted into the reactor core, a neutron absorber made of an aqueous solution of a compound of an element with a larger neutron absorption cross section than boron is injected into the pressure vessel housing the reactor core. A method for emergency shutdown of a nuclear reactor, characterized by cold shutdown of a nuclear reactor. (2) The method for emergency shutdown of a nuclear reactor according to claim 1, wherein the compound is gadolinium nitrate.