JPS6030917B2 - Reactor decontamination cooling method and decontamination cooling device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a decontamination cooling method and a decontamination cooling device for a nuclear reactor.

The reactor has a reactor coolant purification system for purifying the coolant in the reactor pressure vessel, and a reactor coolant purification system for purifying the coolant in the reactor pressure vessel, and when the reactor is isolated, i.e.
A steam condensation system is provided to remove the decay heat of the reactor when the main steam isolation valve is fully closed.

FIG. 1 shows these reactor coolant purification system 2 and steam condensation system 5. The reactor coolant purification system 2 includes a pump 21
, a non-regenerative heat exchanger 23 provided with a cooling device having a refrigerant circulation pipe 22, a regenerative heat exchanger 24 provided to reduce heat loss, and a regenerative heat exchanger 24 provided to purify the coolant. The coolant passing through the core section 11 of the nuclear reactor 1 is provided with a filter 25 and a demineralizer 26.
7 leads through piping 28 from the regenerative heat exchanger 24 to the non-regenerative heat exchanger 23, where it maximizes the purification performance of the additives in the filter 25 and the resin in the demineralizer 26. temperature, cooled to below 60°C, filter 25,
Impurities in the coolant are removed by the demineralizer 26, reheated by the regenerative heat exchanger 24, and then returned to the reactor through the pipe 29, thus purifying the coolant in the reactor. .

Note that the filter 25 and the demineralizer 26 are configured to be bypassable by a switching valve 30. In addition, the steam condensing system 5
The system includes a system connected to a turbine 52 through a steam pipe 51, a heat exchanger 53, and a pump 54 operated by a turbine 52.
It consists of a system with

That is, when the reactor pressure vessel 1 is isolated, the steam generated when the coolant passing through the reactor section 11 in the reactor pressure vessel 1 is heated by the decay heat of the fuel is transferred to the steam pipe 55 and the pressure reducing valve 56 when the reactor pressure vessel 1 is isolated. It is guided to the heat exchanger 53.

A refrigerant circulation pipe 57 is attached to the heat exchanger 53, and the soot flowing inside the cold soot circulation pipe 57 cools the steam led to the heat exchanger 53, condenses it into condensate, and further cools it. do. The condensate that has been condensed and cooled by the heat exchanger 53 is led to the pump 54 through the control valve 58 and piping 59, and is then sent to the piping 60 and the injection device in the reactor pressure vessel 1 by the drive of the turbine 52. 12 into the reactor pressure vessel 1. At this time, the amount of condensate injected into the reactor pressure vessel 1 is determined by a signal transmitted from a water level gauge 61 attached to the heat exchanger 53 or a flow meter 62 attached to the piping 60'.
2 through the steam pipe 51 to control the speed of the turbine 52. The pseudo-steam that has been supplied to the turbine 52 and has done work is led into a pressure suppression chamber 64 where cooling water is stored, where it is condensed and stored. In this way, the decay heat of the reactor is removed by vaporizing the coolant in the reactor pressure vessel 1, removing the latent heat of the vapor using the heat exchanger 53, and returning it to the reactor as condensation. As described above, when the reactor is isolated, the steam inside the reactor is guided to the heat exchanger 53, the latent heat is removed by the liner, and the condensed water is injected into the reactor to cool the reactor. In order to reduce rapid cooling, the water level in the heat exchanger 53 is measured by the water level gauge 6 to measure the amount of steam condensation.
1 or a flow meter 62 at the outlet of the pump 54. In this device, control valves 56 and 58 are provided before and after the heat exchanger 53. This water level control proved to be very difficult as the water levels interfered with each other.

In addition, the condensate that has exited the heat exchanger 53 is returned to the reactor by the pump 54 driven by the turbine 52, but the condensate air from the turbine 52 is discharged into the pressure suppression chamber 64, so the pressure is suppressed. This results in an increase in radioactivity in the chamber 64 and an increase in radioactive waste, which poses a problem in its disposal.

In addition, the steam condensing system 5 includes a heat exchanger 53, a pump 54, a turbine 52, a medium circulation pipe 57, pipes connecting these, and control instruments 61, 62 that control the water level, and controls the equipment used. It is uneconomical because there are so many of them, and the large number of them also contaminates the equipment and piping with radioactivity.
A radiation shield is required. Although the reactor coolant purification system 2 can purify the coolant, it also removes or reduces radioactive crud adhering to the internal structures 13 in the reactor or the surface of the reactor core 11. It turned out that this was not possible.

In other words, the radioactive crud, as shown in Figure 2,
Adheres to the surface of the reactor pressure vessel/1 or the internal structure 13 or the reactor core 11 as a hard scale-like clad 130 or a colloidal clad 131,
As shown in Figure 3, these surface doses were found to increase as the operating period of the reactor became longer. The operating time (years) is plotted on the axis of the figure, and the surface dose of reactor internals (mR/h) is plotted on the vertical axis. The present invention aims to provide a nuclear reactor beam removal cooling method and a beam removal cooling device that can prevent the expansion of the radiation contaminated area of a nuclear reactor and the increase in radioactive waste. In a beam removal cooling method for a nuclear reactor, the coolant in the vessel is cooled by a regenerative heat exchanger and a non-regenerative heat exchanger, and then purified by a coolant purification means, and then circulated to the reactor vessel,
The cooling efficiency of the regenerative heat exchanger and the non-regenerative heat exchanger is adjusted in two stages by switching the refrigerant circulation of these heat exchangers, and the coolant that has been cooled and purified is cooled in the reactor vessel. A regenerative heat exchanger, the first feature of which is that circulation is performed by injection into at least the vapor phase within the reactor vessel, and the regeneration heat exchanger has a bypass flow path in a regeneration side flow path connected in series to the reactor vessel. and a non-regenerative heat exchanger, a coolant purifying means for purifying the coolant cooled by these heat exchangers, and a means for injecting the coolant purified by cooling into the reactor vessel. In the girder cooling system, the regenerative heat exchanger has a refrigerant channel capable of inserting and removing non-regenerative heat exchange, and the means for injecting the coolant into the reactor vessel is configured to inject steam in the reactor vessel. A second feature of the nuclear reactor is that it has an injection device that opens into the nuclear reactor vessel and removes radioactive crud adhering to the inner walls and surfaces of internal structures within the reactor vessel.

That is, the present invention makes it possible to adjust the cooling efficiency in two stages by combining two cooling systems, a reactor coolant purification system and a steam condensation system, and using a regenerative heat exchanger and a non-regenerative heat exchanger connected in series. At the same time, the coolant that has been cooled and purified is circulated into the reactor vessel by injecting the coolant not only into the middle of the reactor core but also into the vapor phase, such as the top of the core and the top of internal structures. This made it possible to achieve the intended purpose.

Examples will be described below. FIG. 4 shows an embodiment of the apparatus, in which the same components as in FIG. 1 are designated by the same reference numerals.

The difference from FIG. 1 is that the steam condensing system 5 in FIG. 1 is removed,
Adding the function of a steam condensation system to the reactor coolant purification system,
Furthermore, the structure has the added function of removing impurities adhering to the inner walls and surfaces of internal structures inside the nuclear reactor. That is, this reactor decontamination cooling system has switching valves 3 on the upstream side and downstream side of the conventional regenerative heat exchanger 24, respectively.
1 and 32 are provided, and both sides are connected to the upstream side of the switching valve 31 and the downstream side of the switching valve 32, and a bypass piping 33 that bypasses the regenerative heat exchanger 24 is provided. A switching valve 34 is provided in the bypass piping 33, and the switching valve 34
A common beam removal pipe 36 is provided via a switching valve 35, with one end connected to the upstream side of the reactor pressure vessel 1, and a pond end connected to the injection devices 12, 141, 142 provided in the reactor pressure vessel 1. The injection devices 141, 12, and 142 are provided at the top of the core 11, the top of the internal structure 13, and an intermediate section, respectively, and are connected to branch decontamination pipes 361, 3, respectively.
62, 363 are branched from the common decontamination pipe 36 and connected, and the branch decontamination pipes 361, 362, 363 are provided with switching valves 371, 372, 373. Also,
A switching valve 38 is installed upstream of the non-regenerative heat exchanger 23 in the refrigerant circulation piping 22 of the non-regenerative heat exchanger 23, and cold soot circulation piping 39, 40 is arranged from upstream of the switching valve 38 to the regenerative heat exchanger 24. The switching valves 41 and 42 are provided both downstream and upstream of the regenerative heat exchanger 24, and when the cold butterfly is circulating in the regenerative heat exchanger 24, the switching valves 31 and 32 are kept closed. A decontamination cooling method using a decontamination cooling device having such a structure will be explained.

First, when the reactor operation is stopped, the switching valve 31
, 34 are closed, the coolant circulates.

That is, the coolant guided from the bypass pipe 33 to the common beam removal pipe 36 is ejected from the injection devices 12, 141, 142, and is sprayed onto the inner surface of the reactor pressure vessel 1, the internal structure 13, and the reactor 0 section 11. Impurities attached to the surface are washed off and suspended in the coolant, and the coolant containing the floating impurities is discharged outside the reactor pressure vessel 1 via the piping 28 and the pump 27, and is used as non-regenerated heat. It is guided to the exchanger 23, cooled to several tens of degrees, further led to the filter 25 and demineralizer 26, purified, and returned to the bypass piping 33. Through this circulation, the reactor is decontaminated. will be carried out. In addition, if the steam coming out of a nuclear reactor is to be isolated in order to temporarily stop power generation for some reason, such as a lightning strike on a power transmission line at a power plant, decay heat remains inside the reactor, so it is necessary to If left in this condition, the pressure inside the reactor will rise and it is dangerous.

For this reason, it is possible to quickly return the reactor to power generation by removing the decay heat generated from the reactor, preventing pressure rise within the reactor, and maintaining the reactor at a high temperature. , the so-called reactor isolation high temperature standby operation,
During such isolated high-temperature standby operation of the reactor, the coolant is discharged from the reactor pressure vessel 1, and the discharged coolant passes through the piping 28 and the pump 27 to the regenerative heat exchanger 24 and the non-regenerative heat exchanger 24. The refrigerant is led to a regenerative heat exchanger 23, where the sensible heat in the coolant is removed and the temperature is cooled from 200-odd degrees to over 10-odd degrees, and then impurities are removed by a filter 25 and a demineralizer 26.
It is guided from the bypass pipe 33 of the regenerative heat exchanger 24 to the common pipe 36 for beam removal, and is injected into the reactor from the injection devices 12, 141, 142 in the vapor phase in the reactor pressure vessel 1,
Through this circulation of coolant, the reactor is cooled.
High temperature standby operation is performed. Figure 5 shows the temperature of the reactor after the decay heat of the reactor was removed by reactor isolation high temperature standby operation using this beam removal cooling system. The time after isolation (hr) and the reactor temperature (°C) are plotted on the vertical axis.

In this figure, A is the case where a conventional reactor purification system is used. In this case, decay heat is not removed because it is reheated in the regenerative heat exchanger 24, and the high-temperature standby operation is performed in the reactor. In order to prevent the pressure from increasing, the temperature inside the reactor is rising, even though it is necessary to lower it below the temperature indicated by D in the figure. On the other hand, lines B and C show the case where the decontamination cooling device described in the example was used, and line B shows the case where the regenerative heat exchanger 24 was bypassed and reheating was not performed. In this case, in the early stage of reactor isolation, the level is higher than the D line, and the cooling of the reactor is insufficient. The C line is connected to the regenerative heat exchanger 24,
This is the case where the coolant is guided and cooled through the cooling chamber circulation pipes 40 and 41. In this case, the temperature is below the D line, and the reactor can be sufficiently cooled even in the initial stage of isolation. The temperature of all lines A, B, and C decreases over time because the decay heat of the nuclear reactor decreases over time. In this way, when the decay heat at the initial stage of the reactor is large, cooling is performed by both the regenerative heat exchanger 24 and the non-regenerative heat exchanger 23, and when the decay heat of the reactor decreases, the switching valves 41 and 42 are turned on. By cooling only with the closed, non-regenerative heat exchanger 23, high-temperature standby operation of the reactor can be made possible. moreover,
The injection devices 12, 141, and 142 can inject cooled coolant into the vapor phase inside the nuclear reactor, thereby producing a depressurizing effect.

Furthermore, if the apparatus of this embodiment is used for high-temperature standby operation, there will be no leakage of radioactive coolant to the outside of the reactor, which is effective in reducing radioactive waste liquid.

In other words, when a conventional steam condensation system is used, the amount of liquid that exits the reactor as exhaust gas from the pump-driven turbine reaches 20 tons per hour, but with the device of this embodiment, this amount can be reduced to zero. can. Further, when the nuclear reactor is shut down, impurity crud attached to the inner surface of the reactor pressure vessel 1, the surface of the internal structure 13, and the surface of the reactor core 11 can be removed.

That is, as is clear from the characteristic diagram in Figure 3 showing the increase in radiation dose due to crud adhesion, the reactor operating period is 10.
In Wang's case, the radiation dose was several tens of milliroentgens or more, and he would be exposed to such high radiation during fuel replacement inside the reactor, but if the decontamination cooling method of this example is used, The radiation exposure can be reduced to a few milli-roentgens or less. In the above embodiment, since the decay heat is large in the early stage of reactor isolation, both the regenerative heat exchanger 24 and the non-regenerative heat exchanger 23 are used for cooling, and when the decay heat becomes low, the switching valve is turned on. Although the high-temperature standby temperature of the reactor was adjusted by cooling only with the non-regenerative heat exchanger 23 using the switching means 41 and 42, a flow control valve was provided at the outlet of the pump 27 or the pump 21, and the non-regenerative heat exchanger 23 was used for cooling. The outlet temperature can also be adjusted using this flow rate control valve. In this case, the reactor temperature can be automatically controlled. Furthermore, the temperature of the nuclear reactor can be limited by dividing the non-regenerative heat exchanger into several units and switching the coolant or liner medium flowing into the heat exchanger. As described above, the beam removal cooling method and beam removal cooling device of the present invention can prevent the expansion of the radioactive contaminated area of a nuclear reactor and the increase in radioactive waste, and have great industrial effects. It is something.

[Brief explanation of the drawing]

Figure 1 is a system diagram of the coolant purification system and steam condensation system of a conventional nuclear reactor, Figure 2 is a cross-sectional view showing the state of crud attached to the surface of the reactor internal structure, and Figure 3 is the atomic A characteristic diagram showing the reactor operating time and the surface dose of reactor internal structures, Figure 4 is a system diagram of one embodiment of the decontamination cooling system of the present invention, and Figure 5 shows changes in reactor water temperature after reactor isolation. FIG. Explanation of symbols, 1... Reactor pressure vessel, 11...
...Reactor core, 12,141,142...Injection device, 13...Internal structure, 23...Non-regenerative heat exchanger, 24... Regenerative heat exchanger, 25.
... Filter, 26 ... Demineralizer. Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Scope of Claims] 1. After the coolant in the reactor vessel is cooled by a regenerative heat exchanger and a non-regenerative heat exchanger, and then purified by a coolant purification means, the coolant is added to the reactor vessel. In a decontamination cooling method for a nuclear reactor that uses circulation, the cooling efficiency of the regenerative heat exchanger and the non-regenerative heat exchanger is adjusted in two stages by switching the refrigerant circulation of these heat exchangers, and A method for decontaminating and cooling a nuclear reactor, characterized in that the coolant is circulated into the reactor vessel by injecting it into at least the vapor phase within the reactor vessel. 2. A regenerative heat exchanger and a non-regenerative heat exchanger having a bypass flow path in the regeneration side flow path connected in series to the reactor vessel, and a coolant purification means for purifying the coolant cooled by these heat exchangers. and means for injecting the cooled and purified coolant into the reactor vessel. and the means for injecting the coolant into the reactor vessel opens into the vapor phase within the reactor vessel to remove radioactive crud adhering to the inner walls and surfaces of internal structures within the reactor vessel. 1. A decontamination cooling system for a nuclear reactor, characterized by having an injection device that does this. 3. The decontamination cooling system for a nuclear reactor according to claim 2, wherein the refrigerant flow path in which non-regenerative heat exchange is possible in the regenerative heat exchanger is a bypass flow path of the refrigerant circulation flow path in the non-regenerative heat exchanger. . 4. An injector opening into the vapor phase within the reactor vessel,
The decontamination cooling device for a nuclear reactor according to claim 2, which is an injection device provided at the top of the core portion and the top of the internal structure of the reactor vessel.