Boiling water reactor nuclear power plant with alcohol injection

The present invention relates to a nuclear power plant in general, and more particularly to a nuclear power plant having a boiling water reactor (BWR).

Background technology Oxidation caused by oxidants such as oxygen and hydrogen peroxide in the cooling water of the BWR can cause stress corrosion cracking (SCC) on the reactor components, and of the zirconium alloy cladding of the fuel pins. Can lead to corrosion. Known SCC reduction measures for reactor components such as reactor pressure vessels (RPVs), BWR internal components are noble metal chemical additions (NMCA: noble metal injection), and hydrogen hydrochemistry (HWC: hydrogen injection). These SCC reduction measures can reduce the SCC of internal components, but can increase the corrosion of fuel pink ruding.

The NMCA method is described, for example, in US Pat. Nos. 5,818,893, 5,904,991, and 6,793,883, where NMCA can include both online and offline addition of precious metals.

The HWC used with NMCA is described in the Background Technology section of US Patent Application No. 2005/0018805, which also describes the application of combinations of reducing nitrogen compounds such as hydrazine with hydrogen. ing. Applications of combining alcohols such as methanol with hydrazine are also disclosed. DE10030726 describes the application of photocatalytic material for deposition on reactor internal components and refers to the injection of hydrogen or methanol.

The application of methanol to reduce the oxidative effect is described in US Patent Application Gazette No. 2005/0135542, and on October 11-13, 2005, in Gyeongju, South Korea, "Proc.Symp.on Water Chemistry and It can also be found in the paper entitled "Study of the Methanol Injection in Reactor Water in Reactor Water of BWR Plants" published by Saneshige et al. In "Corrosion of Nuclear Power Plants in Asia".

Termination and subsequent activation of the BWR can occur at regular intervals, eg every 1 to 3 years, and there is a very different hydrochemistry than during normal operation. For example, as discussed in the article "The First Application of Hydrogen Water Chemistry during Start-up for Mitigation of SCC initiation in Tokai-2 BWR" by Takiguchi and Otoha, the oxidant concentration in the filtered water is during activation. high. This paper describes the addition of HWC during activation via an additional hydrogen injection system.

U.S. Patent Publication No. 2005/0018805 also describes the addition of hydrogen and reducing nitrogen compounds during activation and termination.

Outline of the present invention Although the use of HWS during startup is known, this procedure has some drawbacks. Contact between hydrogen and air pockets (which may be present during activation) should be avoided to prevent the possibility of an explosive reaction. In addition, the use of HWC during startup has some other drawbacks listed in the article "The First Application of Hydrogen Water Chemistry during Start-up for Mitigation of SCC initiation in Tokai-2 BWR". For example, it is not possible to maintain an appropriate target concentration during a specific starting operation condition. Changing conditions during both start-up and termination, such as changes in the amount of coolant circulating through the reactor, and changes in reactor temperature make the proper supply of gaseous hydrogen extremely difficult. Moreover, hydrogen injection cannot be done at other times, such as during repairs or failures.

Precious metals also often begin to diminish their catalytic effectiveness at certain times, such as when operating at temperatures below 250 ° C and when hydrogen injection is not available. During start-up and end-of-life, temperatures drop below these levels, and hydrogen injection is cumbersome.

The object of the present invention is to reduce oxidation during periods when HWC is unavailable or undesirable, such as during HWC injection system failure, or during reactor start-up or termination, and reactor core components and fuel cracks. For dings is to reduce corrosion. Other alternative or additional objects of the invention are safer, lower cost, and / or less cumbersome redox.

The present invention provides a nuclear power plant including a BWR, a reactor cooling system for cooling the BWR, an HWC hydrogen injection system connected to the reactor cooling system, and an alcohol injection system connected to the reactor cooling system. is there.

By installing a separate alcohol infusion system in addition to the hydrogen infusion system, the use of hydrogen or alcohol for various operating regimes, for example during start-up and termination that differs from normal operating conditions, is advantageously controlled. can do. Alcohol can also be advantageously installed as a backup injection system when the hydrogen injection system is inoperable or otherwise unavailable. The use of alcohol (which can be supplied in liquid form and does not explode in contact with air pockets) has an advantage in improving safety, reducing the need for monitoring attention, and for complex plumbing fixtures. The need is reduced.

Additional components such as reducing nitrogen compound injection systems and NMCA injection systems can also be advantageously provided.

The present invention also provides a method of operating a nuclear power plant, including supplying alcohol to a BWR during a start-up or end-run.

Alcohol was generally not considered suitable for activation or termination. This is because, as described in US Patent Gazette No. 2005/0018805, during activation and termination, the radioactivity level is weak and alcohol is generally useful in the presence of gamma rays. Because it was considered. However, the present invention favorably allows some redox by using alcohol instead of HWC during start-up and termination, reduces the risk of explosion, and simplifies the equipment required. To become. Additional alcohol injection systems may be installed in addition to existing BWR nuclear power plants or in new power plants, such as reactor water purification systems (CUW), emergency core cooling systems (ECCS), etc. It may be connected to the primary coolant in the reactor via a primary loop recirculation system (PLR) or control rod drive cooling system (CLD).

Advantageously, hydrazine or other reducing nitrogen compounds can be fed to the BWR primary cooling circuit at the same time as alcohol and hydrogen to improve the overall redox performance of the additive.

The present invention also provides a method of operating a nuclear power plant, comprising supplying both hydrogen and alcohol to a BWR primary cooling circuit during normal operation of the power plant.

Traditionally, methanol has been considered a substitute for hydrogen. By supplying both hydrogen and methanol, this mixture of hydrogen and methanol can be modified as desired to result in proper redox. Moderately negative electrochemical potentials (slightly less than -240 mV) are obtained, plus two species that reduce oxygen. Furthermore, for example, when the amount of hydrogen stored for HWC is insufficient, or when hydrogen injection is eliminated, methanol can be supplied with hydrogen to reduce the amount of hydrogen used, which provides backup protection. ..

Preferred embodiments of the present invention will be described with reference to the following figures.

<figref num="1">An embodiment of a nuclear power plant according to the present invention is shown.</figref><figref num="2">The details of the hydrazine injector and the methanol injector of the embodiment of FIG. 1 are shown.</figref><figref num="3">The amount of hydrogen and methanol to produce an effect equivalent to 1.2 ppm of hydrogen in the core of the BWR 900MWe reactor is shown.</figref><figref num="4">Shows the effect of polarity on oxidation and hydrogen pickup (HPU) of zirconium in water at 315-350 ° C.</figref>

Description of preferred embodiments FIG. 1 schematically shows one preferred embodiment of the BWR nuclear power plant 10 according to the present invention. The nuclear power plant 10 has a BWR20 having a core 22 with a plurality of fuel rods, eg uranium dioxide fuel in a zirconium alloy tube, a downcomer 26, and a riser 28, which are schematically shown. The downcomer 26 is connected to the primary coolant intake port 24, and this intake port receives water from the primary coolant pipe 30. The core 22 heats the water from the primary coolant pipe 30, which has a hot leg 32 that steams the turbine 40 to operate the generator 42. The cooler 44 cools the steam to water, which leaves the cooler to the cold leg 34 of the coolant pipe 30 and is pumped back to the intake port 24 and the downcomer 26.

The control rod drive cooling system (CLD) 50 can be installed to cool the drive for control rods inserted in the core 22. The HWC hydrogen injector 60 can inject hydrogen into the cold water pipe 34, and the NMCA injector 62 can supply a precious metal, eg platinum, to the cold water pipe 34 as well, so that the reactor 20 is in operation. You can receive HWC and NMCA during the normal period of.

ECCS70, PLR80, and CUW90, all outlined, can also be installed.

A special embodiment of FIG. 1 comprises a methanol injector 100 and a hydrazine injector 110, which are connected to a CUW 90, eg, downstream of a CUW pump. In this way, methanol and hydrazine can be injected into the water entering the cold water pipe 34 of the primary coolant pipe 30 via the CUW 90, and these can be circulated through the reactor 20. The cooled CUW sample tube can also be used to receive the liquid in syringes 100, 110. Syringes 100, 110 may also be located at ECCS70, PLR80, or CLD50. Alternatively, existing syringes, such as those used for sodium 24 injection and connected to CUW90, can be modified as injectors 100 or 110. The preferred location is after any resin floor.

The amount of methanol and hydrazine injected can be controlled by an input from one or more sensors 130, eg, a control unit 120 capable of receiving monitoring of the concentration of methanol, hydrazine or hydrogen in the downcomer 26. it can. The preset amount of methanol can be injected in consideration of the hydrogen value in the downcomer 26, for example. Sensor 130 can also measure the electrochemical potential (ECP) of one or more components of the reactor 20 or core 22, such as fuel pink rubbing.

FIG. 2 shows one embodiment of the methanol injector 100 and the hydrazine injector 110, which can include tanks 104, 114 connected to the CUW 90 piping, respectively. Metering pumps 102 and 112 can release methanol and / or hydrazine into CUW90, respectively, and can be individually controlled via control unit 120. The control unit 120 may be the same as the control unit that controls the start operation and the end operation, or may be a separate control unit. Alternatively, in the form of a gravity-supported injector, the amount of methanol or hydrazine supplied can be controlled by opening or closing the valve, and these tanks are suspended above the pipe.

While methanol is preferred, other alcohols, including ethanol and propanol, can also be delivered, which are also preferred. However, formic acid, formaldehyde, and acetaldehyde are examples of other suitable alcohols.

While hydrazine is the preferred reducing nitrogen compound, other compounds such as ammonia (NH)₃) Is also available.

In one preferred method of the invention, alcohol is injected into the primary coolant during start-up or termination, or during another time when the HWC60 is not running, for example when the HWC is out of order, downcomer. The alcohol concentration in 26 should be 0.1 to 300 μmol / kg (0.0032 to 9.6 ppm with respect to methanol). Most preferably, the alcohol concentration is less than 10 μmol / kg.

Preferably, hydrazine is also supplied to the primary coolant during termination and activation to bring the maximum hydrazine concentration within Downcomer 26 to 300 μmol / kg.

Advantageously in the other preferred method of the invention, both hydrogen infusion and methanol infusion are used during normal operation. It is also possible to use all hydrogen-containing chemical injectors, such as those for hydrogen, methanol, and hydrazine, at the same time. Depending on the different operating phases, different hydrogen-containing chemical injectors may be introduced or removed in stages. Preferably, the combination of hydrogen-containing chemicals added should be stoichiometrically equivalent for hydrogen and maintained in an amount approximately equal to or less than 10 μmol / kg of methanol. A metered supply of hydrogen or alcohol, or hydrazine, can lead to some adverse consequences above certain limits, so most preferably any limit of the hydrogen-containing chemicals injected is 300 μmol of methanol. Do not exceed the equivalent amount of / kg.

Figure 3 shows that the effect in the reactor core should be injected into the 900 MW standard electric BWR supply water during normal operation, similar to the effect of injecting 1.2 ppm hydrogen into the supply water. The amount of methanol. This is an explanation of stoichiometric calculations involving only two components (methanol and hydrogen). Diffusion of hydrogen into downcomers and carryover of hydrogen by steam are taken into account in the calculations in Figure 3. Therefore, the first row is the hydrogen supply water concentration FC supplied by HWC60, the second row is the predicted downcomer concentration RC during normal operation, and the third row is the predicted core concentration CC of hydrogen during normal operation. The fourth column is the difference in hydrogen that is expected to be lost from the core as the hydrogen concentration in the feed water decreases, and the fifth column is the equivalent amount of methanol that must be supplied to make up for it. And the 6th, 7th, and 8th columns stoichiometrically indicate the desired amount of methanol in the feed water, downcomer, and core to compensate for the decrease in hydrogen injection due to HWC60, respectively. If there are three or more components, the same calculation is done and one component replaces the other in subsequent steps (decrease in one component increases the other).

In addition, methanol is more effective than hydrogen in terms of reduction hydrogen peroxide concentration and in producing negative ECP values, for example in October 2004 in San Francisco. The paper "Reasons and Criteria for Selection of Methanol as Alternative to Hydrogen for BWR" presented by Bernhard Stellweg and Wilfried Ruehle at the 5th International Workshop on LWR Coolant Water Radiolysis and electrochemistry. It is discussed in "Plants" and its contents are disclosed in its entirety by reference. Experimental data in the field of radiation show that hydrogen peroxide is one-half less than hydrogen peroxide in the same mole of oxygen ratio for methanol. Methanol is also about three times more efficient than hydrogen in reaching the same ECP as the function of the molar ratio of oxygen.

Sensor 130 can be installed to ensure accurate downcomer concentration RC through monitoring of hydrogen and methanol concentrations within downcomer 26.

It is a preferred embodiment to use a mixture of three injectors 100, 110, 60, which includes: A. Increased hydrazine injection and decreased hydrogen injection (end) while injecting methanol at a constant level; B. No hydrogen injection (early start-up) with increased both methanol and hydrazine injections; C. Injecting methanol at a constant level with further increase in hydrazine, no hydrogen injection (end of activation); D. Methanol is infused at constant levels while hydrazine is reduced and hydrogen infusion is increased (early stage of normal operation of HWC or NMCA); E. Increase or decrease of methanol injection to compensate for hydrogen injection loss during normal operation; and F. During online NMCA injection, increase or decrease of methanol injection to compensate for the effect on ECP;

Figure 4 summarizes a number of studies, which are zirconium hydrogen pickup (HPU) or hydrogen pickup fraction (HPUF) if the fuel pin's ECP becomes cathodic (negative) and below -300 mV. , And show a dramatic increase in oxidation. Therefore, an ECP level of -300 mV or greater is preferred as long as fuel operation is involved. The concentration in the feed water of all reducing agents (hydrogen + methanol + hydrazine) applied to BWR has an ECP potential of about -300 mV, or about -300 mV, to the Pt (platinum) reference electrode to provide a reducing environment. It may be characterized by being larger (eg -260 mV). To protect the internal components of the BWR reactor and also to maintain an increasing increase fuel operation margin, the ECP potential with respect to the Pt (platinum) reference electrode minimizes the SCC of the internal components. Therefore, it should be kept at a value of about -300 mV or greater (eg -260 mV) rather than the -500 mV normally imposed by the operator.

In the present invention, it is preferable to use methanol. Alternatively, other suitable alcohols, such as ethanol or propanol, or any mixture thereof may be used.

In the aforementioned part of the specification, the present invention has been described with reference to special exemplary embodiments and examples thereof. However, as set forth in the following claims, it is clear that various modifications and modifications can be made to these without leaving the broader essence and scope of the invention. Therefore, the specification and drawings should be considered descriptive rather than restrictive.

10 BWR type nuclear power plant, 20 BWR, 22 core, 24 intake, 26 downcomer, 28 riser, 30 coolant pipe, 32 hot water pipe, 34 cold water pipe, 40 turbine, 42 generator, 44 cooler, 50 Cooling System (CLD), 60 Hydrogen Injector, 62 NMCA Injector, 70 ECCS, 80 PLR, 90 CUW, 100 Methanol Injector, 102 Pump, 104 Tank, 110 Hydrazin Injector, 112 Pump, 114 Tank, 120 Control , 130 sensor