Method of evaluating amount of foreign matter passed through recirculation sump screen

Acquiring sets of test data on amounts of foreign matter passed through a recirculation sump screen when different amounts of foreign matter are input; forming a passed foreign matter amount approximate line that approximates the amounts of passed foreign matter with respect to the amounts of input foreign matter on the basis of the sets of test data on the amounts of passed foreign matter; forming a passed foreign matter amount envelope tangent to the passed foreign matter amount approximate line; and estimating a total passed foreign matter amount with respect to the amounts of input foreign matter on the basis of the passed foreign matter amount envelope to evaluate the recirculation sump screen are provided.

FIELD

The present invention relates to a method of evaluating an amount of foreign matter passed through a recirculation sump screen that is used in a system that circulates a coolant in a containment when a loss-of-coolant accident occurs in a reactor.

BACKGROUND

For example, a nuclear power plant including a pressurized water reactor (PWR) uses light water as a reactor coolant and a neutron moderator, which is light water serving as a high-temperature and high-pressure water that does not boil over the reactor internal of the reactor, sends the high-temperature and high-pressure water to a steam generator to generate steam by heat exchange, and sends the steam to a turbine generator to generate power. The steam generator transmits the heat of a primary cooling water with a high temperature and a high pressure from the reactor to a secondary cooling water to generate steam with the secondary cooling water.

In such a nuclear power plant, when a loss-of-coolant accident occurs due to a break of a pipe in the reactor, it becomes difficult to sufficiently cool the reactor with the coolant. For this reason, the reactor is cooled urgently by pumping up the cooling water in a refueling water storage pit with a pump, supplying the cooling water into the reactor, spraying the cooling water toward the reactor from multiple spray nozzles that are arranged at an upper part of the containment. In this case, foreign matter caused due to the break of the pipe falls into the refueling water storage pit and, for this reason, a recirculation sump screen is placed on the top of the refueling water storage pit. Accordingly, the foreign matter is blocked by the recirculation sump screen to inhibit the foreign matter from entering the refueling water storage pit, which prevents the pumps and pipes from being damaged due to the foreign matter.

Note that there is the device according to the following Patent Document 1 as a reactor emergency cooling device.

CITATION LIST

Patent Literature

SUMMARY

Technical Problem

The above-described recirculation sump screen filters out foreign matter to prevent the foreign matter from entering the facility on the downstream side with respect to the screen; however, small foreign matter passes through (is not filtered out by) the recirculation sump screen. For this reason, it is necessary to evaluate in advance how much foreign matter passes through the recirculation sump screen when an accident occurs. In the containment, however, multiple refueling water storage pits are provided. It is difficult to uniquely determine how much foreign matter is transferred to each recirculation sump screen as it depends on multiple parameters, such as the position of the break of the pipe and the state of damage of the foreign matter. In other words, it is difficult to evaluate the amount of foreign matter that reaches each recirculation sump screen and the amount of the passed foreign matter and then quantitatively calculate the total amount of the passed foreign matter.

The present invention is aimed at solving the above-described problem and an objective of the present invention is to provide a method of evaluating an amount of foreign matter passed through a recirculation sump screen enables easy calculation of a total amount of foreign matter passed through multiple recirculation sump screens.

Solution to Problem

To achieve the above-described object, a method of evaluating an amount of foreign matter passed through a recirculation sump screen according to an present invention includes acquiring sets of test data on amounts of foreign matter passed through a recirculation sump screen when different amounts of foreign matter are input, forming a passed foreign matter amount approximate line that approximates the amounts of passed foreign matter with respect to the amounts of input foreign matter on the basis of the sets of test data on the amounts of passed foreign matter, forming a passed foreign matter amount envelope tangent to the passed foreign matter amount approximate line, and calculating a total amount of passed foreign matter with respect to the amounts of input foreign matter on the basis of the passed foreign matter amount envelope to evaluate the recirculation sump screen.

Accordingly, the passed foreign matter amount approximate line is formed on the basis of the multiple sets of test data on the amounts of passed foreign matter, the passed foreign matter amount envelope tangent to the passed foreign matter amount approximate line is formed, and the total amount of passed foreign matter with respect to the input foreign matter amount is calculated on the basis of the passed foreign matter amount envelope to evaluate the recirculation sump screen. Accordingly, it is possible to calculate the total amount of passed foreign matter easily and evaluate the recirculation sump screen accurately, without individually evaluating the amounts of foreign matter reaching the multiple recirculation sump screens and the passed foreign matter amounts and without necessity of calculating a ratio of the passed foreign matter.

In the method of evaluating the amount of foreign matter passed through the recirculation sump screen according to the present invention, the passed foreign matter amount approximate line is a quadratic curve and the passed foreign matter amount envelope is a primary expression straight line.

The passed foreign matter amount approximate line is a quadratic curve and the passed foreign matter amount envelope is a primary expression straight line and accordingly it is possible to calculate the total amount of passed foreign matter accurately according to the single simple expression.

The method of evaluating the amount of foreign matter passed through the recirculation sump screen according to the present invention includes forming a passed foreign matter amount approximate straight line on the basis of the passed foreign matter amount approximate line and forming the passed foreign matter amount envelope on the basis of the passed foreign matter amount approximate straight line.

Forming the passed foreign matter amount approximate straight line on the basis of the passed foreign matter amount approximate line and forming the passed foreign matter amount envelope thus make it possible to calculate an average ratio of the passed foreign matter between the multiple recirculation sump screens and calculate a total passed foreign matter amount easily.

In the method of evaluating the amount of foreign matter passed through the recirculation sump screen according to the present invention, a passed foreign matter amount envelope is set in a shifted area defined by the passed foreign matter amount envelope tangent to the passed foreign matter amount approximate line and a passed foreign matter amount envelope shifted to a pre-set side where the passed foreign matter amount increases.

The passed foreign matter amount envelope in the shifted area moved to the side where the passed foreign matter amount increases is set such that a sufficient factor of safety is secured.

In the method of evaluating the amount of foreign matter passed through the recirculation sump screen according to the present invention, the shifted area is an area moved to a side where the amount of passed foreign matter is smaller than a maximum value of the sets of test data on the amounts of passed foreign matter.

The shifted area is the area moved to the side where the amount of passed foreign matter is smaller than the maximum value of the sets of test data on amounts of passed foreign matter, and thus the efficiency in processing can be improved without securing an excessive factor of safety.

Advantageous Effects of Invention

According to the method of evaluating an amount of foreign matter passed through a recirculation sump screen according to the present invention, the passed foreign matter amount approximate line is formed on the basis of the multiple sets of test data on the amounts of passed foreign matter, the passed foreign matter amount envelope tangent to the passed foreign matter approximate line is formed, and the total passed foreign mater amount with respect to the input foreign matter amount is calculated on the basis of the passed foreign matter amount envelope to evaluate the recirculation sump screen, and accordingly it is possible to calculate the total passed foreign matter amount easily and evaluate the recirculation sump screen accurately.

DESCRIPTION OF EMBODIMENTS

With reference to the accompanying drawings, a preferred embodiment of the method of evaluating an amount of foreign matter passed through a recirculation sump screen according to the present invention will be described in detail below. The embodiment does not limit the invention. If there are multiple embodiments, the invention will cover ones configured by combining the embodiments.

First Embodiment

FIG. 1is a schematic configuration diagram illustrating a main part of a nuclear power plant.

In the present embodiment, a nuclear power plant includes a reactor. The reactor is a pressurized water rector (PWR) that uses light water as a reactor coolant and a neutron moderator, which is light water serving as a high-temperature and high-pressure water that does not boil over the reactor internal, sends the high-temperature and high-pressure water to a steam generator to generate steam by heat exchange, and sends the steam to a turbine generator to generate power. The reactor may be a boiling water reactor (BWR).

As shown inFIG. 1, in a nuclear power plant10, a PWR12and multiple steam generators13(one steam generator is illustrated) are stored in a containment11. The PWR12and each of the steam generators13are connected via a high-temperature feeding pipe14and a low-temperature feeding pipe15, and a primary cooling water pump16is provided on the low-temperature feeding pipe15. The bottom of a pressurizer17is connected to the high-temperature feeding pipe14.

In the PWR12, a reactor internal18is arranged. The reactor internal18consists of multiple fuel assemblies (fuel rods) (not illustrated). Although it is not illustrated, multiple control rods are arranged between the fuel assemblies in the reactor internal18and the control rods can be moved vertically by a control rod driver device. Inserting the control rods into the reactor internal18and extracting the control rods from the reactor internal18enables control on the output of the reactor.

In the steam generator13, heat transmission pipe group consisting of multiple heat transmission pipes having the inversed shape of the shape of U are arranged, one end of each of the heat transmission pipe is connected to an end of the high-temperature feeding pipe14and the other end is connected to an end of the low-temperature feeding pipe15.

In the containment11, a reactor emergency cooling device21is provided. Multiple refueling water storage pits22are provided at the bottom of the containment11and a cooling water dispersion line23that returns from each of the refueling water storage pits22into the containment11through the outside of the containment11and extends above the PWR12is provided. The cooling water dispersion line23has a middle part where a spray pump24is provided and has a tip where a large number of spray nozzles25are provided. A recirculation sump screen26is placed on each of the refueling water storage pits22to cover the top of the refueling water storage pit22.

A low-pressure cooling water supply line27is a low-pressure water feeding system that returns from the refueling water storage pits22into the containment11through the outside of the containment11, that is connected to the PWR12, and that is provided with a low-pressure injection pump28is provided. A high-pressure cooling water supply line29is a high-pressure water supply system that returns from the refueling water storage pits22into the containment11through the outside of the containment11, that is connected to the PWR12, and that is provided with a high-pressure injection pump30. A fuel replacement water tank31is arranged outside the containment11and is connected to the cooling water dispersion line23, the low-pressure cooling water supply line27, and the high-pressure cooling water supply line29via a cooling water supply line32.

In the PWR12, the fuel assemblies in the reactor internal18heat the light water serving as the primary cooling water and, in a state where the primary cooling water at a high temperature is kept at a given high pressure by the pressurizer17, the primary cooling water is sent to the steam generator13through the high-temperature feeding pipe14. The steam generator13generates secondary steam by performing heat exchange between the primary cooling water at a high-temperature and a high-pressure and the secondary cooling water, and the cooled primary cooling water is returned to the PWR12. The control rod driver device adjusts the nuclear fission in the reactor internal18by extracting the control rods from the reactor internal18and inserting the control rods into the reactor internal18. By inserting all the control rods into the reactor internal18, the control rod driver device is able to stop the PWR12.

Each of the steam generators13has a top end that is connected to a power generation facility34via a steam supply pipe33, and the power generation facility34is connected to the steam generator13via a condensed water return pipe35. The power generation facility34consists of a steam turbine facility, a power generator, a condenser, etc. In the steam generator13, the secondary steam that is generated by performing heat exchange between the secondary cooling water and the primary cooling water at a high temperature and a high pressure is sent to the steam turbine of the power generation facility34via the steam supply pipe33, and the steam drives the steam turbine to generate power with the power generator. The condenser uses sea water to cool the steam having driven the steam turbine and generate the condensed water, and the condensed water is returned to the steam generator13through the condensed water return pipe35.

When an accident of a break of the cooling pipe occurs in the nuclear power plant10, the spray pump24is driven to send the primary cooling water stored in each of the refueling water storage pits22to the large number of spray nozzles25via the primary cooling water dispersion line23and the primary cooling water is dispersed from the large number of spray nozzles25to the inside of the containment11. Accordingly, the primary cooling water is dispersed to a large amount of steam that occurs in the containment11, where the cooling water draws a large amount of energy, cools the inside of the containment11, falls with its temperature thus increased, and is returned to the refueling water storage pits22via a collection route. Accordingly, it is possible to draw the energy emitted into the inside of the containment11by using the dispersed primary cooling water, and thus integrity of the containment11can be maintained.

Furthermore, each of the injection pumps28and30is driven to send the primary cooling water stored in each of the refueling water storage pits22to the low-temperature feeding pipe15via each of the cooling water supply lines27and29or to the PWR12via the high-temperature feeding pipe14. The cooling water then cools the reactor internal18of the PWR12, which makes it possible to inhibit the temperature of the reactor internal18from increasing.

As described above, when an accident of a break of the cooling pipe occurs in the nuclear power plant10, the cooling water in the refueling water storage pits22is dispersed from the spray nozzles25into the containment11and is sent to the PWR12, which makes it possible to urgently cool the containment11. When, for example, a cooling pipe breaks, foreign matter, such as fractions of the broken pipe and the insulator of the pipe, is caused, falls into the refueling water storage pits22, and gets into the cooling water. For this reason, the recirculation sump screen26is placed on each of the refueling water storage pits22to cover the top of the refueling water storage pit22. Accordingly, the recirculation sump screen26hinders the foreign matter to inhibit the foreign matter from entering the refueling water storage pits22, which prevents each of the lines23,27and29from being damaged due to the foreign matter getting into each of the lines23,27and29.

The recirculation sump screen26consists of, for example, a porous plate and thus is capable of filtering out foreign matter having a large particle diameter but is unable to filter out foreign matter having a small particle diameter and the foreign matter passes through (is not filtered out by) the recirculation sump screen26. For this reason, when an accident of a break of the cooling pipe occurs, it is necessary to evaluate in advance how much foreign matter passes through the recirculation sump screens26.

FIG. 2is a schematic diagram representing a testing device for measuring an amount of foreign matter passed through a recirculation sump screen.

As illustrated inFIG. 2, in a testing device40for measuring an amount of foreign matter passed through a recirculation sump screen, cooling water can be stored in a test tank41. A cooling water supply unit42is provided on a wall on one end of the test tank41and a cooling water discharge unit43is provided at the bottom of the other end. In the test tank41, while a foreign matter inputter44and a stirring unit45are provided on the side of the cooling water supply unit42, the recirculation sump screen26can be set above the cooling water discharge unit43at the bottom on the other end. A cooling water supply line47provided with a pump46has a tip that is connected to the cooling water supply unit42. A cooling water discharge line50provided with a pump48and an open/close valve49has a base end that is connected to the cooling water discharge unit43and has a tip that is connected to a filter51. The filter51has an outlet port to which the base end of the cooling water supply line47is connected.

When each of the pumps46and48are driven and the open/close valve49is opened, the cooling water in the test tank41is discharged into the cooling water discharge line50through the cooling water discharge unit43and is filtered at the filter51and then is returned from the cooling water supply line47into the test tank41through the cooling water supply unit42. Accordingly, in the test tank41, a flow of the cooling water from one end to the other end occurs. Here, when foreign matter in a size on which fractions and an insulator of the cooling pipe is assumed is input from the foreign matter inputter44and is stirred by the stirring unit45, the foreign matter input from one end flows to the other end and is filtered out by the recirculation sump screen26. Foreign matter having a small diameter however passes through the recirculation sump screen26, is discharged into the cooling water discharge line50from the cooling water discharge unit43, and is filtered out by the filter51. Measuring the weight of the foreign matter filtered by the filter51thus makes it possible to know the amount of foreign matter passed through the recirculation sump screen26(passed foreign matter amount).

A method of evaluating an amount of passed foreign matter through a recirculation sump screen of the present embodiment includes acquiring sets of test data on amounts of foreign matter passed through the recirculation sump screen26when different amounts of foreign matter are input; forming a passed foreign matter amount approximate line that approximates the amounts of passed foreign matter with respect to the amounts of input foreign matter on the basis of the sets of test data on the amounts of passed foreign matter; forming a passed foreign matter amount envelope tangent to the passed foreign matter amount approximate line; and calculating a total passed foreign matter amount with respect to the amounts of input foreign matter on the basis of the passed foreign matter amount envelope to evaluate the recirculation sump screen26.

The method of evaluating an amount of foreign matter amount passed through a recirculation sump screen of the present embodiment will be described in detail below.

FIG. 3is a graph for explaining the method of evaluating an amount of foreign matter passed through a recirculation sump screen according to the present embodiment, representing a result of measuring amounts of foreign matter passed through a recirculation sump screen.FIG. 4is represents an approximate expression of the amounts of foreign matter passed through the recirculation sump screen.FIG. 5represents a calculated value of the amounts of foreign matter passed through the recirculation sump screen.

In the method of evaluating an amount of foreign matter passed through a recirculation sump screen according to the present embodiment, first of all, with the above-described testing device40, multiple (five in the present embodiments) tests in which the amounts of foreign matter input from the foreign matter inputter44are different from one another are carried out, and test data on the amounts of the passed foreign matter is obtained by measuring the amounts of the passed foreign matter passed through the recirculation sump screen26when the different amounts of foreign matter are input.

As illustrated inFIG. 3, sets of test data B1, B2, B3and B4on the amounts of the passed foreign matter passed through the recirculation sump screen26when the different amounts of foreign matter are input are graphed and a passed foreign matter amount approximate line La (dotted line inFIG. 3) that approximates the passed foreign matter amounts with respect to the input foreign matter amounts is formed on the basis of the multiple sets of test data B1, B2, B3and B4. The passed foreign matter amount approximate line La is a quadratic curve with an upper convex shape, representing that, while the passed foreign matter amount increases with an increase in the amount of input foreign matter, the degree of the increase (amount of change) lowers.

A passed foreign matter amount approximate straight line L0is then calculated on the basis of the passed foreign matter amount approximate line La. Accordingly, it is possible to obtain the following Equation (1) according to the passed foreign matter amount approximate straight line L0, where L is the amount of input foreign matter and a and b are coefficients associated with the passed foreign matter amount.
passed foreign matter amount=aL+b(1)

Furthermore, because the passed foreign matter ratio is a function of the input foreign matter amount L, it is possible to calculate a passed foreign matter amount L·f(L) according to the following equation (2) with the passed foreign matter amount f(L).
L·f(L)=aL+b(2)

It is possible to calculate a total amount of passed foreign matter according to the following Equation (3) where i(n) is the number of recirculation sump screens26(the number of tests).

The passed foreign matter amounts L·f(L1), L·f(L2), L·f(L3) . . . are equal to or smaller than the total input foreign matter amount Ltand therefore it is possible to obtain the following Equation (4).

In other words, as shown inFIG. 4andFIG. 5, a passed foreign matter amount envelope L1that is parallel to the passed foreign matter amount approximate straight line L0and that is tangent to the passed foreign matter amount approximate line La is calculated. The passed foreign matter amount envelope L1is a primary expression straight line having the same obliqueness as that of the passed foreign matter amount approximate straight line L0.

The passed foreign matter amount envelope L1is set in an area shifted to a shifted area W moved from a position of tangent of the passed foreign matter amount approximate line La to a pre-set side where the passed foreign matter amount increases. The shifted area W is an area moved to a side where the amount of passed foreign matter is smaller than the maximum value B4of the sets of test data on the amounts of passed foreign matter. In other words, the shifted area W is an area between the passed foreign matter amount envelope line L1and a passed foreign matter amount envelope line L2, and the passed foreign matter amount envelope line L2is set such that its minimum value is the maximum value B4of the sets of test data on the amounts of passed foreign matte.

The total passed foreign matter amount with respect to the total input foreign matter amount is then calculated on the basis of the passed foreign matter amount envelope line L1(the passed foreign matter amount envelope L1to the passed foreign matter amount envelope L2) and the recirculation sump screen26is evaluated.

As described above, the method of evaluating an amount of foreign matter passed through a recirculation sump screen according to the present embodiment includes acquiring sets of test data on amounts of foreign matter passed through the recirculation sump screen26when different amounts of foreign matter are input; forming a passed foreign matter amount approximate line that approximates the amounts of passed foreign matter with respect to the amounts of input foreign matter on the basis of the sets of test data on the amounts of passed foreign matter; forming a passed foreign matter amount envelope tangent to the passed foreign matter amount approximate line; and calculating a total passed foreign matter amount with respect to the amounts of input foreign matter on the basis of the passed foreign matter amount envelope to evaluate the recirculation sump screen26.

Accordingly, it is possible to calculate the total passed foreign matter amount easily and evaluate the recirculation sump screen26accurately, without individually calculating and evaluating the amounts of foreign matter reaching the multiple recirculation sump screens26and the passed foreign matter amounts and without necessity of calculating a ratio of the passed foreign matter.

In the method of evaluating an amount of foreign matter passed through a recirculation sump screen according to the present embodiment, the passed foreign matter amount approximate line is a quadratic curve and the passed foreign matter amount envelope is a primary expression straight line. Accordingly, it is possible to calculate the total amount of passed foreign matter accurately according to one simple formula.

In the method of evaluating an amount of foreign matter passed through a recirculation sump screen according to the present embodiment, the passed foreign matter amount approximate straight line is formed on the basis of the passed foreign matter amount approximate line and the passed foreign matter amount envelope is formed on the basis of the passed foreign matter amount approximate straight line. Calculating the passed foreign matter amount approximate straight line thus makes it possible to calculate an average ratio of the passed foreign matter between the multiple recirculation sump screens according to the obliqueness, which makes it possible to easily calculate the total passed foreign matter amount.

In the method of evaluating an amount of foreign matter passed through a recirculation sump screen according to the present embodiment, a passed foreign matter amount envelope is set in a shifted area defined by the passed foreign matter amount envelope tangent to the passed foreign matter amount approximate line and a passed foreign matter amount envelope shifted to a pre-set side where the passed foreign matter amount increases. Accordingly, it is possible to calculate the total amount of passed foreign matter while a sufficient factor of safety is secured.

In the method of evaluating an amount of foreign matter passed through a recirculation sump screen according to the present embodiment, the shifted area is set in the area moved to a side where the amount of passed foreign matter is smaller than the maximum value of the sets of test data on the amounts of passed foreign matter, and thus the efficiency in processing for calculating the total amount of passed foreign matter can be improved without securing an excessive factor of safety.

In the above-described embodiment, the passed foreign matter amount envelope is a primary expression straight line; however, it may be a quadratic curve.

REFERENCE SIGNS LIST