JP4106239B2 - Non-condensable gas risk assessment system and risk assessment method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a technique for monitoring and evaluating the accumulation of flammable non-condensable gas in a nuclear power plant, and more particularly to non-condensable gas in a steam pipe.Risk assessment system and risk assessment method thereofAbout.
[0002]
[Prior 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) 2 in a reactor containment vessel (hereinafter referred to as PCV) 1 as shown in FIG. Is stored, and a reactor pressure vessel vent system 3 is provided as a gas processing facility around the top of the RPV 2.
[0003]
  In the BWR plant, steam generated in the RPV 2 is guided to the steam turbine 5 through the main steam system 4, and a generator (not shown) is driven by the steam turbine 5. The steam that has worked in the steam turbine 5 is condensed in the condenser, becomes condensed water, and then returns to the RPV 2 through a condensate / water supply system (not shown). Reference numeral 6 denotes a reactor pressure vessel head spray system.
[0004]
  On the other hand, the core 7 is accommodated in the RPV 2 and the core 7 is immersed in the reactor cooling water 8. The RPV 2 is partitioned into a liquid phase part in which reactor cooling water (reactor water) is stored and a gas phase part 9 above the liquid phase part.
[0005]
  In the reactor cooling water 8 in the RPV 2, hydrogen gas and oxygen gas decomposed and generated from the cooling water 8 due to neutron irradiation accompanying the nuclear reaction in the core 7 or, in some cases, a small amount of Kr leaks from the fuel rod. , Xe, and other non-condensable gases such as radioactive noble gases. For this reason, the BWR plant is provided with a gaseous waste treatment system (not shown) for treating non-condensable gas.
[0006]
  During normal operation of the BWR plant, non-condensable gas generated in the RPV 2 is guided from the RPV 2 through the main steam system 4 to the steam turbine 5 together with the main steam, and flows into the steam turbine 5. The non-condensable gas that flows in with the main steamThrough the steam turbine,After that, the steam turbine 5 leads to a condenser and is processed by a gas waste treatment system provided in the condenser. Main steam isolation valves 10 a and 10 b are respectively provided on the upstream side and the downstream side of the PCV (reactor containment vessel) 1 in the pipe 4 a of the main steam system 4.
[0007]
[Problems to be solved by the invention]
  During normal operation of the boiling water reactor, the non-condensable gas generated in the RPV 2 is basically transferred from the condenser to the gas waste treatment system via the main steam pipe 4a and the steam turbine 5, and this gas Although it is processed in the waste processing system, there is no gas processing facility provided when it collects at the rising portion of the branch pipe.
[0008]
  On the other hand, during normal operation of the boiling water reactor, hydrogen gas and oxygen gas, which are the main components of the non-condensable gas generated in the RPV2, flow together with the steam, so that they gradually accumulate at the rising part of the pipe. There is knowledge of.
[0009]
  In addition, there are hundreds of dead-end pipes 10 that do not flow in the pipe branched from the main steam pipe 4a per BWR plant. Since these dead-end pipes 10 are all different in conditions such as branch routes, the generation conditions such as combustion due to hydrogen accumulation of non-condensable gas and the possibility thereof are different. In addition, uncertain events such as valve leaks are added, and it is difficult to monitor non-condensable gas accumulation and permanently evaluate problems due to gas accumulation.
[0010]
  Accurately monitor and evaluate gas accumulation at locations where non-condensable gas may accumulate in nuclear power plant steam piping, and prevent and prevent combustion, etc. in advance. The inventor has found that this is possible.
[0011]
  In addition, in order to further improve the reliability of the BWR plant, it is possible to determine a place where the possibility of accumulation of non-condensable gas is determined, monitor the temperature of the place where gas can be accumulated, and evaluate the gas accumulation state. It is important to prevent combustion and the like in advance.
[0012]
  However, the gas accumulation of the non-condensable gas in the gas accumulation possible place is not monitored, and the evaluation method of the gas accumulation data has not been established. For this reason, in a nuclear power plant, establishment of the technique which monitors and evaluates the gas accumulation of non-condensable gas in gas accumulation possible places, such as steam piping, is strongly desired.
[0013]
  The present invention has been made in consideration of the above-mentioned circumstances, and quickly and accurately monitors the gas accumulation of non-condensable gas at a gas accumulation possible place, and performs risk assessment to prevent damage in advance. Of non-condensable gasRisk assessment system and risk assessment method thereofThe purpose is to provide.
[0014]
  Another object of the present invention is to monitor and evaluate the gas accumulation of the non-condensable gas accumulation area, thereby reliably performing damage risk management and preventive maintenance for hydrogen gas combustion, and highly reliable non-condensable. GasRisk assessment system and risk assessment method thereofTo provide.
[0015]
  Still another object of the present invention is to provide a non-condensable gas that can quickly and efficiently monitor gas accumulation of non-condensable gas at a gas accumulable location, and that can be risk-predicted to prevent damage in advance.Risk assessment system and risk assessment method thereofThe purpose is to provide.
[0016]
[Means for Solving the Problems]
  The present inventionIn order to solve the above-mentioned problem, the risk assessment system for non-condensable gas according toClaim 1As described in 1., the piping in which non-condensable gas may accumulate, the temperature sensor provided at the location where gas can be accumulated in the site, and the piping where the gas can be accumulated from the temperature data measured by this temperature sensor Calculation means for calculating the temperature and calculating the gas partial pressure of the non-condensable gas from the calculated temperature in the pipe, and the moles of hydrogen and oxygen constituting the non-condensable gas from the obtained gas partial pressure of the non-condensable gas A determination evaluation means for performing a combustion analysis using the ratio as an initial condition, comparing a predicted combustion pressure with a predetermined determination condition, and calculating a stress or a strain of a non-condensable gas accumulation location; and a determination evaluation means And a risk evaluation unit that evaluates the damage risk of the gas accumulable location based on the stress or strain of the gas accumulable location calculated in (1).
[0017]
  In order to solve the above-described problem, the risk assessment system for non-condensable gas according to the present invention is:Claim 2As described above, the calculation means obtains the temperature history of the gas accumulation possible location from the measurement data from the temperature sensor, while the determination evaluation means evaluates the temperature history of the gas accumulation possible location and tends to decrease in temperature. If there is, you can predict the amount of non-condensable gas accumulation in the future where gas accumulation is possible,Claim 3As described above, when the temperature accumulation tendency is present at the location where gas accumulation is possible, the determination / evaluation means predicts / evaluates the combustion pressure generated at the time of ignition from the predicted non-condensable gas accumulation amount, and evaluates the combustion Calculate the stress or strain of the gas accumulable location due to pressure, and the risk evaluation means determines and evaluates the damage risk of the gas accumulable location based on the calculated stress or strain, orClaim 4As described above, when there is a tendency for the temperature to decrease in a portion where gas can be accumulated, the determination / evaluation means evaluates the combustion pressure generated at the time of ignition from the predicted non-condensable gas accumulation amount, and sets this combustion pressure in advance. On the other hand, the risk evaluation means determines and evaluates the damage risk of the gas accumulable portion by comparing the combustion pressure with a predetermined determination condition.
[0018]
  On the other hand, the risk assessment method for non-condensable gas according to the present invention is to solve the above-described problems.Claim 5As described in, measure the temperature of the fluid piping at the non-condensable gas accumulation location where non-condensable gas accumulation is expected, and calculate the temperature in the piping and the gas partial pressure of the non-condensable gas from the measured piping temperature. From the obtained gas partial pressure of the non-condensable gas, a combustion analysis is performed with the molar ratio of hydrogen and oxygen constituting the non-condensable gas as an initial condition, and the combustion pressure due to the non-condensable gas is calculated and evaluated. In this method, the stress or strain at the non-condensable gas accumulation location due to the evaluated combustion pressure is calculated, and the risk of damage to the non-condensable gas accumulation location is determined from the calculated stress or strain.
[0019]
  In addition, in order to solve the above-described problem, the risk evaluation method for non-condensable gas according to the present invention includes:Claim 6As described in, when there is a tendency to decrease the temperature by measuring the temperature of the fluid piping, it is a method for predicting the future non-condensable gas accumulation amount in the gas accumulation possible place,Claim 7As described in, when the location where gas can be accumulated tends to decrease in temperature, the combustion pressure generated at ignition is calculated from the estimated non-condensable gas accumulation amount and evaluated, and the gas can be accumulated with the estimated combustion pressure. It is a method of calculating the stress or strain of the fluid piping at the location, determining the damage risk of the location where gas can be accumulated from the calculated stress or strain, and evaluating it,Claim 8If the location where gas accumulation is possible tends to decrease as described in, the combustion pressure generated at ignition is calculated from the predicted non-condensable gas accumulation amount, evaluated, and the estimated combustion pressure is set in advance. This is a method for judging and evaluating the damage risk of the gas accumulable portion based on the comparison judgment.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
  Non-condensable gas according to the present inventionRisk assessment systemEmbodiments will be described with reference to the accompanying drawings.
[0021]
  FIG. 1 shows a non-condensable gas according to the present invention.Risk assessment system1 is a schematic system diagram of a boiling water nuclear power plant (BWR plant) 20 equipped with
[0022]
  The BWR plant 20 stores a reactor pressure vessel (RPV) 22 in a reactor containment vessel (PCV) 21, and the reactor containment vessel 21 around the reactor pressure vessel 22 is defined as a dry well 23. The A reactor core 24 is stored in the reactor pressure vessel 22, and the reactor core 24 is immersed in the reactor cooling water 25. A liquid phase part storing the reactor cooling water 25 is formed at the lower part of the reactor pressure vessel 22, while a gas phase part 26 is formed above the liquid phase part.
[0023]
  When passing through the reactor core 24, the reactor coolant 25 in the reactor pressure vessel 22 is heated and vaporized by receiving neutron irradiation by a nuclear reaction. The generated steam is separated into steam and water in the reactor pressure vessel 22, dried, then sent to the steam turbine 28 through the main steam system 27, where the steam turbine 28 performs work, and a generator (not shown). Drive. Main steam isolation valves 29a and 29b are provided on the main steam pipe 27a constituting the main steam system 27 on the upstream side and the downstream side of the PCV 21, respectively. The expanded steam that has worked in the steam turbine 28 is condensed in a condenser (not shown), and then returned to the RPV 22 through the reactor condensate / water supply system.
[0024]
  A number of branch lines are branched from the main steam pipe 27a of the main steam system 27, including the reactor isolation cooling system 30, the turbine bypass system 31 and the main steam drain system (not shown). There are many dead-end pipes inside.
[0025]
  Further, the reactor pressure vessel (RPV) 22 of the BWR plant 20 is provided with a reactor pressure vessel top vent facility 35, and this vent facility 35 includes a reactor pressure vessel (RPV) vent system 36 and a reactor pressure. A branch vent system 38 branched from a container head spray system (hereinafter referred to as an RPV head spray system) 37.
[0026]
  The RPV vent system 36 has a reactor pressure vessel (RPV) vent pipe 40 connected to the top of the reactor pressure vessel (RPV) 22. The RPV vent pipe 40 is connected to an RPV head vent nozzle 41 formed at the top of the RPV 22, and an electric valve 43 that is remotely operated as an on-off valve is provided in the middle. The downstream side of the electric valve 43 is connected to the main steam pipe 27a on the upstream side of the main steam isolation valve 29a in the reactor containment vessel 21.
[0027]
  The branch vent system 38 includes a vent branch pipe 47 branched from the downstream side of the check valve 46 of the reactor pressure vessel (RPV) head spray pipe 45. The vent branch pipe 47 is provided with an electric valve 48 as a remote control valve, and the downstream side of the electric valve 48 is connected to the RPV vent pipe 40 of the RPV vent system 36 on the upstream side of the electric valve 43. A branch portion of the vent branch pipe 47 is provided at a top position of the RPV head spray pipe 45 so as to rise downstream of the check valve or the injection valve 46. The branch portion of the vent branch pipe 47 is provided as close as possible to the check valve 46.
[0028]
  Further, the RPV head spray system 37 is connected to a reactor pressure vessel head spray nozzle (hereinafter referred to as an RPV head spray nozzle) 49 having an RPV head spray pipe 45 provided at the top of the RPV 22. The RPV head spray pipe 45 of the RPV head spray system 37 may also serve as a cooling water injection pipe of a reactor isolation cooling facility (hereinafter referred to as RCIC) 50. The RCIC 50 is a facility that cools the gas phase portion 26 of the RPV 22 by using cooling water of the cooling system at the time of shutdown in order to lower the residual pressure of the upper dome of the RPV 22 when the boiling water reactor is shut down.
[0029]
  On the other hand, the RPV head spray piping 45 of the RPV head spray system 37 is provided with a check valve 46 and a reactor containment isolation valve (PCV isolation valve) 51a, 51b in the middle. The PCV isolation valves 51a and 51b are respectively installed inside and outside through the reactor containment vessel 21, and are normally closed during the operation of the reactor.
[0030]
  By the way, the RPV vent system 36 constituting the reactor pressure vessel top vent facility 35 and the branch vent system 38 using the RPV head spray system 37 cooperate to operate a gas of non-condensable gas around the reactor pressure vessel 22. A non-condensable gas is led out from the accumulable location 54 and discharged to the main steam pipe 27.
[0031]
  An RPV vent system 36 and a branch vent system 38 using an RPV head spray system 37 are provided at the top of the reactor pressure vessel (RPV) 22 to cooperate with each other. May accumulate near the top ofGas accumulation location 54Oxygen gas, hydrogen gas, and non-condensable gases such as Kr and Xe radioactive noble gases can be discharged smoothly and smoothly to the main steam pipe 27a, and non-condensable gas accumulates around the top of the RPV 22 This is surely prevented in advance.
[0032]
  Further, in the BWR plant 20, the non-condensable gas accumulation monitoring and evaluation system 53 shown in FIG. 2 is configured in a gas accumulation-possible portion 54 such as a pipe or a portion where a combustible non-condensable gas may accumulate. A temperature sensor 55 and a pressure sensor 56 are provided. The gas accumulation location 54 is a vent branch pipe 47 of the branch vent system 38, or a branch pipe or branch pipe that branches from the main steam pipe 27a of the main steam system 27 and rises.
[0033]
  As shown in FIGS. 2 and 3, the temperature sensor 55 and the pressure sensor 56 are attached to a gas accumulation possible portion 54 of a steam pipe where accumulation of combustible non-condensable gas is expected, for example, a pipe surface of a fluid pipe. The materials used for the fluid piping and its heat insulating material are known, and the fluid flowing in the fluid piping is also known in advance, so know the heat conductivity and fluid heat transfer coefficient of the fluid piping and its heat insulating material in advance. Can do. The temperature data measured by the temperature sensor 55 and the pressure data measured by the pressure sensor 56 are input to a computer 58 such as a personal computer or a central processing unit via a measuring device 57 as a measuring means. The measuring device 57 has a function of digitizing an analog signal, but the measuring device 57 may be incorporated in the computer 58.
[0034]
  By the way, the computer 58 calculates the vapor partial pressure of the gas accumulable location 54 and the gas partial pressure of the non-condensable gas based on the temperature data from the temperature sensor 55 and the pressure data from the pressure sensor 56. 60 and the calculation result of the vapor partial pressure and the non-condensable gas partial pressure of the gas accumulable portion 54 are compared with a predetermined determination condition to determine whether or not the combustion region, the detonation region, and their neighboring regions. Determination and evaluation means 61 for determining and evaluating, and alarm means 62 for issuing an alarm when the determination and evaluation means 61 determines that the gas storage location 54 is the combustion region, the detonation region, and the vicinity thereof. The alarm signal output from the alarm means 62 is output to the alarm generating device 63 or is output to the display means 64 of the computer 58, and the display means 64 or the alarm generating device 63 outputs the alarm signal. It is adapted to emit an alarm through the sense and hearing. Reference numeral 65 denotes an operation board of the computer 58.
[0035]
  The computing means 60 of the computer 58 calculates the steam partial pressure from the temperature data measured by the temperature sensor 55 using the steam table data or the like, or does not condense from the pressure data measured by the pressure sensor 56. It is obtained by calculating the gas partial pressure of the sex gas. When the pressure sensor 56 is not installed, the gas partial pressure of the non-condensable gas may be obtained by calculation from the vapor partial pressure of the gas accumulable location 54 obtained from the temperature data from the temperature sensor 55.
[0036]
  Further, the computer 58 incorporates an evaluation determination table 66 that stores steam table data, combustion pressure-generated stress / equivalent plastic strain relationship data for the piping component configuration, and the like. The evaluation evaluation means 61 of the computer 58 incorporates an evaluation program 67 so that non-condensable gas accumulation amount evaluation, prediction evaluation of non-condensable gas accumulation amount, ignition combustion pressure evaluation, and fluid pipe strength evaluation can be performed. It is.
[0037]
  As shown in FIG. 2, the evaluation program 67 of the computer 58 includes a non-condensable gas accumulation amount evaluation system 70, a non-condensable gas accumulation amount prediction system 71 that predicts the future, an ignition combustion pressure evaluation system 72, and a pipe strength evaluation system. 73 as well as a risk evaluation system 74 as a risk evaluation means.
[0038]
  This risk evaluation system 74 uses an evaluation program 67 built in the computer 58 to evaluate the non-condensable gas accumulation amount of the gas accumulation potential 54, the prediction evaluation of the non-condensable gas accumulation amount, the ignition combustion pressure evaluation, and the pipe strength evaluation. Are used to evaluate the current gas accumulation status of the gas accumulating location 54, the risk assessment when operating until the regular inspection, and what kind of damage risk will occur, the present situation and the future damage risk Information is presented. The damage risk assessment includes the possibility of non-condensable gas ignition, the gas accumulation location 54, and the possibility of deformation of the fluid piping, and the possibility of damage.
[0039]
  By the way, the data representing the flammability limit curve and detonation limit curve of the hydrogen-oxygen-water vapor system is built in the judgment evaluation means 61 of the computer 58 as preset judgment conditions.
[0040]
  In the BWR plant 20, since the non-condensable gas generated from the nuclear reactor is derived from the radiolysis of water, the molar ratio of hydrogen: oxygen is 2: 1 and usually non-condensable gas exists. Since saturated steam exists at temperature, it does not become a combustible region (combustion region). However, if the temperature of the gas storage location 54 decreases due to the gas storage of the non-condensable gas, the gas partial pressure of the non-condensable gas with respect to the steam may be relatively increased due to partial condensation of the steam, leading to a combustible region. There is. In the BWR plant 20, the gas accumulation location 54 formed at a branch rising portion from a fluid pipe such as a steam pipe is a system in which steam and combustible non-condensable gas coexist, that is, a hydrogen-oxygen-water vapor system. It is composed.
[0041]
  By the way, generally, the flammability limit curve A of the hydrogen-air-water vapor system is known as shown in FIG. In the hydrogen-air-water vapor system, both the water vapor and the nitrogen component in the air act as a gas that suppresses combustion. In the piping of a reactor system in which no nitrogen component exists, evaluation can be performed by replacing the nitrogen component with steam.
[0042]
  FIG. 5 shows the hydrogen-air-steam system flammability limit curve B obtained by converting the hydrogen-air-steam system shown in FIG. Since the region surrounded by the flammable limit curve B is a flammable region (combustion region) C, the gas storable portion 54 is located outside the flammable region C in order to reliably prevent combustion at the gas storable portion 54. This is a condition.
[0043]
  On the other hand, since the non-condensable gas is hydrogen and oxygen generated by radiolysis of water, their abundance ratio (molar ratio) is hydrogen: oxygen = 2: 1, and is represented by a one-dot chain line D. When the ratio of hydrogen, oxygen, and steam (steam) that may exist at this hydrogen: oxygen molar ratio is determined from FIG. 6, a one-dot chain line D that is a hydrogen / oxygen molar ratio curve and a flammability limit curve B The ratio of steam is determined by the intersection with. The ratio (molar ratio) of this steam is 85%. When the proportion of steam is 85% or less, it becomes the combustible region C.
[0044]
  Taking the operation state of the BWR plant 20 as an example, the pressure in the reactor pressure vessel (RPV) 22 is 7 MPa, and the steam temperature is 286 ° C. Hydrogen and oxygen produced by radiolysis are on the order of ppm by weight compared to steam and are in trace amounts. The reactor pressure of 7 MPa is a saturation pressure determined by steam.
[0045]
  Here, when the vapor partial pressure of 85% which is the flammability limit shown in FIG. 6 is calculated, the vapor partial pressure value is 5.95 MPa. The steam temperature at a saturated steam pressure of 5.95 MPa is 275 ° C. when referring to the steam table data edited by the Japan Society of Mechanical Engineers.
[0046]
  That is, when the steam temperature is reduced by 11 ° C. from the steam temperature of 286 ° C. at the rated output of the BWR plant 20, it can be determined that there is a possibility that the gas storage location 54 may reach the combustible region C, and an alarm is generated. ing.
[0047]
  By the way, since the set value of the alarm signal actually generated from the alarm means 62 is one of the main purposes to notify the vicinity of the combustible region, for example, from the steam temperature of 286 ° C. at the rated output, For example, it can be generated when the temperature drops by 5 ° C. By notifying that the vicinity of the combustible region has been reached, preventive maintenance against hydrogen gas combustion can be performed reliably and stably.
[0048]
  In the non-condensable gas accumulation monitoring and evaluation system shown in FIGS. 2 and 3, a pressure sensor 56 is installed. By installing this pressure sensor 56, even in a pressure system different from the reactor pressure, the temperature of the saturated steam corresponding to the pressure value is obtained from the detected value of the pressure sensor 56 as an initial value. A steam temperature corresponding to a steam partial pressure of 85% may be obtained. These basic data are based on the steam table edited by the Japan Society of Mechanical Engineers, and are input to the computer 58 in advance.
[0049]
  Further, it is known that the detonation limit of the water-air-steam system is represented by a detonation limit curve E as shown in FIG. In the water-air-steam system shown in FIG. 4, both the steam and the nitrogen component in the air act as a gas that suppresses combustion. Therefore, in the reactor system fluid piping in which no nitrogen component exists, nitrogen is converted into steam. It can be replaced and evaluated.
[0050]
  When the detonation limit curve E of the water-air-steam system shown in FIG. 4 is converted into a hydrogen-oxygen-steam system, the detonation limit curve F is represented as shown in FIG.
[0051]
  On the other hand, hydrogen and oxygen, which are non-condensable gases, are hydrogen and oxygen generated by radiolysis, so the abundance ratio (molar ratio) is hydrogen: oxygen = 2: 1, and is represented by a one-dot chain line G in FIG. It is. Determining the vapor ratio (molar ratio) from the intersection of the detonation limit curve F and the one-dot chain line G considering the molar ratio of hydrogen and oxygen gives 70%, and when the vapor ratio is 70% or less, the detonation region H It becomes.
[0052]
  As shown in FIG. 3, the non-condensable gas accumulation monitoring and evaluation system 53 has a temperature sensor 55 and a pressure sensor 56 attached to a gas accumulation capable position 54. Sensor signals from the temperature sensor 55 and the pressure sensor 56 are taken into a monitoring or judgment / evaluation computer 58 via a measuring means, and an evaluation is made as to whether or not the detonation region H has been reached.
[0053]
  Taking the operating state of the BWR plant 20 as an example, for example, the reactor pressure is 7 MPa and the steam temperature is 286 ° C. Hydrogen and oxygen produced by radiolysis are on the order of ppm by weight compared to steam and are in trace amounts. The reactor pressure of 7 MPa is a saturation pressure determined by the reactor steam. Here, the pressure value indicated by the steam partial pressure of 70% of the reactor pressure of 7 MPa is 4.9 MPa, and the steam temperature at the saturated steam pressure is 263 ° C.
[0054]
  From this, the non-condensable gas accumulation monitoring and evaluation system 53 can determine that the detonation region H has been reached when the steam temperature has decreased by 23 ° C. from the steam temperature of 286 ° C. during rated operation, and an alarm is issued.
[0055]
  In addition, about the set value of an alarm, since it is also one of the main purposes to notify the vicinity of a detonation area | region, you may set so that it may generate | occur | produce, for example by about 20 degreeC fall.
[0056]
  In addition, in the non-condensable gas accumulation monitoring and evaluation system 53, since the pressure sensor 56 is installed at the gas accumulation possible position 54, even if the piping pressure system is different from the reactor pressure, the detection of the pressure sensor 56 is performed. The value of the saturated steam corresponding to the detected pressure may be obtained from the value as an initial value, and the temperature of the saturated steam corresponding to the vapor pressure of 70% may be obtained from this initial value.
[0057]
  Next, the non-condensable gasRisk assessment systemThe operation of will be described.
[0058]
  A temperature sensor 55 and a pressure sensor 56 are attached to a portion 54 where the non-condensable gas can be accumulated like a branch pipe rising portion of the steam pipe of the BWR plant 20.
[0059]
  The vapor partial pressure of the gas accumulable location 56 is obtained from the temperature data obtained by the temperature sensor 55 by the calculating means 60, and the non-condensable gas partial pressure of the gas accumulable location 54 is obtained from the pressure data obtained by the pressure sensor 56 Ask for.
[0060]
  While the gas accumulation and gas accumulation history of the non-condensable gas are monitored from the obtained vapor partial pressure and non-condensable gas partial pressure, it is preset from the vapor partial pressure and non-condensable gas partial pressure results. It is possible to determine whether or not the combustion region, the detonation region, or the vicinity thereof has been reached under the determined determination conditions, and can be evaluated.
[0061]
  That is, the non-condensable gas accumulation monitoring and evaluation system 53 measures the temperature or pressure of the non-condensable gas accumulation location 54 and monitors changes in the temperature, etc. of the gas accumulation location 54 over time. While monitoring the accumulation status and its history, this monitoring data is compared with the judgment criteria set in advance, and it is judged and evaluated whether or not it has reached the combustion region or detonation region or the vicinity thereof. It is possible to provide an evaluation method capable of evaluating the risk of combustion of the non-condensable gas accumulated in the accumulable location 54 in advance and reliably.
[0062]
  Specifically, the non-condensable gas accumulation monitoring and evaluation system 53 in the pressure power plant detects the temperature by the temperature sensor 55 provided in the gas accumulation location 54 of the non-condensable gas and the fluid flowing in the fluid piping. The temperature inside the fluid piping is obtained from the heat transfer coefficient and the thermal conductivity of the fluid piping and its heat insulating material. The saturated vapor pressure in the fluid pipe is obtained from the obtained pipe temperature, and the gas partial pressure of the noncondensable gas in the fluid pipe is obtained from the difference between the pressure in the fluid pipe and the saturated vapor pressure.
[0063]
  Then, from the saturated vapor pressure in the fluid piping, the gas partial pressure of the non-condensable gas, and the partial pressure ratio (molar ratio) of hydrogen and oxygen in the non-condensable gas determined in advance, hydrogen, oxygen in the fluid piping, By calculating the vapor molar ratio and performing combustion analysis with this molar ratio as the initial condition, the combustion pressure of the non-condensable gas can be predicted, and the stress or strain at the location where gas can accumulate can be calculated from this combustion pressure. The degree of risk of pipe damage can be evaluated. That is, the degree of elasticity / deformation and plastic strain can be evaluated.
[0064]
  In addition, as a function of the evaluation determination table 66, a standard table that can determine the degree of elastic deformation and plastic strain from the evaluation result of the representative part of the elbow in the straight pipe portion and the straight pipe portion with respect to the flow pressure (dynamic pressure) By creating and comparing the non-condensable gas accumulation and pressure determined and evaluated by the evaluation system 53 using a standard table (combustion pressure-generated stress / plastic strain relationship, etc.), fluid piping The degree of risk of damage can be assessed.
[0065]
  Further, in the non-condensable gas accumulation monitoring and evaluation system 53 in the nuclear power plant, the non-condensable gas accumulation and monitoring at the gas accumulation possible portion 54 of the fluid piping can be efficiently monitored and evaluated. The shape of the piping, the ratio of the branch pipe diameter d which is the gas storage location 54 and the branch length L (L / d), the ratio of the diameter D of the fluid pipe which is the mother pipe and the branch pipe diameter d (d / D) Then, an arrangement table in which physical quantities such as the Re number are standardized from theoretical analysis and experimental data is created as one of the functions of the evaluation determination table 66. For example, the relationship between the diameter d of the branch pipe and the branch length L L / d = 3, 5, 10, 15, 20,... And an evaluation judgment table organized by d / D values. Using this evaluation judgment table, the measured value (physical quantity) of the non-condensable gas gas accumulation location 54 is compared, and the branch pipe of the gas accumulation location 54 has no accumulation, has accumulation, and cannot be denied. Can be quickly evaluated and evaluated. Instead of the evaluation determination table, an evaluation determination formula (for example, A = a · (d / D))^b・ (Re)^c/ (L / d)^eHowever, a, b, c, and d are constants), and a numerical value (physical quantity) measured at the gas accumulating location 54 is substituted into this evaluation judgment formula to quickly judge and evaluate the gas accumulation state. You may do it.
[0066]
  In any case, the non-condensable gas accumulation monitoring and evaluation system 53 in the nuclear power plant links the measuring device 57 including the temperature sensor 55 and the pressure sensor 56 with the evaluation system, thereby providing a gas accumulation monitoring and evaluation system. It is composed.
[0067]
  FIG. 8 relates to the present invention.Risk assessment system for noncondensable gasesThis shows a second embodiment of the present invention.
[0068]
  FIG.The non-condensable gas accumulation monitoring and evaluation system 53A shown in FIG. 5 is a gas accumulation location where the rising portion of the branch pipe branched from the steam piping 75 such as the RPV head spray piping 47 of the BWR plant is a gas accumulation location 54. A temperature sensor 55 is attached to 54. The point that the pressure sensor is not provided is different from the system 53 shown in the first embodiment of FIGS. 2 and 3. Other configurations and operations are the same as those of the non-condensable gas accumulation monitoring and evaluation system 53 shown in FIGS.
[0069]
  The non-condensable gas accumulation monitoring and evaluation system 53A shown in FIG. 8 includes a temperature sensor 55 provided at a rising portion of the branch pipe from the steam pipe, and processes temperature data measured by the temperature sensor 55. By monitoring the gas accumulation of the non-condensable gas at the gas accumulating location 54, the non-condensable gas is accumulated at the gas accumulating location 54 and reaches the combustible region (combustion region), detonation region, or the vicinity thereof. Whether or not it has been done can be notified accurately and reliably by an alarm.
[0070]
  In the BWR plant 20, the steam flows into the steam pipe 75 at the start of the nuclear reactor, and the steam also flows into the gas storage location 54, and the temperature rises. The temperature becomes constant when the nuclear reactor is in a rated operation state and the gas storage location 54 is filled with steam.
[0071]
  After that, the combustible non-condensable gas contained in the steam accumulates in the gas accumulable portion 54 that is a branch rising portion from the steam pipe 75, so that the temperature of the gas accumulable portion 54 gradually decreases. To go. By measuring this temperature change with the temperature sensor 55, gas accumulation of non-condensable gas can be observed.
[0072]
  The saturated vapor pressure at the maximum temperature measured by the temperature sensor 55 is obtained, and in the case of evaluation of the flammable region, the saturated vapor temperature at 85% of the saturated vapor pressure, and in the case of the detonation region, saturated steam is obtained. The temperature at which the alarm is issued at the saturated steam temperature at 70% of the pressure. When an alarm is generated in the vicinity of each of the combustible region and the detonation region, the temperature setting for generating the alarm may be increased.
[0073]
  Also in the non-condensable gas accumulation monitoring and evaluation system 53A in the nuclear power plant shown in FIG. 8, the gas accumulation of the non-condensable gas in the gas accumulating location 54 can be monitored. When the accumulable location 54 reaches the combustible area, the detonation area, or the vicinity thereof, an alarm can be issued to call attention.
[0074]
  FIG. 9 relates to the present invention.Risk assessment system for noncondensable gasesThe 3rd Embodiment of is shown.
[0075]
  FIG.The non-condensable gas accumulation monitoring and evaluation system 53B shown in FIG. 1 sets the branch pipe rising portion branched from the steam pipe 75 of the BWR plant 20 as a gas accumulation possible position 54, while the gas accumulation possible position 54 and this gas Temperature sensors 55a and 55b are respectively attached to the branch portions of the accumulable location 54. No pressure sensor is provided. The configuration other than the temperature sensors 55a and 55b attached to the gas accumulating portion and the branching portion of the gas accumulating portion 54 is the same as the non-condensable gas accumulation monitoring and evaluation system 53 shown in FIGS. Therefore, the same reference numerals are given and description thereof is omitted. The branch portion is a portion where the steam flowing in the steam pipe 75 is always flowing or a location near the portion.
[0076]
  As the reactor of the BWR plant 20 is driven, the steam flows into the steam pipe 75, and the steam also flows into the gas accumulating location 54, and the temperature rises. The temperature becomes constant when the nuclear reactor is in a rated operation state and the gas storage location 54 is filled with steam.
[0077]
  Thereafter, when the operation of the nuclear reactor is continued, the non-condensable gas contained in the steam of the steam pipe 75 accumulates in the gas accumulating location 54, so that the temperature of the gas accumulating location 54 gradually decreases. To go. As non-condensable gas accumulates, a difference occurs in the temperatures measured by the temperature sensors 55a and 55b. The temperature measured by the temperature sensor 55b at the branching portion is almost constant because it is the temperature of the steam, but the temperature of the non-condensable gas accumulating portion gradually decreases as the gas accumulates.
[0078]
  By measuring this temperature difference with both temperature sensors 55a and 55b, gas accumulation of non-condensable gas can be observed and monitored.
[0079]
  The saturated vapor pressure at the temperature of the branch portion measured by the temperature sensor 55b is obtained, and in the case of flammable region evaluation with respect to this saturated vapor pressure, the saturated vapor temperature at 85% of the saturated vapor pressure is calculated as the detonation region. In the case of the evaluation, the saturated steam temperature at 70% of the saturated steam pressure is set as a temperature for generating an alarm. When an alarm is generated in the combustible region or detonation region, the temperature setting for generating the alarm may be increased.
[0080]
  In the non-condensable gas accumulation monitoring and evaluation system 53B shown in FIG. 9, the example in which the temperature sensor 55b is provided at the branch portion from the steam pipe 75 has been described. However, the temperature sensor is not necessarily installed at the branch portion. Alternatively, an existing temperature measurement sensor for measuring the temperature in the steam pipe 75 may be used.
[0081]
  In the system diagram of the BWR plant 20 shown in FIG. 1, an example in which the electric valve 48 is used as the remote control valve for the vent branch pipe 47 of the branch vent system 38 is shown. In this case, the vent branch pipe 47 is used. May be directly connected to the main steam pipe 27a, and as shown in FIG. 10, an orifice 77 as a throttle mechanism may be provided upstream of the motor-operated valve 48. Furthermore, the motor-operated valve 48 is not necessarily provided in the vent branch pipe 47, and a vent branch pipe that does not include an electric valve or an orifice may be connected to the upstream side of the motor valve 43 of the RPV vent system 36.
[0082]
【The invention's effect】
  According to the present inventionNoncondensable gas risk assessment system and risk assessment method thereofCan quickly and accurately measure and monitor the accumulation of non-condensable gas at locations where nuclear power plants can store gas, and determine and evaluate the risk of damage to locations where gas can be stored. It can be surely prevented, an efficient and quick response can be performed, and a reliable and stable operation can be maintained.
[0083]
  In addition, by monitoring, predicting and evaluating the gas accumulation of flammable and non-condensable gases where gas accumulation is possible, damage risk management and preventive maintenance for hydrogen gas combustion can be performed reliably and highly reliable.Noncondensable gas risk assessment system and risk assessment method thereofCan provide.
[Brief description of the drawings]
FIG. 1 relates to the present invention.Risk assessment system for noncondensable gasesFIG. 1 is a system diagram partially and schematically showing a boiling water nuclear power plant including
FIG. 2 relates to the present invention.Risk assessment system for noncondensable gasesThe system diagram which shows 1st Embodiment.
FIG. 3 relates to the present invention.Risk assessment system for noncondensable gasesSchematic which shows 1st Embodiment of this.
FIG. 4 is a diagram showing a combustible region and a detonation region in a hydrogen-air-water vapor system.
FIG. 5 is a diagram showing a combustible region obtained by replacing a hydrogen-air-water vapor system with a hydrogen-oxygen-water vapor system.
FIG. 6 is a diagram showing a relationship between a combustible region and a vapor amount in a hydrogen-oxygen-water vapor system.
FIG. 7 is a diagram showing a relationship between a detonation region and a vapor amount in a hydrogen-oxygen-water vapor system.
FIG. 8 relates to the present invention.Risk assessment system for noncondensable gasesSchematic which shows 2nd Embodiment of this.
FIG. 9 relates to the present invention.Risk assessment system for noncondensable gasesSchematic which shows 3rd Embodiment of this.
10 is a schematic system diagram showing a modification of the boiling water nuclear power plant shown in FIG.
FIG. 11 is a schematic system diagram showing a conventional boiling water nuclear power plant.
[Explanation of symbols]
20 BWR plant
21 Reactor containment vessel (PCV)
22 Reactor pressure vessel (RPV)
23 Drywell
24 core
25 Reactor cooling water (liquid phase part)
26 Gas phase part (vapor phase part)
27 Main steam pipe
27a Main steam pipe
28 Steam turbine
29a, 29b Main steam isolation valve
30 Cooling system for reactor isolation
31 Turbine bypass system
36 Reactor pressure vessel vent system (RPV vent system)
37 Reactor pressure vessel head spray system (RPV head spray system)
38 Branch vent system
40 Reactor pressure vessel vent piping (RPV vent piping)
41 Reactor pressure vessel head vent nozzle (RPV head vent nozzle)
43 Electric valve (remote control valve)
45 Reactor pressure vessel head spray piping (RPV head spray piping)
46 Check valve
47 Vent branch piping
48 Electric valve (remote control valve)
49 Reactor pressure vessel head spray nozzle (RPV head spray nozzle)
50 Cooling equipment for reactor isolation (RCIC)
51a, 51b Primary containment isolation valve (PCV isolation valve)
53, 53A, 53B Non-condensable gas accumulation monitoring and evaluation system
54 Gas accumulation points
55 Temperature sensor
56 Pressure sensor
57 Measuring device (measuring means)
58 computer
60 Calculation means
61 Judgment evaluation means
62 Alarm means
63 Alarm generator
64 display means
65 Operation board
66 Evaluation judgment table
67 Evaluation program
70 Non-condensable gas accumulation evaluation system
71 Noncondensable gas accumulation amount prediction system
72 Ignition Combustion Pressure Evaluation System
73 Pipe strength evaluation system
74 Risk assessment system
75 Steam piping

Claims (8)

A temperature sensor provided at a location where non-condensable gas can accumulate, a location where gas can accumulate in the site, and
Calculating means for calculating the temperature in the pipe at the location where gas can be accumulated from the temperature data measured by the temperature sensor, and calculating the gas partial pressure of the non-condensable gas from the calculated temperature in the pipe;
From the obtained gas partial pressure of the non-condensable gas, combustion analysis is performed with the molar ratio of hydrogen and oxygen constituting the non-condensable gas as the initial condition, and the predicted combustion pressure is compared with preset judgment conditions. Determination and evaluation means for calculating the stress or strain of the non-condensable gas accumulation location;
A risk assessment system for non-condensable gas, comprising: a risk assessment unit for assessing a damage risk of a gas accumulable location based on a stress or strain of the gas accumulable location calculated by the judgment evaluation unit. While the calculation means obtains the temperature history of the gas accumulating location from the measurement data from the temperature sensor,
The non-condensation according to claim 1 , wherein the determination and evaluation means evaluates the temperature history of the gas accumulable location, and predicts the future non-condensable gas accumulation amount of the gas accumulable location when the temperature tends to decrease. Sex gas risk assessment system. The judgment and evaluation means predicts and evaluates the combustion pressure generated at the time of ignition from the predicted non-condensable gas accumulation amount when there is a temperature decrease tendency in the gas accumulation possible location, and the gas accumulation location by the evaluated combustion pressure Calculate the stress or strain of
The non-condensable gas risk evaluation system according to claim 1 , wherein the risk evaluation unit determines and evaluates a damage risk of a gas accumulable portion based on the calculated stress or strain. The determination evaluation means evaluates the combustion pressure generated at the time of ignition from the predicted non-condensable gas accumulation amount when there is a temperature decrease tendency in the gas accumulation possible place, and compares this combustion pressure with a predetermined determination condition. While judging
The non-condensable gas risk evaluation system according to claim 1 , wherein the risk evaluation means determines and evaluates a risk of damage to a gas accumulable portion by comparing a combustion pressure with a predetermined determination condition. Measure the temperature of the fluid piping at the non-condensable gas accumulation location where non-condensable gas accumulation is assumed,
From the measured pipe temperature, calculate the pipe internal temperature and the gas partial pressure of the non-condensable gas,
From the calculated partial pressure of the non-condensable gas, combustion analysis is performed with the molar ratio of hydrogen and oxygen constituting the non-condensable gas as an initial condition, and the combustion pressure due to the non-condensable gas is calculated and evaluated.
Calculate the stress or strain of the non-condensable gas accumulation location due to the evaluated combustion pressure,
A risk evaluation method for non-condensable gas, characterized by determining and evaluating a risk of damage to a non-condensable gas accumulation location from the calculated stress or strain. The risk evaluation method for non-condensable gas according to claim 5 , wherein when the temperature tends to decrease by measuring the temperature of the fluid piping, a future non-condensable gas accumulation amount at a location where gas can be accumulated is predicted. If the location where gas accumulation is possible tends to decrease in temperature, calculate and evaluate the combustion pressure generated during ignition from the predicted non-condensable gas accumulation amount,
Calculate the stress or strain of the fluid piping at the location where gas accumulation is possible due to the evaluated combustion pressure,
The risk evaluation method for a non-condensable gas according to claim 5 or 6 , wherein the risk of damage of a gas accumulable portion is determined and evaluated from the calculated stress or strain. If the location where gas accumulation is possible tends to decrease in temperature, calculate and evaluate the combustion pressure generated during ignition from the predicted non-condensable gas accumulation amount,
The judged combustion pressure is compared with a preset judgment condition,
The risk evaluation method for non-condensable gas according to claim 5 or 6 , wherein the risk of damage to a gas accumulable portion is determined and evaluated based on the comparison determination.

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