KR100597726B1 - Determination method of failed fuel discrimination ratio by applying the correction factors compensated for the flow rate differences among the coolant sampling lines - Google Patents

Abstract

       The present invention relates to a method for determining the defect ratio of defective fuel in the nuclear fuel monitoring system of the heavy water reactor.

The present invention relates to a method for determining a defective fuel discrimination ratio in a nuclear fuel monitoring system of a heavy water reactor, comprising: flowing coolant from a channel of the reactor to a detector through a radioactive sample tube; Measuring each coolant flow rate in the sample tube as a flow meter; Determining a flow rate correction factor for each channel by using the measured flow rate; Reflecting the flow rate correction factors in the radioactivity concentration measurement value of each channel; and calculating a discrimination ratio defined by the radioactivity concentration ratio for each channel; determining a defective fuel by applying a coolant flow rate correction factor Provide a nondeterministic method.

      The present invention, by considering the correction factor representing the difference in the flow rate of the coolant generated in the sample tube of each channel by minimizing the influence of the determination ratio due to the flow rate difference of the sample tube improved effect to accurately determine the fuel defect channel Obtained.

Heavy water reactor, nuclear fuel monitoring system, defect fuel, flow rate correction factor, radioactivity concentration measurement, defect fuel discrimination ratio determination

Description

DETERMINATION METHOD OF FAILED FUEL DISCRIMINATION RATIO BY APPLYING THE CORRECTION FACTORS COMPENSATED FOR THE FLOW RATE DIFFERENCES AMONG THE COOLANT SAMPLING LINES}

1 is a block diagram showing a system of a heavy water reactor to which a defect fuel discrimination ratio determination method applying a coolant flow rate correction factor according to the present invention is applied;

2 is a flowchart showing a method of determining a defect fuel discrimination ratio using a coolant flow rate correction factor according to the present invention in a stepwise manner;

3 is a block diagram showing a system of a heavy water reactor according to the prior art;

4 is a schematic diagram illustrating a gaseous fission product monitoring system (GFP) in a heavy water reactor according to the prior art;

5 is a block diagram showing a faulty fuel position detection system in a heavy water reactor according to the prior art;

FIG. 6 is a block diagram showing a sample line for radioactive concentration measurement for detecting a location of a defective fuel in a heavy water reactor according to the related art.

       <Description of Symbols for Main Parts of Drawings>

10,20,30,40,50 ... steps of the invention

200 .... reactor 210 .... channel

212 .... Pump 214 ... Steam generator

216 .... Heather 220 .. Gas fission product monitoring system

222 .... High Purity Gamma Detector

230 .... Defective fuel position detection system 210-S .... Sample tube

234 .... Sampling line 236 .... Neutron detector (BF ₃ )

The present invention relates to a method for determining the determination ratio of defective fuel in the fuel monitoring system of a heavy water reactor, and more specifically, the flow rate difference of the sample tube by considering a correction factor that compensates for the difference in the flow rate of the coolant generated in the sample tube of each channel. The present invention relates to a method for determining a defect fuel discrimination ratio by applying an improved coolant flow rate correction factor to accurately determine a fuel defect channel by minimizing the effect of determining the discrimination ratio due to

In general, deuterium reactors have an instrument system, as shown in FIG. 3. That is, a plurality of 380 channels 210 are formed in a closed loop form in the reactor 200, and include a fuel pipe loaded with nuclear fuel, and a coolant is circulated therein. have.

In such a heavy water reactor, a fuel channel 210 loaded with nuclear fuel is provided, which constitutes a circuit circulating through the pump 212, the steam generator 214, and the header 216, respectively. Each fuel channel 210 must be safely operated without leaking fuel and fission products therein.

In order to ensure the operation safety of the heavy water reactor, it is very important to accurately determine whether the fuel and fission products leak from the fuel into the coolant, and this fuel monitoring system is shown in FIG. A gaseous fission product monitoring system (GFP) 220 and a defective fuel location detection system 230 as shown in FIG.

When the deuterium reactor 200 in operation fails in the cladding of nuclear fuel loaded in each fuel channel 210 during operation, the nuclear fission product leaks into the coolant, and the nuclear species that emit gamma rays in the fission product. These are detected by a high purity gamma ray detector (HPGe detector) 222 in the total radiation monitoring system 220 as shown in FIG. The detection of gamma rays indicates that defective fuel is generated somewhere in the core.

However, in order to accurately track the faulty fuel channel 210 position, the faulty fuel position detection system 230 is used, which is shown in FIGS. 3, 5 and 5 in the coolant line circulated through each channel 210. As shown in FIG. 6, a separate sample tube 210-S is connected to form a sampling line 234 made in the form of a coil, and a detector 236 is inserted into the nuclear fission product leaked into the coolant. It should be measured.

That is, the sample tube 210-S is connected from each of the 380 channels 210 provided in the reactor, and the radioactive concentration of the coolant in the sampling line 234 made by the neutron detector 236 in the form of a coil is measured. It was to measure.

Current deuterium reactor 200 utilizing these detectors 236 uses delayed neutron (DN) measurement for the detection of defective fuel in each channel 210.

The calculation method of counting ratio and discrimination ratio used in conventional DN measurement is as follows.

   In the case of a loop of 2N channels as shown in FIG. 5, the radiation concentration measured from the detector 236 is as follows.

     1) Radiation concentration of defective fuel channel 210-D and its surrounding channel 210-A in loop-half with defective fuel:

..... [수식1]

..... [Equation 1]

Where λ is the decay constant, R is the fission product release rate from the defective fuel, F is the flow rate of the coolant in the channel sample tube, r is the radioactive concentration reduction factor due to the coolant circulation in the heat transfer system, and N is the number of fuel channels.

The radiation in the peripheral channel 210 -A is as follows.

....... [수식2]

....... [Equation 2]

     2) Radiation concentration of each channel 210-B in half-loop without defect fuel:

....... [수식3]

....... [Equation 3]

    3) and the discrimination ratio defined as the ratio of the radiation concentration (S ') in the defect channel 210-D to the average radiation concentration (S) of each channel 210 measured by the detector 236 as described above ( discrimination ratio (DR) becomes

....... [수식4]

....... [Equation 4]

Here, the average radioactivity concentration S is (S '+ S _A + S _B ) / 2N.

In addition, the ratio between the average value of the loop-Half channel 210-A with the defective fuel and the Loop-Half channel 210-B without the defect fuel may be expressed as follows.

....... [수식5]

....... [Equation 5]

In the conventional defect location detection method as described above, the determination operation is performed on all the channels 210 of the 2N number, and when the determination ratio DR obtained in any one channel 210-D exceeds 1.3, the corresponding channel ( In 210-D), it is determined that a defect occurs in the fuel. The criterion implemented by the current determination method is a channel 210-D in which the history discrimination rate of the corresponding channel 210-D occurs more than 1.1 three times or the determination rate 1.5 or more two times among the observation target channels. The internal fuel pipe is classified as a suspected nuclear fuel pipe.

However, in the defect fuel detection method of the heavy water reactor, the coolant flow rate is different for each sample tube 210-S due to the accumulation of impurities in the sample tubes 210-S of all the channels 210. As a result, it is difficult to determine the discrimination ratio, which is the basis of the defective fuel judgment criteria.

That is, as shown in the above formula, the radiometric concentration of each channel 210 includes the release rate (R) of the fission product leaking from the defective fuel to the coolant, the decay constant (λ) of the released nuclide, the flow rate of the coolant (F), Parameters such as radioactivity concentration reduction factor (r) according to the coolant circulation are implied. In particular, in the above equation, since the fuel cladding tube is broken and the number of nuclides releasing gamma rays has relatively been leaked into the coolant, which is heavy water, the flow rate F of the coolant among the above items is determined in all the sample tubes 210. The same must apply in -S).

That is, in the case of the sample tubes 210-S having the same inner diameter, the same flow rate flows inside the sample tube 210-S according to the same flow rate per unit of time in all the sample tubes 210-S. Since the flow rate has a direct effect on the flow rate of the coolant flowing per radioactivity concentration measurement time, the flow rates must be kept the same for sample tubes 210-S having the same inner diameter.

However, in the case of heavy water reactors, the diameters of the sample tubes 210-S are all the same, but in fact, the coolant flow rates on the sampling line connected to some channels 210 are known to be different.

Its main cause is that micro weld by-products that may occur during the initial plumbing process or fine debris from nuclear fuel or reactor structures during reactor operation accumulate in a certain area within the sample tube 210-S of the measuring channel 210 It can be judged that it is because it disturbs the flow. Therefore, measuring the radioactivity concentration in a state in which the coolant flow rates of the respective channel sample tubes 210-S are different and applying the defective fuel determination criteria based on this means that the defective fuel cannot be accurately detected.

As such, the present inventor has a coolant flow rate variable among the factors for determining the current defective fuel discrimination ratio, but if this flow rate is assumed to be the same constant in all the channels 210, in reality, all sample tubes 210-S We found that there is a problem in interpreting the data to find the defective fuel because of the difference in flow velocity.

Accordingly, the present invention is to solve the conventional problems as described above, the objective is to accurately detect the fuel channel in which the defect is generated by minimizing the influence of the determination ratio determination due to the difference in the flow rate generated in the sample tube of each channel The present invention provides a method for determining a defect fuel discrimination ratio using an improved coolant flow rate correction factor.

In order to achieve the above object, the present invention provides a method for determining the defect ratio of the defective fuel used in the nuclear fuel monitoring system of the heavy water reactor,

Allowing coolant to flow from the respective channels of the reactor to the detector through a sample tube;

Measuring each coolant flow rate in the sample tube as a flow meter;

Determining a flow rate correction factor for each channel by using the measured flow rate;

Reflecting the flow rate correction factors in the radiation concentration measurement of each channel; and

Comprising the step of calculating the determination ratio defined by the radioactivity concentration ratio for each channel; provides a method for determining the defect fuel determination ratio applying the coolant flow rate correction factor, characterized in that it comprises a.

Defective fuel determination ratio determination method (1) applying the coolant flow rate correction factor according to the present invention, as shown in Figure 2, but determines the determination ratio of the defect fuel used in the nuclear fuel monitoring system in the heavy water reactor 200, The discrimination ratio of the defective fuel is determined in consideration of the flow rate of the coolant flowing through the sample tubes 210-S connected to all the channels 210.

To this end, the method for determining the defect fuel discrimination ratio using the coolant flow rate correction factor according to the present invention first considers the following.

That is, according to the present invention, when the coolant flow rate in the sample tubes 210-S of each channel 210 continuously changes in the deuterium reactor 200, the impurities in the sample tubes 210-S are destructive. There is no countermeasure other than the removal by the method. However, if the coolant flow rate does not change over time and remains substantially constant for a long time, the inside of the sample tube 210-S is normal and a normal flow rate is detected, and the impurities inside the sample tube 210-S are abnormal. Due to this, there may be a case where the coolant flows abnormally.

In such cases, consideration should be given to correcting these between normal and abnormal flow rates.

The flow rate in the sample tube 210-S connected to each channel 210 should be selected to measure without penetrating the tube in order to prevent leakage of heavy water, which is a coolant.

Therefore, the flow rate measuring sensor should be attached to the outer wall of the sample tube 210-S and measured remotely, and a method capable of measuring the flow rate during operation of the reactor 200 is most suitable.

Defective fuel discrimination ratio determination method (1) applying the coolant flow rate correction factor according to the present invention, as shown in Figure 2, through each of the channels 210 of the reactor 200 through the radioactivity measurement sample tube (210-S) A step 10 is provided for flowing coolant toward the detector 236.

In addition, the present invention includes a step (20) of measuring the coolant flow rate in the sample tube (210-S) as a flow meter, respectively, the flow rate measuring step 20 is the flow rate for each sample tube (210-S) Can be measured to obtain the measured value.

Alternatively, each sample tube 210-S may be formed in a group to measure the flow rate at the discharge tube side of a confluence tube (not shown) in which these groups are gathered, and the flow rate measured value may be measured in these sample tube ( 210-S) is set to the representative value of the group. For example, as shown in FIG. 1, the 380 channels 210 of the reactor 200 are divided into eight groups, that is, divided into four groups of 48 and four groups of 47. The flowmeters 26 are mounted on the rear end of the valve 24 of one return tube 22 formed at the rear end of each of the eight conduit tubes in which the divided sample tubes 210-S are gathered. After the measurement, these eight flow rates are set as representative values of the sample tube 210-S flow rate of the group to reflect the sample tube 210-S flow rate of the respective groups.

In this case, eight different flow rate correction factors can be obtained by obtaining at least eight different flow rates for each group.

In addition, if a tracer is to be added to the coolant during the flow rate measurement, it may be necessary to determine whether the flow rate is measured after examining whether or not it affects the safety of the reactor 200.

In addition, the present invention is a step 30 of determining the flow rate correction factor for each channel 210 by using the flow rates measured as described above.

In this step 30, if the flow rate in each coolant sample pipe 210-S is different, the flow rate F may be a constant having a constant value in the radiation concentration formula (1) of the defective fuel channel 210. none.

Therefore, if the average value of the flow rate measured value Fi of each coolant sample tube 210-S is called Fav, and normalizes to 1, the flow rate correction factor Ci of each sample tube 210-S will be

....... [수식6]

....... [Equation 6]

Becomes

Therefore, the flow rate correction factor of each sample tube 210-S is determined as mentioned above by measuring the flow rate in the sample tube 210-S. When the flow rate correction factor is determined for each of the sample tubes 210-S as described above, a step 40 of reflecting the flow rate correction factors to the radioactivity concentration measurement value of each channel 210 is performed.

In this step 40, in the case of the loop of the 2N channel 210 as shown in Fig. 5, the radioactivity concentration measured from the detector 236 is expressed by the following equations (1), (2) and (3). ) Can be expressed as an expression of the flow rate correction factor Ci instead of the flow rate F.

    4) Radioactivity of defective fuel channel 210-D and its surrounding channel 210-A in loop-Half with defective fuel:

....... [수식7]

Equation 7

The radiation in the peripheral channel 210 -A is as follows.

....... [수식8]

Equation 8

    5) Radiation concentration of each channel 210-B in half-loop without defect fuel:

.......[수식9]

Equation 9

As described above, in the step 40, the flow rate correction factors are reflected in the radioactivity concentration measurement value of each channel 210, and then the determination ratio defined by the radioactivity concentration ratio for each channel 210 is calculated ( 50) are executed.

In this step 50, the determination ratio defined as the ratio of the radiation concentration (S ') in the defect channel 210-D to the average radiation concentration (S) of each channel 210 measured by the detector 236 ( discrimination ratio (DR) is expressed as

....... [수식10]

Equation 10

Here, the average radioactivity concentration (S) is (S '+ S _A + S _B ) / 2N, and A is a constant generated by applying a correction factor. By calculating the defect fuel discrimination ratio (DR) by applying the equation considering the flow rate correction factor, it is possible to find the channel 210 -D where the defect fuel is generated more accurately than the present.

According to the present invention as described above, after measuring the coolant flow rate in a non-destructive manner from the sample pipe (210-S) connected to each channel 210, based on the average flow rate of the normal coolant flow channel 210 It is determined by the value, and the ratio with the flow rate value of the abnormal flow channel 210 is used as the flow rate correction factor. In this way, by accurately determining the flow rate correction factor and applying it to the calculation of the defect fuel discrimination ratio, the defect fuel determination accuracy can be greatly improved.

In addition, the present invention minimizes the influence of the determination ratio determination due to the difference in the flow rate generated in the sample pipe 210-S of each channel 210 as described above to determine the defect fuel discrimination ratio, so that the fuel channel in which the defect is generated An improved effect is obtained so as to accurately determine 210-D.

Claims (5)

In the method for determining the defect ratio of the defective fuel used in the nuclear fuel monitoring system in the heavy water reactor 200, Allowing a coolant to flow from the respective channels 210 of the reactor 200 to the detector 236 through the sample pipe 210 -S; Measuring (20) the coolant flow rate in the sample tube (210-S) as a flow meter (26), respectively; Determining a flow rate correction factor for each channel 210 by using the measured flow rate (30); Reflecting (40) the flow rate correction factors in the radioactivity concentration measurement of each channel 210; and Calculating (50) a discrimination ratio defined as a radioactivity concentration ratio for each channel (210). The method of claim 1, wherein the step (20) of measuring the coolant flow rate in the sample tube (210-S) as a flowmeter 26, respectively, form a plurality of sample tubes (210-S) in a plurality of groups (Group) And measuring the flow velocity at the discharge tube side of the confluence tube where these groups gather, and setting the flow rate measurement value to a representative value of the sample tube 210-S group. How to decide. The method of claim 1, wherein the determining of the flow rate correction factor (30) is called an average value of the flow rate measured values Fi of each coolant sample tube 210-S, and normalized to one. The flow rate correction factor Ci of each sample tube 210-S is

....... [Equation 6] Defective fuel discrimination ratio determination method applying the coolant flow rate correction factor characterized in that. The method of claim 3, wherein the step 40 of reflecting the flow rate correction factors Ci to the radioactivity concentration measurement of each channel 210 is In the half-loop with defective fuel, the radiation concentration of the defective fuel channel 210-D and its surrounding channel 210-A is:

Equation 7 And, the radiation concentration in the peripheral channel 210 -A is:

Equation 8 In addition, the radiation concentration of each channel 210-B in the loop-half without defect fuel is:

Equation 9 Where λ is the decay constant, R is the release rate of fission products from the defective fuel, r is the radioactivity concentration reduction factor due to the coolant circulation in the heat transfer system, and N is the coolant flow rate correction factor applying coolant flow rate correction factor. How to decide. The method of claim 4, wherein in calculating the discrimination ratio defined by the radioactivity concentration ratio for each channel 210, the discrimination ratio DR is:

....... Equation 10 Here, the average radiation concentration (S) is (S '+ S _A + S _B ) / 2N, A is a constant generated by applying a correction factor, r is a radioactivity concentration reduction factor due to the coolant circulation in the heat transfer system, N Defective fuel discrimination ratio determination method applying the coolant flow rate correction factor, characterized in that the number of fuel channels.

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