JP4316338B2 - Criticality safety monitoring method and criticality safety monitoring device - Google Patents

Description

  The present invention relates to criticality safety monitoring of an area containing a substance containing a fissile substance or a substance possibly containing a fissile substance.

  When storing a substance containing a fissile substance or a substance that may contain a fissile substance, it is necessary to monitor the critical safety of the contained substance.

  For example, when storing spent fuel assemblies in storage racks, spent fuel transport containers transport / storage containers (casks), as a method for monitoring the critical safety, spontaneous neutrons released by spent fuel There is a method (spontaneous neutron multiplication method) for evaluating the subcriticality by using both the measured value and the calculated value using the method (see Patent Document 1).

  This method calculates the neutron emission rate using information such as the fuel type, initial enrichment, burnup, power density, and cooling time of the spent fuel assembly to be measured. This is a method for obtaining the effective neutron multiplication factor (subcriticality) using the value of neutron flux (neutron counting rate) obtained by measuring spontaneous neutrons from fuel.

  In addition, in the reprocessing process co-decontamination (process for decontamination of fission products (FP) and curium), distribution process and / or purification process, reprocessed fuel is supplied to the equipment that performs criticality control by Pu concentration installed. As a method for monitoring the criticality safety when storing, a method for monitoring the criticality safety using spontaneous neutrons released from reprocessed fuel (spontaneous neutron multiplication method) is known (patented) Reference 2).

In this method, the relationship between the Pu isotope composition and the neutron emission rate per unit weight of Pu is calculated, and the maximum Pu concentration that can be received in the reprocessed fuel and the range of the Pu isotope composition of the reprocessed fuel that is received, Calculate the range of neutron count rates that can be measured, calculate the alarm value of the neutron count rate by taking into account the background count etc. in addition to the minimum value, and calculate the alarm value and spontaneous neutrons from reprocessed fuel The measured neutron count rate is compared and monitored.
JP-A-1-169398 Japanese Patent Laid-Open No. 4-256897

  In the spontaneous neutron multiplication method, when subcriticality is calculated using the neutron emission rate and neutron count rate, there is the complexity that it is necessary to obtain information on the measurement target in advance and obtain the neutron emission rate .

  Further, in the method of obtaining and monitoring the alarm value of the neutron count rate using the relationship between the Pu isotope composition and the neutron emission rate, the neutron count rate is a super isotope that emits neutrons such as the Pu isotope composition, Cm244 and Am241. Since it also changes due to mixing with various types of Pu reprocessing fuel, it must be an alarm value with a very low neutron count rate, and there is a problem that an alarm is issued even if it is not necessary to issue an alarm originally. .

The present invention is a criticality safety monitoring method and a criticality safety monitoring device which are made to achieve the above object, and the criticality safety monitoring method according to claim 1 is measured at every measurement time τ by a neutron detector. A step of measuring the number of neutron pulses per time a plurality of times, a step of _obtaining an average value n _ave and a variance σ of the number of neutron pulses measured a plurality of times for each measurement time τ, and an average value n _ave and a variance σ A step of obtaining a coefficient Y defined by the following equation (1) using each measurement time τ:
^{_{Y τ = σ 2 / n ave}} -1 (1)
Obtaining a prompt neutron decay constant α and a constant Y _sat so that the distribution of the coefficient Y obtained in the step according to the measurement time τ is fitted with Y (τ) defined by the following equation (2) :
Y (τ) = Y _sat {1- (1-e− ^ατ ) / ατ} ( 2)
A step of _obtaining a difference E _τ between a value Y _{τ of the} coefficient Y defined by the following equation (3) and Y (τ) obtained by the equation (2) ;
_{E τ = Y τ -Y (τ} ) (3)
Variance of E _tau or, determining a difference between the maximum value and the minimum value of E _tau, the variance of E _tau or, if the difference between the maximum value and the minimum value of E _tau is a predetermined value or more, calibration Repeat the steps from inserting the radiation source into the measurement area of the neutron detector and measuring the number of neutron pulses multiple times with the calibration source inserted to the step of determining the prompt neutron decay constant α and constant Y _sat Measuring the prompt neutron decay constant α again.

The criticality safety monitoring method according to claim 2 is characterized in that the total delayed neutron ratio β and prompt neutron lifetime L determined using a general-purpose nuclear calculation code system, and E _τ Depending on whether or not the difference between the maximum value and the minimum value is greater than or equal to a predetermined value, the prompt neutron decay constant α measured with the calibration source not inserted or with the calibration source inserted And using the following equation (4) to determine the subcriticality ρ:
ρ = β−αL (4)
Obtaining a neutron effective multiplication factor k by the following equation (5);
k = 1 / (L-ρ) (5)
Generating a scram signal when the effective neutron multiplication factor k is larger than a preset value.

The criticality safety monitoring method according to claim 3, wherein the number of neutron pulses per measurement time measured with the calibration source inserted is smaller than the number of neutron pulses per measurement time measured last time. And a step of discharging the calibration radiation source from the measurement region of the neutron detector.

The criticality safety monitoring device according to claim 4 measures a neutron detector that detects neutrons and generates electric pulses, a measurement circuit that converts electric pulses into rectangular pulses, and a pulse measurement value that is the number of rectangular pulses Multi-channel scaler, time width measurement count setting means to set the measurement time τ and measurement count of the pulse measurement value in the multi-channel scaler, and the average value n _ave and dispersion of the number of neutron pulses from the multi-channel scaler pulse measurement value statistical calculation means for obtaining σ for each measurement time τ, and for obtaining the coefficient Y defined by the following equation (1) using the average value n _ave and variance σ for each measurement time τ;
Y = σ ² / n _ave −1 (1)
An attenuation constant calculating means for determining the prompt neutron attenuation constant α and the constant Y _sat so that the distribution of the coefficient Y determined in the step according to the measurement time τ is fitted with Y (τ) defined by the following equation (2): ,
Y (τ) = Y _sat {1- (1-e− ^ατ ) / ατ} (2)
(3) below is defined by the equation, after obtaining the difference E _tau between the value Y _tau coefficient Y and (2) determined by the equation Y (tau), the variance of E _tau or the maximum value of E _tau obtains the difference between the minimum value and the dispersion value of E _tau or, if the difference between the maximum value and the minimum value of E _tau is a predetermined value or more, to direct insertion of the calibration radiation source to the measurement region of the neutron detector A checking source insertion signal generating means for generating a signal;
_{E τ = Y τ -Y (τ} ) (3)
Checking source activation means for inserting a calibration source into the measurement region of the neutron detector according to a signal from the checking source insertion signal generation means, and the statistical calculation means is in a state in which the calibration source is inserted. The average value n _ave of the number of neutron pulses and the variance σ are obtained for each measurement time τ from the pulse measurement values of the multichannel scaler in FIG. 1, and the coefficient Y defined by the equation (1) using the average value n _ave and the variance σ For each measurement time τ,
The attenuation constant calculation means is a prompt neutron attenuation so that the distribution of the mean value n _ave and dispersion σ for each measurement time τ obtained by the statistical calculation means with the calibration source inserted is fitted by the equation (2). A constant α and a constant Y _sat are obtained.

The criticality safety monitoring device according to claim 5 is a total delayed neutron ratio calculating means for obtaining a total delayed neutron ratio β and prompt neutron lifetime L using a general-purpose nuclear calculation code system, and a total delayed neutron ratio calculating means. The state where the calibration source is not inserted depending on whether the difference between the total delayed neutron ratio β and the prompt neutron lifetime L obtained using the maximum value and the minimum value of E _τ is equal to or greater than a predetermined value Alternatively, using any of the prompt neutron decay constants α measured with the calibration radiation source inserted, the subcriticality ρ is obtained by the following equation (4), and the neutron to obtain the effective neutron multiplication factor k by the following equation (5) An effective multiplication factor calculating means;
ρ = β−αL (4)
k = 1 / (L−ρ) (5)
And scram signal generating means for generating a scram signal when the effective neutron multiplication factor k is larger than a preset value.
The criticality safety monitoring device according to claim 6, wherein the number of neutron pulses per measurement time measured with the calibration source inserted is less than the number of neutron pulses per measurement time measured last time. And a check source discharge signal generating means for generating a signal for discharging the calibration radiation source from the measurement region of the neutron detector, and the checking source activation means is responsive to the signal from the check source discharge signal generating means. The calibration radiation source is discharged from the measurement region of the neutron detector.

  According to the present invention, since it is not necessary to obtain the neutron emission rate using the information to be measured, it is simple and the frequency at which a signal judged to be dangerous is generated when sufficient critical safety is originally secured. If there is a problem with criticality safety, criticality safety can be monitored with proper judgment.

  In the criticality safety monitoring method according to the embodiment of the present invention, first, a spontaneous neutron multiplication method is applied to a neutron from a measurement region containing a substance containing a fissile substance or a substance possibly containing a fissile substance. And an alarm signal is generated when the neutron count rate is greater than the measured value.

  At this time, measurement of neutrons and generation of an alarm signal can be performed in the same manner as the invention disclosed in Japanese Patent Laid-Open No. 4-256897.

  However, in this embodiment, an alarm signal is not generated to deal with an alarm, but when an alarm signal is generated, prompt neutron decay occurs due to the statistical nature of the neutron measurement result (neutron pulse). Find the constant α. This method of determining the prompt neutron decay constant α from the statistical properties of neutron measurement results is called the reactor noise measurement method. For example, “Advanced reactor noise measurement and new applications” Research Expert Committee, “Noise the Revival: Toward New Developments in Furnace Noise Research” Japan Atomic Energy Society, November 2001, p. 12-56.

In addition, the rate of total delayed neutrons using a separate general-purpose nuclear calculation code system, for example, “Japan Atomic Energy Research Institute SRAC95; general-purpose nuclear calculation code system” disclosed in JAERI-Data / Code 96-015 (1996) Determine β and prompt neutron lifetime L. And subcriticality (rho) is calculated | required by (1) Formula.
ρ = β−α L (1)
Next, the neutron effective multiplication factor k is obtained from the equation (2) using the obtained subcriticality ρ.
k = 1 / ( L− ρ) (2)

  A scram signal is generated when the obtained neutron effective multiplication factor k is larger than a set value, that is, when it is determined that the subcriticality has become shallow. By generating this scram signal, an appropriate countermeasure can be taken.

  In addition, instead of performing scram signal generation when the neutron effective multiplication factor becomes larger than the set value, it is determined that the subcriticality ρ is smaller than the set value, that is, the subcriticality is shallow. You may make it perform in a case.

  As the furnace noise measurement method, the Rossi-α method or the Feynman-α method can be used.

In the Rossi-α method, if a neutron pulse is detected at time t = 0, the probability P (t) that a neutron pulse is detected at time t is c, This is a method using what is expressed by the following equation when d is a constant.
P (t) = c + d · exp (−α · t) (3)
The probability P (t) is obtained from the detection result of the neutron pulse, and the prompt neutron attenuation constant α is obtained so as to fit the equation (3).

  On the other hand, the Feynman alpha method is obtained by using the relationship between the measurement time (gate width) τ of the neutron pulse, the average of the neutron count value and the dispersion thereof, and the prompt neutron decay constant α, which will be described in detail later.

According to the criticality safety monitoring method of the present embodiment, the neutron count rate is set based on the Pu isotope composition, the neutron count rate set by mixing in various types of reprocessed fuels that emit neutrons such as Cm244 and Am241. even if it exceeds, the scram signal if an increase in the effective neutron multiplication factor was determined using Rozatsu sound measurement method is confirmed (alarm) is not generated, it is possible to suppress the occurrence of unnecessary alarms.

  On the other hand, in the reactor noise measurement method, when the neutron count rate is low, the statistical accuracy is insufficient, and it is considered that an alarm is erroneously generated due to a problem of accuracy. However, according to the criticality safety monitoring method of the present embodiment, only when the neutron count rate exceeds the set value, the increase in the effective neutron multiplication factor obtained by using the reactor noise measurement method is monitored to detect the scram signal. Since (alarm) is generated, the above-mentioned accuracy problem can be solved, and the occurrence of an erroneous alarm can be suppressed.

  Therefore, while suppressing the occurrence of these false alarms, if the effective neutron multiplication factor increases, the neutron count rate increases and the margin of subcriticality decreases, the scram signal must be generated reliably. Can do.

Further, in this embodiment, the total delayed neutron β and prompt neutron lifetime L obtained by analysis greatly depend on the amount of fissile material such as U235, Pu239, Pu241 and the like. On the other hand, the neutron emission rate varies depending on the type of higher Pu and ultra Pu elements such P u 239. And the analysis error of the isotopic composition ratio of this higher-order Pu or super-Pu element is larger than the analysis error of the amount of fissile material such as U235, Pu239, Pu241.

Therefore, as compared with the critical safety monitoring method by the conventional spontaneous neutron multiplication method using the value obtained by analysis as the neutron emission rate, the total delayed neutron ratio β and prompt neutron lifetime L obtained in this embodiment are: Since there are few analysis errors, according to this Embodiment, the precision of critical safety monitoring can be improved.

The criticality safety monitoring device according to a first embodiment of the present invention will be described with reference to FIG 1 and FIG 2. Figure 1 is a block diagram of the criticality safety monitoring device of Example 1, FIG. 2 is a diagram for explaining the flow of criticality safety monitoring method using a criticality safety monitoring device of Example 1 is there. In the criticality safety monitoring apparatus of the present embodiment, a case where the Feynman Alpha method is used will be described.

  A neutron detector 2 is arranged in a measurement region 1 that requires critical safety monitoring, such as a fuel region that contains a material containing a fissile material or a material that may contain a fissile material. This measurement area 1 is for a spent fuel storage rack, a cask or a mixer setra on which a spent fuel assembly is loaded. Moreover, since the neutron from the measurement area | region 1 should just be measured, you may arrange | position the neutron detector 2 in the outer side of the measurement area | region 1, for example, the outer side of a fuel area | region.

  When neutron is detected by the neutron detector 1, an electric pulse signal is generated. Usually, when one neutron is detected, one electric pulse is generated. The electric pulse from the neutron detector 1 is amplified by the amplifier 3, and the amplified electric pulse is converted into a rectangular pulse by shaping the waveform of the electric signal in the measuring circuit 4.

  The rectangular pulse from the measurement circuit 4 is input to the rate meter 5 to obtain a neutron count rate that is the number of pulses per unit time. The steps from the generation of the electric pulse in the neutron detector 2 up to this point to the determination of the count rate by the rate meter 5 are the neutron count rate measurement step (S1) shown in FIG. In the following description, when it is described as neutron count rate measurement (step S1), it means that neutrons generated from the measurement region by the same operation are measured as the neutron count rate.

  The count rate obtained by the rate meter 5 is sent to the count rate display means 6, and the count rate is displayed on the count rate display means 6 (step S2).

The signal of the neutron count rate obtained by the rate meter 5 is sent to the computer 7. The computer 7 includes input means (keyboard, mouse, etc.), output means (monitor, printer, etc.), storage means (memory, hard disk, etc.), communication means (rate meter 5 etc.) that a normal computer has, It has a network, etc.) to exchange, such as other computers and information, the means to function computer 7 can perform input and output of data from such the storage means. Further, the computer 7 can be constituted by a plurality of computers, and each means that causes the computer 7 to function may be realized by different computers. Each means that causes the computer 7 to function is generally realized by loading a computer program into a general-purpose computer. However, some means or all means may be realized by a dedicated device. it can.

The entered count rate to the computer 7, an alarm signal generating means 8, is compared with the value of the preset alarm signal generator (step S3), and if the count rate is greater than the preset value, an alarm Signal 9 is generated. At this time, the alarm signal generating means 8 notifies the time width measurement number setting means of the generation of the alarm signal (step S4). The generation of an alarm signal based on a count rate such as a set value in the alarm signal generation means 8 can be performed in the same manner as the invention disclosed in Japanese Patent Laid-Open No. 4-265897.

Next, the time width measurement number setting means 10 having received the notification of the occurrence of the alarm signal, based on the information stored in the storage means of the computer 7 and the like, the number of times of measurement by the multi-channel scaler (MCS) 1 1 and once. The measurement time (gate width) τ is obtained, and the obtained number of times and the measurement time τ are set in the multichannel scaler 11 (step S5). Number and measurement time may be stored in either storage means for setting in advance how, or receive count rate from an alarm signal generating means 8 may be configured to calculate on the basis of the value .

  Next, the multichannel scaler 11 measures and stores the number of rectangular pulses (corresponding to neutron pulses) from the measurement circuit 4 during the measurement time τ (pulse measurement value) a set number of times. The stored measurement value is sent to the computer 7 together with the measurement condition (step S6).

Statistical calculator 12 of the computer 7 calculates the average value n _ave and variance σ of the same calculation conditions (same measurement time tau) measurement value of (the number of rectangular pulses during the measurement time between tau) (step S7) .

Statistical calculation unit 12 obtains the Y by the following equation and the calculated average value n _ave from variance sigma (Step S 8).
Y = σ ² / n _ave −1 (4)

  The statistical calculation means 7 determines whether measurement of a predetermined number of samples for a plurality of measurement times τ has been completed based on the information stored in the storage means of the computer 7. The width measurement number setting means 10 is notified to measure a measurement value that has not been measured.

  Upon receiving the notification, the time width measurement count setting means 10 returns to the process of step S5 and measures the measurement value (step S9).

Thus, Y is obtained for each measurement time during tau, with the correlation between tau. Y (τ) can be expressed by the following equation using the prompt neutron decay constant α.
Y (τ) = Y _sat {1- (1-e− ^ατ ) / ατ} (5)

When the predetermined number of samples is completed (step S9), the value of Y _τ (Y of the measurement time _τ is expressed as Y _τ ) from the statistical calculation means 12 via the storage means of the computer 7 or the like is an attenuation constant calculation means. It handed over to 13, the attenuation constant calculating unit 13, as the distribution of Y _tau is off I potting in (5), obtains the prompt neutron attenuation constant α and Y _sat (step S10).

At this time, the total delayed neutron ratio calculating means 14 obtains the total delayed neutron ratio β and the prompt neutron lifetime L by a general-purpose nuclear calculation code system. The total delayed neutron ratio calculating means 14 may be configured to be executed by a computer different from the computer that executes the attenuation constant calculating means 13, or the total delayed neutron ratio β calculated in advance by a general-purpose nuclear calculation code system. and prompt neutron lifetime L a is stored in the storage means of the computer 7 together with the calculation conditions, the damping constant computing means 13 in prompt neutron decay constant α conforming to the calculated conditions all Osohatsu neutron fraction β and The prompt neutron lifetime L may be extracted from the memory hand throw of the computer 7 (step S11).

Next, the effective neutron multiplication factor calculation means 15 uses the prompt neutron attenuation constant α obtained by the attenuation constant calculation means 13, the total delayed neutron ratio β obtained by the total delayed neutron ratio calculation means 14, and the prompt neutron lifetime L. Then, the subcriticality ρ is calculated by the above-described equation (1) (step S12).

Next, effective neutron multiplication factor calculation unit 15, from the subcriticality ρ determined (2) determine the effective neutron multiplication factor k by equation (step S13).

The neutron effective multiplication factor k obtained by the neutron effective multiplication factor calculation means 15 is sent to the neutron effective multiplication factor display means 16, and the neutron effective multiplication factor display means 16 displays the obtained neutron effective multiplication factor k ( Step S14).

  Further, the neutron effective multiplication factor k obtained by the neutron effective multiplication factor calculating means 15 is also sent to the scram signal generating means I7. The scram signal generation means 17 compares the determined neutron effective multiplication factor k with a preset neutron effective multiplication factor setting value (step S15), and if the value exceeds the value set by the scram signal generation means 17 The scram signal 18 is generated by the scrum signal generation means 17 (step S16).

Set value of the effective neutron multiplication factor, the value of牲子effective multiplication factor in where it is determined as a dangerous When exceeded the measurement region 1 may be set.

  The generated scrum signal 18 itself can be used as an alarm, or an alarm can be generated based on the scrum signal 18. Further, based on the scrum signal 18, it is possible to start a measure to be taken when it is determined that the measurement area is dangerous. For example, when the spent fuel storage rack or cask is in the measurement region 1, when the scram signal 18 is generated, it can be treated to prohibit the loading of the spent fuel assembly on the spent fuel storage rack or cask. .

  On the other hand, when the scram signal generation means 17 determines that the effective neutron multiplication factor is not more than the set value, the process returns to step S1 and the critical safety monitoring is continued.

  A second embodiment of the present invention will be described with reference to FIG. The same devices as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  Spent fuel assemblies 28 are stored in alignment in a spent fuel storage rack 27 that can be arranged in 8 rows and 7 columns. Even if the spent fuel storage rack 27 is a spent fuel storage cask, the present embodiment can be applied.

  The neutron detector 2 a and the neutron detector 2 b are arranged on both sides of the spent fuel storage rack 27. Electric pulses from the neutron detector 2a and the neutron detector 2b are amplified by the amplifier 3a and the amplifier 3b, respectively. Each amplified electric pulse is converted into one electric pulse by the mixer 19. For example, the mixer 19 receives the electric pulse of the amplifier 3a and the electric pulse of the amplifier 3b and converts them into an electric pulse obtained by adding them.

  The electric pulse converted by the mixer 19 is sent to the measuring circuit 4 and converted into a rectangular pulse by the measuring circuit 4.

  Since the measurement circuit 4 and subsequent circuits are the same as those in the first embodiment, the illustration and description thereof with reference to FIG. 3 are omitted.

Loading the spent fuel storage rack 27 spent fuel assemblies 28 to the first, loaded with spent fuel assemblies 28 shown in _{F 1, thereafter, F 2, F 3, F} 4, F 5 , F ₆ , F ₇ , F ₈ , F ₉ ,. In this loading method, loading is performed so that the neutron multiplication factor is easily monitored from a state where the neutron spectrum around the detector is stabilized and the multiplication factor is lowered.

  At this time, when the spent fuel assembly 28 is loaded at a position close to the neutron detector 2a, the neutron count rate of the neutron detector increases. However, when the spent fuel assembly 28 is loaded at a position far from the neutron detector 2a, the neutron count rate of the neutron detector hardly increases. Accordingly, the increase in the neutron count rate varies greatly depending on the place where the spent fuel assembly 28 is loaded, and the critical safety of the spent fuel storage rack 27 cannot be determined based on this neutron count rate.

  On the other hand, since the neutron detector 2b is disposed on the opposite side of the spent fuel storage rack 27, when the spent fuel assembly is loaded at a position close to the neutron detector 2a, it hardly increases. When the spent fuel assembly is loaded at a position far from the neutron detector 2a, the position is close to the neutron detector 2b, and therefore the neutral hand count rate increases. That is, if the neutron count rate is obtained based on the electrical pulse obtained by adding the electrical pulse of the neutron detector 2a and the electrical pulse of the neutron detector 2b, the change due to the loading position of the spent fuel assembly is suppressed, and the neutron count rate is reduced. Can be requested.

  Therefore, according to the second embodiment, even when the distance at which the spent fuel assembly is loaded from the neutron detector is changed, the influence of the distance can be reduced and appropriate criticality safety can be monitored.

A third embodiment of the present invention will be described with reference to FIGS. The like same equipment and steps as in Example 1 will not be described are denoted by the same reference numerals.

  In this example, when the present embodiment is applied to the mixer setra and it is determined that the accuracy of the statistical value of the neutron pulse for calculating the prompt neutron attenuation constant α is not sufficient, the checking source (calibration source) ), For example, californium 252 (Cf252) or the like is inserted to measure neutron pulses.

As shown in FIG. 4, the mixer setra 23 has a fuel solution section 24 at the top and a neutron detection section 26 at the bottom, with a neutron absorber (cadmium) 25 interposed therebetween. In the neutron detector 26, the neutron detector 2 is usually disposed inside the neutron moderator 29. When the accuracy of the statistical value is determined not to be enough, by Ji E Tsu King source activation device 20 can be inserted is Ji E Tsu King source 19 position is provided in the mixer-settler 23.

  From the measurement of the neutron count rate (step S1) to the calculation of the prompt neutral hand attenuation constant α (step S10) using the measured value of the neutron pulse (the number of rectangular pulses during the measurement time τ) (step S10), Example 1 The detailed steps are omitted because they are the same steps by the same means.

In this embodiment, the value of the prompt neutron decay constants α and Ysat the measurements Y _tau from decay constant calculating unit 13 is delivered to checking the source insertion signal generating means 21 via a storage means of the computer 7, checking the source insertion signal generating means 21 determines the difference E _tau and actual measurement values as the Fitting I ring (5) from the following equation (step S17).
_{E τ = Y τ -Y sat {} 1- (1-e -ατ) / ατ} (6)

Next, the variance value of E _τ of the checking source insertion signal generation means 21 is obtained, and when the variance value of E _τ is smaller than a predetermined value, it is determined that the accuracy of the statistical value is sufficient (step S18).

Instead of _obtaining the variance value of E _τ , the difference between the maximum value and the minimum value of E _τ is obtained, and when the value is smaller than a predetermined value, it is determined that the accuracy of the statistical value is sufficient. Also good.

When the checking source insertion signal generation means 21 determines that the accuracy of the statistical value is sufficient, the neutron effective multiplication factor calculation means 15 is notified of this. Thereafter, processing similar to that in step S12 and subsequent steps in the first embodiment is performed. The same applies to the process of step S 11 in all Osohatsu neutron ratio calculating means 14 as in Example 1.

If the accuracy of the statistical value is determined to be not sufficient in checking the source insertion signal generating means 21, checking the source insertion signal generating means 21 sends the switch E Tsu King source insertion signal to checking the source activation apparatus 20. Checking the source insertion signal checking source activation device received the 20 inserts Ji E Tsu King source 19 at a predetermined position of the mixer-settler 23 (step S19 in FIG. 7).

After the checking source 19 is inserted into a predetermined position of the mixer setra 23, the neutron count rate is measured in the same manner as in step S1 of the first embodiment, and the count rate is sent to the computer 7 (step S1).

  The checking source discharge signal generation means 22 of the computer 7 stores this count rate in the storage means of the computer 7 (step S20).

The checking source discharge signal generation means 22 instructs the time width measurement number setting means to perform the measurement with the multi-channel scaler. Thereafter, it performs the same process by the same means as steps S 5 of Example 1 to the step S 13.

When the scram signal generation means 17 determines that the effective neutron multiplication factor exceeds the set value, the scram signal generation means 17 performs the same process as step S16 in the first embodiment.

On the other hand, scram signal generating means 17, when the effective neutron multiplication factor is determined to be equal to or less than the set value, notifies the switch E Tsu King source outlet signal generator 22. In this case, steps S 1 and likewise new counting rate of Example 1 is measured and transmitted to the computer 7 (Step-up Sl).

In scram signal generating means 17 switch notifies the received from E Tsu King source outlet signal generating means 22, setting the count rate measured by the step S 1 to the new, determined from count rates measured immediately after inserting the checking source value, for example, Ji E Tsu compared to 0.8 times the value of the measured value immediately after inserting the King source, the smaller the count rate measured in the new than this value, it is determined that the counting rate is reduced (step S 21) .

Checking the source discharge signal generator 22 for counting rate is judged to have decreased, sends the determination result to the checking source activation device 20, Ji E Tsu King source activation device 20 discharges the checking source 19 from mixer-settler 23 (step S 22).
Then, the process returns to the first step S1 shown in FIG. 6 and the critical safety monitoring is continued.

  On the other hand, if it is determined that the counting rate has not decreased, the checking source discharge signal generation means 22 instructs the time width measurement number setting means 10 to perform measurement with the multi-channel scaler, and the process proceeds to step S5 in FIG. Return and criticality safety monitoring continues.

According to this embodiment, spontaneous neutron increases, despite the neutron count rate is increasing, the statistical accuracy of the measurement value (the number of the rectangular pulses during the measurement time between tau) is not sufficient, Even if the prompt neutron decay constant α cannot be obtained accurately, a neutron count rate is increased by inserting an inexpensive and easy-to-handle checking source into the mixer setra, and the measured value (measurement time τ The critical accuracy can be monitored by improving the statistical accuracy of the number of rectangular pulses between) and the accuracy of the prompt neutral hand attenuation constant α, and as a result, the monitoring accuracy is improved.

  The criticality safety monitoring device of the present invention can be applied as long as it can perform criticality safety monitoring using spontaneous neutrons.For example, in the reprocessing step, not only mixer-settler but also various measuring tanks, The present invention can also be applied to an adjustment tank, an evaporator, a storage tank, a concentrate storage tank, a product storage tank (for example, a plutonium powder or solution storage tank), and the like.

1 is a block diagram for explaining a criticality safety monitoring apparatus according to Embodiment 1. FIG. FIG. 3 is a flowchart for explaining the criticality safety monitoring apparatus according to the first embodiment. FIG. 6 is a schematic diagram illustrating an example of rack loading according to a second embodiment. FIG. 6 is a schematic diagram illustrating an example of a mixer setra according to a third embodiment. The block diagram explaining the criticality safety monitoring apparatus of the implementation fall 3. FIG. FIG. 6 is a flowchart for explaining a criticality safety monitoring apparatus according to a third embodiment. The flowchart of the criticality safety monitoring apparatus which added the checking source of Example 3. FIG.

  DESCRIPTION OF SYMBOLS 1 ... Measurement area | region, 2 ... Neutron detector, 3 ... Amplifier, 4 ... Measuring circuit, 5 ... Rate meter, 6 ... Count rate display means, 7 ... Computer, 8 ... Alarm signal generation means, 9 ... Alarm signal, 10 ... Time width measurement number setting means 11 ... Multi-channel scaler (MCS) 12 ... Statistical calculation means 13 ... Decay constant calculation means 14 ... Total delayed neutron ratio calculation means 15 ... Neutron effective multiplication factor calculation means 16 ... Neutron effective multiplication factor display means, 17... Scrum signal generation means, 18... Scrum signal, 19... Checking source (calibration source), 20. Checking source discharge signal generating means, 23 ... mixer setra, 24 ... fuel solution part, 25 ... neutron absorber (cadmium), 25 ... neutron detection part, 27 ... Use spent fuel storage rack, 28 ... spent fuel assemblies, 29 ... neutron moderator.

Claims (6)

A step of measuring the number of neutron pulses per measurement time several times by a neutron detector every measurement time τ;
Average value n of the number of neutron pulses measured a plurality of times _ave And calculating dispersion σ for each measurement time τ,
The average value n _ave And a step of obtaining a coefficient Y defined by the following equation (1) using the variance σ for each measurement time τ:
Y _τ = Σ ² / N _ave -1 (1)
Prompt neutron decay constant α and constant Y so that the distribution of coefficient Y obtained in the above step according to measurement time τ is fitted with Y (τ) defined by the following equation (2). _sat A step of seeking
Y (τ) = Y _sat {1- (1-e ^-Ατ ) / Ατ} (2)
  The value Y of the coefficient Y defined by the following equation (3) _τ And the difference E from Y (τ) obtained by equation (2) _τ A step of seeking
E _τ = Y _τ -Y (τ) (3)
E _τ Variance value or E _τ Determining the difference between the maximum and minimum values of,
E _τ Variance value or E _τ If the difference between the maximum value and the minimum value is equal to or greater than a predetermined value, inserting a calibration source into the measurement region of the neutron detector;
From the step of measuring the number of neutron pulses a plurality of times with the calibration radiation source inserted, the prompt neutron decay constant α and constant Y _sat Repeating the steps up to determining the prompt neutron decay constant α,
A criticality safety monitoring method characterized by comprising: The total delayed neutron fraction β and prompt neutron lifetime L determined using a general-purpose nuclear calculation code system, _τ Depending on whether the difference between the maximum value and the minimum value is greater than or equal to a predetermined value, the prompt neutron attenuation constant α measured without the calibration source or with the calibration source inserted The step of obtaining the subcriticality ρ by the following equation (4) using any one of the following:
ρ = β−αL (4)
Obtaining a neutron effective multiplication factor k by the following equation (5);
k = 1 / (L-ρ) (5)
Generating a scram signal when the neutron effective multiplication factor k is greater than a preset value;
  The criticality safety monitoring method according to claim 1, further comprising: When the number of neutron pulses per measurement time measured with the calibration source inserted is smaller than the number of neutron pulses per measurement time measured last time, the calibration source is connected to the neutron detector. Discharging from the measurement area;
The criticality safety monitoring method according to claim 1 or 2, further comprising: A neutron detector that detects neutrons and generates electrical pulses;
A measurement circuit for converting the electric pulse into a rectangular pulse;
A multi-channel scaler for measuring a pulse measurement value that is the number of the rectangular pulses;
Time width measurement number setting means for setting the measurement time τ and measurement number of the pulse measurement value in the multi-channel scaler,
The average value n of the number of neutron pulses from the pulse measurement values of the multichannel scaler _ave And variance σ are determined for each measurement time τ, and the average value n _ave And statistical calculation means for obtaining the coefficient Y defined by the following equation (1) using the variance σ for each measurement time τ:
Y = σ ² / N _ave -1 (1)
Prompt neutron decay constant α and constant Y so that the distribution of coefficient Y obtained in the above step according to measurement time τ is fitted with Y (τ) defined by the following equation (2). _sat A damping constant calculating means for obtaining
Y (τ) = Y _sat {1- (1-e ^-Ατ ) / Ατ} (2)
The value Y of the coefficient Y defined by the following equation (3) _τ And the difference E from Y (τ) obtained by equation (2) _τ E _τ Variance value or E _τ The difference between the maximum value and the minimum value of _τ Variance value or E _τ If the difference between the maximum value and the minimum value is equal to or greater than a predetermined value, a checking source insertion signal generating means for generating a signal instructing insertion of a calibration source into the measurement region of the neutron detector,
E _τ = Y _τ -Y (τ) (3)
In response to a signal from the checking source insertion signal generating means, checking source activation means for inserting the calibration source into the measurement region of the neutron detector;
Have
The statistical calculation means calculates an average value n of the number of neutron pulses from the pulse measurement value of the multichannel scaler with the calibration source inserted. _ave And variance σ are determined for each measurement time τ, and the average value n _ave And a coefficient Y defined by the equation (1) using the variance σ and for each measurement time τ,
The attenuation constant calculating means has an average value n for each measurement time τ obtained by the statistical calculation means with the calibration source inserted. _ave And neutron decay constant α and constant Y so that the distribution of σ and dispersion σ is fitted by the above equation (2) _sat A criticality safety monitoring device characterized by: A total delayed neutron ratio calculating means for obtaining a total delayed neutron ratio β and prompt neutron lifetime L using a general-purpose nuclear calculation code system;
Depending on whether or not the difference between the total delayed neutron ratio β and the prompt neutron lifetime L obtained using the total delayed neutron ratio calculating means and the maximum value and the minimum value of E _τ are not less than a predetermined value. Then, using either the prompt neutron decay constant α measured with the calibration source not inserted or with the calibration source inserted, the subcriticality ρ is obtained by the following equation (4), 5) a neutron effective multiplication factor calculating means for obtaining an effective neutron multiplication factor k according to equation (5),
ρ = β−αL (4)
k = 1 / (L−ρ) (5)
Scram signal generating means for generating a scram signal when the neutron effective multiplication factor k is larger than a preset value;
The criticality safety monitoring device according to claim 4, further comprising: When the number of neutron pulses per measurement time measured with the calibration source inserted is smaller than the number of neutron pulses per measurement time measured last time, the calibration source is connected to the neutron detector. A checking source discharge signal generating means for generating a signal to be discharged from the measurement area;
The said checking source starting means discharges | emits the said calibration source from the measurement area | region of the said neutron detector according to the signal from the said checking source discharge | emission signal generation means, The Claim 4 or Claim 5 characterized by the above-mentioned. The criticality safety monitoring device described in 1.

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