JP5542767B2 - Radiation monitor - Google Patents

Description

  The present invention relates to a radiation monitor used for emission management or radiation management of a nuclear reactor facility, a spent fuel reprocessing facility, or the like.

Radiation monitors used in nuclear reactor facilities, spent fuel reprocessing facilities, etc. cover a wide range of signal pulse repetition frequencies from about 10 cpm (count per minute) to about 10 ⁷ cpm as a result of detecting radiation. However, it is required to ensure and measure the required accuracy without switching the range. Further, when the repetition frequency of the output pulse of the radiation detector changes from the background level to a high count rate region including a high alarm point, a response with a fast count rate is required. For this reason, a count rate calculation method in which the time constant changes in inverse proportion to the count rate and the standard deviation is controlled to be constant has been widely introduced.

  Based on this method, the conventional radiation monitor divides the measurement range into two, the low count rate region and the high count rate region, and the low count rate region sets the standard deviation to be small and performs measurement with priority on measurement accuracy. In the high count rate area, the standard deviation is set to a large value and priority is given to responsiveness. The count rate calculation process is performed independently for both standard deviations, and the count rate output at the boundary point is automatically set. Switching is made (see Patent Document 1). Patent Document 2 discloses a radiation monitor having a characteristic of constant integration time at a low count rate and a characteristic of constant integration count value at a high count rate.

JP-A-61-128184 JP-A-11-326523

Since the conventional radiation monitor is configured as described above, there is a problem that a level difference caused by a different database occurs at a counting rate with a different standard deviation. Therefore, since there is a sudden change in a part of the trend that should change continuously when monitoring, there is a risk of erroneous determination such as equipment failure.
The present invention has been made to solve the above-described problems, and can prevent a discontinuous change in the standard deviation or the indication at the time of switching the measurement time, and can provide a highly reliable radiation monitor that achieves both response and visibility. The purpose is to obtain.

In addition, the radiation monitor according to the present invention is a radiation detector that detects radiation and outputs an analog signal pulse, and outputs a digital pulse when the analog signal pulse is input and the wave height level is within an allowable range, A wave height discriminator that removes noise as a noise when it deviates from the allowable range, a counting unit that receives the digital pulse, counts at a constant cycle and outputs a count value, and stores the count value for a predetermined number of data in a first-in first-out method In addition, the storage means for storing the latest data of the count rate calculation process, the count rate is calculated at regular intervals based on the count value , and the alarm determination is performed on the calculated count rate or the engineering value obtained by converting the count rate comprising calculating means for outputting the count rate or engineering values and alarm determination result, the display means for displaying the count rate or the engineering value and alarm determination result, before Calculating means calculates the count rate in the count rate for each area set in the set count rate region boundary, when switching from the counting rate based on the measured time count rate based on the standard deviation, in that calculation period When switching from the count rate based on the standard deviation to the count rate based on the measurement time, switching is performed when the difference between the count rates is within the allowable range. is there.

  According to the radiation monitor of the present invention, switching can be performed without causing a difference in counting rate at the switching point, and a highly reliable radiation monitor that achieves both response and visibility can be obtained.

It is a block diagram which shows the radiation monitor in Embodiment 1 of this invention. FIG. 3 is a flowchart showing a calculation process in a calculator of the radiation monitor according to the first embodiment. It is a figure which shows the count rate in Embodiment 1, and a response time characteristic. 6 is a diagram showing an instruction response to a step input in the first embodiment. FIG. 6 is a block diagram showing a radiation monitor in the second embodiment. FIG. FIG. 10 is a flowchart showing a calculation process in a calculator of the radiation monitor according to the second embodiment. FIG. 10 is a flowchart showing calculation processing in the calculator of the radiation monitor according to the third embodiment. It is a figure which shows the count rate in Embodiment 3, and a response time characteristic. FIG. 10 is a diagram showing an instruction response to a step input in the third embodiment. It is a figure which shows the example in the frequency | count in the fixed count rate of the standard deviation in Embodiment 3, and a count rate. It is a figure which shows the example in the count in the fixed count rate of measurement time (SIGMA) (DELTA) T in Embodiment 3, and a count rate.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described with reference to the drawings. In FIG. 1, a radiation detector 1 detects radiation and outputs an analog signal pulse. When the analog signal pulse output from the radiation detector 1 is input to the wave height discriminator 2 and the voltage level (that is, the wave height level) is within a set level range (that is, within an allowable range). The input analog signal pulse is regarded as a signal pulse and a digital pulse is output. However, if it deviates from the set allowable range, it is regarded as noise and the digital pulse is not output.

  The digital pulse output from the wave height discriminator 2 is input to the counter 3 (counting means), and the counter 3 (counting means) counts at a constant period and outputs a count value ΔN. The computing unit 4 receives the count value ΔN (current) output from the counter 3 and stores it in the memory 5 (storage means). The arithmetic unit 4 (calculation means) calculates a count rate at a constant cycle based on the count value stored in the memory 5, converts the count rate into an engineering value, performs an alarm judgment on the engineering value, and calculates an engineering value. And the alarm judgment result is output. The display 6 (display means) can display the count rate (engineering value) and the alarm determination result, and can perform setting value input and operation from the screen. The engineering value may be the count rate itself depending on the application, or it may be multiplied by a constant that converts the engineering value into a radiation dose. In the following description, the case of engineering value = count rate will be described.

Next, the calculation for obtaining the count rate m with a constant standard deviation in the calculator 4 will be described. The count rate of the previous calculation cycle is m (previous), the addition / subtraction integrated value of the previous calculation cycle is M (previous), the counter counting time for each calculation cycle is ΔT, and the addition / subtraction integration value of the current calculation cycle is M (current) Assuming that the count rate of the current calculation cycle is m (current), M (current) and m (current) can be obtained by equations (1) and (2), respectively.
M (current) = M (previous) +2 ^α × {ΔN (current) −m (previous) × ΔT} (1)
m (this time) = exp {γM (this time)} (2)

The count rate m obtained by the equation (2) is controlled with the standard deviation σ = constant as shown in the following equation (3).
σ = 1 / (2mτ) ^1/2 = constant (3)
Further, the time constant τ is inversely proportional to the count rate m, inversely proportional to the square of the standard deviation, and inversely proportional to γ as in the following equation (4). γ is proportional to the square of the standard deviation as shown in the following equation (5), and is obtained from the equation (2) by, for example, counting by weighting with 2 ^α using a constant α relating to counting weighting. The count rate m responds by following the change in the repetition frequency of the output pulse of the wave height discriminator 2 with a first-order lag of the time constant τ.
τ = 1 / (2mσ ² ) = 1 / (mγ) (4)
γ = 2σ ² = 2 ^α × 2 ⁻¹¹ × ln2 = constant (5)

(5) In the equation, by the weighting count in 2 ^alpha, when the reference weighted ² 0 = 1 alpha = 0, the counting alpha = 2 weighting ² 2 = 4 in the tau 1/4, alpha = 4 weighting 2 ⁴ = 16, τ is 1/16, α = 6 weighting 2 ⁶ = 64, and τ is 1/64. By increasing the weighting of the count, the response becomes faster.

Next, the calculation processing procedure in the calculator 4 will be described with reference to the flowchart of FIG. In S1, m _B is a known average background count rate, k ₁ is the ratio of the count rate corresponding to the standard deviation switching point (σ ₁ → σ ₂ ) and m _B , and k ₂ is The ratio between the count rate corresponding to the standard deviation switching point (σ ₂ → σ ₁ ) and m _B , and α ₁ and α ₂ are constants related to the weighting of the count. Further, the relationship is k ₁ <k ₂ as shown in S12, and the relationship is α ₁ <α ₂ as shown in S6. k ₁ m _B , k ₂ m _B , α ₁ , and α ₂ are respectively stored in the memory as set values. At S1, ΔN (current), m (previous), M (previous), k ₁ m _B , k ₂ m _B are input, M (current) is obtained by S1 in S2, and (2) in S3 To find m (this time).

In S4, it is determined whether there is a flag of m (current) ≦ k ₁ m _B. If NO, it is determined in S5 whether m (current) ≦ k ₁ m _B , and if YES, m (current) ≦ Raise the k ₁ m _B flag and α ₁
The switch to the α _2. In S7, m (current) ≤ low alarm set point is determined. If YES, a low alarm is output in S8. In S9, m (current) ≥ high alarm set point is determined. If YES, high alarm is determined in S10. , M (current) is output in S11, the current calculation cycle is terminated, and the process returns to S1. If NO in S7, the process proceeds to S9, and if NO in S9, the process proceeds to S11. S4 performed m (time) ≧ _k 2 _{m B} Kano determination is YES if The S12, m (this time) in S13 if YES ≦ _k 1 resets the flag of _{m B,} switching the alpha ₂ to alpha ₁ S7 Proceed to If NO in S12, the process proceeds to S7.

From the lower limit of the fluctuation including the background count rate to the upper limit of the measurement range, the count rate is calculated so that the standard deviation σ ₁ determined by the request from the measurement accuracy is reached. If it falls and deviates from the lower limit of the fluctuation, a low alarm is issued as soon as possible to minimize missing data.

In FIG. 3, if the standard deviation switching point (σ ₁ → σ ₂ ) of c with respect to the low alarm set value L is set to a count rate of, for example, 1/2 × (m _B + L), the current count of σ ₁ When the rate m (current) falls below the switching point counting rate is switched from the standard deviation sigma ₁ to sigma ₁ <sigma ₂ becomes sigma _2, (5) corresponds to ₁ constant α is sigma relating to weighting of the counting of formula The α ₁ corresponding to σ ₂ is switched to α ₂ corresponding to σ _2, and the time constant τ is shortened by the equation (4). As a result, the response from g to h is accelerated as shown in FIG. In this case, in FIG. 3, the lower limit of fluctuation is set to m _B (1−4σ ₁ ) assuming a width four times the standard deviation σ ₁ from the average background count rate m _B of e, and the probability of erroneous switching. In consideration of the above, the switching point of c is set. In the next calculation cycle after switching, when calculating M (current) in equation (1), M (previous) corresponding to m (previous) before switching is taken over, and a constant α relating to the weighting of the switched count. _{In step 2} , m (current) is obtained from equation (2).

When the background count rate m _B returns, a count rate of, for example, 1/4 × (3 m _B + L) between the standard deviation switching point (σ ₁ → σ ₂ ) of c and m _B is set to the standard of d. A hysteresis is provided as a deviation switching point (σ ₂ → σ ₁ ).

As described above, since the standard deviation is switched by taking over the count rate at the switching point, the switching can be performed without causing a difference in the counting rate at the switching point, and a desired output with respect to a change in input can be achieved. A response can be easily obtained, and a highly reliable radiation monitor having both response and visibility can be obtained. Since hysteresis is provided at the standard deviation switching point (σ ₁ → σ ₂ ) and the standard deviation switching point (σ ₂ → σ ₁ ), hunting at the standard deviation switching point can be prevented and stable switching can be performed. it can.

Embodiment 2. FIG.
In the first embodiment, the counter 3 counts the digital pulses output from the pulse height discriminator 2 at a constant cycle and outputs a count value ΔN, and the calculator 4 outputs the count value of the current calculation cycle output from the counter 3. ΔN (current) is input and stored in the memory 5, and the count rate is calculated at a constant cycle based on the count value. In the second embodiment, the up / down counter 7 is replaced with the counter 3 in FIG. The up / down counter 7 includes a control circuit 8 and a pulse generator 9 (frequency synthesizer circuit). The up / down counter 7 receives the digital pulse output from the pulse height discriminator 2 as input to the addition input terminal 71 and outputs the digital pulse output from the pulse generator 9. A pulse is input to the subtraction input terminal 72, and the resultant addition / subtraction integrated value is output. In the second embodiment, this addition / subtraction integrated value is set to M (1) in the first embodiment.
Use as an alternative to this time.

Integration control circuit 8 controls the up-down counter 7 to count the addition input and subtraction input of the up-down counter 7 by weighting with the basis of the standard deviation (5) of 2 ^alpha. The pulse generator 9 receives the accumulated difference value output from the up / down counter 7 and converts it into a repetition frequency that responds with a temporary delay of a time constant with respect to the repetition frequency of the addition input, and the subtraction input of the up / down counter 7 Subtract input to terminal 72. The arithmetic unit 4 receives the addition / subtraction integration value output from the up / down counter 7, stores the addition / subtraction integration value and the latest data of the count rate calculation process in the memory 5, and based on the addition / subtraction integration value (2 ) Calculate the counting rate using the formula. The computing unit 4 performs a standard deviation constant count rate calculation for obtaining a count rate based on the accumulated difference value.

Next, the calculation processing procedure in the calculator 4 will be described with reference to the flowchart of FIG. Note that m _B , k ₁ , k ₂ , α ₁ , and α ₂ are the same as those in FIG. In S21, M (current) (output of up / down counter 7), k ₁ m _B , and k ₂ m _B are input, and in S22, m (
This time) is obtained, and it is determined in S23 whether m (current) ≦ k ₁ m _B flag is present.
24, it is determined whether m (current) ≦ k ₁ m _B. If YES, a flag m (current) ≦ k ₁ m _B is set in S25, and α ₁ is switched to α ₂ . In S26, it is determined whether m (current) ≤ low alarm set point. If YES, a low alarm is output in S27. In S28, m (current) ≥ high alarm set point is determined. If YES, high alarm is determined in S29. , M (current) is output in S30, the current calculation cycle is terminated, and the process returns to S21. If NO in S26, the process proceeds to S28, and if NO in S28, the process proceeds to S30. S23 performs m (time) ≧ _k 2 _{m B} Kano determination is YES if S31 in, m (this time) in S32 if YES resets the flag of ≦ _k 1 _{m B,} switching the alpha ₂ to alpha ₁ S26 Proceed to If NO in S31, the process proceeds to S26.

  As described above, by taking over the count rate at the switching point and changing the weighting control of the count of the up / down counter 7 by the integration control circuit 8 and switching the standard deviation, the switching point is changed as in the first embodiment. Switching can be performed without causing a difference in counting rate, a desired output response to an input change can be easily obtained, and a highly reliable radiation monitor that balances response and visibility can be obtained. Since the addition / subtraction integrated value can be obtained by hardware, the calculation time can be shortened and good linearity can be obtained up to a high count rate.

Embodiment 3 FIG.
In the first embodiment, the arithmetic unit 4 inputs the count value ΔN (current) of the current calculation cycle output from the counter 3 and stores it in the memory 5, and the standard deviation is constant based on ΔN (current) at regular intervals. A standard deviation constant count rate calculation flow for calculating the count rate m (current) is provided, and a desired count rate response is obtained by switching the standard deviation.

Instead, in the third embodiment, the arithmetic unit 4 inputs the count value ΔN (current) output from the counter 3 and stores it in the memory 5 in a first-in first-out manner, and based on ΔN (current) at regular intervals. Standard deviation constant count rate calculation flow that calculates count rate m (current) with constant deviation, and count value is integrated retroactively from the current calculation cycle to the set number of calculation cycles to obtain integrated count value ΣΔN It is equipped with both a constant measurement time calculation flow to obtain a count rate n (current) by dividing by the integration time ΣΔT of the counting time ΔT of each calculation cycle, and the measurement range, for example, the measurement range lower limit and the low alarm, It is divided into a low count rate area including the background level and a high count rate area including the high alarm and the upper limit of the measurement range. The low count rate area is covered by a constant time count rate calculation, and the high count rate area is standard deviation. Constant counting rate Covered by calculation, the current count rate n (current) is obtained by the following equation (6) in the low count rate region, and the current count rate m (current) is obtained by the equation (2) in the high count rate region.

    n (current) = ΣΔN (current) / ΣΔT (6)

When the count rate rises from the background level and exceeds the first switching point, n (current) is taken over and m (current) is output. In preparation for the next calculation cycle, M is calculated according to the following equation (7). (This time) is obtained, and the calculation is switched.
M (this time) = ln {m (this time)} / γ (7)
When the count rate falls from the high count rate region and falls below the second switching point, the output is switched when the count rate after switching is within the allowable range with respect to the count rate before switching in the calculation cycle. Do.

Next, the calculation processing procedure in the calculator 4 will be described with reference to the flowchart of FIG. n _B is the average background count rate that is known, and k ₃ is the time / standard deviation switching point (ΣΔ
The ratio of the count rate corresponding to T → σ) and n _B , and k ₄ is the time / standard deviation switching point (σ → ΣΔT)
Is the ratio of the count rate corresponding to and n _B , σ is the standard deviation, and k ₅ is the coefficient of the standard deviation. Also, _{k 3} and _{k 4} as shown in and S53 are in a relationship of _k 3> _{k 4.} k ₃ n _B , k ₄ n _B , and k ₅ σ are respectively stored in the memory as set values.

In step S41, ΔN and k ₃ n _B arranged in time series are input, and in step S42, n (
This time) is determined. In step S43, it is determined whether n (current) ≧ k ₃ n _B. If NO, it is determined in step S44 whether n (current) ≦ low alarm set point. If YES, a low alarm is determined in S45. In S46, it is determined whether n (current) ≧ high alarm set point. If YES, a high alarm is output in S47 and the process proceeds to S48. If NO in S44, the process proceeds to S46, and if S46 is NO. Advances to S48, outputs n (current) in S48, ends the calculation cycle, and returns to S41.

If YES in S43, n = m is set in S49, M (current) is obtained by equation (7), and the process proceeds to S57. In S57, it is determined whether m (current) ≧ high alarm set point. If NO in S57, the process proceeds to S59. In S59, m (current) is output to end the calculation cycle, and the next calculation cycle starts from S50. At S50, ΔN, m (previous), M (previous), k ₄ n _B , and k ₅ σ are input, M (current) is obtained by equation (1) in S51, and m (current) is calculated by equation (2) in S52. ), M (current) ≦ k ₄ n _B is determined in S53, and if YES, ΔN arranged in time series in S54 is input, and in S55, n (current) is calculated using equation (6). calculated, m (this time) in S56 -k _{5 σ} ≦ n (current) ≦ m (current) makes a determination of + _{k 5} sigma, in the case of YES, the process advances to S44, and if NO, it proceeds to a S57.

FIG. 8 shows the count rate and response time characteristics. In the low count rate region near the upper limit of the measurement range to the normal fluctuation upper limit, the count rate is obtained with ΣΔT = constant of i. the high count rate region including the high alarm set point - measuring range limit counting rate is obtained by j of sigma = constant, two times p to k ₃ n _B of the boundary of the area, standard deviation switching point (ΣΔT → sigma) is set, the count rate becomes more than k ₃ n _B rises, calculation for obtaining the count rate is switched from i of ShigumaderutaT = constant j of sigma = constant. When the increased count rate returns to the background, if k ₄ n _B or less, the time / standard deviation switching point (σ → ΣΔT) of s is set to k ₄ n _B where k ₃ > k ₄ In s, j is switched from σ = constant to ΣΔT = constant, and hysteresis is provided at the switching point between ascending and descending.

  FIG. 9 shows the response of the count rate to the step input. When u and y are ΣΔT = constant, the response is linear, and when v and w are constant, the response is an exponential function.

  In addition, FIG. 10 is a figure which shows the example of the frequency and count rate in the fixed count rate of a standard deviation. FIG. 11 is a diagram illustrating an example of the frequency and the count rate at a constant count rate of the measurement time ΣΔT. From these, FIG. 11 shows a Gaussian distribution, and FIG. 10 shows that the Gaussian distribution is distorted to the high count rate side.

  As described above, the measurement range is divided into two areas, the low count rate area and the high count rate area. For example, the low count rate area is covered by the constant count rate calculation, and the high count rate area is calculated by the standard deviation constant count rate calculation. In the case of ascent, the calculation rate is switched to take over, and in the case of descent, the calculation rate is switched when the count rate of both operations is within the allowable range. Switching can be performed without generating a step, a desired output response to an input change can be easily obtained, and a highly reliable radiation monitor in which both response and visibility can be obtained.

  Moreover, by setting the switching point at the time of lowering to the switching point at the time of rising, hunting can be prevented and stable switching can be performed. In addition, the standard deviation constant count rate has a quick response because the time constant is inversely proportional to the count rate, but the count rate distribution is distorted from the Gaussian distribution to the plus side, so the accuracy is reduced. On the other hand, the constant time count rate has a constant response, but it is characterized by high accuracy due to the Gaussian distribution. By switching, high accuracy measurement can be performed at the background level, and the indication rises. In response to this, it is possible to send a high warning in a short time by giving priority to the response.

DESCRIPTION OF SYMBOLS 1 Radiation detector 2 Wave height discriminator 3 Counter 4 Calculator 5 Memory 6 Display 7 Up / down counter 71 Addition input terminal 72 Subtraction input terminal 8 Integration control circuit 9 Pulse generator

Claims (3)

  A radiation detector that detects radiation and outputs an analog signal pulse, and outputs a digital pulse when the analog signal pulse is input and its crest level is within the allowable range, and is removed as noise when the allowable range is exceeded. A pulse height discriminator for counting, a counting means for inputting the digital pulse and counting in a fixed period and outputting a count value; storing the count value for a predetermined number of data in a first-in first-out method; and the latest data of the count rate calculation process And a storage means for calculating the count rate at regular intervals based on the count value, performing alarm determination on the calculated count rate or the engineering value converted from the count rate, and calculating the count rate or engineering value and the alarm determination result. A calculation means for outputting, and a display means for displaying the count rate or engineering value and the alarm determination result, the calculation means for each set count rate area When calculating the number rate, and switching from the count rate based on the measurement time to the count rate based on the standard deviation at the set count rate region boundary, the count rate before switching in the calculation cycle is taken over and switched, A radiation monitor characterized in that, when switching from a count rate based on a standard deviation to a count rate based on a measurement time, switching is performed when the difference between the count rates is within an allowable range. The calculation means reads data from the storage means, subtracts the product of the previous count rate of the previous calculation cycle and the constant cycle count time from the current count value to obtain the current addition / subtraction, and multiplies the current addition / subtraction by a weighting factor. The current addition / subtraction integration value of the previous calculation cycle is added to obtain the current addition / subtraction integration value, and the standard deviation constant count rate calculation means for calculating the current count rate based on the current addition / subtraction integration value, and the past including the current count value And a measurement time constant count rate calculating means for integrating the count values for the calculation cycle set retroactively and dividing the integrated value by the corresponding integration time to obtain the current count rate. The radiation monitor according to claim 1 . The calculation means sets the switching point when the counting rate is lowered to a lower switching point when the counting rate is higher than the switching point when the counting rate is increased at the switching point for obtaining the counting rate by switching between different standard deviations or standard deviation and measurement time. The radiation monitor according to claim 1 , wherein hysteresis is provided.

Images