Radiation monitor

The radiation monitor includes: a shutter; a calculation section; an AC solenoid; a temperature switch which is attached to the AC solenoid; a circuit protector which has a contact and is connected in series to the AC solenoid; and a mode selection switch connected in series to the AC solenoid. The shutter is maintained in a closed state when the mode selection switch is set to a normal mode; the mode selection switch is changed from the normal mode to a check radiation source mode, thereby flowing an AC current through the AC solenoid to change the shutter from the closed state to an opened state; and the contact of the temperature switch is reversed from the opened state to the closed state, thereby disconnecting the contact of the circuit protector to interrupt the AC current that flows through the AC solenoid.

TECHNICAL FIELD

The present invention relates to radiation monitors and, more particularly, relates to a radiation monitor provided with a normal mode and a check radiation source mode.

BACKGROUND ART

A radiation monitor which includes a detection unit and a measurement unit and can select between a normal mode and a check radiation source mode is installed in nuclear reactor facilities, spent fuel reprocessing facilities, and the like (for example, see Patent Documents 1 and 2). The detection unit of the radiation monitor is equipped with: a radiation detector which detects radiation and outputs a detection signal; and a check radiation source irradiation section which irradiates radiation for inspection to the radiation detector by remote operation. The check radiation source irradiation section includes an AC solenoid.

A signal processing section, a calculation section, a mode selection switch, and a circuit protector are installed in the measurement unit of the radiation monitor. The signal processing section measures the radiation by being inputted with the detection signal outputted from the radiation detector. The calculation section converts a measurement value thereof into an engineering value as a radiation dose per unit time and provides an output. A display section displays the engineering value.

The mode selection switch performs selective operation between the normal mode in which normal measurement is performed and the check radiation source mode in which measurement is performed in a state where the radiation for inspection is irradiated to the radiation detector. If the AC solenoid of the check radiation source irradiation section exceeds a set current value, the circuit protector trips a contact thereof to interrupt the current of the AC solenoid by time delay characteristics depending on the size of the current value and mechanically self-maintains its contact state.

“Japan Electric Association Guide (JEAG) 4606-2003, Guideline for radiation monitoring of nuclear power plants” is defined as Japanese domestic guidelines relating to the radiation monitor. When the check radiation source mode is selected, the check radiation source is irradiated to the radiation detector to confirm soundness of the radiation monitor based on the guideline. When there occurs abnormality in the AC solenoid of the check radiation source irradiation section and accordingly an overcurrent flows, the current is interrupted by the circuit protector to protect the radiation detector.

PRIOR ART DOCUMENT

Patent Document

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

During a normal inspection of the radiation monitor, an operation that confirms soundness, more particularly, soundness of the radiation detector is performed. Even in a state where there occurs a fault in the nuclear reactor facilities and the environmental temperature of the detection unit becomes a high temperature, as in the inspection during the normal time, the soundness of the radiation monitor, more particularly, the soundness of the radiation detector needs to be confirmed.

When the check radiation source mode is selected during a fault, an environmental temperature rise due to the fault is added to a normal temperature rise of the check radiation source irradiation section; and thus, it is assumed that the AC solenoid exceeds a rated temperature and is to be burned out. If the influence of the burnout is large, there continues a state where the radiation of the check radiation source is incompletely irradiated to the radiation detector; and accordingly, the normal mode cannot be restored in the worst case.

The present invention has been made to solve the above described problem, and an object of the present invention is to provide a highly reliable radiation monitor which surely prevents burnout of a check radiation source irradiation section even under circumstances during a fault.

Means for Solving the Problems

According to the present invention, there is provided a radiation monitor including: a shutter installed between a check radiation source and a radiation detector; a calculation section which calculates a radiation dose from a detection signal outputted by the radiation detector; an AC solenoid to be operated by an AC power source; a temperature switch which is attached to the AC solenoid and whose contact is reversed from an opened state to a closed state when temperature thereof is equal to or more than a set value; a circuit protector which has a contact and is connected in series to the AC solenoid; and a mode selection switch connected in series to the AC solenoid. In the radiation monitor, the shutter is maintained in a closed state when the mode selection switch is set to a normal mode; the mode selection switch is changed from the normal mode to a check radiation source mode, thereby flowing an AC current through the AC solenoid to change the shutter from the closed state to an opened state; and the contact of the temperature switch is reversed from the opened state to the closed state, thereby disconnecting the contact of the circuit protector to interrupt the AC current that flows through the AC solenoid.

Advantageous Effect of the Invention

According to the radiation monitor according to the present invention, there can be provided a highly reliable radiation monitor which surely prevents a check radiation source irradiation section from burning out even under circumstances during a fault.

MODE FOR CARRYING OUT THE INVENTION

Radiation monitors according to embodiments of the present invention will be described below with reference to drawings. Incidentally, the same reference numerals/characters are given to those identical or equivalent to constitutional portions in the respective drawings and the size and/or the scale size of the corresponding respective constitutional portions are respectively independent. For example, in the case of illustrating the same unchanged constitutional portions between sectional views in which a part of the configuration is changed, the size and/or the scale size of the same constitutional portions may be different. Furthermore, actually, there includes a further plurality of members in the configuration of the radiation monitor; however, for simplicity of explanation, only portions necessary for explanation are described and other portions are omitted.

Hereinafter, Embodiment 1 of the present invention will be described with reference to drawings. InFIG. 1, a radiation monitor100includes a detection unit1and a measurement unit2. The detection unit1includes a radiation detector11, a check radiation source irradiation section12, and a detection unit cover13. The radiation detector11detects radiation and outputs a detection signal. The check radiation source irradiation section12irradiates radiation for check to the radiation detector11during an inspection. The detection unit cover13electrically shields and protects the radiation detector11and the check radiation source irradiation section12from circumstances.

In the case of measuring environmental radiation, there can be applied a Si-PIN semiconductor detector as the radiation detector11, the Si-PIN semiconductor detector having a three-layer structure composed of a depletion layer (or I layer), a P layer (anode) disposed on the incident plane side, and an N layer (cathode) disposed on the opposite side of the P layer (anode), the depletion layer being sandwiched between the P layer and the N layer. In order to detect the radiation, a reverse voltage is applied between the P layer and the I layer (depletion layer). The material and thickness of the detection unit cover13are selected in consideration of transmittance so that the energy characteristics of radiation measurement becomes flat in combination with the Si-PIN semiconductor detector.

The measurement unit2is provided with a signal processing section21, a calculation section22, a display section23, a mode selection switch24, an AC power source25, and a circuit protector26. The signal processing section21measures the radiation by being inputted with the detection signal outputted from the radiation detector11. The calculation section22converts a measurement value thereof into an engineering value (counting rate, dose rate, or the like) as a radiation dose per unit time and provides an output. The display section23displays the radiation dose (engineering value) calculated by the calculation section22.

The mode selection switch24switches between a normal mode in which normal measurement is performed and a check radiation source mode in which radiation for check is irradiated to the radiation detector11. In the drawing, the mode selection switch24is set to the normal mode; and the shutter124is maintained in a closed state. The AC power source25supplies an alternating current (AC) voltage to the check radiation source irradiation section12of the detection unit1when the check radiation source mode is selected. The circuit protector detects an overcurrent of the check radiation source irradiation section12and interrupts an AC current that flows through the AC solenoid125.

The detection unit1is connected to the measurement unit2by a composite cable3in order to perform remote operation from the measurement unit2. The composite cable3has a detection signal cable31and a control cable32. The detection signal outputted from the radiation detector11is transmitted to the measurement unit2through the detection signal cable31. The AC voltage is applied from the AC power source25to the check radiation source irradiation section12via the circuit protector26of the measurement unit2through the control cable32.

The check radiation source irradiation section12is provided with a check radiation source121, a holder122, a brace123, a shutter124, an AC solenoid125, a spring126, a temperature switch127, and a resistor128. The check radiation source121releases the radiation for check. The check radiation source121is attached to the holder122. The brace123fixes the holder122. The shutter124is disposed between the radiation detector11and the check radiation source121(and the holder122) and, for example, moves up and down.

The AC solenoid125is operated by the AC power source and is remotely operated by the operation of the mode selection switch24of the measurement unit2to open or close the shutter124. The spring126restores the opened shutter124to be closed. The temperature switch127is closely fixed to the AC solenoid125; and a contact of the temperature switch127is reversed from an opened state to a closed state by the principle of bimetal when the temperature switch127reaches a temperature equal to or more than a set value. The resistor128is connected in series to the temperature switch127.

In the check radiation source mode, the shutter124is kept in an opened state to irradiate the radiation for check of the check radiation source121to the radiation detector11. In the normal mode, the shutter124is kept in a closed state to shield the check radiation source121against the radiation detector11. The shutter124absorbs beta-rays (β-rays), thereby blocking the irradiation of the radiation for check to the radiation detector11. There can be applied strontium-90 (Sr-90) whose half-life period is long _28.8 years as a nuclide of the check radiation source121, and which is a β-ray source that is easy to be shielded. The Sr-90 is easy to be obtained and energy of β-rays of yttrium-90 (Y-90) that is radiative equilibrium is large—2.28 MeV.

The shutter124is several mm in thickness and substantially absorbs braking X-rays to be radiated with the absorption of β-rays. When the shutter124is opened and the β-rays are directly made incident on a ceramic substrate on the back side of a Si semiconductor detector, the β-rays are absorbed by the ceramic substrate. The braking X-rays associated with the absorption thereof acts on the depletion layer of the Si semiconductor detector to serve as the check radiation source mode. As for the circuit protector26, subdivided rating protectors are commercially available and therefore a desired protector can be obtained in accordance with a rated current of the AC solenoid125.

The AC solenoid125is composed of a plunger1251and a coil1252. When the AC voltage is supplied from the AC power source25to the AC solenoid125, the built-in coil1252is excited. When the plunger1251of the AC solenoid125is suctioned against the spring126, the shutter124is reversed from the closed state to the opened state. When it becomes a state where the plunger1251is not suctioned to a predetermined position due to stuck dust or the like during operation and is caught halfway, an overcurrent flows through the AC solenoid125and the AC solenoid125abnormally generates heat. When the temperature switch127closely fitted to the AC solenoid125reaches a set temperature or more, the contact of the temperature switch127is reversed from the opened state to the closed state.

The contact of the temperature switch127is connected in series to the resistor128; and the series connection is connected in parallel to the coil1252of the AC solenoid125. The contact of the temperature switch127is reversed from the opened state to the closed state; and thus, an overcurrent flows through an internal coil261of the circuit protector26of the measurement unit2. Therefore, an internal contact262connected in series to the internal coil261is tripped and is self-maintained in its state to interrupt the AC current to be flown to the AC solenoid125.

The circuit protector26has characteristics in which tripping operation of the contact becomes faster with an increase in transient current equal to or more than the rated current; and there is selected a circuit protector having a rated current, which is not operated by the transient current during the operation of the AC solenoid125. Generally, the circuit protector26is selected in conformity with the rated current of the AC solenoid125so as not to exceed the rated current.

The temperature switch127is set to the rated temperature of the AC solenoid125in operation temperature. When the normal upper limit environmental temperature of the detection unit1is represented by T1, the upper limit environmental temperature during a fault by T2, the rated temperature of the AC solenoid125by T3, and a normal temperature rise value of the AC solenoid125by ΔT, a solenoid assumed to be T3>T1+ΔT is selected as the AC solenoid125.

It is premised that an environmental temperature T of the detection unit1during a fault cannot be actually grasped and temperature measurement is not performed. Even when the check radiation source mode is selected during the fault by protecting the AC solenoid125by this manner, inspection can be performed if T3>T+ΔT is established. Furthermore, if T3≦T+ΔT is established with respect to the environmental temperature T, the circuit protector26is automatically opened to protect the AC solenoid125.

The AC solenoid125is protected by constituting in the manner described above; and therefore, even in a state where the environmental temperature of the detection unit1during the fault cannot be grasped, the temperature switch127automatically determines the propriety of the selection of the check radiation source mode. When the determination of the check radiation source mode is possible, soundness of the radiation monitor can be confirmed even during the fault. When the determination of the check radiation source mode is impossible, the circuit protector26is made to operate to protect and automatically restore the AC solenoid125to be in a measurement state.

In temperature circumstances during the fault, it is assumed that the AC solenoid125is burnt out by the operation of the check radiation source mode. As a result of burnout, if the check radiation source stops halfway of movement and does not move, a state where the shutter124cannot be restored to the measurement state is likely to be occurred. Such a state can be avoided by the configuration of Embodiment 1; and therefore, there can be provided a highly reliable radiation monitor through during the normal time and during the fault.

The radiation monitor according to this embodiment includes the detection unit and the measurement unit. The detection unit has: the radiation detector which detects the radiation and outputs the detection signal; and check radiation source irradiation means which irradiates the radiation for inspection to the radiation detector by remote operation.

The measurement unit has: the signal processing section which measures the radiation by being inputted with the detector signal; the calculation section which converts the measurement value thereof into the engineering value as the radiation dose per unit time and provides the output; the display section which displays the engineering value; mode selection means which performs selective operation between the normal mode in which normal measurement is performed and the check radiation source mode in which measurement is performed in the state where the radiation for inspection is irradiated to the radiation detector; and overcurrent protection means which performs overcurrent protection of the check radiation source irradiation section.

The check radiation source irradiation means has: the check radiation source which radiates the radiation for inspection; shield means which shields the radiation for inspection during the normal mode; the AC solenoid which moves the shield means or the check radiation source so that the radiation for inspection is irradiated to the radiation detector during the check radiation source mode; the temperature switch which is closely attached to the AC solenoid and whose contact is reversed when the temperature switch reaches the set temperature or more; and the resistor connected in series to the contact of the temperature switch.

The overcurrent protection means interrupts a current by the contact having characteristics in which tripping operation becomes faster with an increase in transient current and mechanically self-maintains its state. The contact of the temperature switch is connected in series to the resistor and the series connection is connected in parallel to the AC solenoid; and when the temperature switch reaches the set temperature or more, the contact of the overcurrent protection means is tripped by intentionally flowing a current suppressed by the resistor.

Incidentally, the detection unit1according to Embodiment 1 is, for example, the configuration corresponding to the case whose measurement object is the environmental radiation. The check radiation source irradiation section12fixes the holder122attached with the check radiation source121to the brace123and shields the check radiation source121by the shutter124disposed between the radiation detector11and the holder122. Opening or closing of the shutter124is performed by remote operation from the measurement unit2.

The configuration of a radiation monitor according to Embodiment 2 is shown inFIG. 2. In this embodiment, a detection unit1has a configuration corresponding to a case whose measurement object is, for example, a sampled sampling gas. The detection unit1includes: a sample vessel14; a radiation detector11; and a shield body15. The sample vessel14defines the volume of the sampling gas to be measured. The radiation detector11detects radiation released from gaseous radioactive materials contained in the sampling gas of the volume defined by the sample vessel14. The shield body15envelopes the radiation detector11and the sample vessel14to shield from environmental radiation.

The check radiation source irradiation section12is composed of a check radiation source121, a holder122, an AC solenoid125, and the like. The check radiation source121is attached to the holder122. The holder122is fixed to a leading end of a brace bar129. The brace bar129is coupled to a plunger of the AC solenoid125. The check radiation source121moves or reciprocates between a facing position and a shield position by the operation of the AC solenoid125. InFIG. 2, the check radiation source121is set at the facing position and the check radiation source121faces the radiation detector11(a normal mode state).

An operation state of the AC solenoid125is set by a mode selection switch24of the measurement unit2. In a check radiation source mode state, the brace bar129is made to move so that the check radiation source121faces the radiation detector11with the sample vessel14being sandwiched therebetween to irradiate the radiation for check to the radiation detector11. In the normal mode state, the brace bar129is made to move so that the check radiation source121is hidden behind the shield body15by a return of the spring126. InFIG. 3, the check radiation source121is set to the shield position.

The radiation monitor according to Embodiment 2 performs similar operation by the configuration similar to that of Embodiment 1. As a result, in the radiation monitor according to this embodiment, the AC solenoid125can be surely protected during the fault as in Embodiment 1; and therefore, reliability of the radiation monitor is improved.

Incidentally, in Embodiment 1 and Embodiment 2, the check radiation source irradiation section12has the resistor128connected in series to the temperature switch127. The resistor128is connected in parallel to the coil of the AC solenoid and the contact of the temperature switch127is reversed from opening to closing; and accordingly, an overcurrent flows through the internal coil of the circuit protector26of the measurement unit2. The internal contact connected in series to the internal coil is moved from closing to opening and is mechanically maintained in its state to interrupt the current.

The configuration of a radiation monitor according to Embodiment 3 is shown inFIG. 4. In this Embodiment, a check radiation source irradiation section12of a detection unit1has a relay120that operates as a load of a temperature switch127. The relay120has a first contact1201and a second contact1202. The first contact1201of the relay120is connected in parallel to the contact of the temperature switch127and the relay120is excited if the contact of the temperature switch127is reversed from opening to closing. The second contact1202of the relay120is connected in series to the AC solenoid125.

The relay120operates such that the first contact1201is made to reverse from opening to closing to self-maintain an excitation state and the second contact1202is made to reverse from closing to opening to interrupt a current of an AC solenoid125. Self-maintaining of the relay120of the check radiation source irradiation section12is released by only returning a mode selection switch24from a check radiation source mode to a normal mode.

By being configured as described above, the AC solenoid125is surely protected through during a normal time and during a fault; and therefore, as in Embodiment 1 and Embodiment 2, reliability of the radiation monitor can be improved by surely protecting the AC solenoid125during the fault. Furthermore, as described in Embodiment 1 and Embodiment 2, a circuit protector26is made to forcibly trip during the operation of the temperature switch127; and therefore, although instantaneous, a simulated short-circuit current suppressed by the resistor128does not need to be flown to a control cable32that constitutes a composite cable3and thus a higher reliable radiation monitor can be provided.

The radiation monitor according to this embodiment includes the detection unit and the measurement unit. The detection unit has: a radiation detector which detects radiation and outputs a detection signal; and check radiation source irradiation means which irradiates radiation for inspection to the radiation detector by remote operation.

The measurement unit has: a signal processing section which measures the radiation by being inputted with the detector signal; a calculation section which converts a measurement value thereof into an engineering value as a radiation dose per unit time and provides an output; a display section which displays the engineering value; mode selection means which performs selective operation between the normal mode in which normal measurement is performed and the check radiation source mode in which measurement is performed in a state where the radiation for inspection is irradiated to the radiation detector; and overcurrent protection means which performs overcurrent protection of the check radiation source irradiation section.

The check radiation source irradiation means has: a check radiation source which radiates the radiation for inspection; shield means which shields the radiation for inspection during the normal mode; the AC solenoid which moves the shield means or the check radiation source so that the radiation for inspection is irradiated to the radiation detector during the check radiation source mode; the temperature switch which is closely attached to the AC solenoid and whose contact is reversed when the temperature switch reaches the set temperature or more; and the relay to be operated by the reversal of the contact of the temperature switch.

The overcurrent protection means interrupts a current by a contact having characteristics in which tripping operation becomes faster with an increase in overcurrent and mechanically self-maintains its state. The contact of the temperature switch is connected in series to the relay; and the contact of the temperature switch is reversed when the temperature switch reaches the set temperature or more. It is characterized in that, according to this, the relay operates and is self-maintained by its contact and the current of the AC solenoid is interrupted by another contact.

The configuration of a radiation monitor according to Embodiment 4 is shown inFIG. 5. This embodiment is based on an idea in which overcurrent protection including rated temperature control of an AC solenoid and short circuit protection of a check radiation source irradiation section line are separately treated. In a measurement unit2, the circuit protector26of Embodiment 3 is replaced with a fuse27to save a space; and therefore, the measurement unit can be reduced in size. More specifically, it is characterized in that the radiation monitor according to this embodiment is provided with the fuse as overcurrent protection means.

The configuration of a radiation monitor according to Embodiment 5 is shown inFIG. 6. In this embodiment, a mode selection switch24of a measurement unit2is a two-step structure. A calculation section22fetches selection mode information for each calculation period and arranges latest engineering value data of a set calculation periodic number in temporal sequence to update the engineering value data for each calculation period. In a normal mode, Qs pieces of set normal mode engineering value data rows are updated and stored. Furthermore, in a check radiation source mode, Ws pieces of set check radiation source engineering value data rows are updated and stored.

In the measurement unit2, when the mode selection switch24is switched from the normal mode to the check radiation source mode, the calculation section22calculates a net value of a check radiation source based on a latest normal mode engineering value and a subsequent latest check radiation source engineering value, determines whether or not the net value is kept within an acceptable value, and provides an output, the values being set by operational flows shown inFIG. 7andFIG. 8.FIG. 7shows ST00to ST09of the operational flows.FIG. 8shows ST10to ST17of the operational flows.

In the calculation section22, a measurement value is read from the signal processing section21in Step S01; and in Step S02, the measurement value is converted into an engineering value to be outputted. In Step S03, a determination is made whether or not the present calculation period is in the check radiation source mode; and if the determination is YES, a determination is made whether or not the previous calculation period is in the normal mode in Step S04. If the selection mode is reversed from the normal mode to the check radiation source mode and the determination in Step S04is YES, a determination is made whether or not the number of data of the normal mode engineering value data row is equal to Ps, the set number of data, in Step S05.

If the determination in Step S05is YES, an average value M(N) as for Ps-pieces of data of the normal mode engineering value data row is calculated and stored, the data row concerned is reset, and creation of the check radiation source mode engineering value data row is started at the next calculation period in Step S06; and then the processing is returned to Step S01. If the determination in Step S05is NO, a message of “DIAGNOSIS IMPOSSIBLE, TIME DEFICIT FOR NORMAL MODE MEASUREMENT” is outputted, the normal mode engineering value data row is reset, and creation of the check radiation source mode engineering value data row is started at the next calculation period in Step S07; and then the processing is returned to Step S01. The message is stored until being reset by switching modes and is outputted for each calculation period.

If the determination in Step S04is NO, a determination is made whether or not the number of data of the check radiation source mode engineering value data row is equal to Us, the set number of data, in Step S08; and if the determination is YES, an average value M(C) averaged as for Us-pieces of data of the check radiation source mode engineering value data row is calculated and a net value deviation is calculated by the following equation in Step S09.
Net value deviation=[M(C)−M(N)/standard check radiation source net engineering value]−1

Further, in the calculation section22, a determination is made whether or not the net value deviation is kept within an acceptable range in Step S10. If the determination is YES, a message of “INSPECTION BY CHECK RADIATION SOURCE: NORMAL” is outputted in Step S11; and in Step S16, the check radiation source mode data row is updated and then the processing is returned to Step S01. If the determination in Step S10is NO, a message of “INSPECTION BY CHECK RADIATION SOURCE: ABNORMAL” is outputted in Step S12; and then the processing is proceeded to Step S16. If the determination in Step S08is NO, a message of “DIAGNOSIS IMPOSSIBLE, TIME DEFICIT FOR NORMAL MODE MEASUREMENT” is outputted in Step S13; and then the processing is proceeded to Step S16.

If the determination in Step S03is NO, a determination is made whether or not the previous calculation period is in the check radiation source mode in Step S14. If the selection mode is reversed from the check radiation source mode to the normal mode and the determination in Step S14is YES, the check radiation source mode engineering value data row is reset, a reset is performed if there stores a message of “DIAGNOSIS IMPOSSIBLE, TIME DEFICIT FOR NORMAL MODE MEASUREMENT” and creation of the normal mode engineering value data row is started in Step S15; and then the processing is returned to Step S01.

If the determination in Step S14is NO, the normal mode data row is updated in Step S17; and then the processing is returned to Step S01. The measurement unit2automatically evaluates the results inspected by the check radiation source in such a procedure; and therefore, effective and highly reliable inspection can be performed.

The radiation monitor according to this embodiment is characterized in that if the selection mode is switched from the normal mode to the check radiation source mode, the calculation section calculates the net measurement value of the check radiation source based on the set latest normal mode measurement value and the subsequent latest check radiation source measurement value, determines whether or not the net measurement value is kept within the acceptable value, and provides the output.

Incidentally, the present invention can freely combine the respective embodiments and appropriately change and/or omit the respective embodiments, within the scope of the present invention.

DESCRIPTION OF REFERENCE NUMERALS