JP4947306B2 - Personal dosimeter for criticality - Google Patents

Description

  The present invention relates to a personal dosimeter for criticality suitable for use in a spent fuel reprocessing facility or the like.

  Conventionally, in facilities that handle radiation, such as spent fuel reprocessing facilities, the dose limits stipulated in the Reactor Regulation Act are not exceeded, and workers are exposed to reduce exposure as much as possible. Management is done. External doses are measured by integrating dosimeters that accumulate energy according to the radiation received over a certain period in a dosimeter and periodically measuring the radiation dose, or electronic doses that digitally display the radiation dose in real time. Various personal dosimeters such as a meter are used (for example, see Non-Patent Document 1), and those who enter the management area are required to wear these personal dosimeters (Ionizing Radiation Hazard Prevention Regulation (September 47, Showa 47)). Ministry of Labor Ordinance No. 41), Article 8, Paragraph 3).

In the above facilities, necessary measures are taken to prevent criticality accidents, but in the unlikely event that a criticality accident occurs, an overexposed person can be quickly selected from a large number of evacuees. It is required to carry to a medical institution, to estimate the radiation dose and to identify the direction of incidence of radiation on the human body, and to promptly determine the treatment policy for the survivor. Regarding the incident direction of radiation to the human body, particularly in the case of a neutron beam, the organs that cause damage differ depending on the incident direction, so if the incident direction is known, it is easy to make a judgment at the time of treatment. In addition, since the effective dose received by the person changes depending on the direction in which the radiation enters from the human body, the radiation incident direction of the human body is extremely important information for dose evaluation.
However, the integrating dosimeter can cope with a certain amount of high dose, but it takes time to measure the radiation dose. On the other hand, the electronic dosimeter requires radiation radiation. Although the dose can be confirmed on the spot, the measurement sensitivity of the high dose rate is unknown, and both dosimeters cannot determine the direction of incidence of radiation on the human body. Met.
“Personal dosimeter (09-04-03-03)”, Nuclear Encyclopedia ATOMICA, [online], February 2005, Japan Atomic Energy Foundation, [October 10, 2007 search], Internet <URL: http : //atomica.nucpal.gr.jp/atomica/09040303_1.html>

  The present invention has been made in view of such circumstances, and even in the event of a criticality accident, an individual for criticality who can easily and quickly carry out estimation of exposure dose and identification of the direction of incidence of radiation on the human body. The purpose is to provide dosimeters.

  A critical personal dosimeter according to the present invention is a neck strap type critical personal dosimeter, which is composed of a flat strap-like strap body to be hung on a neck and a plurality of thresholds made of indium flakes contained in the strap body. And a detector.

In the above-mentioned critical personal dosimeter, in the state where the strap body is hung on the neck, the mounting positions of the threshold detectors are arranged such that the plurality of threshold detectors are arranged at substantially equal intervals around the neck. Can be set respectively.
Further, in the above personal dosimeter for criticality, a length adjusting member capable of adjusting the length of the loop portion to be hung on the neck is attached to the strap body, and a mark indicating the attachment position of the threshold detector is attached to the strap body. It is possible to make it the structure attached | subjected to.

Here, the threshold detector is a detector utilizing the characteristic that neutrons cause nuclear reactions with various substances. In addition to indium, the materials include gold, copper, sulfur, etc., each having a different activation cross section and threshold value. Therefore, by using the above characteristics, it is possible to estimate the exposure dose with, for example, one type of threshold detector. If a plurality of such dose detectors are used, the radiation dose to the human body can be estimated as described later. It is possible to specify the incident direction. Further, by combining a plurality of types of threshold detectors such as indium, gold, copper and sulfur, it is possible to obtain a more detailed exposure dose and neutron spectrum.
In the present invention, (1) it is possible to cope with a high dose at the time of a criticality accident, and it is possible to appropriately estimate the dose of wear of the wearer, (2) it is possible to specify the incident direction of radiation to the human body, (3) soft Indium is used as a threshold detector because it can be easily molded into thin pieces (foil-like), can be used without feeling a sense of incongruity when embedded in the neck strap fabric, and (4) can be manufactured at low cost. Yes.
In this threshold detector, radiation emitted from a substance activated by neutrons is measured with a portable radiation meter (survey meter), etc., and the exposure dose derived in advance from the measured activation amount. By using the correlation between the amount of radiation and the amount of activation, the wearer's approximate exposure dose can be derived.

According to the present invention, even when a criticality accident occurs, it is possible to easily and quickly carry out estimation of the exposure dose of an exposed person and identification of the incident direction of radiation.
Therefore, even if a criticality accident occurs, it is possible to quickly select overexposed persons from a large number of evacuees, and it is possible to promptly determine a treatment policy for those overexposed persons.
In addition, since indium is used as the threshold detector, the critical personal dosimeter according to the present invention can be manufactured at a low cost. Can be distributed and required to be worn. In other words, when introducing an accident countermeasure system using the personal dosimeter for criticality, the introduction cost is an appropriate cost range based on the fact that it is a countermeasure for an event that is evaluated to be impossible in terms of facility design. Can fit inside.

  Furthermore, since the neck strap type critical personal dosimeter is used, the critical personal dosimeter can be used as a normal neck strap. As described above, persons entering the controlled area must use personal dosimeters such as integrating dosimeters and electronic dosimeters (personal dosimeters for measuring external exposure dose during normal work: Therefore, by using the critical personal dosimeter as a neck strap for these individual personal dosimeters, it is possible to use the critical individual without burdening the operator. The dosimeter can be worn thoroughly. In addition, since it is a neck strap type, it can be easily confirmed whether or not it is worn, and it is possible to prevent the critical personal dosimeter from not being worn, such as inadvertently forgetting to attach it or not intentionally attaching it. .

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a perspective view showing an embodiment of a neck strap type critical personal dosimeter according to the present invention. This critical personal dosimeter 1 has a flat strap-like strap body 2 that hangs around a neck, and the strap body 2 includes a plurality of threshold detectors 3 made of indium flakes.

  The strap body 2 is formed in a ring shape by connecting both ends of a flat string-like fabric made of a material that hardly absorbs moisture, such as nylon, and is not burdened to the wearer such as the touch like a normal neck strap. Considered sewing and processing. In the present embodiment, a fabric having a width of 0.5 to 1 cm, a thickness of 0.1 to 0.3 cm, and a fabric having a length of 100 cm, and a fabric having a width and thickness of the same and a fabric having a length of 120 cm are used. The ones used are prepared.

  The strap body 2 is provided with a detachable adapter 4 that allows the personal dosimeter 10 to be detachably attached to the strap body 2 and a length adjusting member 5 that can adjust the length of the loop portion that hangs around the neck. The detachable adapter 4 and the length adjusting member 5 are both made of hard rubber, and the detachable adapter 4 is attached to the strap body 2 via the attachment ring 6. The length adjusting member 5 is attached to the attachment position of the detachable adapter 4. And is attached to the strap main body 2 in a slidable state so as to change the length of the loop portion over a range from the folding position to the other end. The detachable adapter 4 is a buckle type comprising a male part 4a and a female part 4b. By inserting the locked piece of the male part 4a into the locking hole of the female part 4b, both are engaged and joined to each other. In this state, the engaged piece of the male part 4a is elastically deformed inward from this state, so that the engagement is released and the two pieces are converted into a separable state. One of the male part 4 a and the female part 4 b is attached to the strap main body 2 via the attachment ring 6, and the other is attached to the normal personal dosimeter 10 via the loop-shaped attachment string 7.

  Further, the strap body 2 has a predetermined interval (for example, 3 to 4 cm) along the length direction thereof, and is symmetrical from the folded position (the other end of the mounting position of the detachable adapter 4). An indium flake (threshold detector 3) is embedded in the fabric. Each embedment position is marked (not shown). In the present embodiment, as shown in FIG. 2, at least four or more indium thin pieces are embedded in the fabric of the strap main body 2, and in a state where the strap main body 2 is hung on the neck, the indium thin pieces are substantially around the neck. Each position is set so that it may arrange | position at equal intervals (that is, the surface of each indium piece faces a mutually different direction). Indium having a purity of 99.99% or more (tolerance is clearly indicated on the quality indication tag etc.) is used, and each mass is 350 mg (tolerance within 10%: explicitly indicated on the quality indication tag etc.). The dimension is set to be equal to or smaller than the diameter (6.18 cm) of the detection unit of the radiation measuring instrument. A report issued by the International Atomic Energy Agency (IAEA) ("DOSIMETRY FOR CRITICALITY ACCIDENTS: A Manual"), Technical Reports Series No. 211, International Atomic Energy Agency ( International Atomic Energy Agency), Austria, February 1982, p. 58, 86) discloses data showing the correlation between absorbed dose and exposure dose for 350 mg of indium. Thus, such data can be easily used, and the performance of the critical personal dosimeter 1 can be confirmed by comparing with the data obtained by the critical personal dosimeter 1 of the present embodiment. . The indium flakes can be formed by cutting to a predetermined size after rolling with a rolling machine. In addition, the indium flakes are embedded in the strap body 2 by, for example, sandwiching between two strap fabrics and applying a double-sided tape to the opposite surface of the fabrics and to both sides of the indium flakes, respectively. Can do.

In the personal dosimeter 1 for criticality having the above-described configuration, the strap body 2 is hung on the neck so that the side of the detachable adapter 4 to which the normal personal dosimeter 10 is attached becomes the lower end, as shown in FIG. It can be easily worn by pulling up the thickness adjusting member 5 to the vicinity of the larynx. At this time, the strap main body 2 fits to the neck and does not move easily, and the indium flakes are arranged at substantially equal intervals around the neck, and the respective surfaces face different directions. .
In this state, when a criticality accident occurs, each threshold detector 3 (indium flake) is irradiated with the neutron beam generated by the accident, and activation corresponding to the absorbed dose is detected for each threshold. Will happen in vessel 3.
Therefore, by measuring the radiation emitted from each threshold detector 3 with a radiation measuring instrument (survey meter or the like), it is possible to estimate the wear dose of the wearer, and from the distribution of the activation amount of the indium flakes, The incident direction of radiation to the human body can also be specified. For example, when the value of the threshold detector 3 disposed in the vicinity of the larynx is relatively large, or when the value of the threshold detector 3 disposed in the vicinity of the cervical spine is relatively small, from the front of the exposed person. It can be estimated that radiation has entered.

For this reason, even if a criticality accident occurs, it is possible to quickly select overexposed persons from a large number of evacuees, and it is possible to promptly determine a treatment policy for those overexposed persons.
Further, since indium is used as the threshold detector 3, the critical personal dosimeter 1 can be manufactured at a low cost, and even if there are a large number of people, the critical personal dosimeter 1 is provided to all the subjects. Can be distributed and required to be worn.
In addition, since the neck strap type is used, the critical personal dosimeter 1 can be used as a neck strap for the normal personal dosimeter 10, thereby preventing forgetting to attach the critical personal dosimeter 1. The critical personal dosimeter 1 can be thoroughly worn. Moreover, since the equipment for entering the management area is the same as before, there is no additional burden on the worker.

1 is a perspective view showing an embodiment of a neck strap type critical dosimeter according to the present invention. FIG. It is a schematic diagram for demonstrating the attachment position of a threshold detector. It is a schematic diagram which shows the use condition of the personal dosimeter for criticality of FIG.

Explanation of symbols

1 Personal dosimeter for criticality 2 Strap body 3 Threshold detector 4 Detachable adapter 5 Length adjustment member

Claims (4)

Neck strap type personal dosimeter for criticality,
A critical personal dosimeter comprising: a strap-like strap body that hangs around a neck; and a plurality of threshold detectors made of indium flakes enclosed in the strap body.   In the state where the strap body is hung on the neck, the mounting positions of the threshold detectors are set so that the plurality of threshold detectors are arranged at almost equal intervals around the neck. The personal dosimeter for criticality according to claim 1.   The strap main body is attached with a length adjusting member for adjusting the length of the loop portion to be hung on the neck so that the strap main body is fitted to the neck so as not to move easily. The personal dosimeter for criticality according to claim 1 or 2.   The critical personal dosimeter according to any one of claims 1 to 3, wherein the strap body is provided with a mark indicating a mounting position of the threshold detector.

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