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(in English)

Vol.8, No.1, NT77
Development of the FLEXible radiation DOSE evaluation software (FLEXDOSE)
TEPCO Systems Corporation (TEPSYS)
Dose evaluation, Air dose rate, direct ray, Dose management
1. Technical summary

3 - C

• New simple dose rate evaluation software FLEXDOSE (FLEXible radiation DOSE evaluation software) has been developed. With FLEXDOSE, it is possible to evaluate the impact assessment of the radiation, more easily, more effectively, more clearly.

• The software is intended to evaluate the dose rate of the direct gamma ray in geometrically flexible 3D space. User can easily evaluate the dose rate by making the 3D objects (by combining the cylinder, the cuboid, the half sphere) in 3D space and setting parameters of the objects (the nuclide, the radioactivity, etc.).

• There are three features of the software. First, the software has equivalent calculation accuracy of the QAD code which is usually used in this field. Second, the software supplies the 3D graphical user interface with which user can understand the environment to be evaluated visually. Lastly, the software assist user to set the calculation conditions like the position, spectrum, and material of the radiation source.

• The functions of the software, it is possible to evaluate and visualize the dose rate distribution at the specified height of the 3D environment. This software searches the optimal buildup material between each radiation point and evaluation point automatically. Therefore, it is possible to evaluate the dose rate at once even in such condition where multiple radiation sources and evaluation points are located. From the measured values of the dose rate, it is also possible to estimate the amount of radioactivity of unknown-radiation sources.

• FLEXDOSE is intended to evaluate easily and quickly the dose rate in the situation where the direct gamma ray is dominant. Therefore, it is impossible to evaluate the effect of the reflection or streaming. On the other hand, the ARES (Air dose Rate Evaluation System)(3), which has been shown here previously, is suitable to evaluate in the situation like outdoor where the influence of the Sky Shine is large.

• As one of the applications of the software, the support of work planning in radiation environment can be considered. By using the software, it is possible to evaluate the exposure assessment flexibly according to condition change of the environment at any time. Therefore, it can be expected that it is possible to more efficient site management.

The detail of FLEXDOSE is described below.

2. Development Phase

Phase 2 : Industrial Confirmation Phase

3. Scope
  1. (1) Components:
    Radioactive, Dose rate evaluate,
  1. (2) Location:
    The nuclear power plant, The radioactive waste treatment plant.
  1. (3) Materials:
  1. (4) Condition:
    The situation in where the direct gamma ray has
    dominant radioactive effect. (The situation that can be ignored radioactive effect by reflect, streaming, and sky-shine.)

4. Features
  1. (1)• Method of evaluation
  2. FLEXDOSE calculates the dose rate based on point kernel method (1)(2). A modeled radiation source is divided into fragments in accordance with input parameters (e.g. the number of meshes of vertical, peripheral, and radius of a cylinder.), and a point source is placed at the center of each fragment. In the dose calculation, the dose rate from each point source is summed. The evaluation formula based on point kernel method in the software is as shown below.
  3. The evaluation formula: D=φ×Ka/φ×f/(E/Ka)×BF×E/Ka×10-6×3600(s)
    D            :Effective dose rate(μSv/h)
    φ            :Non-collision photon fluence rate(光子/(cm2・s))
    Ka/φ       :Air kerma conversion coefficient(pGy・cm2)
    f             :Effective dose conversion coefficient*(Sv/Gy)
    BF          :Irradiation dose buildup factor

    E/Ka      :Effective dose per air kerma(Sv/Gy)
  4. *Maximum coefficient for each energy. It calculates the minimum value of the ratio of the E / Ka as 1.0

  5. (2)• Accuracy of FLEXDOSE
  6. FLEXDOSE and the QAD code are compared under the same geometric conditions. The differences of the evaluated values in two codes are within -0.4% and 0.1%. For example, the comparison of the same cylinder model radiation source is as shown below. (Fig.1)

  7. Fig.1 Comparison of FLEXDOSE and the QAD code by the cylinder model radiation source

  8. • Object Setting
  9. User can add, delete, and edit the objects. Settable items and values by the user are as shown below.

  10. Fig.2 Objects and Setting Parameters

  11. If the value of radiation is set to zero, the object is regarded as a shield object. If it is set to greater values than zero, the object is regarded as a radiation source. In addition, user can specify the nuclides. By inputting nuclide name, and gamma ray spectrum in a configuration file of FLEXDOSE, user can use any of the nuclide in the software.
  12. An example in object layout set by FLEXDOSE, as shown below. (Fig.3)

  13. Fig.3 An example in object layout set by FLEXDOSE

  14. (2)• Dose rate evaluation at specified point.
  15. The dose rate and contribution from each radiation source at specified point can be evaluated according to the user input as shown below. (Fig.4)

  16. Fig.4 Result of Dose rate evaluation at specified point

  17. (2)• Dose rate evaluation in whole area at specified height.
  18. The software can evaluate the dose rate in whole area at specified height, and can visualize as a coloring graphic map and/or a contour plot by the specified mesh width. User sets parameters of evaluation height and mesh width. The coloring map is indicated bottom of the 3D space as shown below (Fig.5 and Fig.6)

  19. Fig.5 The coloring map and contour plot of the dose rate in whole area. (TOP VIEW)


    Fig.6 The coloring map and contour plot of the dose rate in whole area. (3D VIEW)

  20. (2)• Automatic searching of the buildup material.
  21. The software automatically searches the buildup material. The search algorithm is as shown below.

  22. (1) The passing length of the radiation ray is calculated for the object in the order of which is placed between the radiation point and the evaluation point, and placed at the closer point to the evaluation point.
    (2) The path length is converted to the factor of the mean free path (mfp). Then if the converted factor is greater than or equal to half of the mfp, the material of the object is judged as the buildup material.
    (3) If the path length is less than half of mfp, the next closest object is searched.
    The processes (1), (2), (3) are repeated until the optimal material is found.
    If the path lengths in all object are less than half of mfp, the material of radiation source or outer plate, whichever is greater value normalized by each mfp, is selected as the buildup material.

  23. This function is very useful in the case of the complicated environment like where there are multiple radiation sources and evaluation points. In such environment, the buildup material cannot be specified by manually. When user evaluates the radioactivity by QAD, user must decide the buildup material in each pair of one evaluation point and one radiation source. When there are many shield material between an evaluation point and a radiation source, user must consider deciding the buildup material from many shield materials. In general, there are many evaluation points under complex geometric environment, user takes a lot of time deciding the buildup material. FLEXDOSE can decide the optimal buildup material between each radiation point and evaluation point automatically according to the search algorithm. An example in which the buildup materials are different is as shown below. (Fig.7)

  24. Fig.7 An example in which the buildup factor is different

  25. (2)• Backward calculation of the radioactivity
  26. The radioactivity of unknown radiation source can be backward calculated based on the measured dose rate. In order to calculate the radioactivity, it is necessary to prepare the same number of measured values and unknown radiation sources.
    If there are known radiation source (e.g. the radioactivity of some radiation source is measured already), the radiation source can be treated as background source.

5. Examples of Application

When evaluating radiation effects indoor, it usually evaluates radiation sources of the wall and floor. FLEXDOSE can model the radiation sources of the wall and floor as shown below. (Fig.8)


Fig.8 An example in radiation sources where attached on the wall and floor modeled by FLEXDOSE

6. Reference

  1. (1) 放射線施設のしゃへい計算実務マニュアル(2015)
  2. (2) ANSI/ANS-6.3.4-1991
  3. (3) EJAM (6-3-NT66) Development of the Air dose Rate Evaluation System (ARES):
7. Contact

Japan Society of Maintenology (