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2007. 09.12 KIM JEONG-IN

Estimation of the effects of a lead vest on dose reduction for NPP workers using Monte Carlo calculations. 2007. 09.12 KIM JEONG-IN. Contents. Introduction Materials and Methods Results and Discussion Future Works Conclusion. Introduction.

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2007. 09.12 KIM JEONG-IN

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  1. Estimation of the effects of a lead vest on dose reduction for NPP workers using Monte Carlo calculations 2007. 09.12 KIM JEONG-IN

  2. Contents • Introduction • Materials and Methods • Results and Discussion • Future Works • Conclusion

  3. Introduction • In the field of medical diagnosis or treatments using radiations, lead vests or aprons are widely used to protect the patients from unwanted irradiation. • In nuclear power plants, it is recommended that the workers should wear a lead vest to reduce the dose for working in high radiation area. • Various models have been designed and changed for convenience and effectiveness for dose reduction

  4. Introduction • Personal dosimeters like TLDs, Film badges have been used to estimate the doses of radiation workers • The dosimeters cannot give the absolute values • Measured values should be modified by comparing the reference conditions with conversion factors • In ICRP 74, These conversion factors are tabulated for various particles, energies and typical phantom geometries.

  5. Introduction • The dose of a worker with a lead vest cannot be estimated directly from the personal dosimeter • Many trials using two or more dosimeters (located in/outside the shield, head and chest respectively) were done. But it still has limitations. • In the concepts of ALARA, conservative approach is not always the best choice. • Through this research, the personal doses with/without a lead vest and the effectiveness were evaluated by Monte Carlo methods

  6. Materials & Methods [ lead vest ] • Used in KHNP nuclear site since 2004 • Two front sides were folded • 2.5cm*32cm*1.5mm lead plates were placed • About 9.3kg

  7. Materials & Methods [ The phantom ] • MIRD-V • Simplified human body with critical organs • Front side : 3mm, back side : 1.5mm

  8. Materials & Methods [ Monte Carlo Method ] • Most of the natural phenomena are random nature. • If we understand the underlying principles, we can simulate the process by Monte Carlo method • Utility of Monte Carlo technique • Sampling • Particle behavior (molecules, radiation) • Reactions • uncertainty

  9. Materials & Methods [ Monte Carlo Method ] • Merits? • Can handle complicated 3-D geometries • Can visualize simulated particle behavior • Can give uncertainty estimates • Drawbacks • Long computing time (geometry tracking) • Limited number of detectors

  10. Materials & Methods [ Monte Carlo Method ] • AP, PA, RLAT, LLAT • Parallel photon beam (0.2, 0.4, 0.6, 0.8. 1.0, 1.2MeV) • MCNP-5 Monte Carlo transport code LLAT PA AP RLAT

  11. Results [ AP ]

  12. Results [ PA ]

  13. Results [ RLAT ]

  14. Results [ LLAT ]

  15. Discussion • The results have some limitations to apply due to the differences between phantom and real body • In most cases, the lead vest decreases the organ doses about 30%. • For low energy (<400keV), the lead vest is very effective to reduce the dose but it is not so good for high energy photon shielding (less than 20%). • Both the shielding effect of lead vest and the delay of working time due to heavy clothing should be considered.

  16. Discussion • For thyroids, the doses to high energy photons increased by 5% on the contrary • These results comes from scattered radiation (Build-up)

  17. Future Works • Monte Carlo results are not always good answers. For verification, real measurements should be done and compared • For the optimal method of dose measurements using personal dosimeters and dose conversion factors from personal dosimeters

  18. Future Works • Other type of phantom models should be used to calculate the dose. • More precise values and build up effects can be calculated.

  19. Conclusion • Using Monte Carlo method, the effects of a lead vest on dose reduction for various irradiation geometries were examined. • In most cases, it had 30% dose reduction effect. But some problems should be considered were also found. • Real measurements and applications to advanced man-like mathematical phantoms are required. • This study may be applied to the better design of personal shielding and dose estimation procedures for practical use.

  20. Thank you neogen21@khnp.co.kr

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