2007. 09.12 KIM JEONG-IN

Estimation of the effects of a lead Estimation of the effects of a lead vest on dose reduction for NPP vest on dose reduction for NPP

workers using Monte Carlo workers using Monte Carlo calculationscalculations

2007. 09.122007. 09.12

KIM JEONG-INKIM JEONG-IN

ContentsContents

IntroductionIntroduction

Materials and MethodsMaterials and Methods

Results and DiscussionResults and Discussion

Future WorksFuture Works

ConclusionConclusion

Introduction Introduction

In the field of medical diagnosis or treatments using In the field of medical diagnosis or treatments using radiations, lead vests or aprons are widely used to protect radiations, lead vests or aprons are widely used to protect the patients from unwanted irradiation. the patients from unwanted irradiation.

In nuclear power plants, it is recommended that the In nuclear power plants, it is recommended that the workers should wear a lead vest to reduce the dose for workers should wear a lead vest to reduce the dose for working in high radiation area.working in high radiation area.

Various models have been designed and changed for Various models have been designed and changed for convenience and effectiveness for dose reductionconvenience and effectiveness for dose reduction

Introduction Introduction

Personal dosimeters like TLDs, Film badges have been usPersonal dosimeters like TLDs, Film badges have been used to estimate the doses of radiation workersed to estimate the doses of radiation workers

The dosimeters cannot give the absolute valuesThe dosimeters cannot give the absolute values

Measured values should be modified by comparing the refMeasured values should be modified by comparing the reference conditions with conversion factorserence conditions with conversion factors

In ICRP 74, These conversion factors are tabulated for varIn ICRP 74, These conversion factors are tabulated for various particles, energies and typical phantom geometries.ious particles, energies and typical phantom geometries.

IntroductionIntroduction

The dose of a worker with a lead vest cannot be estimated The dose of a worker with a lead vest cannot be estimated directly from the personal dosimeterdirectly from the personal dosimeter

Many trials using two or more dosimeters (located in/outside Many trials using two or more dosimeters (located in/outside the shield, head and chest respectively) were done. But it the shield, head and chest respectively) were done. But it still has limitations.still has limitations.

In the concepts of ALARA, conservative approach is not In the concepts of ALARA, conservative approach is not always the best choice.always the best choice.

Through this research, the personal doses with/without a Through this research, the personal doses with/without a lead vest and the effectiveness were evaluated by Monte lead vest and the effectiveness were evaluated by Monte Carlo methodsCarlo methods

Materials & Methods [ Materials & Methods [ lead vestlead vest ] ]

Used in KHNP nuclear site since 2004Used in KHNP nuclear site since 2004

Two front sides were foldedTwo front sides were folded

2.5cm*32cm*1.5mm lead plates were placed 2.5cm*32cm*1.5mm lead plates were placed

About 9.3kgAbout 9.3kg

Materials & Methods [ Materials & Methods [ The The phantomphantom ] ]

MIRD-VMIRD-V

Simplified human body with critical organsSimplified human body with critical organs

Front side : 3mm, back side : 1.5mmFront side : 3mm, back side : 1.5mm

Materials & Methods [ Materials & Methods [ Monte Carlo Monte Carlo MethodMethod ] ]

Most of the natural phenomena are random nature.Most of the natural phenomena are random nature.

If we understand the underlying principles, we can If we understand the underlying principles, we can simulate the process by Monte Carlo methodsimulate the process by Monte Carlo method

Utility of Monte Carlo techniqueUtility of Monte Carlo technique– SamplingSampling– Particle behavior (molecules, radiation)Particle behavior (molecules, radiation)– ReactionsReactions– uncertaintyuncertainty

Materials & Methods [ Materials & Methods [ Monte Carlo Monte Carlo MethodMethod ] ]

Merits?Merits?– Can handle complicated 3-D geometriesCan handle complicated 3-D geometries– Can visualize simulated particle behaviorCan visualize simulated particle behavior– Can give uncertainty estimatesCan give uncertainty estimates

DrawbacksDrawbacks– Long computing time (geometry tracking)Long computing time (geometry tracking)– Limited number of detectorsLimited number of detectors

Materials & Methods [ Materials & Methods [ Monte Carlo Monte Carlo MethodMethod ] ]

AP, PA, RLAT, LLATAP, PA, RLAT, LLAT

Parallel photon beam (0.2, 0.4, 0.6, 0.8. 1.0, 1.2MeV)Parallel photon beam (0.2, 0.4, 0.6, 0.8. 1.0, 1.2MeV)

MCNP-5 Monte Carlo transport codeMCNP-5 Monte Carlo transport code

PA

APRLAT

LLAT

Results [ Results [ APAP ] ]

Results [ Results [ PAPA ] ]

Results [ Results [ RLATRLAT ] ]

Results [ Results [ LLATLLAT ] ]

DiscussionDiscussion

The results have some limitations to apply due to the The results have some limitations to apply due to the differences between phantom and real bodydifferences between phantom and real body

In most cases, the lead vest decreases the organ doses In most cases, the lead vest decreases the organ doses about 30%. about 30%.

For low energy (<400keV), the lead vest is very effective For low energy (<400keV), the lead vest is very effective to reduce the dose but it is not so good for high energy to reduce the dose but it is not so good for high energy photon shielding (less than 20%).photon shielding (less than 20%).

Both the shielding effect of lead vest and the delay of Both the shielding effect of lead vest and the delay of working time due to heavy clothing should be considered.working time due to heavy clothing should be considered.

DiscussionDiscussion

For thyroids, the doses to high For thyroids, the doses to high energy photons increased by 5% energy photons increased by 5% on the contraryon the contrary

These results comes from These results comes from scattered radiation (Build-up)scattered radiation (Build-up)

Future WorksFuture Works

Monte Carlo results are Monte Carlo results are not always good answers. not always good answers. For verification, real For verification, real measurements should be measurements should be done and compareddone and compared

For the optimal method of For the optimal method of dose measurements using dose measurements using personal dosimeters and personal dosimeters and dose conversion factors dose conversion factors from personal dosimetersfrom personal dosimeters

Future WorksFuture Works

Other type of phantom models should be used to calculate Other type of phantom models should be used to calculate the dose. the dose.

More precise values and build up effects can be calculatedMore precise values and build up effects can be calculated..

ConclusionConclusion

Using Monte Carlo method, the effects of a lead vest on Using Monte Carlo method, the effects of a lead vest on dose reduction for various irradiation geometries were dose reduction for various irradiation geometries were examined.examined.

In most cases, it had 30% dose reduction effect. But some In most cases, it had 30% dose reduction effect. But some problems should be considered were also found.problems should be considered were also found.

Real measurements and applications to advanced man-Real measurements and applications to advanced man-like mathematical phantoms are required.like mathematical phantoms are required.

This study may be applied to the better design of personal This study may be applied to the better design of personal shielding and dose estimation procedures for practical shielding and dose estimation procedures for practical use.use.

Thank youThank you

[email protected]@khnp.co.krr