Implementation%20Program%20of%20Two-dosimeter%20Algorithm%20for%20Better%20Estimation%20of%20Effective%20Dose%20during%20Maintenance%20Periods%20at%20KNPPs

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Implementation Program of Two-dosimeter Algorithm
for Better Estimation of Effective Dose during
Maintenance Periods at KNPPs

• 2007. 09. 12
• Hee Geun Kim
• Nuclear Power Laboratory
• Korea Electric Power Research Institute

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I. Introduction

• Effective Dose
• ? Primary protection dose quantity.
• - HE ICRP-26 (1977), E ICRP-60 (1991).
• - Provide risk-based radiation
  protection system.
• ? Not directly measurable.
• ? Measure radiation dose outside the body and
• convert it to E.

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I. Introduction

• Effective Dose
• ? A single dosimeter on the chest
• - Hp(10) ? E.
• - acceptable only for frontal incident
  radiations.
• ? If photon beam comes from the back or high?
• - severe underestimation (7-10 times).
• - ICRP-75 (1997) ? dosimeter should be
  worn
• at an appropriate position on the body
• ? How do we solve this problem? Two-dosimeter
  approach.

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Topics for Presentations

• Introduction
• Two-dosimeter Approach
• Application Test
• Test Results
• V. Implementation Program

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II. Two-dosimeter Approach

• Two-dosimeter Approach
• ? Several investigators suggested using two
  dosimeters.
• - Chest Back or Chest Head
• - at least one dosimeter always directly
  exposed.
• ? NCRP-122 (1995) recommended using two
  dosimeters
• for scenarios where the irradiation
  geometry or photon
• energy is unknown or difficult to
  characterize.
• ? How do we combine these dosimeter readings
• for the best estimation of E? Chest and
  back position.

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II. Two-dosimeter Approach

• Results of Two-dosimeter Approach
• The best combination of dosimeter weighting
  factors are the various values for the chest and
  back dosimeters or the chest and head dosimeters.
• Underestimation problem for posterior incident
  radiation was completely avoided by using two
  dosimeters and the developed algorithm.
• Overestimation problem does exist for typical
  beam directions, but significantly decreases in
  real situations.

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II. Two-dosimeter approach

• Relocate the Whole Body TLD Dosimetry
• (INPO 91-014)
• ? Known work area dose-rate gradients make it
• likely that total dose to a portion of the
  whole
• body will exceed the chest dose by more than
  
• 50 (e.g., dosimeter worn on the head when
• most of the dose rate in the work area is
  from
• overhead piping) and
• ? Dose rates in the general work area exceed
• 100 mrem/hr(1mSv/hr).

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II. Two-dosimeter approach

• Issue the Multi Whole Body TLD Dosimetry
• (INPO 91-014)
• ?Measured or anticipated work area dose-rate
• gradients make it possible for dose to one or
  more
• portions of the whole-body to exceed that of
  the
• chest by more than 50 percent or
• ?Dose rates in the work area exceed 100 mrem/hr
• and dose gradients are unknown or varying and
• ?Whole-body dose in excess of 300 mrem(3mSv) is
• expected during the job.

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II. Two-dosimeter Approach

• Current Two Dosimetry Practices in Korea
• ? Protection guideline and procedure for
  multi-TLD
• - Upper level program of dosimetry or health
  physics
• - Procedure of External dosimetry or dose
  assessment
• ? Maintenance of Steam Generator (SG), Reactor
  Coolant
• Pump(RCP) and Reactor Head Internal(RHI)
• ? Applying the two-dosimeter (chest and head)
• ? Hp(10)maximum ? E (No applying the
  two-dosimeter algorithm)
• ? The issued conditions of two-dosimeter are
  based on the
• INPO Guideline (INPO 91-014 1995)

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II. Two-Dosimeter Approach

• According to previous study results
• ? Single-dosimeter approach significantly
  underestimates
• HE (E) in some exposure situations.
• ? Two-dosimeter approach does not underestimate
  HE (E)
• by more than 5.
• ? 7 two-dosimeter algorithms have specific
  techical bases
• - Two dosimeters readout Chest/head or
  chest/back
• - Specific weighting factor
• - Solid and specific technical background
• - Application high radiation field (ex, SG
  chamber)

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II. Two-Dosimeter Approach

• Two-Dosimeter Algorithms
• ? Considered the 7 algorithms based on previous
  investigation results.

1. Canadian Utility (OPG) Algorithm 2. ANSI
N13.41 (1997) Algorithm 3. NCRP(70/30) Algorithm
(NCRP-122 1995) 4. NCRP(55/50) Algorithm
(NCRP-122 1995) 5. EPRI Algorithm (NRC RIS
2004-1) 6. Lakshmanan Algorithm (1991) 7.
Kim(58/42) Algorithm (1999)
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II. Two-Dosimeter Approach

• Canadian OPG Algorithm
• ANSI N13.41 (1997) Algorithm
• NCRP(70/30) Algorithm (1995)
• NCRP(55/50) Algorithm (1995)

E 0.11 Hp(10)head 0.89
Hp(10)torso
HE ? WcHp,c(10) 0.10 Hp,head and neck(10)
0.90 Hp,rest(10)
HE(estimate) 0.7 Hp(10)front
0.3 Hp(10)back
HE(estimate) 0.55 Hp(10)front
0.50 Hp(10)back
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II. Two-Dosimeter Approach

• EPRI Algorithm USNRC, RIS 2004-01
• Lakshmanan Algorithm (1991)
• Kim Algorithm (1998)

Hp(10)max. of front
or back Hp(10)avg. of front and back
HE(estimate) ---------------------

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Hp(10)front
Hp(10)back HE(estimate) -----------
1.5
HE(estimate) h(HE) 0.58 HP(10)front 0.42
HP(10)back
0.9 HE(AP) where h(HE)
------------- ? 1.02
0.58 Hf(AP) 0.42 Hb(AP)
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II. Two-Dosimeter Approach

• Effective WT for Exposure of Head/Neck Chest
  of OPG Program

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II. Two-Dosimeter Approach

• Compartment Factor of ANSI N13.41 (1997)

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III. Application Test

• Steam Generator Geometry

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III. Application Test

• Steam Generator General
• ? Combustion Engineering type S/G
• ? Radiation field in a S/G channel head depends
  on
• many factors.
• ? However, dominated by 60Co and 58Co (95)
• ? Source term and photon field from upper U
  tubes
• ? Dose rate is non-uniform and gradient from
  high to low
• ? Dose rate exceeds few mSv/hr and gradient of
  the chest
• by more than 50

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III. Application Test

• Application Test during Maintenance Periods
• ? Algorithm considered 7 algorithms
• ? Pilot plant Yonggwang unit 4 and Ulchin unit
  4
• ? Target work very high radiation dose or
  gradient
• (ex, Steam Generator, Pressurizer and
  Reactor Head
• Penetration Test)
• ? Fully explain to workers before test
• ? Issue 6 dosimeters (3 TLDs and 3 ADRs)
• ? Readout the TLD and calculated the effective
  dose

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III. Application Test

• Application Test during Maintenance Periods
• - 3 TLDs and 3 ADRs provided to radiation
  workers
• wearing at head, chest and back
  simultaneously.
• - The effective dose(E) are calculated based
  on deep dose
• of 2 TLD readouts for the purpose of the
  adoption of two-
• dosimeter algorithm for KNPPs among several
  algorithms.
• - E is analyzed and sorted for searching of
  algorithm trend
• analysis from high effective dose to low E.
• - Technical approach and work convenience
  (interview)
• - Consult and comment (independent review)
  from the
• experts of Monte Carlo Simulation and
  specialists

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IV. Test Results

• Deep Dose at Yonggwang Unit 4

(Unit mSv)
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IV. Test Results

• Effective Dose at Yonggwang Unit 4

(Unit mSv)
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IV. Test Results

• The Comparison of Two-Dosimeter Algorithm at YG

Effective Dose (mSv)
TLD Numbers
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IV. Test Results

• The Comparison of Two-Dosimeter Algorithm at YG
• ? The TLD Number is sorted by effective
  dose(E) from high E to low E

Effective Dose (mSv)
TLD Numbers
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IV. Test Results

• The Comparison of Two-Dosimeter Algorithm at YG
• ? The TLD Number is sorted by effective
  dose(E) from high E to low E

Effective Dose (mSv)
TLD Numbers
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IV. Test Results

• The Comparison of Two-Dosimeter Algorithm at YG

Effective Dose (mSv)
TLD Numbers
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IV. Test Results

• The Comparison of Two-Dosimeter Algorithm at YG

Effective Dose (mSv)
TLD Numbers
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IV. Test Results

• The Comparison of Two-Dosimeter Algorithm at YG

Effective Dose (mSv)
TLD Numbers
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IV. Test results

• Deep Dose at Ulchin Unit 4

(Unit mSv)
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IV. Test Results

• Effective Dose at Ulchin Unit 4

(Unit mSv)
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IV. Test Results

• The Comparison of Two-Dosimeter Algorithm at UC

Effective Dose (mSv)
TLD Numbers
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IV. Test Results

• The Comparison of Two-Dosimeter Algorithm at UC

Effective Dose (mSv)
TLD Numbers
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V. Implementation Program

• We investigated the application practice and
  considered the seven two-dosimeter algorithms for
  implementing test.
• 3 TLDs provided to workers wearing the head,
  chest and back simultaneously based on algorithm
  characteristics during maintenance periods at
  KNPPs
• The best combination of two-dosimeter algorithms
  is the chest back or chest head dosimeters ?
  chest back
• The trend of effective dose is almost same (any
  algorithm is OK) except Laksmanan algorithm.
• Finally NCRP(55/50) algorithm was adopted because
  its work convenience, reliability technical
  aspects for implementing to KNPPs.

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V. Implementation Program

• TLD Issue condition INPO 91-014 Guideline
• 2 mSv
  for single job
• Target work S/G, PZR RCP etc
• Number of TLD issued Two
• TLD position issued Chest and Back
• Algorithm adopted NCRP(55/50)
• Application schedule From January 2006
• (already reviewed by Korean regulator and
  implemented to NPPs)

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Thank you for attention!!