1. Implementation Program of Two-dosimeter Algorithm for Better Estimation of Effective Dose during Maintenance Periods at KNPPs
Hee Geun Kim
Nuclear Power Laboratory
Korea Electric Power Research Institute

2. 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.

3. 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.

4. Topics for Presentations
Introduction
Two-dosimeter Approach
Application Test
Test Results
V. Implementation Program

5. II. 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.

6. 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.

7. II. Two-dosimeter approach
Relocate the Whole Body TLD Dosimetry
(INPO )
 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).

8. II. Two-dosimeter approach
Issue the Multi Whole Body TLD Dosimetry
(INPO )
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.

9. 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 ; 1995)

10. 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)

11. 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 )
6. Lakshmanan Algorithm (1991)
7. Kim(58/42) Algorithm (1999)

12. 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 Hp(10)torso
HE =  WcHp,c(10) = 0.10 Hp,head and neck(10) Hp,rest(10)
HE(estimate) = 0.7 Hp(10)front Hp(10)back
HE(estimate) = 0.55 Hp(10)front Hp(10)back

13. II. Two-Dosimeter Approach
EPRI Algorithm; USNRC, RIS ;
Lakshmanan Algorithm (1991);
Kim Algorithm (1998);
Hp(10)max. of front or back + Hp(10)avg. of front and back
HE(estimate) = ───────────────────── 2
Hp(10)front + Hp(10)back
HE(estimate) = ───────────
1.5
HE(estimate) = h(HE) [0.58 HP(10)front HP(10)back]
0.9 HE(AP)
where h(HE) = ─────────────  1.02
0.58 Hf(AP) Hb(AP)

14. II. Two-Dosimeter Approach
Effective WT for Exposure of Head/Neck & Chest of OPG Program
Compartment
Name
WT from
ICRP 60
Fraction of WT
Assigned to
Weighting
Factor for
Associated Organs & Tissues
Head/Neck
0.12
0.05
0.01
0.18
0.60
1.00
0.40
0.33
0.022
0.030
0.050
0.004
0.003
0.11
Bone Marrow (red)
Esophagus
Thyroid
Skin
Bone Surface
Total for Compartment (Rounded)
Thorax
0.41
0.30
0.049
0.120
0.048
0.020
0.31
Lung
Stomach
Breast
Liver
Abdomen
0.20
0.200
0.072
0.58
Gonads
Colon
Bladder
Remainder

15. II. Two-Dosimeter Approach
Compartment Factor of ANSI N13.41 (1997)
☞ Almost similar to Canadian OPG Algorithm
Area of the Body
Head and neck
Thorax, above the diaphragm
Abdomen, including the pelvis
Upper right arm
Upper left arm
Right thigh
Left thigh
Compartment Factor, Wc
0.10
0.38
0.50
0.005

16. III. Application Test Steam Generator Geometry 195 cm 200 cm 120 cm
(0,0,0)
AS BS
photon field from U-tubes
TOP VIEW
SIDE VIEW
tubesheet
divider plate
interior wall
phantom

17. 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%

18. 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

19. 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

20. IV. Test Results
Deep Dose at Yonggwang Unit 4
(Unit: mSv)

21. IV. Test Results
Effective Dose at Yonggwang Unit 4
(Unit: mSv)

22. IV. Test Results The Comparison of Two-Dosimeter Algorithm at YG
Effective Dose (mSv)
TLD Numbers

23. 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

24. 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

25. IV. Test Results The Comparison of Two-Dosimeter Algorithm at YG
Effective Dose (mSv)
TLD Numbers

26. IV. Test Results The Comparison of Two-Dosimeter Algorithm at YG
Effective Dose (mSv)
TLD Numbers

27. IV. Test Results The Comparison of Two-Dosimeter Algorithm at YG
Effective Dose (mSv)
TLD Numbers

28. IV. Test results
Deep Dose at Ulchin Unit 4
(Unit: mSv)

29. IV. Test Results
Effective Dose at Ulchin Unit 4
(Unit: mSv)

30. IV. Test Results The Comparison of Two-Dosimeter Algorithm at UC
Effective Dose (mSv)
TLD Numbers

31. IV. Test Results The Comparison of Two-Dosimeter Algorithm at UC
Effective Dose (mSv)
TLD Numbers

32. 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.

33. V. Implementation Program
TLD Issue condition: INPO 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)

34. Thank you
for attention!!