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

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.

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.

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

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.

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.

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).

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.

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)

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)

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)

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

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) = ───────────────────── 2 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)

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

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

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

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%

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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)

Thank you for attention!!