ML15012A368
| ML15012A368 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 01/12/2015 |
| From: | Entergy Corp |
| To: | NRC/RGN-III/DRMA |
| Lougheed V | |
| References | |
| EA-14-168 | |
| Download: ML15012A368 (62) | |
Text
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Effective Dose Equivalent External (EDEex)
January 13, 2015 NRC Regulatory Conference Palisades Nuclear Plant 1
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Introduction Tony Vitale - Site Vice President Tony Williams - General Manager Plant Operations Otto Gustafson - Regulatory & Performance Improvement Director Doug Watkins - Radiation Protection Manager (RPM)
Jeff Hardy - Regulatory Assurance Manager David Mannai - Sr. Manager Fleet Regulatory Assurance Jim Fontaine - Radiation Protection (RP) Support Supervisor David Moore - Corporate RPM David Smith - Certified Health Physicist (CHP)
Dr. George Chabot - Professor Emeritus, UMass-Lowell 2
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Agenda Topic Presenter
Background
Tony Vitale Apparent Violations Tony Williams Lessons Learned Tony Williams Dose Assessment Jim Fontaine 3rd Party Reviewer Comments Dr. George Chabot Significance Determination Input Otto Gustafson Conclusions Tony Williams Closing Remarks Tony Vitale 3
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BACKGROUND Tony Vitale 4
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Background
Palisades replaced 44 control rod drive (CRD) housings in the 1Q14 refueling outage Detailed planning of work activities was necessary due to:
- Physical limitations
- Significant radiological fields
- High precision machining 5
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Background
- Dosimetry was assigned in accordance with Entergy Procedure EN-RP-204 Special Monitoring Requirements
- Six monitoring locations were selected (comprising a pack)
- Head
- Chest
- 2 x Upper arms
- 2 x Thighs
- Two types of dosimetry were used at each location
- Optically Stimulated Luminescent Dosimeters (OSLDs) and
- Telemetric Electronic Alarming Dosimeters (EADs)
- Two-sided tungsten vests were also available 6
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Background
- This project was previously performed in 2001
- The dose expended in 2001 was 166 person-rem
- Dosimetry relocation was assessed and criteria requiring relocation to the thigh (1.5x) was not met
- 2014 radiological conditions were similar to 2001
- The total Radiological Work Permit (RWP) dose estimate in 2014 was 162.4 person-rem
- The EDEex dose assessed for the CRD housing replacement project was 113.7 person-rem 7
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APPARENT VIOLATIONS Tony Williams 8
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Apparent Violations
- 10 CFR 20.1201, Occupational Dose Limits for Adults, for failure to ensure that radiation worker dosimeters were located at the highest exposed portion of the respective compartment.
- Tech Spec 5.4.1, Procedures, for failure to ensure the procedure met the minimum requirements of 10 CFR 20.1201 for all practical workers positions and shielding geometries prior to implementation. Procedure EN-RP-204 did not contain requirements to locate the dosimeter at the highest exposed portion of the respective compartment.
9
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Apparent Violations Continued
- Entergy agrees that a performance deficiency occurred
- Entergy has additional information that should be considered during the final significance determination of the finding 10
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LESSONS LEARNED Tony Williams 11
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Lessons Learned
- Root Cause
- EN-RP-204 does not fully implement the requirements of Regulatory Guide 8.40, Methods for Measuring Effective Dose Equivalent from External Radiation Exposure, for the use of EDEex, and
- EN-RP-204 does not adequately address the use of tungsten vests
- Contributing Causes
- Inadequate field oversight and reinforcement of fundamentals
- RWP planning did not validate that body positioning assumptions remained valid for all aspects of the project 12
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Lessons Learned
- Key Corrective Action
- Revise EN-RP-204 to align with Regulatory Guide 8.40 Additional Planned Corrective Actions
- Require a documented evaluation for the use of EDEex
- Institute timely in-progress reviews for extended use of EDEex
- Enhance briefings for use of EDEex and tungsten vest use
- Implement tracking mechanism for use of tungsten vests 13
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DOSE ASSESSMENTS Jim Fontaine 14
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Initial Re-Assessment
- The inspector initially debriefed the performance deficiency on September 24, 2014
- In early October 2014, Palisades chose to reassess EDEex using a simple but conservative methodology to ensure no individual challenged the annual dose limits:
- Expand the abdomen and thorax compartment to include the thighs
- Apply the highest thigh dose to the entire compartment volume using a weighting factor of 0.89
- The total additional dose from this re-analysis was 86.6 person-rem 15
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Subsequent Re-Assessment Overview In November 2014, a subsequent dose re-assessment was performed in four steps 1.
Determine, using each workers personal dosimetry, whether a sufficient dose gradient existed to have warranted relocation of dosimetry 2.
If a sufficient gradient exists, assess the dose at the abdomen in accordance with 10 CFR 20.1201(c) and Regulatory Guide 8.34. Each individuals personal dosimetry was used to ascertain the dose at the abdomen 3.
Address the impact of tungsten vest use 4.
Calculate EDEex in accordance with Regulatory Guide 8.40, Section C.1 using compartment weighting factors 16
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STEP 1 - GRADIENT TEST 17
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Compartments and Relative Position 18
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Aggregate Data
- Note that the following graphs present aggregated data for all EDEex packs
- These are shown for illustrative purposes and model development only Symbol Notation
- Solid blue marker indicates actual, unshielded OSL dosimetry data
- Solid red marker indicates actual chest data
- Empty red marker represents projected chest and abdomen data for model development uses 19
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Aggregate Data This slide presents aggregate data from all EDEex packs of interest. These graphics are useful in illustrating the effective dose gradient, but have not been used to apply a global curve fit to individuals.
20
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Straight Line Interpolation Between Arms and Thighs DDE at the chest and abdomen locations may be conservatively projected by interpolating between the thigh and arm. Position 8 is used for the lower abdomen and position 10 for the chest.
21
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Gradient Test Design 22
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Gradient Test Design 23
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Gradient Test Design Y = Thigh Average Arm Average
5 = 0.5 x CH 2
Y = 1.25 x CH or
=. x 24 Y
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Example Gradient Test (Actual Data) 25
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STEP 2 - ASSESS ABDOMEN DOSE 26
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Abdomen Dose Assessment
- Step 2: Assess the dose at the lower abdomen, the part of the abdomen receiving the highest exposure
- This step was only performed if the gradient test was satisfied
- This step used each individuals assigned dosimetry to assess the dose at the abdomen; as we would do in accordance with 10 CFR 20.1201(c) and Regulatory Guide 8.34 for a broken, lost, or improperly placed dosimeter 27
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Abdomen Dose Assessment 28
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STEP 3 - VEST USE CORRECTION 29
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Tungsten Vest Gap Definition: T-Vest Wear Fraction = EAD dose (when T-vest worn) / total EAD dose 30
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- Assume that T-vest covers 5/6 of the torso
- Dosimeter worn under T-vest under-represents the gap region dose by 17%
=
x 1 6 + x 5 6
= 1.17 x x 1 6 + x 5 6
= 1.0283 x
= x [1 + x 0.0283 ]
Tungsten Vest Gap 31
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STEP 4 - CALCULATE EDEex 32
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Calculate EDEex Step 4: Calculate EDEex in accordance with Regulatory Guide 8.40, Section C.1, using compartment weighting factors 33
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METHOD DEMONSTRATION Jim Fontaine 34
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Example - Pack 1907 (Name Available, but Withheld) 35
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- Step 1 - Gradient Test:
- The chest dose is greater than the upper arm average dose so the chest dose value is selected for the gradient test
- Test: Is thighs average - arms average > 1.25 x CH ?
- 2116 - 783.5 > 1.25 x 968 2116 - 783.5 968
= 1.377 > 1.25 YES
- Yes, the quotient is 1.377, so a gradient exists
- The gradient test is satisfied Example - Pack 1907 (Name Available, but Withheld) 36
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- Step 2 - Interpolate Abdomen Dose:
- = 0.6 x +
- = 0.6 x 2116 783.5 + 783.5
- = 1583
- Step 3 - Assess Tungsten Vest Impact:
- = 968 x 1 + (0.021 x 0.0283)
- = 968.58 Example - Pack 1907 (Name Available, but Withheld) 37
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- Step 4 - Calculate EDEex:
- Compartment Contributions
- = 0.10 x 582 = 58.2
- = 0.38 x 968.58 = 368.06
- = 0.5 x 1583 = 791.5
- = 0.005 x 828 = 4.14
- = 0.005 x 739 = 3.695
- = 0.005 x 2148 = 10.74
- = 0.005 x 2084 = 10.42
- Sum to Determine EDEex
- 1907 = 58.2 + 368.06 + 791.5 + 4.14 + 3.695 + 10.74 + 10.42
- 1907 = 1246.8 Example - Pack 1907 (Name Available, but Withheld) 38
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Example - Pack 1902 (Name Available, but Withheld) 39
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- Step 1 - Gradient Test:
- The chest dose is greater than upper arms average dose, so chest dose value is used for the test
- Test: Is thighs average - arms average > 1.25 x CH ?
- 1665.5 922 > 1.25 x 939 1665.5 922 939
= 0.792 > 1.25
- No, the quotient is 0.792, so a gradient does not exist
- The gradient test is not satisfied Example - Pack 1902 (Name Available, but Withheld) 40
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- Step 2 - Interpolate Abdomen Dose:
- This step is not applicable
- Chest dosimeter is appropriate for both TH and AB
- Step 3 - Assess Tungsten Vest Impact:
- = 939 x 1 + (0.226 x 0.0283)
- = 945
- = 939 x 1 + (0.226 x 0.0283)
- = 945 mrem Example - Pack 1902 (Name Available, but Withheld) 41
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- Step 4 - Calculate EDEex:
- Compartment Contributions
- = 0.10 x 598 = 59.8 mrem
- = 0.38 x 945 = 359.1
- = 0.5 x 945 = 472.5
- = 0.005 x 944 = 4.72
- = 0.005 x 900 = 4.5
- = 0.005 x 1661 = 8.305
- = 0.005 x 1670 = 8.35
- Sum to Determine EDEex
- 1902 = 59.8 + 359.1 + 472.5 + 4.72 + 4.5 + 8.305 + 8.35
- 1902 = 917.3 Example - Pack 1902 (Name Available, but Withheld) 42
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Dose Re-Assessment Results No individual exceeded an administrative dose guideline No individual exceeded an alarm setpoint (and would not have if the additional dose from the re-assessment was applied)
The highest dose assessed for a pack was 1742 mrem The largest dose adjustment for an individual was 531 mrem from all entries The original reported doses totaled 113.744 rem for 205 packs The current re-assessment yields 120.433 rem for the same 205 packs 43
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3RD PARTY REVIEWER COMMENTS Dr. George Chabot 44
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3rd Party Reviewer Comments
- I believe that Palisades original monitoring and assessment plan provided an acceptable level of worker protection with uncertainties within generally accepted ranges.
- Given that Palisades has accepted the performance deficiency, the re-assessment is appropriate, reasonable, and compliant with regulations.
- On a par basis, comparing single badge deep dose equivalent (DDE) to EDEex, the relocation criteria selected by Palisades are significantly conservative.
45
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Relative Effect of Relocation on EDE Normal Practice: Single dosimeters DDE is used for EDEex and represents all seven compartments 1.5 x relocation criterion applies The highest compartment dose, though almost never known, might be up to 1.5 x the compliant recorded dose In EDEex, compartment dosimeter relocation is also at a 1.5 x decision level Highest single weighted compartment is the abdomen (0.5)
==
Conclusion:==
not relocating abdomen dosimeter at 1.5 x AB/chest ratio results, worst case, in a 1.28 x net effect on EDEex To make significance of all EDE decisions uniform, a higher compartment relocation factor is justified in EDEex cases One truly gradient dosimeter is seen (84 mrem total EDEex) 46
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Proof: 1.28 x Maximum Net Effect on EDE when No Relocation at 1.5 x AB/Chest Ratio Usually, there is some dose recorded in every compartment To maximize the effect on EDE when relocation is not chosen at 1.5 x AB/chest ratio, zero out all dosimeters except for the chest and AB If chest represents both AB and TH, EDEex = 0.38 CH + 0.5 CH = 0.88 CH If AB was 1.5 x CH and had been separately monitored, EDEex = 0.38 CH + 0.5 x 1.5 CH = 1.13 CH The ratio of these is 1.13/0.88 = 1.28 The general form is:
EDEex(1) = 0.88 CH + D5 [D5 = EDEex from other 5 dosimeters]
EDEex(2) = 1.13 CH + D5 As D5 0, EDEex(2)/EDEex (1) = 1.28 As D5 >> 1.13 CH, EDEex(2)/EDEex(1) = 1.0 (AB/Chest ratio unimportant) 47
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Option Going Forward: Solving for AB/Chest Ratio that Corresponds to a Net Impact of 1.5 x on EDE From the previous slides information, the explicit general form is:
EDEex(1) = 0.88 CH + D5 EDEex(2) = 0.38 CH + 0.5 x ratio x CH + D5 Setting EDEex(2) / EDEex(1) = 1.5 (i.e. the tolerable level):
1.5 = 0.38 CH + 0.5 x ratio x CH + D5 0.88 CH + D5 And solving, ratio = 1.5 x 0.88 CH + 1.5 x D5 - 0.38 CH - D5 = 0.94 CH + 0.5 D5 0.5 CH 0.5 CH 48
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Option Going Forward: Solving for AB/Chest Ratio that Corresponds to a Net Impact of 1.5 x on EDE (cont.)
and simplifying:
ratio = 1.88 + (D5/CH)
The AB/Chest ratio has a minimum 1.88 value and is dynamically larger on the basis of D5 and the chest DDE. The ratio is pack-specific.
49
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Option Going Forward: Solving for AB/Chest Ratio that Corresponds to a Net Impact of 1.5 x on EDE (cont.)
What does all this mean?
The packs torso DDE and non-torso EDEex contributions go into the determination of gradient at this whole body level of concern You can customize the AB/Chest ratio to obtain gradient detection for every multipack at the recorded equivalent whole body level of concern (1.5 x) rather than at the intermediary compartment level of concern There is one gradient pack result (out of 205) 50
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SIGNIFICANCE DETERMINATION INPUT Otto Gustafson 51
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Significance Determination Input
- Palisades ability to assess dose was not compromised
- Dose assessment was performed in accordance with applicable regulations and guidance 52
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Ability to Assess Dose
- Palisades ability to assess dose was not compromised as evidenced by:
- Each worker was assigned 6 OSLDs and 6 EADs which yielded ample information for dose assessment
- The cumulative dose on re-assessment was within 6% of the original
- No individual exceeded the applicable administrative dose guideline
- No individual exceeded an alarm setpoint (and would not have if the additional dose from the re-assessment was applied) 53
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Ability to Assess Dose
- Failures to monitor conservatively, to the extent that they occurred, were not chronic
- There was adequate monitoring and oversight to maintain exposure control
- In terms of the effect on whole body dose dosimetry relocation was necessary for only 1 of 205 packs 54
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Ability to Assess Dose Performance deficiency is not similar to the failures or improper practices cited in IMC 0609, App C.
- the licensee's failure to use a National Voluntary Laboratory Accreditation Program (NVLAP) certified dosimeter processor when required by 10 CFR Part 20, or
- failure of the electronic dosimeters (EDs) to respond to, or record, radiation dose, or
- the improper calibration of instruments or monitors which are used as a basis for establishing protective controls, or
- the improper analysis of bioassay data that results in missed intakes of radioisotopes, or,
- the failure to recognize a radiologic hazard in the work place (i.e., the potential for exposure to alpha emitting, radionuclides resulting in the failure to appropriately assess intakes of these nuclides).
55
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Dose Assessment Inspection Report states:
The inspectors questioned the validity of using the results from all the dosimeters, regardless of worker actions or work activity, to develop the curve to extrapolate virtual abdomen results for workers performing welding/machining activities Palisades response:
The referenced curve was only intended to provide a visible cue into the assumptions that went into the gradient test described earlier. The curve was not used to extrapolate abdomen results for individual workers.
56
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Dose Assessment
- Dosimetric methods are compliant with 10 CFR 20.1201(c)
- Allows assessment of DDE from surveys or other radiation measurements
- If the monitoring device was not in the region of highest exposure
- Or, if the results of individual monitoring are unavailable 57
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Dose Assessment
- Dosimetric methods are aligned with Regulatory Guide 8.34
- Allows evaluation to estimate the actual maximum dose if post exposure evaluations indicate that the maximum dose to a part of the whole body was substantially higher than the dose measured
- EDEex method was used as prescribed in Regulatory Guide 8.40
- EDEex was calculated in accordance with Section C.1 using compartment weighting factors 58
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CONCLUSIONS Tony Williams 59
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Conclusions
- Palisades agrees with the performance deficiency and understands the importance of accurately determining worker exposure:
- The procedure did not adequately incorporate Regulatory Guide 8.40
- Oversight was not adequate for prudently monitoring EDEex use and tungsten vest use 60
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Conclusions
- Palisades has completed a comprehensive dose analysis and determined:
- Actual dose for the CRD housing replacement was 120.4 person-rem versus an original assessment of 113.7 person-rem
- In 17 cases, sufficient gradient existed to warrant dosimeter relocation
- However, less than 1% of entries were > 100 mrem over what was initially assessed
- Based on the results of our analysis, it is reasonable to conclude that the ability to assess dose was not compromised
- Therefore, Palisades considers the safety significance to be very low or green 61
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CLOSING REMARKS Tony Vitale 62