ML20011B116
| ML20011B116 | |
| Person / Time | |
|---|---|
| Issue date: | 11/18/1981 |
| From: | NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| To: | NRC OFFICE OF ADMINISTRATION (ADM) |
| References | |
| NUDOCS 8112040017 | |
| Download: ML20011B116 (1) | |
Text
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t, UNITED STATES 30, 40, 70 Docket I
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MEMORANDUM FOR:
Document Control Desk Document Management Branch Division of Technical Information ar.d Document Control, ADM FROM:
IE Document Management Section Administration Branch Training and Administration Staff, IE
SUBJECT:
SANITIZED OVEREXPOSURE REPORT - PART 20.405 The attached Overexposure Report (Part 20.405) has been sanitized in accordance with the Privacy Act and can now be made publicly available.
IE Document Management Section Administration Branch Training and Administration Staff Office of Inspection and Enforcement
Attachment:
As Stated Above 6.ef)l@Q 9
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AUTOMATION INDUSTRIES, INC.
Fors onal Privacy Infor=ation Delotod-SPERRY PRODUCTS DIVISION in.Accoreance with the SHELTER AOCK ACAD Freedom of Information Act CANBURY. CCNN. C6810 (203) 748-3581 November 4, 1981 E:148
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Re: Docket No. 30-5998 Materials License No. 37-00611-09
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Dear Sir:
On May 15, 1981 a preliminary report on the evaluation of radiation exposure to three of our employees was sent to your office pursuant to 10 CFR 20.405.
Enclosed is a copy of the final Report of Dosimetry Investigation of Overexposure Incident prepared for Automation Industries, Inc. by the consulting firm Radiation Management Corporation. While reaching essentially the same conclusion as to the integrated dose to the extrem-ities of the employees, this report describes in detail the assumptions, methodology, and computations used to estimate dose, Please note that the identity of the three employees is letter-coded throughout the report and that Appendix I is the code key.
The code used in the preliminary report (without a key) accidentally reversed employees A and B.
This report concludes Automation Industries, Inc. investigation into the technical factors of this overexposure incident. Should you have questions concerning this material, please let me know.
Sincerely, N
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Parker E. More and, Jr.,
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Operations Manager - Phoenixville N.E.F.
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REPORT OF 00SIMETRY INVESTIGATION OF OVEREXPOSURE INCIDENT
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TABLE OF CONTENTS i
PAGE I
INTRODUCTION --------------------------------------------------
I EXPERIMENTAL METHODOLOGY --------------------------------------
5 Task A: So u rce De fi n i ti o n --------------------------------
5 Task B1: Tine and Motion Studies, Video Taping -----------
5 Task C: Be a m Do s i me t ry -----------------------------------
6 s
Task B2: Finger Segment Exposure Times and Distances -----
9 Task D:
De p th-Dose De te rmi n a ti on -------------------------
9 8
Task E: Normalized Dose Dete rminations -------------------
10 Task F: H i s to ri c al D a ta ----------------------------------
16 Task G: Dos e Cal cul a ti o n s --------------------------------
16 i
22 ERROR ANALYSIS ------------------------------------------------
F CON CLUS IONS AN D RECOMMEN DATIONS -------------------------------
23
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AP P E N D I X I - -- - -- - - - -- - - -- -- - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - --- - -
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LIST OF TABLES PAGE 1
Beam Dose-Rate Profile 8
11 2.1 Exposure Tines and Distances - Subject A 12 2.2 Exposure Tines and Distances - Subject B 2.2 Exposure Times and Distances - Subject B (cont.) ----------- 13 8
2.3 Exposure Times and Distances - Subject C 14 s
15 3
Mrem Per Curie Per Wipe 1
j 4
Source Production and Labor Distribution 17 5.1 Exposure Data for Subject A 13 i
1 5.2 Exposure Data for Subject B 19 0
5.3 Exposure Data for Subject C 20 1
6 Error Determination Summary 22 6
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LIST OF FIGURES PAGE d
1 1
Ir-192 Sources 2
2.1 Source Cleaning Bank 2
2.2 Cross Section of Cleaning Bank 2
3.1 Operator U;ing Cleaning Bank 2
a 3.2 Close-up of Hands 1
3 4
Right Hand of Subject A, Feb.1981 i
5 l
5 View of Experimental Layout 6
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Typical Dosimetry Array 7
7 Typical Dose-Rate Profile l
8 Dose-Rate as a Function of Distance 8
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Relative Depth-Dose Finger Phantom i
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10 Relative Depth-Dose Within Finger Phantom 10 11.1 Dose Distribution for Subjects A, B, and C 21 6
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J IllTRODUCTI0ff 2
The purpose of this report is to describe the method and document the data used to assign doses to three individuals at Automation Industries (AI) who 3
have been involved in the source cleaning procedure using the ten hole clean-ing bank.
The facility is a producer of Ir-192 sources used for industrial radiography.
The product is an encapsulated sealed source, at the end of a flexible steel cable, as per Figure 1.
The markings are for this test and not a part of the typical source.
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P Fi9 1 - Ir-192 Sources The sources arrive as irradiated Ir-192 metal slugs.
From 10 - 250 curies of these slugs are loaded into the capsule, welded-closed, grossly decon-taminated, then calibrated for output. All of these operations are per-formed with remote manipulators within the hot cell. The sources are then remotely transferred from the hot cell into a cleaning and storage fixture.
This device is a lead cylinder, approximately 14" diameter by 14" long, and contains ten "J" shaped cavities, approximately 1/2" in diameter. When the sources are fully inserted into the cleaning bank, the shielding is sufficient that external dose rates are less than 100 mR/hr at the surface.
Figures 2.1 and 2.2 show the source cleaning bank and a cross section of the J-tube.
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In order to comply with HRC requirements for sealed sources, a leak test must be performed documenting that external contamination is less than 0.005 uCi.
I The testing procedure simply involves inserting several pipe-stem cleaners, moistened with "Radiac Wash" (a conmercially available cleansing agent), into
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the J-tube and manipulating them to assure maximum contact with the source.
t Since the sources are produced inside a hot cell, they are routinely contami-nated to a small degree on the exterior, and therefore the first few wipes function as a cleaning step, while the last one is the leak test.
The general technique the operators used, although each operator had his own variation, was to grasp the connector end of the source with his right thumb and fingertips, withdraw it past the retaining ball to allow insertion of the pipe-stem cleaners, insert the cleaners with his left hand, manipulate the i
source both up and down about an inch while rotating it, for about 30 seconds, and finally withdrawing the cleaners and restoring the sources to the fully inserted position.
Figures 3.1 and 3.2 show the operator body and hand positions.
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In January 1981 two of the three e@loyees involved in the cleaning operation exhibited unusual and identical symptoms and were sent to Radiation fianagement Corporation for examination. A medical diagnosis of chronic radiodermatitis was made.
1 Retrospectively it was determined that Egloyee A had first noticed a distor-ted nail on his right thunt in February,1979.
In July 1980 there was marked distortion of this nail.
In addition, the right thumb was red with dry, scal-ing skin. The latter signs were present to a lesser degree on the distal (outer) portion of the right first finger and less so on the distal portion of the right second finger. Figure 4 shows the hand of Subject A in February, 1981.
Employee B first noted cracking of the thumb nail and redness, dryness and fissuring of the distal right thunb in July,1980. He also had less in-volvement of the right first and second fingers with minimal changes in the 8
left first and second fingers.
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%.8 Fig. 4 - Right Hand of Subject A, Feb.1981 It was only after two of the three subjects exhibited identical symptoms, that it was realized that this procedure was deficient. Because the tube is a J-shape instead of the "C" or "S" shapes used on shields designed to be sold with the sources, there is a relatively long straight section of the source tube.
Thus when the connector end of the source is withdrawn about 1", the source is essentially unshielded about the axis of the straight position of the J-tube.
Therefore, during the bulk of the cleaning time, the position of the fingertips, in a 1/2" radius cylinder above the entrance of the J-tube, were about 61/2" from an unshielded nominal 100 Ci source.
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The nature of the overexposure presented several difficulties, complicating an accurate and precise dosimetry assignment. The exposures were incurred over a long period of tine (2 months to 8 years). The beam was quite narrow ( 1" in diamete r). The exposure was dependent upon the cleaning techniques of the par-ticular individual performing the task, and was different for the various dif-a i
ferent sources being cleaned. Budget and time constraints did not allow an extremely detailed study. Because of the previous overexposure, and the resul-tant medical complications, any experimental technique resulting in additional extremity dose above the annual whole body limit wes also ruled out.
A study protocol was then devised to derive dose estimates adequate in accuracy for medical use in reconmending appropriate treatment or follow-up, with suffi-cient detail to serve as an adequate scientific record of the exposure for his-torical projections, and sufficient to satisfy regulatory criteria for overex-posure investigations.
The study protocol consisted of the following tasks:
A) A review of sources produced over the past 10 years to select those representing at least 90% of the total dose.
B) Using mock sources of those configurations, perform time and motion studies to determine the time of exposure per wipe and the fingertip positions during the exposure period.
I C) Using TLDs, map the vertical and radial dose profile of the exposure beam.
D) Using thin TLDs, in an " extrapolation chamber" arrangement, determine the depth-dose profile.
L E) Using information from B, C, and D, derive the dose per curie of source per wipe for each individual.
F) Using historical production records and interviews with the subjects and other personnel, obtain:
- 1) Average curies per source
- 2) Number of sources per year of each type 3)
Fraction of sources cleaned by each subject per year
- 4) Average number of wipes 'used per source G) Using information from E and F, calculate the total dose to each ex-
. posed portion of the finger and the dose to the maximum finger segment for each year.
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EXPERIMEllTAL HETH0D0 LOGY Task A: Source Definition.
2 The results of the source production history greatly simplified the study. The facility encapsulates both Co-60 and Ir-192 sources, but the Co-60 source pro-duction figures are a very small percentage of the total, and those sources have 8
a very long flexible cable. Therefore, when those sources are cleaned, they are held much further away.
It was therefore concluded that Co-60 sources contribu-ted a negligible amount to the fingertip dose.
Although there are at least 6 other varieties of sources, there are only two major source types which need to be considered. They are models A and li. The other source types are only minor variants of these and these variations are well within the dosimetry tolerances. Therefore, only source types A and li were in the study.
Task B1: Time and Motion Studies, Video Taping.
i On April 15, 1981, these tests were conducted. The three employees were briefed prior to the test.
It was stressed that the purpose was to accurately determine the dose, not to assess blame. They were instructed to clean the dunrqy sources exactly as they had been in the past. The subjects were very cooperative, and there is no reason to believe that they performed these tests in a manner dif-I ferent from the real source cleaning procedure.
J The tests were conducted in the same area and under the same conditions as during p
the cleaning. The only modifications were to allow video taping of the procedures and reasonably accurate measurement of the finger locations on the replay of the j
tapes. Figure 5 shows the setup.
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8 To aid in the data reduction, the cleaning bank was marked to show the axis of the beam. The duply sources were marked in 1/2" grids to determine the distance from the fingertip to the scurce. A ruler, marked in 1" gradua-tions was also in the video camera's field of view for measurement calibra-tion during playback. T1e mirror was in the field of view to simultaneously view the beam area from two directions. A clock was in the field of view to determine the exposure time. Each employee was fitted with surgical gloves. The gloves were then marked with black ink to separate the joints and to separate the lateral and medial portion of each joint (see Figure 3.2).
Since the employees routinely wore gloves during this procedure, it was not felt that this changed their cleaning technique significantly.
Each employee, without being watched by the others, performed 10 cleanings of the "A" source and 10 cleanings of the "N" source. A card with the iden-tification of the person, the source type, and the cleaning sequence number i
l was also in the field of view of the camera.
Task C: Beam Dosimetry.
The purpose of this task was to define the limits of the exposure beam for various source wathdrawl positions, and to detemine the dose within the beam.
The dosimeters and readout service was provided by Teledyne-Isotopes.
For this task, the dosimeters were LiF-7 Teflon rods, Imm diameter x 6mm long.
During the simulated cleaning tests, it was observed that the maximum distance the connector end was withdrawn was 21/2". Survey meter readings indicated that until the source is withdrawn greater than 1", the dose rate is negligible.
Therefore, the distance range of 1" - 3" was mapped. The rod TLDs were inserted into a styrofoam fixture block in the configuration shown in Figure 6.
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2 Shown is one-half of the block. The other half is identical, but is at 90 to 8
the plane formed by the dosimeters shown. This dosimetry array was fixed to the cleaning bank, with the center line of the array on the center line of the straight portion of the source J-tube. The dosimeters were 1", 2" and 3" above the sur-face of the cleaning bank.
Four exposures were made using four separate dosimetry fixtures. One exposure each was made with the connector end of the source withdrawn 1",1 1/2", 2" and 2 1/2". Exposure times were 10 - 15 minutes, and used a 63 Ci Ir-192 N type source. Since the overall length of the N and A sources are within 1/8" of each other, only the N source was used.
Figure 7 presents the typical set of results.
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Cleaning Sant Ants Cleaning Bank Amis DOSIMETRYPOSITION(INCHESFROMh Fig. 7 - Typical Dose-Rate Profile t
Several of the graphs showed some assymetry, as this one, or show a dip in the center of the curve.
It is believed that these are artifacts of the dosimetry placement procedure, or attenuation by the cable. An average dose rate was calculated by averaging the highest group of points, and a beam width was calculated from the widest half of the curve. The beam profile was assumed to be ideal, i.e., it was assumed to have uniform dose rate across the beam, and zero dose rate outside the beam. The results are pre-sented in Table 1.
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TABLE 1 BEAM DOSE-RATE PROFILE SOURCE D0SIMETER SOURCE TO C0fitlECTOR DISTAtlCE FR0!!
DOSIMETER DOSE RATE BEAM WIDTH POSITI0tl(in.)
BAtlK (in.)
DISTAtlCE mr/sec.
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7 1/2 22 3/4 3
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51 1
2 1
5 1/2 112 1/2 2
6 1/2 62 1
3 7 1/2 57 1
2 1/2 1
5 100 1 1/2 2
6 83 1 1/4 3
7 60 1 1/4 Figure 8 is a plot of dose rate for the 64 Curie source. As can be seen, once the source has been withdrawn', past the point where the connector is 1 1/2" above i
the cleaning bank, the dose rate is independent of the withdrawl distance. The j
dose-rate is only dependent upon source-to-detector distance. When the connec-tor is 1" extended, the dose rate at a fixed source-to-detector distance is re-duced by 50%. It was therefore assumed that fingertips were only exposed when I
the source connector was withdrawn 1" gmater, and that the exposure dose-rate is as per the average line in Figure 8, and is constant across the beam diameter of dimensions in Table 1.
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Fig. 8 - Dose-Rate as a Function of Distance 8
J Task B2: Finger Segment Exposure Times and Distances.
e The video tapes of the source cleanings were reviewed. The conical exposure region of dimensions in Table 1, was marked upon the playback screen. The s
maximum time of exposure for each exposed finger segment, and the distance from the finger segment to the source was recorded. The exposure time was obtained by viewing each nominal 30 second cleaning procedure. A stop watch was started when both the finger segment was within the beam and the connector was withdrawn more than 1".
The source-finger distance was constant for each cleaning, as the grip did not change. This distance was calculated using the graduations on the source cable, and the ball as a reference. Tables 2.1, 2.2 and 2.3 give this data for each finger segment.
8 Task D:
Depth-Dose Determination.
I In order to determine the relationship between the " free-air" dose in Task C and the dose to the skin or bone, relative depth-dose measurements were made.
This was done using an " extrapolation chamber" arrangement consisting of TLDs in a plexiglass finger phantom, t
2 Two thicknesses of LiF-7 Teflon TLDs were used. Those labeled "u" were 5 mg/cm 1
thick x 6m diameter. Because of their small size, they were individually cali-brated by a post igradiation exposure. These thin TLDs were stacked to covgr the first 15 mg/cm' entrance position of the finger. A spacer of 160 mg/cm' plexiglass was then used, followed by a 40 mg/cm' x 6mm diameter LiF-7 Teflon 4
TLD disc. These discs were manufactured as 1 cm diameter, but were cut to j
size with a punch. They were then individually calibrated by a post-irradia-tion exposure. The exposure apparatus is as per Figure 9.
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were placed in 6m diameter holes drilled on 7mm center line spacings.
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a The rod was exposed at approximately 2" distance, with the source connector withdrawn two inches. The rod was positioned with the center line of the "A" group of dosimeters on the axis of the center line of the straight portion of 2
the J-tube. At three positions (A, B and C) at 200 mg/cm depth, both a thin and thick dosimeter was placed. This indicated a relative over-response of the thin dosimeters by 26%. The thin readings were reduced by this factor.
Figum 10 shows the results of the relative depth-dose measurements.
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I Fig.10 - Relative Depth-Dose Within Finger Phantom The curves from Figure 10 indicate some bgild-up within the beam areas (curve A),
1 but this occurs within the first 10 mg/cm of tissue. All other points, including i
those which would be occupied by the basal gkin layer and the bone of the finger-tip am within 15% of that at 40 - 50 mg/cnf, the average thickness of the TLD mds used in the Beam Dosimetry Study, Task B.
Therefore there is no reason to assign skin or bone doses any diffemnt from each other or from the doses derived from data using Table 1.
Task E: Normalized Dose Determinations.
The data in Table 2.1 through 2.3 along with the dose rate vs. distance curves in Figum 8 were used to detennine the normalized dose.
For each finger segment half, the exposum time was multiplied by the dose rate at that distance, to de-termine dose. This was done for all ten cleaning trials of the first subject.
The consistency of the data, indicated that only 5 viewings would be adequate for the others. Table 3 sunmarizes these results.
In all-cases, the medial portion of outer joint of the right thunb received the maximum dose. Al so, the -
"A" source, as speculated, caused the highest dose per cleaning. This is due to the position of the mtention ball, as the cleaning is easier when the ball is outside the J-tube, 1
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TABLE 2.1 EXPOSURE TIMES AND DISTANCES - SUBJECT A SOURCE WIPE #
LEFT HAND RIGHT HAND Dist(in)
THUMB INDEX FINGER MIDDLE FINGER THUMB INDEX FINGER MIDDLE FINGER Joint 1 2
1 2
3 1
2 1
2 1
2 3
1 2
Time (sec) 1 0
1 0
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N 1
Dist.
51 55 -
66 55 -
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6 66 6 66 66 6 64 6 66 6 66 6 64 6
13 13 7 7 6 6 6 6 3 3 7 7
3 3
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Time 4
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- 56 6 -
2 Dist.
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7 7 3 3
3 Di s t.
56 5$ -
64 55 -
6 66 6 66 64 6 64 6 66 6 64 6 64 6
56 6 3
3 -
14 14 7 7 7 7 7 7 4 4
7 7 3 3
- 3 3 -
Time 3
3 U$
4 Dist.
56 55 64 SI -
6 66 6 64 64 6 64 6 64 6 64 6 64 6
- 54 6
4 4 -
18 18 9 9 9 9 9 9 4 4 9 9 4 4
4 4
Time 4
4 5
Dist.
56 Sj 64 Sj -
56 6 -
6 66 6 64 66 6 64 6 64 6 66 6 61 6
4 4 -
- 4 4 -
20 20 10 10 10 10 10 10 5 5 10 10 5 5
Time 4
4 A
1 Dist.
56 SI -
64 Sj -
54 6 -
6 66 6 66 66 6 64 6 64 6 66 6
66 6
3 3-23 23 11 11 16 16 16 16 4 4
7 7 4 4
Time 3
3 3
3 64 6{ -
2 Dis t.
56 SJ -
- 56 6 -
6 66 6 66 64 6 64 6 66 6 64 6 66 6
Time 2
2 2
2
- 2 2 -
24 24 12 12 16 16 16 16 4 4
8 8 4 4
Sj 55 -
- 55 Sj -
6 66 6 64 66 6 64 6 64 6 64 6 64 6
3 Di s t.
6 6
5 5 -
25 25 13 13 17 17 17 17 5 5 8 8 4 4
Time 5
5 5
5
-. 5j SI -
- SI 55 -
6 66 6 66 64 6 66 6 64 6 64 6 66 6
14 Dist.
6 6
2 2 -
- 2 2 -
23 23 11 11 15 15 15 15 5 5 7 7 3 3
Time 2
2 5
Dis t.
6 6
- S$ 55 -
6 66 6 66 66 6 66 6 64 6
64 6 64 6
Time 7
7 7
7 -
22 22 11 11 14 14 14-14 3 3 6 6 2 2
m.
w TABLE 2.2 EXPOSURE TIMES AND DISTANCES - SUBJECT B SOURCE WIPE #
LEFT HAND RIGHT HAND Dist(in)
THtM INDEX FINER MIDDLE FINER THts INDEX FINGER MIDDLE FINER Joint 1 2
1 2
3 1
2 1
2 1
2 3
1 2
Tine (sec) 1 0
1 0
1 0
1 0 1 0
I O i 0
I O
I O I O I O I O
I O
1 0
N 1
Dist.
56 54
- 56 56 64 66 7 7
6 d 6 e6 6 M M7 7
6 6
Tine 4
4 4
4 4
4 4 4
12 12 9 9 12 12 9 9 9 9 9 9 -
2 Dist.
56 5
- Si Si 66 S7 7 - -
6 e6 64 6 6 d M7 7 6 6
Tine 4
4 4
4 4 4 4 4 - -
10 10 8 8 10 10 8 8 8 8 8 8
3 Dist.
56 S$
Si 56 66 6i 7 7 - -
6 66 6 61 6 6 64 66 7 7 6 6 -
Tfse 4
4 4
4 4 4 4 4 - -
17 17 13 13 17 17 13 13 13 13 13 13 -
4 Dist.
Si Sj 51 56 66 66 7 7 -
6 66 6 61 6 6 61 66 7 7 6 6
to Tine 4
4 4
4 4 4 4 4 -
16 16 12 12 16 16 12 12 12 12 12 12 -
5 Dist.
56 55 -
54 51 66 64 7 7 -
6 66 6 64 6 6 64 66 7 7 6 6
Tine 4
4 4
4 4 4 4 4 -
14 14 10 10 14 14 10 10 10 10 10 10 6
Dist.
Si SI Si 54 66 64 7 7 -
6 66 6 6i 6 6 64 60 7 7 6 6 -
Tise 4
4 4
4 4 4 4 4
13 13 9 9 13 13 3 9 9 9 9 9 -
7' Dist.
56 Sj
- 56 56 66 66 7 7
6 66 6 6! 6 6 65 66 7 7 6 6
Time 5
5 5
5 5
5 5 5 -
17 17 13 13 17 17 13 13 13 13 13 13 8
Dist.
56 55
- 56 56 66 61 7 7 -
6 66 6 64 6 6 65 66 7 7 6 6 -
Tise 6
6
- 6 6
6 6 6 6 -
17 17 14 14 17 17 14 14 14 14 14 14 -
9 Dist.
53 55 51 Si Gi 66 7 7 -
6 61 6 66 6 6 65 61 7 7 6 6
Time 4
4 4
4 4 4 4 4 -
18 18 14 14 18 18 14 14 14 14 14 14 -
10 Dist.
Sg 5! -
- 56 56 61 66 7 7 -
6 65 6 64 6 6 61 65 7 7 6
'6 Time 4.5 4.5 4.5 4.5 4.5 4.5 4.5 4.5-20 20 16 16 20 20 16 16 16 16 16 16 -
.,w.
an -
_~
_w
_m a
TABLE 2.2 (cont.)
EXPOSURE TIES AND DISTANCES - SUBJECT 6 SOURCE WIPE i LEFT HAND RIGHT HAND Dist (in)
THUMB INDEX FINGER MIDDLE FINGER THUMB INDEX FINGER MIDDLE FINGER Joint 1 2
1 2
3 1
3 1
2 1
2 3
1 2
Time (sec)
I O
I O
I O I O
I O I O I O
I O I O I O I O I O
I O
I O
A 1
Dist.
56 51 54 56 66 66 7 7 -
6 66 6 Si 6 6 64 El 7 76 6
- 5 5.5 5
5 5 -
- 26 26 20 20 26 26 20 20 20 20 20 20 Time 5
5 2
Dist.
56 Sj 6
64 6 66 6 6 64 66 7 7 6 6
56 56 66 66 7 7
- 6 6 6 6 6 6 -
19 19 15 15 19 19 15 15 15 15 15 15 Time 6
6 3
Dist.
Si - 53
- Si 54 64 66 7 7 -
6 64 6 66 6 6 66 66 7 7 6 6 -
18 18 14 14 18 18 14' 14 14
'14 14 14 Time 3
3 3
3 3 3
3 3 -
- 56 56 66 66 7 7 -
6 66 6 66 6 6 64 bi 7 7' 6T6 4
Dist.
56 55
[3 Time 5
5 5
5 5 5
5 5 -
- 20 20 16 16 20 20 16 16 16 716 16-16 5
Dist.
56 SI -
- 56 56 66 64 77 7 -
6 64 6 61 6 6 66 61 7 7 6 6
- 4 4 4 4
4 4 -
19 19 15 15 19 19 15 15 15 15 15 15 Tine 4
4 e
4
TABLE 2.3 EXPOSURE TIES #iD DIST# ICES - SUBJECT C LOURCE WIPE #
LEFT HAND RIGHT HAND Dist (in)
THUMB INDEX FINGER MIDDLE FINGER THUMB INDEX FINGER MIDDLE FINGER Joint 1 2
1 2
3 1
2 1
2 1
2 3
1 2
Tine (sec)
I O
I O
I O I O I O I O I O
I O I O I O I O I O
I O
I O
5 -
6 66 6 66 6 6 66 6 7 7 -
56 5-N 1
Dist.
54 54 -
24 24 5 5 24 24 12 12 5 5 -
Time 4
4 4
4 -
1 -
2 Dist.
56 55 -
56 51 -
6 66 6 66 6 6 66 6 7 7
7 7 -
32 32 7 7 32 32 12 12 5 5 -
Time 7
7 3
Dist.
56 5 56 55 -
6 66 6 66 6 6 66 6 7 7 -
7 7 -
30 30 5 5 30 30 15 15 3 3
Time 7
7 4
Dis t.
56 5$ -
54 55 -
6 66 6 66 6 6 64 6 7 7
s.
32 32 5 5 32 32 17 17 5 5 -
Time 12 12
- 12 12 5
Dist.
Si 55 -
56 55 -
6 66 6 64 6 6 66 6 7 7
5 5 -
42 42 4 4 42 42 20 20 7 7
Time 5
5 A
1 Dist.
56 S$ -
- 56 S$ -
6 64 6 64 6 6 66 6 7 7 -
13 13 -
47 47 10 10 47 47 20 20 10 10 Time 13.13 66 64 -
6 66 6 64 6 6 64 6 7 7 -
2 Dist.
6 6
Time 14 14
- 14 14 -
31 31 8 8 31 31 15 15 8 8 -
5$ 5 -
6 66 6 66 6 6 66 6 7 7 -
3 Di s t.
6 5
- 24 24 5 5 24 24 12 12 5 5
Time 5
5 5
5 4
Dist.
Si 5! -
SI Si-6 65 6 65 6 6 6i 6 7 7 -
Time 8
8 8
8 -
38 38 12 12 38 38 19 19 4 4 -
3 3
6 666 666 6 66 6 7 7 -
- 51 54-5 Di s t.
Sn 5x Time 6
6
- 6 6
38 38 15 15 38 38 20 20 4 4 -
9
a __
u.
~
TABLE 3 MREM PER CURIE PER WIPE RIGHT HAND LEFT HALO THUps INDEX FINER MIDDLE FINER THlNB INDEX FINGER MIDDLE FINGER SUBJ SOURCE Joint 1 2
1 2
3 1
2 1
2 1
2 3
1 2
CODE TYPE I
O I
O I
O I
O I
O I
O I
O I
O I
O I
O I
O I
O I
O I
O A-A 5.3 5.4 5.6 5.6 4.7 4.4 32.3 27.5 16.0 13.6 18.3 21.5 18.3 21.5 4.9 5.8 8.5 9.9 4.0 4.7 N
5.9 5.4 4.8 5.4 5.9.5.0 21.3 18.1 11.0 9.4 8.9 10.5 8.9 10.5 4.5 5.2 9.4 11.0 4.2 5.0
% of 21.3 20.1 19.4 20.5 19.8 17.5 100 85.1 50.4 42.9 50.7 59.7 50.7 59.7 17.5 20.5 33.4 39.0 15.3 18.1 max.
8' A
7.6 6.9 7.6 7.6 5.4 5.4 4.6 4.6 28.2 24.0 22.1 18.8 28.2 28.2 18.8 18.8 15.2 15.2 22.1 22.1 j
l N
7.2 6.6 7.2 7.2 5.1 5.1 4.1 4.1 21.3 18.1 16.3 13.9 21.3 21.3 13.9 13.9 11.2 11.2 16.3 16.3
% of 29.9 27.3 29.9 29.9 21.2 21.2 17.6 17.6 100 85.1 77.6 66.1 100 100 66.1 66.1 53.3 53.3 77.6 77.6 max.
C A
14.2 13.5 14.2 14.0 12.5 12.5 49.2 41.8 13.8 11.4 49.2 49.2 20.2 23.8 5.9 5.9 N
11.6 10.6 11.6 10.6 1.7 44.2 37.6 7.2 5.844.244.217.921.0 4.8 4.8
. % of 27.6 25.8 27.6 26.3 15.2 13.4 100 85.0 22.5 18.4 100 100 40.8 48.0 11.5 11.5 ma x.
V J
Task F: Historical Data.
4 The infomation within this section has been supplied by the source production facility personnel. The production has been remarkably stable in terms of pro-duct distribution and quantity of sources produced. Production records were used to determine the total number of sources produced from 1972 through January 1981, when this cleaning technique was discontinued. The distribution of sources by source stmngth was not easy to find for earlier years, but personnel indica-ted the product mix has been essentially constant from year to year.
1980 pro-duction data indicates sources were produced from 25 to 250 Ci, with 75% of the sources being nominally 110 C1. The average source strength of 97 Curies was detemined by dividing the total number of Curies produced by the total number of sources produced.
The mlative distribution of A and N sources was independently estimated by several production personnel and the estimates averaged.
The fraction of sources cleaned by each technician was obtained from the average of independent estimates from each of the technicians.
The average number of wipes per source was obtained from recent historical records, and for earlier years from average independent estimates by the technicians.
In 1980, the average number of wipes per source dramatically incmased. This was due to two factors. Prior to 1980, the supplier of I
the irradiated encapsulated pellets was GE, Vallecitos. After that reactor d
was shut down, the material supplied by Oak Ridge contained significantly mom loose contamination, thus requiring more decontamination. Also a large p
(US government) customer began specifying contamination levels ten times more mstrictive than NRC regulations, therefore requiring more cleanings per source. The summary of the information obtained in this task is pre-sented in Table 4.
Task G:
Dose Calculations.
This task was simply to multiply the relevant data by year and source type as per the following formula.
DOSE
"# of ~
97 Ci '
~
~
fraction fraction ~
-maximum ~
~
- of FOR wipes per sources of sources of sources mr/ wipe
=
x SOURCE per source per of that cleaned by
-per Ci -
TYPE
_ source _
year _
type subject _
This was done for each year for each subject, for both source types and for the r
maximum finger segment half. The doses for source A and source N were then added to determine the dose per year. The total dose is simply a sum with the yearly doses. Tables 5.1, 5.2 and 5.3 contain the data used and the results obtained.
The number of ssignificant figures in the final dose does not represent a corres-ponding level of precision. The dose to the other finger segments were estimated using the maximum finger segment dose and the average % of maximum entry in Table 3.
These results are graphically presented in figures 11.1, 11.2 and 11.3 16
TABLE 4 SOURCE PRODUCTION AND LABOR DISTRIBUTION 1981 1980 1979 1978 1977 1976 1975 1974 1973 (Jan)
Sources Produced 54 864 1009 1012 899 892 916 793 773
% Cleaned by A
0 80 85 85 85 85 85 85 70 8
~0 12 15 15 15 15 15 15 0
C 100 8
0 0
0 0
0 0
0 Avg wipes per source 14 14 6
6 6
6 6
6 6
% by type A-20 20 20 20 30 50 70 90 100 of source N
80 80 80 80 70 50 30 10 0
4 g
G1 J
TABLE 5.1 i
EXPOSURE DATA FOR SC3 JECT A i
YEAR SOURCE
- OF AVG f MAXIMUM Nt#EER SOURCE FRACTION JOSE SEGMENT OOSE TO TYPE WIPES OF Cl w/ WIPE OF SOURCES TYPE OF SOURCES FOR LOCATION MAXIMUM PER PER PER C1 PER YEAR FRACTION CLEANED SEGMENT NUMBER SEGMENT 8
SOURCE SOURCE FOR YEAR BY SUBJ.
(R)
(REM)
-1981 A
14 97
- 32. 3 54
.20 0
0 17 0
N 14 97 21.3 54
.80 0
0 17 1980 A
14 97 32. 3 864
.20
.8 910 17 22066 N
14 97 21.3 864
.80 2400 17
- ~
1979 A
6 97
- 32. 3 1009
.20
.85 569 17 11730 i
N 6
97 21.3 1009
.80 1501 17 19 78 A
6 97
- 32. 3 1012
.20
.85 571 17 11764 N
6 97 21.3 1012
.80 1505 17 I
1977 A
6 97 32.3 899
.3
.85 760 17 10937 N
6 97 21.3 899
.7 1170 17 1976 A
6 97
- 32. 3 892
.5
.85 1258 17 11826 N
6 97 21.3 892
.5 829 17 r
19 75 A
6 97 32.3 916
.7
.85 1808 17 13141 N
6 97 21.3 916
.3 511 17
?
1974 A
6 97
- 32. 3 79 3 9
.85 2012 17 12234 N
6 97-21.3 793
.1 14 7 17 1973 A
6 97 32.3 773 1.0
.7 10172 17 10172 N
6 97 21.3 773 0
0 17 i
TOTAL
- 103g10, e-4 i
4 s
18
-e 4
=
J s
3 TABLE 5.2 EXPOSURE DATA FOR SUBJECT B s
YEAR SOURCE f 0F AVG f MAXIMUM NWBER SOURCE FRACTION DOSE SE9tEffr DOSE TO TYPE WIPES OF Ci er/ WIPE OF SOURCES TYPE OF SOURCES FOR LOCATION MAXIMUM PER PER PER Ci PER YEAR FRACTION CLEANED SE(MENT NUIEER SEGMENT SOURCE SOURCE FOR YEAR BY St2J.
(R)
(REM) 1981 A
14 97 28.2 54
.20 0
0 17 0
N 14 97 21.3 54
.80 0
0 17 1980 A
14 97 28.2 864
.20
.12 5294 17 3193 i
N 14 97 21.3 864
.80 15995 17 1
1979 A
6 97 28.2 1009
.20
.15 2815 17 1998 N
6 97 21.3 1009
.80 8506 17 i
1978 A
6 97 28.2 10 12 20
.15 2824 17 2004 N
6 97 21.3 1012
.80 8531 17 I
I 1977 A
6 97 28.2 899
.3
.15 3762 17 1834 N
6 97 21.3 899
.7 6631 17 I
i 1976 A
6 97 28.2 892
.5
.15 6222 17 1927 N
6 97 21.3 892
.5 4700 17 19 75 A
6 97 28.2 916
.7
.15 8945 17 2090 N
6 97 21.3 916
.3 2896 17 4
1974 A
6 97 28.2 793
.9
.15 9956 17 1904 N
6 97 21.3 793
.1 836
. 17 1973 A
6 97 28.2 773 1.0 0
8881 17-0 N
6 97 21.3 773 0
0
-- 17 TOTAL 14950 1
i t
19
2 a
TABLE 5.3 EF05URE DATA FOR SUBJECT C YEAR SOURCE
- OF AVG i MXIMUM NUlGER SOURCE FRACTION COSE SEGriENT DOSE TO TYPE WIPES OF Ci ar/ WIPE OF SOURCES TYPE OF SOURCES FOR LOCATION MAXIMUM PER PER PER Ci PER YEAR FRACTION CLEANED SEG4ENT NUMBER SEGMENT SOURCE SOURCE FOR YEAR BY SUBJ.
(R)
(REM) 1981 A
14 97 49.2 54
.20 1
722 17 3315 N
14 97 44.2 54
.80 1
2593 17 1980 A
14 97 49.2 864
.20
.08 924 17 4243 N
14 97 44.2 864
.80 3319 17 19 79 A
6 97 49.2 1009
.20 0
0 17 0
N 6
97 a4.2 1009
.80 0
17 1978 A
6 97 49.2 10 12
.20 0
0 17 0
N 6
97 44.2 10 12
.80 0
17 1977 A
6 97 49.2 899
.3 0
0 17 0
N 6
97 44.2 899
.7 0
17 I
j 19 76 A
6 97 49.2 892
.5 0
0 17 0
N 6
97 44.2 892
.5 0
17 19 75 A
6-'
97 49.2 916
.7 0
0 17 0
N 6
97 44.2 9 16
.3 0
17 1974 A
6 97 49.2 793
.9 0
0 17 0
N 6
97 44.2 793
.1 0
17 1973 A
6 97 49.2 773 1.0 0
0 17 0
N 6
97 44.2 773 0
0 17 TOTAL 7558 l
i i
l l
20 9
3 ESTIMATED TOTAL DOSE IN THOUSANDS OF REM TO FINGER SEGMENTS d
Ch r
- f R
J t
G
^
\\
l CJ SUBJECT A g&
t e
/
I 4
RIGHT HAND urt mMD 8
\\
o l
P
- 4 a
s O
t^ m I
I
{
l m
1 SUBJECT B
/
h Op RIGHT HAND LEFT HAND
\\
Ch p
q s
I e
SusaECT C TT h
/
LEFT HAND RIGHT HAND
\\
Figures 11.1, 11.2, 11.3 - Dose' Distribution for Subjects A, B, and C 21 li
O ERROR ANALYSIS 1
e e
o 7
a I
L t
A e
4 l
1 1
a.
s a.
a ERROR ANALYSIS i
In an attempt to estimate the.overall uncertainty in the assigned results, a simplified non-rigorous error analysis was made. No atte@ t was made to 3
separate errors in accuracy from errors in precision. Both were included.
Each step of the calculation was evaluated to determine an error estimate.
Some were sigly estimated, as no hard data exists. Some errors were cal-culated from the range of possible choices. The relative range of data or 8
msults was assumed to be equal to 4 standard deviations. Where multiple observations of data were made, the percent standard deviations was calcu-lated.
Since the calculation procedure is essentially a series of multiplications, each standard deviation was expressed as a % of the mean, and all results 3
conbined in quadrature to get the total error estimate. Table 6 sumarizes i
this data. The overall error estimate is 46% which is believed to fairly represent the uncertainty of the dose estimates at any one point of the i
finger segment.
1 TABLE 6 ERROR DETERMINATION
SUMMARY
SOURCE.0F ERROR
' % STANDARD METHOD *
(
DEVIATION i
Neglecting Co-60 contribution 2
E Assuming only 2 source types 1
C Precision of TLD-rod readings 1
M Accuracy of TLD-rod readings 10 E
Dose rate vs distance from source 17 M
Finger exposure time 10 C
Finger distance from source 4
C Depth dose non-unifomity 8
C Spatial variation over exposed portion of fingers 8
C Cleaning technique precision 28 M
Cleaning duty assignment 15 E
Wipes per source 20 E
Source type production 10 E
Average source stmngth 5
E Total combined error estimate 46 estimated l
E
=
calculated from relative range C
l
=
measumd from multiple observations M
=
22
C CONCLUSION & RECOMfENDATIONS U
T f
i f
4 1
L
[
8 a
l i
I s
a-i
I CONCLUSIONS AND RECOMMEllDATIONS J
It is recommended that the following doses be assigned for the subjects. The location of the maximum dose is the left (medial) half of the outer joint of J
the right thumb.
Depth dose measurements indicate the sane dose for the skin as for the bone of the thumb. The subject identification is as per Appendix I, Subject Identification. The number of significant figures does not indi-cate a corresponding level of precision. The uncertainty in the dose estimate 3
is 46%.
s DOSE IN REM TO MAXIMUM FINGER SEGMENT S UB.
1981 1980 1979 1978 1977 1976 1975 1974 1973 TOTAL Jan A
0 22,066 11,730 11,764 10,937 11,826 13,141 12,237 10,172 103,870 B
0 3,193 1,998 2,004 1,834 1,927 2,090 1,904 0
14,950 t
C 3,315 4,243 0
0 0
0 0
0 0
7,558 These doses are consistent with the onset and degree of clinical signs on the right first, second and third fingers of Employees A and B.
The fingers could m
have received a few hundred rem per month for years without developing obvious
' r J
changes to a lay person.
It is likely that the higher exposures ' received by Employees A and B in early 1980 combined with the cumulative exposures over the past years resulted in the noticeable changes in the fingers in the latter i
part of 1980. The dosimetry supports this conclusion more so for Employee A than fer Enployee B.
W i
23
c APPENDIX I I
s=
1 9
1 4
1 L
O
[.
a e
a e
4 I
i 1
A.
a.
e S.
O
5 APPENDIX I
)
SUBJECT CODE FLAME A
0 4
C M
24
-