ML20213F769
| ML20213F769 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 11/10/1986 |
| From: | Standerfer F GENERAL PUBLIC UTILITIES CORP. |
| To: | Travers W Office of Nuclear Reactor Regulation |
| References | |
| 4410-86-L-0197, 4410-86-L-197, NUDOCS 8611170153 | |
| Download: ML20213F769 (17) | |
Text
.
E GPU Nuclear Corporation g
ggf Post Office Box 480 Route 441 South Middletown, Pennsylvania 17057-0191 717 944 7021 TELEX 84 2386 Writer's Direct Dial Number:
(717) 948-8461 4410-86-L-0197 Document ID 0134P November 10, 1986 TMI-2 Cleanup Project Directorate Attn: Dr. W. D. Travers Director US Nuclear Regulatory Commission c/o Three Mile Island Nuclear Station Middletown, PA 17057
Dear Dr. Travers:
Three Mile Island Nuclear Station, Unit 2 (TMI-2)
Operating License No. DPR-73 Docket No. 50-320 Inspection Report 86-11 Special Inspection Report 50-320/86-11 dated October 7, 1986 addressed the circumstances resulting in the unplanned exposure to the hand of a worker due to the handling of a sealed radioactive source on August 27, 1986. As requested in the Inspection Report, this letter documents the corrective actions which have been taken to improve the handling of sealed sources at FMI-2.
In addition, relevant portions of GPU Nuclear memorandum 9210-86-1903, which contains the summary of the assigned dose calculations, are provided as requested during the Exit Interview on September 18, 1986.
The following corrective actions have been completed or are ongoing.
o The Source Custodian who was responsible for control of the sealed radioactive source in this event was counseled.
o A Procedure Change Request (PCR) to TMI-2 Implementing Procedure 4000-IMP-3601.01, " Data Acquisition Using Portable and Semi-Portable Radiation Detecting Instrumentation and Devices" has been submitted.
This PCR clarifies sealed source handling requirements during data acquisition activities.
I 8611170153 861110 ADOCK 0500 O
gDR GPU Nuclear Corporation is a subsidiary of the General Public Utilities Corporation
\\ l
Dr. Travers November 10, 1986 4410-86-L-0197 o
The TMI-2 Source Inventory was inspected to ensure proper labeling, o
By memorandum from the Acting Radiological Controls Director, TMI-2, TMI-2 Radiological Engineers were directed to ensure that the movement of small radioactive sources with high contact dose rates receive a proper pre-job review.
o TMI-l and TMI-2 radioactive sources have been screened by calculating the exposure rate at 1 inch from the source and/or performing actual radiation surveys. For cases where extreme contact exposure rates are encountered and additional controls are deemed necessary, appropriate radiological protective measures will be applied. For example, an aluminum transit container, which shields low energy photons and reduces contact dose rates, will be provided for transport /use of small radioactive sources.
o By memorandum from the Acting Radiological Controls Director, TMI-2, Radiological Controls Personnel were directed to ensure that all support personnel who may come into contact with sealed sources participate in pre-job briefings, are made aware of the presence of the sealed source, and are advised of the appropriate precautions for handling them.
o A discussion of this event, including the lessons-learned, has been incorporated into the current cycle of Radiological Controls Technician training scheduled for completion by the end of 1986.
o The event was discussed at the Rad Awareness Meeting on September 17, 1986 and has been discussed in the TMI Info Update.
o The Acting Radiological Controls Director, TMI-2 discussed the radiological aspects of handling small radioactive sources at the 3rd quarter Safety Meetings which were held during the period of September 29, 1986 through October 17, 1986.
GPU Nuclear believes that the above corrective actions will contribute significantly in preventing a reoccurrence of this type of event.
Sincerely, 1
I f
[
t
'F. R. Standerfer Vice President / Director, TMI-2 FRS/CJD/eml
ATTACH!!E!!T 4410-86-L-0197 Nuclear memoranderd **
October 1,1986 Dose Assessment for Unplanned Date:
Subject:
Hand Exposure TMI-2 Manager,. Radiological Health Location:
From.
9210-86-1903
/
Director, Licensing & Nuclear Safety To.
~
- t. $
~
kfh*g-9,C On August 27, 1986, as a result of misinterpreted instructions, a laborer (NA*4E DEIETED)
) working for TMI Unit 2 Reactor Building entry support hand carried in close geometry a 30 millicurie Ce-144 source.
Radiological Controls personnel intnediately recognized the potential for an unplanned exposure and conducted an investigation. Background information is contained in Attachment 1:
1-a. TMI-2 Event Report 50-320-86-072 (DEIETED) 1-b. Description of Events (DELETED) 1-c. Ce-144 source description and schematic I-d. Ce-144 source calibration certificate I-e. Cc-144 autoradiograph I-f. Ce-144 energy emission spectrum (GeLi detector) i RADIATION DOSE ASSESSMENT From personnel interviews and reenactment of events, the following assumptions were made in assessing extremity exposure dose:
1 1.
Exposure time: 20 seconds.
2.
Dose determination was based on a 1 cm8 target area.
3.
Extremity doses were determined for 7 mg target depth.
4.
Source to extremity target distance:
5 mm.
1 A0000648 8 83
Fags Two Initial Several methods were used in determining extremity exposure dose.
methods to determine exposure dose employed a free-air, parallel beam geometry of 10 cm and 20 cm, source to detector distances. A Capintech air ionization chamber and Panasonic TLD's (model 802) were used to measure dose rates. By target means of the inverse-square law, the dose at 5 mm source to a 1 cm8 was calc'ulated to be 3954 mrem and 4236 mrem, respectively, for the 20-second exposure time (Attachments II-a and II-b).
Based on the manufacturer's specifications, however, which identified the active diameter of the source to be 4.3 mm (Attachment I-c) and the autoradiograph (Attachment I-e), it was concluded that the source was planar.
Consequently, the extrapolation of dose through the application of the inverse-square law for a 5 mm source to target distance was deemed Therefore direct dose measurements at 5 mm distance from the inappropriate.
Ce-144 source were performed using Panasonic (model 802) dosimeters by two independent methods:
The first element (lithium borate) of each of four separate TLD's was 1.
positioned 5 mm f rom the Ce-144 source for a one-minute exposure The element correction factor for element #1 for each of the 4 time.
The TLD's was used to manually define the corrected 7 mg dose rates.
average dose for a 20-second exposure was determined to be 1984 mrem (Attachment II-c).
The Panasonic 802 TLD is a 4 element dosimeter. The fully automated 2.
computerized processing of the dosimeter for dose assessment involves the conversion of " raw element reads" to corrected dose reads by means of complex algorithms. A basic requirement for this computation method, however, is for the TLD to be exposed to a uniform field of radiation such as a parallel beam exposure condition.
In order to allow for normal TLD processing (i.e., application of established algorithm for all 4 elements) under the restrictive 5 mm source to dosimeter distance, the following irradiation conditions and manipulations were performed to simulate nornel conditions; The respective elements E, E, E, Eu of four individual t
2 3
badges were each separately irradiated for a one-minute exposure time by placing the Ce-144 source directly above each element.
The " raw element reads" of E, E, E, and Eu of the four i
2 3
badges were artificially introduced into the Panasonic computer to simulate a single badge in order to allow for normal algorithm processing.
l I
I
Page Three This synthesized or chimera TLD showed element ratios which closely resemble The element ratios for parallel beam exposure in free air (Attachment II-d).
algorithm corrected and normalized dose rate at 7 mg target depth was defined by this chimera TLD as 6568 arem/ min. For a 20-second exposure, the total dose was 2189 arem.
Sunnary of Dose Determinations Dose for 20 see Assumptions in Method Exposure (arem)
Calculated Dose 1.
Capintech Air Ion 3954 1.
Point source is truly Chamber in free air a point source even for short source to (10 cm) target distance.
2.
Panasonic TLD in 4236 2.
Attenuation thickness of encapsulating free air material remains (10 cm) constant as a function of distance from target.
s 3.
Panasonic TLD Contact
- Exposures a.
Corrected E, 1984 None for 4 badges b.
Chimera 2189 l
l
5 mm CONCLUSION The most reliable determination of extremity dose for the conditions under investigation is best obtained by empirical dose measurements which simulate actual exposure conditions and Panasonic computational methods involving element ratios and their associated algorithms. The extremity dose value obtained from the synthesized or chimera TtD of 2189 mrem will, therefore, be i
assigned to (NM DEIETED),
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CERTIFICATE OF 3
RADIOACTIVITY CALIBRATION Half-Life: 2 t4 51, f.* ol CL-IV4 Isotope:
' Source No.: H - 4bl 4 9. I O Was assayed as containing:
M*^ %I9W As of:
METHOD OF CALIBRATION;The source was assayed on ti with a
~
MeV peak (a value of single channel analyzer, using the
(
)
i st gamma rays per decay was used in the calculations),aga n a low The source was assayed in an internal proportional /large a standard No.
standard No.
(
)
background counter against face barrier The source was assayed by alpha spectrometry on a sur analyzer, against a single-channel in the same geometrical arrangement.
detector in conjunction with
(
)
l ti n whose standard No.
The source was prepared from a weighed a i
b
(
)
ll type The source was assayed in a pressurized westd. # t u o*5-1 O. 8 W ionization chamber, against (X)
ERROR CALCULATION: _
b) Uncertainty due to random Uncertainty due to systematic Precision of source count,e4 errors:
a) standard count e and back-g errors:
- 1. In assay of standard: e n
a ground count e :
f
- 2. In weighing (s):
s
= r t Vei + ej + ej = 2 c) Total uncertainty:
l TU = a + b = 1 5.0 h
t establishandmaintain NOTES
)
IPL participates in a NBS measurement assuran (andlater NBS j
certification) of Standard Reference Materials. (As in 95 The total uncertainty is calculated at theThis calibratio d d Reference
( X)
(X)
Material No. W o t o.- 0-i s-LL.
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I I[VB Q
Ouality Osntrol ISOTOPE PRODUCTS LABORATORIES 1800 No Keystone St, aurbank Cahtornia 91504 w
Ce-144 Dose Measurements CAPINTEC Air Ionization Chamber:
1.
Free Air Measurements Distance Attenuator Time Dose Rate (cm)._
fMock PC's)_
(min) jmrem/ min)_
10 12.3 20 no 10
$1.2 10 no 10 46.2 10 yes
Determination of Average Dose for 1 cm2 Point Source
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R.
R R,
R, R.
R / R.,..
i 1 cm2 circle 1.
Source to target distance: 5 mRo 2.
Radius of 1 cm2 circle: 5.64 m Distance From Source (m)
% of Doseq, 5 of 1 cm2 R,
5.00 100 0.00 R
5.10 96 3.14 R,
5.38 86 12.56 2
R, 5.83 74 28.26 R.
6.40 61 50.24 R,
7.07 50 78.50 R,,,,
7.53 38 100.00 l
Percent of Percent of Area -
Doseg,.--.
100 100 90 90'
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60-50 50-N
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1 Radius
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Weichted Dose Weighted Average Dose Area Dose -
.0307
.98 x
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.91 x
.0942
=
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.1256
.80 x
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.1483
.675 x
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=
1 6417 Average dose for 1 cm2 target at a distance of 5 mm
=.642 DoseRo from a point source Dose calculation for individual handling source under following conditions:
1.
Source to target distance (minimum): 5 mm 2.
Assuming a point source 3.
Dose averaging fer 1 cm2 4.
Exposure time: 20 sec Dose at 10 cm: 46.2 mrem / minute or 15.4 mrem /20 see Doseg, at 5 mm: 15.4 mrem /20 sec x (100 mm)2 = 6160 mrem /20 sec
(
5 mm)2 i
Average dose for 1 cm8 = 6160 mrem /20 sec x 0.642
= 3954 mrem /20 set l
t l
l
h Panasonic TLD (Model 802) Free Air Measurements 11.
Free __.ir Measurements
^
Exposure Distance Attenuator Dose Rate (mrem / min)
TLD #
(min)
(cm)
(Mock PC's) 7 ma 300 ma 19 3.63 9980 11 20 no 11.4 1.7 9615 10 20 yes 49.5 8.7 8861 10 10 yes Dose calculation for individual handling source under following conditions:
1.
Source to target distance (minimum):
5 mm 2.
Assuming a point source 3.
Dose averaging for 1 cm2 4.
Exposure time: 20 sec Average dose for 1 cm2 = 4236 mrem /20 sec.
tMG3 sum Panasonic TLD (Model 802) Source Contact Measurements III.
Element (E )
Time Corrected Dose Dosimeter (mrem)*
ECF (min)
Rate (mrem / min)
Comments 3
0003786 5335 1.00 1
5335 Ce-144 source was positioned 0006804 5664 1.17 1
6626 above E with 3
mock PC 0008538 6028 0.80 1
4882 attenuators as spacer for total 0009485 5956 1.17 1
1168 of 5 mm spacing.
Average Dose =
5952 mrem / min 1984 mrem /20 sec
=
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I III. Chimera TLD 4
RAW ELEMENT READ g
(mrem)*
r;-
a 5n Rn S y
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Comments 2
3 m
w w
w w
Dosimeter 0008861 0.58 13.31 0.04 1.10 52.4 47.5 27.5 2.1 49.5 8.7 2.0 Normal exposure in free air at 10 cm Contact exposure of 7311 E, and E, E,four separate 0009584 g
E, of 7077 TLD's with Ce-144 0009194 source. This "TLD Com-3035 posite" was subsequently I
0003786 fed into computer for 184 normal algorithm 0009485 Chimera 0.43 16.49 0.03 1.03 7311 7077 3035 184 6568 1170 176 treatment of Element reads to Dose values.
Dose to individual using Chimera TLD value as defined by sha110w-7 (B + y) dose of 6568 mres/ m l
_ = 2189 mrem for a 20 sec. exposure time.
6568 mrem / min X 20 sec 60 sec/ min A'
M
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Autoradiograph of Ce-144 Source
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05-SEP-86 14:10:31 ISOFRODUCTS CE-144 c;CURCE AT 2
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GRAPH OF:
COUNTS FULL SCALE = LOG COUMTS VS. KE ENCF:CIEO:
RIGHT ENEF:GY 4133.867 KEV i
LEFT ENERGY
-5. 969 KE'.'
ELAPOED:
REAL TIME 00:18:14 TOTAL 0
LIVE TIME 00:16: 40 i
CUAD (t10tt8)
-22.698 SLCPE 1.011 ZERO
-6.981 CAL:EPATIOM:
l' 05 CCP-06 1-'.:46:1" DACKGP,0U:!D WITil COLLIMATCn CPC::
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GRAPH OF:
COUNTS FULL SCALE = LOG COUNTS VS. KEV Et1EF:GIEO:
RIGHT ENERGY 4133.E67 KEV LEFT ENERGY
-5. 969 KE'.'
ELAPOED:
REAL TIME 00:16:40 TOTAL 0
L I'.'E T IME 00:16: 40 OUAD (*10t*E)
-00.69E SLCPE 1.011 ZERO
-6.921 CALIEPATIC:::
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