ML20149L667
| ML20149L667 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 02/19/1988 |
| From: | Martin T NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Heider L YANKEE ATOMIC ELECTRIC CO. |
| References | |
| NUDOCS 8802240359 | |
| Download: ML20149L667 (2) | |
See also: IR 05000029/1987010
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FEB 191988
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Docket No. 50-29
Yankee Ato.mic Electric Company
ATTN: Mr. t. H. Heider
Vice President of Oper1tions
1671 Wottester R0ad
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Framingham, Massachusetts 01701
Gentlemen:
Subject:
Inspection 50-29/87-10
This refers to your letter dated September 23, 1987 in response to our letter
dated August 24, 1987.
Thank you for informing us of the corrective and preventive actions documented
in your letter. These actions will be examined during a future inspection of
your licensed program.
Your cooperation with us is appreciated.
Sincerely,
,
Orldnal Signcd By:
Ronald R. Bollainy
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Thorras T. Martin, Director
Division of Radiation Safety
and Safeguards
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cc:
N. N. St. Laurent, Plant Superintendent
J. E. Tribble, President
G. J. Papanic, Jr., Senior Project Engineer - Licensing
Peter W. Agnes, Assistant Secretary of Public Sefety
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Commonwealth of Massachusetts
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Nuclear Safety Information Center (NSIC)
NRC Resident Inspector
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September 23, 1987
FYR 87-96
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United States Nuclear Regulatory Commission
Washington, DC 20555
Attention:
Document Control Desk
References:
(a)
License No. DPR-3 (Docket No. 50-29)
(b)
USNRC Region I Letter to YAEC, dated
August 24, 1987
Subject:
Reply to a Notice of Violation
(Inspection No. 50-29/97-10)
Dear Sir:
This letter is in response to the Notice of Violation
resulting from Inspection No. 50-29/87-10 conducted during
the period June 15-19, 1987.
identified two items which apparently were not conducted in
full compliance with NRC requirements.
In accordance with
Section 2.201 of the NRC's "Rules and Practices", Part 2,
'fitle 10, Code of Federal Regulations, we hereby submit the
following information:
Apparent Violation A
A.
10 CFR 20.101(a) limits the exposure to the skin of the
whole body of any individual ir. a restricted area to 7.5
rems per calendar quarter.
Contrary to the above, on May 30, 1987, a worker at the
facility was contaminated with a radioactive "hot
particle" and received a dose to the skin of the who?.e
body (1 cm" of the skin of the scalp) of 10.5 rum,
raising his cumulative exposure during the second
calendar quarter of 1987 to 11 rem.
This is a Deverity Level IV violation.
M o 3/3 8-00 0 7
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FYR 87-96
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R_ g y.p a n s e
We acknowledge the Notice of Violation as stated and further
explained in Inspection Report No. 50-29/87-10.
Using
calculational methods such as those contained in the computer
code "VARSKIN" and the isotopic data available for the hot
particle, a dose of approximately 10.5 rem to 1 square
centimeter of the skin of the whole body can be calculated.
However, it is our opinion that dosimetric evaluations,
including those for skin dose due to hot particles, should be
based on valid measurement techniques whenever possible.
'
Calculational techniques should be employed when measurements
can not be performed.
Dased on the measurement techniques
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used, we feel that the measured dose of 6.5 rem is a more
accurate estimate of the dose actually received than the
calculated estimate of 10.5 rem.
In addition to the
measurements of dose performed for the subject hot particle,
(as discussed in Inspection Report No. 50-29/87-10), further
measurement techniques have been developed to validate this
measured dose and to assess skin dose due to hot pa.-ticles.
Attachment A is a summary of the techniques developed by the
Yankee Nuclear Services Division (YNSD) Environmental
Laboratory and the results obtained.
This attachment is
included for your review uith the intent of prr-eviding
constructive data to aid in addressing the significant,
industry wide, "hot particle" problem.
I
Evaluation
The root cause of this event has been attributed to
personnel error.
Radiation Protection management failed
to have adequate evaluation techniques in place to
conservatively estimate the dose rate to the skin due to
the presence of the hot particle.
Extensive
decontamination efforts to remove the hot particle,
resulting in significant physical effects such as
reddening and bleeding of the scalp of the individual,
were not effective.
It was deter;nined that more radical
surgical techniques should be performed only by a
physician.
The dase evaluation techniques in place at
the time led to a significant underestimate of the dose
rate to the scalp of the individual.
Based on this
underestimate, the hot particle was allowed to remain on
the scalp of the individual for a period of 75 hours8.680556e-4 days <br />0.0208 hours <br />1.240079e-4 weeks <br />2.85375e-5 months <br />.
The subsequently calculated exposure of 10.5 rem is a
direct result of the residence time of the hot particle
on the individuals scalp.
Although this period of time
allowed the hot particle to be easily removed on the
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morning of 6/2/87, surgical removal at a much earlier
time would have avoided the overexposure.
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FYR 87-96
II
Corrective Actions Which Have Deen Taken And Results
Achieved
This is the first occurrence of this nature.
Based on
this occurrence, a number of program and procedural
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changes were developed and implemented.
These changes
were effective in controlling and minimizing subsequent
exposures of personnel to hot particles and were
reviewed in Inspection No. 50-29/87-10.
Specifically,
the following changes were implemented:
1)
All protective clothing in use at the time was
removed and segregated.
New protective clothing was
issued.
2)
Protective clothing used for work in areas with high
potential for hot particle contamination,
(e.g.
rubber gloves for Shield Tank Cavity work,
protective clothing for Steam Generator entr ies)
was discarded after use.
3)
Two hour stay times were established for work in the
Vapor Container.
Personnel were then required to
use the whole body contamination monitors prior to
returning to work.
Exceptions required by the
nature of the work were handled by establishing
alternate controls,
(e.g. the issue of new
protective clothing).
4)
The protective clothing policy was changed to
require removal of protective clothing at the Vapor
Container exit rather than at the control point.
5)
One hundred percent of all laundered protective
clothing was frisked prior to return to service.
A
limit of 13000 cpm was established, protective
clothing above this limit was segregated and not
returned to service.
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6)
Paper coveralls were worn over cloth coveralls for
work in the Vapor Container.
7)
Masslin and sticky tape rollers were used to survey
areas to more effectively monitor areas for the
presence of hot particles.
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0)
A portal monitor was set up at the exit from the
control point to the radiological control area as an
additional check for exceptionally high activity hot
particles.
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FTR 87-96
9)
OP-8430, "Personnel Contamination Monitoring and
Decontamination," uas revised to insure that
regulatory limits would not be exceeded.
Actions,
including transport to an off-site medical facility,
are required prior to approaching a regulatory
limit.
III
Corrective Actions Which Will Ee Taken To Prevent
Recurrence
The corrective actions described above proved to be
effective in the prevention of further overexposures due
to hot particles throughout the remainder of the
refueling outage.
Specifically, clear procedural guidance is now provided
in OP-8430 to both adequately assess dose from hot
particles and assure hot particle removal prior to
exceeding regulatory limits.
IV
The Date That Full Compliance Was Achieved
Full compliance was achieved upon institution of
adequate dose assessment techniques on June 2,
1987.
The individual's dose of record for the second quarter
of 1987 will be changed to reflect a dose to the skin of
the whole body of 11.0 rem.
In accordance with 10 CFR 20.409(b), the individual will be notified in writing of
the change to his dose of record for the second quarter
of 1987.
This notification will be transmitted prior to
September 24, 1987.
.
Apparent Violation 8
10 CFR 20.201(b) requires that each licensee make such
surveys as may be necessary to comply with all sections of
Part 20.
As defined in 10 CFR 20.201(a), "survey" means an
evaluation of the radiation hazards incident to the
production, use, release, disposal, or presence of
radioactive materials or other sources of radiation under a
specific set of conditions.
Contrary to the above, on May 30, 1987, a proper survey
(evaluation) of a hot particle located on the skin of the
head of an individual was not made to assure compliance with
10 CFR 20.101(a), which limits the radiation exposure to the
skin of the whole body in any calendar quarter.
Specifically, the initial dose evaluation following
identification of the contaminated hot particle was based on
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FUL 87-96
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an inappropriate assumption concerning the size of the
contaminant, in that the contaminant was of smaller
dimensions than assumed in the initial assessment.
As a
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result, the initial dose rate estimate (8 mrem /hr) was in
error.
Subsequent calculations indicated a dose rate of
greater than 100 mrem /hr.
This is a Severity Level IV violation.
Resoonse
We concur with the Notice of Violation as described above, in
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that a proper survey was net performed to adequately assess
dose to the skin.
I
Evaluation
The root cause of this event has been attributed
+o
personnel error.
As was described in Ap'
ent Violation
A, Radiation Protection management faile_ to have
adequate evaluation techniques in place to
conservatively estimate the dose rate to the skin due to
the presence of a hot particle.
The failure to perform
an adequate survey was a direct result of using the
guidance in place at the time in OP-8430, "Personnel
Contamination Monitoring and Decontamination."
Although
we were aware that the contaminant was a point source,
(hot particle), initial dose calculations effectively
treated the hot particle as a plane source by including
the active area of the radiation detector, (15 cm"),
in
the denominator of the equation used.
A more thoro' ugh
technical review of the draft industry document used as
the basis for OP-8430 would have identified a
misapplication of the equations presented for skin dose
c a l ct- 1 a t i o ns .
11
Corrective Actions Which Have Been Taken And Results
Achieved
Upon removal of the hot part'icle from the scalp of the
,
individual, a quantitative isotopic analysis was
performed.
Using this data, the inadequacy of the
initial dose estimate was identified.
The following
corrective actions were implemented to immediately
establish an adequete dose assessment methodology:
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1)
A computer code similar to "VARSKIN" was obtained
from another facility and dose conversion factors
for all isotopes of interest were tabulated.
An
adequate method for dose assessment of subsequent
hot particle contaminations was available as of
1700, June 2,
1987.
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FYR 87-96
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2)
With the assistance of the YNSD Environmental
Laboratory, the computer code "VARSKIN" was obtained
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and made available for use.
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3)
OP-8430 was revised to includes
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a)
A conservative dose conversion factor for dose
assessment of hot particles with G-M Friskers.
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b)
Action leve1w requiring isotopic analysis.
c)
Tabulated done conversion factors for applicable
isotopes.
d)
The use of the computer code "VARSKIN".
4)
Gamma spectroscopy systems were calibrated to
measure both hot particles removed from the skin and
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hot particles still on an individual.
5)
The hot particle was transported to the YN3D
Environmental Laboratory for confirmatory gamma
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isotopic analysis and further evaluation.
6)
A hot particle of similar isotopic composition was
transported to the YNSD Environmental Laboratory for
"'Sr,
'oSr-Y measurements.
Using the data obtained,
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methods to estimate "'Sr,
'oSr-Y activity based on
the activity of various gamma emitting isotopes were
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developed.
This methodology was available for use
on June 15, 1987 and included in a subsequent
revision to OP-8430 which was PORC approved July 9,
1987.
III
Corrective Actions Which Will Be Taken To Prevent
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Recurrence
The corrective actions described above were effective in
quickly implementing adequate survey techniques for hot
particle contaminations.
Although refinements to the
program will continue to be made, an adequate hot
particle program is currently in place.
IV
The Date That Full Compliance Was Achieved
Full compliance was achieved on June 2,
1987 when
adequate survey techniques for hot particle
contaminations were established.
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FYR 87-96
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If you have any questions or desire additional information,
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please contact us.
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Sincerely,
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H. Heider
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Vice President and Mgr. of Operations
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Region I
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ATTACKMENT A
REFERENCES
1.
Memorandum to R.A. Mellor from W. Stanford, "Final Report and Evaluation
of Yankee Plant Hot Particle", dated June 10, 1987. EL 355/87.
2.
"Design and Operation of an Extrapolation Chamber with Removable
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Electrodes" by R. Loevinger and W. C. Trott, International Journal of
{
Applied Radiation and Isotopes, 1966, Vol. 17, pp. 103-111.
3.
"Use of a Victorian 500 Electrometer to Determine Ionization Chacber
Collection Ef ficiencies", by P. R. Almond, Medical Physics Journal,
Vol. 8
No. 6. Nov./Dec. ,1981.
!
4.
Memorandum from R. A. Mellor to C. M. Babineau, "Independent Estimation
of Sr-89 and Sr-90 Concentrations in the 5/30/87 Scalp particle", dated
June 15, 1987, CH 057/87.
5.
"Mathematical Theory of Radiation Desimetry", by J.J. Fitzgerald,
C.L. Browncil and F.J. Mahoney, Gordon and Breach Science Publishers,
Inc. New York, NY, copyright 1967.
6.
Radiological Decay Data Tables by David C. Kocher Technical Information
Center, U.S. Department of Energy, 1981.
This report presents further research and testing concerning the use of
the Vinten extremity dosimeter for direct measurement of skin dose resulting
from irradiation by a hot particle.
The two concerns which were raised in WRC
inspection report #50-29/87-10 concerning this technique have been addressed.
The areas of concern are:
1) the accuracy of the dosimeter effective arca
value and 2) the effect of the underresponse of the dosimeter to low energy
beta radiation.
In addition, data is presented from a definitive comparison
between this technique, the VARSK1W cocputer code and extrapolation chamber
ceasurements of a hot particle similar in composition to the originally
measured particle.
The results of this comparison show the Vinten dosimeter
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measurement to provide excellent agreement with the extrapolation chamber
,
while the VARSK1W mode'l overestimates the dose significantly,
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,E_f f ec t ive Area
The standard Vit. ten extremity dosireter has a 5 mg/cm2 layer of
phosphor over an area of 0.6 cm x 1.0 cm or 0.6 cm2
Due to the limiting
dimensions of the plate on which the dosimeter is mounted for processing and
the collimation of the photomultiplier tube (Figure 1), the actual area of
phosphor over which thermoluminescence is gathered is calculated to be
0.29 cm2
As the ostimated dose to 1 cm2 is very ser.sitive to this
parameter, an exptriment was devised to verify this calculated value.
To verify the maximum ef fective area of the dosimeter, Vinten
Ins t rument s . L7!.' was requested to manufseture a batch of dosimeters with
phosphor areas 7 f varying lengths.
In addition to the normal 1.0 cm length,
groups were manuf actured at
.8,
.7,
.6 and .5 cm Jengths.
All five groups of
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disimetoro were manufcetur:d f ria tha same batch cf phosphtr s3 that a
comparison of sensitivities would indicate the dependence of sensitivity on
length.
The smaller dosimeters were expected to produce a reduced signal
,
compared to the full sise batch only when their length became the limiting
dioension, i.e. when the length of the phosphor approached the diameter of the
co111eator.
Figure 2 contains illustrations of the relative dimensions with
the calculated areas of interest indiceted. The ratio of the response of any
given dosineter length to that of the standard I cm length was expected to be
equal to the ratio of the calculated effective areas for equal delivered
dose.
Ten dosimeters from each of the five groups of test TLDs were erposed to
a uniform field of 137 s garna radiation. All of the dosimeters were
C
processed following normal protocol, centering the phosphor area over the
opening of the mounting plate.
The responses of tts Gee
eters, corrected for
background using unirradiated dosimeters of the sat a gruv}
were averaged for
each group.
The average group responses were then ,1videf by the average
response for the standard 1 cm batch.
The results, which .re presented in
Table 1, indicate excellent agreement between the c at:<*s ed ratio of responses
and the ratio of the calculated effective areas, suPracting the technique f or
calculating the effective phosphor area.
TABLE 1
OBSERVED VERSUS PREDICTED RATIOS OF THE RESPONSE OF
DIFFERENT LENGTH DOSIMETERS
Calculated
Ratio of
Effective
Effective Area
Observed Ratio of
Area
to 1.0 cm Dosimeter
response to 1.0 cm
2
Length (cm)
(cm )
Effective Area
Dosimeter Response
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1.0 1 .01
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0.8 1 .01
.289
1.00
1.02 1 .09
0.7 i .01
.289
1.00
1. 0 0 i . 09
0.6 1 .01
.280
0.97
0.97 1 .08
0.5 1 .01
.247
0.85
0.85 1 .07
Response to Low Enerr.y Beta Radiation
An estimate of the underresponse of the dosimeter due to low energy beta
radiation of 20 percent was quoted in the NRC inspection report.
This number,
which was felt to be somewhat conservative, was checked by the DSC using a
acre rigorous method.
In order to evaluate the expected underresponse of the Vinten dosimeters,
Loevinger's expression (Referene,e 5) was enployed to calculate the apparent
absorption coef ficient br.srd on the end point energies (Reference 6) of the
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individual bet- perticles smitted by tha isotope involvsd.
Tha mecn value
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theorem was used to average the exponential attenuation of each beta energy
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over the 5 as em- 2 thickness of the vinten dosimeter. The fractional yield
,
of the bete energy and the fraction of the total dose delivered to 1 cm2
area under 7 mg em-2, based on the VARSK1W code, was used to weight the
effect of the individual underresponses.
The summation of these individual
underresponses yicided an est '. mated overall underresponse of approximately 10
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percent.
Comparison with Extrapolation Chamber
To further test the accuracy of this method of seasuring skin dose from a
hot particle, a comparison was cade with extrapolation chamber measurements.
The Yankee Plant staff obtained a second hot particle (actually three
discernable particles, each raeasuring approximately 200 vm and contained in
an area of less than 2mm) of suf ficiently high activity to allow precise
extrapolation chamber measurements using a 1 cm2 collectine electrode.
The particle (logged as "STC UPNR Sump Speck") was held on a piece of
masking tape which was in turn covered by a layer of 0.8 mg/cm2 clear cylar
film.
This configuration was used for both dosimeter irradiations and
extrepolation chamber measurements.
The radionuclide co.: position of this second hot particle was evaluated
using gamma ray spectroscopy and found to be similar to the original particle,
validating a comparison of dosimeter performance.
The relative abundance of
the major constituents of each particle, as determined with garem ray
analysis, are tabulated oclow.
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TABLE 2
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COMPOSITION OF ORICINAL AND WEW HOT PARTICLE
% of Total Activity
R9dionuclide
Original
New
952r
16
16
95Nb
21
23
144 e
11
16
C
144Pr
11
16
141 e
11
7
C
103 u
8
J
R
140 a
5
<1
L
140 a
4
<1
ll
106Ru
2
1
106 h
2
1
R
1311
1
..
137 s
1
1
C
89se
7
10
90 r
1
2
S
90Y
1
2
posimeter Measurements
Vinten dosimeters were used for dose measurements using the same
techniques that were outlined for the original particle in June of 1987
(Reference 1)'.
The particle was placed on top of the five dosimeter
configuration (Figure 3) and lef t in contact with the center dosimeter for a
measured time period.
The four noncentral dosimeters were then ust.d to
calculate the dose delivered to the 1 cm2 area, outside of the 0.29 cm2
effective area of the central dosimeter. The five replicate irradiations
using this configuration resulted in an average dose rate estitute of 46.31
6.0 rad /hr.
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,Ex t ra p o l c t i on Ch ambe r M e e cu rrme n t s
On July 31, 1987 the YAEL extrapolation chamber w3s used to determine the
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absorbed dose rate at 7.0 mg em-2
Six layers of 0.86 mg em-2 aluminized
mylar were placed between the previously described particle configuration ani!
the window of the extrapolation chamber. The weight of the plexiglass sheet
was allowed to bear down upon the mylar sheets to avoid any air gaps between
the sheets.
This arrangement yielded a 6.9 mg cm- 2 density thickness
between the particle and the active volume of the extrapolation chamber.
The extrapolation chamber was equipped with a special electrode having an
scLive area of 1 em2, manufactured spacifically for these measurements.
The
electrode is a one inch thick 4 cm radius lucite cylinder coated with a fine
layer of colloidal graphite. A thin (11/1000 inch) groove was etched through
the graphite into the lueite to isolate a 0.564 cm (1 cm2) circle from the
outer annulus. The machining of the electrode's active area was verified
using the capacitance techniques outlined in Reference 2 to be well within
I percent of I cm2
The particle was centered over the active volume by
moving the particle across the window until the ionization current reading on
the electrometer was maximized. This pocitioning technique was repeated
several tines and the maximum current verified.
Plate spacings of 0.1 mm
increments were used to minimize any geometrical ef fects associated with a
changing active volume. The ionization collection efficiency for each plate
separation was determined to be at least 99.7 percent using the methodologies
of Reference 3.
An extrapolation, which was performed between 0.8 and 0.4 rn,
yielded an absorbed dose rate of 46.5 1 0.86 rad /hr based on a least squares
fit to the measurement data.
This measurement was performed in accordance
with YAEL Procedure 950 and the data is maintained in data file E8721113.
VARSKIN Analysis on STC UNR Sump Speck"
The ganma spectroscopy analysis performed at the Yankee Plant was used
for input in the VARSKIN computer program. The results of the gamma analysis
and the corresponding VARSK1W dose estimates are contained in Table 3.
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TABLE 3
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CAMMA AND VARSK1W ANALYSIS OF STC UWR SUMP SPECK
JULY 31, 1987
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Absorbed Dose Rate
(rem /hr) over
Isotope
pCi
pCi"See (3)
I em2 9 7 mg cm 2
Mb-95
6.04
2.17 E4
5.2
Zr-95
4.04
1.45 E4
19.6
Ru-103
1.52
5.47 E4
3.2
Rh-106
.339
1.22 E3
3.2
Ru-106 (1)
.339
1.22 E3
0.00
.165
5.92 E2
1.1
La-140 (1)
.115
4.14 E2
1.0
Ba-140
.100
3.59 E2
0.7
cc-141
1.82
6.54 E3
10.1
Ce-144
4.07
1.46 EA
13.2
Pr-144 (1)
4.07
1.46 E4
38.2
Sr-89 (2)
2.47
8.90 E3
21.5
Sr-90 (2)
0.43
1.54 E3
2.9
Y-90 (2)
0.43
1.54 E3
3.9
123.8 i 7.5(4) rem /hr
(1) Activity for these isotopes based on activity of associated parent
isotope.
(2) Calculated based on core inventories as outlined in Reference 4.
(3) The time interval used was 3600 seconds in order for the VARSKIN code to
-
calculate rem /hr.
(4) Total uncertainty in the VARSKIN estimate is based on a propagation of
the uncertainly in the counting statistics.
.
-
6
The racults of tha thraa techniques are listod below.
Fcr particles of
this sise and radionuclide mixture, the technique using the Vinten dosimeter
,
has been shown to accurately estimate the skin dose, while the VARSKIN model
substantially ovtrestimates the dose.
TABLE 4
COHPARISON OF THREE TECHNIQUES TO EVALUATE
SKIN DOSE FROM A HOT PARTICLE
(RESULTS IN RAD /HR)
Extrapolation
Vinten
Chamber
Dosimeter
VARSKIN
46.5 1 0.9
46.3 1 6.0
123.8 i 7.5
Summary
The work presented in this report verifies the accuracy of direct skin
dose measurements of submillimeter radioactive particles using the Vinten
extremity thermoluminescent dosirc.eter. The actual effective area over which
dose is averaged by the dosimeter has been experinentally verified. Most
importantly, the accuracy of this technique has been verified for a particle
of mixed fission products using a direct comparison with extrapolation chamber
mensurements.
.
7
.
.
'
. .-
- *
TICURE 1
-
Relative Dimensions of I cm x 0.6 cm Vinten Extremity
Dosimeter, Dosimeter Mounting Plate and Photomultiplier
Tube Collinator
Photomultiplier
Tube Collimator
Radius = 0.325 cm
/
_
/
/
Dosimeter Plate
7__
- Opening
0.8 cm x 0.5 cm
/
_- - . _
nocimeter
Phosphor
1 cm x 0.6 cm
'
= -
,
,
.
/
/
-
2
Area = .289 cm
.
Sc' ale = 10:1
-_
pe-
~
4
- - -
-
---
-
-
_ _ _ _ _ _ _ _ _ _
-
FICURI 2
,
..
Relative Dinensions for Test Dosimeter Croups Showing Phospbor
Area. Ef fective Reader Area and Total Effective Dosimeter Ares
,
/ /
,
/
/
.
l
.
/
/
/
/
/
)
/
/
/
0.8 cm x 0.6 cm
2
Ef fective crea = .289 en
Scale = 6.5:1
,/
_/
s
/
-
Area of Collimator
y
and Dosimeter Pla't
//
Area of Dosimeter
/
//
Phosphor
j
<
,
/
/ /
/ / /
I
0.7 cm x 0.6 m
Total Effective
Ef fective area = .289 cm
/_ /
s
/
. c.,py
'
s
EM8M
t
/- /
/ //
0.6 cm x 0.6 cm
2
Effective Area = .281 cm
1x /
//
s
(18f9
'
.
ncaz 3
.
TOP VIEW - 0051ETER CONFIGURATION
-
,
,
. _ -
l
West
East
Dosimete
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Dosimeter
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