ML20235F964
| ML20235F964 | |
| Person / Time | |
|---|---|
| Site: | University of Virginia |
| Issue date: | 07/21/1971 |
| From: | Meem J, Quarles L VIRGINIA, UNIV. OF, CHARLOTTESVILLE, VA |
| To: | US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20235F939 | List: |
| References | |
| NUDOCS 8707140053 | |
| Download: ML20235F964 (11) | |
Text
._
UNIVERSITY OF VIRGINIA SCHOOL OF ENGINEERING AND APPLIED SCIENCE CH ARLOTT ES VILLE. 22901 b
c EP A%TM ENT OF NUCLEAR ENGINEERahO TELEPHONE:
703 924 7136 CEACTCR FACIUTY 8
July 21,1971
{
Division of Reactor Licensing U. S. Atomic Energy Commission
{
j Washington, D. C.
Reference:
Docket No. 50-62 1
Gentlemen:
g u
An amendment is requested to facility license No. B-66, Docket 50-62, to receive and possess not more than 70,000 curies of Cobalt-60. The cobalt vill be stored under at least 20 feet of water in the reactor pool, and will be used as a gamma irradiation facility for experiments.
Because of the great depth of water there is no hazard to personnel once the cobalt is transferred to the bottom of the pool. A safety analysis report by Dr. C. A. Erdman on the transfer of the Cobalt-60 from the l
shipping cask to the pool is attached.
It is concluded that the transfer s
can be made without risk to the public, and without personnel of the f
reactor facility receiving exposures in excess of those specified'in
[
(
)
Very truly yours, l
i J. L. Meem, Director Reactor Facility
]
e JD1/1t Lawrence R. Quarles, Dean Attch.
School of Engineering and Applied Science l
l l
Subscribed and sworn before ce this date of 1971 l
l Jean M. Holliday, Hotary Public i
Ny commission expires 8707140053 B70702 l
PDR ADOCK 05000062 P
PDR l
l SAFETY ANALYSIS REPORT ON CO TRANSFER C. A. ERDMAN i
I.
Transfer Procedure A.
General The procedure outlined here is essentially the reverse, of a procedure perfomed at the University of Virginia Peactor Facility several years ago in shipping fuel elements from the reactor.
Many of the reactor personnel who participated in that operation are still at the facility and will be able to apply their experience to the proposed Co transfer.
Co is in the form of doubly encapsulated rods 0.9h-inch The in diameter and 10.7 inches long.1 Each source contains about 60 950 Curies of Co. Sixty-eight to seventy of these sources, i.e.,
6h,600 to 66,500 Curies, vill be involved in the transfer.
During all transfer operations personnel areas vill be monitored to insure that the exposure limits specified in 10 CFR Part 20 are observed. A guard will be posted at the gate of the security fence to prevent entrance of unauthorized personnel.
B.
Outline of Procedure The Co will arrive at the facility on a flat bed trailer in a shipping cask meeting DOT specifications. The cage surroundin6 the shippinc; cask vill be removed and the cask unbolted from its base platform. The lid of the cask vill also be unbolted but vill be left in place temporarily.
I 1
n A crane vill be used to lift the six ton cask from the l
trailer bed and place it inside a transfer tank tilled with water. The transfer tank is a twelve foot diameter, twelve l'
foot high cylindrical steel tank which is being constructed as The tank will a pemenent addition to the Reactor Facility.
L
- be used in future shipping and receiving operations for reactor l
fuel elements. After the shipping cask is in the water-filled tank, the crane vill be used to remove the cover, and a transfer cask placed in the tank beside the shipping cask.
All Co source handling involved in moving the sources from the shipping cask to the transfer cask vill be perfomed l
1-in the transfer tank under water. The water chielding vill be sufficient to protect the handlers and all other personnel in the transfer area.
The 60 a urces will be removed from the shipping cask to Co the transfer cask. The transfer cask vill accommodate four of the Co sources at a time.
l The lid will be placed on the transfer cask while in the The crane vill then be used to remove the transfer cask water.
from the tank and place it on a fork lift truck located a few feet from the tank. The truck vill then be driven into the reactor building, where an overhead crane vill be used to remove In the cask from the truck and lover it into the reactor pool.
the pool, under a sufficient depth of water, the cask will be unloaded, and the slugs vill be placed in a source holder (see Section II).
l 1
i l
)
l i
l
/
i
/
/
o80"
$?o oc N
O O
v O O)GJO. ~
/
LY l
l 1
l'
/
i
/
l l s e
{.
t'-- :
/
3__
l v
G i
t i
~
F igure 1.
Sketch of proposed source holder showing one source in place.
l l
e 9
j
. i l
II. Source Holder The source holder for the Co sources will consist of two parallel, horizontally positioned 6061 aluminum plates. The plates vill be spaced five inches apart and will be connected near the corners vith four 3/4 inch diameter aluminum rods.
One inch diameter holes vill be drilled through the top plate to accommodate the sources. The bottom plates will have blind holes to position the bases of the sources. A six inch diameter hole in the center of the top plate vill permit positioning of samples for irradiation.
The source holder vill be designed to either rest on the pool bottom or be suspended from two A-frame handles. These handles vill facilitate loading sources and moving the source holder from place to place in the pool. A sketch of the holder showing one source in position is given in Figure 1.
The pool vnter and surrounding vails and earth will provide execlient shielding for the loaded source holder. When it is located a Ibe pool bottom under at least twenty feet of water, no activity above background is expected at the top of the reactor pool.
In future irradiation vork the slugs may be stacked two ' deep.
Tais can easily be accomplished by the use of ten inch long aluminum sleeves with a plug or stop screw at the midpoint of the sleeve. In such an arrangement the sleeve vill be slipped down over one source, and a second source vill be placed inside the top half of the sleeve.
This arrangement is practical because of the small weight (about one pound) of the individual slugs.
a 8
_h.
III. Shielding Calculations A.
Sources in Transfer Tank As noted in Section I,A, the material being transferred is 1
in the form of slugs or rods of about 950 Ci activity each.
Seventy or fever of these sources will be involved.
A single slug treated as a point source located at the bottom center of the transfer tank would have a side shield of six feet of water at the base of the tank. Such a source would result in a maximum exposure rate at the rank surface of less than 120 mR/hr as calculated using the equations below.
~0 ER = 1.82Tx10 hv " " 4 (I) 0 4 = B(pr) S " pr (II) '
2 hur where ER is the exposure rate in Roentgens / sed h is the photon energy in MeV is the mass energy absorption coefficient of air for 2
P photons of energy hv in em /gm 2
4 is the photon flux density in photons /cm - see B(pr) is the buildup factor for a point source in water S is the source strength in photons /see u is the linear attenuation coefficient of water for
~l phote.nc of energy hv in em r is the distance from the source in cm.
The 1.17 lieV and the 1.33 MeV photons from the Co were, of course, treated separately, and the resulta vere added.
n
. This calculated exposure rate from a single slug is actually 1
higher than that which would be observed during the transfer operation at the tank surface next to the personnel work area, because the slug would be handled off center in the tank and more than six feet away from the valls next to the work area.
Moreover, it is anticipated that there vill be no need for personnel to be in the area immediately adjacent to the tank.
The workers handling the actual transfer from cask to cask vill be on scaffolding around the top of the tank and on platforms on the top of the tank.
If it is necessary to empty all the sources into the transfer tank at once, this vill be done in a confined area of the tank near the side away from the work area as discussed in II.B.
Usin6 Eqns. I and II, calculated exposure ratet for a pin point source of seventy clugs (66,500 Ci) shielded by eight feet of water were found to be about 175 mR/hr. All personnel work areas vill be protected by at least this amount of water or equivalent shielding (i.e., combination of distance and other shields such as the reactor building vall. ) To further reduce exposure rates, available lead sheets 1" x 3' x 3' can provide extra shielding either inside the tank or against its outside vall if necessary.
Once again it should be emphasized ' hat personnel are not expected to be needed in the highest radiation areas, i.e.,
approaching 175 mR.
The major work areas vill show exposure rates of only a few mR/hr.
. i i
l B.
Loaded Transfer Cask An indicated above, four slugs or about 3800 Ci vill be in the transfer cask each time it is moved from the transfer cask to the reactor pool.
The transfer cask is an eighteen inch diameter cylinder con'sisting of Icad contained in a steel can.
The inner chamber is a centered 3" x 3" x 3' parallelopiped. By placing iron or lead inserts in the corners and positioning the sources as shown in Figure 2, a minimum shield of seven inches of lead or its i
equivalent would be obtained.
In eciculating the exposure rate at the surface of the cask, the four sources were treated as a single infinite line source with strength per unit lenCth equal 1
to four times that of a single source. The resulting exposure i
rate at the surface of a seven inch thick lead shield was calculated to be 2.8 R/hr using the equation below (III) in conjunction with Eqn.(I).
I S
1 4=2a F(fpa)+apaK (pa)
(III) 1 l
where $ = photon flux density (#/cm -sec)
S = source strength per unit length (photons /sec-cm) a = distance from line source in cm l
a = linear buildup factor for Pb for photons of energy, hv p = linear attenuation coefficient for photons of energy, l
hv, in em F(f,pa)=Sievertintegral K (pa) = zero order modified Bessel function of second kind.
l 1
l
_______-__-a
,l i
. e--
kh%
< //
\\ \\
\\
.zW,//
'N
\\
A We.
N i
~
'N,'N
. \\,,
\\
s
/,[p/ '
N,['N 'N. \\
\\
////((
g s
![
' N.\\,
/ [
,/,
j
%ds s cale ;
l=
Va inch l
i i
i, T
I I
l t
Figure 2.
Source arrangement in chamber of transfer cask l
l l
l 1
_7-This calculation is very conservative because it icnores the following things:
1.
Presence of water surroundin6 sources in the cask, 2.
Self-absorption in the sources, 3
Mutual shadowing of the scurces, and h.
Distances of the sources from the insides of the various cask walls.
A more realistic estimate of less than 2 R/hr can be justified when these factors are considered.
IV Personnel Exposure Based on the experience of loading fuel elements for shipping, the entire transfer operation should require less than ten hours.
If the sources can be removed one by one from the shipping cask for loading in the transfer cask as discussed in Section I,B, the i
exposures of most personnel vould be well under 5 mR.
Even if all sources are placed. in the tank at once, a realistic upper limit on exposure is 200 mR based on ten hours in 20 mR/hr field. The only times that anyone vould need to be in a field of more than a few mR/hr are during operation of the fork lift truck and while attaching and removing crane hooks from the transfer cask.
Physical separation of the truck driver from the cask would. result in reduction of exposure rates to the driver of about a factor of ten from the surface 2 R/hr indicated in Section III,B.
!!oreover, less than a minute is required to drive the truck the thirty feet or so from
o 6 the transfer tank to the reactor pool.
Assuming even three minutes driving time per transfer for eighteen transfers, a single criver making all the trips would receive less than 200 inR.
The truck operations will, of course, be divided amoung various personnel.
All these personnel exposure estimates are well within the guidelines of 10 CFR Part 20.
(1) llorne, Thomas, Nucleonics 21, 72 (1963)
(2) !!orgen, Turner, Principles of Radiation Protection, Chapter 9 4