•
A
13
.
i
"*"
.:..
::
I OFL.
ORNL P
2126
.
ta
1
•
)
"
.
.
in
.
1.
0
.
.
votreberica
Y
.
t
.
4
T!
.
.
1
.
.
.
.
.
.
.
7
11.25 4 1.1.5
MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS - 1963
I
.
"
.
.
C
ORNU 8-21966
Cant-6609an-1
MASTER

MAY 10 1966
MODEL AND UNDERGROUND STUDIES OF THE INFLUENCE OF STRESS, TEMPERATURE
AND RADIATION ON FLOW AND STABILITY IN ROCK SALT MINES, O
R. L. Bradshaw, T. F. Lomenick, W. C. McClain, and F. M. Empson
CESTI PRICES
Healt}. Physics Division
Oak Ridge National Laboratory,
Oak Ridge, Tennessee

RELEASED FOR ANNOUNCEMENT
H.C. $ 4.00; MN_50
IN NUCLEAR SCIENCS ABSERICH
I.
INTRODUCTION
Reprocessing of nuclear power reactor fuel produces a radioactive
waste which must be isolated from the environment for centuries. The
most promising disposal method for these heat-generating westes is con-
version to solids, followed by final disposal in a salt mine. In order
to be able to design a radioactive waste disposal facility in a salt
mine, it is necessary to be able to predict the effects on mine stability
of both supporting-pillar stresses (produced by the superincumbent earth
strata) and elevated temperatures (produced by radioactive decay of the
fission products in the waste).
Research in this area has been carried out in the laboratory using
model pillars, and in a 1000-ft-deep (305 m) salt mine in Kansas using
reactor fuel and electrical heaters in a specially excavated area.
S
.
.
.
..
.
...
For publication in the Proceedings of the International Society
of Rock Mechanics, First International Congress, September 25 to Octo-
ber 1, 1966, Lisbon, Portugal.
Research sponsored by U. S. Atomic Energy Commission under con-
tract with Union Carbide Corporation.

NOT ARABoyЕрте
р
La
n gai
orientation
HEAEG AND HIS the
2. SAIT MOVEMENT IN MINES
In general, when an opening is created in a salt mine, there is a
flow of salt into the opening. The rate at which the opering closes is
dependent won such factors as depth of the mine, percentage of the area
extracted, extent of the area already mined, shape and height of the pil-
lars, temperature of the salt, and time since creation of the opening.
In flat-lying (bedded) deposits where shale is interbedded with the
salt, the flow of salt frequently causes separation of layers of salt
from the shale layers with resultant floor heaves and ceiling sags. If
too much salt is exüracted, if the supporting pillars are not properly
sized, or if the thickness of the layers of salt in the floor and in the
roof (down to and up to the first shale layers) is not great enough, the
floor heaves may be large enough to interfere with the movement of ma-
.
chinery, and hazardous roof falls may occur. Even in mines where salt
flow does not cause trouble during the mining operation, roof falls and
floor heaves may occur after an extended period of time, perhaps decades.
Sufficient empirical data on existing salt mines are available to:
enable predictions to be made on the stability of mines at ambient tem-
perature, but no data or experience are available which are directly
applicable at elevated temperatures. Recent work by Seratat and Obert
.
at ambient temperatures has shown that flow in rock-salt mines may be
approximated by testing scale-model specimens uniaxially by providing
proper horizontal restraint over the floor and roof portions of the
model.
-...
.
.
.
. . .
.
.
- -
LEGAL NOTICE
This roport me preparod an account of Government sponsored work, Nuither the United
Statau, dor ebe Commission, nor any person acting and behalf of the Commiundon:
A. Makss way warranty or repromatatha, expressed or implied, with raspect to the accu-
racy, completeness, or wofalnou of the information contained in this report, or that the word
of any information, apparatu, mothod, or procesu discloved in the report may not infring
privately owned richta; or
D. Asnimos hay liabilues with respect to the une of, or for damage resulter from the
on of any information, apparitus, molbod, or procou dixcloued to this report
As med in the above, "parrow nothing on behalf of the Commiustom" laoludne way on.
ploys or contractor of the Commission, or employee of such contractor, to the extrat det
noch employee or contractor of the Commission, or employee of much contractor preparou,
dhiminates, or provides access to, wam laformaatios partient to Me employment or contract
with the conaminaton, or his employweat with such contractor.
.
ni
it
.
..
.
3.
3. MODEL STUDIES ON EFFECTS OF TEMPERATURE AND STRESS
,
..
We have studied the behavior of scale-model pillers at temperatures
up to 200°c and stresses up to 10,000 psi (703 kg/cm?).” To simulate
pillar, roof, and floor conditions in mined cavities in rock salt, sample
specimens were fabricated to represent scale models of salt pillars and
their surrounding rooms. The test, specimens were cylindrical in shape,
with a portion of the center ground out to form the pillar and surround-
ing rooms (Fig. 1). Steel rings attached around the ends of the samples
effectively supplied confining pressure to the roof and floor portions
of the models as they were loaded.
1.
The following approximate empirical equations have been fitted to
the results of these pillar-model tests for times from 10 hr on.
€ = 3.2 x 10-36 720.9 -3.2 +-0.65
E = 9.2 x 10-36 710.9 23.2 +0.35+ A
:
where
Se
ė = strain rate (vertical convergence, 1 in. in.-hr-?),
: € = cumulative deformation (u in. in.--),
T = absolute temperature (°K),
o = average pillar stress (psi),
t = time (hr), and
A = constant adjusted to fit experimental curve at 10 hr.
U
· Extrapolation of the rate equation produces predicted creep-closure
:
*
rates which are in reasonable agreement with rates measured in the Kansas
mines since 1959.* The relationships between vertical and horizontal
closure rates measured in the models also have been corroborated by meas-
urements in the mines.
2
5
t
.
. *
.
W
IK
.
.
:.
.
ORNL-OWG 65-1543
..

.->
Til
Wi;
.
INTIIMIIMILLUS
.
LTUMTU
.
.
'PILLAR
ROOF
'FLOOR
STEEL RING
one ano foi o 2010 sets *** *
fig.!.. Model of Salt Pillar
REY
5
.
wit.*
..
.
.
1.
In a model of the type shown in Fig. 1, 1/8-in.-diam (0.32 ca).
horizontal holes were drilled at the top and bottom of the pillar and
filled with colored salt before the sample was deformed about 60%. The
floor-to-ceiling dimension was reduced from 1 in. (2.5 cm) to about 0.4
in. (1 cm). After deformation, the model was saved in half, vertically,
along the plane containing the holes. The result is shown in Fig. 2.
**
It is evident that the sait-filled holes are no longer horizontal and
are much closer together at the sides of the pillar, thus showing that
some of the salt from above and below the pillar has flowed out into
3.1
2.
.
*
ܝܪܫ ܕܝܺܫܺܫܫ
*
:
*
ts
.
I
the floor and roof of the cavity. Strain gages attached to the steel
restraining rings showed that a horizontal (radial) stress, equal to
about 50% of the average vertica). pillar stress, was transmitted to the
rings. The model tests have thus shown, in a qualitative way, why floor
heaves and roof sags take place.
Cavity closures, as functions of time, for models axially loaded
to 4000 10/in.2 (280 kg/cm?) and 6000 16/in.2 (420 kg/cm²) at temperatures
of 22.5°, 60°, and 200°C are shown in Fig. 3. It is clear that elevated
temperature has a marked effect on deformation rates. Note also that the
12
-.
.
deformational behavior of the pillar loaded to 4000 psi at a temperature
16
Ihr
of 60°C is approximately the same as the sample loaded to 6000 psi at
.
SA
roor. temperature. This illustrates that the effects of elevated tempera-
ture on deformational betavior are much the same as those of increased
stress. However, at temperatures of 100°C and above, the deformational
behavior of the models departs somewhat from that produced by increased
stress. This is illustrated by the pair of curves for the 60° and 100°C
samples at 6000 and 4000 psi in Fig. 3. At higher temperatures, the pil-
.
.
.
lars tend to behave more plastically with consequently reduced spalling.
V
!"
Ki


-.AFT
day. 2. Section that in allen anal After
*
sonra
Domodo
..
: : :.
RO.
memori.....:
.
.
ideo conosna
...
siamo
i
in modo sin tid med hont
concise manne and can commodo consenso ai dedicada en musica
. w
.....
.
.
.
.
--
-
'
.
S
1
W. H
Y
.
.

222
-
VY
S72TYS

Watch
12
بيا
ORNL-DWG 65-1542

6000 psi 100 °C
VERTICAL SHORTENING OF PILLARS (in.)
4000 psi 100 °C
.
.
96000 psi 60 °C
i
2
.
-
*
4000 psi 60 °C
6000 psi 22.5 °C
4000 psi 22.5 °C
A
3.
.
i.
.
.
oo
50
100
200
250
300
ET
150
TIME (hr)
dia 3. Deformation of models at Different
y temperatures and stresses.

422
-
?
In many cases salt is mined to a shale. layer (sometimes called a
"parting") since these layers are planes of weakness at which the salt
will readily separate. The presence of shale partings can have a sig-
nificant effect on the rate of cavity deformation, depending on whether
the shale is at the top and bottom of the pillar or in the center of it.
This is shown in Fig. 4 by the deformation curves of model pillars de-
formed both with and without simulated shale partings (greased teflon
sheets) in the piilar. The actual effects to be expected in a mine would
lie somewhere between the two extremes show in Fig. 4.
E
'
S.
P:
t
-
EXPERIMENTAL FACILITY IN KANSAS MINE
TL
.
.
97
.
.
.
.
.
-
.
.
7711
.
15
9,.
.
4
The demonstration disposal of high-level radioactive waste solids,
initiated in November 1965 in the Carey salt mine at Lyons, Kansas, is
known as "Project Salt Vault."5,6 Among the objectives of the demonstra-
.
..
.
.
.
.
_
Lar.
tion are confirmation of feasibility and safety of disposal in salt mines,
12
SET
.
IND
.
1.-1!
and collection of information on creep, plastic flow, and mine stability
which are needed for the design of an actual waste-disposal facility.
Since highly radioactive waste solids are not available currently, ir-
radiated reactor fuel assemblies with supplemental heaters are used as the
heat and radiation source.
It might be expected that a logical choice of space for waste dis-
posal would be in existing mined-out areas. However, in the Lyons mine,
as in most other mines in bedied (flat-lying) salt deposits, the salt be-
neath the floor (where the holes for the waste containers would be drilled)
contains layers of shale with a few percent water content which is driven
out at temperatures above 100°C. This could produce problems of increased
Si
..
,
'
$
E
?
"
ORNL-DWG 65-10988
.
:
0.24
WITH FRICTION REDUCER
AT FLOOR AND CEILING
VERTICAL SHORTENING OF PILLARS (in.).
WITHOUT FRICTION REDUCER
WITH FRICTION REDUCER AT CENTER OF PILLAR
0 20 40 60 80 100 120 140
TIME (hr)
Deformation of Model Rock Sali Pillars at 4000 psi.
dig. 4. affects of Shale Partings on Deformation
.
i

nc
MA
TY
litru
MAI
Wir
10
corrosion of the waste containers and possible movement of radioactivity
out iuto the mine. Also, floor heaves, rocf falls, and sagging roof in
LE
all but the most recently mined areas (Operating period of the Lyons mine
was from the 1890's to 1948.) pose rehabilitation problems which might
be as expensive as mining new space. Therefore, it was decided to create
a newly mined area at the periphery of the mine, at a higher level and
of the most desirable gecmetry, so as to have the purest salt strata in
the floor where the radioactive sources will be located.
The layout of the specially mined, 300-ft-long (91 m), expérimental
area is shown in Fig. 5. In the first room is located the main radioac-
tive array which consists of seven 12-ft-deep (3.7 m) holes in the floor.
70
.
Seven 7-ft-long (2.1 m) reactor fuel containers were placed in the holes
GET
in November 1965. For comparison with the main radioactive array, a
TRX-
geometrically similar array, containing electrical heat sources, is low
cated in the fourth room. A third array, duplicating the main radioactive
array but located in the original mine floor, will ne loaded with used
radioactive sources about June 1966. In adlition, the temperature beneath
the center pillar of the experimental area will be raised to about 100°C .
by means of electrical heaters in the floor. Since this pillar-heating
.
test may produce extreme salt movements, it will not be started until near
the end of 1966.
5.
THERMAL STRESS EFFECTS IN THE MINE
At the end of December 1965 (46 days after start-up) the salt tem-
perature at the wall of the peripheral holes of the main radioactive { rray
was about 120°c, and at the wall of the center hole approximately 135°C.
ORNL-DWG 63-774 AR2

DU
WO
UVOD
FEET
50 100
150
.
ELECTRICAL
ARRAY
.
250
30 ft
40ft
FEET
C
AA
118-A-5-17
HEATED
PILLAR
109-A-N-2
-111-A-U-3
F. 105-A-U-37
ARRAYS
MAIN
100 RADIOACTIVE
50
.
SPECIALLY MINED
AREA 14-ft ABOVE
EXISTING FLOOR-
LEVEL
WASTE CHARGING
SHAFT FROM
SURFACE
U
30 ft
RAMP UP
*
*
C
C
.:
P
EXISTING MINE WORKINGS SHOWN
APPROXIMATE
FLOOR FABIOACTIVE
.
FLOOR RADIOACTIVE
ARRAY
11-
DO
PEARL
.
.
AN
2
.
fig. 5. Layout of Expenmental Area
12
In the vertical cente. planes of the main radioactive and electrical
arrays - about 9 ft (2.7 m) below floor level - essentially the entire
area with a circle formed by the peripheral holes (that is, a circle of
about 10-ft (3 m) diameter) was at or above 100°c.
Vertical thermal expansion of the floor in the center of the arrays
had reached nearly an inch (2.5 cm) by the end of December 1965. The
MO
PE
cx
floor uplift (measured in feet) as a function of time for each array at
".
.
the center and 10 ft (3 m) from the center 18 shown in Fig. 6b. It may
be observed that the rate of rise in and near the array is slowing down.
This is due to the fact that the rate of rise of the salt temperature
is also slowing down.
In Fig. 6a is shown the uplift profiles for room 1 (radioactive array),
along the north-south and east-west axes of the room. It is apparent that
thermal expansion of the material in the floor extends to 40 or 50 ft
(12 to 15 m) from the center of the array. The north-south uplift profile
shows the restraining effect produced by the presence of the adjacent
...
E
pilla-s.
c. Figure 70 shows the transverse expansion (in inches) taking place
in the pillar which borders the radioactive array room on the north side.
The curve labeled 109-A-N-2 is a measure of the amount of horizontal ex-
pansion taking place between the surface of the pillar (about halfway up
from the floor on the south face of the pillar) and a point about 10 ft
in toward the center of the pillar. The curve labeled 118-A-S-1 is the
corresponding measurement made from the north face of the pillar. (Lo-
cations of the gages are shown in Fig. 5.) The power was turned on in
the array at 806 "standard days" (November 15), and almost immediately
.
ORNL-DWG 66-618

la)
50.050
: FLOOR UPLIFT (ft)
NORTH-SOUTH PROFILE
EAST-WEST PROFILE
CENTER OF
al EXPERIMENTAL AREAL .
NORTHERN ENTRY TUNNEL
EDGE OF ROOM
0.025
SOUTHERN
EDGE OF ROOM
:
.
25
15
5 5 15 25 35
DISTANCE FROM CENTER OF ARRAY (ft)
45
0.100

0.075
CENTER OF ARRAY To
FLOOR UPLIFT (ft)
0.050
10 ft FROM CENTER
ū0.025
O ROOM 1 (RADIOACTIVE ARRAY)
ROOM 4 (ELECTRICAL ARRAY)
0 10 20 30 40 50 60 70
TIME (DAYS)
(a) Floor Uplift Profiles in Room 1 as of December 30, 1965.
(6) Floor Uplift in Array Rooms.
figure 6. Iloor Uplift Due to Thermal
Expansion :
ORNL-DWG 66-619

lo)
105-A-U-3
ill
Co-o-oto-o-o-200 111-4-u
STARTUP
INCHES

(6)
109-A-N-2
20-0°448-A-S-1
--
STARTUP
06288=:=8=:*:-
850
900
650 700 750 800
STANDARD DAYS
(a) Movement of Ceiling Relative to Six Feet Up.
(6) Transverse Expansion in Pillar 1-2..
dig. 7 Pillar and Roof hovement Due to
- Thermal Stresses

.
:
the other that comel.. 1*
the expansion rate on the south side of the pillar increased from about
0.15 in./yr (0.38 cm/yr) to about 0.45 in./yr (1.14 cm/yr), a threefola
increase. This marked increase in expansion rate halfway up the pillar
was due primarily to a transfer of thermal stress from the center of the
floor, since the increased rate was detected before any appreciable tem-
perature rise had taken place beneath the pillar. The fact that the ex-
pansion rate has not tended to decrease with time (as has the rate of
floor uplift) is due to the fact that some temperature rise 18 now tak-
ing place beneath the pillar (about 10°c at the south edge of the pillar
as of December 30). It will be noticed that the north side of the pil-
lar has also experienced a slight increase in stress (curve 118-A-S-1).
A similar behavior has been observed in the wall on the south side of
the room, and the behavior of the electrical array room is also essen-
tially the same.
The transfer of stress has not been limited to the adjacent pillars,
but has extended to the ceiling as well. That this should be so is at-
tested by the results of the pillar model tests described earlier. There,
it may be remembered, an axially applied load resulted in movement of
salt from above and below the piller out into the roof and floor of the
2
opening. Figure 7a shows the movement of the ceiling relative to a point,
6 ft (1.8 m) up into the roof. The curve labeled 111-A-U-3 is the roof-
gage data for a point 10 ft from the center of the radioactive array (10 ft
toward the mouth of the room, Fig. 5). The other curve (105-A-U-3) is for
a point about 45 ft (14 m) from the center of the array, out in the middle
of the access corridor (Fig. 5). It will be noticed that almost immediately
after start-up (806 "standard days") there was about a fivefold increase
in the rate of roof movement near the array (increase in rate of sag from
$.
y
ciutat
ciutat
*.
VES
about 0.12 to 0.55 in./yr (0.30 to 1.40 cm/yr), and a substantial increase
in the sag rate out in the entry corridor (from about 0.16 to 0.42 in./yr -
0.41 to 1.04 cm/yr). The data for the electrical array room show similar
movements taking place. Most of this movement appears to be separation
of the 2-ft-thick (0.6 m) salt layer in the roof from the thin shale layer
immediately above it. Movement rates would be expected to be lower if
the salt layer were thick enough to resist buckling, and a test is planned
to determine if the 2-ft-thick layer can be effectively bolted to the
3-ft-thick (0.9 m) salt layer above the shale parting.
.
Salt flow behavior in both the radioactive and electrical array rooms
has been essentially the same. It 18, therefore, concluded that thermal
effects on salt flow are much more important than radiation effects.
CONCLUSIONS
The pillar-model tests have proven themselves to be useful for under-
standing the way in which salt movements take place, and it is reasonable
to expect that the predictions based on the elevated temperature models
will be valid also.
No measurable effects of radiation on the flow of salt were expected,
and none have been observed during the first 50 days of operation of the
demonstration.
Thermal expansion of the floor, and increased transverse expansion
rates in the pillars adjacent to the array rooms, have been about as
expected.
The acceleration of movement in the ceiling (separation of a 2-ft-
thick salt layer) has exceeded that which was anticipated from the thermal
27
effects in the floor; however, the magnitude of the movement 18 such
that no trouble 18 expected from this source during the operation of
the demonstration. Even in an actual operation, movements of this mag-
trouble se
ected from this sourc
on of
nitude (or even greater) should not cause trouble during the time when
a room 18 still being filled with radioactive waste, and, after the room
18 filled, it is anticipated that it will be backfilled with crushed
salt. The increased roof movement does Indicate, however, that an extra
margin of stability must be allowed in the initinl design of the waste
disposal facility.
..
18
7. REFERENCES
1.
S. Serata, "Theory and Model of Underground Opening and Support Sys-
tem," in Proceedings of the Sixth Symposium on Rock Mechanics, Rolla,
Missouri, October 1964, University of Missouri at Rolla, 1964, pp.
260-292.

2.
and Potash Ore," in Proceedings of the Sixth Symposium on Rock Mechanics,
Rolla, Missouri, October 1964, University of Missouri at Rolla, 1964,
pp. 539-560.

. 3.
2.
T. F. Lomenick and R. L. Bradshaw, "Accelerated Deformation of Rock
Salt at Elevated Temperature," Nature 207(4993), 158-159 (July 10,
.1965).
.
4. R. L. Bradshaw, W. J. Boegly, Jr., and F. M. Empson, "Correlation
of Convergence Measurements in Salt Mines with laboratory Creep-Test
Data," in Proceedings of the Sixth Symposium on Rock Mechanics, Rolla,
Missouri, October 1964, University of Missouri at Rolla, 1984, pp. 501-
514.
.
R, L. Bradshaw, J. 0. Blomeke, W. J. Boegly, Jr., F. M. Empson, F. L.
Parker, J. J. Perona, and W. F. Schaffer, Jr.; "Disposal of High AC-
tivity Power Reactor Wastes in Salt Mines: A Concept and Field Scale
Demonstration," Nuclear Structural Engineering 2, 438-446 (October
1965).
W. J. Boegly, Jr., R. L. Bradshaw, F. M. Empson, W. F. Schaffer, Sr.,
F. L. Parker, and J. O. Blomeke, "Project Salt Vault: A Demonstra-
tion Disposal of High-Level Radioactive Solids in Lyons, Kansas, Salt .
Mine," Health Physics 12, 417-424 (March 1966).

+
-
1
END
DATE FILMED
*
.
2
SE-
1
.
-
.
.
.
.
*
N
*
.
N
277
5.
2
W
14
LY!
-