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Note: TAB 10
This is a draft of a paper to be presented for a Sturly Group on
Research Reactor Experimental Techniques to be held in Bucharest,
Romania, October 1964. Contents of this paper should not be
quoted or referred to without permission of the authurs.
MASTEK

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SOME ASPECTS OF LOW TEMPERATURE IRRADIATION FACILITIES
R. R. Coltman, C. E. Klabunde and G. F. Helder
SOLID STATE DIVISION
QAK RIDGE NATIONAL LABORATORY
Operated by
UNION CARBIDE CORPORATION
for the
U. S. Atomic Energy Commission
Oak Ridge, Tennessee
October 1964
SOME ASPECTS OF LOW TEMPERATURE IRRADIATION FACILITIES
R. R. Coltman, C. E. Klabunde and G. F. Fielder
Solid State Division, Oak Ridge National Laboratory
Oak Ridge, Tennessee
INTRODUCTION
It is well known that a large fraction of radiation damage in
pure metals recovers at low temperatures. To understand the basic damage
mechanisms which cause property changes it is desirable to carry our
irradiations and subsequent recovery studies at low temperatures. Further,
it is known that the character of radiation damage and the associated
property changes depend strongly upon the energy transferred to the pri-
mary atom in an atomic collision or recoil. Although reactor irradiation
dama ge has been studied for some years, only recently has the capability
of reactors to provide high fluxes of neutrons of well-defined energy
been exploited. These techniques in conjunction with advances in cryo-
genic techniques can serve to improve our basic knowledge of radiation
dama ge. Some of the considerations necessary for this type of research
are described in this report. Because of the authors' familiarity, this
report deals mainly with the low temperature irradiation facility lo-
cated at Oak Ridge National Laboratory (ORAL). It must be pointed out
that a particular low temperature facility is limited in its applic-
ability. The design and operation of a facility is dependent upon the
reactor structure and operation and on the requirements of particular
experiments. However, the description of a particular facility serves
to acquaint the reader with the common aspects and the scope of the '. ..**
work in this field.
SPECIFIC FLUX CONDITIONS
Various portions of a reactor neutron spectrum are known to
produce different types of damage. Figure l shows the isochronel re-
covery of resistivity changes in copper caused by various types of
Research sponsored by the U. S. Atomic Energy Commission under contract
with the Union Carbide Corporation.
-2.
irradiation. The effects shown here are observed in other metalst with
greater differences seen in many cases. Thermal neutron damage arises
from the recoil of an atom from the emission of energetic gamma rays at
the time of thermal neutron capture. Atom recoil energies are relatively
low for this mechanism and produce from one to a few interstitial atoms
and vacant lattice sites per capture. For some elements the effect of
transmutations must also be cons:dered. A fast neutron can transfer a
large amount of energy to an at sm by collision and through a cascade pro-
ce88 this struck atom produces a localized region of high defect concen-
tration involving several hundred displaced atoms. These different damage
configurations are believed to account for the difference in recovery be-
havior. Details of this problem, however, are not presently understood
and additional theoretical and experimental investigation 18 needed.
Irradiation with reactor spectrum neutrons produces a mixture of the
two types of damage in a ratio dependent upon the neutron flux spectrum
of the reactor and the nuclear and physical properties of the element.
For many elements and flux conditions, neither type of damage is pre-
dominant, and the interpretation of data can be difficult.
Using known methods, some specific flux conditions can be
obtained from reactor spectra. These conditions can have a purity
and intensity which are well suited to better defined radiation damage
studies. Figure 2 shows the cryostat-reactor arrangement of the CRNL
liquid helium facility. The light-water moderated swimming pool re-
actopmoperates at 1 megawatt with a thermal neutron flux of 1 x 10+
.n/cm/sec. at the reactor face. One purpose of this facility is to ob-
tain a reasonably pure thermal neutron flux at the cryostat. This is
accomplished by locating an aluminum tank 45 cm thick containing heavy
water between the cryostat and a face of the reactor. This provides a
thermal neutron flux at the cryostat of 8 x 1011 n/cm2/sec. with a ca
ratio (for Au) of 86. In terms of radiation damage it is found that
the thermal neutron portion of the total damage 18 about 85% for copper,
* which has only a 3 barn capture : cross-section. For other higher cross-
section elements, much greater damage purity can be obtained. In using
this general approach to obtain a pure thermal neutron flux, some judgment
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must be exercised. By increasing the moderator thickness, better flux
purity is obtained at the expense of flux intensity.
In Fig. I it is seen that the recovery beliavior of reactor fast
neut::ons (3 slug fast) damage is different from fission neutron damage.
Fast neutron spectra differ widely between renctors and between various
locations in the same reactor. This makes the interpretation of radi-
ation damage data very difficult for some types of experiments. The
f'ission neutron spectrum is well known and is confined to a relatively
narrow energy range compared to many reactor fast neutron spectra.
Fission neutrons, then, are a source for producing high energy dame.ge
wherein the defect configurations can be better defined and have less
variation than those obtained from reactor fast neutrons. Under certain
conditions, us converter tubes or plates can be used to obtain a suit-
able fission neutron flux. It 18 desirable to locate the converter in
a position where the reactor fast neutron flux is low or is known to
produce negligible damage compared to the fission neutron flux. A
moderator adjacent to the converter can cause a feedback of degraded
neutrons which will adulterate the fission neutron spectrum in the con-
verter. This is prevented by removing adjacent moderator for a modest
distance from the converter. Finally, the converter must be lined (or
the experiment surrounded) with a thermal neutron absorber such as cad-
mium or boron to eliminate thermal neutron damage effects.
We have made electrical heating tests on a mock-up of a converter
tube to be lowered around the cryostat (Fig. 2) which indicate safe behavior
at 500 watts power output with no external cooling. Cooling takes place
by natural convection of the helium gas in the cryostat housing dissi-
pating the heat to the pool water. Such a converter should produce a
fission neutron flux of about 6 x 101° n/cm/ sec. which is sufficient
for damage rate and recovery studies of some properties. With this
scheme no cooling failure safety precautions are required. The converter
can be lowered around the sample chamber at any time, allowing the al-
ternate study of thermal and fission neutron damage on the same specimens. ' ...
Energetic gamma rays produce damage in metals similar to that
produced by thermal neutrons." By surrounding a specimen or the sample
4-
chamber of a cryostat with a black neutron absorber such as cadmium or
gudolinium, a capture gamma-ray flux sufficiently energetic and in-
tense to study damage effects might be obtained. The cross-section .
for defect production by gamma rays is relatively small, and such &
scheme would require substantial reduction of any fast neutron flux in
the interest of dana ge purity. For the same reason, attainable gamma
ray dama ge concentrations will be small, even for a substantial thermal
neutron flux of 2.04 n/cm</sec. The scheme seems feasible for certain
types of experiments and offers one possible advantage. If the irradi-
ated portion of the cryostat sample chamber 18 completely covered with
neutron absorber, non-radioactive specimens can be removed from the
facility for study. This is of great advantage 1f removal is made
under cryogenic conditions.
Certain positions in some reactors already possess specialized
flux conditions. For example, T. H. Blewitt and co-workers at Argonne
National Laboratory have constructed a liquid helium facility. whose cryo-
stat is located in the graphite blanket of a CF-5 reactor where a high-
purity thermal flux of about 5 x 10+2 n/cm/sec. is available. A second
cryostat in the same liquid helium circuit incorporates a high power
converter with a flssion flux of about 1 x 1012 n/cm/ sec. This flux
makes possible. the study of intense damage and of saturation effects.
REACIOR OPERATING SCHEDULE AND GENERAL
DESIGN CONSIDERATIONS
The operating schedule of a reactor may influence cryostat
design for some types of research. For many experiments it is found
that the time required after irradiation for detailed recovery studies
is quite long and may exceed the irradiation time. If all measurements
are to be made on specimens in the irradiation position, additional dose
during lengthy recovery studies must be avoided. If operation of the
reactor can be subordinated to the operation of the low temperature
facility, no problem exists. Similarly, if the facility 18 designed
chiefly for removal of specimens at cryogenic temperature immediately
after irradiation, there should be little operational conflict. When
.
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the reactor is movable, as in the case of the ORNL facility, isolation
of the facility from irradiation 18 easily obtained with only a shor'
interruption of reactor operation. A moveable reactor can satisfy the
needs of many experiments, provided the number of fixed irradiation
positions is not too large. For more restricted operating conditions,
as with a fixed reactor, a cryostat with a long, cold sample chamber
may be used. Using appropriate seals between the experiment rig and
the access to the cryostat, the rig may be moved to a region of no flux
after irradiation without a change in temperature. Schilling and co-
workers at Munich have constructed a high heat capacity facility where-
in one of the liquid helium transfer lines serves as the sample chamber
of a cryostat located in a vacant fuel element position of a swimming
pool reactor. After irradiation the experiment is raised away from the
flux, and the refrigerant bypasses the irradiation portion of the sample
chamber through suitable low temperature valves. Another feasible ap-
proach to the fixed reactor problem is through the use of flexible trans-
fer lines which allow the cryostat to be moved during operation. This
is considerably more difficult since all transfer lines are vacuum
jacketed, and in the case of liquid helium additional refrigerated
shields inside the vacuum are usually necessary.
HEAT LOAD
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The heat absorbed by a low temperature irradiation system is,
of two distinct types--radiant and gamma ray. Since convective heat
loads from the atmosphere would be enormous, it is assumed that all
cold surfaces are vacuum jacketed. Radiant heat can be reduced through
the use of multiple reflective shield layers where conditions permit or
by wrapping cold surfaces with a low emissivity material such as alwai-
num foil. The principle of "super insulation" (concentric isolated
shields surrounding a cold surface, each theoretically reducing the
radiant heat load by a factor of 2) cannot be applied to that portion.
of the cryostat located in a gamma-ray field. Gamma-ray heating of an
isolated shield in a vacuum rai ses its temperature higher than ambient
and actually increases the radiant heat load on the system. If the
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ambient temperature at the irradiation portion of the cryostat 18 rela.
tively high, radiant heat input may be substantially reduced by auxiliary
cooling applied to this portion of the cryostat vacuum jacket. This can
be accomplished in several ways, including water cooling or a contained
flow of room temperature helium gas diverted from the helium circuit of
the facility. Since radiant heat input is proportional to the fourth
power of the absolute temperature of the vacuum jacket, the effects of
high ambient temperature should not be underestimated. In the interest
of efficiency, it may be expedient to reduce radiant heating by sur-
rounding cold surfaces with shield which are refrigerated to more easily
obtained intermediate temperatures. For example, with liquid nitrogen
systems the heat capacity of nitrogen from the boiling point to room
temperature (about equal to the heat of vaporization) can be used to
good advantage. For liquid helium systems, where the absolute heat
capacity is relatively low, refrigerated shields are essential. Clean-
liness, absence of leaks, and good pumping speed of the vacuum jacket
are particularly important for liquid nitrogen temperature systems where
the cryopumping action 18 limited. Heat leak through the vacuum in-
creases markedly at pressures above 10°3 mm. The cryopumping action
of lower temperature systems (4--20°K) gives considerable assistance
in maintaining a good vacuum..
Reactor gamma rays entering a cryostat more or less uniformly
heat thin materials and constitute a heat load which must be removed at'
the irradiation temperature. The mass of portions of the cryostat and
experiments located in the irradiation zone should be minimized. If
: space permits, gamma-ray heating can be reduced by surrounding the
cryostat with heavy element shields such as lead, bismuth, or tungsten..;
: The selection of a particular material depends upon whether a thermal
or fast neutron irradiation facility is being considered. Because of
capture cross-section considerations, tungsten is suitable for fast but
not thermal neutron facilities. Where gamma-ray intensity is high,
auxiliary cooling of these shields 18 sometimes necessary. Also, when
the refrigeration system 18 off and the reactor 18 on, it must be deter-
mined that the irradiated portion of the cryostat inside the vacuum
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jacket will not reach a dangerously high temperature due to gamma-ray
heating. This difficulty can be alleviated by venting the vacuum jacket
or by circulating a room temperature 2001ant such as helium through the
cryostat.
The intensity of gamma-ray heating can determine the design
and operating procedures for the cryostat sample chamber. If the sample
chamber is not part of the refrigeration circuit, experiments are easily
inserted and removed without circuit purging or the danger of radioactive
contamination of the circuit. Also, control of the sample chamber en-
vironment during irradiation and subsequent recovery studies is usually
easier. In this scheme gamma-ray heat generated in the experiment 18
transferred to the sample chamber wall via an exchange medium. It 18
assumed that the outer wall of the sample chamber is kept cold by the
circulating refrigerant. The temperature difference between the speci-
men and the operating temperature of the facility depends upon the ex-
change medium, the gamma-ray heating and mass of the experiment. For
modest heat loads (gamma-ray heating ~ 5 x 10 watts/gm and experiment
mass ~ 300 g) helium gas at about 1 atm. 13 used as a convenient ex-
change medium resulting in a few degrees difference between operating
and irradiation temperatures. For liquid nitrogen temperature facilities
with higher experiment heat loads, high purity nitrogen can be condensed
in the sample chamber to take advantage of the better exchange qualities
of a liqui.d. For all systems with high heat loads, it becomes necessary
to flow the refrigerant directly through the sample chamber to maintain
reasonable specimen temperatures.
CRYOGENIC IRRADIATION HAZARD
When oxygen is allowed to condense in the presence of high in-
tensity ionizing radiation, a considerable portion of the condensate is
converted to ozone. Systems for circulating or replenishing a cryogenic
vessel with commercial liquid nitrogen in the radiation field of a re-
actor tend to accumulate increasing concentrations of ozone. The ozone
originates from oxygen impurity in the nitrogen and accumulates because
-8.
Its boiling point is higher than that or either oxygen or nitrogen.
Similarly, in other types of systems the accidental admittance of air
to cold surfaces in the irradiation field can lead to deposits of liquid
or solid ozone. At certain concentrations ozone can spontaneously de-
compose or react with other materials explosively, either at low tempera
atures or upon subsequent warming. Several of these explosions have
occurred at various installations.”0 Details of the explosive mechan
ni sm do not seem to be completely understood, and safe operation 18
achieved through the positive exclusion of air from the facility. The
use of a single charge of high-purity nitrogen gas condensed in a system
for exchange purposes has operated successfully, since there was no
accumulation of oxygen impurity.
LIQUID NITROGEN SYSTEMS
Because of its relatively high heat of vaporization, commer-
cial availability, and modest cost, liquid nitrogen 18 presently used
in the operation of several irradiation facilities. Bochirol, Doulat,
and Weil have developed a system using the principle of the reflux con-
denser. The upper end of an aluminum sample chamber tube located out-
side the strong irradiation field of the reactor is cooled by commercial
liquid nitrogen. A single charge of high purity nitrogen is introduced
into the sample chamber where it condenses and falls to the bottom of
the chamber located in the irradiation field. A continuous reflux
action maintains a stable liquid level covering the irradiated speci-
mens. The system can operate continuously, has a thermal neutron flux
of 1 x 10+3 n/cm? / sec. and consumes about 80 liters of liquid nitrogen
per day. J. T. Howe et al. constructed a system using circulating
helium gas cooled by liquid nitrogen. The aluminum cryostat had a
sample chamber 1" in diameter and 22" long located in a thermal neutron
flux of about 4 x 104 n/cm/sec. of the CRNL Graphite Reactor. A sche-
matic circuit diagram is shown in Fig. 3. It may be noted that use is
made of the cold nitrogen gas evaporated from the liquid nitrogen pot.
The system could operate continuously and consumed about 75 11ters per .
day.
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The difficulty of removing radioactive specimens at cryogenic
temperatures after irradiation 18 much more easily handled at nitrogen
temperature than at lower temperatures. Using a single-walled specimen
irradiation can (usually aluminum) filled with liquid nitrogen, removal
without warmup 18 accomplished by rapid withdrawal and immediato in-
sertion of the can into a shielded Dewar vessel.
CASEOUS HALIUM REFRIGERATURS
Helium gas systems can provide irradiation temperatures of
'about 12--15°K. A schematic flow diagram of one such system used at
ORAL” 18 shown in tigo 4. Higli-pressure helium gas cooled by the re-
turn flow in a counterflow heat exchanger 18 further cooled by adlabatic
expansion in two expansion engines operating at low temperatures. The
cold engine exhaust gas at low pressure circulates through a cryostat
returning through the heat exchanger to the compressors which complete
the circuit. This type of system can have good reliability for sus-
tained operation and can be designed for relatively high heat loads.
The QRNL system had a heat capacity of about 500 watts at: 20°K and a
terminal temperature (no external heat load) of about 10°K.
LIQUID HAIUM REFRIGERATORS
In addition to the Argonne and Munich facilities mentioned
earlier, Swanson and Piercy°.9 have studied fission neutron damage in
pure metals at 1.74°K using a pumped helium dewar located in an ex-
ternal beam of the MRU reactor at Chalk River. Making careful, resis-
tivity measurements they studied dans.ge in metals with a flux of only
5 x 10° n/cm? / sec. and doses of about 2 x 1074 n/com?. Liquid helium
consumption was 6 liters per day during irradiation.
Figure 5 shows a schematic flow diagram of a recently com-
pleted liquid helium facility at QRRL. To briefly describe the opera-
ting principle of thi 3 system, it is convenient to divide the circuit
into two portions, the engine circuit and the liquefier circuit. In
the engine circuit, high-pressure helium fjs enters the main heat
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exchanger at room temperature, where it is cooled by the returning low-
pressure flows. It is then adiabatically expanded to a low pressure in
the expansion engines, where the final cooling in this circuit takes
place. It then enters the heat-sink exchanger, where it is warmed by
the high-pressure liquefier flow enroute to the Joule-Thomson (J.T.) .
valve. This constitutes the heat load on the engine circuit. The re-
turning flow is further warmed to room temperature in the main heat ex-
changer enroute to the first-stage compressor. In the liquefier circuit
a portion of the total high-pressure flow bypasses the engines and 18
further cooled to the engine exhaust temperature in the heat-sink ex-
changer. This flow is still further cooled by returning liquefier flow
in the J.T. heat exchanger. It is then isenthalpically expanded at the
J.T. valve, and the gas-liquid mixture proceeds through the cryostat,
where most of the liquid is evaporated; but little, if any, temperature
rise occurs. The returning flow is progressively warmed to room temper-
ature in the three heat exchanger sections enroute to the liquefier com-
pressor, where it is compressed and brought into the suction of the
second-stage main compressor. It may be noted in this system that
since the liquefier flow is returned to the discharge rather than the
suction of the first-stage compressor, the mass flow and to a great
extent the refrigeration capacity of the engine circuit is fixed by
the displacement of the first-stage compressor (for a fixed value of
the first-stage suction pressure). It follows then that the total ma88
flow through the system is variable, depending upon the demand of the
liquefier circuit. It is believed that this scheme leads to a some-
what more stable behavior of the liquefier circuitry and simplifies
the adjustment of the system to varied heat loads.
The system was tested with an electrical heat load to simulate
the effect of the cryostat. With a 20-watt heat load on the liquefier
circuit a stable temperature of 3.6°K was maintained using a flow of 20
standard cubic feet per minute (scim). (Engine-circuit flow under these
conditions was about 180 scfm.) from the general behavior of the entire
system under these, test conditions, it was alear that a heat" load of
about 40 watts could be absorbed at less than 5°K.,
-11-
:
Since the radiant heat load is a large fraction of the total
in this system, the use of a refrigerated shield surrounding all lique
fier circuitry offers great economy. A small flow (1 to 2 scfm) of high-
pressure cola (~16°K) helium gas taken from the engine inlet line 18
routed through a small tube down to the sample chamber of the cryostat,
where the line is attached to a heat trap and refrigerated shield for
the sample chamber (see F4g. 6). It is then returned along a shield
which surrounds the liquid-helium transfer lines and the shield supply
line, absorbing radiant heat en route. The flow rate 18 adjusted accord-
ing to its temperature after having covered all liquefier circuitry. In
test runs with an electrical heat load of 25 watts to simulate the radiant
heat load of the cryostat, a flow of 1.2 scfm was required to maintain a
shield return temperature of 125°K. It is estimated that the shield re-
duces the liquefier radiant heat load by a factor of about 100. When
operating with the cryostat it is possible to adjust the shield return
temperature for optimum performance of the liquefier. The remaining
heat capacity of the shield gas 18 used to cool additional shielding
which surrounds the colder parts of the main heat exchanger. It then
returns to the suction of the second-stage compressor via a flow regu-
lator. High-prussure gas. is used for the refrigerated shield circuit,
since it can be transmitted through small-diameter low-mass tubes where-
in the associated pressure drop ha's little effect on the remainder of
the system.
All cold portions of the system are vacuum jacketed. Under
operating conditions ine vacuum is better than 10° torr. In addition
to the vacuum, "super insulation" in the form of alternate layers of
aluminum foil and 15-mil-thick fiber glass sheets have been wrapped on
all sections. Seven foil and six glass layers are used on the heat ex-
changers and most transfer lines. Flve foil and four glass layers are
used on the refrigerated shiela (except in the irradiation zone where
a single layer of foil 18 used).
The main heat exchanger in this system weighs about 600 lbs,
and considerable refrigerator running time is required to cool the system
to terminal temperature in preparation for an experiment. To reduce
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-12
is.
running time and hence maintenance, a liquid-nitrogen precooling system
has been installed. By use of a small compressor as a pump, liquid nitro-
gen is drawn through a 3/4" tube located in the center of the main heat
exchanger. After precooling overnight (~16 hr), one-half of the heat
exchanger 18 at about 800K, and a good gradient 18 established in the
remainder, then four hours after startup of the engine circuit the heat-
sink exchanger reaches about 13°K, and the liquefier is ready for oper-
ation.
Figure 6 shows a sketch of the cryostat. The U-shaped arrange-
ment is used to reduce the diameter of the vacuum jacket around the
sample chamber as much as possible, so that the smallest possible con-
verter can be employed for f18sion-neutron bombardment. Thin-walled
stainless steel tubes are used for all the transfer lines and most of
the vacuum jacketing. The gas entering through the refrigerated shield
(~16°K) is first applied to a 12" long copper heat trap, which is
separated from the sample chamber by 2 in. of thin-walled stainless
tubing. After leaving the heat trap it cools a copper shield around
the cryostat proper. The upper end of the heat trap is connected to
a thin-walled stainless tube, which travels 8 in. before exiting from
the vacuum jacketing and continues to the top of the facility cerving
as a sample tube. Now, in operation helium is condensed in the thin-
walled copper sample chamber, so that an experiment is immersed in non-
boiling liquid helium. The mass of that portion of the cryostat and of
that portion of the refrigerated shield circuit located in the gamma-
ray field is about 250 gm each. The associated gamma-ray heat load,
however, 18 small compared with the radiant heat load on the total
shield circuit. Camma-ray heating in this facility 18 estimated at
10°C watts/gm. With the cryostat in the refrigerator circuit as seen
in Fig. 2, a bombardment temperature of 3.55°K is obtained at full
reactor power and 3.05°K at one-tenth full power.
Reliability of the refrigeration system 18 an important design
criterion for an irradiation facility. Inadvertant warming of a specimen
due to refrigeration failure requires a repetition of the experiment.
Uninterrupteå runs up to 400 hours have been made with the ORNL facility.
-13-
TEMPERATURE MEASUREMENTS
The accurate measurement of temperature is important to most
irradiation experiments. The well-known vapor pressure-temperature re-
lationships of liquid nitrogen and helium can be used to determine
irradiation temperature when these liquids are used in the sample
chamber of the cryostat. Since warmer liquid rises, the actual irradi-
ation temperature may be slightly lower than indicated by the vapor
pressure. Copper-constantan thermocouples give suitable response down
to about 30.-40°K and are found to be quite stable up to integrated
doses of at least 1010 n/cm2. Small carbon resistors (nominal 1000
1, 1/2 or 1/10 watt) have good sensitivity below about 50°K and are
reasonably stable under irradiation and thermal cycling. Their response
rate is fast and they require relatively simple measuring instruments.
However, a temperature calibration of each resistor is required. A
helium gas thermometer is not affected by irradiation or thermal cy-
cling, has long term stability, and is capable of great accuracy. How-
ever, its response is slow.
i
In a recent experiment on cadmium performed in the ORNL
facility, temperature measurements believed to exceed the stability of
the carbon resistor were required. Figure 7 shows a diagram of a small
experiment can along with various thermometers. This assembly is in-
serted into the sample chamber of the cryostat. Before irradiation,
helium is condensed in the sample chamber and can. During annealing
studies after irradiation the sample chamber 18 evacuated. The heater
current is turned on and the liquid in the can is allowed to evaporate
at a pressure of about 1.5 atm. The helium at this pressure remains
in the can serving as an exchange gas during the annealing pulse.
The usual concept of a gua thermometer as a large bulb with
a fine capillary having negligible volume leading to a pressure meter
also of negligible volume is useless here. The sample chamber of the
cryostat 18 about 6 meters down in the reactor pool and 5 additional
meters are required to reach the instrument laboratory. A capillary
of this length fine enough to keep the parasitic volume small would
.
be so fine as to reduce the response rate to nearly zero. Instead of
this approach the external or parasitic volume 18 purposely made large.
Since the cold zone of the cryostat 18 qui te short, only about 60 cm
of capillary is required to isolate the sensing bulb located in the
sample can from ambient temperature, and 3 mon copper tubing 18 used
to reach a sensitive pressure meter in the laboratory. An additional
bulb at room temperature brings the total external volume to 20 times
that of the sensing bulb. This scheme gives a pressure-temperature .
response which is non-linear and very sensitive up to about 30°K. A
careful determination of the ratio of warm and cold volumes and a de-
tailed calculation of the pressure-temperature relation provides a
practical thermometer reproducibly readable to 0.1% of the absolute
temperature in the range of 3--30°K. To reach a pulse temperature
the fast response of the carbon resistor 18 ured, while final deter-
mination 019 temperature is made with the gas thermometer. Thus, the
best features of each technique are combined to give accuracy and fast
response.
Special techniques for carrying out particular types of ex-
periments involving the measurement of stored energy, length change,
damping, yield stress and resistivity have been adequately described
elsewhere. 3,10,11,12
A NOTE IN 'CONCLUSION
The recent experiences of several research workers using the
1 megawatt, open swimming pool reactor at ORAL show that this type of
reactor has great advantages for solid state work. Direct access to
the core from the water surface permits easy insertion and removal of
experiments and bulky, facilities. The large free space around the core
permits the use of converters, shields or moderators to produce various
flux conditions. For many experiments the problems associated with
biological shielding are easily solved. If the reactor 18 moveable,
even greater versatility 18 obtained since the scheduling of neutron
flux at a particular location 18 quite flexible.
-15-
•
:
ACKNOWLEDGMENT
-
-
-
-
-
-
.
It is a pleasure to acknowledge the valuable assistance of
J. K. Redman, J. T. Howe and W. E. Busby of ORAL throughout the design
and construction of the new liquid helium facility. The excellent
support of D. L. McDonald of the Australian Atomic Energy Commission
during the design stage and Prof. R.L. Chaplin of Clemson University
during the final assembly and testing stages of the system are most
gratefully recognized. The continued support and encouragement of
F. W. Young, Jr. and D. S. Billington of CRNL throughout the entire
project are sincerely appreciated..
-
- -
-
-------
--
--
-
-
-
--
-
-
-
.
om
.
.! wi..
.
REFERENCES
...
1. R. R. Coltman, Jr., C. E. Klabunde, D. L. McDonald and J. K. Redman,
J. Appl. Phys. 33, No. 12, 3509-3522 (1962).
2. 0. 5. Oen and D. K. Holmes, J. Appl. Phys. 30, 1289 (1959).
3. R. Strumane, J. Nihoul, R. Gevers and 8. Amelinckx, The Interaction
of Radiation with Solids, North Holland Publishing Co., Amsterdam
(1964).
4. N. Riehl, W. Schilling, H. Meissner, Research Reactor Journal 3,
9 (1962).
5. R. R. Coltman, T. H. Blewitt and T. 8. Noggle, Rev. Sci. Inst. 28,
No. 5, 375-380 (1957).
6. L. Bochirol, J. Doulat and L. Well, Cryogenics 1, No. 1, 44-46 (1960).
7. J. T. Howe, W. E. Busby and R. R. Coltman, Solid State Div. Ann.
Prog. Rept., Aug. 31, 1958, ORNL-2614, p 72. i
8. M. L. Swanson and G. R. Piercy, Can. Jour. of Phys. 42, 1605-1623
(1964).
9. D. J. Mackinnon and G. R. Piercy, Atomic Energy of Canada Ltd. Rept.
No. 1423, (1961).
10. F. E. Hoare, L. C. Jackson and N. Kurti, Experimental Cryophysics,
Butterworth Press (1961).
11. R. R. Coltman, Radiation Damage in Solids, I.A.E.A., Vienna (1962)
pp 205-229.
12. T. H. Blewitt, "Low Temperature Irradiation Studies," Rendiconti '
della Scuola Internazionale di Fisica "E. Fermi", XVIII Corso,
Academic Press, London (1963) p 630..
:
:
-
-
FICUIU CAPRIOTS
Fisi.
Fis: 2.
.
Fio. 3.
Ihc Isochroval Recovery or Varicu Types of Neutron Dariage in
Copper. (DAG 67:8607;
the Cryostat and Reactor arrangement of the Liquid Feliwn
rradiation Facility at Chris. (DWG 63-2214)
Schematic Circuiü D üren oi a Liquid Nitrogen Irradiation
l'ucility at OMIL. (C 777)
Schematic Diüran Ui: ORL rivals Gas Facility. (D:G 17752A)
Suncratic Flow Diura O Con Lista de um Facility.
(DHU 03-2215;
Liguid jiriini tivi. 0:"7053 wodü. (Dr 63-1770)
Liquid llciu. S n aviüüion 4seztüly. DC 611-44519)
vect.
Fi:. 5.
C.
Lu?
11:;: 1.
Fii. .
T
-
u
12
.
.
.
'
.
-
t
.
.
(6.13.8)
UNCLASSIFIED
ORNL-LR-DWG 64869R

RECOVERY (%)
FLUX Ap(10-92cm) Il
O FISSION (87%) 1.01
• 3-SLUG FAST (82%) 2.36
O "NORMAL"
2.68
•"THERMAL" (67%) 1.27
3-min PULSES
.
RECOVERY(%/°K)
0
10 20 30 40 50 60 70
TEMPERATURE (ⓇK)
Isochronal Annealing of Irradiated Gul Fig i.

Christine
.
UNCLASSIFIED
ORNL-OWG 63-2214
LIQUID HELIUM TRANSFER LINES.
-
BIOLOGICAL SHIELD
MW
SAMPLE TUBE –
HOUSING TUBE
· (6-in. OD)
18 ft
SAMPLE CHAMBER
REACTOR
CORE
28 in.
020
CRYOSTAT HOUSING
BOX (912 X 12 in.)
I aim HCLIUM
GRID PLATE
Fią2
.
260.16 STAINLESS BALLAST SLAB
POOL FLOOR
UNCLASSIFIED
ORNL-LA-OWO 42771
Na OFF GAS
....'.

----
-
---
-
-
-
FM PRESSURE
HELIUM FROM CRYOSTAT
.
HELIUM TO CRYOSTAT
UTITI
COUNTERFLOW EXCHANGER
ENCLOSED IN VAPOR
COOLED SHIELD
LIQUID Nat -
FLOWMETER
70-1b
RELIEF
VALVE
-
VACUUM JACKET
TO LOAD
-
---
---
1
BY
PASS
PASS
RELIEF VALVE
FUME FILTER
SSD-C-1335-19
-
--
-
3.
---
OIL
SEPARATOR
SSD-C-1335-18
-
.
-,
EXHAUST
-
1
-
:-
-
HELIFLOM
HELIFLOW
TYPE-12XF12
*
-
.
-
- ... -r--.-
-
OIL
DUMP
-.
.--
EVACUATION
..
(Fig 3
.
OIL RETURN
.
HELIUM CHARGE
.
.
CARRIER
COMPRESSOR
MODEL 6F25
23.9 cm DISPLACEMENT
EXPANSION
TANK
1
SX4
--
.
.
.
.
:
.
SER
.
.
.
.
.
.
XVN
.
2
LI
O TV
· UNCLASSIFIED
ORNL-LR-DWG 17752A

FIRST
STAGE
SECOND
STAGE
EXPANSION
ENGINES
WATER COOLED
50-hp COMPRESSOR SECTION
HOLE 12
CRYOSTAT
EXPANSION
TANK
COUNTER FLOW
HEAT EXCHANGER
Fiąt
Schematic Circuit Diagram of Arthur D. Little Helium Refrigerator.
.
-
HAI
2
.
UNCLASSIFIED
ORNL-OWG 63-2215
EXPANSION ENGINES

12 am
16°K
1.4 atm
10°K
ANNULAR
PASSAGE
.
.
REFRIGERATED SHIELD
..
.
300°K
2-4
.
J.T. VALVE
'.
OUTER
.
A
MIDDLE
O
INNER
C
S
LIQUEFIER
(184)
(184)
CRYOSTAT
3.5-5°K
COMPRESSOR
STAGES
(DISPL.-cim)
FLOW
REGULATOR
(100)
MAIN
HEAT SINK JOULE - THOMSON
5 in. OD x 29 17 5 in. OD x 211 1/2 in. OD X 8 f1
CONCENTRIC TUBE-RIBBON PACKED
COPPER HEAT EXCHANGER
(40)
CIRCUIT LEGEND
ENGINE 160-200 sctm
LIQUEFIER 3-30 scfm
REFRIGERATED SHIELD 1-2 scom
(20)

UNCLASHFIED
OM-Owo tonu

SAMPLE TUBE
e
--
- STAINLESS STEEL
HEAT TRAP, 8 in. LONG
.
-
-.-
-
------
THIN COPPER
REFRIGERATED HEAT
TRAP, 12 in. LONG
-
-
--
- 180K
-
-
-
-
.
IBH
TOTAL
SYSTEM
-STAINI.ESS STEEL
HEAT TRAP, 2 in. LONG
VA
THIN.COPPER
REFRIGERATED
SHIELD
LIQUID HELIUM
3.5 TO 50K
REFRIGERATED SHIELD.
THIN-WALI.ED COPPER
SAMPLE CHAMBER,
l-in. 1D X 842 in. LONG
TI
VACUUM JACKET
>
-in-00 COPPER
TUBING
-
-..
-
PATEL
INCHES
XVII
- REFRIGERATED SHELD SUPPLY
- LIQUEFIER SUPPLY
LIQUEFIER RETURN
I fir 6
.
UNCLASSIFIED
ORNL-DWG 64-4619

to
7-in. THIN-WALL STAINLESS
-in. THIN-WALL STAINLESS
-
0.032-in. OD STAIN
LESS SHEATHED
"HEATER
0.020-in. ID CAPILLARY 30-in. LONG
.-
.--.
.
-
-
-
------
-
WIRE BUNDLE
(ALL WIRES GO TO
BOTTOM FIRST)
--
FIRED LAVITE SPACER DISK
-
-
-
-
-
-
-
-
- COPPER CAN (3 x A-in. DIAM
X 0.010 in. WALL
-
.
..
GAS THERMOMETER BULB
(5 cm3)
..
.
-
.
.
.
THERMOCOUPLE
.
nte...
CS
TY
- 10-W CARBON RESISTOR
(THERMOMETER)
.:
:
-
I
T
'
-
.
.
- CADMIUM SAMPLE
(0.0012 0.031 x 1/4-in.)
.,
KUWAHUSAY
:
MS
1
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.
LA
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-
At
.
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.
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.
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.
.
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How
.
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2.
..
at
Cadmium Sample Rig
Fię z
DATE FILMED
12/31 /64

pse
LEGAL NOTICE
This report was preparod as an account of Govornment sponsored work. Neither the United
States, nor the Commission, nor any person aoting on behalf of tho Commission:
A. Makes any warranty or representation, expressed or implied, with respect to the accu-
racy, completeness, or 'usofulness of tho Information contained in this roport, or that the uso
of any information, apparatus, mothod, :r process disclosod in this roport may not infringo
privatoly owned rights; or
B. Assumos any liabilities with respoot to the use of, or for damagoi rosulting from the
use of any information, apparatus, mothod, or process disclosed in this roport.
As used in the abovo, “porson acting on behalf of the Commission" includes any om-
ployee or contractor of tho Commission, or omployee of such contractor, to the oxtont that
such omployoc or contractor of the Commission, or omployee of such contractor preparos,
dissominatos, or provides aCCOSI to, any information pursuant to his omployment or contract
with the Commission, or his omploymont with such contractor.
END