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DATE "_; August 5 1971

   

  

_T___i'_'-'FURTHER DISCUSSION OF 1NSTRUMENTATION AND CONTROLS L
DEVELOPMENT NEEDED FOR THE MOLTEN SALT BREEDER | j. R

  
    
  

R Prevaously pubhshed mformahon (J.R. Tallcckson ’ R. L Moore ; und S J Dlflo, |
Efifi_;f-;.,--l'{_f..;.-Insi‘rumem‘c:tu:m and Controls Development for Molten=-Salt Breeder Reactors, ORNL-TM-
1858, May 1967) concerning the development and evaluation of Process instrumentation
S -'?"_'_‘app‘hccble to molten-salt breeder reactors: (MSBR) was updated. Areas. where Snstrumenta- v
'~ “tion techniques and components tested durmg Operahon of the Molten-Salt Breeder |
" Experiment may be applicable to the MSBR are described and recommendation for further - -
-~ ... development are stated. In thls study to date, no problems are foreseen that cre beyond o
Tl ;ihe present sfate of the art, s 7 S St

 
 

ST _eywords Developmenf flu:d-f redcfors:fusedsali'smsfrumenfcfion,MSRE, o
L, "_j__;__-’_;zy'-iMSBE MSBR reactors S e T L e T e

 

LT -ZIU“cEThls “document ° eontoms mformahon of a prehmmory nature -
- .2 and-was_prepared- primarily. for -internal .use at the Ock Ridge Nahonal _ -
o 'Luborufory At s sub;ect #o fevmon or correction and therefore does T
e "nof represem o finalreport. .. . | : S .

 

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This report was prepared as an_account of work sponsored by the Uni__fed

States Government. Neither the United States nor the United States Atomic

Energy Commission, nor any of their 'emplrdyees, nor any of their contractors,

subcontractors, or their employees, makes any warranty, express or implied, or -
assumes any legal liability or responsibitity for the accuracy, completeness or-

usefylness of any information, apparatus, product or process disclosed, or
represents that its use would not infringe privately owned rights.

 

 

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Introduction

General Comments
Temperature Meosureme nt

Pressure Measure ment

CONTENTS

leferenhal Pressure Measurement

" Flow Measuremenf
Level Measuremenf

,Salt lnventory Measureme

nf

- Containment Penetrahon Seals

' Gas-System Control Valves

 

 

 
 

 

 

“NOTICE-

This  report was- piepared as an- account of work
sponsored by the United States Government. Neither

. | the United States nor the United States Atomic Energy | -
~."| ‘Commission, nor any -of ‘their employees, nor any of |
| -their’ contractors, subcontractors, or their employees, |
--'| ‘makes any warranty, express or implied, or assumes any .
=+ 7} legal . Hability or responsibility for the accuracy; com-
..} pleteness or usefulness of any information, apparatus,
| ‘product or process disclosed, or represents that its use

 

 

 

=l would not infrmge privately owned rights

. BISTRIBUTION OF THIS DOCUMENT IS ENLIMITED

 

Page

W O S~ M

11

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15
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1. INTRODUCTION

In a previous report,® Tallackson, Moore, and Ditto had discussed
their evaluation of instrumentation tested during operation of the Molten Salt
Reactor' Experiment (MSRE) and its suitability and deficiencies for gpplication
to molten-salt breeder reactors (MSBR's).27® Many of the instrument components
used successfully in the MSRE will be directly applicable'fo the MSBR. This
report summarizes and updates the material covered in the previous (ref. 1)
report. The scope of coverage is confined to process instrumentation; it does not
cover nuclear instrumentation because recent advancements in the development
of high temperature nuclear detectors would make such discussion premature.
After these latter developments have been adequately reviewed and evaluated for
application to MSBR's, they too will be reported. -

2. GENERAL COMMENTS

Although it is reasonable to expect that MSBR process instrumentation.
will require designs beyond the present state of the art, no problems are
foreseen that could not be resolved by further developme nt of components and
techniques. Many instrument components used successfully in the MSRE will be
directly applicable to the MSBR. Similarly, experience being gained by the
utilities industry with instrumentation of supercritical pressure steam systems will
be applicable to the MSBR.

MSBR process instrumentation located outside the biologically shielded
areas and not an integral part of the containment system can be conventional
equipment. Some standard components, however, may require some upgrading,
and a strict quality control program will be required to ensure a level of relidbility
and performance commensurate with MSBR requirements.

 

1 J. R. Tallackson, R. L. Moore, and S. J. Ditto, Instrumentation and
Controls Development for Molfen Salt Breeder Reactors, ORNL-TM-1856
(May 22, 1971).

 

2pP. R. Kasten, E. S. Bettis, and R. C. Robertson, Design Studies of
1000-Mw(E) Molten-Salt Breeder Reactors, ORNL-3996 (August 1966).

 

. 2R. B. Briggs, Summary of Objectives and a Program of Developmenr of
Molten-Salt Breeder Reactors, TM-1851 (June 1967).

 

-
 

 

(" ".\ "

S

All process tnstrumentohon components Iocored wrthm the contommenf
cells or as an _integral part of the containment system must. probobly be considered

" developmental. - These componenfs are predominantiy primary sensing elements

for measurement of flow rates, pressures,. levels, weights, and temperatures in

the salt-containing pipes and vessels, in the associated purge and off-gas systems,
and in the salt chemical processing facilities. Other such components are final
control elements (such as off~gas control valves), leadwire and piping connections

to the sensing and final control elements, remotely operated disconnects, and

containment penetrotlon seals. .

| Present plons,-,fo-,control the temperature of the reactor, drain, and steam=
generating equipment by furnace heating will preclude the use of some devices
and techniques that were employed successfully in the lower-temperature environ-
ment of the MSRE. The physical size of the components and the space available
for equipment could restrict otherwise acceptable techniques, such as weighing

~sqalt tanks, and tend to oggrovofe some problem areas, such as insulation shunf
- resusfonce in signal cobles., S |

Tl'le elecrrrcal conduchvrty of fhe MSBR salts wrll be a srgmfrcont factor in

e lecting the type of primary sensing elements that can be used. Although the con-

ductivities of MSBR salts are not known with certainty, they are estimated to be
about 1 mho/cm--about the same as MSRE salts. If these conductivities were an

“order.of magnitude less, some of the MSRE devices could not be used. Conversely,

if these conductivities were significantly higher, the existing devices would perform

better; and possibly some techniques that could not be used in the MSRE could be
- used in an MSBR. For example, srgnrfsconfly I-ngher conduchvrhes would permit use
of @ mognehc flowmeter. s ,

Development of other equrpment and techmques, such as an electr:cul
penetration into salt-containing pipes and vessels, would undoubtedly lead to

 improved instrumentation and new ideas for development. Some development
will also be required to adapt 'MSRE ‘control components to fhe hrgh pressures and
| ---remperotures in some portsons of rhe MSBR | -

e --_3.3-TEMPE-RATUREMEA’SUREMENT:__-'_' R

The materials and rechnlques that were used for measurement of MSRE

“temperatures should be odequate for most MSBR opplrcohons, although furnace

heating of the MSBR reactor cell will create new problems that might require.

*further development. It is expected that much of the test data and equipment
procurement standards being developed in the LMFBR thermometry program will be

applicable to the selection and development of instrumentation for MSBR tempera-
ture meosuremenf
 

 

6

The reactor cell temperature of ~ 1000°F will require development of in-cell
leadwire, disconnects, and containment penetration seals.  Additional development
‘will be required to obtain greater measurement ac¢uracy and to ensure long=term
(30-year) performance. Development effort could also be profitably applied to
methods of thermocouple attachment, to an investigation of radiation pyrometry
- techniques, and to measurement of srnall dnfferentml femperafures at elevcfed
temperctures.

| 4

Although ‘the performance of ‘MSRE thermocouples was very encouraging,
improved measurement accuracy and drift stability are needed. Measurement of -
small differences between two high temperatures was not satisfactorily accomplished.
The accuracy obtained with series~opposed (bucking) thermocouples and extreme
care in design and installation was generally adequate for MSRE purposes, but, -
without furfher development, it msght be only marginal for the MSBR.

- The femperatures of heated pipes and vessels in the MSRE were measured
by mmerul-msulated Inconel-sheathed, Chromel-Alumel thermocouples.  Results
of developmental tests and observation of the field performance of this type of
thermocouple indicate that an initial (hot junction) measurement accuracy of +2°F
- and a long=term (noncumulative) drift rate of less than 2°F/year can be obtained
~ ot operating temperatures.in a range from O to 1300°F if (1) the thermocouples are
carefully selected and calibrated, (2) attention is paid to details during design,
fabrication, and installation, and (3) strict quality control is maintained. In
particular, the materials must be handled and assembled with cleanliness, the
composition of the insulation must be controlled to specified values, and the grode
and homogeneity of the thermocouple wire materials must be carefully controlled. To
obtain highest accuracy, the design of the sensors and their installation must protect
them against stray radiative and convective heat sources which might result
in heat transfer to or from the sensor and, thus, biaosed measurements.

~ There is a good possibility that improved accuracy of both absolute and
differential measurements of high temperatures in molten=-salt systems can be obtained
by using ceramic-insulated platinum resistance thermometers. Several companies
have recently marketed resistance thermometers rated for operation at MSBR tempera-
tures and higher. Several thermometers rated at 850°C (1562°F) were tested at
ORNL for stability.® Although the calibration shifts were excessive in initial thermal
cycle tests, it was later demonstrated that these shifts would be decreased to accept-
able levels by operating the thermometers at the maximum rated temperature for more
than one week. Although the results obtained aofter high-temperature stabilization

 

¢ Molten-Salt Reactor Program Semiannual Progress Report for Penod
Ending August 31, 1967, ORNL-4191, pp. 22-24, 47.

 

® Molten-Salt Reactor Program Semiannual Progress Report for Perlod
Ending August 31, 1968, "ORNL-4344, pp. 94-95.

 

 
 

 

"

w'

( o’ . ¥

7

- were: encourqglng , more data are needed to determine the long-term stability of
 these devices. The LMFBR Thermometry Program at ORNL mcludes plans for:
= repeatmg cmd expandmg these tests. =

Multlconductor, gloss-msulated silicone=impregnated, copper-sheathed
thermocouple cables used in the MSRE between the in-cell disconnects and the
out=of=cell junction boxes will not be usable in the MSBR hlgh-temperature reactor
and drain cells, and probably will not be suutable for long-term operation in areas
where the radiation level is extremely high (> 100 R/hr) due to insulation degradation

“and the effects of radiation-induced outgassing of the silicone-insulating materials.

In the MSRE, outgassing produced excessive pressure buildup in organically insulated

- cables that were exposed to high radiation and sealed at the containment penetration

and the in-cell (dlsconnect) ends. Inorganic-insulated leadwire would be preferred
in all high radiation areas in the MSBR.and probably would be mandatory in the
furnace-heated cells. In these cells profective sheathing will be required for all
in-cell thermocouple wiring. Also for use in these cells, disconnect devices must
be developed which will be compatible with the furnace atmosphere and remote

‘maintenance requirements. Multiconductor, mineral-insulated, sheathed-thermocouple
~ cable assemblies probably will be satisfactory for all in-cell leadwire and containment

penetration service, but the major problem will be to develop a satisfactory method of
sealing the ends of the cable. Although it would be more difficult to develop seals
and techniques for installing multiconductor cable through a penetration than for
installing a thermocouple through an individual penetration, the advantages to be
realized from fewer penetrations required for multiconductor cables would more than

| _-|ust|fy the development cost, Other considerations, however, such as maintenance

requirements and separation of safety system channels could influence the decision
toward use of individual penetratnons, . Both methods need to be studied and evaluated
in greater detall

The thermocouple attachment technlques used for the MSRE probably will be

_, sqtlsfactory for the MSBR, although they were sometimes time consuming and costly..
~~ Small improvements in these techniques.could yield sugmflcant dividends, because a
~_lorge number of thermocouples wall be requ u‘ed (over 1000 were. mstolled on the

o MSRE).

Infrared photographlc and rqdlatlon pyrometry devuces mlght enable mappmg

_7: "'of temperature contours of . large exposed surfoces (such as the MSBR reactor vessel),

possibly by use of a closed-tircuit television camera equipped with an infrared filter.

~ Sucha temperature profile might be determined more accurately by mechanically
| maneuvermg a radiation pyromefer to produce a scan pattern similar to the raster -
~ produced on a television scréen. Since the feasibility of these devices would be
- . strongly dependent on the physical geometry of the system viewed and of the sur-
‘rounding area, an investigation of their fecmb:hty and the deve lopment of equipment
- and techniques should be initiated early in the program.  Pyrometric devices whose

design is based on usinig the preceding principles are commercnally available, and

they may be adaptable to MSBR needs.
 

 

8

~ Ultrasonic devices have been applied recently to measure temperature, and
some devices are now available commercially. Although we have not determined
the need for such devices in the MSBR, they might be usable for special applications,
such as measurement of in-core temperatures. The LMFBR Thermomerry Program also
includes investigation of ultrasonic sensors.

4. PRESSURE MEASUREMENT

Measurement of pressures in systems not containing molten salfs or hlghly
redioactive fluids will not present significant problems. In systems containing
molten salts some pressures might be indirectly measurable with MSRE techniques
* and others might be directly measurable with NaK-filled transmitters. However,
no pressure measuring device is available that is suitable in its present form for .
dlrectly mecrsurmg pressures (or dlfferenhal pressures) of fhe fuel salt. o

In the MSRE molfen-salf Ioops the pressures were defermmed mdlrecfly by
measuring the pressures in gos=purge or supply lines connected to gas spaces in the
“drain tanks and pump bowls. This technique will not be usable in the MSBR where
- gas purges cannot be tolerated or where high-frequency response is required.
Additional work would be required to develop a means of directly measuring salt
pressures, since part, or all, of the pressure measuring device would have to be
located close to the pressure tap. within the containment vessel and, thus, the
device would have to withstand the effects of high temperature, radiation and a varying

ambient pressure. In particular, if the reactor and appurtenances are to be heated
~in a furnace, then all pressure transmitter components must be located outside the
heated zone or be capable of operating ot the high cell temperatures.

NaK-filled pressure transmitters offer the best prospects for direct measurement
of cover gas or fluid pressures in molten-salt systems. If this device is to be used, the
possibility that a small amount of NaK would enter the system if the seal diaphragm
breaks must be acceptable. Additional work will be required to reduce the effects of
process temperature on the transmitted signal, to measure pressures > 50 psig at > 1200°F,
and, if the transmitting element is to be installed outside the secondary containment,
to ensure adequate containment of the reactor system. If the transmitting element is
- to be installed inside the secondary containment, the element must be improved to reduce
the environmental effects of temperature, radiation, and varying ambient pressure to
acceptable levels.

Another, but less promising, way to measure pressure directly is to 'possfbly
adapt a thermionic diode type of pressure transmitter.® This method is being developed

 

8 A..J. Cassano and R. E. Engdahl, "Pressure Transducer for,:LiquidrMeral
Application," pp. 165-186, Proc. Conf. Application of High-Temperature
Instruments to Liquid Metals Experiments, Sept. 28-29, 1965, ANL-7100.

 

 
 

 

w

9

by others for use in high-temperature quu id=-metal systems, and its progress will
be followed to determine whether it can be applied to molten=salt systems.

5. DIFFERENTIAL PRESSURE MEASUREMENT

As in measurement of pressures, the measurement of differential pressures

~in the MSBR will be more difficult in the systems containing molten salt and

highly redioactive liquids and gases,

| Except for the coolanf—solt venturi pressure drop meosuremenf (Secr 6),
no direct differential pressure ‘measurements were made in salt-containing

_equipment of the MSRE. The differential pressure measurements needed to
determine molten-salt levels and gas flow rates to and from the molten-salt

systems were made on gos lines connected to gas spaces cbove the salt, The
performance of the differentlal pressure transmitters for measuring ges flow was
satisfactory. Some difficulties were experienced in measuring salt flow rates with

~ the NoK~-filled differential pressure cells during initial operations of the MSRE. 7

The performance of some of these transmitters was satisfactory, but that of others:

~was not, and procurement of oll fronsmurrers was difficult,

 The problems ossocroted with direct measurement of dtfferenflol pressures
in the liquid-filled equipment of the MSBR salt sysrems are similar to those associ="
ated with pressure measurement (Sect. 4); the main difference is that the differential
pressure transmitter is not affected by variations in embient pressure and usually is
required to megsure much smaller variations in pressures. In applications such as
level measurements, where relatively small spans might be required, the effects of
variations of ambient temperature, process remperoture, and process pressure on
the span and zero of the transmitter are of prime importance and could be the decid-
ing factor In determining the sultability of NaK-filled differential pressure trans-
mitters for o given application. . If the performance of the transmitters were to be -

| improved sufficiently by further development, measurement of level in the drain tanks
- might be considered as an acceptable alternative to weighing.. Another, less
‘promising approach to direct measurement of differential pressures in molten-salt systems

Is to use thermionic diode l’ype elements presently bemg developed by ofhers for I-he

B : 'hqmd metols progroms e

 

 

7 Molten-Solf Reactor Progrem Semlonnuol Progress Report for Perlod Endmg |

,August3| i 35 ORNL-3872, p /0.
 

 

10

6. FLOW MEASUREMENT

Measurement of a variety of flow rates will be required in the MSBR.
Most will be conventional measurements of liquid, steam, and gas flows in areas
outside the fuel processing and reactor containments. Little development will be
required in these applications. However, further development will be needed
to obtain satisfactory measurements of salt and off-gas flows. The fuel-salt
processing system may also present some special flow measurement problems.

The flow rate of molten salt in the MSRE coolant-salt system was measured
by a venturi meter section operated at system temperature; the differential pressure
was measured by a high-temperature, NaK-filled differential pressure transmitter.
The performance was adequate, and this type of system probably would be acceptable
for similar service on the MSBR .~ This system was not acceptable for measurement
~of MSRE fuel salt flows, because there was a possibility that NaK could be released
into the fuel-bearing salt and possibly precipitate the uranium. This consideration -
might not apply to the MSBR, because the volume of NaK is very small compared with
the volume of salt. Development would also be required for the venturi, NaK=Ffilled
D/P transmitter system for measurement of fuel-salt flow in the MSBR, as menhoned
above,

Ultrasonic techniques offer promise for molten-salt flow measurement. A
commercially available ultrasonic flowmeter is capable of measuring liquid flows
in pipes from 1 to 6 in. in diameter. Since this instrument makes use of piezo-
electric transducers, it probably will be necessary to use force-insensitive mount
techniques (developed by Aeroprojects, Inc., and used in the level probe of the
MSRE fuel storage tank) to allow the heat and rodiation=sensitive components to be
installed outside the reactor containment and shielding. Such a flowmeter could
operate at temperatures > 1300°F and would be compatible with the environmental
conditions. It would be of all-welded construction and would not require an
electrical or piping penetration into the meter body or the containment vessel.

Other devices considered for measurement of molten-salt flow are the turbine
and magnetic type flowmeters. Both types can be constructed for high temperature -
service and have been used in liquid-metal systems with varying degrees of success.
Neither type has been applied to molten-salt service to date; however. The nuclear
magnetic resonance type flowmeter might be applicable in the MSBR system and
should be investigated. A turbine flowmeter developed for the ANP program
operated satisfactorily at 1600°F for a short period before it failed. The major
problem with this flowmeter is that the physical properties of the turbine blade
and bearing materials must- withstand high temperatures. Perhaps the improved
materials now available and lower operating temperature proposed for this service
would permit development of a flowmeter of this type for MSBR service.

O
 

 

 

.yt

C’

1

Magnetic flowmeters have been used extensively at high temperatures
(1600°F) in liquid-metal systems and af lower temperatures for the measurement of the
flow of many fluids over a fairly wide range of rates. But this type of flowmeter
cannot be used for measurement of molten-salt flows in its present form because
of consideration of containment, materials compatibility, and molten-salt
conductivity, as follows: containment and material compatibility prevent use of

~ electrical lead-through penetrations of the meter body such as those used in con-
ventional magnetic flowmeter construction; and the relatively poor (1 mho/cm) -

conductivity of the moli‘en salt prevents measurement of the signal voltage at the
ovtside surface of the meter body, as is.accomplished with liquid-metal flowmeters.

If satisfactory electrical lead-through penetrations could be devised, then magnetic

flowmeters for molten=salt service regardless of salt conductivity could be developed.
There is o good possibility that such a penetration could be developed by protecting
a nearly insoluble insulator material, such s beryllmm oxide, with a frozen-solf
film or plug. - - |

7. LEVEL MEASUREMENT

Several mei'hods were used successfully for smgle-pomf and continuous
mecsurement of molten-salt levels in the MSRE system. All these methods could -
be used in the MSBR under sumllar condlhons, although oll hove certain limitations.

Molten—sclf levels in the MSRE coolant and fuel-solt pump bowls were
measured continuously by bubbler (dip tube) and float level systems. A develop-
mental pump installation included a float level transmitter. Two-level, single-"
point measurements of molten=salt level in the MSRE fuel and coolant system drain
tank were made by conductivity level probes. With the information obtained
from these probes, the performance and calibration of the tank weighing systems
were checked. The probe signals operated lamps (and other binary devices) that
indicated whether the level was above or below two preselected points. An ultra-

- sonic probe was used for smgle-pomt measurement of level in the fuel storage
~tank. Except that it is a "one-level" device, the information obtained with
~ the ultrasonic probe is identical to that obtained with the conduchvn'y probe, and

information from both probes was used for fhe same purpose.

AII of fhe sysfems for meosuremenf of molten-solt Ievel in the MSRE were

| developed for a particular service, and further developmenf or redesign would be
. required for other oppll_oohoos.r The bubbler systenf is the simplest and the most

 

& Molten=Salt Reocfor Progrom Semlonnuol Progress Report for Period Ending

 

 Jan. 31,7963, ORNL-34T9, p. 43.
 

 

12

versatile method of measuring molten=-salt level under relatively static

conditions of level and cover-gas pressure. This system can be used for narrow

or wide ranges of levels, and the vessel modifications required to install the system
are simple and inexpensive.. However, since: performance of the bubbler system
depends on a steady flow of purge gas through a dip tube, this system can be
used only where the purge gas'can be tolerated. Also, the response characteristics
of this system depend on the purge flow rate which, in turn, depends on the supply
pressure, cover-gas pressure, and other factors. In general, the low purge rate -
required for accurate measurement is not compatible with requirements for fast =~
response. Fast changes of cover-gas pressure, such as can occur in the drain tanks

and pump bowl during filling and draining operations, can make the system inopera-

tive unless there are corresponding changes in the flow rate of the purge gas: A"
disudvantcge of the bubbler technique for measurement of levels in systems confam-
ing radioactive fluids is that it is necessary to detect and prevent a release of
activity through the purge line. Development of a system that would recycle the :
purge gas within primary and secondary containments would greatly extend the
usefulness of bubbler systems,

The float level system® offers the best method of continuous measurement of
molten-salt levels over narrow ranges. Such a device would be completely con-
tained, have a fast response, and require only electrical penetrations into the
secondary containment. Present designs are limited to measurement spans <10 in.
Although the span probably can be increased, this device is better suited to - - -
low-span than to hngh-—span measurements.

The conduchv:ty level prob performed well in MSRE service. ‘Except
that redesign of the tank penetration might be necessary to improve containment .
and to withstand high temperature ambient conditions in furnace heated areas, = =
the present probe design could be adapted to installation in MSBR tanks. Adis-=
odvantage of this probe is that the walls of the tube extending into the tank must -
be thin, which makes the tubing unsultable in corrosive environments. Since the
output signal obtained from the MSRE conductivity probes was much greater than
expected, possibly a more rugged and corrosion-resistant single-point probe with
a thicker tube wall could be developed. A continuous-type conductivity probe
similar to those used in liquid-metal systems also has possibilities.

 

® MSRE Design and Operations Report, Nuclear and Process Insfrumenfatlon ’
ORNL-TM-729, part IIB, Sect. 6.9 (in preparation).

1°1bid., Sect. 6.10.

C.
 

.}

.

«d

13

Recent dafa on the conduchvnty of molten scnlfs11 have led to a better
understanding of the mechamsms that influence the measurement of molten-salt

- conductivities and to a possible explanation of the drift characteristics that

have deterred development of conductivity probes for application to continuous
measurement of molten-salt levels. These data indicate that it might be possible

to reduce the drift rates of present developmental designs to acceptable levels
| by usmg a l‘ngher excttahon frequency and phcse defechon fechmques.

Except for some problems wafh oscnllafor frequency drlft fhe Aeroprolecfs,
Inc., ultrasonic level probe! ? hds been dependable and accurate. Development -
will be required to improve the main chassis electronics and packaging, and routine
redesign and development testing should be sufficient to resolve the remaining’

'problems. The Aeroprojects single=point ultrasonic level probe is more rugged and

corrosion resistant than the conductivity type probe, and, when the remaining

problems are solved, this could be the preferred device for smgle-pomt level

measurement in msfclllahons where it s ‘applicable.

Level measuremeni' by a dlffereni'lal hecd-pressure method was noi' used in

_ ‘fhe MSRE because a suitable device for measuring differential pressure was not
_available. As discussed previously, if the performance of low-span, NaK-filled,

differential pressure transmitters could be improved, this dewce could be consudered
for the MSBR. - | _. o

With the possable excephon of i'he dlfferenhal (head) pressure mei'hod all

methods previously discussed would be compatible with the MSBR design concept

of furnace heating the reactor and drain tank cells. The float-type level trans~
mitter should be given great consideration, because its transformer and other

| parts could operate at the proposed MSBR sysfem temperatures. Poss:bly, the con-

ductivity and vltrasonic probes could be used in a furnace atmosphere in their

~ present form; however, some additional development work on leadwire, penetrations,
~ and disconnects will probably be needed. The effects of temperature on the

transmission line characteristics of the- ultrasomc level system must be investigated

- before furfher cons:derahon <an be gwen to use. of fhns system in. furnace-heated
| _areus. - B S -

o8 SA'L'T'.'-INVENTORYM.EAS‘UREMENT i

Measuremenf of the amounf of salt in various: MSBR systems wnll be requured

o 'bofh durmg operuhon and shutdown, because this informahon wull be necessqry

 

 

. 11G.D. Robbms, Electrical Conduchvufy of Molfen Fluorrdes, A Rev:ew,

_.oRNL-TM-zlso (March 26, T9¢8).

 

12 MSRE Design and Operahons Reporl' Nucleur and Process Insh'umentahon,

| ORNL-TM-729 part IIB, Sect. 6.11 (in preparation).
 

 

 

14

for calculating reactivity and for accounting for the amount and location of
fissionable materials. Information obtained from lnvenfory lnstrumentchon will -
also be valuuble and necesscry aid to operahon. | S

The molten salt in the MSRE dram and storage tanks wes inventoried by
pneumatic weighing systems. These systems use diaphragm-type cells and cutomatic
force-balance (negative feedback) principles of operation. Except for special piping
connections that permitted operation under varying subatmospheric environmental
pressures, the: wenghmg systems were standard commercial items.. This 's'ystem is not
aoffected by radiation, is insensitive to varying ambient pressure, and is relchvely
~ insensitive to varying ambient temperature at < 150°F. The basic principle of -opera-
tion and method of installation of this system are such that its sensitivity and span
‘calibration can be checked during reactor operation at a control panel outside the
containment and the biological shields. A disadvantage of the system is that it
requires several pneumatic tubing penetrations of the containment, and these rust
be guarded by safety block valves. Except for some difficulties with drift of the
zero sefting, which were probably due to changes in pipe loading, and with some
peripheral equipment, the performance of the MSRE systems was acceptable. Although
the measurement accuracy of weighing systems might be lessened by shifts of the zero
setting due to pipe loading, the weighing system offers the best possibility for accurate
determination of MSER salt inventory where env:ronmenfal conditions and fotal tank
weights permit its use. . :

-Tank inventories could also be determined by measurement of level,
ulfhough this measurement requires correction for tank geometry and salt density.
Also, as discussed previously, odditional level system development would be
required unless measurements of tank inventories are to be made under static
pressure conditions and a continuous gas purge into the tanks can be tolerated. It
is possible that a combination of level and weight measurements will be required
to obtain a total salt inventory. Present indications are that the tare and live
loads of the main MSBR drain tanks and the ambient temperatures in the cells
in which these tanks are to be installed will preclude use of fhe MSRE system for
measurement of salt inventories in these tanks.’ : |

The pneumatic weigh cells used in the MSRE were the largest that were
commercially available at the time. Larger cell capacities are possible, but a
considerable amount of redesign and developmental testing would be required to
obtain significant increases in individual cell capacity. Although a number of
"brute force" design techniques, such as beam balance systems of multiple cells
with mechanical averaging, could be used to obtain large weighing capacities,
considerations of space and cost may preclude their use. Also, the 150°F maximum
temperature rating of the pneumatic weigh cells prevents their use at the 2 1000°F
ambient temperatures which may be present in the MSBR drain tank cell. One weigh
sysfem by a Swedish company shows considerable promise. The load cell in this system
is essentially a fransformer that makes use of the magnetic anisotropy in a magnetic
 

 

 

 

wi

np’?

w/ d

15

material under mechanical stress, The desirable features of the cell include its

high load capacity, electrical output, solid-state structure, low output impedance,
low sensitivity to temperature effects, and high output signal. Although the standard
model load cell is not suitable for extended service in high level radiation or high
temperature (1200°F) environments, information is available that. indicates that

.adequate radiation resistance could probably be obtained by replacement of organic

electrical insulation materials with inorganic materials. The moximum operating
temperature might be sahsfocforlly extended by air coolmg the load cells.

Another promlsmg techmque is the use of a NaK—fllled load cell. Oil- and
mercury-fulled hydraulic systems having high load capacity and accuracy are
commercmlly available . Substitution of NaK for oil should permit operation of the
primary load cell at 1200°F In this system, weight would be converted to NaK
pressure, which would be transmitted via a capillary tube to a transducer located in
g more hospltoble envaronment.

One possuble desugn would be to mstall vessel suspensuon rods through the
containment overhead with bellows seals to weigh cells located above the biological
shielding. Although this design would permit use of a variety of basic weighing
systems, it would, however, introduce serious structural, operational, and mainten-
ance problems. A variation would be to weigh a side tank rather than the entire
tank, thereby easing the problem of load cell capacity. However, this variation
would require removal of afterheat from the side tank and elimination of extraneous

loads produced by stresses in piping connecting the side tank to the main tank.

9. CONTAINMENT PENETRATION SEALS

Electrical power and instrument signals were carried into MSRE containment
by (1) mineral-insulated cables; (2) sheathed, glass-insulated, silicone~impregnated
multiconductor cables with soldered hermetic seals inside the cell and with organic
seals outside the cell; and (3) hermehcclly sealed connectors welded to the contain-

- ment vessels. Seals were required on these cables at both ends and at the point of
~ penetration fo prevent escape of radioactive gases and particulates and to exclude

moisture from the cables. Labor costs to install these seals were high. The performance
of these seals was marginal. -Development of new techniques will probably be required

 in the MSBR for furnace=heated containment areas. Extensive seal development will
 be required unless seals can be installed in a cool area. A seal different from that
 ysed in the MSRE will be required for thermocouple penetrations because the MSRE
leadwire cable will not withstand the temperatures of furnace-heated cells.
 

16
10. GAS-SYSTEM CONTROL VALVES

Helium-purge flow and cover-gas pressures in the MSRE were controlled by
throttling valves. Due to the low flow rates and pressure drops, the clearances in
“these valves were extremely small. These small clearances together with poor lubri-
cation resulting from dry helium service and limitations imposed on the type and
amount of lubricant that could be used were the apparent causes of trim galling that
caused many of the valves to fail. The valve assembly procedures were improved, but
additional work is needed to develop better valves for confrollmg small helium flows.

The MSRE operating experience ind icated a need for a suntable means of

- controlling very low flow rates of helium contaminated with particulates and hydro-
carbons. It is evident that similar conditions will exist in the' MSBR and that |
conventional valves and flow elements will clog and stick in such service. Three
lines of attack are suggested: (1) eliminate the contaminants, (2) develop special
“valves, and (3) develop other (and probably unorthodox) methods of controllmg Iow
flow rates of dirty helium. | - -
 

 

gl

o

“87. M. T.Kelley

17

82.

 

ORNL-TM-3303
INTERNAL DISTRIBUTION .
1-2,  MSRP Director's Offlce - 38..J. J. Keyes
3. R. K. Adoms 39. A. I. Krakoviak
4. A. H. Anderson 40. J. W. Krewson
5. J. L. Anderson 41, M. L. Lundin
6. C. F. Baes 42. R. N. Lyon
7. S. E. Beall 43, H. G. MacPherson
8. M. Bender 44. R. E. MacPherson
9. E. S, Betts 45. H. E. McCoy
10. D, S. Billington 46. L. E. McNeese
11. E. G. Bohlmenn 47, J. R. McWherter
12, C. J. Borkowski 48. H. J. Metz
13. G, E. Boyd 49. A. S. Meyer
14. C. Brashear 50-55. R. L. Moore
15. R. B. Briggs 56. C. A. Mossman
16. R. H. Chapman 57. E. L. Nicholson
17. F. L. Culler 58. L. C. Oakes
18. J. W. Cunninghem 59. A. M. Perry
19. D. G. Davis 60. J. L. Redford
20. J. R. Distefano 61. R. C. Robertson
21. S. J. Ditto é2. D. P. Roux
22, W. P. Eatherly 63, Dunlap Scott
23. J. R, Engel 64, W. H. Sides
24, D. E. Ferguson 65. M. J. Skinner
25. L. M., Ferris 66. 1, Spiewak
26. J. H. Frye o 67. J, R, Tallackson
27, G.W, Greene = 68, R. E. Thoma
28. W. R. Grimes R 69. D. B. Trauger
29. A. G, Grindell 70. A. M. Welnberg
- 30. R. H. Guymon 71, J. R. Weir
31, €. S Heerill 72, M, E. Whatley
- 32, P. N. Haubenreich - 73. J. C. White
33, P.G. Herndon 74. Gale Young
34. H. W. Hoffmen | 75-76 Central Research lerary
35, P. P, Holz ~ 77-78. Document Reference Section
36. W, H. Jordan 79-81. Laboratory Records

Loborutory Records, ORNL R.C.
 

 

83.
84.
85.
86"87 ¢

89-103.

.
EXTERNAL DISTRIBUTION

D. F. Cope, AEC-Washington =

"Roneld Feit, AEC~-Washington

Kermit Laughton, AEC-OSR
T. W. Mcintosh, AEC=Washington
M. Shaw, AEC-Washington
DTIE | -