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MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS -1963
eRNVA12741
1.
ORNA-P-9741
CONF-667206-2
CPUTI PRICES
THE NATIONAL CRITICALITY DATA CENTER*
E. B. Johnson
Oak Ridge National Laboratory
Oak Ridge, Tennessee 37830
64 63.00; WN-65
DEC : 5 1966

ABSTRACT
A Criticality Data Center has been established at the Oak Ridge
National Laboratory under the sponsorship of the USAEC for the purpose
of collecting from sources, both in the United States and abroad, .....
formation applicable to criticality safety problems. The principal
output of the Center is typified by TID-7028, "Critical Dimensions of
Systems Containing (235, Pu239, and 1233," and TID-7016, "Nuclear
Safety Guide," both of which were originally the results of grup
efforts not under the sponsorship of the Center. The former document
summarizes most of the data available at the time of its publication
and will require frequent expansion. The latter document is presently
under revision to incorporate the results of more recent measurements
and to reflect the development of reliable theoretical analysis. Both
documents are internationally known and used.
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*Research sponsored by the U. S. Atomic Energy Commission wider contract
with the Union Carbide Corporation.
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LEGAL NOTICE
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This report was prepared as an account of Government sponsored work. Neither the United
States, nor the Commission, nor any person acting on behalf of the Commission:
A, Makes any warranty or representation, expressed or implied, with respect to the accu-
racy, completeness, or use!ulness of the information contained in this report, or that the use
of any information, apparatus, method, or process disclosed in this report may not Infringe
privately owned rights; or
B. Assumes any liabilities with respect to the use of, or for damages resuliing from the
use of any information, apparatus, method, or process disclosed in this report.
so used in the above, "person acting on behalf of tho Commission" includes any em-
ployoe or contractor of the Commission, or employee of such contractor, to the extent that
auch omployue or contractor of the Commission, or employee of such contractor prepares,
provides access to, any information pursuant to his employment or contract
with the Commission, or his employment with such contractor.
...
---
The Criticality Data Center has been established at the Oak Ridge
National laboratory under the sponsorship of the USAEC. The purpose of
the Center is to col.lect, collate, ur. publish information applicable
to nuclear criticality safety problems. It should be emphasized that
this is a data center as contrasted with an information center; its
output is primarily in the form of publications. Typical or these
formal pubiications are TID-7028, Critical Dimensions of Systems
Containing 1235, Pu239, and 233," and TID-7016, "Nuclear Safety Guide."
Both of these documents were originally the results of group erforts
prior to the establishment of the Center and both are internationally
known and used.
Much effort, both in this country and others, has been directed
toward the experimental anú theoretical determination of critical para-
meters of fissile isotopes. The data have been used extensively in
the field of criticality safety to specify conditions of handling,
fabrication, processing, storage, and transportation under which a
chain reaction will not occur. These data have been generated in a
few laboratories designed particularly for this purpose and staffed by
groups well aware of the need for information and of much of its in-
tended application. Close informal communication and the issuance of
formal reports resulted in the evolution of a small well-informed group
of experts in nuclear criticality safety and its bases. Today, however, in
our rapidly expanding nuclear industry, it has become necessary and desir-
able that there be a greater awareness of the work that has been and is
being done in order that not only safe but also economic limits may be ap-
plied in all areas. On the other hand there are instances of specialized
operations requiring information in only a narrow band of the field.
This wide variety of existing needs made desirable the collection of
existing data, the conversion of them to a form of more general useful.
ness, and their publication in a compilation. More recently the AEC
has given its support to such endeavors in the establishment of the
Criticality Data Center.
Although the Data Center is officially located at the Oak Ridge
National Laboratory, its input data originate in many laboratories in
this country, the United Kingdom, and France. In a very real sense its
participants include anyone generating information applicable to
lear cri.
ticality safety, particularly those whose primary concern is the general
availability and applicability of data. The following discussion will
give some measure of the scope of and the participation in Data Center
activities.
The "Nuclear Safety Guide," TID-7016, was originally published in
1956 as a clàssified AEC report (LA-2063), then distributed as an un-
classified document with essentially no change in content. It was
revised in 1961 by Subcommittee 8 of the American Nuclear Society Standards
Committee. This document is now being revised again to reflect the
results of more recent measurements and the develoyment of more reliable
theoretical analysis. As stated in the document, the values specified
in the "Nuclear Safety Guide" include true safety factors as well as
factors determined by the uncertainties in the experimental and analyti-
cal data on which the specifications are based. Most of the current
effort of the Center is directed toward revision of this document.
The predecessor of "Critical Dimensions," TID-7028, was an ASC
report, "Critical Data for Nuclear Safety Guidance," IAMS-2415, which
served as the basis for the greatly enlarged document. This newer
document summarizez most of the experimental data available at the time
of its publication in 1964; these data originated in laboratories in
this country, in the United Kingdon, and in France. Of great importance
is the extensive bibliography which references original work for the
benefit of those requiring more detailed information.
It is obvious that these two documents are closely related and
serve complementary purposes. The curves of the "Nuclear Safety
Guide" are derived from critical data such as those presented in "cri-
tical Dimensions"; therefore as more information on critical quantities be-
ccmés available, it should be reflected in specified safe quantities.
.
Careful perusel of "Critical Dimensions" indicates that data for
bighly enriched uranium in simple geometry is fairly complete except
for gaps at low moderation. The French are presently doing experiments
with UFG slightly moderated by HF; the uranium is enriched to above 90%
in 2550. There are few experimental data for uranium of intermediate
enrichments, although recent experiments at ORNI, with aqueous uranyl
fluoride solution enriched to 5% in 250 help to remedy this deficiency.
The only data available for the compilation for water-moderated
ará -reflected lattices of uranium rods were those for 2350 enrichment
no greater than 3% and originated at Hanford, Brookhaven, Bettis, and
Savannah River. Measurements now in progress at ORNL will extend the
range of this type of data to lattices of uranium rods enriched to 5%
in su. These data will also serve to authenticate the relevant portion
of the calculational summary recently published by Clark' of Savannah River
for water-moderated and -reflected lattices of rods of various diameters,
moderation, and enrichment. There are data for other rod lattices in the
design reports for several reactors; however, one serious difficulty in most
of these lattice data is the perturbations resulting from the presence of
control rods and structural compo:ients characteristic of reactor concepts,
making conversion to "clean" systems very uncertain.
Few data have been obtained to guide the storage and shipping of reactor
fuel elements although such operations are being conducted safely. It should
be poseible to realize considerable savings in cost were appropriate data
available. The limited data which exist originated at ORNI from studies with
MIR-type fuel elements, elements for the Experimental Cas Cooled Reactor, for
the Heat Transfer Reactor Experiment, for the High Flux Isotope Reactor, and
for various production reactors. As power reactors become more numerous, it
will be increasingly important to have "clean" critical data for application
to the design of shipping casks and storage facilities. It may be that the
necessary information can be obtained as a part of the experimental program
necessary to the establishment of the design of the reactor itself.
The data for plutonium have recently been extended by programs at two
laboratories. One series of experiments at the Pacific Northwest Laboratory
utilized spheres, reflected and not, of plutonium solution containing 4.6% 24°Pu
at concentrations up to about 300 g of Pu/liter. Another series utilized homo-
geneous compacts of a mixture of Pub, and polystyrene at low moderation; two sets
of compacts were tested, one containing plutinium with 2.2% -4°Pu and the other
having 89 240pu. That laboratory is analyzing the data for inclusion in "Critical
Dimensions." Additional data have been reported from the French laboratory at
Dijon describing the criticality of plutonium solution contained in a single
annular cylinder and the neutron interaction between two annular cyl.inders of
solution, reflected by air or by water. The solution concentration ranged from
18.8 to 104 g/11ter and extends the earlier work sw.marized in TID-7028.
Comparatively few experiments have been done with
u. ORNL is
preser:tly accumulating a quantity of aqueous uranyl nitrate solution of
SPU in order to extend the int'ormation for single units, to investigate
solutions containing glass Raschig rings as a fixed neutron absorber,
as well as to study interacting arrays of individually subcritical units.
A recent evaluation by the AEC expressed the need for ever more extensive
measurements with 233u:
"... experimental data on U-233 salt, (low moderation), solution
and metal. systems are required. Though it is doubtful thege
--xperimental data should be as numerous as the extensive data on
U-235 systems, sufficient data are needed to verify the variation
of a criticality parameter as a function of moderation, e.g. in
the range 0 < H/U-233 < 20, for homogeneous systems, as well as
the effect of metal rod size similar to the data summarized in
T'igure 20 of Ref. (21) (TID-7023). It is anticipated that the
computational schemes now under development can be applied to
U-233 systems, for all moderations; particular attention should
be paid to comparing such results with new U-233 data.
"Experimental data are also needed on U-233 systems containing
thorium in rod lattice configurations.
Though one can employ in
a crude way data from low enrichment uranium experiments to
establish safety in the use of U-233-thorium oxide rods, experi-
ments should be undertaken to obtain data on maximum bucklings
and critical masses for various rod diameters."
The above discussion indicates only a few of the areas in which
information is either lacking or incomplete; there are more. Examples
are mixed fissile materials, sean as uranium and plutonium, and the use
of solid and soluble neutron absorbers in solutions of materials.
It
1s obvious tliat "Critical Dimensions" will require expansion and revision
as more data become available.
Additional information for inclusion in revisions of the Center's
publications derives from renent experiments with arrays of individually
subcritical units of fissile material, as both solutions and unmoderated
material, and the successful application of methods of analysis to these
experiments. A report on this subject by Thomas is included in these
Proceedings. This work leading to successful calculation of array cri-
ticality has been supported by the Center.
ta
Also relevant to the revision of these documents is the extensive
calculational effort by Hansen of Pacific No: thwest Laboratory for the
Data Center on the criticality of various "practical" compounds of
plutonium, such as Puyoz, Pufz, Pun, and Putz, some of which are frequently
encountered in processing and fabrication operations. I sen first
authenticated his calculational method with experimental critical data
and then computed the critical dimensions of compounds of plutonium for
which no experiments have been performed. Since many of these compounds
are found in chemical processes at less than theoretical densities, it
was necessary to provide a means of converting the quantities critical
at theoretical density to those critical at reduced experimental density.
The Center is actively engaged in the preparation of standards
applicable to nuclear criticality safety. This topic will be presented
in detail by Callihan in these Proceedings.
United States of America Standard (USAS) N6.1-1964, "Safety Standard
for Operations with Fissiyavle Materials Outside Reactors," was adopted
in 1964 as the first national nuclear safety standard and governs the
handling, storage, and transport of missile material.
It is presently
being revised by a Work Group, chaired by Clark of Savannah River, of
Subcommittee 8 of the ANS Standards Committee.
The revision will include
"single parameter limits" for the three most abundant fissile isotopes.
These limits should, of course, describe quantities of material which
will be subcritical wider most favorable conditions and still be as
large as possible for reasons of economy. The task of authenticating
the values which will become a part of the proposed revised standard
has been undertaken by laboratories active in the field: Los Alamos
will provide values applicable to 2350 and plutonium metal; Pacific
Northwest those for moderated plutonium, Oak Ridge for moderated 2550
and 2330, and Savannah River for uraniun enriched to 5% or less in 23%u.
In each case the validity of the calculational method will be established
by comparison with "clean" critical experiments. The recommended
values of limiting dimensions will be reduced below those observed to
be critical by the visual factors of safety as well as by an amount de-
pendent upon the uncertainty in both the calculation and in the experinent
by which the calculation is judged. Richeys of Pacific Northwest lab-
oratory reported values of these parameters for Pu(NO) solution and
for 239Pu-ho mixtures at a recent meeting of the ANS. Webster of ORNL
is determining parameters for moderated 2350 and 233, by transport
theory, Siv, calculations. Clark*» of Sevannah River hos published
the results of calculations for uranium-water and for uranium oxide-water
mixtures at enrichments up to in 39 and for nonuniform mixtures
of fissile materials. Smith of 1.431 ias computed values for uranium
09
metal at 100% enrichmore. It is intended that the details of each of
these efforts be publis..eci in the open literature in order to facilitate
reference to the bases for the recommended parameters.
As a part of their concern and sense of responsibility to the
industry, those associated with the Center have consistently, either
as individuals or through their organizations, submitted comments on
regulations intended to govern the transportation of fissile materials.
Several papers in these Froceedings discuss the topic of regulation.
This brier discussion has given a description of the scope, interests,
and potential usefulness of the Criticality Data Center. It should be
emphasized that the intended purpose of the Center is to serve the re-
quirements of the nuclear ,dustry, not by providing answers to specific
questions but by making available tlie criticality data which have been
generated, in a forn which will be most useful in application to parti-
cular problems. Success in rilling this need will depend on the input
from the programs at 'e critical experiments laboratories.
10
REFERENCES
1.
2.
H. K. Clark, "Critical and Safe Masses and Dimensions of Lattices
of U and vo, Rods in water," DP-1014, Savannah River Laboratory
(1966).
Ad Hoc Committee on Basic Criticality Studies, I. F. Zartnan,
Chairman, "Technical Revićw of Basic Criticality Studies,"
January 11, 1965.
C. R. Richey, "Theoretical Analyses of Homogeneous Plutonium
Critical Experiments," Trans. Ail. Nucl. Soc. 9, 515 (1966).
Criticality Control of Fissile Materials, International Atomic
Energy Agency (1966).
H. K. Clark, "Effect of Distribution of Fissile Material on Critical
Mass," Nucl. Sci. Eng. 24, 133 (1966).
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