Fission Parameters Measurements for Np, Pu, Am, and Cm Isotopes Inside a Salt Blanket Micromodel Page: 3 of 10
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. the MA cross sections must be known to at
least the same accuracy as the U and P isotope
cross sections when studing and desighning spe-
cialized eractors-transrnuters (malten salt reactors,
accelerator-driven systems) with large MA contri-
bution in the fuel.
The true accuracy can be estimated in the integral
experiments by comparing between the experimental
and calculated fission functionals in terms of different
databases. It is the experiments with the salt system-
emulating micromodels that are discussed in the present
work.
DESCRIPTION OF THE MAKET CRITICAL
FACILITY
The ITEP salt blanket micromodel (SBM) is cylinder-
shaped of 230-mm diameter and 522-mm height. The
SBM was fastened on the central fuel channel (FC) at
a 400-mm height above the lower fuel lattice in the
MAKET core. The entire SBM channel structure (see
Fig. 1) has been made of zirconium at Chepetsky Me-
chanical Plant (Glazov, Russia). The S.BM is filled with
the 0.52NaF + 0.48ZrF4 melt. An additional salt insert,
which raises the salt melt content, or bushing-type fuel
elements can be placed in the central FC of a 58-mm
external diameter. The experimental samples were irra-
diated on being placed in the 0.52NaF + 0.48ZrF4 melt-
filled containers, which were downed into the channels
located at 46.5-mm, 72.0-mm, and 96.5-mm radial dis-
tances from the SBM axis (0 mm is the center of the
additional salt insert).
The experiments were supported by forming two 100-
mm step hexagonal fuel lattices assembled of FCs with
the bushing-type fuel elements that contained uranium
of 90% 235U enrichment. One of the fuel lattices was
assembled of 34 FCs and 67,272 g of the melt (the salt
insert in the central FC). Another lattice was assembled
33 FCs and 65,592 g of the melt (the fuel elements in
the central FC).
REACTION RATE MEASUREMENT TECH-
NIQUES
The 235U, 237Np, 238Pu, 239Pu, 240pu 241Pu 242m Am,
243Cm, 245Cm, and 247Cm fission reaction rates were
measured by the solid-state nuclear track detector (SS-
NTD) techniques.
The high-enriched U, Pu, Am, and Cm samples were
prepared in the SM-2 electromagnetic mass separator
with the sectored magnetic field, H = HoRo/R, of
mean radius R0=1000 mm and a 2-radian (1140) bend-
ing angle. The mass dispersion is 20 mm per 1% ofrelative difference in masses at a 60-100-mm total tra-
jectory length.
The enriched samples were mass-spectrometered to
not worse than 0.1% (at a >102 relative content of the
impurity isotope) and to 1-3% (at a <10- impurity
content). In most of the samples, the basic isotope
enrichment was not worse than 98% (as of the sample
manufacture date).
After chemical purification, the fissile substance was
applied to a stainless steel substrate by electrolysis of
nitrates from aqueous or alcohol solutions. The spot
diameter was 6 mm in all the target layers. The distri-
bution uniformity of the active substance over a spot
was tested by self-radiography.
The samples were "weighed" (i.e., the numbers of fis-
sile nuclides were determined in the layers by a- and -y-
spectrometry methods and on the basis of spontaneous
and thermal- neutron-induced fission of nuclei. The
semiconductor detectors with the standard electronics
outfit were used in the a- and -y-spectrometers. As
regards the spontaneous and thermal neutron-induced
fission, the "weighing" was realized by the same tech-
niques as in the main measurements, i.e., SSNTDs were
used. The ~3.3% weighing error arises mainly from the
uncertainty in the number of nuclei in the benchmark
sources, as well as from the errors in the periods of the
spontaneous and thermal neutron-induced fission.
The SSNTDs used in the measurements were made
of silicate glass and polycarbonate film of molecular
mass 90,000. The detectors are insensitive to the
a-, -, y-, and n-emissions and, given appropriate
conditions, provide for 100% efficiency in recording the
fission fragments.
The glass or polymer plates were placed in parallel
to, or coaxially with, a fissile isotope layer at 6 mm
from the layer in the containers used as measurement
chambers. A purposed diaphragm confined a circle to a
6-mm diameter on the detector surface. The accuracy
of all the dimensions in the measurement chambers was
monitored using an instrumental microscope.
The polymer film was used in so called shutter cham-
bers, wherein a device like camera shutter was mounted.
The shutter chambers permit a high-accuracy time in-
terval in recording the fission fragments with SSNTD,
which is necessary when operating with the samples of
a high spontaneous fission activity, as well as in the case
of neutron spectrum variations when the irradiator op-
eration mode is reached.
The geometric efficiency, Q, of the chamber (i.e., a
probability for a fragment to appear in the detection
domain) was calculated on assumption of a uniform dis-
tribution of a fissile substance over the layer. It should
be noted that the < nQ > value was measured directly
when "weighing" the layers by spontaneous or ther-2
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Titarenko, Y. E. (Yury E.); Batyaev, V. F. (Vyacheslav F.); Karpikhin, E. I. (Evgeny I.); Zhivun, V. M. (Valery M.); Koldobsky, A. B. (Aleksander B.); Mulambetov, R. D. (Ruslan D.) et al. Fission Parameters Measurements for Np, Pu, Am, and Cm Isotopes Inside a Salt Blanket Micromodel, article, January 1, 2001; United States. (https://digital.library.unt.edu/ark:/67531/metadc934333/m1/3/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.