=Paper=
{{Paper
|id=Vol-2763/CPT2020_paper_s2-8
|storemode=property
|title=Development of the design method for the optimal design of the Neutron Converter experimental plant
|pdfUrl=https://ceur-ws.org/Vol-2763/CPT2020_paper_s2-8.pdf
|volume=Vol-2763
|authors=T.R. Smetanin,E.A. Gureva,V.V. Andreev,N.P. Tarasova,N.G. Andreev
}}
==Development of the design method for the optimal design of the Neutron Converter experimental plant==
https://ceur-ws.org/Vol-2763/CPT2020_paper_s2-8.pdf
Development of the design method for the optimal design of the Neutron
Converter experimental plant
T.R. Smetanin1, E.A. Gureva1, V.V. Andreev1, N.P. Tarasova1, N.G. Andreev2
smetanintimur@yandex.ru | infantoplus@yandex.ru | vyach.andreev@mail.ru | tar0611@rambler.ru | andreyev@mail.ru
1
Nizhny Novgorod State Technical University, Nizhny Novgorod, Russia
2
JSC «OKBM Africantov», Nizhny Novgorod, Russia
The article discusses methods for optimizing the design of the Neutron Converter research plant design with parameters that are
most suitable for a particular consumer. 38 similar plant structures with different materials and sources were calculated, on the basis
of which the most optimal options were found. As part of the interaction between OKBM Afrikantov JSC and the Nizhny Novgorod
State Technical University named after R. E. Alekseev, the Neutron Converter research plant was designed and assembled. The
universal neutron converter is a device for converting a stream of fast neutrons emitted by isotopic sources into a "standardized" value
of flux density with known parameters in the volume of the central part of the product, which is the working part of the universal
neutron converter. To supply neutron converters to other customer organizations (universities, research organizations and collective
centers), it is necessary to take into account the experience of operating an existing facility, as well as rationalize the design process of
each specific instance in accordance with the requirements of the customer.
Keywords: neutron converter, sources of ionizing radiation, gamma radiation, neutron radiation, biological protection, neutron
deceleration.
2. Persons involved in the work of the converter:
1. Introduction employees and students of the department - must be
The scheme and method of arrangement of isotopic considered personnel of group B, and all other persons -
neutron sources selected in the project provide the the population. This separation should be taken into
maximum possible uniformity (isotropy and uniformity account when allowing specialists to work with the plant
of axial-radial distribution) of thermal neutron flux and in the room where it is located.
density in the scope of the working part of the universal 3. The operating organization (department "Nuclear
neutron converter [1]. reactors and power plants" of the Institute of Nuclear
The goal is to develop a universal design method for Energy and Technical Physics named after Academician
the optimal design of the Neutron Converter experimental F.M. Mitenkov) should develop regulations for the
plant to select the most suitable version of the plant for a operation of the plant, the procedure for admission to it,
particular consumer. In order to achieve this goal, it is as well as organize its maintenance and radiation control.
necessary to perform the following tasks: to study the Based on these documents, conclusions were drawn
normative documentation on the use of ionizing radiation about the necessary degree of protection during the
sources; examine the design of the existing experimental operation of the plant.
plant and construct and calculate the model of the It was calculated that in order to comply with the
existing design model; develop a methodology for standards for dose limits received by personnel when
finding the most suitable plant parameters for a particular working with a neutron converter, the biological
consumer; calculate neutron fluxes and radiation doses at protection of the plant should provide a total equivalent
various versions of the experimental installation; analyze dose rate of neutron and gamma radiation at a distance of
the results of the calculations. 10 cm from the hull of not more than 1.15 mSv/h. This
value is the determining value when designing the
2. Regulatory documentation biological protection of the converter.
Neutron sources are required for neutron converter 3. Analyze the design of an existing plant
operation. Therefore, documents regulating ionizing
radiation sources operation were reviewed. The main The universal neutron converter is a device for
documents are: Federal Law No. 170-FL "On the Use of converting a stream of fast neutrons emitted by isotopic
Atomic Energy" [2], Radiation Safety Standards sources into a stream of thermal neutrons in the volume
(NRB-99/2009) [3] and Basic Sanitary Rules for of the central part of the product (Fig. 1).
Ensuring Radiation Safety (OSPORB-99/2010) [4]. To convert the fast neutron flux, it is necessary to
The above regulations postulate. reduce their energy by "converting" them to thermal
1: During the design and installation of the converter, ones. This process occurs due to the deceleration of
measures must be taken to ensure biological protection neutrons during scattering of the moderator elements on
that meets the above requirements. Biological protection the nuclei. The periphery of the universal neutron
shall ensure that doses and dose capacities established for converter performs the functions of biological protection.
radioactive material handling are not exceeded.
Copyright © 2020 for this paper by its authors. Use permitted under Creative Commons License Attribution 4.0 International (CC BY
4.0)
Fig. 1. Design diagram of neutron converter: 1- neutron sources, 2 - plugs, 3 - biological protection, 4 - paraffin, 5-graphite, 6 -
housing, 7 - working cavity
The advantages and disadvantages of the design of beryllium (fast neutron sources (FNS) - FNS-6, FNS-8)
the existing plant were analyzed. Both used and and Californium sources were considered, their radiation
potentially suitable as retardant and/or biological spectra necessary for further calculations in programs
protection of the converter structural materials were were identified and digitized.
considered during the analysis. It was concluded that it is For the design of this type of installations, the dose
possible to create a variant of the installation design that capacities outside the existing installation and the density
provides the required parameters of neutron radiation, but of the thermal neutron flux in its working cavity were
with smaller weights or overall dimensions than the calculated using DOT III programs, and DotGeom
existing version of the converter design. designed to automate the entry of the DOT program
As neutron sources in the plant, various plutonium- setting zones (Fig. 2) [4].
Fig. 2. Thermal neutron flux distribution in existing plant, n/(cm2·s): 1-working cavity, 2- retarder layers, 3-biological protection
layers, 4-sources, 5-housing
Dose capacities outside the existing plant, and the output characteristics is found. After analyzing and
density of the flux of thermal neutrons in its working comparing the optimal implementations of each of the 38
cavity were calculated. variants, it was concluded that the most preferred
4. Technique of optimizing converter design embodiment was the best structural materials and neutron
procedure sources for use in the plant.
Since the efficiency of the combined protection
To create an optimal neutron converter design differs from the monolithic one, combinations of two
procedure, a basic set of 38 versions of the plant was materials were selected as the initial data. All design
compiled and calculated, differing in the neutron sources versions of neutron converter are given in Table 1.
and moderator and protection materials used. In each of
these embodiments, the best combination of input and
Table 1. Versions of neutron converter
Ver. Source type First Material Second Material
1 Californium Paraffin Graphite
2 Californium Graphite Water
3 Californium Loose mix
4 Californium Polyethylene Graphite
5 Californium Polyethylene Paraffin
6 Californium Titanium hydride Polyethylene
7 Californium Paraffin Titanium hydride
8 Californium Concrete
9 Californium Graphite Vaseline
10 Californium Graphite Concrete
11 Californium Water Lead
12 Californium Polyethylene Lead
13 FNS-6 Concrete Graphite
14 FNS-6 Titanium hydride
15 FNS-6 Graphite Titanium hydride
16 FNS-6 Concrete Polyethylene
17 FNS-6 Graphite Paraffin
18 FNS-6 Paraffin
19 FNS-6 Concrete Water
20 FNS-6 Paraffin Lead
21 FNS-6 Graphite Polyethylene
22 FNS-6 Vaseline Graphite
23 FNS-6 Water Graphite
24 FNS-6 Loose mix Graphite
25 FNS-6 Vaseline Polyethylene
26 FNS-8 Concrete Graphite
27 FNS-8 Titanium hydride
28 FNS-8 Graphite Titanium hydride
29 FNS-8 Concrete Polyethylene
30 FNS-8 Graphite Paraffin
31 FNS-8 Paraffin
32 FNS-8 Concrete Water
33 FNS-8 Paraffin Lead
34 FNS-8 Graphite Polyethylene
35 FNS-8 Vaseline Graphite
36 FNS-8 Water Graphite
37 FNS-8 Loose mix Graphite
38 FNS-8 Vaseline Polyethylene
The calculation of each version of the neutron of the plant. When choosing the thickness of the layers,
converter design consisted of 2 stages: the calculation of the main criterion was the flux of thermal neutrons in the
the moderator and the calculation of biological working area. Criteria such as weight and size parameters
protection. The task of the first stage of neutron converter and cost were secondary, since most of the cost, weight
design is to select and calculate moderator thicknesses, and size of the plant provides biological protection (Fig.
which provide the maximum possible, when using these 3, 4).
materials, flux of thermal neutrons in the working cavity
Fig. 3. Moderators in vertical section of converter: 1- source; 2-
air in the source channel; 3- source sleeve; 4- first layer of
Fig. 5. Biological protection in vertical section of converter: 1-
moderator; 5 - shell of the central channel; 6- air in the central
source; 2- air in the source channel; 3- source sleeve; 4- the first
channel of the converter; 7- the cell in which the object to be
layer of biological protection; 5- space around converter; 6-
irradiated will be located; 8-second layer of moderator
converter housing; 7- neutron and gamma radiation dose rate
calculation cell; 8 - second layer of biological protection
Fig. 4. Example of neutron flux density distribution in one of
design variants
The second stage is the calculation of biological
protection. The main task of designing the biological
protection of the neutron converter is to select and Fig. 6. Example of calculation results of neutron radiation dose
calculate the necessary thicknesses of biological rate distribution for one of design options
protection materials that provide the maximum
permissible dose rate level at a distance of 10 cm from All versions of the column were divided into 3 groups
the column body with the minimum possible values of of three types of sources: Californium, FNS-6 and FNS-8
their weight and size parameters. (Figs 7-9).
To do this, a calculation was made in R-Z geometry,
which is part of the vertical section of the column in the
direction from the source to the surface of the column
(Fig. 5, 6).
Fig. 7. Generalized coefficient N and flux density of thermal neutrons in the working area of the converter in Californium source
design embodiments
Fig. 8. Generalized coefficient N and flux density of thermal neutrons in working area of converter in versions with source FNS-6
Fig. 9. Generalized coefficient N and flux density of thermal neutrons in working area of converter in versions with source FNS-8
All converter characteristics during design can be defining characteristics. When comparing different
divided into 2 groups: input and output. Input options, it becomes necessary to analyze a 4-dimensional
characteristics are: source type, biological protection system of parameters, which is quite difficult without
materials (BP) and retardant. The output characteristics using additional tools. Therefore, in the process of
are: the thickness and materials of the layers necessary to optimizing the design procedure, it is necessary to bring
obtain the highest density of the thermal neutron flux some parameters to relative values and then convolve
while observing radiation safety standards, the density of them as part of a complex criterion in order to reduce
the thermal neutron flux in the working cavity of the their number. The parameters of the mass, size and cost
plant, mass and size and cost parameters of the converter of the column materials were led to relative values,
[5-8]. which, in turn, were reduced to one value - a
In order to obtain the most efficient installation, it is comprehensive indicator of the quality of the design
necessary to strive to increase the parameter of the procedure - generalized coefficient N. The result of using
thermal neutron flux in the center and to reduce the this procedure is to reduce the number of output
values of mass, size, cost. characteristics in the considered versions to two, as a
Each embodiment of the neutron converter has 4 result of which analysis and comparison of the calculated
versions of the neutron converter design is carried out
according to the value of heat flux in the working zone
with a minimum coefficient N, which determines weight
and size and cost characteristics.
5. Calculation results
38 versions of neutron converter design were
analyzed and 3 versions were defined, one for each type
of source, having an optimal set of parameters: maximum
flux of thermal neutrons in the working area of the plant
with minimum weight and size parameters and cost.
Among the options using the Californium source, the
best way was to achieve the maximum density of thermal
neutron flux in the working zone of the plant, equal to 4.2 Fig. 10. An example of how to find the best option for a
· 105 n/cm2 • s. The cost of the converter in this design is particular customer
585 thousand rubles, the weight of the installation is 4.8
tons, and the outer radius of housing is 1.2 m. For example, the customer's design requirements are
Polyethylene was considered as a biological protection as follows: it is necessary to design a neutron converter at
material and retardant in this version. the following specified parameters:
The best option of all using the Pu-Be source FNS-6 1. total cost: not more than 80 thousand rubles;
was the version in which the maximum density of 2. total weight: not more than 2 tons;
thermal neutron flux in the working zone of the plant was 3. installation radius: not more than 0.58 m;
achieved, equal to 800 n/cm2·s. The cost of the converter 4. neutron source: FNS-6.
in this design is 18 thousand rubles, the mass of the As shown in Fig. 8, the customer's stated
installation is 1 ton, and the outer radius of housing is requirements are met by options 17,19 and 23.
0.53 m. Water was considered as a biological protection The highest density of thermal neutron flux in the
material and retardant in this version (Fig. 6). working area of the plant: 800 n/cm2·s is achieved in
Among the variants using the Pu-Be source FNS-8, version 19. Therefore, it is advisable for the customer to
the best option was similar to the one discussed above for propose a project with the characteristics of 19 version, in
the source FNS-6 (Fig. 7). which concrete with water is used as the moderator
Based on the results obtained, it is possible to materials, water as the biological protection (Table 1).
optimize the design process of experimental plants of this
6. Conclusion
type with various parameters, depending on the
requirements set by the consumer. During the development of the method for optimizing
As a result of the calculation for each version of the the design procedure of the experimental neutron
converter, the most advantageous characteristics were converter installation, the following results were
obtained: mass, cost, dimensions obtained:
For a potential customer, it is this output that will be 1. The regulatory documentation was analyzed.
boundary conditions, and it will be for them to choose the 2. A method for optimizing the neutron converter
most suitable option. Each customer has a range of design procedure has been developed.
allowable values of each parameter, and having found 3. Based on the calculations made, a database of
options, all the parameters of which will lie in the parameters of plant design implementation options was
corresponding ranges specified by the customer, it will be created, which became the basis of the method of
possible to offer him for consideration only those that optimizing the converter design procedure.
satisfy all the requirements of the customer. 4. Analysis of the obtained calculation results was
This technique allows you to find the most suitable carried out, the most preferred materials for the plant
options for each particular consumer as soon as possible, design were identified, the most optimal design of the
without wasting time calculating and selecting the plant was determined.
necessary parameters, since all possible options have Using the base of neutron converter design options
already been calculated. and the method of optimizing the design procedure, it is
To visualize and simplify this method, three- possible to briefly present to potential customers optimal
dimensional space was used, the ports of which are plant design options that meet all the requirements both
determined by three parameters set by the customer: the from the consumer and from supervisory authorities.
mass, dimensions and cost of the neutron converter. Each
variant is shown as a point whose coordinates are Acknowledgments
determined by its corresponding parameters. Customer- The paper was performed with the support by RFBR,
defined ranges define a three-dimensional shape. If the Grant № 19-07-00455.
point falls within the scope of this shape, then this means
that the parameters of this option meet all the References
requirements of the customer (Fig. 10).
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About the authors
Smetanin Timur R., master’s Degree student of IYAEITF
Nizhny Novgorod state technical university n. a. R. E.
Alekseev. Е-mail: smetanintimur@yandex.ru.
Gureva Elizaveta A., master’s Degree student of IYAEITF
Nizhny Novgorod state technical university n. a. R. E.
Alekseev. Е-mail: infantoplus@yandex.ru.
Andreev Vyacheslav V., Head of the Department «Nuclear
reactors and power plants», Grand PhD of Sciences in
technology, associate professor, Nizhny Novgorod state
technical university n. a. R. E. Alekseev. E-mail:
vyach.andreev@mail.ru
Tarasova Natalia P., senior lecturer of Nizhny Novgorod
state technical university n. a. R. E. Alekseev. Е-mail:
tar0611@rambler.ru.
Andreev Nikolai G., chief specialist JSC «OKBM
Africantov». Е-mail: andreyev@mail.ru