Technical section
RADIATION SAFETY SYSTEM FOR HANDLING REPROCESSED
URANIUM
Natalya Kolotilkina
Engineer
Joint-stock company «Mashinostroitelny zavod»
Electrostal, Moscow region, Russia
The enterprises of the nuclear industry use nuclear materials based on natural and
reprocessed uranium for a long time.
In conformity with the industry specification TY 95.780-88 the enterprises of ОАО
«TVEL», including ОАО «Mashinostroitelny zavod» in Electrostal (ОАО «MSZ»),
are allowed to manufacture fuel pellets from reprocessed uranium. In this case the
assurance of radiation safety is of paramount importance.
The activities relating to reprocessed uranium at OAO MSZ are carried out under the
permissions and licenses of Gosatomnadzor of the Russian Federation. The receiving
inspection of the isotopic composition of the received feed material is carried out by
the plant Central Laboratory, which is equipped with up-to-date hardware and
procedures.
All the workshops of ОАО «MSZ» engaged in processing of enriched uranium have
radiation and hygienic releases to work with enriched uranium, containing up to
2,0*10-7 W % of U-232.
Radiation monitoring is a very important part of the radiation safety system at the
plant. Its objective is first of all to control the observance by OAO MSZ of the
radiation safety principles and requirements of the normative documents as well as to
obtain the information needed for the protection improvement and for undertaking
the decisions to interfere in case of radiation emergency situation. On the basis of the
radiation monitoring results the staff effective radiation dose is calculated.
At OAO MSZ radiation monitoring is performed in conformity with the requirements
of the Radiological Safety Norms (HBP-99) and Basic Sanitary Norms (OSPORB99). The department of the nuclear and radiological safety checks radiation and
occupational exposure in compliance with the requirements of HPB-99 and
OSPORB-99. The basic parameters to check are the following:
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annual effective and equivalent doses;
annual assessment of the radionuclides intake ;
volume or specific activity of radionuclides in the air, water, food, building
materials, etc.;
contamination on skin, shoes and working surfaces;
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Technical section
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dose and dose rate from the external source;
flux density of particles and photons.
Every year the reference levels are revised and agreed upon with the Gosatomnadzor
of the RF with the purpose not to exceed the dose limits and to implement the
principle providing for the least radiation levels.
The establishment at the site of the dosimetry control was preceded by the issue of
the document “Justification of uranium content limits in the analysed objects during
radiation monitoring in the fuel rod production.” This document defines the
maximum content in the reprocessed fuel of U-232 isotope as equal to 1,9*10-7 w%.
It is said in the Justification that the total alpha-activity of uranium isotopes is
characterised by U-234 mainly. In case of lower enrichments there is a tendency to
shift to U-238, but at higher enrichments the content of U-234 isotope is decisive.
Uranium-232 in quantity below n*10-8 w% does not effect the total reduced
activity. But U–232 in quantity up to 2,0*10-7 w% contributes to the total reduced
activity by 1,3%, causing the decrease of the total activity. Uranium –232 and its
decay products contribute mainly to external gamma-irradiation.
Besides, it is mentioned in the Justification that do define correctly the staff and
population effective doze, they calculated the allowed reduced levels of different
uranium isotopes content in the water and in the air.
Thus the radiation monitoring of the uranium content in the analysed objects is
performed on the basis of the measurements of the total alpha- and beta-activity by
radiometric methods.
For work with enriched uranium the value was calculated for the allowed volume
alpha-activity in the air of the production premises equal to 0,94 Bq/m3 as the upper
allowed limit. The allowed volume of alpha-activity for discharges of the plant and
for air makes up 3,3*10-2 Bq/m3.
In conformity with item 5 of the document the allowed volume alpha-activity values
were corrected. Year 1997 saw the issue of the document “Justification of allowed
volume alpha-activity of aerosols in the uranium source material with different
impurities content.” Due to the fact that the above values turned out to be less rigid
than the current ones (0,94Bq/m3), no further corrections followed.
The activities related to processing of the feed material with higher content of U-232
are carried out at OAO MSZ together with State Biophysics Research Centre; the
specialists of this institute have the licenses to do this type work and they specify all
the required radiation characteristics to predict the occupational doses.
To define the effective doze in conformity with the recommendations of the Expert
Report, the following scheduled activities are to be carried out. The schedule, agreed
upon with Gosatomnadzor of the RF, contains the parameters to be controlled, points
of control and periodicity of control:
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Measurement of doses of external irradiation is done by thermoluminescence
dosimeters of grade DTA-01 in a set with readers of the company RADOS.
For alarm control of neutron irradiation doses in neutron fields alarm dosimeters
GNEIS are used. Individual dosimeter measurement of neutron irradiation is not
performed, as the doses of neutron irradiation are less than control level - 2
mSv/year regulated by methodical documents.
Measurement of skin and hands dose is done during the most critical operation,
that is visual inspection of pellets through measurements of beta-particles flux
density and of the data of the State Biophysics Research Centre specialists
participating in the activities with the reprocessed uranium because at present
there are no qualified dosimeters for skin which could be used in real production
conditions.
Individual doses of inner irradiation are measured in conformity with the
Procedures. Measurement of the inner dose exceeding is done in accordance
with the Justification on the basis of more rigid values.
If any suspect as to radionuclides overshot, the employees of the plant are to go
to the Biophysical laboratory for urgent analysis to be taken with the purpose to
measure radionuclides (radionuclides in the air are identical to those in the feed
material).
Control of volume alpha-activity of aerosols in the air of the production area is
done in conformity with the procedures valid at the plant. After exposition of
aerosol samples the measurements are done on the scintillation alpharadiometers UDZA-09P, BLUDZA-09P, PROGRESS-AP and proportional
alpha and beta-counter FHT 77OR.
Activity assessment of the plant discharges is done at the site of OAO MSZ and
in the sanitary protected zone of the plant. Measurements are done by
alpharadiometers PIA-o1B, PROGRESS-AP, beta-radiometer SNIP and aerosol
alpha-beta-monitor ABPM-2001S.
Individual annual intake of decay products of rodon is measured according to the
Procedure for gamma-radiometers PGA –20P, PPA-01 and IZV-3M. Thoron is
not measured, as its activity is very small and does not exceed 1,5% of aerosol
activity of all isotopes of uranium (thoron is decay product of U-232 and its
activity in the total alpha-activity of 5% enrichment U does not exceed 1,5%).
Contamination control of the plant site and of sanitary zone is done by means of
radiometric devices according to qualified procedures to perform measurements
Contamination control of working surfaces of the equipment and means of
individual protection is done by radiometers SPAR and DAZ.
Impact of different radionuclides is controlled (measurement of inner and outer
irradiation doses).
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Discharges of radionuclides are measured as to total alpha-activity. Total alphaactivity of liquid discharges is classified as well as the total annual activity.
Specific alpha-activity of samples mainly does not exceed 2Bq/kg and does not
achieve the value of 29Bq/kg specified in OSPORB. Liquid wastes with specific
alpha-activity>29Bq/kg are sent to a storage facility for tails. Spread of
radionuclides from the storage tank is controlled by measurements of alphaactivity of samples taken from a special observation well.
Control of contamination levels of the environmental objects in the sanitary zone
and in the observation zone is done by radiometric methods using the equipment
available at OAO MSZ.
In conformity with the requirements of OSPORB-99 all the persons working at MSZ
with the sources of ionizing irradiation are subject to annual medical examination.
During last years no occupational diseases were found associated with impact of
ionizing irradiation. Detail data about occupational doses are described in the reports
annually addressed to Gosatomnadzor(GAN). The data of radiation control show that
there is no exceeding of main limits of doses and levels during normal work, which
can be considered a proof of good operation of the system of radiation safety
assurance at OAO MSZ.
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