4.1. MU is aimed at improving and enhancement of reliability of the occupational dose determination having in mind implementation of the optimization principle with respect to radiation protection of workers during radiation hazardous operations of SNF and RW management.
4.2 Dose monitoring under regulated conditions of work using radiation sources is performed with the purpose of reliable determination of:
• individual effective doses of external and internal occupational exposure;
• individual equivalent doses of external exposure to some organs.
4.3 Subjects of monitoring are individual effective doses, as well as equivalent doses to the skin, hands, feet, and to the lens of the eye for the personnel "A" and "B" groups. Dose monitoring of the bottom abdomen surface is also introduced for female personnel "A" group, up to 45 years old.
4.4 The facility administration makes a list of persons ascribed to the personnel "A" group under agreement with the federal authority responsible for the sanitary and epidemiological supervision.
4.5 The attached persons not employed to SevRAO and involved into some operations performed in radiation hazardous areas are subjected to dose monitoring; after termination of this work, as necessary, they can receive the certificate illustrating the incurred dose to submit this certificate to the place of permanent work.
5 Monitoring of external exposure
5.1 Personal dose monitoring for the controlled groups of workers
5.1.1 The following techniques are applied for dose monitoring of external occupational exposure:
• personal dose monitoring (PDM) , involving determination of individual occupational doses based on consecutive measurements of individual characteristics of whole body, skin, hand/feet and lens of eye exposure of workers from the personnel "A" group; these measurements are conducted using individual dosimeters during the specific control period.
• group dose monitoring (GDM) involving determination of individual occupational doses based on consecutive measurements of radiation situation characteristics over the specific control period both in workplaces and in some parts of the industrial site taking into account duration of the personnel staying in those workshops and/or at those areas.
5.1.2 Personal dose monitoring of external occupational exposure covers those workers from group "A", whose doses in the workplaces exceed or (according to prediction) can exceed the following levels of monitoring introduction (Lmi):
• Annual effective external photon dose - 1 mSv;
• Annual equivalent dose to the lens of the eye - 50 mSv;
• Annual equivalent doses to the skin, hands and feet - 50 mSv;
• Monthly equivalent dose to the surface of the bottom abdomen of up to 45-year women – 0.2 mSv.
5.1.4 PDM of external photon exposure to the personnel "A" group is performed using individual thermo-luminescent dosimeters (TLD) (1 g/cm2 thick tissue-equivalent body), carrying on the chest.
During management of both SNF and high level RW, reading frequency is monthly, while for the personnel of the RW treatment Combine this frequency is quarterly. Indications of such dosimeters define external gamma radiation contribution into total effective dose.
5.1.5 With the purpose of operative monitoring of the shift (daily) whole-body external gamma dose, individual direct reading dosimeters are applied with established threshold of the particular reference level exceeding (DKG AT-2503 type or similar).
5.1.6 Dose monitoring of the occupational external exposure is performed according to the techniques:
• Dose monitoring of the occupational external exposure using the direct reading dosimeters.
• Dose monitoring of the occupational external exposure using the thermo-luminescent dosimeters.
5.1.7 The person on-duty from the radiation safety division distributes dosimeters before the beginning of work and he takes them away after the termination of work. Reading of individual dosimeters, account and registration of occupational external doses is performed:
• under normal (routine) radiation situation – after termination of workday, or a shift;
• during a radiological accident – just after departure from the emergency area.
5.1.8 PDM of equivalent doses to the bottom abdomen is introduced for up to 45-year women. Such monitoring frequency is once in a month.
5.1.9 Monitoring of equivalent doses to the lens of the eye, to the skin and to hands/feet of workers involved into SNF and high level RW management, must be performed using individual dosimeters.
5.1.10 In case of individual dosimeter absence, calculation is permitted of beta equivalent dose to the skin by means of the equation:
Hexternal = 3.6 х 106 х Δ t х ∑ϕ (ЕR) х h(ЕR)тexternal
. , (5.1) where: t-work time duration, during which personnel stays in the workshop, hours per year;
ϕ (ЕR)-average density of R-type particle fluence with ЕR energy in the workplace, part/cm2sec (tab 8.2.
NRB-99);
h(ЕR)тexternal-equivalent external dose to the organ Т per unit fluence of R-type particles with ЕR energy at exposure to the parallel beam under face-back geometry (NRB-99 tab 8.2.);
3,6х106 –transfer coefficient both of hours into sec, and Sv into mSv.
If there are no data on beta-emitter energy, the average density can be calculated using the equation:
ϕ (ЕR)=Рbeta/159.6, (5.2)
where: Рbeta-contamination with beta-active substances being measured using KRAB-2, KRAB-3, KRBG-1, or KRB-1 type radiometer distr./cm2min;
159.6 - transfer coefficient from distr./cm2min into part./cm2sec..
5.1.11 To evaluate maximum annual equivalent dose both to the lens of the eye, hands, feet, to the skin and to the bottom abdomen, relative coefficients are permitted to be used; such coefficient is a ratio between dose to the particular organ or tissue and dose, which individual dosimeter has registered at the area of chest in the course of annual PDM.
5.1.12 Under regulated conditions of the radiation source management ay SevRAO facility No.1, monitoring of individual neutron dose using personal dosimeters is unreasonable.
5.1.13 Individual external neutron doses during SNF management are calculated as a product of neutron dose rate over the particular period:
Н=Pn х t, (5.3) where Рn-neutron dose rate, μSv/h;
t-exposure duration, hour.
DKS-96N neutron dosimeter measures equivalent neutron dose rate.
5.2 Individual dose monitoring by means of group dose monitoring
5.2.1 Group dose monitoring means determination of individual occupational doses based on measurements of ambient external dose equivalent (gamma or neutron) Н. (10)i (ambient dose rate) either in the workshop or on-site, taking into account duration of worker staying there.
Effective external dose value is calculated using the following the equation:
E external =
∑ × Δ
i
Н & ( 10 )
it
i, (5.4)where Δti – duration of worker staying in the i-th workshop over the controlled period (in hours) at the average ambient equivalent dose rate Н. (10)i, μSv/h.
5.2.2 Gamma ambient external dose rate is determined on the base of DTU dosimeter readings. These dosimeters are equipped with DTG-4 detectors from DVG-02T kit and located in workplaces in workshops and in buildings at STS technical area having in mind the exposition time. The group monitoring dosimeters are read after termination of work, while for the shift on-duty and for the armed guard – daily, after termination of duty.
6 Monitoring of internal exposure
6.1 Personal monitoring of internal exposure
6.1.1 Individual internal dose calculation is based on personal monitoring of radionuclide intake, performed using WBC spectrometry kit by means of direct measurements of workers.
6.1.2 Monitoring is performed under standard geometries – «whole body» - determination of 137Cs intake, «Lung» - determination of 137Cs and 60Co intakes, and «Thyroid» - determination of 131I intake.
Monitoring is performed according to the following techniques:
• Measurement procedure of man-made radionuclides in human organism using WBC.
- Calculation of committed effective internal dose.
Monitoring frequency:
• the personnel "A" and "B" groups – annually, at the end of each calendar year;
• the personnel involved into radiation hazardous operations, are subjected to monitoring before and after termination of work.
6.1.3 The results of internal monitoring are registered in the relevant protocol and recorded in the personnel dose cards annually.
∑
τ ×∑ { }
×Δ×
= τ
G ,
U k
k k G , U внутр
G , U
гр 1,4 e( ) Q t
) (
E (6.1)
where внутр
G ,
)U
(
eτ - committed effective internal dose per unit intake of U radionuclide compound, which is ascribed to G type at inhalation (hereinafter referred to as dose coefficient, for short) under standard conditions of internal exposure, Sv/Bq;
Δtk - duration of the personnel staying in the k-th workshop (in the k-th workplace) during a calendar year (in hours), at the average annual activity concentration {QU,G}k of G type U compound in the k-th workshop (in the k-th workplace), Bq/m3. If the type of compound is unknown, maximum of внутр
G ,
)U
( eτ values from NRB-99 Annex A-1should be set. As for SevRAO facility No.1,137Cs, 90Sr and 60Co are radionuclides, which must be taken into account in calculation of committed effective internal doses under regulated conditions of radiation source management.
Δtk values are determined on the base of time study of staying in the workplace (in the workshop).
7 Individual dose registration
7.1 Individual effective dose is a sum of individual external gamma effective doses and individual effective internal dose.
7.2 Doses being determined using individual or group monitoring, are registered in the worker's individual card, if they exceed the record level equal to:
• for annual effective dose – 1 mSv;
• for annual equivalent dose to the lens of the eye – 2 mSv;
• for annual equivalent dose to the skin – 5 mSv.
7.3 Individual external gamma dose over the work shift is registered in the Journal of dosimeter distribution with the further recording in the individual card and in the electronic database of the occupational dose account (individual Dose Card).
Results of personal occupational dose monitoring are stored during 50 years.
A chief of RM section analyses occupational dosimetric costs monthly and informs (in a written form) a chief of the radiation safety division, he also summarizes annually data of the occupational external exposure and submit these data to the chief of the laboratory from the radiation safety division to fulfill individual dose cards of the personnel.
7.4 Individual dose account and their comparison with dose limits are carried out in terms of nominal values without any uncertainties.