4. NUCLEAR POWER PLANTS

4.1. General

By the time of the USSR collapse the nuclear power of this country had become an important constituent of the national electrical power system, 12.6% of total electricity output, playing the key role. In the largest united electrical power systems of the North-West, Center and Middle Volga nuclear electricity outputs were particularly important with produced in 1991 32%, 21.3%, and 13.8%, respectively.

Naturally, in NPP operation some quantity of radioactive materials is released to the environment, and the NPPs themselves are a potential source of radiation impact to the personnel, population, and environment during accidents. The NPP reactor plants are designed so that the largest part of radioisotopes produced are isolated from the biosphere, and only a small amount of radionuclides are released to the environment with gas and aerosol discharges and liquid effluents, where they are dissipated in the atmosphere and surface water of the NPP location region. However, as more than 40 years experience with the radiation monitoring of environment in the USSR (Russia) shows the access of such quantities of radionuclides to the biosphere do not result in changing the natural radiation background in the area surrounding NPP site.

Before the USSR disintegration in 1991 there were 17 NPPs with 51 power units of a total installed capacity of 38.2 GW (including four units with AMB-100, AMB-200, VVER-210, VVER-365 at Beloyarsk and NovoVoronezh NPPs at the stage of decommissioning and two VVER-440 units at Armenian NPP have been shutdown upon the earthquake in 1989).

After the collapse of the USSR nine NPPs with 28 power units of a total installed capacity of 20,242-GWe remained in Russia, five NPPs with 14 power units of a total installed capacity 12, 88 GWe are in Ukraine, Lithuania has Ignalina NPP with two RBMK-1500 units, Armenia - two VVER-440 units having been shutdown upon the earthquake, and Kazakhstan has one BN-350 power unit.

In view of the energy crisis in Armenia caused by political and economic problems Unit-2 of the Armenian NPP was again put into operation in November 1995 with participation of Russian specialists.

The information about the NPP locations in the ex-USSR, reactor plant types, number of units and their capacity is given in Table 4.1.

Table 4.1

Nuclear power plants of ex-USSR in 1991

4.2. Characteristics of radioactive materials and wastes produced in NPP operation

4.2.1. Radioactive material and waste sources at NPP

In NPP operation three main groups of radioactive materials (RM) and radioactive wastes (RW) have to be distinguished, which are accumulated in:

• reactor storages of spent nuclear fuel (fuel ponds) and separate storages;
• liquid and solid radwaste storages at NPP site.

Table 4.2 lists the data on the amount of spent nuclear fuel stored at NPP sites and spent nuclear fuel storages (SNFS) (cooling ponds), including separately SNFS at NPP with RBMK, as well as the estimate of the total FP activity in the spent fuel.

Table 4.2

The data on the amount and activity of fission products (FP) in the spent nuclear fuel (SNF)stored at the NPP sites

As the spent fuel is continuously transported from the NPP with VVER-440 to a reprocessing facility, and from the NPP with VVER-1000- to a centralized repository, the quantity of these fuel at NPPs continuously changes. Therefore, in the input database the amount of spent fuel at a given moment can be only indicated. Another radioactivity source at the NPP is solid and liquid wastes produced in the course of the plant operation. The classification of liquid and solid radioactive wastes adopted in Russia according to their specific activities, gamma-ray dose rate formed by them at 0.1 m or to surface contamination with radionuclides is shown in Table 4.3.

Table 4.3

The categories of radioactive wastes

The a-emitter activity and contamination values are ten times lower than the b-emitter ones

At present at the NPP the solid wastes are divided into different categories only by measurement of gamma-ray dose rate at 0.1 m from the container, cask, package, bag, etc. which is the simplest method to be used for this purpose.

Solid radwastes are formed during scheduled repairs and overhauls (process equipment, control and measurement detectors, pipes, tools, cloths etc.) as well as in the process of decontamination of liquid and gaseous radioactive wastes (filters, sorbents, ion-exchange resins etc.).

Liquid wastes are produced in operation of the NPP devices maintaining the water-chemical conditions of the process circuits of the reactor unit and purification of waters with low salt concentrations during the decontamination of equipment, rooms and cloths, in coolant leaks etc. By their physical and chemical composition liquid radwastes are homogeneous water and organic solutions as well as heterogeneous systems (pulps, emulsions, suspensions) in acidic and alkaline states. The nuclide composition of NPP radwastes involves some radionuclides-fission products (cesium, strontium, iodine), and radionuclides-products of activation of the reactor plant structural materials (cobalt, nickel, manganese). Among the radionuclides of this set there are no significant amounts of isotopes with half-lives exceeding 30 years. This makes it possible to consider conceptually the possibility of burying the radwastes of this category in the repositories securing their isolation for only 300-500 years as within this period they nearly completely decay.

The rate of operation radwaste production at NPP depends on the type of the reactor unit, quality of NPP operation and many other factors. The quantitative indices of radwaste formation per year and some of their characteristics for different reactor unit types are given in Table 4.4.

Table 4.5 presents the data on solid radioactive wastes accumulated in the storages at the sites of the Russian and ex-USSR NPPs.

Table 4.6 lists the general data on radioactive wastes produced in operation of the ex-USSR and Russia nuclear power plants.

At present at most Russian NPP the storages are filled with liquid wastes by about 75-100%, and with solid wastes by over 60%. The fraction of high-active wastes makes by volume no more than 1%.

Note that some numerical data of the tables are continuously changing because the operating NPP are producing new radioactive wastes while the stored RW are being subject to reprocessing.

Table 4.4

Quantitative indices of RW production rate at NPP

Table 4.5

Solid Radwaste Storages

*) - the data as of 01.01.95

**) - the data as of 01.01.94

Table 4.6

Liquid radioactive waste storage

*) The data as of 01.01.95

**) The data as of 01.01.91

4.2.2. Gas-aerosol releases and liquid waste disposal from NPP

4.2.2.1. Gas-aerosol releases from NPP

By convention the sources of gas-aerosol releases from the NPP can be divided into two large groups:

- coolant leaks into NPP rooms;

- process blowouts from the NPP water system tanks.

The coolant leaks are in the main accompanied with radioactive aerosol (long-lived nuclides - LLN) and radioactive iodine (I) releases. The process blowouts leads primarily to releases of noble radioactive gases (NRG).

As these three constituents of release to the atmosphere (LLN, I and NRG) are in different physical states, possess different physical and chemical properties, different methods are used to reduce their escape to the atmosphere through the NPP vent stack.

The vent air is cleaned from aerosols and iodine by installation of aerosol and special "iodine" filters into the exhaust ventilation systems.

Process blowouts are cleaned from NGR in special radiochromotographic systems. The exposure chambers are used only at the power units of the first generation (Kursk and Leningrad NPPs). The NPP systems of gas-aerosol release cleaning currently in operation ensure 80-99.9% cleaning efficiency.

To reduce the radiation effect of NPP on the population and environment the USSR (Russia) nuclear safety regulatory bodies established that during the normal operation of the NPP they shall not cause any additional irradiation of the population with a dose exceeding 0.2 mSv per year from gas-aerosol releases and with a dose of 0.05 mSv per year because of radionuclides contained in the effluents.

The annual gas-aerosol release and liquid waste discharge from the NPP, established for not exceeding the above dose rates according to the acting "Sanitary regulations of NPP designing and operation" are called the admissible release (AR) and admissible discharge (AD). However as up to now no standard method for AR calculation has been adopted in Russia, all NPPs use as admissible ones, lower AR values, established by the nuclear safety regulation bodies in 1979. These values were adopted basing on the reference values of actual releases from NPP. The values of admissible releases per one power unit of NPP currently in operation are listed in Table 4.7.

Table 4.7

The data on the actual values of daily average gas-aerosol releases from the USSR (Russia) NPPs in 1991 and 1995 by standardized components (NRG, LLN, I) are displayed in Table 4.8.

In 1994 a significant reduction (by about four times) in the NRG releases to the atmosphere took place at the Russian NPP due to implementation of a system of suppression (by increasing the exposure before the discharge) of Ar-41 activity, whose contribution to the releases had exceeded 60%.

Table 4.8

The daily average gas-aerosol releases from NPP

*) The data as of 1995;

**) the data as of 1991

The values of 1995 gas-aerosol releases, listed in Table 4.8, created an additional irradiation dose to the population less than 0.01 mSv, which cannot be measured by any instrument at the level of the natural irradiation dose, (about 1 mSv), and did not cause a change in the radiation situation in the areas of NPP locations.

4.2.2.2. Liquid waste disposals from NPP

For all Russian NPPs the admissible radwaste discharges have been established by the nuclear safety regulation bodies basing on the calculation values which take into account the specific features of water reservoirs, where the debalance waters from the NPP are discharged, and guarantee not exceeding the additional dose of 0.05 mSv/yr from the natural sources in all possible kinds of water management.

In the ideal case the NPP process cycle in the primary and secondary circuits must be closed, without production of "debalance water" (i.e. the difference in the quantities of the water from the process circuits, transferred for cleaning and that arriving at these circuits). However, because of different design solutions adopted at different power units and of the levels of their operation this "debalance" water is produced. Having passed through cleaning in the evaporator and ion-exchange systems, this water accumulates in special (control) tanks and, after the radiation control, can be discharged from the NPP to surface water reservoirs.

Each discharge of debalance water from the power unit is provided with a specification with the data on the quantity of the water to be discharged and the volume and total activity of all radionuclides it contains.

The disposal of the NPP debalance water is permitted if two conditions are fulfilled:

• the volume activity of the water does not exceed the value established in the Standards of Radiation Safety (i.e. it does not fall into the category of radioactive wastes);
• the total activity of all nuclides discharged with the debalance water from the NPP from the beginning of the year does not exceed the admissible value (AD).

The data on the volumes in the "debalance" waters discharged from the NPP and the activity values as percentage of the AV value are given in Table 4.9.

Table 4.9

Discharge of radionuclides with NPP liquid waste disposals into the environment

*) data as of 01.01.95

***) by the main dose-producing radionuclide, Co-60

**) data as of 01.01.91

****) lower than the minimum detected activity

It should be pointed out that high percentage of discharges from some NPP are not due to high values of the activity released (in absolute units they are about 1GBq/yr) but rather to the strict standards currently in force in Russia.

4.2.3. Radiation incidents and accidents at NPP

The international scale of nuclear-hazardous events (INES) worked out by IAEA was adapted and has been used in Russia since 1991.

Before the adapted INES was admitted in the USSR (Russia) a three-level scale of estimation of the magnitude of radiation accidents at NPP had been used. According to the extent of exceeding the designed boundaries and the quantity of radioactive materials released, all accidents were divided into localized, local and general.

• Localized accident is a failure in the NPP operation resulting in the release of radioactive products or ionizing radiation beyond the specified boundaries of equipment, process systems, buildings and structures in amounts exceeding the standards established for normal operation.
• Local accident is a failure in the NPP operation when the radioactive products escaped into the NPP sanitary protection zone in amounts exceeding the standards established for normal operation.
• General accident is a failure in the NPP operation when the radioactive products released beyond the boundaries of the NPP sanitary protection zone in amounts exceeding the standards established for normal operation.

It can be tentatively considered that relation between the previously used NPP accident scale and the current INES scale can be presented as follows:

In designing the NPP a great set of initial events (equipment failures, personnel errors, etc.) leading to accidents is analyzed for substantiating the NPP safety.

To prevent the development of accidents and to mitigate their consequences the design provides the safety systems (control, protection, localizing, etc.). The requirements to the safety of the NPP reactor units were continuously heightened, which was reflected in normative documents (ND) on NPP safety and introduced to the designs. By the safety level all USSR (Russia) NPP power units can be divided into two generations:

- power units of the first generation developed and put into operation before the main nuclear safety ND were issued (Units 1,2 of Beloyarsk, NovoVoronezh, Kola, Leningrad and Kursk NPPs);

- power units of the second generation (all later ones) designed and constructed in accordance with ND corresponding to the main international approaches, such as OPB-72, OPB-82, OPB-88 and others.

Taking into account the data on the accident at the Chernobyl NPP and basing on the additional safety state analysis the works on enhancement of the safety of all operating NPPs in the USSR (Russia) were carried out. The higher nuclear safety level of the NPP with RBMK was reached due to the reduction in the positive void coefficient of reactivity, increase in the response of the designed emergency protection of the reactor, and introduction of an additional quick-acting emergency protection. As a result, the possibility of occurring the accident with rapid uncontrolled transient overpower of the reactor, similar to the Chernobyl accident, has been excluded. At the NPP with VVER-1000 measures ensuring the required reliability of the mechanical emergency have been introduced protection have been introduced. Some longer-term measures for enhancement of the safety and reliability of the NPP units both with RBMK and VVER reactors, including those providing a higher resistance of the VVER reactor vessels to brittle fractures and refit of Units 1 and 2 of the Leningrad and Kursk NPPs have been worked out and are being realized.

The nuclear safety regulation organization (RF Gosatomnadzor) has establish a special operation regime for the NPP with the first generation power units, including issuing of annual reports with analysis of the actual state of safety and obtaining permits for further operation. The similar practice relative to the NPP which do not completely meet the current safety requirements also exists in other countries such as Great Britain, France, USA who were the first to develop nuclear power and where some NPPs are still equipped with out-of-date power units.

The information on events (incident and accidents) at the USSR (Russia) NPPs having led to radiation consequences is given in Table 4.10.

With the exception of the Chernobyl accident, no one of accidents listed in Table 4.10 resulted in changes in the radiation situation outside the NPP site, and no special measures were required for protection of the population.

The Chernobyl accident whose initial events, development and consequences were studied both in the USSR (Russia) and in many other countries, has been described in detail in the literature [4.7, 4.8, 4.12-4.20].

In the present Analytical Review we shall confine ourselves to presenting new data on the radiation doses received by the people who participated in the operations on mitigating the consequences of this accident [4.7] and to description of its impact on the environment [4.20-4.33].

4.2.3.1. Radiation doses from the CNPP accident

In 1986, after the Chernobyl accident, the all-Union distributed registry (AUDR) of persons having subjected to irradiation was set up in the USSR. By the time of the USSR collapse the AUDR database had involved the medical and dosimetrical information on 660.000 persons including 275.000 participants in the mitigation of the Chernobyl NPP consequences (MAC).

Since 1992 the Russian State Medical and Dosimetrical Registry (RSMDR) has been functioning. At present the Registry involves 370.000 persons (Russian citizens) subjected to irradiation in nuclear accidents.

Now (as of 07.95) the RSMDR contains the data of the states of health of 159.027 emergency workers.

For 125.771 emergency workers the external radiation dose values are put into the RSMDR basing on the health certificates delivered in the zone of MAC (mitigation of accident consequences) operations.

For a more detailed analysis of radiation doses rates the efforts were made on establishing the geographical coordinates of the settlements were the emergency workers had lived. Such data was found for 119.782 emergency workers with the available dosimetric data. For further analysis the recordings were chosen from the Registry database with the external radiation dose not exceeding 50 cGy. The radiation doses of 366 emergency workers, contained in the Registry, were higher than 50 cGy, and these data are not allowed for in the data shown below.

Table 4.11 lists the average values and standard deviations of the radiation doses for emergency workers, time of their residence in the zone where the works were carried out and "effective exposure dose rate" (EEDR) depending on the date of their arrival at the contaminated zone.

Table 4.10

Incidents and accidents at NPPs in the USSR (Russia)

Table 4.11

The average characteristics of dose rates to liquidators

N - number of liquidators, prs

D - average absorbed dose, cGy

T -average time of residence in the contaminated zone, day

P - average EEDR, mR/h;

From the data of Table 4.11 the conclusion can be made about the dynamics of the average radiation dose rates in performing main works in the zone of accident. Some increase in the average dose for emergency workers arriving at the zone in 1990 can be accounted for by the fact that mass works in the zone had been in the main completed and, therefore, only "professionals" were sent to the zone for carrying out special operations.

Table 4.12 (1,2,3) displays the similar average characteristics for different distances from the residence or working area to the CNPP in 1986-1988.

(R1-R2) is the distance from the residence or work area to CNPP, km.

1986. Table 4.12.1

1987. Table 4.12.2

1988. Table 4.12.3

To sum up, from the data of Table 4.11 the collective radiation dose received by most MAC participants can be determined, which is:

1986 - 7405.4 msV;

1987 - 4327.0 mSv;

1988 - 600.9 mSv;

1989 - 175.2 mSv;

1990 - 371.5 mSv;

Total in 1986-1990 - 12880 mSv.

Further work on the systematization of the data on the dose rates received from the Chernobyl accident is continued at the (RAMS) Medical Radiological Research Center in Obninsk.

4.2.3.2. Territories contaminated with radionuclides from NPP accidents.

Accident at Chernobyl NPP

The accident at Unit-4 of CNPP began with a thermal explosion of great violence in the core. As a result a high-temperature flame-colour ball containing a complete set of radionuclides, having been accumulated in the reactor by that time, was discharged into the atmosphere.

A large radioactive cloud, formed after the explosion, began to spread in the prevailing wind direction, which initiated radioactive contamination of the environment. The fire on the graphite stack following the explosion was kept up by high energy released in the continuing decay of radionuclides emerging from the reactor. This resulted in a radioactivity discharge into the atmosphere in the form of a jet which continuously changed its initial direction, following the wind direction. The intense jet discharge was observed for about ten days.

On April 26, 1986 a part of air mass trajectories was directed from CNPP through Byelorussia and Baltic states to Finland, Sweden and Norway (most probably, it was an "explosion" discharge), another part - through the Ukraine and Poland to Germany, Denmark, Belgium, Netherlands and the northern France.

On April 27 the atmospheric trajectories went from CNPP again through Byelorussian and Scandinavian countries but with a turn via the Kola Peninsula to the east. On April 28 the prevalent situation was nearly calm, the wind still turning to the east, on April 29 the trajectories had mainly the east direction, and on April 30 they turned to the south and then to south-west and west. Consequently, the contaminated air has spread over the European part of the USSR and over the whole Europe even in the first days of the accident.

The evaluation, measurements and analysis of the radiation situation and radioactive contamination of the environment began from the first day of the Chernobyl accident and have continued up to now.

Prompt radiometric (and later, gamma-spectrometric) surveys were carried out using ground and aviation means.

The first complete map of the near-ground trace (at up to 100 km from the accident location) was built on May 1 and submitted to the Governmental Commission on May 2, 1986. In the first days such maps were built practically every day. In May 1986 the decisions were also made concerning the evacuation of the population from the zone where the annual dose might be 10 rem and higher (an evacuation criterion established by USSR Ministry of Public Health). This dose corresponded to the earth surface radiation levels (at a height of 1 m) of 5 mR/hr as for the date of May 10, 1986.

Decisions on alienation zones (with radiation levels > 20 mR/h as for May 10, 1986) and partial settling out (with radiation levels from 3 to 5 mR/h as of the same date) were made. For comparison as on 10.05.86 the zone areas were as follows: alienation zones - 1100 km2, settling-out - 2940 km², while at the same time the USSR territory contaminated with radioactive discharges from CNPP to levels exceeding 0.2 mR/h was about 50 000 km².

As early as in the beginning of May the full-scale studies of radionuclide contamination of the environment began (although some samples had been analyzed from the first days of the accident).

In the atmosphere a wide set of radionuclides: ⁸⁹Sr, ⁹⁰St, ⁹¹Y, ⁹⁵Zr, ⁹⁵Nb, ⁹⁹Mo, ¹⁰³Ru, ¹⁰⁶Ru, ¹²⁵Sb, ¹³¹I, ¹³²Te, ¹³²I, ¹³³I, ¹³⁴Cs, ¹³⁶Cs, ¹³⁷Cs, ¹⁴⁰Ba, ¹⁴⁰La, ¹⁴¹Ce, ¹⁴⁴Ce, ²³⁹Np and some others were measured. The studies revealed that relative to ⁹⁵Zn and ¹⁴⁴Ce ruthenium isotopes exhibit an increased volatility, and ¹³¹I, ¹³²Te, ¹³²I, ¹³³I, ¹³⁴Cs, ¹³⁶Cs and ¹³⁷Cs - a high volatility. The measurement of concentration of ^239,240Pu in the near-earth surface air level beyond the 30 km zone showed that at all sampling points its concentration in the air were lower than the permissible concentration (1.11x10^-8 Bq/l) even in the first month after the accident.

In soil samples taken within several days of the accident all above radionuclides as well as ²³⁸Pu, ^239,240Pu isotopes were detected. ²⁴¹Pu, ²⁴¹Am, ²⁴²Cm, ²⁴⁴Cm were identified somewhat later.

A noticeable fractination of radionuclides, differing depending on the radioactivity transfer direction (south, west, north) was detected on the earth surface even in May, 1986. The radionuclide composition of contamination of the nearest CNPP zone is shown in Table 4.13 which lists the data on all the samples for which the gamma-ray dose rates measurement at a height of 1 m were made in May-June 1986. Doses ranged from 2 mR/h to 10 mR/h (although there were doses of high or lower radiation levels). It is seen from the table that the radionuclide composition of fallout in the nearest CNPP zone is represented by a complete set of fission fragments (additionally to them ¹³⁴Cs and ²³⁹Np are induced in the relations not much differing from those in which they had been accumulated in the reactor by the onset of the accident. Only ¹³¹I and ¹³²Te in the north sector are an exception for it.

Table 4.13

Relative radionuclide composition of radioactive fallouts in May-June 1986 in the nearest zone of Chernobyl NPP

(A_i/A₉₅ is the ratio of the i-th radionuclide activity to that of zirconium-95 at the time of onset of the accident, f_i,95 is the coefficient of the fractionation of the i-th radionuclide relative to zirconium-95)

By the 15th day the fraction of volatile nuclides in the nearest section of the trace (up to 40 km) had been up to 5% of ¹³²Te and 5.1% of ¹³¹I, and 1.6% on the average. The latter values is estimated by the relation of the total energy releases of radionuclides on the trace and in the reactor (by the moment of accident onset) reduced D+15.

From May 5, 1986 the data on an unusual radionuclide composition of the air contamination began to be reported from research ships carrying out current works in the North part of Atlantic and in the Pacific. According to the data from the ships there were only nine "Chernobyl" radionuclides detected: ⁸⁹Sr, ⁹¹Y, ¹⁰³Ru, ¹³¹I, ¹³²Te, ¹⁴⁰Ba, ¹³⁴Cs, ¹³⁶Cs, and ¹³⁷Cs, ¹³¹I, ¹³²Te and cesium isotopes prevailing. Thus, it was found that the largest fraction of radioactive particles transferred with air currents for long distances were "volatile" radionuclides: krypton and xenon isotopes, ¹³¹I, ¹³²Te, (¹³²I), ¹³³I, such isotopes as ¹³⁴Cs, ¹³⁶Cs, ¹³⁷Cs as well as ¹⁰³Ru and ¹⁰⁶Ru represented a somewhat smaller fraction. ⁹¹Y and strontium isotopes, ⁸⁹Sr and ⁹⁰Sr, are much less volatile (they were recorded on NIS) in trace quantities .

In May of 1986 the criteria for the maximum permissible contamination of the environment with long-lived radionuclides were established (basing on the standards of maximum permissible concentrations for ^239,240Pu in air and maximum permissible dose rates). They were 2,59x10¹¹ - 5,55x10¹¹ Bq/km² for ¹³⁷Cs, 1,11x10¹¹Bq/km² for ⁹⁰Sr, and 3,7x10⁹ Bq/km² for ^239,240Pu.

In terms of the criterion established plutonium radionuclides, ²³⁸Pu, ^239,240Pu (3,7x10⁹Bq/km²) were found to be mainly localized within the 30 km zone of CNPP, and ⁹⁰Sr (1,11x10¹¹Bq/km²) within about 60 km. Studies carried out on the Russian territory revealed that in neither of the most intense spots of radioactive contamination did the radioactive contamination exceed 1,11x10¹¹Bq/km² for ⁹⁰Sr and 3,7x10⁹Bq/km² for ^239,240Pu.

In the initial period of the Chernobyl accident the radioactive contamination of the territory was essentially due to the release of short-lived radionuclides which later lost their ecological significance. In a year after the accident the radiation situation on the largest part of the European territory of the USSR was determined by long-lived isotopes of cesium: ¹³⁷Cs and ¹³⁴Cs and in three years by ¹³⁷Cs. Therefore much attention was given to map-making of environmental contamination with just cesium-137, special state finance was provided for investigations and making state maps of environment contamination. Creating these maps is a result of a wide scientific generalization of the information obtained, basing on unified methodical basis, from different activities, by different methods, using up-to-date equipment.

In accordance with the RF Law "On special protection of persons exposed to radiation from the catastrophe at Chernobyl NPP", the isoline 1 Ci/km² (37kBq/m²) for ¹³⁷Cs is the lower threshold for establishing privileges for the population. The law specifies the dwelling zone with a privileged socioeconomic status 1-5 Ci/km² or 37-185 kBq/ m²); the dwelling zone with the right of settling out (5-15 Ci/km² or 185-555 kBq/m²); zone of settling out (more than 15 Ci/km² or more than 555 kBq/m²). The annual dose of internal and external irradiation of the population must not exceed 1 mSv (100 mrem). Similar laws have been adopted in Ukraine and Byelorussia.

A great amount of work was carried out for obtaining the information on the contamination levels in settlements. In Russia 11457 settlements in 23 administrative regions were inspected in 1995. For the whole post-accident period about 90000 soil samples were taken which were subjected to the gamma-spectrometric and partly to radiochemical analysis. Basing on these data it has been established that the levels in excess of 1 Ci/km² or 37 kBq/m² are observed in 4581 settlements. The calculations revealed that the excess of the permissible irradiation level in 1 mSv (0.1 mrem) can be expected in 527 settlements in 1995, the contribution of plutonium-239 + 240 being less than 1%.

A great volume of investigations of the contamination of large and small territories of the European part of the USSR, and later Russia, was accomplished using the aero-gamma-spectrometric method which permitted the data on the settlement contamination to be supplemented and data to be obtained outside the settlement territories. The aero-gamma-spectrometric survey of environment contamination with various radionuclides (⁹⁵Zr, ⁹⁵Nb, ¹⁴⁰La, ¹⁰³Ru, ¹³⁴Cs, ¹³⁷Cs, ¹⁴⁴Ce) had been carried out since the end of May 1986. By the present time (early 1997) the European part of the ex-USSR and Sibirian territory to about the geographical latitude of the Yenisei has been covered by the survey.

The aero-gamma-spectrometric survey and soil sampling were performed in the administrative regions [6]. The interroute distances in the aero-gamma-spectral survey were determined by the levels of expected radioactive contamination: > 15 Ci/km² (>555 kBq/m²) for ¹³⁷Cs - 0.5 km (surveying scale 1:50.000); 0.5-15 Ci/km² (20-555 kBq/m² (1:20000); <0.5Ci/km² -(<20 kBq/m²) - 10 km (1:1.000.000). The elementary route sections where the gamma-ray spectra are recorded during the flight are 0.1 km; 0.4 km and 2.0 km, respectively. To construct a map of the European part of the ex-USSR (Fig.4.1) 800.000 complete spectra of aero-gamma-spectral measurements (by the European part of Russia 440.000 spectra were used) were obtained and used. A special ground test accompanying the aero-gamma-spectral survey was carried out at several thousands of points. In addition, in constructing the maps the results of the analysis of dozens of thousands of soil samples taken in settlements were used. The relative mean-square deviations in the ¹³⁷Cs contamination values taken from the aero-gamma-spectral and ground data did not normally exceed 40%, being as a rule, 20-25%. The systematic discrepancy were taken into account in constructing the maps.

Fig.4.1 presents the summary map of the cesium-137 contamination of the European part of the ex-USSR as of 1992. The range of mapped contamination levels, from the background ones lower than 0.1 Ci/km² (3.7 kBq/m²) resulting from the atmospheric nuclear tests, mainly of the 60s-70s, to the highest ones reaching 500 Ci/km² (18500 kBq/m²) and higher in the nearest zone of Chernobyl NPP.

On the territories with the contamination levels exceeding 0.2 Ci/km² (7.4 kBq/ m²) the fallouts due to the CNPP accident are notoriously present. This contamination was recorded on an area of 1.011.400 km², which constitutes about 23% of the European part of the former USSR. It should be pointed out that the territories of Russia, Urkaine and Byelorussia with the contamination levels above 1Ci/km² (higher than 37 kBq/m²) constitute 145.300 km², i.e. about 3.3% of the European territory of the ex-USSR.

The summary data on the distribution of the cesium-137 contaminated areas over the whole European part of the former USSR (1993) are listed in Table 4.14.

Table 4.14

Cesium-137 contaminated areas of the ex-USSR European territory, thousand.km² (1993)

The fraction of cesium-137 discharged from the reactor, that fell out on the European territory constituted about 15% of its amount having accumulated in the reactor by the moment of the accident or about 7x10¹⁶ Bq, nearly 4x10¹⁶ Bq of this amount deposited on the USSR territory.

After the accident at CNPP the radiological inspections of forests and arable lands were carried out. The results of these inspections as of 1993 are listed in Table 4.15-4.16.

Table 4.15

¹³⁷Cs contaminated arable lands (thousand.ha)

Table 4.16

¹³⁷Cs contaminated forests (thousand.ha)

The radioactive contamination of water reservoirs, including rivers, on the territories of Russian Federation, Ukraine, and Byelorussia has been continuously monitored from the very beginning of the accident, particularly where are "cesium spotsquot; in the water catchment areas.

The CNPP is located on the territory with a developed hydrographic network. The 30 km zone and the main part of the radioactive trace are in the catchment basin of the Dnieper and its tributaries. To control the situation a monitoring system was urgently deployed in the post-accident period, which covered all big and small water courses in the zone of radioactive contamination, all water storages of the Dnieper cascade as well as the Baltic, Black and Azov seas.

Table 4.17 lists the maximum concentrations in the rivers of the CNPP nearest zone for the period of observations beginning from 26.04.86.

The total activity of the amount of radionuclides, falling into the water from the cloud and jet, was 2x10⁵ Ci (7.4 PBq), the fraction of strontium-90 being about 10³ Ci(0.037 PBq). The concentration of radionuclides in water reservoirs is determined by wash-off of about 0.5% of all strontium-90 and 0.1% of cesium-137 from the water catchment area in the first post-accident years. This wash-off could not form the water contamination which would have exceeded the standards established.

The isotope analyses of sea water samples, suspended solid materials and sea-floor deposits revealed that the concentrations of radioisotopes of Chernobyl origin, such as cesium-141, 144, ruthenium-103,106, zirconium-95, niobium-95, cesium-134,137, strontium-90, plutonium-238,239,240, tritium are 100 times lower than the maximum permissible levels for drinking water and are not harmful for man's health.

Table 4.17

Maximum radionuclide concentrations in the nearest zone rivers, Bq/l^*

^*- The values of concentrations of medium- and long-lived radionuclides such as ¹⁴⁴Ce, ¹⁰⁶Ru, ⁹⁰Sr, ¹³⁴Cs and ¹³⁷Cs are not presented in the Table, because in the time period from April, 26 to May, 6, 1986 their contribution in the human exposure was insignificant.

The evaluation of the contamination of the bottom deposits of Dnieper's reservoirs was made as early as in may, 1986. It revealed that the bottom grounds (silt) in the Kiev water storage in the section adjacent to the Pripyat' mouth are the most contaminated ones. In the south part of the Kiev storage as well as in the Kanev storage the contamination level was found to be lower by tens and hundreds of times.

After the accident dozens of holes were drilled to the depth of water-bearing level around CNPP at several hundreds of meters from each other for monitoring the water quality. The observation of the strontium-90 concentrations in the water of these holes for several post-accident years showed that these concentrations do not exceed the background values.

Based on the data on the radioactive contamination resulting from the accident at CNPP the estimation of the external doses of the Russian population was carried out (Table 4.18) which can be considered as an important indication of the existence of radiation hazard for human health.

The analysis of the whole volume of collected material for the past decade makes it possible to show the results of the evaluation of the amounts of the main radionuclides discharged from Unit-4 of CNPP during the accident. Below a table prepared for publication in the set of explanatory texts to Atlas of cesium deposition on Europe after the Chernobyl accident [4.21] is given. The data listed in Table 4.19 should be considered as preliminary ones since so far the scientists of the international community have not come to full agreement about the magnitude of some radionuclide releases.

Table 4.18

Estimated rates of collective dose commitments for a 50 year period after the CNPP accident made for the most contaminated regions of Russia

Table 4.19

Evaluation of the main radionuclide release, resulting from the CNPP accident

*) According to the data presented in the Atlas [4.23] the quantitty of ¹³⁷Cs deposited on the Europe’s territory was 70 PBq.

4.3. Handling of RAM and RAW at NPP

The spent nuclear fuel from the NPP reactors contains a significant quantity of fissile isotopes, in the breeders the final amount of these isotopes being higher than the initial quantity, which is the physical basis of nuclear fuel breeding. Therefore the spent fuel is another significant element of the raw material reserve of nuclear power and cannot be considered as its radioactive wastes.

At present the only facility reprocessing the spent fuel from the VVER-440, BN-350, BN-600 is in operation in Russia, town Ozersk, Chelyabinsk region. It accomplishes reprocessing of all spent fuel from these reactors both from the ex-USSR countries and ex-socialist East-European states and Finland where the NPP, having been built by the Soviet designs and using the uranium fuel fabricated at the Russian works, are being operated. The uranium separated in spent fuel reprocessing is used for producing new nuclear fuel for the RBMK-type reactors.

The RBMK spent fuel is stored in special repositories at the NPP sites. For the economic reasons no provision for reprocessing of this type fuel has been made.

At present the VVER-1000 spent fuel from the Russian and Ukrainian NPP has been transferred for temporary storage to a special repository being constructed at Krasnoyarsk Mine and Chemical Combine for reprocessing this fuel. The 6000 ton repository will have been fully filled by 2000.

Up to recently the practice of NPP radwaste handling has represented storage of solid and evaporated liquid (still residue) wastes in special repositories at the NPP sites. In the last decade some technologies of radwaste conditioning begin to be introduced because the current method for solid and liquid radwaste storage at the NPP can be only considered as a temporary measure. Further development of nuclear power demands designing and implementation of a complete radwaste handling system based on a concept (technical policy). The concept determines the development of the problem of reprocessing, storage, shipment and final disposal of radioactive wastes.

The final objective of the concept accomplishment is the check and test of the technologies and equipment on radwaste reprocessing, projects of their safe storage and disposal as well as working out guides and standards on radwaste handling. Taking into account the actual conditions in Russia the "Concept..." on NPP radwaste handling stipulates five stages of radwaste handling at the NPP (Fig.4.2) and a final disposal stage.

At present no Russian NPP has a complete set of facilities for radwaste conditioning. At some NPPs liquid wastes are reprocessed in bituminous installations (Leningrad, Kalinin) or on deep evaporation facilities (NVNPP and Balakovo NPP). Solid radwastes are compacted, upon sorting, at Beloyarsk, Kola, and NovoVoronezh NPPs, and combustible radwastes are burnt up at Beloyarsk and Kola NPPs. At other NPPs SRW are stored without reprocessing. Some of home-made facilities for waste conditioning need modernization.

RF Minatom has developed a radwaste handling program for nuclear industry. The program has a section on NPP radioactive wastes handling. This and the NPP radwaste handling concept were used as the basis for development of the "Working Program on radioactive wastes handling at NPPs of the State Concern "Rosenergoatom". The "Working Program" involves the following aspects of the NPP RW handling problem:

• main trends of activities on improving the NPP radwaste handling system;
• realization of the main trends of activities on improving the NPP radwaste handling system.

The main trends of activities include:

• Development of normative documents regulating radwaste handling operations.
• Construction of LRW grouting facilities.
• Construction of facilities for burning combustible radwastes.
• Construction of SRW compaction facilities
• Construction of facilities for vitrification of salt fusion cake and ashes.
• Development of technologies and equipment for removing salt cakes from LRW tanks.
• Development of technology and equipment for reprocessing filtering materials and slurry cakes.
• Development of technology for removing radwastes from SRW storage compartments.
• Organization of process of sorting and transferring SRW for reprocessing.
• Construction of complex for metal waste reprocessing.
• Manufacturing containers for conditioned wastes.
• Development of designs of storages for reprocessed radioactive wastes.
• Development of dry repositories for spent nuclear fuel.

Fig.4.2. Scheme of NPP radwaste handling concept

The realization of the main trends of NPP radioactive wastes handling suggests completing of R&D works on technologies and equipment for RW reprocessing and providing all NPPs with a full set of these technologies and equipment.

In the framework of "Working Program..." research projects on the development of radwaste reprocessing technologies are being carried out, aimed at the reduction of waste quantity in the final reprocessing stage (prior to storage) by concentrating activities as well as on the reuse of useful materials separated.

Unfortunately, because of financial difficulties in nuclear industry and in the whole Russia, Working Program had been fulfilled only by 15-20% for the first 3 years, mainly in the part of testing new technologies at the stage of radwaste conditioning. These developments have formed the basis for works on new radwaste reprocessing facilities jointly with Western companies. As before, a weak point of the nuclear industry program and Working Program for nuclear power plants is the lack of real advances in creating regional NPP radwaste burials as this requires implementing of expensive scheme of long-term storage of conditioned radioactive wastes at NPP sites.

The data on the quantities of RM and RW at NPPs, given in Section 4.2 are complete. However up to now the records on nuclear materials in Russian nuclear power have been kept at each NPP in the form adopted at this NPP, with the exception of the RBMK NPPs whose data on spent fuel are taken into account in the form of State statistic reports (form 3-TEKh).

In accordance with RF President Decree of 15.09.94 "On urgent measures on improvement of accounting and security of nuclear materials" in the Utility organization (concern Rosenergoatom) efforts are being undertaken on the development of the NPP database on nuclear materials at NPPs.

The data on FP activity in the spent fuel stored at the NPP sites are reliable, under assumptions (all fuel discharged from the reactors was considered as having the rated burnup with a correction for the half-life made once a year) taken into account in the calculations. This characteristic can be improved after developing methods for taking into account nuclear materials, typical for all NPPs, and creating the central database in the Utility organization.

Less reliable are the data on the activity of solid and liquid radioactive wastes stored at the NPP sites. This is accounted for by the SRW classification method of SRW classification (by the gamma-radiation dose rate) adopted in USSR (Russia) normative documents on NPP safety and by the methodical difficulties with determination of the activity of LRWs with a high salt content. However taking into account that the activity of the SRW and LRW stored at NPP sites is much lower than the FP activity in spent fuel, the error in the determination of this type RW can be neglected.

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