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By V.N. Shalimov,

Unsolved problems of radiation safety at nuclear power plants with VVER-1000 reactor

Proceedings IV International Radioecological Conference "Utilization of Plutonium: Problems and Solutions"
Russia, Krasnoyarsk, June, 5-10, 2000

V.N. Shalimov, Ph.D. (Technology), Associate Professor, Volgodonsk Institute South-Russian State Technical University, Chairman, Volgodonsk Branch of Social-Ecological Union, Volgodonsk, Russia

In compliance with the substantiation principle defined by the Federal Law of the Russian Federation "On radiation safety of the population" of 05.12.95 (article 3) "...all kinds of activity employing sources of ionizing radiation at which the use obtained for a human and society does not exceed the risk of possible damage done by the radiation in addition to the natural radiation background" are forbidden. This law and the radiation safety standards (1) state basic numerical values for admissible exposure of the population and in-plant staff both for normal operation and in possible emergencies. These standards are considered to be based on the so-called acceptable risk values, according to which admissible is the exposure that causes only stochastic (probabilistic) effects.

Official radiobiological doctrine considers inadmissible only manifestations of determined effects of public exposure during accidents at nuclear power plants (2). Even more so, some specialists make statements speculative statements about plausible favorable effect of small doses on human health. This hypothesis is known as @"hormesis". However, recent systematized studies of this problem strongly suggest that there is no "threshold" dose" and even minimal possible doses with low linear transfer of energy give rise to cancer diseases. It has been proved that safe doses and safe dose rate do not exist (3). Nevertheless, individual risk limit for population from all possible sources of radiation is taken as 5x10-5 1/year which is annual dose limit equal to 0,1 Sv/year (1). Yet, even today, e.g. with Rostov nuclear power plant still not in operation total radiation background around Volgodonsk city is 2.5 - 3.0 times as much as the standard annual limit (4). Total genetic load on the population within the thirty km zone around Rostov NPP does not, at this, take into account that owing to nuclear tests, Chernobyl accident and operation of Novovoronezh NPP bottom sediments of Tsymlyansk reservoir have amassed 20-22 TBq of radioactivity, contributed mostly by Cs-137 Sr-90. Radiation contamination around Volgodonsk and Tsimlyansk cities can be expected to increase further. This is intimidated by the data that upt o 15% of sediment matter discharged into the reservoir by the Mid-Don migrates into the dam pools (6).

Commissioning of the station is expected to additionally increase annual discharge of radioactive emissions into the atmosphere by 50 TBq (in terms of 1 year of continuous wok with nominal power of one power block.

Table 1. Normalized atmospheric emissions from one VVER-1000 block


Radioactive emission

Total activity
TBq/(GW ? year)


Radioactive noble gases






Long-living radionuclides



Carbon - 14



Iodine - 131


Total: 53,2

Radionuclides get into liquid wastes with water leaking from the intermediate circuit, from turbine condenser cooling systems and with disbalance waters. Tritium is the major contribution into contamination of heat sinks. At nuclear power plants with VVER-1000 tritium discharge into the hydrosphere is 25-30 NBq/(GW/year)(5). Nuclides of corrosive origin ( r-51, Mn-54, Fe-59, Co-58, Co-60, Zn-65) and nuclides - fragmentary fission products of light uranium isotope (Sr-89, Sr-90, Cs-134, Cs-137) also make a certain Total activity of this discharge is 0,4 GBq/(GW/year) (5).

WE should note that application of normalized values used today to calculate expected collective dose of the the population not infrequently lead to understating of results. E.g. a work by Nizhny Novgorod NIIPLI "Atomenergoproject" cites data on radioactive noble gas emissions at NPP with VVER-1000 reactors that exceed normalized emission values (Table 1) in the same years for Balakovo NPP - 6 times, Kalinin NPP - 9 times (7).

It is apparent that the scale of emissions and radionuclide composition depend on reactor type, condition of the core and equipment, efficiency of purification and operation conditions of the power block.

In accidents without damage of structural units radionuclides discharge into atmosphere due to leakage in the pressurized zone specified by daily leak of air at certain pressure difference and temperature inside and outside the containment. Off-normal growth of aerodynamic resistance of charcoal iodine canisters AU-1500 and AUI-1500 is among principal causes of air leaks. In actual operation with normal air flow after 8-12 months most of these adsorbers substantially increase aerodynamic resistance (8) and the systems fail to maintain rated negative pressure and gas-aerosol activity of the air in the reactor controlled area. At NPP with VVER-1000 containment leaks reach up to several per cent of its volume per day. As a result, discharge of radionuclides can last from several days to several weeks (9).

Loss-of-off-site power accident can cause even more serious ecological consequences. Contribution of on-site loss-of-power accident into the probability of a serious NPP core disruptive accident is from 2x10-5 to 1x10-4 1/(power block/year). In the USA frequency of such accidents is about 10x-1 1/(power block/year)(10). On the Russian power blocks the frequency of power loss is close to this value (11).

Among little-studied risk factors is feasibility of development of extremely dangerous exogenous geological processes that manifest in areas with elevated seismic activity. Worth of attention is the fact that the ratio of engineering-geological risk defined on the basis of dynamics of exogenous geological processes for the south of Russia as compared to rated technological and seismic risk factors is ten and more times. Probability of such an event is evaluated at 10x-3 1/10-3/year. Given 30 years` operation of a nuclear power plant with 2-4 blocks with 50 years of total operation of the industrial zone the cumulative probability of risk of combined detrimental effect of earthquakes and exogenous geological processes is 5x10-3 - 1x10-2 1(power block/year) 5x10-3 - 1x10-2 (power block/year)(12). This factor must, in particular, be taken into account in risk evaluation for beyond-the design basis accidents at Rostov NPP. An earthquake of 5 magnitude (Richter) took place on 14 January 1990 in Volgograd, in 1991 several earthquakes of magnitude 4 were recorded in Samara, the same year - an earthquake of magnitude 5 0 in Kamyshin (11). Probability of disastrous seismogeological phenomena in Rostov NPP area is supported by the results of public ecological examination (13).

Radiation safety of a nuclear power plant cannot be confidently assessed without critical analysis of the status of main equipment and reactor core.

Among disadvantages in VVER-1000 power control is the fuel loading process peculiar in fuel assembly arrangement along the core perimeter. As a result the effect of fast neutrons embrittles the reactors vessel.

Probability of a large-scale disruption of VVER-1000 vessel in the wield is 2,510-4 1/( power block/year) 2.5x10-4 /power block/year (14). bend, cobble, contortion, crooking

As a results of possible bending of fuel assemblies in VVER-1000 core the space between them can either increase to 10 mm or decrease to 0 mm; this, first increases power energy release power in neighboring fuel rods by 11-36% (15) and, second makes rod insertion difficult. These difficulties are to the bend of guide pipes because of non-uniform elongation of fuel rods and deformation of the fuel assemblies during their third cycle (16).

Designer of Rostov NPP seems to have been well aware of these and other disadvantages of -1000 power block, and the rated probability of a serious beyond the design-basis accident was made below the target reference of OPB-88, which is 10-5 1/( ) 10-5/power block/year. In his calculations it is 2,710-4 1/(power block/year) 2.7x10-4/power block/year (7). It is not surprising that the examination commission of the state ecological examination board thoroughly avoided detailed analysis of the probability of a beyond the design-basis accident for Rostov NPP (17).

WE should note that the value of 2,710-4 1/(power block/year) 2.7x10-4/power block/year has been derived for the hypothetical version of ideal construction quality of major objects of Rostov NPP.

Numerous documented infringements of construction standards and deviations from the project most of which have not been eliminated (13, 18) were not taken into account in assessment of radiation safety of the station. To evaluate contribution of this factor into the total risk of a major accident involving emission of radioactivity into the environment without comprehensive engineering examination of ready objects of Rostov NPP by a skilled (financially or structurally independent of Minatom of the Russian Federation) group of experts is impossible. The only thing obvious is that the risk is apparently higher than 10-4/power block/year 10-4 1/(power block/year).

In this connection mandatory qualitative-probabilistic evaluation of nuclear object safety in compliance with OPB-88 requirements have turned into a formal "ritualistic" procedure. This is evidenced by the choice of initial data for probabilistic analysis of radiation consequences of an accident at Rostov NPP on the basis of "Minites of workshop on coordination of initial data for calculating public exposure: of 13.08.1991, "Moscow". As a result, book 4-1 "Radiation impact on environment " optimistically concludes that even with the most grave scenario (-) with prognosis confidence 99,5% does not need special protective measures (19). With a more conservative determined approach with the assumption that in case of an accident the radioactive cloud moves towards Volgodonsk and Tsimlyansk cities collective doses are higher than in the probabilistic approach 10 times for the maximum design-basis accident and minimum 50 times for the beyond the design-basis accident. Effective dose equivalent for the residents of the said cities are estimated in the probabilistic approach as @52 3, and with determined approach - minimum as @2900 3 (20). Of course, preference should be given to the conservative methods of evaluating radiation consequences. Yet, for the designer this would mean considerable increase of costs for protective measures plan and for the population this risk would be unacceptable.

Both approaches share a common drawback to predict consequences of radiation impact (with fairly large uncertainty) for an individual conditionally isolated element of biocenosis. Yet, their limits make impossible to assess the synergetic effect of radiation and emissions (releases) of contaminants on the entire biosocial system on the whole even within the 30 km zone of the nuclear power plant. Without such an assessment there is not point to present the probabilistic and determined approaches methods as an instrument to estimate potential damage of exposure of large population groups. Generally nuclear power plants are placed in the vicinity of large cities with high concentration of industrial potential and transport means. Water is supplied from large water ways or reservoirs. Consequently, the ecological situation specific for areas adjacent to nuclear power plants is adverse. E.g. in Volgodonsk in the recent five years average annual concentrations of suspended substances are 1.1 admissible limits. Maximum one-time concentrations exceed admissible limits in terms of suspended substances 2 times, nitrogen dioxide - 3.2 times, carbon oxide - 1.2 times, formaldehyde- 3 times. Since 1998 Tsimlyansk reservoir waters increased annual average content of easily oxidized organic substances, compounds of nitrogen, iron and copper and exceed admissible limits 2-3 times (21).

Today the question what limit radiation dose and what limit concentration of toxic substance are admissible is still open. Modern radiation safety and standardization of toxic substances should be based on thresholdless concept. Even though the statement of thresholdless effect of these factors is controversial for many representatives of science up to date there are not convincing arguments that would unequivocally make possible to reject the thresholdless concept (22).

Deteriorating human habitat is becoming an ecological imperative to search for new integral criteria of comprehensive impact on biosocial systems of radiation, chemical, bacteriological and other factors. Only these criteria can make possible to have an objective evaluation of ecological prosperity of urbanized territories.


1. Radiation safety standards (-96). .: Goskomsanepidnadzor Rossii, 1996 - 127p.

2. Ye. A. Ivanov, L.P. Khamyanov. Methodological aspects of risk estimate for NPP are community with account of possible radiation accidents. Atomnaya energiya, v.83, vyp.3, 1997 - p.222.

3. J. Hofman. Small dose cancer: independent analysis of the problem. 2 books. - .: SOES, 1994.

4. V.S. Karpukhin. "Zero" radiation background of planet Earth and 30 km surveillance zone around Rostov NPP/ New Materials, Instruments and Technologies. - Scientific Transactions. - Novocherkassk, 1998, p.147.

5. I.I. Kryshev, Ye. P. Ryazantsev. Risk estimate of radioactive environmental contamination in NPP operation. - Atomnaya energiya, v.85, vyp.2, 1998, pp.158-164.

6. ..Bessonov, ..Davydov, S..Nareskin et al. Radionuclide content in bottom sediments of Tsimlyansk reservoir. - Atomnaya energiya, v.77, vyp.1, 1994, pp.48-51.

7. V.N. Chistyakov, Yu. V. Gorelov, V.B. Kasatkin. Rostov NPP. Comparative effect of emissions of noxious substances into atmosphere from power sources of Volgodonsk city, including nuclear power plant. - Nizhni Novgorod, 1994, p.30.

8. L.I. Fedorova, P.Ya. Poltinin, L.V. Karnatsevich et al. Aerodynamic resistance of AU1500-type canisters from NPP ventilation systems. - Atomnaya energiya, v. 88, vyp.1, 2000, p.74.

9. Ye.A. Ivanov, T.V. Ramzina. A method of estimating radiation consequences of nuclear power plant accidents for the environment. - Atomnaya energiya, v.79, vyp.3, 1995, p.215.

10. L. Cave. On-site loss-of-power accidents. - Atomnaya tekjhinka za rubezhom, N2, 1991, p.31.

11. R.Z. Amionov, A.E. Borisenkov. Estimate of frequency of loss-of-off-site power at NPP with VVER. - Atomnaya energiya, v. 83, vyp.2, 1997, pp.124-128.

12. Ye.A. Yakovlev. NPP safety estimates with account of seismic and engineering-geological factors. - Atomnaya energiya, v.69, vyp.2, 1990, p.114.

13. Proceedings of public ecological examination commission on Rostov NPP design (official documents). Compiled by: V.N. Shalimov, I.S. Reznikova, N.P. Sushkova, Volgodonsk, 2000, p.70.

14. ..Tutnov, An..Tutnov, A.S. Kiselev et al. Design substantiation of strength and probability of VVER vessel disruption. - Atomnaya energiya, v.87, vyp.2, 1999, p.139.

15. G.L. Ponomarenko. Account of VVER-1000 fuel assembly bending on fuel rod power. - Atomnaya energiya, v.87, vyp.3, 1999, p.210.

16. Yu. Laksonen. VVER-1000 - advantages and disadvantages. - Atomnaya tekjhinka za rubezhom, N10, 1994, p.24.

17. Findings of examination board of State ecological examination of Rostov NPP construction design/ Ed. N.I. Gvozdevsky. Volgodonck, 2000, p.72.

18. V. Shalimov, I. Reznikova. Evolution of hatred, P. 1. - Lights of the city. - Volgodonck municipal newspaper. - N40 of 03.10.1996.

19. P.K. Golovshenko, A.V. Zharkov, Yu.P. Kormushkin et al. Estimate of Rostov NPP impact on environment. Basic Provisions./ Ed. E.N. Mustafinov, 1992, p.88.

20. M. Davydov. Findings on book 4-1 of "Radiation impact on environment" od Rosto NPP construction design made by Nizhny Novgorod NIPKII "Atomenergoproject" (1991). Of 22.11.1993. - Donskoi krai - newspaper of Cossak Union of the Don river Voisko - March-April 1994.

21. State report "On environment status in Rostov oblast in 1998". - Rostov-on-the-Don, 1999, p.274.

22. A.L. Kononovich, S.V. Barbashov, B.Ya. Oskolkov et al. Standardization of discharges and emissions of radionuclides and noxious substances into environment. - Atomnaya energiya, v.76, vyp.6, 1994, p.524.

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