Impacts of Radioactive Waste Storage at the territory of RRC-Kurchatov Institute

In February 2003 International Institute of Systems Analysis (IIASA) received the TACIS-Bistro grant for a 6 months pilot study of “Impact of Radioactive Waste Storage at the Territory of Russian Research Center-Kurchatov Institute in Moscow”.

In last quarter of the 20th century there was significant growth of urbanization throughout the world. As a consequence of this urbanization and growth of megacities, the expanding housing areas have resulted in the de-facto sitting of waste disposal facilities in densely populated urban areas. This represents a global problem where past waste management practices located in the suburbs of the city could seriously affect the public. These past waste disposal sites could be of chemical, industrial, municipal or mixed origin. The location of radioactive waste storage sites in what are now urban areas is an extreme example of this phenomenon.

The nuclear legacy in urban environment was mostly created by earlier nuclear facilities, such as experimental nuclear reactors of research, testing and educational centers created in 40-70s of 20th century. Such nuclear facilities are not only a source of radioactive wastes that are often stored under inadequate conditions at the facility site, but also create dangerous targets as they have no protection against airplane crashes or missiles.

Literature search has shown that the Moscow case is not an isolated problem. The former practice to launch nuclear centers in or nearby big cities could be easily traced throughout the world. French nuclear center “Saclay” is about 20 km from the center of Paris, more or less the same situation with nuclear institutions in Budapest, Sofia, Berlin, London, Grenoble, San Diego, etc.

As a result of intensive development of nuclear science and technology in the former Soviet Union (FSU), Moscow and Moscow Region accumulated dozens of nuclear centers and institutions that possess nuclear installations like research reactors (RRs), radiochemical labs, thousands of radiation sources, and then – as a result of their functioning – temporal storages of spent fuel and sites of temporal storage of radioactive waste. Russian Research Center-“Kurchatov Institute” (RRC-KI) is the biggest and the oldest nuclear center in this megacity. Currently it possesses more than 9 RRs, some of them are still in operation, 17 critical assembles, hot laboratory for material testing and certainly spent fuel storages and sites of temporal storages of RW with inevitable soil contamination around them.

As a result of more than half of century operation of nuclear facilities a huge amount of radioactivity were generated and partially stored at the territory of RRC-KI:

• Total activity of spent fuel stored there estimated as 3 MCi,
• Total activity of RW at the site of temporal storage is about 0.1 MCi.

Living close to such “neighbour” inevitably causes concerns of the inhabitants and visitors of Moscow about environmental security of their living, as:

1. The closest residence building area is only about 100 meters from the radioactive waste storage site,
2. The territory between the inner fence of the storage site and adjacent section of the outer fence of RRC-KI is actually occupied by municipal car parking place. Though the access to it limited to people using the area for parking of their cars, it is not really restricted area for citizens,
3. The municipal road along the outer fence of the RRC-KI passes in a distance of several meters from the outer fence of RRC-KI. In rush hours the traffic on this city road makes up to 3000 vehicles per hour.

It was stipulated that the study would be focused on:

• Collection, analysis and collation of currently available data regarding radioactive source term and environmental properties.
• Modeling of radionuclide migration due to erosion by surface (run-off) water and assessment of the radiological impact of radionuclide migration in terms of dose uptake by critical population groups, and general reduction of environmental security.
• Identification of further need of experimental study to reduce uncertainty of forecasts.

The project was carried out according to the Terms of Reference. Some of the results are described below:

• Analysis of environmental and radiological characteristics of the site definitely showed that they were far from being comprehensive. This is a reflection of a real situation with:
• The data from the early years of site operation that are incomplete and not consistent;
• Insufficient experimental studies performed for exploration of the site characteristics that would be of use in this study;
• And also disturbances from the recently started site rehabilitation program that introduced their contribution to uncertainties of input data.

Basing information on surface contamination at the storage site applied in the study is the g-survey of the site surface carried out with the help of portable radiometer. Measurements were made with a step of 10 m on distance of 1-1,5 m from the surface. This provided the field of exposure dose rate (EDR) that typically varies from 30 mR/h to 3000 mR/h, and at some places even higher than 3000 mR/h. The map of surface contamination by 137Cs and 90Sr were created by recalculation of the EDR field under supposition of the 15 cm locally homogeneously contaminated surface soil layer. The recalculation procedure bases on average 137Cs and 90Sr concentration measured in 7 samples taken from the site. Though this statistics is not sufficient for the very heterogeneously contaminated site it still thought to serve as a first approximation.

Other uncertain parameter is the soil hydraulic conductivity. The range of values for this parameter available now is extremely wide. It should be emphasized that these data are based on different methodology: laboratory sample’s testing, field study of water pumping from observation wells, rate of restoration of created depression zone, etc. No cross-cutting comparison of these results was possible due to short duration of the project and limited information about details of the measurements. After careful discussion of that uncertainty it was recommended to use an expert’s judgement that so called “urbranosem” type of soil is on average similar to the site soil that covered by grass.

In these circumstances the run-off modeling was orientated to a scoping analysis rather than site-specific analysis. The scoping analysis was focused on evaluation of the scale and possible limits of the redistribution and washout phenomenon, thus providing first insight into the seriousness of the situation with run-off transfer and giving recommendation for further experimental studies needed to reduce uncertainties.

Consequently the study, while hopefully scientifically rigorous, should be based more upon consequence analysis and general principles, rather than the very rigorous site specific features.

The choice of run-off scenarios that has been examined within this pilot study was made on the base of analysis of three main factors impacting the outcome of the modeling, namely:

• Precipitation rate;
• Soil properties within the site;
• Quality of the inner fence of the site as an engineer barrier against run-off transfer outside the RW storage site

For the upper limit that characterizes a 100 mm of “heavy rain/downpour” precipitation was taken that responds the meteorological records for Moscow area for the last 37 years. Precipitation of 35mm was taken for a low limit of rain that responds to year average maximum of daily precipitation.

According to the above mentioned approach soil hydraulic conductivity was taken within the interval of 40-150 mm/hour.

The inner fence that currently surrounding the RW storage site is not a perfect watertight barrier: tiny holes within each 2m concrete section of the fence are up to 5-10 mm. Moreover, the factual absence of the fence on the eastern part of the fence could result in formation of water runoffs towards the territory of KI and radionuclides washout from the territory of the waste storage site. It was also decided to simulate the situation of a particular concrete section of the fence removed either due to, for instance being repaired, or the section bed is totally eroded and thus do not obstruct at all the water flow. A preliminary analysis of storm water runoff field on the site and its neighbourhood reveals few sectors of the fence subjected to increased water erosion and, correspondingly, to higher risk to be destroyed or to be repaired more often than other sectors.

These considerations for run-off scenarios were applied for simulations of the run-off erosion. The LISEM model, a physically based hydrological and soil erosion model developed in Utrecht University (Netherlands) in the frame of EU Spartacus Project was applied with small modification responding to the peculiarities of the RRC-KI waste storage site.

Despite of all the limitations that have to be introduced for modeling of potential implication of run-off radioactivity transfer from the RRC-KI radioactive waste site, the analysis indicates that the redistribution of surface contaminants within the site and potential run-off transfer of radioactivity from the site cannot be ignored, because:

• Under current condition of the inner fence around storage site that plays a role of a physical barrier on the way of run-off water and lack of any specific drainage system at the site, the topography of the site does not prevent run-off washout from the site:
• The run-off modeling showed that under unfavorable meteorological condition (period of lengthy drizzling rain followed by a downpour of maximal intensity observed in Moscow) the run-off water could transfer contaminated soil particles outside the perimeter of the storage site and further down to the area used for municipal car parking located between the inner fence of the storage site and adjacent section of the outer fence of RRC-KI, resulting in surface contamination of about dozens of kBq/m2
• The potential redistribution of soil contaminants inside the territory of the storage site (about 100 m2 could have contamination twice as much as before the run-off event). This should be taken into account while planning of site rehabilitation program.

The assessment of dose uptake by critical population groups, following the realization of hypothetical scenarios of run-off from the RRC-KI radioactive waste storage site, shows that natural events, such as average or heavy rain, are unlikely to cause considerable reduction of environmental security, as the calculated dose rates of hypothetical exposure of members of the public, vary from 0.02% up to 20% of annual dose limit, established at a level of 1 mSv /y.

However, the results of runoff scenarios show that radionuclides can be washed off outside the RW site and even reach the city street. This result itself may be a psychological factor for public anxiety, because the radiation background at the local areas adjacent the RW site can be noticeably elevated by the runoff events. These local areas need to be under a systematic dosimetric control.

The study performed indicates that earlier practice to manage the radioactive waste at the nuclear centers in urban environment could result in r/a washout from the limits of the site. Though in this particular case, the run-off natural events, such as average or heavy rain, are unlikely to cause considerable reduction of environmental security, the potential run-off transfer outside the storage site could create a constant and growing concern of inhabitants of the nearby residential area.

It is pointed out that due to time constraints the project did not evaluate the possibility of gradual accumulation of radionuclides due to the repeated wash-off events over long period of time. This point could be of special importance for planning of remediation program, as it is hardly possible and even reasonable to remediate to”zero“level of contamination. Thus, acceptable level of residual contamination that should provide no “substantial” release from the site for long period of time should be examined and defined. It was emphasized that it is strongly advisable to extend run-off studies to evaluation of cumulative, long term consequences of run-off transfer from the site with residual contamination;

Recommendations to reduce uncertainty of the forecast and to evaluate other pathways of radionuclide migration from the radioactive waste storage site to the city areas, namely migration with ground waters, direct re-suspension of dust from site and air transfer by strong wind were made.

As for specific recommendations to reduce potential run-off washout from the RRC-KI radioactive waste storage site, the following points were listed and discussed:

• First of all, the RRC-KI radioactive waste storage site should have a special drainage system designed for interception and control of run-off waters at the site;
• Should the repairing work of the inner fence around the RRC-KI radioactive waste storage site be of need, it is recommended to do that during winter time;
• A number of potential engineering methods of reducing the run-off transfer outside of storage site should be carefully evaluated and choices should be made as to the optimum method or methods of so doing;
• The necessity to use international experience for solving technological problems caused by radioactive contamination.

One of the efforts to cope with this situation is an organization of a "Round Table" activity which stipulates meetings aimed at improved exchange of views and opinions between social groups living nearby the RRC-KI and RRC-KI administration. In addition, it should be recommended that these meetings will include communication with international experts and discussion of the information about the situation and solutions in other countries, where the contamination due to activities of nuclear complexes in urban environment took place. Such comparison could help to identify commonalities and differences in coping with radiation legacy in big cities and work out recommendations for further improvements. A due and deeper attention to these aspects should be recommended.