MOSKVORECHYE ENVIRONMENT RADIOACTIVE CONTAMINATION COMPLEX INVESTIGATION AND ESTIMATION CAUSED BY MEPHI IRT (STANDARD RESEARCH REACTOR)-2000 REACTOR LONG-DURATION USE.

INTRODUCTION

Today in Moscow region there is a long-lived diffuse technogenic radioactive contamination mainly caused by 1986 Chernobyl accident and nuclear weapon tests products. Russian nuclear power industry emission influence on this contamination forming is ignorable.

"Moskvorechye-Saburovo" municipal district (South administrative district of Moscow) characteristic property is extra environment radioactive contamination caused by set of factories. Here we mean standard or emergency factory work environment contamination. We have not considered environment contamination caused by radioactive materials loss or thefts.

MEPhI IRT-2000 reactor (standard research reactor) was started in the end of 1967 placed on Moscow Engineering Physics Institute territory and is the safest in that type nuclear-technical installation. In more than 30 years use there has not been an emergency accompanied with an extra radioactive products environment emission. Nevertheless MEPhI IRT-2000 reactor is formally classified as nuclear-dangerous object and surrounding territories extra radioactive contamination caused by its (reactors`s) long-duration use was able to form.

In region there are some factories (except MEPhI) and their work is able to cause marked environment radioactive contamination. So the conclusion about pollution origin (caused it by IRT-2000 reactor use or other factories) can be made using technogenic radionuclides environment content and distribution detailed information.

1. Sampling objects and measurement technique.

For radionuclides (MEPhI IRT-2000 reactor long-duration use products) Moskvorechye environment surface ecosystems elements ingress and accumulation estimation the following samples selection on above-mentioned territory were executed: surface ground layer with depth up to 2 cm, surface ground layer with vegetation rest in (grass root, moss) and fallen leaves and branches (if they were) with depth up to 2 cm, layer-by-layer ground samples with depth up to 30 cm (one layer depth is between 1 and 3 cm).

For estimation of atmospheric radionuclides receipt influence on studied territory litter contamination snow cover and annual grass vegetation samples selection was executed.

Planning and sampling operative correction with regard to measurement results were executed using "Moskvorechye" GIS developed in our Laboratory. Ground and vegetation sampling was executed after complete snow cover melting. To increase sampling sensitivity sample collection was executed in natural concentrators (if it was possible) such as hollow, narrow gully etc. Other territory sampling frequency was more rare and sampling places choice was executed in much the same way.

Similar environment objects samples were collected at 50 Moscow and vicinity auditorial locations placed far enough from IRT-2000 reactor, that is off its influence zone. The same sampling places choice techniques and sampling itself were used. These samples analysis technique was the same and the same radionuclide set content was measured as the samples chosen at Moskvorechye territory.

In this research for studied region environment objects technogenic and natural gamma-radiation radionuclides content information receipt HPGe low-background gamma-spectrometry technique was used. It was necessary to measure more than 400 samples technogenic ¹³⁷Cs, ¹³⁴Cs, ⁶⁰Co, ⁵⁴Mn and other radionuclides specific activity at a level of ~0.05-0.1Bk/(sample kg) with this sample natural ²²⁶Ra and ²³²Th radionuclide activity at a level of 10-40 Bk/kg and ⁴⁰K at a level of 100-600 Bk/kg.

Snow sample ³T content measurement was executed using liquid scintillation spectrometry.

Auditorial sampling points in Moscow and vicinity.	Sampling points in Moskvorechye district.

2. Research results.

2.1. Average radionuclide content.

Given below (table and picture) are average (among measured samples) radionuclide content values:

2.2. Natural radionuclides.

Natural radionuclides (⁷Be, ⁴⁰K, ²²⁶Ra, ²³²Th, ²³⁸U) content given in the table above conforms to standard surface ground layers radionuclide content. There is a major radionuclide concentration spread caused by organic material heterogeneity and structural and other ground rubbish.

Presented results application points to the absence of statistically significant differences between Moskvorechye and auditorial locations. ⁷Be concentrations differences is caused by sample organic material content distinction.

Average total activity of natural radionuclide in soil is more than 500 Bk/kg.

2.3. Technogenic radionuclides.

¹³⁷Cs, ¹³⁴Cs and ³H technogenic radionuclides are detected in statistically significant quantity in Moskvorechye environment samples.

Moskvorechye territory surface ground layer ¹³⁷Cs and ¹³⁴Cs specific activity average values are 7.5 Bk/kg and 0.08 Bk/kg accordingly. From these values comparison with natural radionuclides average specific activity (500 Bk/kg) and structural materials (370 Bk/kg) or food stuffs (100 Bk/kg and more) ¹³⁷Cs concentration (allowable by sanitary standards) follow that such ignorable values can`t influence potent on studied territory radioactive situation.

From 7.5 Bk/kg value 4.1 Bk/kg are caused by Chernobyl accident, the rested 3.4 Bk/kg – by nuclear weapon tests global fall, MEPhI reactor and other factories placed on the studied territory and worked with radioactive materials use.

¹³⁷Cs ground average activity supply is estimated by 0.05 Ki/km² value.

There are no significant Cs isotopes spatial distribution macro-heterogeneity. ³⁷Cs soil content key factor is relief.

2.3. GIS-technologies in environment radioactivity research outlook.

As the presented work practice implies, region radiation-ecological situation investigation effectiveness can be significantly increased by GIS-technologies use. The GIS key advantage is not only that they allow received during research data to accumulate and display, but also and mainly different information layers comparison and mutual analysis possibility.

Evidently that if different ecological data are pooled to GIS project, it is possible to receive quickly and effectively general ecological criteria for territory in question.

CONCLUSION.

The research executed main results are the following.

1. Environment gamma-radiation radionuclides and T content measurement precious technique based on HPGe low-background gamma and liquid scintillation spectrometry was developed.
2. GIS-technologies technique for environment radioactive contamination research and investigation results analysis and representation was designed.
3. Natural and technogenic radionuclides content research for Moskvorechye district and for distanced from MEPhI IRT-2000 reactor locations was executed.
4. Moskvorechye environment radioactive contamination MEPhI IRT-2000 reactor influence was estimated. It is shown that environment radioactive contamination caused by long-duration reactor use is ignorable as compared with natural radionuclides content and contamination caused by Chernobyl accident fallout.
5. GIS project "Moskvorechye" was designed. The use of this project allows to analyse environment characteristics together with other spatial data on the early stage of research. This GIS was based on digital map of Moscow developed by "Geocentre-GIS" company.
6. Recommendations were developed for techniques worked-out and results received usage during Moscow region ecological monitoring organizing and carrying out.

Click picture to enlarge...

¹³⁷Cs distribution
(29 Kb)

¹³⁷Cs distribution comparing with average (20 Kb)

¹³⁴Cs distribution
(32 Kb)

⁴⁰K distribution
(29 Kb)

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