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17 Industrial Nuclear Explosion Sites in the Russian Federation: Recovery and Institutional Monitoring Problems V. V. Kasatkin, Ye. N. Kamnev, and V. A. Ilyichev, Russian Federal Atomic Energy Agency (Rosatom), All-Russian Research, Design, and Surveying Institute of Production Technology CLASSIFICATION OF INDUSTRIAL NUCLEAR EXPLOSION SITES CONTAMINATED WITH RADIONUCLIDES This paper presents a classification of industrial nuclear explosion sites contaminated with radionuclides and covers problems associated with site de- contamination and radiation monitoring. There were 81 underground nuclear explosions in the Russian Federation from March 1965 to September 1988. A number of these explosion sites are contaminated with radionuclides as a result of the explosions themselves, the boring of holes leading to the explosion zones, or subsequent technogenic and natural processes. The scope of the problems involved in recovery at such sites and their monitoring will depend on contamina- tion type and current site status. In terms of radionuclide contamination genesis, nuclear explosion sites may be classified as follows: 1. Sites where there was a planned release of technogenic radionuclides (including alpha-emitters) to the earthâs surface during discharge-oriented explo- sions (the Taiga site) and bucklings (the Kristall site), resulting in the generation of radioactive buildup and a fallout trace. 2. Sites where explosions took an unplanned turn, resulting in the release 116
INDUSTRIAL NUCLEAR EXPLOSION SITES 117 of radionuclides that formed a fallout trace, such as occurred following the two botched explosions Kraton-3 and Globus-1. The radiation consequences of these explosions were determined by the channels by which the blast products reached the surface, the time it took for this to occur, and the gas content in the rock at the point where the nuclear device was placed. At the Kraton-3 site, explo- sion products began erupting through the loading-hole shaft 5 seconds after the explosion and lasted for about 10 minutes. During this explosion in the carbon- ate reservoir rock, in addition to fission fragment radionuclides, alpha-emitters were also discharged, yielding a fallout trace (based on a commitment dose of 5 mSv) reaching about 30 km in length. At the Globus-1 site, radionuclides be- gan to be discharged 17 minutes after the explosion. Because of the high fume characteristics of the rock (limestone), site contamination with fission-fragment radionuclides along the trace did not exceed several hundred meters despite the long duration of gaseous product (carbon dioxide) outflow (more than 10 days). Radionuclides were discharged through the casing space of the loading hole as a gas-water gryphon, which partially cleansed the gas of nonvolatile radionuclides. A pressure-induced gas eruption from the explosion zone also occurred at the Globus-3 site. In the latter case, the gas eruption began about 12 minutes after the explosion and lasted for 7 hours. This time, the gas flow rate and site contamina- tion level were considerably lower than at the Globus-1 site, since the Globus-3 nuclear device had been placed in clay rock with sandstone layers. 3. Sites contaminated as a result of hole boring in the central explosion zone, particularly in connection with loading-hole recovery. Recovery of load- ing holes in rock salt resulted in the controlled emission of various forms of tritium and inert radioactive gases, which did not lead to any long-term site contamination. The boring of holes in a water-bearing horizon leading to the central explosion zone resulted in contamination of the immediate site grounds with cesium-137, strontium-90, and tritium entrained in drilling fluid and sludge, as well as stratal water extraction from the explosion zone during hydrodynamic survey works. This was the case with the Globus-1, Globus-2, Kama-1, and Kama-2 sites. At the Kama-1 site, the primary cause of site contamination was the unplanned discharge of carbon dioxide and radioactive water from the load- ing hole during its recovery. The contaminated zone exceeded 30,000 m2 in area. It should be noted that the cesium-137 and strontium-90 contamination of the Globus-1 site was mainly caused by hole boring in the explosion zone. 4. Sites where technogenic radionuclides were released to the earthâs sur- face and distributed in the soil as a result of violations of technical procedures. The most typical example in this category is the Grifon site. At this site, a product (crude oil) was extracted from the explosion zone along with radioactive water, which after being separated from the oil was used for repressuring. Leakages in the injection wellheads resulted in the contamination of dozens of wellhead zones with cesium-137, strontium-90, and tritium, while accidental pipe ruptures contaminated areas beyond the immediate drilling sites.
118 CLEANING UP SITES CONTAMINATED WITH RADIOACTIVE MATERIALS 5. Sites where technogenic radionuclides were discharged to the earthâs surface due to natural processes. This situation is most typically observed at a number of reservoirs formed in rock salt by nuclear explosions at the Vega site, but it may also be found at many other sites. Such reservoirs tend to decrease gradually in volume. This process leads to radioactive brine extrusion, corrosion failure of wellhead valve threaded connections, and the release of brine on the surface around the wellheads. In addition, brine escape and equipment contami- nation may result when accumulated water is pumped out of such reservoirs or when borehole cavities are repaired or liquidated. The above classification is somewhat simplified, as radioactive contamina- tion may be caused by various factors; however, it offers a basis for systematic application of site recovery methods. DEACTIVATION OF CONTAMINATED TERRITORIES Covering a site with clean soil is the simplest deactivation method. This technology has been implemented at relatively small remote sites (Globus-3 and, to a certain extent, Globus-2). At the Kama-1, Kama-2, and Grifon sites, a layer of contaminated soil was removed with bulldozers, loaded into trenches or piles, and isolated with a layer of clean soil. However, it is impossible to restore natural background radiation levels simply by removing soil with heavy equipment. Therefore, after the soil was removed, a layer of clean soil was scattered over the site. Site deactivation work has been under way for several years at the Grifon site, with the radioac- tive soil being buried in a specially designed subsurface container constructed in compliance with existing rules and regulations. At the Kama-2 site, soil and equipment are collected in subsurface containers arranged as trenches in a thick clay layer above groundwater level. At the Kama-1 site, in view of the high groundwater level, more than 3,000 m3 of radioactive soil has been collected in a pile, the âphysicalâ protection of which is provided by a clean soil layer 5-20 cm thick and a concrete barrier. As yet, no decision has been made on the future fate of this repository. The Globus-1 site is the most problematic. It includes contaminated soil areas, subsurface repositories of radioactive soil and fine particulate materials in sand, and subsurface soil areas up to 3 m thick that contain radionuclides and are covered with a sand layer 5-100 cm thick. The site is located on a riverbank and may be affected by spring floods. This may flood the wellhead zone, possibly washing surface sand out into the river. A site recovery project that has been developed, including onsite containment of radioactive products, is not being implemented due to lack of funding (the calculated budget exceeds 36 million rubles in 2002 prices).
INDUSTRIAL NUCLEAR EXPLOSION SITES 119 The Kraton-3 site includes a well-equipped repository for contaminated soil and equipment that has been in existence for more than 27 years. Currently, it is being renovated in accordance with an approved project. The radioactive trace area is a woodland with uneven terrain marked by granite outcrops. Recently, because of a number of technical and financial issues, the idea of decontaminat- ing the trace was dropped. Radiation warning signs are currently being installed along the boundary of the radioactive trace area (0.5 Ã 2.5 km in area). The same decision was made regarding the Taiga site, where, apart from warning signs around the perimeter, plans call for cutting trails into the forest and installing additional warning signs at various distances up to 1.2 km from the site. At the Kristall site, the radioactive trace area and piles were covered with a thick layer of rock refuse from the diamond quarry in 1992 and again in 2006. Beyond the bounds of the site, there may be points of soil contamination with gamma-radiation dose levels only slightly exceeding natural background level. MONITORING ISSUES Because of the presence of contaminated areas and radioactive soil reposi- tories, procedures must be established for monitoring all of the industrial nuclear explosion sites, including those where there are currently no signs that any ra- dionuclides have been released. At most of the sites, the radiation situation may be characterized as consistent with natural radiation background levels, which can vary widely. However, the possibility of future radionuclide releases cannot be completely ruled out if well-casing column corrosion and cement degradation occur near water pressure horizons in the explosion zone or beneath the explo- sion cavity. As yet, there is no officially established uniform system of radiation moni- toring. Most of the sites in operation have monitoring systems supported by the radiation safety services of the respective facility operators. As for the other sites, radiation monitoring is being mainly provided by the Nuclear Safety Laboratory of Rosatomâs All-Russian Research, Design, and Surveying Institute of Produc- tion Technology. Contaminated sites are monitored periodically, while other sites are checked on a case-by-case basis. The scope of radiation monitoring depends on the site status and as a rule includes the following: â¢ Visual survey of changes in site surface topography, including the pres- ence of possible soil subsidence over the explosion cavity and newly apparent water sources (springs, brooks, discharges from loading and other nearby holes, and so forth); â¢ Survey of gamma-radiation dose rate, automatically mapped and linked with site coordinates
120 CLEANING UP SITES CONTAMINATED WITH RADIOACTIVE MATERIALS â¢ Analysis of gamma-radiation dose rate dynamics â¢ Flux density measurement of beta- and alpha-particles in locations where the gamma-radiation dose rate is increasing â¢ In-field gamma-ray spectrometry of contaminated areas â¢ Sampling of soil, water, vegetation, fungi, and so forth, and their analy- sis for tritium, strontium-90, and cesium-137 content Monitoring types and schedules are set on a project-by-project basis.