Journal of Environmental Radioactivity 101 (2010) 1013e1023
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Decommissioning a phosphoric acid production plant: a radiological protection case study V. Stamatis a,1, S. Seferlis a, V. Kamenopoulou a, *, C. Potiriadis a, V. Koukouliou a, K. Kehagia a, C. Dagli b, S. Georgiadis c, L. Camarinopoulos a, 2 a b c
Greek Atomic Energy Commission (GAEC), P.O. Box 60092, 15310 Ag. Paraskevi, Greece Protypos Company, Geraniou 30, 105 52 Athens, Greece Environmental Protection Engineering S.A., Dervenakion 24, 185 45 Piraeus, Greece
a r t i c l e i n f o
a b s t r a c t
Article history: Received 11 December 2009 Received in revised form 26 April 2010 Accepted 15 July 2010 Available online 1 September 2010
During a preliminary survey at the area of an abandoned fertilizer plant, increased levels of radioactivity were measured at places, buildings, constructions and materials. The extent of the contamination was determined and the affected areas were characterized as controlled areas. After the quantitative and qualitative determination of the contaminated materials, the decontamination was planned and performed step by step: the contaminated materials were categorized according to their physical characteristics (scrap metals, plastic pipes, scales and residues, building materials, etc) and according to their level of radioactivity. Depending on the material type, different decontamination and disposal options were proposed; the most appropriate technique was chosen taking into account apart from technical issues, the legal framework, radiation protection issues, the opinion of the local authorities involved as well as the owner’s wish. After taking away the biggest amount of the contaminated materials, an iterative process consisting of surveys and decontamination actions was performed in order to remove the residual traces of contamination from the area. During the final survey, no residual surface contamination was detected; some sparsely distributed low level contaminated materials deeply immersed into the soil were found and removed. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: NORM Phosphoric acid Phosphogypsum Decommissioning Radiation protection Radioactivity
1. Introduction In August 2001, the Greek Atomic Energy Commission (GAEC), the national authority for radiation protection, was informed about the activation of the portal radioactivity detectors installed at the entrance of a metallurgic site, when a scrap metals load entered the plant. This load originated from the dismantling of the phosphate fertilizer plant of Drapetsona (west of the port of Piraeus) and contained metallic objects contaminated with 226Ra. Since, the equivalent dose rate measured in contact with these objects was in the order of 40 mSv/h, the metals were isolated and their use was prohibited.
* Corresponding author. Tel.: þ30 210 6506731; fax: þ30 210 6506748. E-mail address:
[email protected] (V. Kamenopoulou). 1 Present address: Technical Support Unit for Solid Waste and Wastewater Projects, Hellenic Ministry for the Environment, Energy and Climate Change, Iteas 2 and Evritanias, 115 23 Athens, Greece. 2 Present address: Department of Industrial Management, University of Piraeus, 80 Karaoli and Dimitriou str, 18534 Piraeus, Greece. 0265-931X/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvrad.2010.07.002
Following the standard procedure, the owner of the fertilizer industry was informed and an on-site inspection took place where structures and sites with high levels of radioisotopes 238U and 226Ra were localized. These areas were delimited, set under surveillance and any further activity (e.g. dismantling) was temporarily postponed. Radiation surveys and collection of samples for laboratory analysis were performed in order to characterize the area from the radiological point of view. Moreover, the most contaminated sites, objects and materials were identified and localized. The Protypos Company, a subsidiary of the National Bank of Greece assigned to GAEC the responsibility to act as its radiation protection advisor, to perform the radiological survey and the radiological management of the site and to provide all necessary measures to clear this region from the radiological point of view. The owner’s wish was that the area be released from any radioactive regulatory control; the site of the phosphate fertilizer industry should be sufficiently decontaminated so that it could be completely released from the radiological point of view and the area “returned to normality”.
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In this context, GAEC’s scope of responsibilities included: preliminary radiological survey of the area; in situ surveys and laboratory measurements for the determination of the natural radioisotope concentrations; evaluation of the technical capability of the companies bidding for clean-up of the site; quantification e radiological categorization of the materials; evaluation and approval (from the radiological point of view) of the techniques and procedures proposed by the private company undertaking the decontamination, clearance, disposal and transportation of the structures and materials. In addition, GAEC undertook the workers radiation protection program and the radiological supervision of the field work. Protypos Company allocated the site decommissioning and decontamination to the private company Environmental Protection Engineering S.A. (EPE). Phosphoric acid production is one of the industries dealing with large amounts of Naturally Occurring Radioactive Materials (NORM) in the ore and waste. This paper aims to describe the experience gained and the lessons learned during this work. 2. Description of the site and the project 2.1. Urban development of the costal zone of DrapetsonaeKeratsini The wide area to the west of the port of Piraeus had been since the 19th century and during an extended part of the 20th, a site where many heavy industries were located, especially ship building and repairing and other installations connected more or less with the sea. In addition to these polluting activities, the presence in this area of the central sewage installations of the whole Athens basin aggravate the environmental conditions of the area. The pressure of the rapidly growing population of the neighboring municipalities and the gradual decline of the industrial sector that has left behind a number of empty old half-ruined buildings, together with the latest efforts to reduce the important pollution of the Athens basin, have pushed towards new forms of urban development. The idea is to improve the infrastructure of the port of Piraeus and develop it into a peripheral maritime and multifunctional centre, the most important of the eastern Mediterranean. Simultaneously a strategically planned large-scale development of the wider area would mark a new urban reality. The large coastal area of Drapetsona and Keratsini could provide the necessary dimension required for a project of urban development with strategic importance and beneficial long term effects on the economy, the employment opportunities and the environmental conditions at local, regional and national scale. This is why a development plan for a site of approximately 640 ha is being promoted in this general area by a group consisting, besides the PROTYPOS proprietor, of the cement company AGET, BP e MOBIL and the Port Authority. The main objectives of the development plant are: re-establish the environmental balance that has been seriously injured from previous industrial activities and create helpful conditions for urban regeneration; open the now closed seafront to the inhabitants of the surrounding municipalities for social, cultural, recreational and sports activities; exhibit the maritime tradition of the Greeks (and especially the Athenians) through history and in particular the influence of the Asia Minor refugees on the economic development using several restored former industrial buildings for this purpose;
improve the efficiency of the shipping services of Piraeus in the eastern Mediterranean sea at an international scale and create employment opportunities in the wider area; combine the existing conditions with the proposed uses in order to create a viable coexistence and avoid competitive situations; acceptance of the development plan by the local authorities and population. The general design will improve the sectors of enterprise and commerce, maritime culture, education and research, new technologies, history and recreation and of course housing. The development data of the plan are presented in Table 1. 2.2. Contaminated sites The fertilizer industry in the region of Drapetsona occupies an area of 2000 m2. Within this specific area, the sites and structures with high levels of radioactivity were (Fig. 1): the phosphoric acid production unit (a three-level construction with basement); the phosphogypsum inventory and the temporary disposal area; the phosphoric acid tanks (named I, II and III). Cutting into pieces Tank I and transferring parts to the metallurgic industry had alarmed the radioactivity detectors. The tank II, the biggest one, was laying in an area distant to the phosphoric acid production unit; the phosphate storehouse; the phosphate treatment and smash/compression unit; the underground waste water transfer channel (pipe); the waste water treatment plant.
2.3. Project structure From the organizational point of view, the project included (GAEC Internal Report No1, 2007): preparation studies; staff training; detach/disassembly/dismantlement/cutting/decontamination of objects; reuse/recycling/disposal of materials; shipment of contaminated materials; demolitions; settlement; laboratory and in situ measurements; radiological survey. The programme was structured in four phases. The work programme of each phase is presented in Table 2. 3. Basic principles and legislation The Radiation Protection Regulations (Joint Ministerial Order 1014 (FOR) 94, 2001) is the national legislation that implements the IAEA Basic Safety Standards (Safety Series No115, IAEA,1996) and Table 1 Development project figures. Total land surface Total built surface Total public-use built surface Common-use land
640 000 m2 388 650 m2 55 000e65 000 m2 300 000 m2 (46%)
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Fig. 1. The phosphoric acid production unit.
the European Directive (Council Directive 96/29/EURATOM, 1996) and gives provisions for the radiation protection of the workers, the public and the environment. This legislation and the relevant EC documents (EC Publications RP 122, 2001; EC Publications RP 89, 1998; EC Publications RP 107, 1999) constituted the legislative basis of this project. In the European Union in the field of NORM, there is no binding legislation covering all aspects dealing with the issue. Particularly, matters like exemption and clearance levels, as well as area release criteria are not treated homogeneously. The same lack is reflected in the national legislations of some Member States, and this is the case with Greece too. In this specific case, taking into consideration the owner’s wish to bring the area at the level of natural background, as well as some additional requirements imposed by the local authorities and the population, the release criteria applied were stricter than the clearance levels proposed by the European Commission, based on specific dose limits. The basis used for the NORM disposal was the EC Radiation Protection 122 Document (EC Publications RP 122, 2001), according to which: as a result of the large volumes of material processed and released by NORM industries, the concept of exemption and clearance merge, and it is appropriate to lay down a single set of levels both for exemption and clearance; while the basic concept and criteria for exemption-clearance for work activities are very similar to those for practices, it is not meaningful to define the levels on the basis of the individual dose criterion for practices (10 mSv/y); instead a dose
increment, in addition to background exposure from natural radiation sources, of the order of 300 mSv/y is appropriate; the management and production of large volume materials with NORM lead to the need to specify limits for the possession, use and disposal of these materials; the basic assumption of this calculation is the prerequisite that the additional dose to the population due to the disposal of these materials shall not exceed 300 mSv/y. For the specific case of 226Ra, this resulted to a concentration of 500 Bq/kg (EC Publications RP 122, 2001). In cases where generic clearance levels were applied, these were specified according to the following criteria: the optimization principle is the basis for the design of the radiation protection program, without ignoring the economic factor; the maximum equivalent dose to the population due to this practice should be less than 10 mSv/y. Based on the above and in particular for phosphogypsum usage as soil conditioner, GAEC has established a concentration limit for 226 Ra equal to 400 Bq/kg (GAEC’s Decision 414/875/2001, 2001). For the scrap metals, the criteria used for their recycling, with no further restrictions, were based on the EC recommended radiological protection criteria for the recycling of metals from the dismantling of nuclear installations (EC Publications RP 89, 1998). Further considerations, like the additional cost or the demand of the scrap metal recycling industries for radioactivity-free material, were not neglected either.
Table 2 Project phases. Preliminary phase (10/2003)
Phase A (10/2003e02/2004)
Phase B (03e04/2004)
Phase C (05e10/2004)
Sampling, measurements and materials categorization. Preparatory studies. Staff training.
Construction of the decontamination site and radiological control. Object categorization according to their level of contamination. Detachment/disassembly/dismantlement/cutting of objects/equipment. Decontamination of pipes/tubes with the knock method. Jackhammer application to the reactor and tanks. Sandblasting of the reactor and tanks. Sandblasting of metallic objects. Shipment of contaminated metals and sandblasting residues to a special foundry. Shipment of material similar to phosphogypsum to a special plant.
Sandblasting of the recirculation reservoir. Sandblasting of the elastic tubes of phosphoric acid transfer. Final radiological survey of the building before its demolition.
Demolition of the recirculation reservoir and reactor. Demolition of the building. Separation of debris and iron bars. Site and area settlement. Final radiological survey of the area.
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4. Materials and methods 4.1. Radiation measurement equipment All radiological surveys, materials characterization and categorization, and the monitoring of the decontamination and restoration works were based on in situ and laboratory measurements. The in situ radiological measurements and controls were performed using the following equipment:
portable gamma spectrometry unit (HPGe 20%, Canberra Inspector); portable gamma spectrometry unit (NaI, Exploranium); surface contamination monitor (Contamat, ESM) ; portable gamma-radiation survey instruments (ESM, Victoreen); portable large volume NaI detector (200 x200 , ESM).
For the final radiological survey the GAEC mobile laboratory (specially modified vehicle) was additionally used, including: portable gamma spectrometry unit (HPGe 30%, Canberra Inspector); plastic detector (Thermo ESM), with portable PC (MOBISYS software). The laboratory measurements (Technical Report Series No295, IAEA, 1989; EML Procedures Manual, US DoE, 1997; NCRP Report No 58, 1978) were performed using the following equipment/systems: Two gamma spectrometry units HPGe 70% and 50% (Canberra) with a computerized 8192-channel analyzer in a total spectrum area of 2870 keV. Phosphogypsum and soil samples were measured in a polyethylene beaker of 260 ml volume. The minimum detection activity (MDA) of the measurement is determined with a confidence level of 95%. Indicative values for the MDAs of the most important radioisotopes for a 15 h measurement are: 40 Bq/kg for 226 Ra (weighted mean of 214Pb (351.93 keV) and 214Bi (609.31 keV, 1120.29 keV)), 20 Bq/kg for 238U (weighted mean of 234Th (63.28 keV, 92.37 keV) and 234mPa (1001.3 keV)) and 10 Bq/kg for 232 Th (weighted mean of 228 Ra and 228Th. 228Ra is in equilibrium with 228Ac (911.2 keV) and 228Th is calculated as the weighted mean of 212Pb (238.63 keV), 208Tl (583.91 keV) and 212 Bi (727.33 keV)). The efficiency was determined by a standard multi-isotopic source having the same geometry and density as the measured samples. Fully automated and integrated alpha spectrometry system (alpha-analyst Canberra) consisting of 12 passivated implanted planar silicon detectors with a 600 mm2 active area. A whole-body counter (shadow shield, Acuscan, Canberra).
4.2. The dismantling working program and decontamination techniques The objectives of the decommissioning were the dismantling of objects and structures, the decontamination of the contaminated materials and the management of the resulting material. The dismantling working program consisted of the following steps: initial localization (through surveys and in situ measurements) of the most contaminated objects and sites; in situ detailed measurements and laboratory analysis of samples, for the characterization and categorization of the materials; detachment/disassembly/dismantlement/cutting/removal of the objects and structures; in situ decontamination and removal of the waste; verification control and cross-check of the consecutive most contaminated objects/sites. In general, different decontamination techniques and management procedures were applied, having always in mind the assessment (minimization) of the environmental impact and the minimization of the waste produced. The radiation protection measures applied are discussed in Section 9. The most appropriate decontamination method was selected according to its effectiveness, the possibility to minimize the waste produced and the impact to workers and the environment. The economic factor was a parameter not neglected either. In order to define the most appropriate method for waste management, we took into account the legal framework, the additional demands imposed by the owner and the additional requirements of the local authorities involved. Before being treated or disposed, the contaminated materials were categorized according to their origin (scrap metals, elastic pipes, scales and residues, building materials etc) and the level of contamination. Four techniques were used, for the decontamination of the materials namely: vacuum systems, knock, jackhammers and sandblast. The minimization of the amount of waste, not inducing secondary waste, was a point of consideration. The vacuum cleaner (system), knocking and jackhammers
methods don’t increase the waste mass, contrary to the sandblast method which produces a mix (sandblast residues) of the waste (pollutants) and the sandblast material used for the blasting (slag). The site where the decontamination equipment was installed was the former area of the phosphoric acid storage tank II (Fig. 1). Initially, a small part of the tank was cut out and used as entrance. The decontamination of the tank was easily performed, since the scales were few and their activity low. To reduce the amount of dispersed pollutants (dust) and for environmental protection, the entrance of the tank was covered with a transparent plastic cover; this method, in addition provided sunlight to the workers and facilitated the observation. The latter technique was also used for the remaining contaminated tanks and reservoirs, which after removal of the internal material, were treated with the jackhammers. If this method proved not sufficient, sandblasting (a more aggressive method) was additionally applied. 4.2.1. Vacuum systems The vacuum cleaner is a special vehicle equipped with a vacuum and piping system. With this system the scattered materials were detached, transported and collected, via the piping into large bags. The vacuum cleaner was the method applied first for the collection of the scattered material from the surface and objects of the building (phosphoric acid production unit). In some cases it was not easy to detach the waste, since it was solidified and manual intervention (scratching) was needed for its detachment. 4.2.2. Knocking The contaminated objects (pipes and metallic parts), after being dismantled and cut into pieces, were transported for initial decontamination through knocking (use of hammers). If this method was not sufficient, sandblasting was additionally applied. The jackhammers method was not applicable to pipes and metallic parts, because of the structure and the shape of these objects. 4.2.3. Jackhammers Jackhammers with three pistons and adapted handles were used. After manually removing the internal material and knocking the inner surface of the tanks and reservoirs, the dose rate on the surface continued to be higher than the natural background, because the inner surface of these constructions was full of deposits. Jackhammer (percussion/friction), a more intense method, was then used to complete the decontamination of the interior of the tanks. When using jackhammers, the fragments particles of the detached material were considerably thick; this fact is considered as an advantage, since it reduces the negative impacts (dissemination of the dispersed pollutants) to the environment and workers. The application of the jackhammers method had unsatisfactory results when applied to the recirculation reservoir, reactor and maturation tanks, since the residual dose rate was relatively high (1 mSv/h). From the in situ and laboratory measurements, performed before and after the application of the method (samples from the inner surfaces and bricks of the tanks and reservoirs), it was concluded that the origin of the residual contamination was the saturation of the brick’s surface. Consequently, a more “aggressive” method (like sandblasting) was needed. The jackhammer method was not appropriate for the phosphoric acid transfer tubes because of their small diameter, and for the metallic structures of the sieves and the frames of the filter; the sandblast method proved to be more efficient in these cases. 4.2.4. Sandblast For the sandblast, slag (ferronickel, with main constituents Fe, Si and Ni) was used and the sandblast residues (slag and detached pollutants) could be treated as contaminated steel and recycled in a special foundry. Gathering and processing the data revealed that a 1 m2 contaminated surface needed about 1e2 kg of slag and 20e40 s blasting time to be satisfactorily decontaminated, depending also on its shape (tube, plane surface etc) and on the required level of “remaining contamination”.
5. Material classification 5.1. Scrap metals To be in compliance with the legislative provisions mentioned before, the dose criterion for metals recycling was converted to specific activity through dosimetric models (GAEC Sub/01/325929/2004, GAEC, 2004; Clouvas et al., 1998). The scenarios took into account the entire sequence of scrap processing, starting with transport and handling of the scrap metal up to exposure from consumer goods made of recycled metal. The different steps in the metal processing have been considered in the greatest possible detail. The exposed population consists essentially of workers employed in the scrap yard, smelter or
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refinery, or manufacturing industry. Workers were supposed to be exposed to external radiation coming from the scrap heap, the disposal of the slag and of the dust to a landfill. Inhalation of suspended dust upon handling and cutting of the scrap or of the fumes in the foundry was another source of exposure. Secondary ingestion through hand contamination and external beta ray exposure of the skin were taken into consideration too. Members of the public might be exposed to external radiation from gamma emitting radioisotopes retained in the final product. The above scenario resulted to the assumption that if the specific activity of 226Ra was less than 300 Bq/kg, the object could be used for recycling (GAEC Sub/01/325929/2004, GAEC, 2004; Clouvas et al., 1998). Greek steel factories apply a system of certification and control in the entrance through portal detectors. The threshold of these systems is defined to be three standard deviations of the background value (3s bgr). In this context the decontamination procedure of the metallic devises for recycling continued until the gamma dose rate reached this value. In case that the decontamination applied was not efficient enough, the scrap metals were exported for recycling to a foreign country with the appropriate infrastructure. The criteria used for their export were imposed by the recycling company, the national legislations of the countries concerned and the international legislation. Stainless steel objects were the most contaminated metals because of their direct contact with the raw material and product; for the majority of them the use of the sandblasting method was required. In many cases, the decontamination efficiency was not satisfactory, because of the objects shape or the infiltration of pollutants into the objects mass. The above unsatisfactory decontaminated materials were exported for recycling to a melting plant for contaminated scrap. The high-concentration phosphates (50e100 kBq/kg 226Ra), coming from the contaminated surfaces, were detached with the sandblasting method, producing sandblast residues (slag and detached pollutants). This material (which was considered as “metal with small weight content NORM”) was exported for recycling to a melting plant as contaminated scrap. 5.2. Phosphogypsum The raw material for the phosphoric acid production is the phosphate ore in the form of calcium phosphate and apatite. During
Dirt Mud
Homogenization, sampling and analysis of each material. Material management according to their chemical and radiological properties.
Scales
Metals
the so-called “wet process”, phosphoric acid is produced from phosphate ore by reaction with sulphuric acid which also results in the production of a by product, the phosphogypsum. About 3 tn of phosphogypsum are produced for every tn of phosphoric acid (Burnett et al., 1996) according to:
It is known that during the wet process of phosphate rock for the phosphoric acid production, the majority (more than 80%) of uranium and thorium present in rocks go to in the phosphoric acid itself, while 226Ra, 210Po and 210 Pb follow to more than 80% the phosphogypsum, as a consequence of the similar chemical behaviour of Ra and Ca. The concentrations of these radioisotopes in the phosphoric acid and in the phosphogypsum have been determined or estimated and are referred in several studies (Guimond and Hardin, 1989; Perianez and Garcia-Leon, 1993; Poole et al., 1995; Bolivar et al., 2000; Lardinoye and Weterings, 1982). During normal operation, the phosphoric acid production plant was cleaned once a week; however, during the last months of its operation the plant was not systematically and properly cleaned. The scattered materials on the site and its surroundings, the internal material of the tanks and reservoirs, the internal material of the tubes and the material of the waste water channel, were temporarily placed in piles, and after the physicochemical and radiological characterization, were categorized in the following three categories: - Phosphogypsum (calcium sulphate 500e2500 Bq/kg 226Ra) and low concentration phosphates (400e1000 Bq/kg 226Ra). The material (slurry) of reservoirs, tanks, channel, tubes (pulp transfer). The main amount of the scattered material of various sites of the production plant. - Phosphate ore (phosphorite 1e2 kBq/kg 226Ra and 1000e1500 Bq/kg 238U). The phosphate ore which remained in the plant. - High-concentration phosphates (50e100 kBq/kg 226Ra). The scales of inner surfaces of the elastic tubes (phosphoric acid transfer) and the scales of inner surfaces of the tanks and reservoirs (after the removal of the slurry/internal material), which they constituted the most contaminated material.
Grouping of materials with similar chemical properties
Reuse ≥500Bq/kg => Disposal/Deposition
> 500Bq/kg => Suitable packing and transfer to special landfill
< 3 (bgr)=> Foundry Initial 1 Main 2 Cleaning > 3 (bgr) => Suitable packing and transfer to special foundry Cleaning
Debris Plastics Woods
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< 3 (bgr) => Disposal/Deposition Initial 1 Main Cleaning 2 > 3 (bgr) => Suitable packing and transfer to special landfill Cleaning
Others
1: Measurement in situ with survey meter 2: Measurement in laboratory with HPGe
Fig. 2. Integrated materials management and decontamination scheme according to their radiological and chemical characteristics.
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Table 3 Results from gamma spectrometry measurements in samples collected during the preliminary phase of the project (minimum and maximum values). Samples
Dose rate in contact (mSv/h)
Depositions from phosphoric acid tank I Depositions from phosphoric acid tank III Phosphogypsum temporary disposal area Depositions on filter Depositions from the basement floor of the phosphoric acid production unit Surface scale from the phosphoric acid transfer tubes Depositions and scale from the phosphoric acid stir reservoir from the waste water treatment plant Sludge from the phosphoric acid recirculation reservoir Samples from the overflow of phosphoric acid tank III
3e40 2e10 0.2e2 0.45e65 0.38e60
226
Ra (Bq/kg)
2000e13 000 560e2800 550e2500 1000e6500 800e1500
U (Bq/kg)
235
U (Bq/kg)
228
Th (Bq/kg)
228
Ra (Bq/kg)
280e420 270e440 240e400 220e300 600e920
10e20 10e20 10e20 10e15 30e45
65e440 15e100 30e70 30e150 50e75
75e480 15e130 30e80 30e160 55e70
400e500
220e900
10e45
20e45
15e50
20 000e100 000
50e200
