EPJ Web of Conferences 56, 05005 (2013)

Considering the EU statements, Romania is engaged to endorse in the near future the IAEA relevant publications on geological repository (CNCAN a ), to update the Medium and Long Term National Strategy for Safe Management of Radioactive Waste and to approve the Road Map for Geological Repository Development. Currently, for example, spent fuel is wet stored for 6 years and after this period it is transported to dry storage in MACSTOR-200 (a concrete monolithic module) where it is intended to remain at least 50 years. The present situation for radioactive waste management in Romania is reviewed in the present paper. Focus will be done on existent disposal facilities but, also, on future facilities planned for storage / disposal of radioactive wastes. Considering specific data for Romanian radioactive waste inventory, authors are reviewing the advance in the radioactive waste management in Romania considering its particularities. The team tries to highlight the expected limitations and unknown data related with cementitious engineered barriers that has to be faced in the near future in case of interim storage or for the upcoming long periods of disposal.


Introduction
The aim of this paper is to foreseen and to mitigate any difficulties to be encountered during the development of the storage and disposal facilities for radioactive wastes in Romania.As provider of industrial and research works for several important entities in Romania (RAAN-ROMAG PROD b , ICIT c Rm. Vâlcea, Cernavodă NPP Unit 1& 2 etc.), the Subsidiary of Technology and Engineering for Nuclear Projects is revising and updating periodically its development strategy in the field of radioactive waste management such mode to be able assist regulatory body and waste generators in future storage and disposal activities.
The paper reveals the point of view of a design organization involved in present / future projects related with storage or final disposal of LILW-SL, LILW-LL or SNF.The financing schemes for radioactive waste management are (according to the Romanian law) created by NPP contribution (fee/MWh produced) or by state budget for research reactors, legacy waste, extractive industries.
Nowadays, the national strategy involves the following:  The institutional waste will be disposed at Băiţa Bihor site;  The NPP Short Lived Low and Intermediate Level Wastes (SL-LILW) will be disposed in a near surface repository to be commissioned probably after 2020.

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The inventories of Long Lived Low and Intermediate Level Wastes (LL-LILW) will be conditioned and stored minimum 50 years and will be disposed together with spent nuclear fuel (SNF) in a deep geologic repository.
Romania, with a relatively young nuclear program, is the unique CANDU reactor operator in Europe and spent fuel is classified as radioactive waste.Currently, spent nuclear fuel is wet stored for 6 years in the Spent Fuel Bay and after this period it is transported to dry storage in MACSTOR-200 (a concrete monolithic module) where it is intended to remain at least 50 years.

Wastes inventories in Romania and potential final disposal concepts
Basically, in Romania [1] , present and future waste inventories are estimated and listed in table 1. Depending on future evolution of Romanian nuclear program, several storage and disposal facilities will be developed (dotted lines in figure 1) based on potential final disposal concepts developed for radioactive waste management.Nuclear installed capacity (present and planned) is shown in table 2.  There are treated and conditioned liquid and solid radioactive wastes from industry, medicine and research entities.All these activities are performed by the Treatment and Conditioning Facility of IFIN-HH (figure 2).Waste drums are emplaced in the disposal galleries and once a gallery is filled with drums it is isolated from the rest of repository by building a masonry wall.Depending on the closure period some galleries are backfilled with bentonite powder (since 1996).
This repository is located in an old mine and there are high disturbances of the hydrology and hydrogeology in the condition of a complex geologic and structural area.For this reason it is extremely difficult to guarantee long term performance and safety of this facility.In 2012 a joint national applied research project (SARAWAD, project duration 2012-2014) was granted by a team of Romanian researchers for the development of the closure strategy of the National Repository for Radioactive Waste Băiţa Bihor.This closure strategy will be developed based on the evolution and optimization of the engineering barriers system in order to improve the radiological safety.The main objectives of the project are:  the increase of the radiological safety at DNDR Băiţa Bihor by improving the technology for filling the storage galleries;  the development of a closure plan for this repository compliant with national and international requirements;  the evaluation of the performance of the DNDR closure systems.
05005-p.4 Steps to be followed for the objectives fulfillment are summarized in figure 3.As could be noticed, focus is directed for the assessment and behavior simulation of the repository engineered barriers.In this context will be developed new site characterization activities, and, also, in-situ and laboratory experimental arrangements.The institutional control period considered is of 300 years.The Băiţa Bihor repository is located in variegated rock formation, consisting from variegated argillites, violaceous-blackish sandstones with green epidot spots and cracks, basalts ().It was reported by previous investigators an intense argilisation (magnesium montmorillonite, quartz and illite).Water flow rates were assessed during former projects for the issue of the preliminary safety analysis report [2].For example, SITON reported in past studies that flows in one disposal gallery vary with rainfall to about several liters per second.More detailed measurements were performed latter during a PHARE project and based on these were evaluated flow rates near disposal areas.Also, during the same evaluation activities it was developed a measurement program to draw an infiltration map for areas backfilled with concrete.Reported data gave an image about the infiltration levels on galleries walls, roof and floor.
The first disposal galleries were not reinforced or waterproofed, but during construction some local infiltration areas were grouted and many repository access surfaces were covered with gunite.Also, the floor of all galleries is concrete covered such mode to form a 50 mm thick floor.Excavations from mining that were not considered useful for disposal were backfilled and sealed with ~ 3 m OPC concrete plugs.

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The waste conditioning method involves cementation in 220 L painted mild steel drums, or, in case of overpacking of some waste packages, cementation in 320 L or 420 L drums.Also, there are smaller containers for final disposal of some containerized HLW quantities or sealed sources.
It is expected that cementitious materials used could limit, during the operational period, the release rate of radionuclides into geosphere in case of package failure by well-known mechanisms.By degradation of these engineered barriers in time considering specific condition inside the repository the overall safety performance could decrease.
IFIN -HH (partner in the SARAWAD project) reports the development of an extensive program of environmental monitoring around the repository, program compliant with Romanian regulations and internal IFIN-HH procedures.Reports contain information on tritium contents in the water samples, too.This, program will indirectly monitor the evolution of some concrete / cement barriers.During past years IFIN -HH simulated in laboratory and inside Băiţa Bihor repository several cement matrices in order to assess the durability of cemented waste (both in repository and under simulated conditions).The exposure period was of seven years.Several cement samples exposed inside the Băiţa Bihor repository were reported by IFIN-HH to simulate the conditioning of radioactive sludge.The preliminary results were presented in a previous paper.Thus, IFIN-HH researchers identified by X-ray diffraction, in the experimental samples, the following compounds during the hardening of cement mixtures: calcium iron oxide (β-Ca 4 Fe 14 O 25 ), calcium iron silicate (Ca 3 Fe 2 (SiO 4 ) 3 ), calcium aluminium iron oxide (Ca 4 Al 2 Fe 2 O 10 ).Preliminary reported results from IFIN-HH showed that iron compounds had an influence on the mechanical characteristics of the tested samples, but more detailed conclusions are announced to be issued after the completion of the SARAWAD project.

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Waste cementation was performed in past with a mixture of Portland type PA35 cement and dry sand.Considering that some packages contain organic materials it could be expected the generation of carbon dioxide primary in a first stage (an aerobic one specific for operational period) followed by a slight transition to more anaerobic conditions based on oxygen consumption into the repository (equation 4) after repository closure and potential flooding.The corrosion of carbon steel drums it is considered as potential mechanism for the consumption of oxygen during the first aerobic stage of the repository, but this hypothesis need to be demonstrated until the completion of the SARAWAD project.If there will be a shift to anaerobic condition, it could be developed a scenario that will be improved latter based on experimental findings:  steel structures and metallic drums corrosion:  degradation of organic materials in the waste packages: Taking into account than the first galleries were not backfilled, the future researchers need to concentrate on the impact of present proposed closure technologies on the long-term safety of the repository.In this stage it is under development a deeper analyze to foreseen the evolution of the repository system considering the actual state.Together with its partner (IFIN-HH), SITON studies within the SARAWAD project the potential development of a new monitoring and measurement program in order to evaluate the conditions prevailing inside the closed galleries.This evaluation will allow us to make assumptions on the evolution of the environment inside the disposal galleries with respect to the expected transition from aerobic to anaerobic conditions.
Considering the nature and inventory of wastes deposited at Băiţa Bihor, wastes could contain 3 H and 14 C that means some gaseous compounds could be re-written as: 14 CO 2 , 14 CH 4 , C 3 HH 3 , 3 HH, 3 HHO.Also, 222 Rn is released inside this old exhausted uranium mine.Some generated volumes of carbon dioxide will participate in the cement carbonatation process if there are not created preferential flow path of generated gases outside from drum.If the release rate through waste form cracks is high enough it is possible to attain a minimum carbonatation of the concrete conditioning matrix.In some cases it is anticipated a sufficient cracking degree of the conditioned waste form as result of degradation of some radioactive organic materials.Moreover, carbon dioxide could dissolve in meteoric water and could be transported to the surface.
Post-closure, it is anticipated physical and chemical degradation of the closure system.Considering the length of the institutional control it is obvious that the evaluation of the performance of the DNDR closure systems it is very important.
For this reason hydro-geology is very important both for corrosion kinetics and for leaching rate of cement components.Those two phenomena are responsible for further degradation of any concrete matrix.An interesting situation will be generated by some waste packages consisting in graphite blocks immobilized in concrete matrix.It is important to understand if in this situation graphite could act as cathode of an ad-hoc corrosion pile inside the disposal gallery.The discharges on graphite surface could lead to gas formation, pressure build-up and concrete cracking.
An inventory of concrete structures that after modernization are to be encountered in the disposal system are cement conditioned waste forms, concrete floor in the disposal and transport galleries, concrete drains set in the floor of the disposal and transport galleries, closure walls used in disposal galleries, concrete drainage collection tank sunk into the ground near the repository entrance and, potential, concrete mixtures used to fill the empty spaces between drums.

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Even there were considered several measures for waterproofing of galleries and drainage of infiltrations, it is expected that post-closure will be created favorable conditions for the direct contact between infiltration waters and engineered barriers or waste forms.
In this situation is forecasted drums corrosion (with formation of voluminous corrosion products) associated with concrete degradation.For shotcrete works was used Xypex concrete (for waterproofing) in order to delay as much as possible water access to drums.As mentioned, galleries closure is intended to be performed with concrete walls.It is anticipated that in old disposal areas (without bentonite backfilling of the empty spaces of the disposal gallery) will arise the first degradation phenomena.These old galleries are located in areas exposed to the most high water flows that favor a more rapid infiltration of water.More than probable the concrete plug in the active drainage system will fail over time allowing contaminated water to flow out of the entrance of the disposal gallery.A similar situation is anticipated for the concrete collection tank that could degrade even with entire loss of its function.
It is intended that at the closure of the DNDR, to be sealed the collecting system and to be decommissioned the collecting tank.
Here, the absence of backfilling with bentonite or other appropriate materials will promote both faster contact of waste packages with water flows and higher degradation rates of waste packages (metallic drums, cementitious conditioning matrix, etc.).Chemical degradation of the waste forms is assumed to occur several years after physical degradation and will alter the sorption capabilities of the cementitious material.
In order to demonstrate the performances of the conditioning technologies of radioactive wastes at Băiţa Bihor and, also, the long term performances of the cement matrices and concrete plugs, the research team from IFIN-HH is continuing an extensive laboratory and in-situ program.Considering the SARAWAD project this program will stress on development of specific cement matrices and concrete formulations in order to simulate closure technologies.Together (SITON and IFIN-HH) are developing an experimental set up to lead to a deeper knowledge of the mechanisms and performances of the cementitious barriers inside the repository.

Near surface repository for SL-LILW from Cernavodă NPP (DFDSMA -Saligny)
This facility is planned to be constructed in Dobrogea area, Saligny site, inside the exclusion zone of the Cernavodă NPP and will cover finally an area of about 40 ha.Will be a surface repository with multiple engineered barriers that has to accommodate LILW-SL generated during operation, refurbishment and decommissioning of the units of Cernavodă NPP (existent and planned).
In case of DFDSMA Saligny conceptual design, concrete components have a more significant role for the long-term safety of the disposal system.The disposal cells and disposal modules are reinforced concrete structures covered by a slab and lined with a waterproof coating.The intended disposal module is a CBF-K type.According to a design report issued in 2010 for the Romanian Nuclear Agency and for Radioactive Waste [5] the current assumption is that the grout mix to be used for conditioning is the same as that used in the UK for similar nuclear wastes.It is possible that future studies may indicate the need to be modified to suit Cernavodă NPP requirements.The mix comprises: 3:1 by weight PFA/OPC; water/cement ratio 0.42.Considering that there are still some data to be revised it is possible that could occur some modification related with he optimization of the grouting formulations.For this reason, it is premature to develop a more extensive description.
But, in this case, must be emphasized the fact that concrete barriers are the main elements for the long term radiological safety and is intended development of modeling programs to anticipate system evolution.For these reason considerations were made on cement conditioning technologies; based on reference [5] were proposed the following mixtures for grouting:  Pulverized Fuel Ash (PFA) + OPC + water; 05005-p.8 NUCPERF 2012

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Blast Furnace Slag (BFS) + OPC + water During the implementation of the conceptual project it is intended to finalize the decision of the appropriate formulation for waste conditioning by cementation considering, also, the ratios mentioned previously for a mixture PFA/OPC/water.

Cernavodă interim dry spent fuel storage facility
The first module was commissioned in 2003.Now there are 4 modules already erected on the site.Site License is for a total storage capacity of 27 MACSTOR modules that have to accommodate spent fuel produced by Cernavodă NPP Unit 1 and 2 for 50 years.
Until now, for this facility, the operator (Cernavodă NPP) report no damage of the concrete structures (no early cracking).There is implemented a surveillance system and, as designers, we propose a deeper survey of these structures.Potential evolutions of the concrete could be as studied for similar structures worldwide.This subject has to be developed and detailed in a future work and will be available from the Cernavodă NPP operator.

Conclusion
The challenge of radioactive waste management was foreseen by regulators and in Romania the licensees had to pay an annual contribution for supporting the activity of Nuclear Agency and for Radioactive Waste (AN&DR), as competent authority for the coordination, at national level, of the safe management of spent nuclear fuel and of radioactive waste, including disposal.For National Repository Băiţa Bihor, concrete elements have the following intended function:  waste matrix is an important physical and chemical barrier for the migration of contaminants and for this reason the conditioning of waste will continue with improvement of cement matrix formulations;  in this stage it is clear that concrete walls and floor provide a lesser benefit for the long-term safety of the repository.The development of a closure technology involving the potentially backfilling of the empty spaces between drums with some concrete mixtures (under study in this moment) will change the present situation.The advances of this program will be reported in a future paper.
In case of conceptual design for the Final Repository for SL-LILW, the concrete components have a more significant role for the long-term safety of the disposal system.During the implementation of the conceptual project it is intended to finalize the decision of the appropriate formulation for waste conditioning by cementation.
The Cernavodă Interim Dry Spent Fuel Storage Facility is relatively new so in this moment there are no problems reported.Potential evolution of the concrete structures could arise and for this reason is to be anticipated in a first stage the development of several RD programs.

Fig. 2 .
Fig. 2. Management strategy for radioactive wastes generated from industry, medicine and research entities.

Fig. 3 .
Fig. 3. Action plan for the completion of SARAWAD project.

Table 1 .
[1]sent and future radioactive waste inventories in Romania[1](to be continued on next page).
0 -HLW -High Level Waste; VLLW -Very Low Level Waste; LILW-SL -Short Lived Low and Intermediate Level Waste; LILW -LL -Long Lived Low and Intermediate Level Waste; SF -Spent Fuel; 1 -currently in storage (m³); 2-total current storage capacity (m³); 3 -estimated year current capacity is completely used.Comments: LILW-LL included in LILW-SL (radioactive waste not yet characterized).The data for HLW and SF correspond to Cernavodă NPP *These data correspond mainly to the IFIN HH site (taking into account total storage capacity on site) *

Concerns related with the performances of cementitious materials used in storage / disposal facilities 3.1 Low -Level Radioactive Waste Repository (DNDR) Băiţa Bihor, Romania [2, 3]
d grouting in standard 220 L carbon steel drums.d Ordinary Portland Cement 05005-p.3