Optimization proposals of the Vrbina LILW Repository Preliminary Design

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1 Optimization proposals of the Vrbina LILW Repository Preliminary Design ABSTRACT Boštjan Duhovnik IBE, d.d., svetovanje, projektiranje in inženiring (IBE) Hajdrihova 4 SI-1000 Ljubljana, Slovenia bostjan.duhovnik@ibe.si Janja Špiler ARAO - Agency for Radwaste Management, Ljubljana (ARAO) Celovška 182 SI-1000 Ljubljana, Slovenia janja.spiler@arao.si In 2009, a Preliminary Design of the Vrbina Low and Intermediate Level Waste (LILW) Repository was prepared. The Design solutions followed the guidelines given in the Comparative Multilateral Study of Alternatives where the solution of disposal in belowground silos was proved to be the most suitable one for the Vrbina site. According to the structures, systems and components extent the Design solutions also complied with the then applicable regulatory requirements and program documents from the field of radwaste management. The Preliminary Design represented one of the bases for adoption of the National Spatial Plan of the Repository at the end of In order to reduce the costs of investment and operation, and increase technical feasibility and safety, an approach to optimizing the Design solutions was initiated immediately after the Preliminary Design had been completed. The opinions of the International Atomic Energy Agency (IAEA) missions and several independent external reviewers were taken into account. At the same time, the each time knowledge in the field of safety analyses and conclusions regarding the required waste acceptance criteria were taken into account in the optimization procedure. The optimization was mainly concluded in 2010 and 2011 in form of several independent studies. The priority solutions indicated by the optimization procedure are mostly as follows: repository operating mode changing from a continuous to an occasional one with a standstill period; disposal of a revised-reduced LILW quantity in optimized disposal containers; solution of the disposal silos by abandoning the access shaft and the inspection gallery and by modified closing-up approaches after the end of operation; waste treatment for disposal in NPP Krško and waste transport by the existing and reconstructed public areas. In the last year, optimization of the Repository non-disposal part was taking place. The optimization solutions depended on a precise definition of individual Repository activities implementation delimitation between ARAO, NEK and other operators. The optimized Design solutions of disposal and other facilities and relating systems will be re-examined from the standpoint of safety while the optimized Preliminary Design relating to the disposal container and waste treatment for disposal will be re-examined from the 808.1

2 808.2 standpoint of waste acceptance criteria for disposal. The re-examined optimized Design solutions will be carried out in the next stages of the design documents implementation. 1 INTRODUCTION In 2009, a Preliminary Design of the Vrbina Low and Intermediate Level Waste (LILW) Repository [1] (PD) was prepared. The PD was developed in accordance with the Terms of Reference where relevant requirements set in the Resolution on the National Programme for Managing Radioactive Waste and Spent Nuclear Fuel, ReNPROJG, Official Gazette of the RS 15/2006, and the then applicable Rules on Conditions for Siting, Construction, Trial Run, Start-Up and Operation of Nuclear Structures (Rules E1), Official Gazette of the SFRJ 52/88 were summarized, and where the Repository was anticipated as an independent nuclear structure with due technological capacities needed for waste conditioning and with capacities enabling independent performance of all other supporting activities. The site and the concept of the disposal solution were formally approved in the scope of the Decree on National Spatial Plan at the end of 2009 (Official Gazette of the RS, No. 114/09, December 31, 2009). In the PD phase the repository was designed and approved for disposal of 9,400 m 3 of LILW produced in Slovenia with a possibility of further extension of the disposal capacities. The capacity corresponded to one half of the LILW generated by the Krško NPP (NEK) within the original, non-extended operational period till 2023, and to all the remaining Slovenian LILW. It was planned that the repository would operate continuously between years 2014 and 2039 and would consist of a disposal part, composed of a set of modular disposal units (silos), and other structures required for the acceptance, conditioning and storage of radioactive waste. Besides technological facilities, an information center, an administrative building and a service building are anticipated on the site as well. All buildings and disposal structures of the repository will be constructed on a platform which will protect them against floods. Prior to disposal, all LILW will be inserted into 1392 concrete disposal containers of N3a type and external dimensions of 2.55 x 2.55 x 3.25 m. In an individual container, 9 tube-type containers (TTC, the most often type of package in NEK) or 27 standard 200-liter drums or unpacked LILW with a volume of approximately 13 m 3 will be placed. The containers will be disposed into two disposal silos of an inner diameter of 27.3 m and useful (net) height of 33 m. The bottom of the silos will be approximately 55 m below the elevation of the handling platform. The LILW placed in the containers will be inserted into the silo by a portal gantry crane. After each of the ten layers with 70 disposal containers is filled-up, the remaining voids between the container walls and between the containers and the silo wall will be backfilled with backfilling material. Water which will eventually seep through the silo walls will be collected in the draining basis of the silo and drained via an inspection gallery to the common self-dependent access shaft, where sampling will be performed prior to its pumping to the surface. 2 OPTIMIZATION PROCESS 2.1 Background, Purpose and Scope Immediately after the PD was accomplished, further design solutions development and optimization activities took place. The development as well as the optimization was mainly focused on verifying the solutions adequacy in relation to the actual requirements, and on increasing technical feasibility and safety. In the optimization process, domestic and foreign PD reviewers remarks [2][3] as well as findings resulting from safety and functional analysis

3 808.3 of the repository were considered. Moreover, opinions of expert missions of the International Atomic Energy Agency (IAEA) on the decommissioning issues [4] and the relating LILW disposal [5][6] were considered as well in the optimization process. The optimization process was influenced also by guidelines of a special IAEA expert mission for disposal facilities [7]. The optimization process with a description of modifications regarding the solutions given in the PD is presented in a simplified form in Table 1. The optimization was mainly concluded in 2010 and 2011 in form of several independent studies, and is described hereinafter. Disposal capacity (m 3 LILW) 1) 9.400:1/2-23 (possibility of extension :1/1-23) 1. 1/ / /1-43 Table 1: Optimization process by optimization steps Mode and period of repository operation Performer and the site of conditioning Original design: Preliminary Design (PD), July 2009 [1] ARAO at the repository. continuous operation continuous; 2. campaign; 3. periodical; a b / Not applicable - NA; as in Preliminary Design (PD) Disposal facilities 2 silos with access shaft (2 additional silos) cover: clay plug, 5 m; gravel backfilling; Disposal container type Optimization step: Examination of the repository operation interruption and introduction of a standstill period; impact on the cost estimate, March 2010 [8] ARAO and outsourced NA (PD) NA (PD) organizations at the repository. Optimization step: Development of the disposal technology solutions, December 2010 [9] NEK at NEK. 2 silos with access shaft (3 for MUZ) 1. N3a 2. N2 2) 3. MUZ 3) Optimization step: Revision and optimization of design solutions Disposal silos, July 2011 [10] NA (PD) NA (PD) Silo 1. silo without common access shaft; 2. double walled silo ; 3. silo with drainage in the wall; Cover plug: 1. silo wall perforation improvement; 2. plug diameter enlargement; 3. plug height enlargement; N3a NA (PD) Optimization step: Revision and optimization of design solutions Disposal technology, October 2011 [11] 1/1-43 NA TTC reworking 3. Disposal in ISO containers 4. Disposal without containers 5. Conditioning at NEK 6. Backfilling of voids in packages 2 silos with drainage (for N3a in N2a) 1. N3a 2. N2a 4) 3. El Cabril 4. Konrad 5. Mochovce 6. Olkiluoto Optimization step: Optimization of the non-disposal part of the repository (in progress) 1/1-43 NA NEK (determination of details) NA N2a vertical position Notes: NA not applicable or no changes regarding PD NA (PD) 1): 1/1 - all LILW from NEK; 1/2- half of LILW; 23/43 NEK operation till 2023/2043; 2): N2 container for 4 TTCs 3): MUZ - minimal universal container, wherein TTC in horizontal and drums in vertical position can be emplaced; 4): N2a - modified N2 container

4 Examination of the Repository Operation Interruption and Introduction of a Standstill Period Early in 2010, a technical and economic study of the Repository Operation Interruption and Impacts on the Cost Estimate [8] was made. In the Study, which was made for several alternatives, it was adopted inter alias that the operational period of the NEK would be extended till 2043 and that complete LILW generated by NEK would be disposed in the repository. At the same time, the possibility of the repository operation with an intermediate standstill period was verified as well. A comparative analysis of costs in case of a specific alternative showed that introduction of a standstill period results in a reduction of the repository costs of operation and that disposal of all waste from NEK (instead of a half of it) does not significantly increase the operating costs. 2.3 Development of the Disposal Technology Solutions In 2010, a Study was prepared in form of a detailed technical analysis made in particular from the aspect of optimization of non-disposal structures and the repository operation, i.e. Development of the Disposal Technology Solutions [9]. The most important optimized solutions were as follows: a. Conditioning of LILW generated by NEK shall be fully performed in NEK. NEK shall take over also conditioning of LILW of other producers. Disposal containers suitable for immediate disposal shall be transported to the repository. Waste conditioning costs, including costs of transport to the repository, shall be borne entirely by the LILW producer. b. The repository (Operator ARAO) shall provide for direct disposal of the containers into the disposal silo, including management, development, construction, maintenance and closing of the disposal capacities. The repository (ARAO) shall provide also for all supporting activities which have to be performed by a nuclear facility. c. Service and supporting activities on the repository shall be performed by outsourced contractors. d. Management and administration activities which are not directly connected with disposal as well as information center activities shall be performed in cooperation with other nuclear facility operators outside the LILW repository. 2.4 Revision and Optimization of Design Solutions Disposal Silo This optimization stage was dedicated exclusively to the disposal silo and was mainly focused on providing maximum tightness of the silo and control over groundwater seepage [10]. To enhance water control performances and to improve construction feasibility the solution of the silos including a common self-dependent access shaft and inspection galleries was abandoned. The access to the lower part of the silo and the groundwater pumping system was re-located into the shaft constructed in the silo wall; besides, two more alternatives were treated, i.e. a double-walled silo and draining from the silo wall. Simultaneously with the silo optimization also the silo closing optimization was dealt with. In particular the issues of the sealing clay plug diameter increase and the sealing plug extension up to the surface level were analysed.

5 Revision and Optimization of Design Solutions Disposal Technology Besides waste conditioning in NEK and LILW packages disposal into disposal containers, some other alternatives were analyzed in the Study [11] as well, i.e.: TTCs reworking, disposal in ISO containers, disposal of LILW packages without disposal containers, and filling of voids in LILW packages. As regards disposal containers, the N3a and N2a types (special design for Krško), and the disposal containers used in El Cabril, Mochovce and Olkiluoto repositories as well as the ones planned for use in Konrad repository were dealt with. A comparative analysis proposed that the most suitable alternative is the one where LILW is conditioned in NEK (without additional processing) and placed in the N2a disposal containers type. These enable better technical feasibility and at the moment represent the only real alternative to the container of N3a type. In the PD, the LILW transport to the repository over public areas was foreseen. In the Study, additional transport possibilities from NEK, following a special corridor within the existing road connections, by a special road directly connecting the repository with NEK and through a special entrance into NEK were analysed. It was established that the solution given in the PD is suitable and that the priority solution covers LILW transport over the existing or reconstructed public areas. 2.6 Optimization of the Non-Disposal Part of the Repository The optimization success depends on allocation of responsibilities in implementing the activities which were in the PD entirely in the domain of ARAO. The optimization of the nondisposal part of the repository is focused on an optimal exploitation of all currently available and also foreseen technological and other capacities and, what is even more important, on determination of holders or contractors of these activities. The optimization of the nondisposal part is made in form of a detailed task sharing which was drafted already in the Development of the Disposal Technology Solutions study [9] and is roughly as follows: ARAO is responsible for the repository operation, for container-packed LILW disposal into disposal silos and for LILW packages transport to NEK; Conditioning of complete LILW with their placing into the N2aV disposal containers is carried out in NEK (N2a disposal containers in vertical position; NEK also provides for disposal container manufacture, for disposal container transport to the repository and for performance of hot works in the repository; Activities including access control point, physical security, protection against fire, radiation protection and radiation monitoring are performed by ARAO in cooperation with NEK; Management and administration activities as well as information activities will be performed in the existing ARAO premises or in additionally leased or acquired areas outside the repository. The optimization described will result in a significantly reduced scope of non-disposal structures, systems and installations of the repository. 2.7 Overall Results of the Optimization Process The overall proposals of the optimization process are generally as follows: a. The repository will be operated by ARAO from 2020 to 2062 with a standstill period during ; b. LILW conditioning will be entirely performed in NEK; c. LILW will be disposed in the repository in disposal containers of N2aV type;

6 808.6 d. For disposal of these waste a disposal silo will be constructed as an independent structure with integrated access shafts and additional draining; and e. LILW transport will be performed over public areas; to the NEK it will be performed by ARAO, and to the repository by NEK. The optimization has a favorable impact on technical feasibility of disposal, on the repository safety and costs. An increased technical feasibility is mainly enabled by the conditioning process transfer to NEK and by introduction of smaller containers. Introduction of silo with integrated access shaft and with the drainage system in the walls as well as modification of the clay plug will result in better sealing properties of the silo and in increased repository safety. Optimization of operation and realization of synergy effects by the repository activities or part of activities performance transfer from ARAO to other stakeholders (in particular transfer of LILW conditioning to NEK) has also a significant impact on cost reduction. The optimized solutions were considered in the Feasibility study, Rev. C [12], which was approved by the Minister in charge of infrastructure and environment on July 8, 2014 as the person responsible of the Investor. In the PD in 2009, the construction and decommissioning/closure costs of structures, systems and installations were assessed to 72,69 mil EUR while the construction and decommissioning/closure costs of the optimized structures systems and installations amount to 31,49 mil EUR (Feasibility study, 2013) [12]. 3 VERIFICATION OF OPTIMIZED DESIGN SOLUTIONS In the scope of next design phase the proposed optimized design solutions should be verified. The design solutions of disposal facilities and associated systems will be verified from the aspect of safety analyses while the design solutions of the disposal container and conditioning will be verified from the aspect of waste acceptance criteria for disposal. A considerable further optimization effects could be achieved by enlargement of disposal capacity to meet complete volume of LILW generated by NEK. ACKNOWLEDGMENTS IBE has made the optimization of the Preliminary Design solutions on the basis of the Contract signed with ARAO and covering technical support in design engineering of the LILW repository in Slovenia. REFERENCES [1] Vrbina LILW Repository, Preliminary Design, Rev. A (PD), IBE, Project No. NRVB- B052/058, Ljubljana, 2009 [2] Review of the Preliminary Design of the Vrbina Low- and Intermediate-Level Waste Repository, URS, May 2010 [3] Peer Review of LILW Repository Preliminary Design, Vrbina, Krško; TECHNUM - TRACTEBEL ENGINEERING; Technical note N P A; June 2010 [4] Preliminary Decommissioning Plan NPP Krško, Doc.-No.: 8215 / CA / F / 05, Siempelkamp - NIS Ingenieurgesellschaft mbh, Alzenau, April 2010

7 808.7 [5] IAEA Mission for revision 2 program of NPP Krško Decommissioning and SF and LILW disposal, ARAO, 27/28 August 2009, A.V. Cotthem, F. Fiedler; IAEA; 2009 [6] Expert Mission for Optimization of Integrated Scenarios in NEK Program - March 8-10, 2010, Čatež, Slovenia; Final Report IAEA TC SLO 3005, 24 March 2010; M. Garamszeghy, J-M. Potier, L. Valencia; IAEA; 2010 [7] Expert Mission on Technical solutions for The Low And Intermediate Level Radioactive Waste Repository, Vrbina, Krško, IAEA TC SLO 3005; J. Pacovsky, R. Chaplow; ARAO, Ljubljana ; IAEA; 2011 [8] Examination of the repository operation interruption and introduction of standstill period, IBE, Project No. NRVB---3X/M12, Ljubljana, March 2010 [9] Development of the disposal technology solutions, Rev. A, IBE, Project No. NRVB--- 3X/M14A, Ljubljana, December 2010 [10] Revision and optimization of design solutions Disposal silos, Rev. A, IBE, Project No. NRVB---3X/M15A, Ljubljana, July 2011 [11] Revision and optimization of design solutions Disposal technology, Rev. 0, IBE, Project No. NRVB---3X/M16, Ljubljana, October 2011 [12] Feasibility study, Rev. C, IBE, Project No. NRVB-B052/058 - NRVB---4X/01C, Ljubljana, December 2013