R5.01/02 Modernisation of Nuclear Materials Accounting at Mayak plant systems Service Part (AP ref. 7.1.4.1)

In the early nineties the Russian Federation decided to join the Non-Proliferation Treaty (NPT). In safeguards agreements pursuant to the NPT, Russia was required to establish and maintain a State System of Accounting and Control of Nuclear Material (SSAC) within its territory, jurisdiction or control. The SSAC falls under the responsibility of Minatom (later Rosatom) and integrates several important components, including the state system of accountancy, nuclear export and import control and physical protection. The system was established in accordance with the “Law on Use of Atomic Energy” and defines the responsibilities of Russia under the Safeguards Agreement between the IAEA and Russia under the NPT.

The Mayak Complex in Ozersk is situated close to Chelyabinsk, a city near the North-western Ural Mountains. Production Association (PA) Mayak is one of the most important nuclear sites of the Russian Federation. Almost all kinds of nuclear activities, with the exception of uranium enrichment and fuel assembly fabrication are covered by the nuclear facilities, including nuclear reactor decommissioning, spent fuel reprocessing (RT-1 Plant), chemical-metallurgical processing of uranium and plutonium, production of radioactive sources - including for medical purposes -, waste conditioning and analytical laboratories.

The RT-1 plant at the PA Mayak complex is an operating nuclear reprocessing facility. At the time of initiation of this project, it was reprocessing civil spent fuel of the VVER-440 and BN-600 nuclear reactors, submarines, ice breakers and research reactors. It was the main Russian plant for current and future reprocessing of nuclear fuel from the Nuclear Power Reactors and Power Research Reactors of the Russian Federation (RF). It was also planned that PA Mayak would play a central role in verifying, storing and, later on, processing Pu from the dismantling of nuclear weapons. For these reasons it was a highly important facility with regard to international nuclear safeguards.

Several Nuclear Material Accountancy and Control (NMAC) system devices and techniques had been installed at the RT-1 plant many years earlier. These had been in service for a long time and were in need of modernisation. They were not automated and had poor accuracy compared to the instruments and techniques employed at similar European radiochemical facilities. Moreover, the entry into force of the SSAC required a restructuring of the accountancy and measurement approaches and the implementation of the new system would require intensive personnel training, both in the use of the instruments and in the application of NMAC procedures.

The European Commission decided to support an approach for the modernisation and enhancement of NMAC systems at the RT-1 plant under the 2002 TACIS Nuclear Safety programme. The RT-1 plant has many facilities for spent fuel reprocessing; however only one line, which handles and treats the spent fuel from VVER-440 (both Russian and foreign) and BN-600 NPPs, was selected to be included in this project.

Brief description of the facility and need for modernisation

This project was focussed on the RT-1 facility dedicated to the reprocessing of spent fuel from VVER-440 and BN-600 NPPs. The final products are uranium nitrate with uranium enrichment of between 2.2%-2.6% for use in RBMK fuel, plutonium dioxide powder from BN-600 spent fuel and plutonium dioxide powder from VVER-440 spent fuel. The capacity of the facilities is 400 t/yr for VVER spent fuel assemblies and 20 t/yr for BN-600 assemblies.

There are many processing facilities in RT-1 where the assemblies are cut, chopped, and dissolved. The main spent fuel solution is transferred to the input accountancy tanks (IAT) and then filtered and reprocessed to separate the fission products from uranium and plutonium from which the final separate products of uranium and plutonium solutions are obtained.

The facility under consideration follows a modified PUREX process with additional separation of Np, which differs from the process followed in European reprocessing plants. The scheme includes 10 technological processes:

1. storage of spent fuel assemblies coming from the VVER-440 and BN-600 reactors;
2. preparation of the assemblies prior to chopping: preparation of batches for dissolution, cutting off the tail end parts and neutron emission measurement;
3. operations line for assembly chopping and dissolving;
4. filtration of the feed solution of the spent nuclear fuel;
5. extraction reprocessing and purification of nitrate solutions of uranium, plutonium and neptunium from fission products; separation of uranium, plutonium and neptunium;
6. Pu oxalate precipitation and calcination to plutonium dioxide powder;
7. evaporation of uranyl nitrate solution with low enrichment (2.4-2.6%);
8. storage of plutonium dioxide product;
9. production of uranyl nitrate concentrate paste and its storage;
10. vitrification and storage for high and medium level waste.

The existing NMAC system in the plant prior to the initiation of this project was as follows. Each division of the plant had to make a physical inventory each month and the NM account was balanced in all divisions of the plant. The base information for NM accounting and Inventory Difference (ID) evaluation was the results of measurements of NM content and mass in reprocessed and final products (spent assemblies, spent fuel solution, uranium and plutonium solutions, liquid wastes, plutonium dioxide powder and Uranyl nitrate paste). Many equipment units and sub-facilities for solution reprocessing might not be cleaned before the physical inventory for technological and operational reasons. Therefore different NDA techniques and instruments for measurement of NM content and mass in the equipment (level meters, neutron coincidence counters, etc) were introduced to estimate hold-up and NM accumulation in the installation. The measurement accuracy for the final product and the main part of solution transactions between divisions was good for NMAC goals, but many techniques and instruments needed to be improved to satisfy the criteria prescribed for ID in the federal rules. Moreover it was necessary to measure and account for all nuclear materials handled by the plant, to perform these measurements accurately and in a timely manner.

In order to implement the NMAC basic rules, reconstruction of the plant NMAC system was required, as well as definition of Materials Balance Areas (MBAs) and re-establishing of Key Measurement Points (KMPs), modernisation of measurement techniques and instruments, implementation of new ones and creation of an NMAC computerised system.

The overall objective of the project was to enhance and improve the RT-1 NMAC system through the implementation of new or the modernization of existing systems, coupled with intensive training in NMAC methodological activities for the staff. The implementation and incorporation of new MBA/KMP structures, the development of detailed specifications for modernised and new measurement techniques and instruments together with a computerised system was a major aspect of the project.

The informatic architectural structure of data acquisition, evaluation and analysis as well as the final NMAC reporting needed to be redesigned, as a consequence of the modernization measures introduced and of the new regulations. Considering the complexity of the plant, with the type of material flow and unit operations performed, an appropriate accountancy plan needed to be developed. The plan would have to integrate the information obtained from various sources (instrumentation, records, etc.) and aim for reliable and automatic accountancy techniques employing modern technology. Information gathering in the so called near-real time with immediate analysis should be employed to allow several elements of near real time accountancy (NRTA) to be achieved.

In order to attain NRTA the following basic elements were required:

• Improvement of bulk measurement methods;
• Computerisation of data acquisition from both the plant and the analytical laboratory;
• Computerisation of record keeping and reporting, data evaluation and verification, measurement sequences;
• Estimation of in process inventory hold-up in order to have up-to-date and frequent material balances, and
• Computerised system with a well-defined architecture for data acquisition and interpretation.

The project consisted of an initial design study of the facilities to identify the main areas/locations for improving NMAC. Then, following the results of the study, Solution Monitoring Systems and other Nuclear Material Accountancy Systems identified in the design study, such as solution mass/volume devices, K-edge, gamma-absorption meters and neutron control detectors, were implemented. Training formed an integral and fundamental part for the successful implementation and utilisation of the instruments and application of the software.

The project comprised 5 main lines of activity:

1. The detailed design study:

This comprised a preliminary detailed study of the plant flow sheets and of the needs for modernization. The scope of the study was to provide an overall detailed analysis of the PA Mayak complex activities, with particular focus devoted to the NMAC aspects. The study was conducted mainly by the RF counterparts (PA Mayak and IPPE), but the project made use of the BNFL experience and the existing Mayak-BNFL studies performed previously under UK DTI funding were carefully taken into account.

The result of the study was to identify all the areas relevant to NMAC within the RT-1 plant of PA Mayak complex, describing the material flows of input/output to Mayak and more specifically to RT-1 plant, the internal process operations and exchange between different MBAs, as well as the current types of accountancy systems and measurement capabilities and the computerised accountancy records applied in the plant to the BN-600 and VVER-440 SFA reprocessing. The study identified and detailed the needs and requirements in the above mentioned areas.

2. Modernization and implementation of solution monitoring systems including application software for data acquisition and processing:

Almost all tanks at PA Mayak were equipped with Russian type so-called high frequency inductive level probes, which measure the variation in level by means of an inductance, transformed to a high frequency signal. These Russian types of level probes are closed and therefore appropriate for all tanks with pressurised transfer system. In total 150 of these level probes were installed in 20 tanks at key measurement points, 10 of which are inventory tanks. In some of these inventory tanks additionally the American TVM system with bubbling probes was installed in 1997 but was not operating properly. This sub-project comprised various activities:

• Procurement and Installation, at the PA “Mayak” RT-1 facility, of bubbling probes; Repair and reinstallation of the TVM probes.
• Modernisation, installation and testing of the Russian high-frequency inductive level probes.
• Calibration of the tanks after mass/volume methodology training at Ispra and the Russian Methodology and Training Centre (RMTC).
• Preparation of mock-up tanks and solutions (to study solution monitoring and process operations such as transfers, sampling and mixing).
• Installation and comparative study of the three types of level probes (bubbling, Russian inductive, Western TDR [time domain reflectometry]).
• Evaluation of the influence of the sampling line on the data.

3. Modernization and Implementation of other NMAC systems, such as K-edge densitometer, NDA equipment and techniques, computerized accountancy system:

This task comprised:

• Upgrading of GAS-GAM gamma spectrometers: NDA techniques for U/Pu concentration measurements with Dip GAS-GAM type gamma-spectrometers were installed at 40 key measurements points. These gamma spectrometers required upgrading in order to enhance their accuracy and reliability with regard to NRTMA.
• Computerisation of the Neutron Control Detectors (NCD). NCD for Pu concentration are requested in various locations for NMAC. Existing NCD devices at 25 KMPs needed to be computerised with auto diagnostics. NCDs were requested also for the NDA of hulls and hold-up (about 20 KMP)
• Procurement of NaI gamma spectrometers: Portable NaI gamma-spectrometers were required for the verification measurements of uranium enrichment in paste items.
• Development or improvement of gamma and neutron NDA techniques for NM content in solution, hulls, accumulation and hold-up in various KMPs for NMAC. Characterisation and certification of these techniques was also required.
• Improvement of the analytical laboratory with upgrade of the Destructive Assay (DA) techniques. The analytical laboratory on site treats all samples of all lines. Beside NDA techniques also DA techniques are used. The applied spectrophotometry of Pu and Davies-Gray titration showed a rather high error and indicated that the accuracy of the analytical analysis on the main input solution was not sufficient for the NMAC. It was proposed to install a hybrid K-edge densitometer with sample changer in the hot cell with an integrated sample line.
• Improvement of NMAC procedures and measurements. NMAC procedures and measurements for BN and VVER PuO2 powders had previously been improved as results of co-operation with US/DOE. NDA for the output storages within this project was oriented at the NMAC measurements of uranyl nitrate paste, which is shipped to the Ulba plant in the Republic of Kazakhstan for RBMK pellets The main problem in this KMP was connected with measurement of net and gross weight of the containers with U paste. The delivery and installation of a crane scale for this measurement was required.
• Procurement and installation of hardware data acquisition systems for archiving of data for analysis.
• Modernisation of computerised accountancy system.
• Procurement and installation of sub-water system with illumination and camera.

4. Near-Real Time Material Accountancy (NRTMA):

Elements of NRTMA for RT-1 plant had to be studied, designed and implemented, allowing information gathering with its immediate analysis. In order to attain NRTMA the following basic elements were required:

• improvement of bulk measurement methods
• computerisation of data acquisition both from the plant and the analytical laboratory.
• computerisation of record keeping and reporting, data evaluation and verification, measurement sequences
• estimation of in process inventory hold-up in order to have up-to-date and frequent material balances
• measurement uncertainties for all in-process inventory contributors

5. Training of trainers, custodians and Nuclear Materials Accountancy officers:

Eight training courses for RT-1 plant personnel were conducted in the RMTC on the following subjects:

• Data acquisition and analysis;
• Development of the software for MC&A systems;
• Measurement of U and Pu isotopic composition;
• Pu hold-up measurement;
• Neutron control of Pu in wastes;
• Solution mass/volume measurement methods (2 courses);
• Complex densitometer.

A total of 32 trainees passed the training on these courses.

RMTC prepared models of tanks of different types, calibrated models of tanks and prepared them for training courses for RT-1 plant personnel on NMAC techniques regarding measurements of solution masses and volumes in the RMTC tank calibration laboratory as well as for comparative research and certification of measurement techniques.

Other activities: In addition to the above activities, the Consultant prepared the Technical Specifications for the procurement of the equipment and instrumentation to be provided to the PA Mayak as part of the project. The Consultant also prepared the tender dossiers and provided technical support to AIDCO for tender reception, evaluation and selection of supplier, as well as for implementation of the Procurement contract and related administrative and financial issues. The equipment was procured under separate TACIS contracts, (project R5.01/02S), as follows:

• Lot1: five bubble probe systems (see contract 112115).
• Lot 2: two NaI gamma-spectrometers and four alpha spectrometers and Lot 3: a Hybrid K-edge densitometer (HKED) (see contract 65070).
• Lot 4: an informatics system for computerized monitoring (see contract 112106).

The contract was signed on 1 September 2004 and was completed on 31 December 2009.

The implementation of the overall project can be considered as a success. The RT-1 line for reprocessing VVER-440 and BN-600 spent fuel has been instrumented to improve the Nuclear Material Measurements as necessary for Safeguards purposes. NMAC software was developed and MAYAK personnel were trained to fully benefit from the project achievements.

Process and solution monitoring allow Near Real Time Accountancy. Even though traditional nuclear material Accountancy and Control with periodical inventory difference verifications are required, the near real time accountancy helps directly in identifying timely and locally problems with nuclear material flows. Solution and process monitoring is the key for a higher automation in process control with enhanced safety and safeguards because it automatically follows the process conditions and the nuclear material flow and inventory. It therefore contributes to the process quality and enhances the accountancy accuracy.

Equipment for mass/volume measurements, for concentration measurements in an analytical laboratory, for material characterization by on-site non-destructive analyses and for computerized monitoring with an informatics network was supplied under the following three contracts:

• Lot1: five bubble probe systems (contract 112115),
• Lots 2 and 3: two NaI gamma-spectrometers, four alpha spectrometers and a Hybrid K-edge densitometer (HKED) (contract 65070),
• Lot 4: an informatics system for computerized monitoring (contract 112106).

See the respective contracts for further information.

Three other lots were initially envisaged and were included in the call for tender:

• Lot 5: Electronic platform scale
• Lot 6: Sub-water illumination system and 2 cameras
• Lot 7: Upgrading of 50 neutron control detectors

No valid offers were received for these 3 lots. Lots 5 and 6 were cancelled. Lot 7, for the upgrading of the neutron control detectors was of high relevance and it was proposed to incorporate this activity in a follow-up TACIS project, Tareg 5.01/05 (Contract 116780).

In addition to its own activities, the Consultant procured the services of three sub-contractors as follows:

• PA Mayak (€480,000; signed in December 2005): The work comprised some studies, equipment upgrade and the implementation of the supplied equipment at the plant. The contract was completed with the last deliverables provided in December 2009.
• Institute of Physics and Power Engineering (IPPE) (€320,000; signed in March 2006): The work comprised mainly studies and training activities. IPPE was the host organisation of the Russian Methodology and Training Centre (RMTC – See contracts 26512, 25661, 24798, 23498 and 23425 for further information on the RMTC). The contract was completed with the last deliverables provided in October 2008.
• Lider (€200,000; signed in July 2007): The work comprised the development of the NMAC software. Lider was the only contractor having access to restricted information of PA Mayak and was selected due to the confidential and sensitive nature of the information and data required for the task. The contract was completed with the reception of the final report in May 2009.

References

1. Janssens-Maenhout, G., Dechamp, L., Richir, P., Janssens, W., Ottmar, H., Ryazanov, B., Skobtsov, A., (2006), Nuclear Material Monitoring for the Reprocessing Plant RT-1 at MAYAK, 47th Ann. Meet. INMM
2. Guardini S., Daures, P., Frigola, P., Hunt, B., Janssens-Maenhout, G., Peerani, P., Ottmar, H., Poucet, A., Gasperini, F., Ryazanov, B., Bogorodskikh, A., Glagolenko, Y., Skobtsov, A., Wark, J., (2003), Modernisation and Enhancement of Nuclear Material Accountancy and Control at the Mayak RT-1 Plant, 44th Ann. Meet. INMM.
3. Ryazanov, B., Gorunov, V., Kuzmin, S., Richir, P., (2010), Modernisation and Enhancement of NMAC at PA Mayak RT-1 Plant, 51st Ann. Meet. INMM.