Spent Fuel Preparation and Removal from Institute of Physics and Power Engineering
A.A. Sarbeev, S.V. Komarov, S.N. Komarov, A. Khudyakov (Sosny Research and Development Company), I. Gusakov-Stanyukovich (Rosatom Corporation), K. Golubkin, V. Ipatov (Mayak)
Nuclear & Enviromental Safety, №3, 2012
The Federal Target Programme "Nuclear and Radiation Safety Assurance for 2008 and Until 2015" makes provisions for implementation of a range of activities to improve safety of storage, prepare for shipment and ship the spent nuclear fuel currently located within the Institute of Physics and Power Engineering (IPPE) site. The practical work in this area was started by Russian companies in 2008.
Storage of spent fuel
Spent nuclear fuel at IPPE is kept in a standalone "dry" spent fuel storage facility. The single-story building, which also houses a storage facility, was de¬signed and constructed in the 1960s to be used for temporary storage of fuel assemblies and experimental fuel rods irradiated in on-site research reactors.
Spent fuel is stored in the basement of the building, which is constructed of monolithic reinforced concrete, inside stainless steel baskets of various lengths.
Over the many years of operation of research reactors, critical test rigs and "hot cells", the on-site IPPE storage facility accumulated a significant amount of spent nuclear fuel of various compositions with various enrichments. As many of the on-site facilities were used for research purposes, the fuel was irradiated in simulated harsh pro¬cess conditions. The spent fuel is largely leaky, and must be effectively treated as failed.
Because of radiation-induced swelling over long storage periods (in certain cases, up to 50 years), fuel in many baskets cannot be retrieved without breaking the basket structure itself. Another problem is that much of the spent fuel falls outside the industry standard for acceptance of spent fuel for reprocessing, chiefly because there are no actual reprocessing technologies available for it. Prior to spent fuel shipment from IPPE to the reprocessing facility, the facility needs to be upgraded to enable acceptance and the necessary permits secured.
Currently the storage facility building is nearing the end of its permitted operating life, requiring that action be taken urgently to upgrade and subsequently de-fuel the facility. As the storage facility is located within direct vicinity to the city of Obninsk, the most urgent objective is to reduce the radiation hazard from the built-up stock of spent nuclear fuel by removing it to the reprocessing plant.To achieve that, a comprehensive radiation-engineering survey of the facility has to be performed, followed by fuel preparation for shipment and eventually shipment to Mayak.
The unit of spent fuel accounting in the IPPE on-site storage facility is the basket; the baskets are placed in individually numbered storage cells. All documentation, including information regarding the weight and content, refers to the unit of accounting, i.e. the basket, which may actually contain spent fuel of various types. At the same time, it is often impossible to identify the type of spent fuel by visual examination. In this connection, there would be the risk that fuel could be shipped to the reprocessing facility for which there is currently no reprocessing technology. In order to identify and certify the spent fuel, it is necessary to firstly, review all accounting docu¬mentation (basket cell certificates, fuel loading logbooks, basket lo¬cation maps, logbooks of previous spent fuel handling operations, etc.). Secondly, the storage cells must be photographed remotely for subsequent visual analysis of their contents. Thirdly, for baskets whose contents cannot be identified using the methods above, non-destructive methods must be developed allowing for identifi¬cation of fuel composition and fuel matrix type in a shielded cell. Destructive methods are highly undesirable as there are strict limita¬tions on airborne radioactivity releases within Obninsk city limits.
For shipment for reprocessing, a leak-tight enclosure must be provided to ensure safe spent fuel loading into the transport cask and interim storage at the reprocessing plant. Hence, most of spent fuel should be placed into leak-tight canisters prior to shipment.
The existing regulations at IPPE forbid operations with the baskets' contents directly within the storage facility. After analysis of on-site facilities it was determined that the best-fitting location for spent fuel preparation and packing is the Physical Research Complex, which, however, would still require major upgrades to its shielded hot cell.
But the most difficult problem hampering large-scale removal of spent fuel from IPPE is the extremely unsatisfactory condition of railroads from the Obninskoye station to the Institute site. The rail¬road was out of operation for many years and became completely unusable. The situation was further exacerbated by the fact that the railroad crosses lands now owned by various unrelated organisations that are not interested in its restoration.
In order to de-fuel the IPPE on-site storage facility, a special process was developed that provides for the following operations to be performed:
– spent fuel inspection in the storage facility;
– retrieval of spent fuel baskets from the storage cells;
– loading of spent fuel basket into the on-site transport cask and transfer to the Physical Research Complex;
– spent fuel basket delivery to the shielded hot cell using a transfer cask;
– spent fuel packaging into canisters;
– spent fuel canisters loading into a TUK overpack.
In order to prepare the VM and AM spent fuel assemblies for shipment, dozens of equipment items and systems were designed, supplied and put into operation, including:
– televised systems for safe inspection of the contents of spent fuel storage cells and monitoring of technological processes in the Physical Research Complex shielded hot cell;
– four A201 manipulators by Walischmiller Engineering Gmbh for the Physical Research Complex shielded hot cell, which are more advanced and reliable as compared to the outdated M-22 manipulators;
– emergency alarm system to signal the occurrence of self-sus¬tained chain reaction in the Physical Research Complex shielded hot cell;
– auxiliary equipment to support safe transfer of shielded transfer cask across the Physical Research Complex central room and its placement on the shielded hot cell transfer gate;
– auxiliary equipment to support safe transfer of TUK-108/1 and TUK-19 overpacks across the Physical Research Complex cen¬tral room, as well as safe loading of spent fuel canisters into the overpacks (fig. 1);
– leaktight canisters for TUK-19 loading of mis-shaped and standard VM SFAs, and TUK-108/1 loading of AM SFA fuel rods;
– set of shielded hot cell equipment for processing of standard baskets, recovery of spent fuel, cutting the VM SFA headpieces to size, canister loading of VM SFAs and AM SFA fuel rods, as well as can¬ister sealing by lidding (fig. 2); the process is controlled remotely by personnel using electric and pneumatic drives from operator rooms;
– purpose-built semi-trailer for automobile transport of one TUK-108/1 in vertical orientation or a 20-foot container loaded with three TUK-19s.
In addition, the existing shielded transfer cask was upgraded.
Results of Federal Nuclear and Radiation Safety Programme implementation
In the course of activities to prepare for shipment and subsequently ship spent fuel from the IPPE site envisaged by the Federal Nuclear and Radiation Safety Programme, substantial progress was made during 2009-2012. Primarily, an inventory was made of spent fuel types that could be accepted and processed by Mayak without upgrading its existing technological processes. Some spent BN fuel was prepared for packaging, loaded into leaktight canisters and placed into temporary storage. In order to ensure delivery of empty TUK overpacks and spent fuel shipment from the IPPE on-site storage facility, the hardware for TUK-19 handling and transport was restored and upgraded.
Selected for a "pilot" shipment were some VM SFAs and all EK-10 SFAs. As the outer dimensions of the VM SFAs were too large to be loaded into the TUK-19, special equipment was developed, manufac¬tured and supplied to IPPE to cut the SFAs to size and load into sealed canisters. After obtaining all the necessary permits and justifications, the SFAs were loaded into 16 TUK-19 overpacks and in August 2011 (for the first time in 15 years) transported by truck to a reloading location and therefrom by rail to the reprocessing facility at Mayak.
As a result of performance of work under the government con¬tract entitled "Improvement of storage safety and preparation for shipment to reprocessing of irradiated research reactor fuel assem¬blies currently stored at IPPE (in Obninsk, Kaluga region)" it was dem¬onstrated that it is feasible to use heavyweight TUK-108/1 overpacks for shipment of large-size spent fuel (AM SFAs) without prior cutting through the fuel-containing region. A transport and handling process was developed for delivery of empty and shipment of loaded TUK-108/1 overpacks. It was demonstrated that regular spent fuel ship¬ments from the IPPE site using heavy overpacks will only be possible after restoration of the access railways. A survey of the railroads was performed to identify the scope of restoration work and a cost esti¬mate was put together.
Some of the spent fuel in storage was inspected. A batch of VM SFAs was selected for shipment from the IPPE loaded into 16 TUK-19 overpacks, and another batch of AM SFAs for loading into a single TUK-108/1 overpack. An empty TUK-108/1 overpack was delivered to IPPE, and the necessary equipment for its handling developed and fabricated. The selected baskets containing AM SFAs were delivered to the Physical Research Complex, spent fuel packaged into canisters and loaded into the TUK-108/1 overpack.
In order to support further shipments of spent fuel from the site, a methodology for identification of spent fuel in the baskets is to be developed and qualified, so that the fuel can be segregated by type and certified. For Mayak to be able to accept spent fuel that currently is not reprocessable, either new reprocessing technologies must be developed or long-term storage capability for that fuel provided. Once that is done, further large-scale shipments of spent nuclear fuel will become possible, eventually securing complete de-fuelling of the IPPE on-site storage facility.
Количество просмотров: 867