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Leakage testing during lateral displacement of metallic seals under mechanical accident impact
(2013)
In context with approval design tests, the IAEA regulations for the safe transport of radioactive material specify tests for demonstrating ability to withstand normal and accident conditions of transport. For 9-m drop test onto an unyielding target the drop orientation of the package must be chosen in a manner so that maximum damage occurs with regard to the safety criteria.
With respect to leak tightness after drop test impacts a horizontal or slap-down orientated test model can cause a lateral displacement of the packaging’s lids, affecting the leakage rate of the closure lid system strongly.
In Germany dual purpose casks with double lid sealing system composed of primary and secondary lid with bolts, metallic seals as well as cask body sealing surfaces are mainly used. Besides free drop tests with full-scale and half-scale models within licensing approval procedure BAM develops experimental testing methods to simulate defined stresses and deformations by means of components testing.
In order to investigate the relation between lateral lid displacement and leakage rate, BAM performs impact tests with small scaled flange-lid systems of transport packages in a drop test machine for guided drop tests.
The test setup is realized in a way that the flange part is fixed while a drop weight is impacting onto the lid’s edge. The dynamic displacement of the lid is measured simultaneously. Because of capturing the drop weight after first impact during a short rebound phase by pneumatic arrest mechanism a secondary impact on lid’s edge is excluded. The guided drop tests were accompanied by various measurements such as leakage rate recording during and after impact, identification of lateral shifting by electro-optical displacement transducer as well as decelerations of the lid and the impacting weight.
This paper describes the test setup, the test and measurement techniques as well as first results concerning the relation between lateral lid displacement and leaktightness.
The shut-down of eight nuclear power plants and the phase out of the nuclear energy generation in Germany, due to a decision of the German government after the Fukushima accident, has rapidly forced the need for transportation and storage of spent nuclear fuel (SNF) from shut-down reactors in this country. In accordance with the present strategy in Germany, which
is characterized by searching for appropriate final repository areas, only the dry interim storage facilities are available for storage nuclear waste of the decommissioned plants as well as the operating plants. Therefore, the transportation and the storage casks must be available for both types of light water reactors. But for the time being this is the bottleneck. Unfortunately the prognoses are neglecting the fact, that such a high number of casks are needed in a very short space of time. This requires the acceleration of formal activeness in relation to the licenses but also an increase of the production. In the meanwhile to get this process started, the only possibility is the storage in the pools at the plant site. Anyway, for the time being, this is one of the problems for dismantling the eight plants which have been shut down due to the decision of the Government, which is now fixed in the last amended German Atomic Energy Act dated 24th of February 2012. Starting to dismantle in the radioactive regions of the plants requires empty pools. For emptying the pools of damaged SNF special procedures regarding the transportation and storage are necessary. The transportation of damaged SNF requires special casks or at least special procedures and therefore also a special licenses.
This paper describes the challenge for the management in transportation and storage of SNF in Germany after the shut-down of the nuclear power plants by reason of the Fukushima accident.
This will is a report from an expert working in this field since 1978, participating in PATRAM conferences since 1980. Exactly in that year 1978 the development and testing of the CASTOR casks started in Germany, with the intention to use these transport casks for interim storage of spent fuel. After involvement in the first full-scale drop tests of those large spent fuel casks for transport package design approval, the official assessment as storage cask started. At the beginning of that new decommissioning technology a series of storage demonstration programs were conducted; most interesting were cases where a cask was loaded in a NPP with fuel assemblies instrumented with thermocouples, equipped with a first lid penetrated by instrumentation cables, closed by a second lid, transported to a research institute and stored there for 2 years, with verification of maximum cladding temperatures and leak-tight closure. In 1982 the basis BAM expert reports for the licensing of CASTOR casks in away-from-reactor storage sites Gorleben and Ahaus were finished. The first cask loading for interim storage was performed in Switzerland in 1983; that CASTOR Ic-Diorit cask, 30 years of age, is the “grandfather” of all dual purpose casks. In 1984, a remarkable transport accident happened, the sinking of the “Mont-Louis” with 30 48-Y-UF6 containers; BAM shortly before had issued the approval for a tank container that could be used for the recovery of some these UF6 containers. The 90s saw the full-scale drop tests with the POLLUX multipurpose cask design ( for transport, interim storage, final disposal), drop test series with new transport packages for fresh fuel assemblies including the “French puncture drop”, finally a spectacular BLEVE blast onto a CASTOR cask. 2004 we were proud to host the PATRAM conference, the second time in Berlin. For the Technical Tours BAM performed drop tests with two full scale SNF casks (the largest ones tested world-wide) at our new 200 t drop test facility. In the meantime a lot of other assessment experience, e.g. in ductile iron brittle fracture, numerical calculations, radwaste disposal container testing etc. was stacked. Changes in safety assessment methodology over the last decades will briefly be addressed.
For interim storage of spent fuel or HLW in many countries transport casks are used. The design of these “dual purpose casks” has to be assessed and approved to transport regulations (based on IAEA SSR-6), and to be assessed within the storage facility licensing procedure. Although the transport cask design differs from the storage cask design, e.g. by use of impact limiters, the majority of cask components is identical for both. Differences occur also in the acceptance criteria; these are for the transport case defined in IAEA SSR-6, and have to be developed for the storage case based on the storage conditions. Considering transport after several decades of storage requires the implementation of ageing behavior into the transport safety case. Additionally the transport package design safety case has to be maintained in an up-to-date state, considering potential regulatory changes and development of scientific and technical knowledge. The review of a transport package design safety case has to be done periodically, implemented in periodic re-assessment for extension of the package design approval certificate. The review process (as a kind of “intellectual periodic inspection”) should be part of the approved applicant’s management system.
From experience we have seen that stability of regulatory requirements for Type B(U) packages was not a major problem, but consideration of ageing and developments regarding the state-of-the-art technology can cause necessary adjustments of specific technical evaluation, with the result of confirmation of package safety, or with the development of appropriate compensatory measures to reach the required level of safety. This paper will draw some examples from the past to explain the problems in periodic transport safety case reviews.
Spent nuclear fuel is generated from the operation of nuclear reactors and needs to be safely managed following its removal from reactor cores. Spent nuclear fuels are usually stored in a reactor pool for a short period of time after defueling, and then they are shipped to its next destination for reprocessing, disposal, or further storage. In some countries, a concept of Dual Purpose Cask (DPC) is considered as an attractive option
for further storage. This is because of that the concept increases flexibility for storage capacity, as well as its economic efficiency that can reduce the complexity of handling highly radioactive spent fuels.
The management of spent fuel using a DPC involves storage of spent fuel as well as on-site and off-site transportation before and after storage. Most countries require package design approval for the DPC to be transported. In addition, it is required in many countries to have a license for storage of the spent fuel in the DPC or a license for a storage facility that contains DPCs. Therefore, demonstration of compliance of the DPC with national and international transport regulations as well as with the storage requirements is necessary.
In June 2010, the IAEA organized “International Conference on Management of Spent Fuel from Nuclear Power Reactors”. In this conference, many countries expressed their interest on harmonizing both transport and storage safety cases for DPCs that has a possibility to establish an effective and integrated regulatory framework in a holistic manner.
Taking into account the increasing needs among Member States, the IAEA set up a new working group following the conference to discuss how to develop an integrated safety case for both transportation and storage.This activity is planned to be completed in 2013. Currently, a technical report is being prepared as an outcome of this activity.
In this paper, the IAEA’s approach to demonstrate the safety of DPCs in a holistic manner is described first, followed by the overview of the draft document. It also presents the difference between the conventional transport cask concept and the DPC concept.
German approach and experience feedback of transport ability of SNF packages after interim storage
(2013)
In Germany the concept of dry interim storage of spent fuel in dual purpose metal casks is implemented, currently for periods of up to 40 years.
The casks being used have an approved package design in accordance with the international transport regulations. The license for dry storage is granted on the German Atomic Energy Act with respect to the recently revised “Guidelines for dry interim storage of irradiated fuel assemblies and heat-generating radioactive waste in casks” by the German Waste management Commission (ESK).
For transport on public routes between or after long term interim storage periods, it has to be ensured that the transport and storage casks fulfil the specifications of the transport approval or other sufficient properties which satisfy the proofs for the compliance of the safety objectives at that time.
In recent years the validation period of transport approval certificates for manufactured, loaded and stored packages were discussed among authorities and applicants. A case dependant system of 3, 5 and 10 years was established. There are consequences for the safety cases in the Package Design Safety Report including evaluation of long term behavior of components and specific operating procedures of the package.
Present research and knowledge concerning the long term behavior of transport and storage cask components have to be consulted as well as experiences from interim cask storage operations. Challenges in the safety assessment are e.g. the behavior of aged metal and elastomeric gaskets under IAEA test conditions to ensure that the results of drop tests can be transferred to the compliance of the safety objectives at the time of transport after the interim storage period.
In context with new cask designs and their approval procedure, the experimental testing of impact limiters under drop test conditions becomes more and more important in order to assess the damage mechanics behaviour and safety margins for validation reasons. In recent years, various designs of impact limiters have been tested by the Federal Institute for Materials Research and Testing within specific component testing and particularly with regard to type B package design approval procedures. The paper focuses on the experimental realisation of impact limiter tests and presents implemented measurement techniques to determine the amount of deformation and to explain the impact behaviour by means of photogrammetric metrology and three-dimensional fringe projection method, high speed motion analysis and adjusted deceleration measurements.
In context with new cask designs and their approval procedure the experimental testing of impact limiters under drop test conditions becomes more and more important in order to assess the damage mechanics behavior and safety margins for validation reasons.
In recent years various designs of impact limiters have been tested by the Federal Institute for Materials Research and Testing (BAM) within specific component testing and particularly with regard to type B package design approval procedures.
The paper focuses on the experimental realization of impact limiter tests and presents implemented measurement techniques to determine the amount of deformation and to explain the impact behavior by means of photogrammetric metrology and 3-d fringe projection method, high-speed motion analysis and adjusted deceleration measurements.
Im Zuge des Rückbaus kerntechnischer Anlagen in Deutschland müssen u. a. Großkomponenten (Dampferzeuger, Reaktordruckbehälter) über öffentliche Verkehrswege in Zwischenlager transportiert werden, in denen sie zerlegt bzw. zwischengelagert werden. Für diese Versandstücke ist eine mechanische Integritätsbewertung, nach den Vorschriften der Internationalen Atomenergie-Organisation (IAEO), notwendig, die in der Regel unter dem Einsatz einer komplexen numerischen Berechnung erfolgt.
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In the course of decommissioning of power plants in Germany large nuclear components (steam generator, reactor pressure vessel) must be transported over public traffic routes to interim storage facilities, where they are dismantled or stored temporarily. For these packages a safety evaluation considering the International Atomic Energy Agency (IAEA) transport regulations is necessary, preferably by a complex numerical analysis.