Abstract The wet storage building of the nuclear power plant Gosgen/Daniken, a 3002 MWth pressurized water reactor, is the first building for the long term wet storage of spent nuclear fuel in Switzerland. Due to the Swiss moratorium against the export of spent nuclear fuel in 2006 and the non-availability of a nuclear repository it was necessary to store the spent fuel locally at the nuclear power plant site. The prolongation of this moratorium in 2016 does not allow reprocessing of spent nuclear fuel in the next years. As a direct conclusion from this moratorium it was decided to build a wet storage pool at Gosgen/Daniken which entered operation in 2008 with a capacity of 504 fuel assemblies. In a second stage of completion another 504 fuel assemblies can be stored in the pool. Two cooling towers will be available for the passive cooling of the wet storage pool with a maximum cooling capacity of 1.5 MW after the second stage of completion. In this wet storage pool only spent nuclear fuel elements will be stored, which have been stored before more than four years in an at reactor spent fuel pool. This means that the nuclear heat of a single 15x15 rod nuclear fuel assembly (FA) used in the NPP Gosgen is at 1.6 kW maximum, when it is stored in the wet storage pool. The present work describes postulated severe accidents with total loss of cooling in the wet storage pool (WSP) of the Gosgen/Daniken nuclear power plant. The accident progression in a spent fuel pool and even more in a wet storage pool is very slow due to the low nuclear decay heat. Therefore the investigation of such kind of accident was not assumed to be of high importance for a long time. The overall accepted assumption of an energy recovery after at least 24 h would not lead to boiling of a spent fuel pool due to the low decay heat. The severe accident in Fukushima Daiichi (2011.03.11) following the great Eastern earthquake and the related tsunami has shown that the power recovery can be delayed much longer, e.g. for more than a week. This long time of loss of cooling could endanger a spent fuel pool especially if the whole core is unloaded into the pool like in Fukushima Daiichi unit 4. Main goal of the work is to achieve information about the timing of postulated severe accidents in the wet storage pool and to define time frames for accident management measures to prevent fuel damage and fission product release. In every of the calculations more than three weeks passes before fuel uncovery would lead to fission product release.

中文翻译：

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NPP Gösgen/Däniken 湿式蓄水池失冷事故计算

摘要 Gosgen/Daniken核电站湿式储存建筑是一座3002 MWth压水反应堆，是瑞士第一座乏核燃料长期湿式储存建筑。由于瑞士于 2006 年暂停出口乏核燃料，并且没有核储存库，因此有必要将乏燃料储存在当地的核电厂现场。2016 年这一暂停期的延长不允许在未来几年对乏核燃料进行后处理。作为暂停的直接结论，决定在 Gosgen/Daniken 建造一个湿式储存池，该池于 2008 年投入运营，容量为 504 个燃料组件。在完成的第二阶段，另外 504 个燃料组件可以储存在水池中。二期工程建成后，将有两座冷却塔用于湿蓄水池的被动冷却，最大冷却能力为1.5兆瓦。在这个湿式储存池中，只会储存乏核燃料元件，这些元件已经在反应堆乏燃料池中储存了四年多。这意味着在 NPP Gosgen 中使用的单个 15x15 棒状核燃料组件 (FA) 的核热在储存在湿蓄水池中时最大为 1.6 kW。目前的工作描述了 Gosgen/Daniken 核电站湿式蓄水池 (WSP) 冷却完全丧失的假设严重事故。由于较低的核衰变热，乏燃料池中的事故进展，甚至在湿式储存池中的事故进展都非常缓慢。因此，在很长一段时间内，对此类事故的调查并未被认为具有高度重要性。由于衰变热低，因此至少 24 小时后能量回收的总体公认假设不会导致乏燃料池沸腾。福岛第一核电站（2011.03.11）在东部大地震和相关海啸之后发生的严重事故表明，电力恢复可以延迟更长的时间，例如超过一周。这种长时间的冷却损失可能危及乏燃料池，特别是如果整个堆芯像福岛第一核电站 4 那样被卸载到池中。 这项工作的主要目标是获得关于湿库中假定严重事故发生时间的信息并确定事故管理措施的时间框架，以防止燃料损坏和裂变产物释放。