著者

Tinoco Hernan Ahlinder Stefan Hedberg Peter

出版者

一般社団法人日本機械学会

雑誌

Proceedings of the ... International Conference on Nuclear Engineering. Book of abstracts : ICONE

巻号頁・発行日

vol.2007, no.15, pp."ICONE1510051-1"-"ICONE1510051-12", 2007-04-22

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A power uprate of Forsmark's Unit 3 from 109 % to 125 % will be implemented during the 2010 refuelling outage. This uprate implies an increase in gamma heating of the core shroud which could lead to temperatures higher than the design thickness-mean temperature, 300℃, according to ASME regulations. To estimate the temperature distribution in the core shroud, a CFD model of the core bypass has been developed using the commercial code CFX 5. The model consists of the core bypass, from the lower core support plate up to the core grid, and the upper plenum, limited from above by the core shroud cover including the steam separator inlets. The bypass flow enters the computational domain at the level of the core support plate. The two-phase core flow enters the computational domain at the level of the core grid where it entrains and merges with the bypass flow. Both flows have been estimated through the POLCA code. The conjugate heat transfer at the core shroud inner wall comprises the gamma heating from the core, considered as volume distributed heat sources, and subcooled boiling of the bypass flow. The effect of subcooled boiling has been taken care of by using the model by Kurul and Podowski. Using a conservative gamma heat source distribution, leads to local temperatures slightly higher than the design temperature, with a maximum thickness-mean temperature that exceeds the temperature limit by approximately 4℃. If a higher temperature limit is accepted, the ASME regulations are not fulfilled, but the consequence is a minor change in the design stress intensity value Sm according to ASME. Using a somewhat realistic gamma heat source distribution, the results show that the maximum thickness-mean temperature is well below the design temperature.