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Melt agglomeration influence on ex-vessel debris bed coolability
KTH, School of Engineering Sciences (SCI), Physics, Nuclear Power Safety.ORCID iD: 0000-0002-0683-9136
2016 (English)In: 17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2017, Association for Computing Machinery (ACM), 2016Conference paper, Published paper (Refereed)
Abstract [en]

A deep pool of water below reactor vessel is employed in some light water reactors in order to arrest the core melt progression in case of severe accident. The melt is expected to fragment and quench in the pool. Coolability of a porous debris bed in a water pool is considered in this work, with emphasis on the effect of agglomerates formed due to incomplete fragmentation of a melt jet, or incomplete freezing of melt particles reaching the debris bed. Agglomerates block the escape paths for vapor generated in the debris bed, increasing resistance to coolant flow and facilitating occurrence of dry zones. Numerical simulations are carried out by DECOSIM multiphase code. Two main types of debris bed inhomogeneity due to agglomeration are considered: (i) solid impermeable “cake” on the debris bed top, and (ii) distributed low-permeability low-porosity zone with properties determined according to prediction of an agglomeration model. In the presence of either type of flow obstruction, dryout occurs at significantly lower decay heat power than in the case of homogeneous non- agglomerated debris. There is a critical agglomeration fraction above which a large dry zone develops in the debris bed. Debris temperature escalates in the dry zone leading to subsequent remelting of the material. On the contrary, below the critical agglomeration fraction, the dry zone temperature is stabilized by vapor cooling. Implications of the obtained results for assessment of severe accident risks are discussed.

Place, publisher, year, edition, pages
Association for Computing Machinery (ACM), 2016.
Keywords [en]
Agglomeration, Coolability, Debris bed, Dryout, Severe accident
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-234526Scopus ID: 2-s2.0-85052513029OAI: oai:DiVA.org:kth-234526DiVA, id: diva2:1246464
Conference
17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, NURETH 2017, Qujiang Int'l Conference CenterXi'an, Shaanxi, China, 3 September 2017 through 8 September 2017
Note

QC 20180907

Available from: 2018-09-07 Created: 2018-09-07 Last updated: 2018-09-07Bibliographically approved

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