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After successful completion of the MCCI Project at Argonne National Laboratory (ANL), a second project using the same ANL facilities was set-up. The MCCI-2 program was carried out from 2006 to early 2010 to help bridge data gaps not fully covered in MCCI-1. Testing falls into four categories:
Combined effect tests to investigate the interplay of different cooling mechanisms and to provide data for model development and code assessment.
Tests to investigate the effectiveness ofnew design features that enhance debris coolability.
Tests to generate additional 2-D core-concrete interaction data for model development
and code validation.
Integral test at larger scale to confirm synergistic effect of different cooling mechanisms and to provide data for validation of severe accident codes.
Aside from these tests, a supporting analysis task was carried out to further develop/validate debris coolability models that form the basis for extrapolating the experiment findings to plant conditions. In total, 10 tests were conducted in this program (all successful).
Four category 1 tests were performed using the Small Scale Water Ingression and Crust Strength (SSWICS) apparatus. Tests were conducted to provide additional crust strength data to confirm the concept of a floating crust boundary condition at plant scale and to investigate the effect of gas sparging on water ingression cooling of corium. Crust strength tests (2) showed that the strength of un-sectioned crust samples was consistent with that of the sectioned specimens tested in MCCI-1. Gas sparging tests (2) showed that the presence of sparging significantly increases the cooling rate of a solidifying corium pool over that observed when sparging is absent.
Category 2 tests to examine the effectiveness of design features for augmenting coolability, i.e. melt stabilization concepts, were of two cooling types:
Water-Cooled Basemat test (WCB-1) addressed cooling with external water-cooled surface(s)
SSWICS-12 and -13 tests addressed water ingress into the melt volume by fragmentation
Category 3 tests were to provide additional 2-D core-concrete interaction data. CCI tests in both the MCCI and French VULCANO facilities have shown a marked dependence of cavity erosion behaviour on concrete type. Tests with limestone/common sand (LCS) concrete generally exhibit a radial/axial power split of ~1; conversely, siliceous tests exhibit splits that are significantly greater than 1. CCI-4 conducted with LCS concrete, but with increased metal content (structural + cladding) to evaluate effect on cavity erosion behaviour. CCI-5 conduced with siliceous concrete, but the apparatus was modified to increase lateral scale to diminish wall effects to the greatest extent possible. Test aspect ratio (cavity width/melt depth) increased from 1 to 3.7.
Category 4 was an integral test to validate severe accident codes. The large scale CCI-6 test was conducted with early flooding to focus on debris coolability. Key features were:
70 cm x 70 cm cross section, 28 cm melt depth: 900 kg (63/25/6/6 wt % UO2/ZrO2/Cr/concrete).
Cavity flooded ~ 1 minute after melt contact with basemat.
Design incorporated an embedded array of water injection nozzles at a depth of 27.5 cm into the concrete. If debris did not quench, then a second test phase would be initiated to provide additional (Category 2) data on bottom water injection cooling. Results demonstrated that: i) early cavity flooding significantly enhances debris coolability, even for siliceous concrete, and ii) melt eruptions are a viable cooling mechanism for siliceous concrete. Test terminated on the basis of debris quench well before water injection nozzles were reached.
A concluding Seminar of the MCCI2 project was held in Cadarache, France, from 15 to 17 November 2010.
Project participants: Belgium, Czech Republic, Finland, France, Germany, Hungary, Japan, Norway, Republic of Korea, Spain, Sweden, Switzerland and the United States.
Project period: April 2006 to December 2009
Project Management: US Nuclear Regulatory Commission (USNRC)
The distribution of this package is restricted and subject to prior approval.
For more detailed information visit http://www.oecd-nea.org/jointproj/mcci-2.html
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M. T. Farmer, S. Lomperski, R. W. Aeschliimann, and D. J. Kilsdonk: A Summary of the CCI-4 Reactor Material Experiment Investigating the Effect of Metal Content on 2-D Cavity Erosion Behaviour, ANS Annual Meeting, Hollywood, Florida, June 26-30, 2011
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Keywords: core concrete interactions, experiment, nuclear reactor safety, reactor materials, severe accidents.