OVERVIEW

CANSWEL2 was developed to calculate the deformation of Zircaloy cladding (clad ballooning) under postulated loss-of-coolant accident conditions (LOCA) in water reactors. Following initial application to SGHWR and Sizewell-B safety studies, it is continually being maintained to support current reactor safety analysis and design/interpretation of experimental facilities and their data over a wide range of conditions.

The code contains phenomenologically-based models for the key physical processes that drive the deformation of Zircaloy and Zr-based cladding under LOCA conditions. Well-proven relationships are used for the most important processes, with a library of material data for commonly used materials. The modular approach enables flexibility to treat additional cladding types through read-in mechanical and oxidation kinetics data or through bespoke variants of the overall code. Material used in PWR. BWR, CANDU and VVER reactors can be treated.

The code includes an efficient numerical solver giving fast run times coupled with a high degree of numerical stability. This speed of execution has enabled CANSWEL2 to be used as the deformation sub-model in reactor accident analysis codes where heat conduction and thermal hydraulic (TH) modules provide its boundary conditions automatically. The code has been tested on a wide variety of Unix and PC platforms.

CAPABILITIES

CANSWEL2 contains physical models for:

• Creep strain of Zircaloy in the alpha, beta and phase change regions (600?1300°C), given the clad pressure and temperature histories
• Two-dimensional (r,q) mechanical deformation to calculate the effect of azimuthal non-uniformities in temperature and clad thickness, and of interaction with neighbouring rods following mutual contact taking into account non-simultaneous burst
• Rupture of the cladding
• The alpha-to-beta phase change including hysteresis effects
• Oxidation of the Zircaloy metal and its feedback on creep rate and rupture strain, including effects of oxide cracking and re-oxidation of newly exposed metal.
• Coupling to TH Codes e.g. MABEL2

ASSESSMENT

The code has been assessed against a wide range of separate-effects and integral data, covering materials used in PWR, BWR and CANDU reactors:

• Single rod tube burst data from tests on cladding from many manufacturers
• Comparative burst tests in inert and oxidising atmospheres
• Rupture strain data in tests where azimuthal temperature profiles have been measured
• High temperature creep tests showing stabilisation of strain by oxidation
• Multi-rod burst tests demonstrating effect of mechanical restraint on the strain/channel flow area relationship
• Participation in OECD/CSNI International Standard Problems 14 (REBEKA-6) and 19 (Phebus-218) on LOCA code assessment.

APPLICATIONS

• Design of experiments where ballooning of Zr-based cladding is likely to be an important phenomenon
• Interpretation of experiments involving clad ballooning
• Benchmarking of simpler ballooning models in reactor systems analysis codes
• Assessment of clad ballooning effects in reactor transients from operational and safety perspectives.

Selected applications

Experimental Design

• Pre-test calculational support for the IFA-54X series in the OECD Halden Reactor Project to compare the effects of electric and nuclear heating on ballooning and channel blockage
• Assisting with definition of test protocols in the CORA early phase core degradation experiments at FZ Karlsruhe, followed by post-test data analysis
• Design studies for the CABRI water loop facility, where ballooning may occur in RIA transients.

Experimental Assessment

• Analysis of the EOLO-JR in-reactor ballooning tests at JRC Ispra
• Analysis of the NRU-MT3 in-reactor experiment which showed pellet/clad asymmetry as the dominant mechanism in reducing overall clad strain and hence subchannel blockage.

Benchmarking

• Assessment of the ballooning models in the USNRC FRAPT and SCDAP/RELAP5 codes

Reactor Applications

• Plant safety assessments in the Winfrith SGHWR pressure tube reactor
• Detailed analysis of reactor transients in support of the initial large break LOCA safety case for the Sizewell B PWR
• Assessment of the effect of choice of cladding materials on the LOCA safety case for reload fuel for Sizewell B.

AVAILABILITY

CANSWEL2 is available under licence from Serco Technical and Assurance Services as part of The ANSWERS Software Service set of codes, under which framework the code is maintained, supported and developed. In addition Serco Technical and Assurance Services experts have considerable experience in the application of CANSWEL2 to a variety of reactor safety studies, design of experimental facilities and analysis of data.

SUPPORT

In common with all ANSWERS products, CANSWEL2 users receive expert support (including a telephone hotline) in using the program and its application to new areas. Training in the use of CANSWEL2 can also be provided.

Contact us

Caroline Middlemas
T: 01305 851 191
F: 01305 851 105
E: caroline.middlemas@serco.com