Delayed Hydride Cracking (DHC) of Zirconium Alloy Fuel Cladding

Closed for proposals

Project Type

Coordinated Research Project

Project Code




Approved Date

23 February 2005



Start Date

1 March 2005

Expected End Date

31 December 2009

Completed Date

23 September 2009


The major goal of the this CRP is to develop experimental procedures for the reproducible measurements of delayed hydride cracking velocity of zirconium alloy cladding tubes so that consistent procedures and interpretations are achieved to allow a meaningful exchange of results between the participating laboratories. In this process, input data for the validation of predictive models of delayed hydride cracking in zirconium alloys will be collected. A secondary but equally important objective would be to provide technology transfer al the laboratory level from the host laboratory and supervisory group of the CRP to the participating Institutes in developing Member States. This CRP will be aimed at the transfer of "know-how", especially in those areas where qualitative and subjective interpretations of results are required.

Specific objectives

The main purpose of the CRP is to develop and validate reproducible experimental procedures through round-robin tests carried out by the participating laboratories. The specific objectives of this CRP has been to assess the suitability of PLT test technique to measure cracking velocity during DHC in Zircaloy fuel cladding materials. The specific research objectives are the following:
• to measure crack growth rate in samples with standard geometry containing a known amount of hydrogen;
• to collect all the input data from the participants for a better understanding of secondary failures in zirconium alloy cladding;
• to contribute to the understanding of the mechanism of delayed hydride cracking in zirconium alloys by comparing the results obtained from the planned CRP and the former CRP.


The CRP participants have benefited from the transfer of advanced Delayed Hydride Cracking (DHC) velocity measurement techniques, as well as from round robin testing and cross-examination of selected Zr alloy fuel cladding materials. The transfer of knowledge and coordinated research improved considerably experimental capabilities in the participating laboratories. As a result of the joint studies a very consistent set of statistically valuable DHC data has been generated, that contributed to better understanding of mechanisms of hydrogen-induced degradation of Zr materials.


Zr alloys are the most important structural materials used in water reactors due to their low capture cross-section for thermal neutrons, combined with good mechanical and corrosion properties. But in the unavoidable presence of hydrogen these properties can degrade due to embrittlement. Under definite circumstances a time-dependent mechanism of DHC can occur. That is why it is of technological importance to evaluate the flaw tolerance capability in core zirconium alloy components as a function of hydrogen content, temperature and operating conditions. The evaluation of crack growth behaviour is needed for the assessment of the cladding integrity, but the experimental methodology is very sensitive to a number of parameters, which are difficult to control. So at the initial stage of the CRP an advanced technique of crack velocity measurement was selected (PLT: Pin-Loading Test, developed in Studsvic, Sweden), and afterwards transferred to participating laboratories through a series of round robin exercises. Those experimental arrangements allowed to harmonize the experimental procedures and to produce consistent sets of data, both within a single laboratory and between different laboratories.

CRP Publications


Proceedings of ASTM Zr Symposium-2010


In press , to appear in ASTM STP/Journal of ASTM international)


The Effect of Microstructure on Delayed Hydride Cracking Behaviour in Zircaloy-4 Fuel Cladding - An IAEA Coordinated Research Programme


China, Chengdu


Proceedings of WRFPM-2008


January 2009


Delayed Hydride cracking in Zircaloy Fuel Cladding - An IAEA Coordinated Research Programme, Nuclear Engineering and Technology, Vol.41, 2009, pp171-178


Rep. of Korea, Seoul

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