Embrittlement correlation methods

Soneda N, Doi K, Nomoto A, Hishida K and Ishino S, Microstructural analysis of RPV materials and mechanism-guided embrittlement correlation method , ibid. Paper No. 19. 

Soneda N, Dohi K, Nomoto A, Nishida K and Ishino S (2010), Embrittlement correlation method for the Japanese reactor pressure vessel materials, Journal of ASTM International, 7, 3, West Conshohocken, PA. 

Embrittlement correlation methods to identify trends in embrittlement in reactor pressure... 

Abstract An embrittlement correlation method is a technique to calcnlate the expected amonnt of neutron irradiation embrittlement for the material of interest at a given time using the information on the material chemistry, irradiation conditions, etc. The first embrittlement correlation method was developed in the 1970s. Since then, different methods have been developed worldwide based on improved nnderstanding of the mechanisms of embrittlement and also on the enhanced snrveillance databases compiled in different countries. In this chapter, the history of the development of embrittlement correlation methods is reviewed first, followed by detailed descriptions of the representative methods together with their background. 

Key words embrittlement correlation method, transition temperature shift, surveillance database, chemical composition, irradiation condition. 

In this chapter, the history of embrittlement correlation methods will be reviewed hrst, followed by descriptions of the representative embrittlement correlation methods in different countries. In particular, the embrittlement correlation methods developed over the last several years are explained in detail. 

The development of embrittlement correlation methods is schematically illustrated in Rg. 11.1, where embrittlement correlation methods are very roughly classified into two groups as mentioned above statistically-based methods and mechanism-guided methods. Most of the embrittlement correlation methods authorized by the regulatory bodies are statistically-based, but the EONY model which is used in the US alternative PTS rule. 

Embrittlement correlation methods 339 where -A is a fitting coefficient which is a function of the product form ... 

In response to the development of the revised EWO embrittlement correlation method, detailed independent review was performed using both mechanistic and statistical bases. The results suggested that a more simplified version of the revised EWO correlation is also appropriate. Five parameters were removed from the mean correlation for simplification the three A parameters were reduced to a single value, the effect of P was removed from the SMD, the effect of flux-time (ft) was eliminated from the CRP fluence function and the long-time bias term was eliminated. This simplified version of the trend equation was approved in ASTM E 900-02. T e simplified version in ASTM E 900-02 follows the form of Eq. 11.4 using the terms SMD and CRP ... 

There are four main types of reactors in France CPO (900MWe), CPY (900MWe), P4 and P 4 (1300MWe) and N4 (1400MWe). The surveillance data from six CPO reactors and 26 CPY reactors as well as the test reactor data, including those obtained after the development of the FIS model, were used for the calibration of a new embrittlement correlation method. The surveillance database includes 139 pieces of base metal data, 130 weld metal data, 131 heat-affected zone (HAZ) data and 93 standard reference material (SRM) data, while the test reactor database contains 36 pieces of... 

More recently, new embrittlement correlation methods were developed for WWER-1000 by Margolin et al. ° and for WWER-440 by Ahlstrand et al. The general form of the embrittlement correlation method is written as ... 

Table 11.3 Coefficients of the revised embrittlement correlation method ...

Ortner performed a preliminary assessment of the recent embrittlement correlation methods with the WRD and the PLOTTER Tool. One of the findings in the assessment was that the goodness-of-fit of the existing embrittlement correlation methods for a limited range of data, for example low-Cu materials, depends on the national databases. Our understanding of the embrittlement mechanisms has been greatly improved to date. Nevertheless, there might be still some hidden parameters that cause a national database effect. Further discussions not only on known unkowns but also unknown unkowns are necessary. 

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