Author's: Evgenii Krasikov
Pages: [53] - [63]
Received Date: November 30, 2015
Submitted by:
DOI: http://dx.doi.org/10.18642/jmseat_7100121589
Influence of neutron irradiation on reactor pressure vessel (RPV)
steel degradation are examined with reference to the possible reasons
of the substantial experimental data scatter and furthermore –
nonstandard (non-monotonous) and oscillatory embrittlement behaviour.
In our glance, this phenomenon may be explained by presence of the
wavelike recovering component in the embrittlement kinetics.
We suppose that the main factor affecting steel anomalous
embrittlement is fast neutron intensity (dose rate or flux), flux
effect manifestation depends on state-of-the-art fluence level. At low
fluencies radiation degradation has to exceed normative value, then
approaches to normative meaning and finally became sub normative. Data
on radiation damage change including through the ex-service RPVs
taking into account chemical factor, fast neutron fluence and neutron
flux were obtained and analyzed.
In our opinion controversy in the estimation on neutron flux on
radiation degradation impact may be explained by presence of the
wavelike component in the embrittlement kinetics. Therefore, flux
effect manifestation depends on fluence level. At low fluencies
radiation degradation has to exceed normative value, then approaches
to normative meaning and finally became sub normative. As a result of
dose rate effect manifestation peripheral RPV’s zones in some range
of fluencies have to be damaged to a large extent than situated
closely to core.
Moreover as a hypothesis, we suppose that at some stages of
irradiation damaged metal have to be partially restored by
irradiation, i.e., neutron bombardment. Nascent during irradiation
structure undergo occurring once or periodically transformation in a
direction both degradation and recovery of the initial properties.
According to our hypothesis at some stage(s) of metal structure
degradation neutron bombardment became recovering factor.
Self-recovering section of RPV steel radiation embrittlement kinetics
as indication of material intelligent behaviour. As a result
oscillation arise that in tern lead to enhanced data scatter. In this
case, we have to consider irradiation as a recovery factor.
For the sake of correctness, it is necessary to remember that there is
an example when contrary to the famous radiation embrittlement in
metals neutron irradiation at some range of fast neutron doses is in
position to improve both the strength and ductility of steel.
Foregoing hypothetical assumptions on “low-dose effects” in terms
“radiation embrittlement contains oscillatory component” and
“radiation annealing of the radiation embrittlement” is
questionable and needs additional experimental verification and
profound scientific study.
reactor pressure vessel, steel, self-recovering section, embrittlement kinetics, material intelligent behaviour.