L - KTH

50 C.J. VV'OOD
4.9 Materials tested (Table 4)
Emphasis on austenltlc alloys is due to the fact that about 95% of BNR and about 15% of
PNR metal surface is constructed of 300 series stainless steel. Inconel 600 is predominant
in PNR steam generators where decontamination has been exclusively applled to date.
Nickel-based alloys ere used in other critical applications, such as internal support welds
(Inconel 82/182), Jet pump end fuel spacer components (Inconel X-750) in BNRs and spllt
pins in PNRs. Vessel nozzles and shell in BNRs as well as vessel shell in PWRs are made of
A533, and carbon-low alloy piping is prevalent in BNR reclrculatlon systems. A
comprehensive llst of materlals comprising BNR components was compiled in reference (13)
which must be considered when e full system chemical decontamination is contemplated.
4.10 Corrosion testln~
Gordon (34) has summarized the results of GE testing as follows. A fuller account is
given by Walker (16).
To date, indications of good performance have been observed in the test programs with
LOMI end in post-decontaminatlon service. The test data indicate that general corrosion
rates during decontamination processing are low for both eustenltic end ferritlc materials
(less than 0. I ~m/h and less than I ~m/h, respectively) (29). No IGA or IGSCC has been
observed to occur during decontamination. Constant extension rate tensile test (CERT),
crack growth and pipe tests conducted in a BWR environment using decontaminated specimens
generally indicate no acceleration in crack growth rates or predisposition towards
accelerated crack initiation as a result of LOMI exposure. For this particular test
program, the only statistically significant deleterious effect of LOMI occurred on the
crack growth rate of Alloy 182 (30). However, this crack growth rate is still typical for
non-decontamlnated Alloy 182 in nominal BNR environments.
To date, indications of good performance have been observed for stainless steels with
NP/LOMI but test results for some materials that may be contained in the reactor vessel
annulus (low alloy steels) have not been as positive. Addltlonelly, other materlels which
are in pump and valve components (e.g., brass end Cu-Ni alloys) may be adversely
affected. General corrosion rates during decontamination processing are low for both
eustenltlc end ferrltlc alloys. The data available for stress corrosion performance of
Type 304 stainless steel are essentially good, although early isolated instances of shallow
IGA in sensitized U-bends of Alloy 600 end shallow IGSCC in one U-bend of welded Type
316L/321SS (one out of nine specimens) are noted. More recently, an NP/LOMI treated crack
growth specimen of A508 Low Alloy Steel exhibited accelerated crack growth in a simulated
BNR environment test, relative to growth rates for reference (untreated) specimens.
Exposure of NP/LOMI to A508 low alloy steel (e.g., feedweter nozzles) should be avoided.
Since feedwater nozzles ere located high up in the reactor vessel, avoiding exposure of
these components is practical.
Various types of general/locallzed corrosion tests have been performed in AP/LOMI
decontamination solutlons (31). Some (0.25 pm) general corrosion has been noted on Type
410 stainless steel after 24 hours of testing. Corroslmeter data on Alloy 600, Type 304
stainless steel and carbon steel revealed no corrosion during a Surry steam generator
decontamination. Some isolated shallow pitting (4 pm) but no IGA were noted on both
furnace sensitized end solution heated Type 304 stalnless steel exposed to LOMI and
AP/LOMI. Studies at Battelle Pacific Northwest Laboratories (15), on various U-bend end
tensile specimens of Type 304 stalnless steel and Alloy 600 revealed no increased
propensities for IGA or IGSCC. Recently studies on AP/LOMI decontaminated highly-
irradiated mill annealed Type 304 stainless steel revealed no corrosion attack in the
presence or absence of crevices or any adverse effect on IGSCC resistance (32).
Crack growth tests on Type 304 stainless steel compact tension specimens indicated no
statistically significant deleterious effect of oxalic acld/cltric ecld/EDTA reagents with
ferric ion control.* However, accelerated crack growth was observed with Alloy 600, Alloy
182 and AI06 carbon steel specimens exposed to these reagents end subsequently tested in e
simulated BNR environment. Also, exposure of an A508 low alloy steel specimen, albeit
early in the ferric ion control development process end possibly under conditions of
galvanic coupling, also resulted in such severe general corrosion that the specimen could
not be tested. No acceleration of crack growth behavior was noted on Type 304 stainless
steel specimens exposed the same reagents wlthan AP preoxldatlon step (30). No corrosion
*Discussion of ferric ion control is given in Reference 14.