ML20077D067
| ML20077D067 | |
| Person / Time | |
|---|---|
| Site: | Oconee, Byron  |
| Issue date: | 11/15/1991 |
| From: | Fyfitch S, Ouellette C BABCOCK & WILCOX CO. |
| To: | |
| Shared Package | |
| ML19311B542 | List: |
| References | |
| 51-1206178-01, 51-1206178-01-R00, 51-1206178-1, 51-1206178-1-R, NUDOCS 9412070224 | |
| Download: ML20077D067 (10) | |
Text
-
I B&W Nuclear Technologies Non-Proprietary Information Document 51-12061780
" Boric Acid Corrosion of Oconee 1 Upper Tubesheet" l
l l
'7412070224 941209 FDR ADOCK 05000454 PDR
BWNr 204404 (1tm.
g gfgh h
ENGINEERfMG INFORMATION RECURD Document identifier 51 1206178-01 Title BORIC ACID CORROSION OF OCONEE UNIT 1 UPPER TUBESHEET PREPARED BY:
REVIEWED BY:
Name CA OUELLETTE Name S FYFITCH Signaturo d8. O Date //!/D9/
b Wr/M ON Signature Date
//'
/l Technical Manager Statement: Initials [
Reviewer is Independent.
Remarks:
This document presents the possible boric acid corrosion rate for the Oconee Unit I upper tubesheet exposed to reactor coolant as a result of a mis-drilled tubesheet hole.
It was concluded that the tubesheet is structurally sound and is acceptable for the next cycle of operation.
- This revision (01) is the NON-PROPRIETARY version of rev. O. *****
Page 1 of 10
51-1206178-01 1.0 Purpose.
The purpose of this document is to determine the expected boric acid corrosion rate (s) of an Oconee Unit I steam generator tubesheet exposed to reactor coolant.
2.0 Backaround During a steam generator tube removal operation at Oconee Unit 1, the upper tubesheet and cladding were inadvertently drilled to a maximum depth of 0.0805 inch into the tubesheet material. The maximum exposed area was determined by direct measurement and video estimation.
The tubesheet is made of a Mn-Mo-Ni allcy and is clad with Inconel.
In the steam generator design, the tubesheet material was clad to avoid exposure to reactor coolant; therefore, concerns with boric acid corrosion exist. This document will present other instances in which carbon and low alloy steels were exposed to reactor coolant and the resulting/ expected corrosion rates of these steels.
3.0 Corrosion of Carbon and Low Allov Steels Carbon and low alloy steels have been exposed to reactor coolant in several instances.
In the following sections, descriptions will be given of several of these occurrences and the correction or acceptance of each situation.
3.1 Boric Acid Corrosion Studies B&W Document 51-1200238-00' lists a number of events in which boric acid corrosion occurred as a result of coolant leakage.
Carbon and low alloy steel components, from the RV head to closure studs, have corroded from boric acid exposure at various leak rates.
Also, this document contains a summary of non-B&W research on the effects of boric acid corrosion on various materials.
See Table 1 for a summary of the non-B&W research data.
3.2 ANO-1 Pressurizer Level Tap A cracked and leaking pressurizer level tap nozzle at ANO-1 led to the exposure of the pressurizer material (carbon steel) to reactor coolant prior to the interim repair of the leaking nozzle.
In an analysis of the ANO-1 interim repair, the following information wa's provided with regard to the various types of corrosion:
Crevice corrosion is probably the most important consideration for the proposed interim fix. The environmental conditions in a crevice can, with time, become aggressive and cause local corrosion.
B&W has conducted several studies on the environmental effects of a Page 2 of 10
51-1206178J01 crevice condition in a pWR environment, particularly in the OTSG tube-tube sheet crevice.
Test results indicate that iron oxide formation, the result of low alloy tube sheet corrosion in the tube-tube sheet crevice, plugged the leak path of the intentionally damaged tube.
Under ambient conditions, the oxide became more tightly packed and appeared to more tightly plug the crevice.
In summary, our expectation is that minimal corrosion will occur in the level tap crevice.
It is also expected that plugging of the crevice wil.1 occur through the formation and deposition of iron oxides.
The gap between the new and old nozzles is expected to corrode somewhat, however, this should be limited to a few mils.
General corrosion will occur in the region between the end of the remaining portion of the level tap (old nozzle) and the new spool piece (new nozzle).
However, general corrosion is not believed to be as great a concern as crevice corrosion, and as shown above, crevice corrosion should be limited to a few mils.
Pittina corrosion may also occur in the base metal within the gapped region. However, the depth of this localized corrosion is similarly expected to be limited to a few mils.
Galvanic corrosion may occur when two different metals in contact are exposed to a conductive solution.
The larger the potential difference between the two metals, the greater is the likelihood of the occurrence of galvanic corrosion.
Low alloy steel is more anodic that Inconel and would, therefore, be subject to galvanic attack when coupled and exposed to reactor coolant.
In studies performed in support of the reactor vessel cladding damage at Yankee Rowe, where low alloy steel was gal /anically coupled to austenitic stainless steel, corrosion tests were conducted with A302 Grade B coupons and A302 Grade B coupons coupled to Type 304 stainless steel and exposed to a simusated PWR environment under deaerated conditions.
Both coupons exhibited similar corrosion rates. Low alloy steel coupons coupled to Inconel 600 would probably ev.hibit less corrosion since Inconel is less cathodic to low alloy steels that stainless steel, as based on relative positions in the electromotive series.
Other investigators have reported corrosion test results for galvanic corrosion between carbon and low alloy steels. Exposure of alloy steels coupled (welded) to stainless steels was carried out in near-neutral, high-purity water for 1000 hours0.0116 days <br />0.278 hours <br />0.00165 weeks <br />3.805e-4 months <br /> at about 546 F in steam, steam-water, saturated water, and subcooled water containing from 0.1 ppm to 15 ppm oxygen and 2 ppm hydrogen in the steam and i
steam-water mixture.
The chloride content of the water was less that 0.1 ppm.
- Visual, macroscopic, and metallographic investigations revealed no traces of galvanic, selective, or accelerated corrosion in or near weld zones of any of the welded specimens.
Other investigators similarly found no evidence of galvanic corrosion when they tested 5% chromium steel and Type 304 Page 3 of 10
51-1206178-01 stainless steel couples at 500'F for 85 days in water containing 3B ppm oxygen and 98 days in water containing 530 ppm oxygen.
In summary, galvanic corrosion is not expected to be a concern at ANO-1 using the proposed interim fix.
i Hydroaen embrittlement is the degradation of a material's properties due to hydrogen interaction / diffusion.
This type of embrittlement is observed most often in plastically deformed alloys in high pressure hydrogen environments and is characterized by loss of ductility and lowering of fracture stress.
Carbon and low alloy steels, in a high strength condition, are especially susceptible to t
hydrogen embrittlement.
Higher strength ferritic and martensitic stainless steels are also subject to hydrogen damage.
The Yankee Rowe reactor vessel and pressurizer have a unique type of cladding. The cladding is a sheet form of Type 304 stainless steel spot wolded to the SA-302B and SA302-B nickel-modified low alloy steel.
Both the reactor vessel and pressurizer have cladding defects. This resulted in extensive investigations on the potential effects of hydrogen on the base metal shells.
In the instance of the pressurizer, the defect was cracking that occurred at the cladding spot welds.
The cracks were postulated to penetrate into the shell material.
It was shown that even under the worst conditions, the hydrogen levels in the base material, at a crack tip, would be far too low to be of concern.
Since the ANO-1 pressurizer is a
- steel, hydrogen
+
embrittlement is even of less concern in consideration of its lower yield strength and hardenability.
Summary -- Only minimal corrosion of the ANO-1 shell material was expected to occur during short-term exposure to the steam space environment.
3.3 Erosion-t '*rosion Single-phase erosion-corrosion of piping is restricted to carbon steel piping components that are essentially free from significant alloying.
Small alloy additions, such as chromium and mol obviating the occurrence of erosion-corrosion.zbgenum, are significant in 4.0 Expected Corrosion Rate (s) of Oconee Unit 1 Steam Generator Tubesheet Based on the above information, the expected corrosion rates of the tubesheet material can be determined.
There are two conditions under which the tubesheet will be exposed:
(1) Operating condition -- high temperature, RCS fluid, low oxygen concentration (2) Shutdown condition -- low temperature, higher oxygen concentration, higher boron concentration.
In each of these conditions, based on the ANO-1 experience, the corrosion rate is expected to be low. For the operating condition, the temperature is high, and the tubesheet will be constantly wetted; thus leading to a Page 4 of 10
2 51-1206178 01 low corrosion rate on the order of a few mils over the cycle, or less than one mil per year (<1 mpy).
The shutdown condition is at a lower temperature and the environment is oxygenated. Corrosion of the tubesheet during shutdown is expected to be slightly higher that at operating j
condition, on the order of less than five mils per year (<5 mpy). A very conservative estimate would be 25 mpy. The alloy content of the tubesheet forging will aid in keeping the corrosion rate low.
5.0 Stress The subject configuration results from the removal of a very small amount of tubesheet base metal.
As discussed previously, corrosion occurring during the next fuel cycle may remove only a very small additional amount of base metal.
The structural adequacy of the tubesheet is justified by the design margin found in the stress report.
Additionally, there is 'a large margin available for cyclic loadings as indicated by the maximum cumulative usage factor.
It is obvious when considering the low number of cyclic loadings (transients) which will occur during the next fuel cycle, that the tubesheet cumulative usage factor will remain well within the code allowable.
Therefore, it is concluded that the tubesheet, with locally exposed base metal, is structurally adequate for operation during the next fuel cycle.
6.0 Conclusj_o.nl The estimates given in Section 4.0 (1.0 and 5.0 mpy for operating condition and shutdown condition, respectively) are based en the corrosion rates discussed above.
The methods of corrosion expected at the Oconee Unit 1 tubesheet will be similar to those expected in the ANO-1 pressurizer base metal.
Based on the above results, the state of the Oconee Unit I upper tubesheet is acceptable for the next cycle of operation.
Page 5 of 10
,m,.. r 51-1206III5(01 '
7.0 References 1.
Quellette, C.A., Modate of Boric Acid Corrosion Events, B&W Document 51-1200238-00, July 31, 1990.
2.
Jones, R., et al., Sinole Phase Erosion-Corrosion of Carbon Steel Pioina, Electric Power Research Institute, Palo Alto, CA, February, 19, 1987.
3.
- Bignold, G.J.,
et al.,
Erosion-Corrosion in Nuclear Steam Generators, CEGB-Report No. RD/L/N 133/80, Central Electricity Research Laboratories, Surrey, England, January, 1981.
f Page 6 of 10
TABLE I (Ref. S)
BCelC ACID CORROS!ON 04T4 06TAINED 8t WOW-85W #EsEARCN Esposure solution Test Corrosion Test fine Chemistry Flow Tesperature Rate Notes Materlat (hours)
(gpn)
Rete
('F)
(irtf yr)
SA-193 e7 500 1000 8 es M 80 0.05 och 15 0.833 55 flature; 3 3 (Cr-Mo ettoy) et 600 F Ref. 3s 350 0.431 SA 540 823 Ctens 4 500 1000 B as H 80 0.05 SFh 175 0.815 ss fixture; 3 3 (Cr-Ni-Mo at toy) at 600 F Re f, 3, 350 0.841 sA 540 824 Class 3 500 1000 8 as M 80 0.05 och 175 0.265 ss fiature; 3 3 (Cr-Ni-Mo alloy) at 600 F g,y, 3, 300 0.722 350 1.29 400 1.69 SA-540 324 Ctess 3 500 1000 5 es N 80 0.05 gm 1 75 0.66 Low alloy steel flature; 3 3 (Cr-Ni-Mc alloy) at 600 F Ref. JJ 350 0.664 Cr-lon Isplanted 500 1000 e as H 90 0.05 oph 175 1.542 tow ettov eteet fixture; 3 3 tow alloy steet at 600'F Ref. 31 Tiu plasma coated 500 1000 e as M so 0.05 sph 175 0.753 Low alter steet fixture; 3 3 low attoy steet et 600 F Ref. St E m t coated 500 1000 s as M 80 0.05 sph 175 2.032 tow attoy steel flature; 3 3 tow attoy steet et 600 F Ref
'At solid Film ttbricated 503 1000 t es 6: 50 0.05 sph 1 75 1.65 tow attny steel fixture; 3 3 tow alloy steet et 600'F Ref. s i SA 533 Grace 3 70 T23 8 as H 50 W/A 350 0.0171 seeker test; 3 3 1.8 Ll; 0.4 N H, 7
Ref. D SA 504 Ctmes 2 70 723 8 es it e0 N/A 350 0.0168 seeker test; s 3 t3 1.8 Ll; 0.C W H m
os 31
)
Ref.27-143 s
O N
N O
O M
~
O o
w
^
TABLE 1 (CONTINUED)
BORIC ACfD CORROSION DATA 08TAlwED Bf WOW-81W RESEARCN Esposure Solution Test Corrosion Test time Cheelstry Flow Teeperature aste Notes pe:eriet (hours)
(gn)
Rete
('F)
(In/yr)
SA-508/sA 533 wetd 70 723 e es N a0 N/A 350 0.0161 ceeker test; g 3 1.8 ti; 0.C N N y1 Ref. 21 sr.533 crede a 392.5 1000 8 es H 80 0.05 0.02 650 0.9660 capitlery sagtes; 3 3 et 600 F opo 1.1626 corros!an rete la meeleue for 0.8106 test; 1.C414 Ref. I?
369.0 1000 8 ea H BO 0.1010.02 650 1.0683 3 3 et 600 F ope 0.9359 392.5 1000 B es N 80 0.05 0.02 650 0.5580 Deposit seaptes; 1
3 3 et 600 F opa not heated 0.3571 Ref. 27 650 0.5133 not heated 0.3794 369.0 1000 a et H 80 0.10 0.02 650 0.5698 3 3 at 600'F 9p=
0.6172 SA106 Grade s 4
79,400 8 es M,80, w/A 220 7.25 Seeker test; Ref.17 6
26,200 8 es M,80, N/A 220 1.63 27 26,200 e se M,80, N/A 220 0.396 24 22,000 8 es H,80, W/A 220 0.752 96 22,000 s es M EO, N/A 220 0.241 t
SA533 Grade 5 6
26,200 3 es H,90, N/A 220 1.416 Seeker test; 27 26 200 s se M so, w/A 220 0.305 g
y 24 22c000 e se H 90, N/A 220 0.651 t
y 96 22.000 3 es N s0, w/A 220 0.358 us g
~
<a CD ws f'O C3 O
th o
N a>
wo b
TABLE I (CONTINUED)
BORIC ".CID CORROSION DATA OSTAlWED BY WOW-58W RESEARCH Esposure Sott.:lon Test Corrosion Test time Chemistry Flow Temperature Rete gotes Heteriet (hours)
(pgn)
Rete
('F)
(Iri/yr)
A193 Grade BT T1.5 4,000 e as H,80 352 0.05 Ref. t 7
72.5 4,000 s as M so, 352 0.042 y
24.33 4,000 s es n,80, 212 0.432 23.3 4,000 9 as H,80, 212 0.124 71.5 H,80,* LION to pH T.3 352 0.054 72.5 H,80 +LiOH to pH T.3 352 0.046 3
24.33 H,80,+ LION to pH T.3 212 0.112 24.75 H,80,+ LION to pH 7.3 212 0.125 T4.67 M BO +LiOH to pH T.3 212 y i 146.67 H,Ba + LION to pH 7.3 212 0.118 i
146.67 H so + LION to pH 7.3 212 0.13 s s 74.67 H 50 *L10H to pH 7.3 212 0.126
_3 3
m m
m
- o Oo, Y
Om
=b
- o e
v,,. -.-,.
=
r TABLE I (CONTINUED) 60RIC ACID Contosl0N DATA cetAINED 8f Wres-88W RESEAACM Esposure solution test Corrosion Test Time Chemistry Flow fe v reture Rate Notes Meteriet (hours)
(ppe)
Rate
( F)
(In/yr)
SA508 Ctese 2 6
26,200 e es n,n3 w/A 220 0.911 seeker teet:
u Ref. 21 27 26,200 s es M,80, w/A 220 0.214 24 22,000 8 as N,00t N/A 220 0.519 96 22,000 s se M 90, N/A 220 0.238 t
A-4135 336 8,750 e es M 90, 70 0.0055 Ref, f s
672 8,750 e as N so 70 0.0041 3 3 0.0042 336 22,750 s se M so 140 0.029 3 3 0.0303 672 22,750 e as N 80 140 0.025 3 3 0.028 336 8,750 e es M 80, 70 0.000024 3
- KOM to pn 7.3 0.000011 1344 5,750 8 as N 80 70
- 0. M 33 3 g
- KOM to pH 7.3 0.000031 336 22,750 e as N 80 140 0.000011 g 3
+ KOM to pH 7.3 0.C000092 672 22,750 e as H 90 140 0.00024 3 3
- KOM to pH f.3 0.000049 1344 22,750 e es N B0 140 0.0034 g 3
+ KOM to pH 7.3 0.0038 A 4130 71.58 4,000 e es M 80 600 0.0256 Ref. 9 3 3 0.0279 t:
0.0254 ut 0.0219 7
a e-.
O O
O i e-e M
- y.
O O
w
.