ML17340A641
| ML17340A641 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 12/12/1980 |
| From: | Hoenes G Battelle Memorial Institute, PACIFIC NORTHWEST NATION |
| To: | Pasedag W Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML17340A640 | List: |
| References | |
| NUDOCS 8101230566 | |
| Download: ML17340A641 (12) | |
Text
December 12, 1980
~ 1981 ROTP~S Pacific Northwest Laboratories P.O. Box 999 Richland, Washington U.S.A. 99352 Telephone f509)
Telex 15-2074 Malt Pasedag U.S. Nuclear Regulatory Commission Washington, DC 20555
Dear Walt:
This letter is in reference to our telephone conversations of November 26 and December 2, 1980, concer'ning the potential drop of a steam generator and the subsequent release of radioactive material.
Your assumption that 205 of the total activity in the steam generator (as calculated prior to decontamination) would be released is, in our view, highly conservative (i.e., it is an overestimate of what twould actually be released).
It is, however, the assumption used by PNL in the assessment for moving a Surry steam generator to Hanford.
We believe that the amount of activity released due to such an occurrence would be on the order of a few percent, certainly less than 105, of the amount on the tubes.
It is likely that some materia) might be removed from the tubesheet by abrasion during the fall, but the radioactive deposits would likely remain attached to the abraded metal..
Our conclusions are based pri-marily on the fact that-PMR corrosion.films are compact (or tightly adherent) and would not shake or break free during the postulated drop.
It is unlikely that the radioactive deposits would be easily released.
I am enclosing an article on deposits in primary systems.
For further infor-mation on decontamination, you may also wish to refer to NUREG/CR-0968, The Im act of Decontamination on LWR Radioactive Waste Treament S stems and to ppen
~x of N RE CR-59 now sn pu
~cation Ra lo o
>ca ssessment of Steam Generator Removal and Re lacement:
U date an Revision.
If you have further questions or need additional information, please call L. G..Faust (444-3613),
L.
D. Perrigo (444-9024) or me (444-3754).
Sincerely, G.
R.
Hoenes Associate Section Manager Dosimetry Technology Section Enclosure g 30Z200ggk,
ee a
C
~~ C~(
e 54.
Nature of deposits on BWR and PWR primary system surfaces,
relation to decontamination A. B. Johnson, Jr., B. Griggs and F. M. Kustas, Pacific Northwest Laboratories, and R. A. Shaw, Electric Power Research Institute BllR and PHR crud/oxide layers on out-of-core surfaces differ in composition and morphology'.
They also differ in response to decontamination reaqents.
imRODUCTIOli Investigations are underway in several countries to improve decontamination methods for nuclear reactor coolant systems.
An important aspect of those investigations is to better understand the compositions and morphologies of the radioactive deposits which must be removed from reactor coolant system surfaces during the decontamination.
2.
Studies have been sponsored by the'Electric Power Research Institute (EPRI) at'Battelle-llorthwest to investigate decontamination methods for boiling water (BMR) and pressurized water (PIJR) reactors.
The work has included detailed examination of radioactive films on specimens from components exposed in Bl<R and PllR reactor coolant systems.
This paper summarizes observa-tions-regarding characteristics of the radio-active films.
Details of reagent studies are given elsewhere (ref. 1-4,9).
Formation of radioactive de osits on reactor coolant s stem surfaces 3.
The need for decontamination of reactor coolant systems arises because radioactive deposits develop on out-of-core surfaces.
'numerous materials, including iron-base, nickel-
- base, cobalt-base and copper -base alloys,. release a fraction of their corrosion product to the reactor coolant.
The species are carried to the reactor core, undergo neutron activation and are re-dispersed to out-of-core locations.
The radioactive coolant-borne species are transported in both dissolved (ionic) and particulate forms 4.
Thus radioactive films on reactor coolant system surfaces arise from two sources:
oxide growth on the metallic surfaces; radioactive ions carried in the reactor coolant are incorporated into the growing oxide; deposition of radioactive particulates on the outer surface of the oxide.
5.
In sundry the rad'ioactive film is a
composite of the deposited crud layer and the growinq oxide on the metal substrate.
6.
The two factors which most stronoly influ-ence the types of films which form are:
the system materials; and the coolant system envi-ronment.
7.
The BllR and. Pl(R reactor coolant systems differ markedly in both materials and environ-ments.
The system characteristics are sumnarized in the BllR and PlfR sections, resoectively.
INVESTIGATION OF BNR DEPOSITS BWR reactor coolant s stem materials and env)ronment The princtnal materials in the RIIR reactor coolant system are:
Zircaloy fuel claddinn, stainless steel pipinq and reactor vessel clad-ding, and cobalt-base alloy (Stellite) hard-facing a'lloys.
Other deposit sources are:
corrosion products 'from the feedwater system (carbon steel and stainless steel);
and species which leak throunh the condensate deminerallzers.
For example, if.the condenser fs Admiralty brass, some zinc and copper carried, into the BMR reactor vessel will be, incorporated into deposits on reactor coolant system surfaces.(5) 9.
The BWR reactor coolant operates at 29D'C, near neutral oH.(normal range:
5.5 to 7.5).
Radiolysis nenerates dissolved oxyqen concen-trations of 0.1 to 0.5 opm (liquid phase).
Thus, deposits on B!iR system surfaces form under conditions which are svbstantially oxldizinq.
10.
The or incipal out-of-core material in BlfR reactor coolant systems is 304 stainless steel.*
The principal source of BHR specimens for this stvdy was 304 stainless steel recircvlation bypass pipe sections from the Vermont Yankee reactor:
Specimens from Hillstone 1 and Ouad Cities 1 reactors were examined for comparison.
/IX Fe, 18% Cr, 8".f(i, 2 in, 1% Si.
,0
~
~
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Ded.'Ontamiflat iOEE ll.
Selected examinations and analyses were conducted on the following types of specimens:
i>i ainu SEH/EOX inspection of the outer film surfaces, before and after reagent treatments; inspection of film cross-sections, before and after reagent treatments; inspection of particles separated from the film during or after reagent treatments, {particles deposited
.on filters or removed from the surface on tape);
inspection of the as-received film.
separated from the substrate by a methano'I-bromine treatment; inspection of particles removed by mechanical scraping.
12.
The scope of the paper permits no more than an overview of the results.
Nor hol ies and Com ositions of BMR fi'Ims Vermont ankee i ms.
A prominent feature surface is a shallow attack. at metal grain boundaries.
A similar attack is evident on archive specimens, suggesting that it was caused by post-fabrication pickling.
14.
The Vermont Yankee crud/oxide layer has four features, summarized in Table 1 and in Figure 1.
The Vermont Yankee fHm morphology was nore complex than films from the other two reactors.
In fact, the dual film structure on Hillstone and Quad Cities oipes apnears to be characteristic of films from several B'llRs.{5-8)
The Vermont Yankee and Hillstone 1 films dif-fered markedly in comnosi tion and morphologyn but the decontamina ion rates were very similar, (4) for example, in an I!EDTA/oxalic acid/citric acid reagent at 180'C.
In both cases, the compact inner film dissolved, while outer layers
- remained, detached but undissolved.
Apnroxi-mately 80 to 90% of the radioactivitY was removed, appearing'o correspond to dissolution of the compact inner layer.
15.
Activity removal from Duad Cities pipe specimens was less effective than for specimens from. the other two reactors.
The guad Cities surface film was superimposed on a rouqh metal surface.
having fissures up to 0.01 in.(250um) deep.(4,6),
As with the shallower (up to ~20um) fissures on other oipe surfaces.
the fissures appear to be a consequence of pre-service pickling.
The hypothesis that radioactive species are trapoed in the fissures is consis-tent with effects o'f ultrasonic vibration on pipe surfaces after decontamination.
About 285 of the residual activity was removed from the Ouad Cities specimen, while the corresnondinq fractions for Hillstone and Vermont Yankee were only 4" and 10", respectively.
Table I
Summary of. BNR Film Characteristics on 304 SS pipe IFeature
~Com os stion a)
A - Vermont Yankee Film Res onse to Reaqents b)
Superficial Particles
~1 to 10um Shroud
~0.lpm'hick Faceted Crystals c) 0.1 to lum Compact Oxide Layer up to 2um thick Fe Cr 85-93 3-7 Unknown 52 18 63-76 12-16 7'
22 5-8 1
9-19 Ni Cu Zn 1-2 1
2-4 Undissolved Dissolved or Mashed Away a
Undissolved - Detached Ilashed Away by Turbulence Dissolved Princinal source of activity B - Hillstone 1 Film(7)
Outer Layer Inner Layer C - Ouad Cities 1 Film(6) 86 7
6 61 11 25 t
1 t
3 Undissolved Dissolved Principal Source of activity IIR NR NR NR Undissolved Dissolved {Efficiency for radio-activity removal reduced by rouoh metal surface)
Outer Layer Inner Layer 90
,5 5
68 18 14 t
~ trace NR
= not reported EOX
= Energy Dispersive X-ray
~a Based on EBE analysis
- llot fully calibrated; percent metallic species norrmliaed to 1BB".
b)Based on exposure to EOTA, NTA, HEOTA, etc.
c)Based on analysis of particles detached by reagent treatments'
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1 Cross Section and Surface Views Pipe Specimens.
'~v ccc~n4 cg PK 4'4%A) A(
(SEM) -,Vermont'ankee BWR Recirculation Bypass I
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2 Cross Section and Surface Views '(SEH) - indian Point 2 PWR Steam Generator Tube Specimens.
275
11 I
I
o".t:nnt amain at ion 16.
Crystallographic analyses by X-ray di ffrac-tion suggested that the principal species on the BWR pipe surfaces are Fe203 and spinels of the type:
Nix Fe3 x04, with radioactive species sub-stituted at cation positions.
The Fe203 remains
.- after the decontamination, and some spinel species also were undissolved.
Studies by General Electric Co. (5-7) suggest that the species which dissolve are nickel ferrites (spinels).
The outer layer, which is higher in iron, remains undissolved.
Our experience suggests that the faceted crystals which do not dissolve are somewhat higher in Cr than the layer which does dissolve, but only mildly so (Table 1).
It is possible that the species higher in Cr are interspersed with a lower Cr species which disso'ives.
If so, the EDX analyses may not properly resolve the lower Cr species.
17.
In sugary, the BWR films respond favorably to common decontamination reagents (e.q.,
EDTAh HEDTA, NTA), most effective'ly when they are re-ducing.
The most important aspect of the decon-tamination appears to be dissolution of the compact layer adjacent to the metal surface.
This layer appears to incorporate a large frac-tion of the radioactivity (e.g.,60Co+2),
probably as metal cations which substitute into the spinel oxide lattice.
~18.
A relatively small fraction of the radio-activity is associated with.species not dis-solved by the decontamination (Fe203 and certain
- spinels, probably relatively high in substituted Cr).
- However, these detached particles (0. 1 to 10um) must be dealt with in a decontamination, by filtration and by assuring flow conditions which will not deposit the particles at unwanted locations.
INVESTIGATION OF PMR DEPOSITS PHR Primar S stem Materials and Environment 9.
e pr>nc>pa mater>a s in the PWR primary circuit are:
Zircaloy fuel cladding, Inconel-600 steam generator tubing and stainless steel piping, reactor vessel cladding; cobalt-base alloy hard-facing materials.
s 20.
The PWR primary coolant has additions of boric acid
(~200(} ppm B) and lithuim hydroxide (0.2 to 2.0 'ppm ILi).
Hydrogen is added to control oxygen at <0.01 ppm during operation.
While metals continue to oxidize, the system is substantially reducing.
The system temperature is 320-340'C.
21.
The principal out-of-core material in most PHR primary systems is Inconel-600 steam gener-ator tubing.
Tubing filmed in two PWR steam generators has been
- examined, by methods indi-cated for OllA films.
lhoroholo ies and Com ositions of PWR Films 22.
he surface of a PWR steam qenerator film had the following characteristics (Fig. 2):
a sparse population of large superficial particles; a layer of fine platlets; a network of dark grain boundaries.
Table 2 sunnarizes compositions of two PWR films, 23.
Fig.
2 also shows a cross'ection of a crud/oxide layer.
The layer thickness is ~0.5um.
Thin filaments of the layer protrude into the metal along what we shall see are grain boundaries.
24.
Confirmation that the film is keyino alonq' grain boundaries developed from treatments which separated the film from the base metal.
Figure 3 shows separated film flakes.
Location A is a
flake oriented to show the side adjacent to the metal.
The filaments embedded in the metal are now evident around the grain boundary contours.
Location B shows a flake oriented to show the coolant side.
25.
Responses of the PWR films to reanent treatments are still being investigated.
To,
- date, the following responses have been observed:
Decontamination occurs slowly in the common reagents (EDTA, HEDTA, NTA)(4)
Addition of H202 to EDTA caused only
/
temporary increases in decontamination rate(4)
Addition of reducing metal ions (e.ose Cr+2) caused Iapid increases in decontami-
.nation rate(4)
Certain oxidizing and reducing reagents dissolved the base metal, undercutting the film, removing it almost completely as flake-'like particles.
DISCUSSION Fd.
Our studies have clearly demonstrated that BHR and PWR films respond differently to common reagents sgch as EDTA, HEDTA and
- NTA, The BHR films are easier to decontaminate, Early in the studies we began to examine the questions:
Do BHR films, formed under oxidizing conditions, respond most effectively to reducing decontamination reagents7 Do PHR films, formed under "reducing" conditions, respond most effectively to oxidizing reagents?
27.
Responses of BMR films to decontamination were in line with the hypothesis:
oxidizing reaqents were not effective; reagent effective-ness increased with increasing reducing character.
28.
Beaker studies also suggested that reduc-tion processes promoted rapid decontamination.
BMR pipe specimens which included freshly-cut metal surfaces had higher decontamination rates than specimens where f)q exoosed metal was coated with si,licone.<
The observation sugqested that corrosion of the fresh metal produced electrons (e.qee Fe' Fe+
+ 2e) which were available for reduction of species in the radioactive film.
29.
The PMR films showed some mildly favorable responses to oxidizing reaqents, aqreeina with the hypothesis proposed above.
- However, the response was not dramatic.
In fact, the PMR films also have shown favorable resnonses to reducing conditions.
(4) 276
!I
~I II
Ril'sgl e
f Lm h
3000X
'Fig. 3A'rud/Oxide Flake Separated'.From Inconel-600 Steam Generator Tube IP2-3-7 During Decontam-ination Treatment at 180'C 2000X
,Fig.
38 Crud/Oxide Flake from IP2-3-7; Oriented to, Show Side Exposed to Reactor
'Coolant Table 2 - Sulmnary of PWR Film Characteristics on Feature
~tom ositiooa)
Fe Cr,Ni Inconel-600
'Si Zn Steam Generator Tubing:
Remarks
'1 2'0 3
Compact Layer detached 9
40 19'7 t
B - Tube I-4-30HL Superficial Particles 2ldm Compact Layer ~n a~
18-31 18-26 40-60 2-4'-2 31 26
'40 2
2.
Compact Layer detached 35 29 31 Compact Layer detached
'24 46 28 4
2 3
Film Removed by Scraping 29-34 25-27 36-38 3-7 1-2 A - Tube IP2 Superficial Particles 40-86 4-15 7-40'-5' 2 to '9lEm Compact Layer ~n aLtu ll 23 63 Compact Layer detached 14 55 18 See Fig. 2,.right-hand views Analysis of cross section, near film outer edge; base metal shine probable Separated, from base metal by'HEP/A/
OXALIC,acid reagent,,
120-150'C o
Separated from'base metal by HEDTA
-acid reagent, 180'C >)
Film up to 3pm thick; minimal base metal shine Film flakes separated from base metal by EDTA/H202 reagent at 180'C b)
Film flakes separated from base metal in methanol-Bromine at 25'C Some base metal possible appears minimal
-'" u normalized to 100..
Reagents also include boric acid and lithium hydroxide, character. istic of PWR system chemistries.
277
il
~ >
ry
Dccon twninntion 30.
On the hypothesis that the radioactive species are largely present at substitutional positions in the compact oxide, removal of the radioactivity appears to require partial or complete dissolution of the oxide, depending on
-- "- - the degree of activity reduction. required.
~ On--
this hypothesis, it does not appear possible to remove the radioactive species (e.g.,
60Co) by selective dissolution even though higher ratios of 60Co to removed film were observed.
This conclusjon also was reached by other investi-gators.<4)
- 31. It is important to minimize post-decontami-nation activity buildup. associated with corrosion of the decontaminated surfaces.
Our studies on oxidized laboratory specimens suggest that the post-reagent film growth at reactor temperatures was proportional to the amount, qf oxide dissolved during the reagent treatment.<9>
This suggests that modest DFs may leave some protective oxide. minimizing subsequent corrosion.
This supposition has not been confirmed on reactor specimens in our studies.
32.
The BWR films comprise Fe203 and a range of
- spinels, some soluble in cormen reagents; some insoluble.
The particulate species which remain undissolved after reagent treatments include Fe203 and certain spinels, apparently those with relatively high Cr contents
(~185).
- However, the major fraction of the radioactivity
.is soluble and therefore may be removed by ion exchange.
while particulates can be removed on filters,.
This technology has been demonstrated in dilute reagent gecontamination performed in Canadian reactors.0>)
33.
The PWg films 'comprise a variety of spinels and:oxides.<1>>
Our analyses indicate that the sparse population of superficial particles tend.
to be high in Fe, but have a wide range of compositions (Table 2).
The radioactive oxide layer is sometimes less than one micron thick, The relative insolubility in common reagents probably relates to the high Cr content (30-55K, Table 2).
- However, we have been able to achieve relatively effqctive decontaminations by metal ion reduction,<"~ or by both oxidizing and reducing reagents which undercut the film, resulting'in a large fraction of the-activity being removed as particulates.
DF Radiation Level Before Decontamination ad>at>on Leve fter Decontamination REFERENCES 1.
JOHNSON, A.B., Jr.,
GRIGGS B.,
REMARK J.F.
Investigation of Chemicals and Methods of Dilute Reagent Decontamination for Potential Application in Light Water Reactors.
Paper 32.
CORROSION/78,
- Houston, TX, Harch 6-10, 1978.
Available from NACE. P.O.
Box 218340,
- Houston, TX 77218.
2.
JOHNSON, A.B., Jr.,
GRIGGS B
, Comparison of Decontamination Characteristics of Films from BWR and PWR Primary Systems.
Paper
- 161, CORROSION/79, Atlanta, GA, Harch 12-16, 1979.
Available from NACE. (see above).
3.
JOHNSON, A.B., Jr.,
DILLON, R. L..
- GRIGGS, B,
REHARK, J.F.,
Investigation of Alternate Methods of Chemical Decontamination--Second Progress Report. January 1,
1977 to December 31,. 1977, BN-SA-703-2, Battelle Northwest, June 1978.
~
P
~
t t g
fl Ji i%' Mite ~ i
'L'
~
~ ~ ~IP
~ ~ ~at Pa 4.
JOHNSON, A.B., Jr.,
GRIGGS, B., DILLON, R.L.
Candidate Reagents for Activity Reduction in BWR and PWR Primary Systems.
Proceedinqs ANS Topical Heeting on Decontamination and Decommis-
- sioning, Sun Valley, ID. September 16-20.1979.
5.
BLOK, J.
Summary Report Water Chemistry Program Extension.
- Company, San Jose, CA, June 1977.
. 6.
ANSTINE, L.D.
BWR Decontamination and Corrosion Product Characterization.
NEOE-12665.
March 1977.
7.
- Characterization of Corrosion Products on Recirculation and Byoass Lines at Millstone l.
HP-949, Electric Power, Research Institute.
Project 819-1, December 1978 IWAHORI. T., MIZUNO T., and KOYAHA, H. Crud Composition on Heat Transfer Surface, Paper 37, CORROSION/78, Houston, TX, available from NACE (see ref.
1 above).
9.
A Study of Dilute Reagent Decontamination for Application in Boiling Water Reactors, NP-Electric Power Research Institute, Project 828-1, (to be published).
10.
LeSURF, J.E.
Water Chemistry of Nuclear Reactor Systems.
Proceedings of BNES Conference, Bournemouth, October 24-27, 1977.
- p. 426.
ll.
PETTIT, P.J.,
LeSURF. J.E.,
STEWART, W.B.,
STRICKERT, R.J.,
and VAUGHAN, S.B.,
Decontami-nation of the Douglas Point Reactor by the CAN-DECON,Process.
Paper 39.
CORROSION/78, Haugh 1978 (see Ref. 1).
12.
SHEE, J.L.
Dissolution Characteristics of Metal Oxides in Water Cooled Reactors.
Proceedings ANS Topical Meeting on Decontami-nation and Decommissioning, Sun Valley, ID.
September 16-20, 1979.
ACKNOWLEDGMENTS The 'fol,lowing have made siqnificant contributions to this study:
R.L. Dillon,. J.L. Daniel, J.E.
- Coleman, D.B. Mackey. and R,L. McDowell.
We are grateful to the Electric Power Research Institute,(EPRI) for permission to publish the results of this study.
- 278,
Vl +