Radiochemistry in Nuclear Power Reactors (1996) / Chapter Skim
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4. ACTIVATED CORROSION PRODUCTS
4. ACTIVATED CORROSION PRODUCTS
Pages 69-112
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From page 69... ...
The activation cross sections and specific activities for some major corrosion products are given in Table 2-5 and Figure 2-12, respectively. The activated corrosion products are released from fuel surface deposits by erosion and spelling caused by hydraulic shear forces in some cases and by dissolution in other cases.
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From page 70... ...
Inner~yer ~3 Outer Layer 1 ~ Figure 41. Axial Distribution of Iron and Cobalt on Fuel Surface (Reproduced with Permission, J
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From page 71... ...
Axial Distribution of Ca-60 and Co-60 Specific Activity on Fuel Surface (Reproduced win Permission, I
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From page 72... ...
As shown in Figure 4-1, the activated corrosion products in the outer layer are only a small fraction of the total activities in the deposit. The specific activities in the inner layer are also generally higher, as expected, because of longer residence time on the cladding surface.
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From page 73... ...
~1~ J ~ ~ ` Sampling tube fuel rods go (a) During sampling sups clamps ~0 4 a{ _ ~ / /' - r ~ u rotary stone or nylon brush (b)
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From page 74... ...
=Pk.C.Q(l-e kt) Initially when W is small, W = P- C- Q -t L and the initial linear deposition rate W =P.c~Q L If k is large, and/or t is long, W may reach an equilibrium value, w=P.c.Q k L ~6 (~2)
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From page 75... ...
The release constant k may vary as a function of water flow velocity and the thickness and chemical composition of the crud deposit. A mathematical model has also been developed to describe the activation of corrosion products in the fuel deposits.
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From page 76... ...
t = time of irradiation (s) = decay constant (s-l)
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From page 77... ...
, the values of k and C are empirically determined for the activities in BWR fuel deposits (Table ~1~. Also given in Table 11 are estimated equilibrium specific activities for some common activated corrosion products.
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From page 78... ...
More recent data have shown much lower activity concentrations, as shown in Table 4-3, in which the activated corrosion products are determined as "soluble" and "insoluble" species separately. Table 4-1 EMPIRICAL RELEASE CONSTANTS AND EQUILIBRIUM SPECIFIC ACTIVITIES FOR ACTIVATION PRODUCTS IN BWR FUEL DEPOSITS Equilibrium Specific Nuclide k(dayl)
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From page 79... ...
100 ^ . _ 0.1 lo a/ 1.0 / / / / / / / / ~ ^ 400 o 800 TINE (days)
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From page 80... ...
b A reference PWR is a 3400 MWt PWR with U-tube steam generators.
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From page 81... ...
. Under normal operating conditions, among common activated corrosion products, only Fe-~5, and Fe-59 are found truly insoluble.+ They are all the nuclear reaction products of iron.
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From page 82... ...
The corrosion product deposit on the fuel cladding surfaces is known to have two distinguishable layers: the inner tenacious layer and the loosely attached outer layer. The characteristics of the deposit depend largely on the thickness of the deposit and the metallic elemental composition in the deposit (or metallic impurity level in reactor water)
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From page 83... ...
Percent Soluble Co-60 as a Function of Iron Concentration in Reactor Water
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From page 84... ...
A typical example of activated corrosion product spiking release during reactor shutdown is shown in Figure 16. 4.2.4 Corrosion Product Transport and Radiation Field Builclup In the Primary System The major radiation source in the BWR for personnel exposure during shutdown maintenance has been identified to be the activated corrosion products, mainly Co-60, deposited on the primary system walls.
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From page 85... ...
% OF I 1 00 500 80 400 60 300 40 200 20 1 00 o 0 1 1 1 10 1.0 ~ L OLUBLE | _ pit _ _: 1 0.1 1 1 1 1 1 1 1 1 1 1 1 1 1 HOUR 0 6 12 18 0 .6 12 18 0 6 12 18 0 6 12 REACTOR WATER TEMPERATURE \/o RATED POWER 11 1 1 1 1 1 1 1 1 ~ ' V DATE | ~5/21 - INSOLUBLE 5/22 - 1- 5/23 - 1- 5/24 Figure 46. Variation of Co-60 Concentration in Reactor Water During Shutdown ~7
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From page 87... ...
Table 44 AVERAGE RADIOISOTOPE CONCENTRATIONS ON BWR RECIRCULATION LINES (Reproduced w~ Permission, EPR]
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From page 88... ...
Table 4~5 CALCULATED DOSE RATE CONVERSION FACTORS FOR 20-28 IN O.D.
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From page 89... ...
._____________________-________ Base Metal . Out-of-Core&Piping Surfaces Corrosion ProductInput ~ -- -- -- SolubleCoand60CoTranspod Insoluble Fe,Coand60CoTranspod ~1 Neutron | Flux I ` In-core \ Materials \ RWCU | .
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From page 90... ...
The nature of the crud plays an important role in the rate of soluble species deposition. Some of the loosely attached deposit in the outer layer may be transformed into a tenacious layer on the fuel surface.
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From page 91... ...
The effects of key water chemistry parameters on the Co-60 deposition have been identified, and some major results are qualitatively summarized below: · The Co-60 activity buildup on as-received stainless steel samples under normal water chemistry conditions can be described by a simple logarithmic rate law. Prefilming the stainless steel surfaces under proper conditions has been shown to reduce the initial activity buildup (Figure ~9~.
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From page 92... ...
304 SS Samples Under Normal Water Chemistry Conditions. The curves represent the best fit of the data to a logarithmic rate law: A= RC In (kt+]
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From page 93... ...
Effects of Chemical Additives on Co-60 Deposition on Received 304 SS Samples Under Normal Water Chemistry Conditions t25
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From page 94... ...
0 500 1 000 1500 2000 EXPOSURE TIME (HOURS) Figure 111 Comparison of Co-60 Deposition on Received 304SS Samples Under Normal Water Chemistry Conditions with Metallic Ions at 15 ppb ~26
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From page 95... ...
Variation of Co-60 Deposition on 304SS Samples Changing from Normal to Hydrogen Water Chemistry ~27 5000
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From page 96... ...
More test results obtained under hydrogen water chemistry (HWC) conditions, detailed discussion on the reaction mechanisms, prefiIming techniques, and the oxide film characterization have been reported elsewhere.~7)
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From page 97... ...
4.3 ACTIVATED CORROSION PRODUCTS IN PWRs 4.3.! Deposition of Corrosion Products on Fuel Surfaces Unlike Bums, corrosion product deposition on fuel surfaces depends on the solubilities of crud which consists of mostly substituted nickel ferrite, NixFeyO4, where x+y=3 and x/v ~ 0.25.
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From page 98... ...
, it is worthwhile to use the well-known chemical properties of magnetite to qualitatively explain the transport behavior of corrosion product on the fuel surfaces. The dependence of solubility of magnetite on pH and temperature has been published by Sweaton and Baes (11)
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From page 99... ...
Typical Axial Power and Temperature Distribution in a PWR Core (Reproduced with Permission, EPRI NP4247, Ref.
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From page 100... ...
104 103 7 5 Ct Cat o Cat 6 102 to- 7 ~r UJ a: 2 an l 2 10° A \ \ \ \~ / l A \ \ 5 _ 2 _ = ~ - ~ _ ~ ~_ 5 ~ ~_, i__ ~ _ TOP _ _ A \ V' Figure 414. Relative Specific Crud Activity of Fuel Deposits (Reproduced with Permission, EPRI NP4246, Ref.
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From page 101... ...
NP-3463, Ref.8) Specific Activities in 1lCi/mg crud + is Co-58 Span Cr-51 Fe-59 Mn-54 Co-58 Co-60 Co-60 6X+18 15+4 18+3 215+40 15+4 15+1 A 6 NDa ND 30+8 916+858 27+9 37+35 5 52+26 13+5 17+5 211+51 14+8 16+2 7 50+6 12+1 18+3 226+24 12+2 19+3 B 6 65+11 16+5 24+6 261+46 15+2 17+3 5 71+9 13+2 20+2 301+19 14+1 21+2 7 35+8 10+3 16+5 198+61 8+1 24+4 C 5 25_1 6+1 10_1 136+15 6+1 25_6 Average 7 52_14 13+3 18_3 236+35 12_3 19_4 Average 6 65_10 16+7 27_5 613+668 21 _9 28+26 Average 5 57+22 11+5 17+4 239+79 12+4 21+5 Core Avg.
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From page 102... ...
60 C: Y 50 J o o in: Can m J o en A o 40 30 20 10 o -- ' 1 1 NEGATIVE TEMPERATURE COEFFICIENT OF SOLUBI LITY 250°C COO LANT TEMPERATURE 300°C \ FUEL SURFACE TEMPERATURE POSITIVE TEMPERATURE COEFFICIENT OF SOLUBI LITY 1 1 1 1 11111 1 300°C 250°C ~1~11111 1 1 11111.1]
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From page 103... ...
One must be cautious when the reactor coolant corrosion product data are evaluated. Problems in withdrawing representative samples from a PWR primary coolant through long sample lines are well reCogrlized.(lo~l2,l3)
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From page 104... ...
Table 4-~3 AVERAGE ACTIVITITES OF SELECTED NUCLIDES IN REACTOR COOLANTS FROM THE BEAVER VAT T BY AND TROJAN PLANTS (Activities in nCi/kg) (Reproduced win Permission, EPRI NP-3463, Ref.
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From page 106... ...
A review of the data obtained from the various out-of-core locations shows that the specific activity of the crud deposits varies, depending upon location and the base material. A comparison of the surface activity concentration on the piping, steam generator tubing, and fuel surfaces of a Westinghouse PWR plant is shown in Figure 4-17.
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From page 107... ...
Comparison of Unit Surface Activities at Three Different Locations and Materials of Construction (Reproduced with Permission, EPRI NP4246, Ref.
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From page 108... ...
33-5 / me,/ §10-2 _ ~ r . NODE 5 l PERMANENT IN-CORE CRUD l ¢2-5 IN-FLUX SYSTEM LEGEND NODE 10 STRUCTU RAL CORE COMPONENTS PARTICULATE TRANSPORT MOLECULAR TRANSPORT PARTICULATION PROCESS Figure 418.
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From page 109... ...
Measured Steam Generator Channel Head Dose Rates and Range of CORA Results (Reproduced with Permission, EPRI NP4246, Ref.
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From page 110... ...
Lin, et. al, "Corrosion Product Transport and Radiation Field Buildup Modeling in the BWR Primary System", 2nd Int.
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From page 111... ...
Cowan, "Effects of Hydrogen Water Chemistry on Radiation Field Buildup in BWRs", Internationai Conference on Chemistry in Water Reactors: Experience ancI New Developments, Vol. 1, 271 (April 2~27)
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