Radiochemistry in Nuclear Power Reactors (1996) / Chapter Skim
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6. RADIATION CHEMISTRY IN REACTOR COOLANT
6. RADIATION CHEMISTRY IN REACTOR COOLANT
Pages 125-142
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From page 125... ...
The radiation energy generated in the reactor core and absorbed in the coolant is mainly attributed to fast neutrons and gamma rays; the contributions from thermal neutron and beta particles are relatively small. The core average total neutron dose rate is estimated at 1.5 x 109 R/hr and the total gamma dose rate is estimated at 3.1 x 108 R/hr for a 50 W/cm3 power density standard plant.
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From page 126... ...
of dissolved hydrogen. it is known that the dose rates decrease as the distance from the core increases, and the fast neutron fluxes decrease faster than the gamma fluxes.
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From page 127... ...
In air-free water, all three radiolytic products reach steady state concentrations at ~200 Gy of total dose (Figures 6-1, A and B)
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From page 128... ...
Radiolytic Products in Water Radiolysis with 1 Gy/s Dose Rate (Reproduced with Permission, Radiochim.
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From page 129... ...
The variation of chemical yields with temperature is significant at reactor operating conditions, and the LET is probably the most important factor when one calculates the chemical yields from gamma rays (low LET) and fast neutron (high LET)
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From page 130... ...
It should be noted that the actual production rate in the BWR core may slightly vary due to differences in design and/or operating characteristics (e.g., core power density, steam void fraction, operating pressure, coolant flow rate, and impurity levels in the coolant)
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From page 131... ...
Radiolytic Gas Production Rates In BWRs (Ref.
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From page 132... ...
and the decrease in H2O2 concentration occurs finally because the overall rate of reactions which destroy H2O2 is faster than that of reactions which produce H2O2 including its radiolytic formation. For the recombination of H2 and O2, a balanced set of reactions can be written as: H2O ~ H + OH 2H2 + 20H ~2H2O + 2H O2 + H ~HO2 H + HO2 ~H2O2 H2O2 + H ~H2O + OH 2H2 + O2 ~2 H2O An example of a radiolysis model calculation for the suppression of dissolved O2 by surplus H2 in water at ambient temperature is shown in Figure ~3.
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From page 133... ...
8) Rate Constant o _ 1 _ 1 Chemical Reactions at 25 C (1 mole s ~ Activation Energy _ 1 K cal mole aq + 1.6 x 10 3.C e ~ + H ~ H 2.4 x 10 3.C e ~ + OH ~ OH ~ OH 2.0 x 10 3.C e q~ + H2O2 ~ OH + OH 1.3 x 10 3.G H + H ~ H2 1.0 x 10 3.0 eaq + HO2 ~ HO2 2.0 x 10 3.0 e ~ + O2 ~ O2- 1.9 x 10 3.0 2e ~ ~ 20H + H2 5.0 x 10 3.0 20H ~ H2O2 4.5 x 10 3.0 OH + HO2 ~ H2O + O2 1.2 x 10 3.0 OH O
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From page 134... ...
Depletion of O2 in Water by Irradiation in the Presence of Surplus H2. Dose Rate at 1 Gy/s (Reproduced with Permission, Radiochim.
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From page 135... ...
, the scavenging effect would significantly interrupt the radiolytic chain reactions. Table 6-3 EXAMPLES OF IMPURITY REACTION RATE CoNSTANTS(7)
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From page 136... ...
Hydrogen and Oxygen Concentrations in Steam as a Function of Hydrogen Concentration in Reactor Water ~12
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From page 137... ...
The equilibrium constant Keq is a strong function of the radiation field in the downcomer region.
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From page 138... ...
~ " . ~ , `6 ~"` ~, ~ `` in"" "" `` in"` "` ~, _ ~ `, 1 1 ~ `` Peach 80Mom-3 ~" 4 \> L O ~ ~ 00 ~ 000 Reck Hydrogen Conc.
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From page 139... ...
6.7 CHEMICAL EFFECTS OF RADIATION IN BWR COOLANT Radiolytic oxidation of impurities including corrosion products (CrO4=) fission products (IO3-, TcO4=, NpO2+)
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From page 140... ...
NO + OH HNO + OH 2NO + O2 HNO2 O2 + H2O 2NO2 NH + H2 ~ NH3 NO2 + H2O ~ HNO3 + HNO2 NO2 + OH ~ H++ NO3 It may be expected that under oxidizing conditions, more NOT and NOT will be formed. Even if ammonia is present in reactor water at low concentrations, ammonia will be converted to nitric acid in the reactor core under conditions of unsuppressed radiolysis of water,fl4~15 l6)
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From page 141... ...
A Study of Simulated Radiation Chemical Kinetics", Water Chemistry of Nuclear Reactor System 1, BNES, paper 33, 229 (1977~; private communication (1991~.
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From page 142... ...
R.J. Law, et al., "Suppression of Radiolytic Oxygen Pro(luced in a BWR by Feedwater Hydrogen Acldition," Water Chemistry of Nuclear Reactor System 3, BNBS Vol.
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