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3. FISSION PRODUCTS
Pages 31-68

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From page 31...
... The fission products from the defective fuel are released into the primary coolant, and some volatile species are subsequently released through the offgas system. The magnitude and composition of the released fission products depend on the size of the defect and the number of defective fuel rods in the core.
From page 32...
... (3-3) For iodine and noble gas isotopes, an average of
From page 33...
... Normally, thermal neutron fission of U-235 is used in calculation; however, in the case with high burnup fuel, contribution from Pu-239 should be considered. 3.~.2 Release of Fission Pro cluct from Defective Fuel into Reactor Coolant The one compartment model of volatile fission product released into the reactor coolant from defective fuel cladding is schematically described in Figure 3-l, ancl the release rate is derived as follows: where Ni dNi = Ri° - LiNi - ViNi - Bikini = inventory in fuel gap, atom Ri = F(p)
From page 35...
... 3.~.3 Release of Fission Products from Fuel Contaminant Even though the reactor core may contain no defective fuel, natural uranium contamination of core construction materials and Zircaloy cladding, as well as enriched uranium contamination of the external cladding surfaces, could be the source of fission products in the coolant during power operations. The recoil range of a fission product is approximately 10 microns; therefore, only the fissions that occur within =10 microns of the outer surface of the Zircaloy cladding can introduce fission products into the coolant.
From page 36...
... in contaminants, fission/s. 3.2 CHARACTERIZATION OF FISSION PRODUCT RELEASE PATTERNS IN BWR 3.2.1 Empirical Methods In the GE source term document,(~)
From page 37...
... is o / / 68-J~ 6£ L-ax 8£ L-ax [8-~N 88-J~ Ws8-J~ sS sax .___~__~ pP L-ay r 7 / i` o o o x 11 a: / 1, , , .
From page 38...
... Split cladding defect; activity release changes exponentially with power. The source term equations, Equation 3-12 or 3-13 can be directly related to the model calculations given in Section 3-1.
From page 39...
... It is also important to note that the release rate is proportional to the escape time constant, vi, in the equilibrium case. 3.2.2 Release of Noble Gas Activities The total activity in the offgas is a direct measure of the total noble gas fission product mixture released from the reactor core, and the analysis of radionuclide distribution of the noble gas fission product mixture is used to determine the specific mechanisms of the activity release.
From page 40...
... The recoil level of fission product release may be estimated by a number of techniques using the noble gas activirv data or the soluble fission product activities measured in reactor water. These techniques are briefly described and compared below: Technique Comment (2)
From page 41...
... to subtract the recoil fraction, since the value of Ri for recoil is identical for all fission products (Ri = Kr)
From page 42...
... Hi = decay constant of species i, ski. 'Bc = reactor water cleanup (RWCU)
From page 43...
... (3-~) The "true" recoil level is established from the cationic fission products in reactor water and the shorterlived noble gas activities.
From page 44...
... of a failed fuel rod from which the fission products are released.
From page 45...
... Calculated C~134 to C~137 Ratio in the fuel as a Function of Fuel Burnup 3-15
From page 46...
... The calculated release rates using U-235 fission yields for the major noble gas and halogen activities are given in Table 3-1. The steady state concentrations of fission product activities in water and steam systems vary from reactor to reactor, sometimes by two to three orders of magnitude, depending on the size of the fuel defect, the number of defective fuel rods in the core, and the capacity of reactor water cleanup system.
From page 47...
... Kr-87 1.37 h 2.0 x 104 1.5 x 104 Kr-88 2.84 h 2.0 x 104 1.8 x 104 Kr-89 3.15 m 1.3 x 105 1.8 x 102 Kr-90 32.3 s 2.8x 105 Kr-91 8.6 s 3.3x 105 Xe-133m 2.19 ~2.9 x 102 2.8 x 102 Xe-133 5.24 ~8.2 x 103 8.2 x 103 Xe-135m 15.3 m 2.6 x 104 6.9 x 103 Xe-135 9.1 h 2.2 x 104 2.2 x 104 Xe-137 3.82 m 1.5 x 105 6.7 x 102 Xe-138 14.1 m 8.9x104 2.1 x 104 Xe-139 39.7 s 2.8x105 Xe-140 13.6 s 3.0x105 Br-83 2.40 h 1.1 x 103 Br-84 31.8 m 4.3x103 I-131 8.04 c! 7.0 x 102 I-132 2.28 h 9/4x103 I-133 20.8 h 2.8x103 I-134 52.6 m 2.8x104 I-135 6.57 h 7.9 x 103 Total noble gases ~1.0 x 105 *
From page 48...
... 7) BwRa pwRb Nuclide Reactor Water Steam Reactor Water Seconciary Coolant Kr-85m Kr-85 Kr-87 Kr-~S Kr-89 Xe-133m I.0 0.004 3.3 3.3 21 0.049 Xe-133 - 1.4 Xe-135m - 4.4 Xe-135 - 3.8 Xe-137 - 26.
From page 49...
... As shown in Section 3.1.2, the activity release from failed fuel may be characterized by Equation 3-8. Depending on the magnitude of the escape time constant, v, Equation 3-8 can be simplified to Equations 3-9 and 3-10: Ai = F(p)
From page 50...
... , the steady-state activity release rate can be calculated from the measured activity concentration in the coolant by: Ai=CiW(\i+p) where Al = activity release rate from fuel, ,uCi/s or Bq/s Ci = activity concentration in the coolant, psi/kg or Bq/s W = reactor coolant mass, kg (excluding the pressurizer mass)
From page 51...
... inside the fuel and fuel gap, the activity concentration ratio increases from ~ 0.065 for the recoil source to ~ 0.2 or greater, depending on the nature and size of fuel defect. By using the measured I-131/I-133 concentration ratio in the coolant, the nature of the fuel defect may be characterized as follows: I-131/I-133 Concentration Ratio Defect Nature Comment <0.1 Possibly no defect 0.1-0.3 Open hole or large crack 0.3-0.~5 20.5 Small hole Pin hole or tight crack Release from tramp fuel or fuel contaminate Coolant in contact with fuel in cladding Release by diffusion Activity release in equilibrium with activity inside the fuel cladding 3-21
From page 52...
... 3.3.3 Estimation of the Number of Failer] Fuel Rods In spite of some suggested techniques to estimate the number of failed fuel rods, the most practical and accurate method is to compare the normalized I-131 concentration from failed fuel (total minus recoil)
From page 53...
... of I-134 comes from recoil sources. 3.3.4 Steacly-State Concentrations of Fission Product Activities In the Pro y Coolant The steady-state concentrations of fission product activities in the primary coolant vary from reactor to reactor, depending on the size of the fuel defect, the number of defective fuel rods in the core, and the capacity of letdown cleanup system.
From page 54...
... A detailed iodine-131 transport distribution in the steam/condensate and feedwater cycle measured at Brunswick-2, which has a forward-pumping system design (the high-pressure turbine condensate arid reheater drains are pumped back to the reactor via the feed wafer train without going through the condensate demineralizersystem) , are showninFigure3-~.~0)
From page 55...
... Iodine Carryover As A Function of Copper Ion Concentration in Feedwater 3-25 10
From page 57...
... 3.4.2 Fission Pro ducts In Me Secondary Coolant System In PWR it is obvious that the radioactiv~ties in the secondary system are the result of steam generator leakage. The standard concentrations of fission products in the reference PWR secondary coolant are given in Table 3-2.
From page 58...
... With the exception of noble gas and tritium activities, most of fission products are transported by the mechanical entrainment mechanism. This is also true for iodine species because of the basic and reducing nature in the secondary coolant chemistry.
From page 60...
... 3.5.1 Release Mechanisms Based on these observations, the mechanisms of fission product release during power transients are proposed as follows: (~) During power reduction, a portion of the fuel cools down, and the liquid water is forced into the defect fuel gap.
From page 61...
... (The total release of I-131 can be easily estimated from the I131 concentration in the coolant, the total mass of the coolant, and the coolant cleanup flow rate during reactor shutdown.) There is no direct relationship between the total release and the equilibrium release rate during normal operation (Figure 3-7~.
From page 63...
... Magnitude of I-131 Spike as a Function of the Ratio of Fission Gas to I-131 Release Rate During Power Operation in BWRs (Ref.
From page 64...
... . It should be noted that the correlation shown in Figure 3-8 may be qualitatively predicted by the measurement of six major noble gas release rates during normal operation.
From page 65...
... (3) American Nuclear Society, "Method for Calculating the Fractional Release of Volatile Fission Products from Oxide Fuel," ANSI/ANS-5.~1982.
From page 66...
... 2000 1 600 1 200 800 20 n 10-3 10-4 ,~5, z 10-3 O _ ~_ ~_ of ~_ an o 100 80 UJ 60 G o : 40 111 OF TEMPERATURE POWER \ \PRESSURE \ \ \ \ \ \ \ l I / J 10-5 L 1 1 1 1 1 1 2000 0 0400 0800 1200 1600 2000 2400 2/20 1 2/21 ~ CLOCK TIME Figure 3-9. Behavior of Cs Isotopes Spiking During Shutdown in a PWR (Ref.
From page 67...
... (8) Westinghouse Electric Corporation "Source Term Data for Westinghouse Pressurized Water Reactors," WCAP 8253, (May 1974~.


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