Document: NUREG-0800
Document ID: ec8e8c49-ea1e-4b46-a508-500ea11caad2
Document Type: srp
Title: ULTIMATE HEAT SINK
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0523/ML052350549.pdf
Revision Date: 2023-06
Chapter: 9
Section ID: 9.2.5
CFR Part: 
CFR Title: 

Content:
and is, therefore, acceptable. In calculating the fission produce decay energy, a 20% uncer- tainty factor (K) should be added for any cooling time less than 103 seconds, and a factor of 10% should be added for cooling times greater than 103 but less than 107 seconds. 2. -Heavy Element Decay Heat The decay heat generation due to the heavy elements U-239 and NP-239 may be calculated according to the following expressions (Ref. 6): P (U-239) = 2.28 x 10-3 C o25 [1 - exp(-4.91 x 10-4 to)] [exp(-4.91 x 10-4 tS)J (3) P0 0f25 P(N-239) P 2.17 x 10-3 Ca25 (4) Po Gf25 {1.007 E1 - exp(-3.41 x 10-6 to)] exp(-3.41 x 10-6 t5) 0.007 [1 - exp(-4.91 x 10-4 t )) exp(-4.91 x 1 0 -4 t )) 0 5 9.2.5-9. Rev. 2 - July 1981 where: P (U-239) = fraction of operating power due to U-239 Po P (N. -239) Po = fraction of operating power due to N P-239 to = cumulative reactor operating time, seconds ts ~ time after shutdown, seconds C = conversion ratio, atoms of Pu-239 produced per atom of U-235 consumed 25 = effective neutron absorption cross section of U-235 0f25 = effective neutron fission cross section of U-235 The product of the terms C * a 25 can be conservatively specified as 0.7. O'f 2 5 The nuclear parameters for energy production by the heavy elements U-239 and N P-239 are relatively well known. Therefore, the heavy element decay heat can be calculated with a conservatively estimated product term of C - 5 without applying any other uncertainty correction factor. af25 3. Figures 1, 2, and 3 give the residual decay heat release in terms of fractions of full reactor operating power based on a reasonably realis- tic reactor operating time of 16,000 hours. 9.2.5-10 Rev. 2 - July 1981 Sieet 1 of 3 * ... s. *  .i.-.I.;.I. - * . . .. -I - ... -.: -,-.*. -. - I  IL .11 IL *-F- - - - 1- . - @, . _1 .. .:. . ... . -I-I. II&... _ T .-- =.. --- -I --- f ---r---T--!-7rq . -. .I . i I _. , j .- i - _;l -- -t I-?_. _.7 * T.- 4.! L. _ ;' i; - - : i: ' Residual Decay Heat Release i Irimii' I *I. 4 .-