Document: NUREG-0800
Document ID: 74415b71-98a0-4109-9ba7-8a72a89a3d18
Document Type: srp
Title: ULTIMATE HEAT SINK
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0520/ML052070520.pdf
Revision Date: 2023-06
Chapter: 9
Section ID: 9.2.5
CFR Part: 
CFR Title: 

Content:
f 16,000 hours is considered to be representative of many end-of-first or equilibrium cycle conditions and is, therefore, acceptable. In calculating the fission produce decay energy, a 20% uncertainty factor (K) should be added for any cooling time less than 10 seconds, and a factor of 10% should be added for cooling times greater than 10 but less than 3 3 10 seconds. 7 P(U 239) Po 2.28x10 3C 25 f25 [1 e 4.91x10 4to][e 4.91x10 4ts] P(U 239) Po 2.17x10 3C 25 f25 [1.007(1 e 3.41x10 6to)(e 3.41x10 6ts) 0.007(1 e 4.91x10 4to)(e 4.91x10 4ts)] 9.2.5-15 DRAFT Rev. 3 - April 1996 (3) (4) 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): 62 where: P (U-239)/Po = fraction of operating power due to U-239 P (Np-239)/Po = fraction of operating power due to Np-239 t = cumulative reactor operating time, seconds o t = time after shutdown, seconds s C = conversion ratio, atoms of Pu-239 produced per atom of U-235 consumed = effective neutron absorption cross section of U-235 25 = effective neutron fission cross section of U-235 f25 The product of the terms C / can be conservatively specified 25 f25 as 0.7. The nuclear parameters for energy production by the heavy elements U-239 and Np-239 are relatively well known. Therefore, the heavy element decay heat can be calculated with a conservatively estimated product term of C / without applying any other 25 f25 uncertainty correction factor. DRAFT Rev. 3 - April 1996 9.2.5-16 3. Figures 1, 2, and 3 give the residual decay heat release in terms of fractions of full 63 reactor operating power based on a reasonably realistic reactor operating time of 16,000 hours. 9.2.5-17 DRAFT Rev. 3 - April 1996 DRAFT Rev. 3 - April 1996 9.2.5-18 9.2.5-19 DRAFT Rev. 3 - April 1996 DRAFT Rev. 3 - April 1996 9.2.5-20 C. REFERENCES 1. J. F. Perkins and R. W. King, "Energy Release From the Decay of Fission Products, Nuclear Science and