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:
iably to the decay energy for decay times less than 103 seconds. Although consistent experimental data are not as numerous (Refs. 4 and 5) and the results of various calculations differ, the effect of all uncertainties can be treated in the zero to 103 second time range by a suitably conservative multiplying factor. B. BRANCH TECHNICAL POSITION 1. Fission Product Decay For finite reactor operating time (t ) the fraction of operating power, o (to, tsar to be used for the fission product decay power at a time t after shutdown may be calculated as follows: n=11 E (m, ts = 1 AnexP(-ants) (1) rn1 go (to ) (1 +K) go (w' t ) go to+ tS (2)l Pao 0' ts Po s 5 Po 0 5 where: -= fraction of operating power to = cumulative reactor operating time, seconds tS = time after shutdown, seconds K = uncertainty factor; 0.2 for o < t5 C 103 and 0.1 for 103 < tS < 107 AnI an = fit coefficients having the following values: 9.2.5-8 Rev. 2 - July 1981 n An an (sec-1) 1. 0.5980 1.772 x 10° 2 1.6500 5.774 x 10-1 3 3.1000 6.743 x 10-2 4 3.8700 6.214 x 10-3 5 2.3300 4.739 x 10-4 6 1.2900 4.810 x 10-5 7 0.4620 5.344 x 10-6 8 0.3280 5.716 x 10-7 9 0.1700 1.036 x 10-7 10 0.0865 2.959 x 10-8 11 0.1140 7.585 x 10-10 The expressions for finite reactor operation may be used to calculate the decay energy from a complex operating history; however, in accident analysis a suitably conservative history should be used. For example, end-of-first- cycle calculations should assume continuous operation at full power for a full-cycle time period, and end-of-equilibrium-cycle calculations should assume appropriate fractions of the core to have operated continuously for multiple-cycle times. An operating history of 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% uncer- tainty factor (K) should be added for any cooling time less than 103 seconds, and a factor of 10% should be