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:
rate can be predicted to within 10% of experimental data (Refs. 3, 7, and 8). The short-lived fission products contribute appreciably to the decay energy for decay times less than 10 seconds. Although consistent experimental data are not as numerous (Refs. 4 and 5) 3 and the results of various calculations differ, the effect of all uncertainties can be treated in the zero to 10 second time range by a suitably conservative multiplying factor. 3 B. BRANCH TECHNICAL POSITION161 1. Fission Product Decay For finite reactor operating time (t ) the fraction of operating power, o P/Po(t , t ), to be used for the fission product decay power at a time o s t after shutdown may be calculated as follows: s P Po (to,ts) (1 K) P Po ( ,ts) P Po ( ,to ts) DRAFT Rev. 3 - April 1996 9.2.5-14 (2) where: P/P = fraction of operating power o t = cumulative reactor operating time, seconds o t = time after shutdown, seconds s K = uncertainty factor; 0.2 for 0 t < 10 and 0.1 for 10 t 10 s s 3 3 7 A , a = fit coefficients having the following values: n n n A a (sec ) n n -1 1 0.5980 1.772 x 100 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% uncertainty