Document: NRC Regulatory Guide
Document ID: 4d46a966-d280-43da-9b03-8b0abe7b29ce
Document Type: regulatory_guide
Title: Alternative Radiological Source Terms for Evaluating Design Basis Accidents at Nuclear Power Reactors (Rev. 1)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2120/ML21204A065.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.183
CFR Part: 
CFR Title: 

Content:
03 0.54 0.543 Alkali Metals 0.003 0.14 0.143 Tellurium Metals 0.003 0.39 0.393 Barium, Strontium 0.00 0.005 0.005 Noble Metals 0.00 2.70x10-3 2.70x10-3 Cerium Group 0.00 1.6x10-7 1.60x10-7 Lanthanides 0.00 2.00x10-7 2.00x10-7 Molybdenum 0.00 0.03 0.03 Table 2. PWR Core Inventory Fraction Released into Containment Atmosphere Group Gap Release Phase Early In-Vessel Phase Total Noble Gases 0.022 0.94 0.962 Halogens 0.007 0.37 0.377 Alkali Metals 0.005 0.23 0.235 Tellurium Metals 0.007 0.30 0.307 Barium, Strontium 1.40x10-3 4.0x10-3 5.4x10-3 Noble Metals 0.00 6.00x10-3 6.00x10-3 Cerium Group 0.00 1.50x10-7 1.50x10-7 Lanthanides 0.00 1.50x10-7 1.50x10-7 Molybdenum 0.00 0.10 0.10 DG-1389, Page 21 Table 3. BWR Steady-State Fission Product Release Fractions Residing in the Fuel Rod Plenum and Gap Group Fraction I-131 0.03 I-132 0.03 Kr-85 0.32 Other Noble Gases 0.03 Other Halogens 0.02 Alkali Metals 0.16 Table 4. PWR Steady-State Fission Product Release Fractions Residing in the Fuel Rod Plenum and Gap Group Fraction I-131 0.07 I-132 0.07 Kr-85 0.40 Other Noble Gases 0.06 Other Halogens 0.04 Alkali Metals 0.20 Figure 1. Maximum Allowable Power Operating Envelope for Steady-State Release Fractions DG-1389, Page 22 3.3 Timing of Release Phases Table 5 provides the onset and duration of each sequential release phase for LOCA DBAs. The specified onset is the time following the initiation of the accident (i.e., time = 0). The early in-vessel release phase immediately follows the gap release phase. The activity released from the core during each release phase should be modeled as increasing in a linear fashion over the duration of the phase.11 For non-LOCA DBAs in which fuel damage is projected, the release from the fuel gap and the fuel pellet should be assumed to occur instantaneously with the onset of the projected damage. The applicability of Table 5 is consistent with the applicability of Tables 1 and 2. Table 5. MHA LOCA Release Phases Phase PWRs BWRs Onset Duration Onset