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:
elease is equivalent to the above burnup-dependent correlations. For volatile, short-lived radioactive isotopes such as halogens (e.g., iodine (I)-131) and xenon (Xe) and Kr noble gases (e.g., Xe-133, Kr-85m), the transient fission product release correlations should be multiplied by a factor of 0.333. For the remaining non-LOCA DBAs which predict fuel rod cladding failure, such as PWR reactor coolant pump locked rotor and fuel handling accident, additional fission product releases may occur as a result of fuel pellet fragmentation (e.g., fracturing of high-burnup rim region) due to loss of pellet-to- cladding mechanical constraint or impact loads. TFGR has been experimentally observed under a variety of accident conditions and should be addressed in future applications. The total fraction of fission products available for release equals the steady-state fission product release fractions in Tables 3 and 4 plus any TFGR prompted by the accident conditions. TFGR may be calculated separately for each axial node based on local accident conditions (e.g., fuel enthalpy rise) and then combined to yield the total TFGR for a particular damaged fuel rod. U.S. NRC, Internal Memorandum (Ref. 24) documents the technical bases of the steady-state fission product release fractions and TFGR correlations. The non-LOCA fission product release fractions and TFGR correlations do not include the additional contribution associated with fuel melting. The event-specific appendices provide guidance for adjusting these gap inventories for fuel rods that are predicted to experience limited fuel centerline melting. DG-1389, Page 20 Table 1. BWR Core Inventory Fraction Released into Containment Atmosphere Group Gap Release Phase Early In-Vessel Phase Total Noble Gases 0.008 0.96 0.968 Halogens 0.003 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