Document: NRC Regulatory Guide
Document ID: c992c9f8-7405-4a7c-afdc-b3d2a6922aad
Document Type: regulatory_guide
Title: Assumptions Used for Evaluating the Potential Radiological Consequences of a Steam Line Break Accident for Boiling Water Reactors
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003739923.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.5
CFR Part: 
CFR Title: 

Content:
ion valves close in the maximum time incorporated or to be incorporated in the technical speci fications. This closure time will be veri fied by suitable periodic testing. 3. The total mass of coolant released is that amount in the steam line and con necting lines at the time of the break plus the amount that passes through the valves prior to closure. (Ruptures within the turbine complex are not con sidered in this guide.) 4. The radioactivity in the coolant is as sumed to be the maximum amount in corporated or to be incorporated in the technical specifications, provided that no further fuel failures are assumed to occur as a result of delays in valve closure. 5. All of the iodine (no credit for plateout is allowed) and noble gases from the released coolant are released to the atmosphere within 2 hours at a height of 30 meters with a fumigation condi tion. 6. The assumptions for dose conversion and atmospheric diffusion are: (a) No correction is made for deple tion from the effluent plume of radioactive iodine due to deposition on the ground, or for the radio logical decay of Iodine 131 in transit. 2 For purposes of this guide a steam line break is defined as a complete severance of the pipe and the pipe centerline is offset by at least the pipe diameter. 'For certain designs other operating modes (i.e., hot standby) may represent a worse condition. These de signs will be evaluated on an individual case basis. 5.1 (b) The breathing rate of persons off- special meteorological, topo site is assumed to be 3.47 x 10-4 graphical, and other charac cubic meters per second. (This teristics which may affect the value is developed from the aver- maximum plume concentra age daily breathing rate [2 x 10' tion. These site related char cm 3/day] assumed in the report of acteristics must be evaluated ICRP, Committee 11-1959.) on an individual case basis. In (c) The iodine dose conversion factors the case of beta radiation, the are given in ICRP Publication 2, receptor is assumed