Document: NRC Regulatory Guide
Document ID: de79d411-4fc9-456e-a5a0-f4a910ca4c9a
Document Type: regulatory_guide
Title: Assumptions Used for Evaluating a Control Rod Ejection Accident for Pressurized Water Reactors (Rev. 2)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2111/ML21119A157.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.77
CFR Part: 
CFR Title: 

Content:
ty, and Information Requests,” Washington, DC, September 20, 2019. (ADAMS Accession No. ML18093B087) DG-1387, Appendix A, Page A-1 APPENDIX A PROCEDURE FOR CALCULATING WEIGHTS OF HAZARDOUS CHEMICALS NECESSITATING THEIR CONSIDERATION IN HABITABILITY EVALUATIONS This appendix describes a simplified multiplication or division procedure to adjust the distance/weight relationships for specific chemical toxicities (i.e., IDLH value), CR airflow rates, and for varying Pasquill stability classes, assuming that the transport of material is moving with the wind directly from the release point to the air intake. The weights presented in Table 2 of this RG were generated from the EXTRAN computer code without the wake-effect correction, based on the following assumptions: • An IDLH value of 50 milligrams per cubic meter (mg/m3) • CR air exchange hourly rates (i.e., ACH) of 0.015, 0.06, and 1.2 • Category F Pasquill stability class If the IDLH value, air exchange rate, or meteorological conditions differ from the assumptions used in Table 2, simplified relationships can be used to determine the new weights guidance of hazardous chemicals that are to be considered for the CR habitability evaluation using Table 2 directly. Varying IDLH Concentration The weights presented in Table 2 are directly proportional to the toxicity concentration; that is, the total chemical weights increase when IDLH value increase. If a chemical had an IDLH of 500 mg/m3, then the allotment of weights in Table 2 (based on 50 mg/m3) should increase by a factor of 10. Varying Air Exchange Rate The weights in Table 2 are inversely proportional to the ACH; that is, the total chemical weights decrease when the ACH increases. If a CR has an ACH of 2.4, then the weights from Table 2 (based on an ACH of 1.2 per hour) decrease by a factor of two. In other words, the weights are appropriately adjusted for the actual fresh-air exchange rate. CRs with automatic isolation capabilities may have leakage