Re-evaluation of superheat conditions postulated in NRC Information Notice 84-90 [nuclear plant]

Information Notice 84-90, “Main Steam Line Break Effect on Environmental Qualification of Equipment”, describes a potential problem regarding existing plant analyses and equipment qualification (EQ) related to a postulated main steam line break (MSLB) with releases of superheated steam. This notice states that certain methodologies for computing mass and energy releases for a postulated MSLB did not account for heat transfer from the steam generator tube bundles if they were uncovered. Due to this potential change in the original environmental analysis, the EQ of various components may not consider the thermal environment which could result from superheated steam. Subsequent technical assessments may determine that the existing qualification basis for equipment/components does not envelop the postulated superheat condition. Corrective actions need to be taken to demonstrate that the affected equipment is qualified. The purpose of this paper is to describe the technical re-assessment of the MSLB/superheat condition