IEEE 497:2016 pdf free download – IEEE Standard Criteria for Accident Monitoring Instrumentation for Nuclear Power Generating Stations
6.4 lsolation
For Type A,Type B,Type C， and Type F variables，the transmission of signals between accidentmonitoring instrumentation and any system not meeting the minimum design requirements for the variabletype shall be through isolation devices. These isolation devices shall be classified as part of the accidentmonitoring instrumentation and shall meet the requirements of this standard. No credible failure external tothe accident monitoring instrumentation shall be transmitted through the isolation device in such a way asto prevent the accident monitoring channel from meeting the performance requirements.A failure of anisolation device is evaluated in the same manner as a failure of other equipment in the accident monitoringinstrumentation. Isolation devices shall meet the requirements of IEEE Std 384-2008/IEC60709:2004.
6.5 Information ambiguity
For Type A,Type B, and Type C variables, the failure of an accident monitoring instrument channel shallnot result in information ambiguity that could lead the accident management personnel to defeat or fail toaccomplish a required safety function (e.g., the redundant displays disagree and the accident managementpersonnel cannot readily deduce which channel has failed). lf analysis shows that credible failures canresult in information ambiguity, measures to resolve the ambiguity shall be provided. If measures to resolvethe ambiguity cannot be automatically accomplished, additional information shall be provided to allow theaccident management personnel to deduce the actual conditions so that they may properly perform theirrole.
7.3 Type C variables
These instrument channels shall be scismically qualified in accordance with IEEE Sid 344-2013/IEC 60980:1989.
Instrument channels shall be environmentally qualified for the worst-case postulated accident environmentat the installed location of the equipment in accordance with the plant’s LBD and IEEE Std 323-2003/IEC 60780:1998. In addition，environmental qualification of instrument channels shall considerperformance testing to the full range of the instrument channels while subjected to worst-case postulatedharsh environmental conditions in accordance with the plant’s LBD.
NOTE—The above environmental qualification requirements for extended range instrument channels does not accountfor steady-state elevated levels that may occur in other environmental parameters associated with the extended range.Since exitended ranges are non-mechanistically determined, extension of associated environmental parameter levels isnot justifiable and has，therefore，not been required.Confidence that the equipment would continue to provideinformation if conditions degrade beyond those design basis events postulated in the safety analysis is provided byaddressing the extended range requirements. Proof of performance that instrumentation provides information to theaccident management personnel for severe accident mitigation may be done by analysis.
7.4 Type D variables
Instrument channels that monitor systems that are expected to be operable following a seismic event shallbe seismically qualified in accordance with IEEE Std 344-2013/IEC60980:1989.
Instrument channels shall be environmentally qualified for the particular accident ‘s postulated environmentat the installed location in accordance with the plant’s LBD and in accordance with IEEE Std 323-2003/IEC 60780:1998.
7.5 Type E variables
These instrument channels are not required to be environmentally or seismically qualified.
lf an instrument channel that is used to determine the magnitude of a radiological release meets theselection criteria of Type A,Type B, Type C, or Type D, then that instrument channel shall meet thequalification requirements for that particular type of variable.