Instrument and Control Systems

DOE-STD-6003-96

In addition to the general design guidance in Section 6.1, the following system-specific

design guidance is provided:

a. I&C system functions may generally be considered either control or safety functions.

Physical separation, electrical isolation, and independence of these functions is

essential in I&C system design to ensure that safety functions, once initiated, will not

be stopped or impeded by control functions. Conversely, safety functions must not

interfere with the operation of the control function when the facility is operating within

the normal design envelope.

b. The design of the I&C systems should be integrated with the design of other facility

systems to ensure an integrated response to process demands.

c. The process variables that are selected as inputs to the I&C system should be a

complete set that permits automatic or manual detection and response to off-normal

conditions that challenge the integrity of designated confinement barriers. The selec-

tion process should consider the measurability, variability, and time response of the

variables, and the operational demands and limitations. Postevent monitoring and

control should be provided where the safety analysis has assumed their continued

function in the postevent environmental conditions.

d. The instrumentation selected to measure a process variable should be analyzed to

determine if its reliability, accuracy, and response time characteristics satisfy the con-

trol or safety needs for all required operating conditions. Taps, ports, and penetrations

should be positioned to obtain the most desirable measurement parameters.

e. Enabling or interlock functions should be designed to prevent facility systems from

entering into off-normal conditions or allowing a transient condition to continue its off-

normal excursion.

Setpoint, instrumentation uncertainty, and response time analysis should ensure ade-

quate margins between normal control and safety setpoints and limits. Control func-

tions should maintain normal operations without unnecessary challenges to or actua-

tion of a safety function. Safety margins and system response times should be suffi-

cient to ensure that conditions do not exceed the robustness of facility systems or do

not exceed consequences documented in the facility authorization basis.

g. Instrumentation should monitor variables over their full anticipated ranges for normal

and off-normal conditions to ensure adequate safety and design margins are main-

tained. The instrumentation should measure, display, and alarm conditions approach-

ing or exceeding limits defined by the safety analysis.

h. Multiple, diverse technologies should be considered in the selection of the sensors

and measuring systems for the in-vessel and near-vessel parameters because these

instrument components will be exposed to harsh environments (potential radiation

117