Safety System

DOE-HDBK-6004-99

Safety System

The Safety System should be capable of maintaining the facility within the design basis safety analysis

limits and provide operator interface (indication, alarm, data collection, and any necessary manual

interaction), during accident or off normal conditions that may be created by any PIE.

A safety system task analysis should be conducted to determine which safety functions are to be

assigned to the operator and which safety functions are to be machine (automatic action) assigned.

The operator should be provided with manual safety action initiating capability for all safety functions

and with feedback information to confirm the occurrence of the proper actuation and completion of

the selected safety function.

Safety Systems should be designed to fail safe on loss of motive force or power. In addition, safety

systems should be designed to meet single failure criteria. The system should be designed to preclude

failure of a component or subsystem from preventing completion of the required safety function.

Diversity in the monitoring of the parameters and actuation of the control systems should be a basic

principle of the safety system design.

To prevent a failure in the basic control system from degrading the operation of the safety system,

isolation should be provided between any interface of the basic control and safety systems and

separation should be provided and maintained between these systems.

Instrumentation

The process variables (parameters) that are selected to provide inputs to the I&C system should be

those which characterize the relevant safety and operational status of the monitored systems and

barriers. This selected set of variables must be analyzed to determine their adequacy to measure and

provide for the necessary control and safety functions. The analysis should include the measurability,

variability, and response action time capability of the process parameter variables and the operational

demands and limitations placed upon the control or safety system design by these parameter variable

properties.

The instrumentation selected to measure a process variable should directly measure the variable,

instead of some secondary parameter. Instrumentation should be analyzed to determine if its

reliability, accuracy, and response time characteristics satisfy the control or safety system needs for

all required operating conditions.

Instrumentation should be provided to monitor variables of the facility systems over their anticipated

ranges for normal operation, anticipated operational transients and occurrences, and for postulated

accident conditions to ensure adequate safety and design margins are maintained.

Potential System Safety Function

The potential safety functions for the I&C Systems are:

1. Monitor and indicate by alarm off normal facility systems operating parameters or transient

conditions.