Physical Layout and Location

DOE-STD-3024-98

the system being controlled. The system boundaries

4.1.4 Principles of Operation

are then usually determined by the interfaces with

the supporting electrical power or instrument air

This section shall describe generally how the system

necessary to make the I&C portions perform

operates with emphasis on how the system

properly.

accomplishes its required functions. This discussion

should also describe other operational features about

A separate I&C system may include sensors,

the system. For ease of understanding, the

controls, signals to actuated equipment, and alarms.

discussion should use a walk-down approach,

For example, an I&C system might include a flow

referring to and following the system and subsystem

sensor, a signal comparator, and a control signal

flow paths in the diagram.

that would open a valve more if the flow were to be

below the desired value, or close the valve if the

The description should not be limited to the required

flow were to be above the desired value. If the I&C

performance, but rather it should reflect the full

system has been designated as a separate system, the

capabilities and capacities of the installed system.

boundaries might be selected at the mechanical

Extra optional capabilities of the system design,

output connections to the flow sensor and at the

beyond that required, such as extra capabilities

input signal connections to the valve actuator.

beyond the safety margins that were added by the

designer or were obtained as part of the procurement

Interfacing systems need to be defined with the level

process should be identified to prevent these from

of detail necessary to ensure proper functioning and

being considered as part of the "safety margin" at

necessary support. The most critical of these

some time in the future. For example, a particular

interfacing systems are "support systems" because

set of components might have been required to be

they provide services that are necessary to the

designed for a 0.20 g earthquake, but the actual

system being described. Electric power (both

equipment was designed and qualified for a 0.35 g

motive power and control power), steam power, and

earthquake.

instrument air are examples. For the current actual

configuration of the system, the important

The discussion should be appropriate to the intended

characteristics of the support systems shall be

audience of the SDD. This discussion should not be

defined.

so detailed as to approach an engineering analysis or

so simplistic as to not add value to the SDD. This

The system being described may also provide

discussion should be developed in coordination with

support that is essential to the performance of

the discussion of the system operational

another system. For example, a particular control

considerations to be provided in Section 4.2

system may be essential for the proper operation of

"Operations" in a manner that avoids unnecessary

a ventilation system.

overlap or repetition.

When components of the system are unusual or

4.1.3 Physical Layout and Location

complicated, the principles of their operation should

The system diagram, being schematic in nature,

be explained. For example, if the system contains a

does not identify the location of the equipment or

proportional-integral-derivative (PID) controller, its

physical configuration. This section (or another

operation should be summarized because many

figure) should explain where the equipment is

readers may need to be educated on this type of

installed (building, room numbers) and its physical

controller or at least reminded.

arrangement within each room. Any special features

regarding the installation, location or arrangement of

4.1.5 System Reliability Features

the equipment should be explained.

This section shall describe any attributes, features,

design or operating characteristics, and other

information important to the reliability of the

system.

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