Instrument and Control Systems

DOE-STD-6003-96

Ceramic Breaks--The use of ceramic breaks should be minimized. When ceramic breaks

are used, they should be qualified by analysis or testing in the anticipated operating and design-

basis off-normal event environment to demonstrate required confinement integrity.

c. Testing

See Section 6.1.3.6 for general guidance. All vacuum vessels and attached components

that provide a confinement barrier should be leak checked at design pressures before initial

operation to demonstrate that leakage requirements specified in the safety analysis are met by

the as-built design. Potential hazards of in-service leak testing at the design vessel pressure

after D-T operations have commenced may not justify such periodic leak testing. In its place, a

program of periodic vacuum leak testing and a formal configuration control program to ensure

vacuum vessel repairs or modifications do not compromise the design pressure rating should be

implemented. Replacement structural components should be pressure tested before assembly

in the vacuum vessel. Local repairs in the vessel should be subject to rigorous NDE.

d. Instrument and Control Systems

Instrument and control systems (I&C), where appropriate, should be provided to monitor

system parameters important to the safety function of the vacuum vessel over their anticipated

ranges for normal operation and off-normal conditions to ensure continuity of the required safety

function. The design should incorporate sufficient redundancy and/or diversity to ensure that

a single failure will not result in a loss of monitoring capability for safety-class systems. The

electric power to operate safety class instrumentation should meet the requirements of IEEE

1980. More information is provided in Section 6.4.1, Instrument and Control Systems, and

Section 6.4.2, Electrical Power Systems.

e. Ventilation and Exhaust Systems

The design of a vacuum vessel confinement ventilation system should ensure the ability

to maintain desired airflow characteristics when personnel access ports or hatches are open.

When necessary, air locks or enclosed vestibules should be used to minimize the impact of this

on the ventilation system and to prevent the spread of airborne contamination within the facility.

Ventilation system components required to be safety-class should provide the required con-

finement capability under all normal operations and off-normal conditions with the assumption of

a single failure in the system. If the maintenance of a controlled continuous confinement airflow

is required to meet evaluation guidelines in DOE-STD-6002-96, electrical equipment and com-

ponents required to provide this airflow should be supplied with safety-class electrical power and

provided with a backup power source. Air cleanup systems should be provided in confinement

ventilation exhaust systems to limit the release of radioactive or other hazardous material to the

environment and to minimize the spread of contamination within the facility as determined by the

safety analysis. Guidance for confinement systems is included in DOE 1989.