System Interaction Effects ("Two Over One Protection")

DOE-STD-1021-93

(d)

Performance Category 2: An SSC shall be placed in preliminary Performance Category 2

(PC-2) if it is not covered in Paragraphs 2.4(b) and 2.4(c) above, and if any of the following

conditions apply:

(i)

The SSCs failure by itself or in combination with one or more SSCs may result in loss

of function of any emergency handling, hazard recovery, fire suppression, emergency

preparedness, communication, or power system that may be needed to preserve the

health and safety of workers and visitors. This includes NPH-caused release of

radioactive and toxic materials that would result in these consequences.

(ii) The SSC is part of a building which is primarily used for assembly of more than 300

persons (in one room), and the SSC failure may adversely affect the life safety of the

occupants.

(iii) The SSC has been classified "safety-significant." For details refer to

DOE-G-420.1-2.

An SSC that does not satisfy the above criteria may also be placed in PC-2 from cost

and mission considerations, e.g., when SSC failure causes excessive downtime, the SSC

is very difficult to replace, or SSC replacement/repair is very costly.

(e)

Performance Category 1: An SSC that is not covered in Paragraphs 2.4(b), 2.4(c), and

2.4(d) above shall be placed in preliminary Performance Category I (PC-1) if any of the

following conditions apply:

(i)

It is a building/structure with potential human occupancy.

(ii)

The SSC's failure may cause a fatality or serious injuries to in-facility workers.

(iii) The SSC's failure may cause damage that can be prevented or reduced cost-effectively

by designing it to withstand NPH effects.

(f) Performance Category 0: An SSC that is not covered in Paragraphs 2.4(b) through 2.4(e) above

may be placed in preliminary Performance Category 0 (PC-0), if it is not important because of

safety, mission, or cost considerations, and if it is more cost-effective to replace or repair it than

to design it to withstand NPH effects; however, an SSC whose failure may have any adverse

effect on the performance of a PC- 1, PC-2, PC-3, or PC-4 SSC shall not be placed in PC-0.

2.5

System Interaction Effects ("Two Over One Protection")

(a)

An SSC that has been placed in a preliminary performance category in accordance with the

basic categorization guidelines of Subsection 2.4 (designate it as "source") shall have

appropriate additional NPH mitigation requirements as provided in paragraphs (b), (c), and

(d) below, if its behavior by itself, or the multiple common cause behavior of it with other

SSCs may adversely affect the performance of another SSC (designate it as "target"). These

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