This standard establishes time response design criteria for
safety-related operator actions to be used in the design of light
water reactor (LWR) nuclear power plants. The criteria are used to
determine the minimum response time intervals for safety-related
operator actions that are taken to mitigate design basis events
(DBEs) which result in an automatic reactor trip. This standard
specifies time requirements that are to be met to receive credit in
the safety analysis for operator actions that initiate or control
Specifically, the criteria provide bases:
(1) For establishing certain requirements for determining
whether a particular action to initiate or control a safety-related
system might be accomplished by operator action or must be
accomplished by an automatic action.
(2) For determining when design modifications can obviate the
need for automatic actions that would otherwise be required.
(3) For general guidance for hardware, such as instrumentation,
controls, indicators, and annunciators necessary to support
safety-related operator actions.
Purpose. This standard provides an objective
approach to ensure plant and systems designs allow time intervals
for operators to perform safety-related actions that fall within
the nominal range of empirically valid response times. The criteria
give the designer a basis for determining or verifying the
acceptability of time intervals provided by the design for operator
actions required to accomplish safety-related functions for DBEs in
nuclear power plants. An intent of this standard is to avoid
excessive operator burden.
The criteria in this standard identify time intervals and other
restrictions that provide an adequate safety margin for
safety-related system design and safety analyses of the DBEs. The
criteria are not intended to serve as a basis for determining
actual operator action times in procedures or training, nor do they
set requirements for operator staffing or qualification. The time
intervals specified in these criteria are minimum values which
shall be provided in the plant design to permit credit for
safety-related operator actions.1
1 The bases for the time tests in the standard are
contained in the Appendix. The rationale behind these criteria and
examples to clarify specific sections are also provided.
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