NUREG-1537, Part 2 - NRC

6 ENGINEERED SAFETY FEATURES
This chapter gives the review plan and acceptance criteria for active or passive
engineered safety features (ESFs) of the reactor facility that are designed to
mitigate the consequences of accidents. The concept of ESFs evolved from the
defense-in-depth'philosophy of multiple design features to prevent or mitigate the
release of radioactive materials to the environment during accident conditions.
The applicant determines the need for ESFs from the SAR analyses of accidents
that could occur, even though prudent and conservative designs of the facility have
'made these accidents very unlikely. The NRC reviewer' may find that the SAR
analyses show that ESFs are not needed for a proposed design.
Normal operation'of a non-power reactor is defined as'operation with all process
variables and other reactor parameters within allowed conditions of the license,
technical specifications, applicable regulatory limits, and design requirements for
the system. Accidents at non-power reactor facilities generally assume a failure of
a major component such as the reactor coolant system boundary or a reactivity
addition event.' Licensees analyze a maximum hypothetical accident that assumes
an incredible failure that leads to breach of the fuel cladding or a fueled eperiment
containmment. These postulated accidents are compared to acceptance criteria such
as the safety limits from the technical specifications or-, where there are radiological
consequences, to accepted regulatory limits (10 CFR Parts 20 or 100). The results
of the accident analyses are given in SAR Chapter 13, "Accident Analyses." ESF
-systems must be designed to function for the range of conditions from normal
operation through accident conditions.
Because most non-power reactors operate at atmospheric pressure, at relatively
low power levels,&and with conservative safety margins, few cedible postulated
accidents result'in significant radiological risk to the public. 'Accident scenarios
that should be discussed by the applicant in SAR Chapter 13 include the following:
* loss of coolant
* loss of coolant flow
-' insertion of excess reactivity (rapid or ramp)
* loss of fuel cladding integrity or mishaiudling of fuel
* -failure or malfunction of an experirent
* other uncontrolled release of radioactive material
* loss of electri6 power
* extehal events such as flo6ds and earthquakes.
In the past, the SAk accident analyses for many non-power reactors have shown
that ESFs are not required, even for ihe maximum hypothetical accident. In other
cases, the accident analyses have shown'that ESFs need to be considered in
mitigating the potential release of hazardous q uantities of radioactive material to
the environment. '
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