EPRI - Core Protection (Engineering Systems Training)
– Q&A
Identify ways a core can fail ✔️Ans -The primary cause of core
failure is an inability to fully remove the heat created by the fuel due to the
following:
1. A failure of the heat removal systems
2. An increase of heat created beyond the ability of the heat removal systems
3. The inability to transfer heat from the fuel
What cooling capabilities could lead to core melt and a loss of core geometry
✔️Ans -Loss of Cooling Capabilities
· Loss of reactor coolant flow
· Loss of coolant
· Loss of feedwater flow
· Loss of decay heat removal
what excessive heat creation could lead to core melt and a loss of core
geometry ✔️Ans -· Failure of the reactor to trip when required
(often referred to as anticipated transient without scram (ATWS))
[anticipated transient without scram (ATWS)- When the reactor protection
system detects an unsafe condition and sends a signal to trip the reactor, but
the reactor does not trip.]
· Rod ejection (PWR)
· Inadvertent deboration (PWR)
[Deboration- Borated water is one method to control reactor reactivity.
Deboration is the reduction of boron in the reactor coolant thus adding
positive reactivity.]
'inability to transfer heat from the fuel' could lead to core melt and a loss of
core geometry ✔️Ans -· Loss of subcooling
· Departure from nucleate boiling
,· Onset of transition boiling
Identify grouped ways core can fail ✔️Ans -loss of cooling
capabilities
excessive heat creation
inability to transfer heat from the fuel
what are the elements of the defense-in-depth philosophy ✔️Ans -
prevention of accidents
termination of accidents when they occur
mitigation of accidents that are not successfully terminated
defense-in-depth philosophy ✔️Ans -The nuclear industry in the
United States has adopted a philosophy of defense-in-depth that calls for
multiple layers of protection for nuclear power plants and ultimately to
protect the health and safety of the general public.
Prevention of accidents ✔️Ans -can be accomplished through high
quality design, construction, inspection, and testing coupled with operation of
the plants in accordance with approved procedures.
Termination of accidents when they occur ✔️Ans -supported by
redundancy and diversity in safety equipment used in conjunction with
approved procedures and strategies.
Mitigation of accidents that are not successfully terminated ✔️Ans
-accomplished through the use of multiple barriers to fission product release
plus approved emergency preparedness Note: Each element of the defense-in-
depth philosophy: prevention, termination, and mitigation, includes aspects of
both design and operation.
Describe the roles of procedures in the defense-in-depth philosophy
✔️Ans -Prevention of accidents is supported by operation within the limits of
normal operating procedures. Those limits are prescribed by the design of the
, plant, are described in the Final Safety Analysis Report (FSAR), and are
included in the applicable plant procedures.
Define a design basis accident ✔️Ans -Accidents are defined as
hypothesized events that affect one or more of the radioactive material
barriers and that are not expected during plant operations. The systems in
nuclear power plants are designed to mitigate specific accidents.
[DBA- A postulated accident that a nuclear facility must be designed and built
to withstand without loss to the systems, structures, and components
necessary to ensure public health and safety.]
A DBA is typically a worst-case accident of interest. According to the Nuclear
Regulatory Commission, a design basis accident is "a postulated accident that
a nuclear facility must be designed and built to withstand without loss to the
systems, structures, and components necessary to ensure public health and
safety". For example, an accident may result in an interruption of core cooling
flow or a loss of electrical generation, but the ultimate goal is to ensure the
safety of the public.
Define the design basis accident types ✔️Ans -· Mechanical failure
of a single component leading to the release of radioactive material from one
or more barriers. The components referred to here are not those that act as
radioactive material barriers. Examples of mechanical failure are breakage of
the coupling between a control rod drive and the control rod, and failure of a
spring used to close an isolation valve.
· Arbitrary rupture of any single pipe up to and including complete severance
of the largest pipe in the nuclear system process barrier: This type of accident
is considered only under conditions in which the nuclear system is
pressurized.
Define PRA ✔️Ans -Probabilistic Risk Assessment (PRA), also
known as Probabilistic Safety Assessment (PSA), is a quantitative assessment
of the risk associated with plant operation and maintenance. This risk is
measured by how often different events that lead to severe core damage
occur. The original goal of PRA was to analyze and understand severe accident
behavior, and then identify and fix the plant vulnerabilities.
– Q&A
Identify ways a core can fail ✔️Ans -The primary cause of core
failure is an inability to fully remove the heat created by the fuel due to the
following:
1. A failure of the heat removal systems
2. An increase of heat created beyond the ability of the heat removal systems
3. The inability to transfer heat from the fuel
What cooling capabilities could lead to core melt and a loss of core geometry
✔️Ans -Loss of Cooling Capabilities
· Loss of reactor coolant flow
· Loss of coolant
· Loss of feedwater flow
· Loss of decay heat removal
what excessive heat creation could lead to core melt and a loss of core
geometry ✔️Ans -· Failure of the reactor to trip when required
(often referred to as anticipated transient without scram (ATWS))
[anticipated transient without scram (ATWS)- When the reactor protection
system detects an unsafe condition and sends a signal to trip the reactor, but
the reactor does not trip.]
· Rod ejection (PWR)
· Inadvertent deboration (PWR)
[Deboration- Borated water is one method to control reactor reactivity.
Deboration is the reduction of boron in the reactor coolant thus adding
positive reactivity.]
'inability to transfer heat from the fuel' could lead to core melt and a loss of
core geometry ✔️Ans -· Loss of subcooling
· Departure from nucleate boiling
,· Onset of transition boiling
Identify grouped ways core can fail ✔️Ans -loss of cooling
capabilities
excessive heat creation
inability to transfer heat from the fuel
what are the elements of the defense-in-depth philosophy ✔️Ans -
prevention of accidents
termination of accidents when they occur
mitigation of accidents that are not successfully terminated
defense-in-depth philosophy ✔️Ans -The nuclear industry in the
United States has adopted a philosophy of defense-in-depth that calls for
multiple layers of protection for nuclear power plants and ultimately to
protect the health and safety of the general public.
Prevention of accidents ✔️Ans -can be accomplished through high
quality design, construction, inspection, and testing coupled with operation of
the plants in accordance with approved procedures.
Termination of accidents when they occur ✔️Ans -supported by
redundancy and diversity in safety equipment used in conjunction with
approved procedures and strategies.
Mitigation of accidents that are not successfully terminated ✔️Ans
-accomplished through the use of multiple barriers to fission product release
plus approved emergency preparedness Note: Each element of the defense-in-
depth philosophy: prevention, termination, and mitigation, includes aspects of
both design and operation.
Describe the roles of procedures in the defense-in-depth philosophy
✔️Ans -Prevention of accidents is supported by operation within the limits of
normal operating procedures. Those limits are prescribed by the design of the
, plant, are described in the Final Safety Analysis Report (FSAR), and are
included in the applicable plant procedures.
Define a design basis accident ✔️Ans -Accidents are defined as
hypothesized events that affect one or more of the radioactive material
barriers and that are not expected during plant operations. The systems in
nuclear power plants are designed to mitigate specific accidents.
[DBA- A postulated accident that a nuclear facility must be designed and built
to withstand without loss to the systems, structures, and components
necessary to ensure public health and safety.]
A DBA is typically a worst-case accident of interest. According to the Nuclear
Regulatory Commission, a design basis accident is "a postulated accident that
a nuclear facility must be designed and built to withstand without loss to the
systems, structures, and components necessary to ensure public health and
safety". For example, an accident may result in an interruption of core cooling
flow or a loss of electrical generation, but the ultimate goal is to ensure the
safety of the public.
Define the design basis accident types ✔️Ans -· Mechanical failure
of a single component leading to the release of radioactive material from one
or more barriers. The components referred to here are not those that act as
radioactive material barriers. Examples of mechanical failure are breakage of
the coupling between a control rod drive and the control rod, and failure of a
spring used to close an isolation valve.
· Arbitrary rupture of any single pipe up to and including complete severance
of the largest pipe in the nuclear system process barrier: This type of accident
is considered only under conditions in which the nuclear system is
pressurized.
Define PRA ✔️Ans -Probabilistic Risk Assessment (PRA), also
known as Probabilistic Safety Assessment (PSA), is a quantitative assessment
of the risk associated with plant operation and maintenance. This risk is
measured by how often different events that lead to severe core damage
occur. The original goal of PRA was to analyze and understand severe accident
behavior, and then identify and fix the plant vulnerabilities.
