EPRI - Core Protection Exam Questions
and Answers
Identify ways a core can fail - Answers -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 - Answers
-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 -
Answers -· 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 - Answers -· Loss of subcooling
· Departure from nucleate boiling
· Onset of transition boiling
Identify grouped ways core can fail - Answers -loss of cooling capabilities
,excessive heat creation
inability to transfer heat from the fuel
what are the elements of the defense-in-depth philosophy - Answers -prevention of
accidents
termination of accidents when they occur
mitigation of accidents that are not successfully terminated
defense-in-depth philosophy - Answers -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 - Answers -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 - Answers -supported by redundancy and
diversity in safety equipment used in conjunction with approved procedures and
strategies.
Mitigation of accidents that are not successfully terminated - Answers -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 - Answers -
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 - Answers -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 - Answers -· 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 - Answers -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.
Define PRA's attributes - Answers -Some of the attributes of a PRA are:
· It realistically models plant design, plant procedures, and human performance
· It is a best estimate
· It is not a safety-related tool
· It is a mathematical model of all important plant systems using plant-specific data for
critical components
· It models the plant response for various initiating events using calculated system
reliabilities
· It takes into account realistically usable mitigating equipment
PRA evaluates internal initiating events such as a LOCA and station blackout, and
external events such as earthquakes, flooding, or a hurricane. PRA calculates the
probability of a specific event that leads to core damage.
Which engineering groups support PRA - Answers -Design engineers
Systems engineers
PRA engineers
Identify how PRA supports various engineering activities, including examples (design
engineers) - Answers -Use PRA when:
and Answers
Identify ways a core can fail - Answers -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 - Answers
-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 -
Answers -· 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 - Answers -· Loss of subcooling
· Departure from nucleate boiling
· Onset of transition boiling
Identify grouped ways core can fail - Answers -loss of cooling capabilities
,excessive heat creation
inability to transfer heat from the fuel
what are the elements of the defense-in-depth philosophy - Answers -prevention of
accidents
termination of accidents when they occur
mitigation of accidents that are not successfully terminated
defense-in-depth philosophy - Answers -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 - Answers -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 - Answers -supported by redundancy and
diversity in safety equipment used in conjunction with approved procedures and
strategies.
Mitigation of accidents that are not successfully terminated - Answers -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 - Answers -
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 - Answers -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 - Answers -· 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 - Answers -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.
Define PRA's attributes - Answers -Some of the attributes of a PRA are:
· It realistically models plant design, plant procedures, and human performance
· It is a best estimate
· It is not a safety-related tool
· It is a mathematical model of all important plant systems using plant-specific data for
critical components
· It models the plant response for various initiating events using calculated system
reliabilities
· It takes into account realistically usable mitigating equipment
PRA evaluates internal initiating events such as a LOCA and station blackout, and
external events such as earthquakes, flooding, or a hurricane. PRA calculates the
probability of a specific event that leads to core damage.
Which engineering groups support PRA - Answers -Design engineers
Systems engineers
PRA engineers
Identify how PRA supports various engineering activities, including examples (design
engineers) - Answers -Use PRA when:
