M2A4: Plant Load Rejection and Its Effect on the Reactor Coolant System
Instructions:
● Prior to attempting this lesson, ensure that you have completed the module reading assignments.
● This form includes supplemental reading material, instructions to navigate through the simulator
lessons, and provides space to complete assignment requirements. You will complete the
assignment by submitting this form for grading via the M2A4 assignment folder.
● Requirements for M2A4:
o Lesson Part B:
▪ Step 8
▪ Step 10
▪ Step 26
o Lesson Part C:
▪ Step 8
▪ Step 24
Lesson Part A: Supplemental Reading: Pressurized Water Reactor Simulator
NOTE: The following reading material provides a description of the PWR simulators Nuclear Steam
Supply System, Reactivity Coefficients, Reactor Coolant System, and the Rod Control System. You
should read the material prior to moving on to Part B of the simulator lesson.
(Material obtained from: Keymaster, Generic PWR Simulator, Training Guide, April 2016, Western
Services Corporation, Frederick, Maryland.)
Nuclear Steam Supply System
The Nuclear Steam Supply System (NSSS) generates saturated main steam in the steam generators.
The NSSS supplies approximately 4000MW of thermal energy from the reactor core, for transfer, via
the steam generators, to the main steam system.
,Reactor Core
The reactor core is fueled with uranium dioxide pellets enclosed in zircaloy or zirlo tubes with welded
end caps. The tubes are fabricated into assemblies in which end fittings limit axial motion and grids
limit lateral motion of the tubes. The control element assemblies (CEAs) consist of NiCrFe alloy-clad
boron carbide absorber rods, which are guided by tubes located within the fuel assembly. The core
consists of 241 fuel assemblies which will be initially loaded with three different U-235 enrichments.
The total number of control element assemblies is 89.
Reactor Summary Description
The reactor is of the pressurized water type using two reactor coolant loops. The fuel assemblies are
arranged to approximate a right circular cylinder with an equivalent diameter of 365 cm (143.6 inches)
and an active length of 381 cm (150 inches). The fuel assembly consists of five (5) guide tubes welded
to spacer grids and is closed at the top and bottom by end fittings. The guide tubes each displace four
fuel rod positions and provide channels which guide the CEAs over their entire length of travel. In-core
instrumentation is installed in the central guide tube of selected fuel assemblies.
Each fuel rod consists of slightly enriched uranium in the form of sintered uranium dioxide pellets,
enclosed in a pressurized Zircaloy tube that forms a hermetic enclosure. Burnable absorber rods are
provided in selected fuel assembly locations, and are mechanically similar to fuel rods.
The reactor coolant enters the inlet nozzles of the reactor vessel, flows downward between the reactor
vessel wall and the core barrel, and passes through the flow skirt section where the flow distribution is
equalized, and into the lower plenum. The coolant then flows upward through the core, removing heat
from the fuel rods. The heated coolant enters the core outlet region where the coolant flows around the
outside of control element assembly shroud tubes to the reactor vessel outlet nozzles. The control
element assembly shroud tubes protect the individual neutron absorber elements of the CEAs from the
effects of coolant cross-flow above the core.
The reactor internals support and orient the fuel assemblies, control element assemblies, and guide the
reactor coolant through the reactor vessel. They also absorb static and dynamic loads and transmit the
loads to the reactor vessel flange. They will safely perform their functions during normal operating,
upset, and faulted conditions. The internals are designed to safely withstand forces due to dead weight,
handling, temperature and pressure differentials, flow impingement, vibration, and seismic
acceleration.
Reactivity control is provided by three independent systems: the control element drive mechanism
control system (CEDMCS), the chemical and volume control system (CVCS), and the Safety Injection
System (SIS). The CEDMCS controls short-term reactivity changes and is used for rapid shutdown.
The CVCS is used to compensate for long-term reactivity changes and can make the reactor subcritical
without the benefit of the CEDMCS. The SIS provides reactivity control for certain postulated design
basis events, such as steam line breaks and Loss of Coolant Accidents (LOCA). The design of the core
, and the reactor protective system prevent fuel damage limits from being exceeded for any single
malfunction in any of the reactivity control systems.
Instructions:
● Prior to attempting this lesson, ensure that you have completed the module reading assignments.
● This form includes supplemental reading material, instructions to navigate through the simulator
lessons, and provides space to complete assignment requirements. You will complete the
assignment by submitting this form for grading via the M2A4 assignment folder.
● Requirements for M2A4:
o Lesson Part B:
▪ Step 8
▪ Step 10
▪ Step 26
o Lesson Part C:
▪ Step 8
▪ Step 24
Lesson Part A: Supplemental Reading: Pressurized Water Reactor Simulator
NOTE: The following reading material provides a description of the PWR simulators Nuclear Steam
Supply System, Reactivity Coefficients, Reactor Coolant System, and the Rod Control System. You
should read the material prior to moving on to Part B of the simulator lesson.
(Material obtained from: Keymaster, Generic PWR Simulator, Training Guide, April 2016, Western
Services Corporation, Frederick, Maryland.)
Nuclear Steam Supply System
The Nuclear Steam Supply System (NSSS) generates saturated main steam in the steam generators.
The NSSS supplies approximately 4000MW of thermal energy from the reactor core, for transfer, via
the steam generators, to the main steam system.
,Reactor Core
The reactor core is fueled with uranium dioxide pellets enclosed in zircaloy or zirlo tubes with welded
end caps. The tubes are fabricated into assemblies in which end fittings limit axial motion and grids
limit lateral motion of the tubes. The control element assemblies (CEAs) consist of NiCrFe alloy-clad
boron carbide absorber rods, which are guided by tubes located within the fuel assembly. The core
consists of 241 fuel assemblies which will be initially loaded with three different U-235 enrichments.
The total number of control element assemblies is 89.
Reactor Summary Description
The reactor is of the pressurized water type using two reactor coolant loops. The fuel assemblies are
arranged to approximate a right circular cylinder with an equivalent diameter of 365 cm (143.6 inches)
and an active length of 381 cm (150 inches). The fuel assembly consists of five (5) guide tubes welded
to spacer grids and is closed at the top and bottom by end fittings. The guide tubes each displace four
fuel rod positions and provide channels which guide the CEAs over their entire length of travel. In-core
instrumentation is installed in the central guide tube of selected fuel assemblies.
Each fuel rod consists of slightly enriched uranium in the form of sintered uranium dioxide pellets,
enclosed in a pressurized Zircaloy tube that forms a hermetic enclosure. Burnable absorber rods are
provided in selected fuel assembly locations, and are mechanically similar to fuel rods.
The reactor coolant enters the inlet nozzles of the reactor vessel, flows downward between the reactor
vessel wall and the core barrel, and passes through the flow skirt section where the flow distribution is
equalized, and into the lower plenum. The coolant then flows upward through the core, removing heat
from the fuel rods. The heated coolant enters the core outlet region where the coolant flows around the
outside of control element assembly shroud tubes to the reactor vessel outlet nozzles. The control
element assembly shroud tubes protect the individual neutron absorber elements of the CEAs from the
effects of coolant cross-flow above the core.
The reactor internals support and orient the fuel assemblies, control element assemblies, and guide the
reactor coolant through the reactor vessel. They also absorb static and dynamic loads and transmit the
loads to the reactor vessel flange. They will safely perform their functions during normal operating,
upset, and faulted conditions. The internals are designed to safely withstand forces due to dead weight,
handling, temperature and pressure differentials, flow impingement, vibration, and seismic
acceleration.
Reactivity control is provided by three independent systems: the control element drive mechanism
control system (CEDMCS), the chemical and volume control system (CVCS), and the Safety Injection
System (SIS). The CEDMCS controls short-term reactivity changes and is used for rapid shutdown.
The CVCS is used to compensate for long-term reactivity changes and can make the reactor subcritical
without the benefit of the CEDMCS. The SIS provides reactivity control for certain postulated design
basis events, such as steam line breaks and Loss of Coolant Accidents (LOCA). The design of the core
, and the reactor protective system prevent fuel damage limits from being exceeded for any single
malfunction in any of the reactivity control systems.
