NPO

What is the first barrier in defense in depth for release of radiation into the environment?

Fuel pellet

What is the second barrier in defense in depth for release of radiation into the environment?

Fuel sheath

What is the third barrier in defense in depth for release of radiation?

PHT Boundary

What is the fourth barrier for release of fission in defense in depth?

Containment

The four garter springs in a CANDU channel that separate the pressure tube and calandria tubes, must be able to have CO2 pass through them (T/F)

True

Fuel that is discharged from the CANDU 9 reactor must stay underwater to be adequately cooled for 6 years. Then it can be transferred to dry storage when it is cooled by air (T/F)

True

In the CANDU reactor, Liquid Zone compartments are used to control different regions in the reactor. This is cause the CANDU reactor is large and parts of the reactor can behave differently. There are 12 compartments (T/F)

False, there are 14 zone compartments

CANDU fuel is a natural uranium fuel. It is UO2, with 0.72% U-235. The ceramic fuel is the first barrier to fission product release (T/F)

True

If we could make the steam generator temperature going to the turbine higher, we could improve the efficiency of energy conversion in our CANDU 9 plant (T/F)

True

Which of the following air systems may have some oil in the air?

Service air to pneumatic tools

If there is a loss of the external grid, what happens to Class 4 supply to a CANDU 9 plant, and Class 3, 2, and 1?

Class 4 supply switches to UST, Class 3, 2, and 1 are not interrupted.

The temperature of D2O coming out of the steam generator when a CANDU reactor at 100% FP is

~260 to 265 deg C

SDS1 is used to shut down the neutron power in a CANDU 9 reactor when needed. It does this by

Dropping rods into the reactor which are normally suspended above the reactor, using a combination of gravity and springs for acceleration

What element is used to coat the SDS1 rods?

Cadmium

In a CANDU 9 reactor, ECI injects which of the following into the reactor following a LOCA?

Light water

In a CANDU reactor at steady state full power, most of the neutrons that are released from a fission create other fissions in the fuel (T/F)

False, most are attenuated or absorbed

An exclusion zone of at least two-kilometer radius around the reactor is required to meet Canadian regulations that limit public exposure to radiation (T/F)

False, it is the distance necessary to reduce radiation release by 90%, typically 1 km

The heat created in the moderator of a CANDU reactor and rejected to the cooling water is the largest source of thermal loss from the CANDU power plant (T/F)

False, the largest source of thermal loss is on the steam side by the condensers

What is the bulk temperature of the moderator?

60 deg C

What is the 'ultimate heat sink' in a CANDU reactor?

The moderator

How many adjuster rods are there and their reactivity worth?

21 rods in CANDU 6, 24 in CANDU 9, -17 mk

How many absorber rods are there and their reactivity worth?

4 absorber rods, 10 mk

The principle source of radiation hazard in a nuclear plant is due to the highly radioactive fission products that accumulate in the fuel (T/F)

True, the main radiation hazard is from the fission products in irritated fuel.

The ALARA principle states that all hazards must be reduced to a level that is "As Low As Reasonably Achievable" (T/F)

True

Control, cool, and contain is the short form of the Golden Rule of Reactor Safety (T/F)

True

Reliable process systems are the first line of defense in reactor safety (T/F)

True

Highly reliable safety systems are the second level of protection to ensure reactor safety. They are poised to act in order to mitigate and if necessary accommodate the consequences of a reactor accident (T/F)

True

The containment system

provides a relatively leak tight envelope that is maintain slightly below atmospheric pressure, is epoxy or steel lined with variations of thickness in the dome

The uranium fuel is molded into ceramic pellets that:

have a high melting point and lock in most of the fission products

The heat transport system is constructed of

high strength pressure tubes, piping and vessels that contain the fuel bundles

The fuel sheath houses

the ceramic fuel and is made of high integrity welded metal (zircalloy)

Under normal operating conditions, heat generated by the fuel is removed by:

the PHT to the steam generators

The calandria is

a horizontal stainless steel vessel that holds the heavy water moderator and reflector

The average residency time of a fuel bundle within a reactor is

1 year

The heat transport coolant is under high pressure to

minimize boiling during normal operations

The RRS computes the signals that position the reactivity control device (T/F)

true

How many flux detectors are there within the RRS?

28 platinum flux detectors are used for measure and another few installed spares for redundancy

How are flux detectors placed physically and what do you they measure?

mounted vertical in the reactor, distributed spatially, and measure total flux and spatial distribution

RRS Instrumentation compares which three measurements to measure what?

flux detector and ion chamber measurements and combines with thermal power measurements to measure bulk and spatial neutron power

Self power in core detectors measure the neutron flux below ~1% FP (T/F)

False, the flux detectors cannot measure flux well below 1% FP, and can only measure local neutron flux from 10% FP to 120% FP.

Platinum flux detectors have what response to changes?

Fast response

Platinum flux detectors respond to

neutrons and gammas

Vanadium flux detectors are sensitive and not sensitive to

neutrons and not gammas

Why can't vanadium flux detectors be used directly for reactor power control?

They have slow response to changes in neutron flux

Vanadium flux detectors are used as an input to what? Therefore, what is the output used for?

an input to flux mapping programs with the output combined with thermal power to adjust platinum flux detectors for spatial flux control

Platinum flux detector signals are calibrated using

thermal power measurements taken on the secondary side of the steam generators

Flux mapping program computes what and from which instrument?

Spatial power distribution from vanadium detector signals

The function of the flux mapping program is to

help the calibration of the platinum detectors for spatial neutron flux

The second function of the flux mapping program is to

prevent overheating of the fuel by detecting local flux peaks

The final function of the flux mapping program is to

provide information to optimize power output and fuel management

What is the reactor setback rate of reduction and the level to which it is terminated? What is it dependent on?

It is dependent on the parameter outside its prescribed limit, typical rates are 0.5 to 1% FP/s and the terminating power levels range to 0 to 60% FP through LZC and adjusters

Reactor stepback routine is to

reduce reactor power rapidly to 0 to 60% FP to protect the reactor, absorber rods are partially or fully inserted into the core

Hardware interlocks are

designed to ensure the maximum amount of rate of reactivity insertion never exceed design limit

Moderator head tank accounts for

swell and shrink conditions due to temperature fluctuations

Moderator cover gas is needed to prevent

moisture in the air to down grade the heavy water concentration and to prevent build up of highly explosive D2 and O2 gases within the moderator due to radiolysis of deuterium

Helium is used in the cover gas because it is

chemically inert and cannot be activated by neutron radiation, but it is expensive

Moderator purification system is to

remove products from the radiolysis of deuterium to prevent further radiolysis corrosion, and crud activation, control the concentration level of the soluble neutron poisons, and remove poisons

Moderator D2O collection is to

collect any heavy water leakage and transfers it to the heavy water management system for clean up and upgrading

How many garter springs are there that separate the fuel sheath the calandria tube?

4

If the Turbine Generator trips, a reactor trip will occur shortly after on a parameter such as Low PHT Flow (T/F)

True, although it is economically sound to keep the reactor operating after a turbine trip and to exhaust steam to a condenser to ultimately prevent poison out by xenon concentration, a low core flow signal is one of the sensing signals to trip SDS1 or SDS2

In alternate mode of OUC of operation, the set-point for the reactor power is done so through which system?

Reactor Regulating System

The pressure tube and calandria tube in a CANDU reactor are separated from each other with typically 5 garter springs per channel and a flow of CO2 in the Annulus Gas System (T/F)

False, there are 4 garter springs that allow CO2 to flow

Steam flow from the HP Turbine first flows through a Reheater and then through a Moisture Separator so that it enters the Low Pressure Turbine in superheated condition (T/F)

False, flow through the HP turbine is first through the moisture separator and then the reheater. The reheater increases the work the steam can do within the low pressure turbine

How is power error calculated?

Power error = P_actual - P_demanded

What does hold power mean?

P_actual = P_demanded

What does a positive power error mean? What does that mean for LZC?

P_actual is greater than P_demanded therefore we need to reduce power by increasing liquid zone levels

What is the function of the boiler blowdown system?

A blowdown system in each boiler allows removal of any impurities that collect in the boilers

What is the function of the deaerator?

The deaerator adds heat to and removes non-condensable gases from the feedwater to prevent corrosion

Why is the deaerator the physically highest vessel in the system?

This is to remove load on the boiler feed pumps by creating a net positive pressure head on the suction side and prevent the condensed heated water to turn to steam and cause cavitation in the pumps

What is pressure of the steam at the condenser and how does it affect the efficiency of the plant?

5 kPa (a), as you create more vacuum, you increase the work that has been extracted from the steam and thus increasing the efficiency of the plant

What happens during a reactor trip?

Shutdown systems activate, stepback triggered to drop absorber rods, adjusters stop moving, liquid zones are filled to an upper level without over filling, stop moderator purification flow

What is a typical regulating program cycle?

Reads input to measure power, calculate power, compare power to setpoint by obtaining power error, decide how to change reactivity to reduce power error, change reactivity, repeat

What systems in a CANDU power plant are designed to withstand a seismic event?

Systems that start with 'emergency'

What is supplied by Class 1?

Protection for switchgears and switchgear operations

What is supplied by Class 2?

Monitoring and control instrumentation

What is supplied by Class 3?

Small pump motors and systems to maintain control, cool, and contain

What is supplied by Class 4?

Bulk power

Why are steam generators placed above the reactor?

To enable thermosyphoning

What air is supplied for instrument air?

Relatively clean and dry air with no particulates or oils due to significantly small clearances used for instrumentation

What are the nine parameters measured to trip SDS1/SDS2?

core flow, PHT pressure, pressurizer level, steam generator level, boiler feedline pressure, neutron power and log rate of power, reactor building pressure, moderator level

What are the sources of thermal power and their percentages?

93% fission, 6% of decay heat, 1% of PHT pump friction

What happens to the plant as moderator temperature goes down?

moderator shrinks, reactivity goes down, less heat is being produced, actual neutron power is decreased, power error is negative, RRS measures power error and adjusts LZC, depending on OUC, BPC adjusts steam flow or reactivity in response, xenon concentration increases

Adjuster rods are made of

stainless steel or cobalt-59 to harvest cobal-60

Level in a liquid zone compartment is controlled by adjusting what?

adjusting the water inflow to the compartment, outflow is set constant

How long are batteries to Class 1 and 2 power able to supply critical loads for?

45 to 60 minutes

What are the three purposes for adjuster rods?

Provide positive reactivity to compensate LZC for xenon transients, flatten neutron flux, account for reduction in reactivity due to fueling incapability

What are the five controls for reactivity by the RRS in order?

LZC, control rods (adjusters/absorbers), poison, and shutdown rods

What are the INSAG four defense in depth in achieving the golden rule in order?

Reliable process systems -> reliable safety systems -> competent and operating maintenance staff -> detect and correct failures

What are the defense in depth design engineering concepts for a reliable process system?

Redundancy, separation, diversity, fail-safe, and margin (ALARA)

What is the definition of redundancy and an example?

If one component fails to perform a certain function, another is there to do the exact same job, for example, class 4 power can be supplied from either the grid or the unit

What is the definition of separation and an example?

The physical separation of systems or components so that a fault in one system will not affect the others, for example, EME are physically separated from standby generators

What is the definition of diversity and an example?

Diversity is an attempt to ensure that there is more than one way of doing a job, for example, SDS1 and SDS2

What is the definition of fail-safe design and an example?

A system or component is called fail safe if after failing it leaves the remainder of the system in a safer state, for example, LZC fail to fill

What is the purpose of the annulus gas system?

CO2 acts as an insulator to keep the heat within the pressure tube away from the cool moderator, it is also used to measure moisture content to detect pressure tube leaks

What provides over protection for the calandria?

The calandria rupture disks

What is the importance of maintaining the isotopic as high as possible within the moderator?

More impurities from light water, more neutron absorption and less moderation, less ratio of power output to fuel burnup

What happens if you stop cooling the moderator?

You introduce boiling in just a few minutes

What are the three methods to achieve guaranteed shutdown state

Fill moderator with gad-nitrate poisoning and stop moderator purification flow, drain the entire moderator, or remove all the fuel

The heat produced in the moderator system in a CANDU 9 is ultimately rejected to the lake or river via the recirc cooling system (T/F)

True

Steam is found in a superheated condition at which one of the following points in a typical CANDU plant?

At the outlet of the reheater, the steam leaves the reheater in a superheated condition at about 230°C and 900 kPa.