Junior Operator Grade I flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Subcooling margin

Saturation temperature at current RCS pressure minus the hottest RCS temperature. A positive margin means the coolant is liquid; a margin approaching zero signals bulk boiling and possible inadequate core cooling.

Inverse count rate plot

A plot of one divided by the count rate against rod position or time during a criticality approach. The extrapolated intercept at 1/CR equal to zero predicts the critical rod position.

Shutdown margin

The reactivity worth of all control rods assumed fully inserted minus the core reactivity at that condition. It must remain positive, including during refueling, so the core cannot go critical by rod withdrawal alone.

Two-out-of-four logic

A protection scheme where a trip requires at least two of four redundant channels to agree. One failed channel does not cause a spurious trip, but it removes the redundancy that the second channel provides.

Fail-safe valve position

The position a pneumatic actuator moves to when air or power is lost, designed as fail-open, fail-closed, or fail-as-is. Operators must know each valve's position before declaring instrument air loss.

Limiting condition for operation

A technical specification requirement that equipment be operable in a stated condition. If it is not met, the operator must enter the action statement and complete the required action within the stated time.

Emergency classification levels

Four escalating classes: Notification of Unusual Event, Alert, Site Area Emergency, and General Emergency. Each has defined entry criteria, and each higher class requires broader notification and protective action.

Critical safety functions

Six status functions checked in emergency operating procedures: reactivity control, core cooling, heat removal, RCS integrity, containment integrity, and RCS inventory. Status trees direct the operator to the appropriate procedure.

Inverse square law

For a point source, dose rate is inversely proportional to the square of distance. Doubling the distance reduces the dose rate to one quarter of its original value.

Half-value layer

The thickness of a shielding material that reduces the dose rate by half. For 1 MeV gamma rays in lead it is roughly 1 cm, but it varies strongly with photon energy and material density.

Three-way communication

The sender states the message, the receiver repeats it back, and the sender confirms the repeat is correct. Required for any command that changes plant configuration or component position.

STAR self-check

Stop, Think, Act, Review. The operator pauses before an action, confirms the component and expected response, performs the action, and verifies the result matches the expectation.

Tagout and clearance

A controlled isolation where equipment is de-energized, locked, tagged, and verified at zero energy. Only the person who owns the tag may remove it after work is complete.

Post-maintenance testing

Testing after maintenance that confirms the component performs its intended safety function before return to service. It verifies function, not merely that a calibration or repair was completed.

Pump affinity laws

For a centrifugal pump, flow varies with speed, head with speed squared, and power with speed cubed. A 10 percent speed reduction therefore cuts power by about 27 percent.

Net positive suction head

NPSH available must exceed NPSH required to prevent cavitation. Available NPSH is the suction pressure above vapor pressure; cavitation occurs when local pressure drops below vapor pressure.

Synchronous speed formula

Synchronous speed in rpm equals 120 times frequency in hertz divided by the number of poles. An induction motor's rotor turns slightly slower, and the difference is called slip.

Three-phase power formula

Real power equals the square root of three times line voltage times line current times power factor. The kVA rating is kW divided by power factor, and the generator must supply that kVA.

Square-root flow relation

Flow through an orifice varies with the square root of differential pressure. A fourfold increase in dP doubles flow, so flow indication errors are amplified when dP is small.

Pressurizer level program

Indicated pressurizer level is temperature-compensated and changes with RCS average temperature at constant inventory. Level alone cannot confirm RCS inventory during heatup or cooldown.

Steam generator tube rupture

Primary coolant leaks into the secondary side. The affected generator shows rising level and radiation; operators isolate it and limit RCS cooldown rate to control primary-to-secondary leakage.

Station blackout

Loss of offsite power combined with loss of all emergency diesel generators. Response relies on battery-backed instrumentation and any qualified alternate AC source available.

Anticipated transient without scram

A transient that should trip the reactor but does not. The operator manually trips, then borates the core and uses available injection and isolation paths per the emergency procedure.

Design basis accident

For a light-water reactor, the large-break loss-of-coolant accident. Emergency core cooling is analyzed against it with limits on peak clad temperature, clad oxidation, and hydrogen generation.

Reportable event

An event requiring immediate notification under 10 CFR 50.72 or a written report within 60 days under 10 CFR 50.73. The immediate notification is made by telephone to the NRC operations center.

ALARA principle

Exposures must be kept as low as reasonably achievable, with regulatory dose limits as the ceiling and ALARA as the operating target below them. It is a requirement, not a preference.

Primary chemistry control

pH is maintained with lithium hydroxide, boron concentration is adjusted for reactivity, and dissolved oxygen is limited by hydrogen overpressure. Chloride and fluoride are tightly limited to prevent stress corrosion cracking.

Dose equivalent conversion

Dose in rem equals exposure in roentgens times the quality factor for the radiation type. One rem equals 0.01 sievert, and one rad equals 0.01 gray.

Containment leak rate test

An integrated test at reduced pressure performed at periodic intervals. The acceptance criterion is a maximum leakage rate expressed as a fraction of containment volume per day.

Surveillance test interval

The period between required tests, set so the probability of an undetected failure stays within the analyzed value. Extending it requires a technical specification change, not an administrative decision.

Error precursors

Conditions that raise the chance of human error: time pressure, fatigue, distraction, vague procedures, and first-time performance. Recognizing a precursor prompts a defensive action before the task begins.

Heat exchanger duty

Heat transferred equals the overall heat transfer coefficient times area times log mean temperature difference. Fouling raises resistance and lowers the coefficient, so the same duty needs a larger temperature difference.