ANS CNP flashcards

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

Effective multiplication factor

Ratio of neutrons produced in one generation to neutrons lost by absorption and leakage in the preceding generation; k_eff = 1 means critical, below 1 subcritical, above 1 supercritical.

Delayed neutron fraction

Fraction of fission neutrons emitted by decaying fission products rather than promptly; about 0.0065 for U-235, providing the time margin needed to control the reactor.

Prompt criticality

Condition where reactivity exceeds the delayed neutron fraction beta, so the chain reaction is sustained by prompt neutrons alone and power rises on a very short timescale.

Reactivity in pcm

Reactivity rho = (k_eff - 1)/k_eff; one percent millirho (pcm) equals 1e-5 in rho, a convenient unit for small reactivity changes from rods or boron.

Xenon-135 poisoning

Fission product with an enormous thermal absorption cross section; its buildup after power changes and post-shutdown peak can insert large negative reactivity.

Reactor period

Time required for reactor power to change by a factor of e; related to startup rate by SUR in decades per minute equal to 26.06 divided by period in seconds.

Inverse counts plot

Plot of 1/M versus rod position or boron concentration used during approach to criticality; extrapolation to zero estimates the critical condition.

Differential rod worth

Reactivity change per unit of rod motion; it peaks where the neutron flux is highest, typically near the core midplane, and is small at the top and bottom.

Moderator temperature coefficient

Change in reactivity per degree of moderator temperature; negative in PWRs because heating lowers water density and reduces moderation, providing a self-limiting feedback.

Boron dilution

Addition of pure water to the primary coolant that lowers boron concentration and adds positive reactivity; it must be controlled carefully during power operations.

Defense in depth

Layered safety approach using multiple independent barriers and administrative and engineered controls so that no single failure leads to unacceptable consequences.

Design-basis accident

Postulated accident that the plant must withstand without exceeding dose limits; examples include loss-of-coolant accidents and control rod ejection.

ECCS acceptance criteria

10 CFR 50.46 limits peak cladding temperature to 2200 F and local cladding oxidation to 17 percent of initial wall thickness during a loss-of-coolant accident.

Limiting condition for operation

Technical specification requirement that must be met during operation; if not met, the action statement requires prompt corrective action or shutdown.

Safety limit

Boundary on plant parameters that must not be exceeded to protect fuel and the public; reactor protection setpoints are set to prevent exceeding it.

Occupational dose limits

10 CFR Part 20 limits: 5 rem per year whole body, 15 rem per year lens of eye, and 50 rem per year to extremities and skin.

ALARA principle

Requirement to keep radiation doses as low as reasonably achievable, weighing social and economic factors, using time, distance, and shielding.

Inverse square law

Dose rate from a point source is inversely proportional to the square of the distance; doubling the distance reduces the dose rate to one quarter.

Half-value layer

Thickness of a material that reduces gamma radiation intensity by half; used to calculate shielding needed to reach a target dose rate.

Derived air concentration

Concentration of a radionuclide in air that, if breathed for a working year, would result in intake equal to the annual limit on intake.

Natural uranium enrichment

Natural uranium contains about 0.711 percent U-235; power reactor fuel is typically enriched to 3 to 5 percent U-235.

Spent fuel pool storage

Spent fuel is stored underwater for cooling and shielding; decay heat decreases over time, allowing later transfer to dry cask storage.

Transuranic waste definition

Waste containing alpha-emitting transuranic isotopes with half-lives over 20 years at concentrations above 100 nanocuries per gram of waste.

Closed fuel cycle

Fuel cycle that reprocesses spent fuel to recover uranium and plutonium for reuse, reducing waste volume but raising proliferation and safeguards concerns.

Type B cask

Transportation package certified to withstand severe accident conditions, used for shipping high-activity materials such as spent fuel under 10 CFR Part 71.

Design-basis threat

Set of adversary characteristics and capabilities against which a nuclear facility's physical protection system must be designed and evaluated.

IAEA safeguards

Verification system using material accountancy, containment and surveillance, and inspections to confirm that nuclear material is not diverted from peaceful use.

Additional Protocol

Instrument strengthening IAEA safeguards by expanding declarations and access, allowing broader verification of a state's nuclear activities.

Material control and accounting

Program of measurement, records, and material balances used to detect loss, theft, or diversion of nuclear material and to investigate anomalies.

Two-person rule

Requirement that at least two authorized individuals be present for access to or handling of vital equipment or Category I special nuclear material.

Duty to report safety concerns

Professional obligation to raise and escalate safety issues through internal channels and, where required, to regulators; retaliation for good-faith reporting is prohibited.

Falsification of records

Intentional misstatement in logs, test results, or reports; a serious ethical and legal violation that can lead to license action and criminal liability.