PE Nuclear flashcards

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

Pressurizer

A PWR vessel holding both steam and water that maintains reactor coolant system pressure using electrical heaters and spray, and provides surge volume to limit pressure swings.

Steam generator

A PWR heat exchanger in which hot primary coolant boils secondary water; the tubes are the barrier between radioactive primary fluid and the non-radioactive steam system, so tube leaks are closely monitored.

ECCS accumulator

A passive nitrogen-pressurized tank of borated water that injects into the PWR cold legs once reactor coolant pressure drops below its check valve setpoint during a loss-of-coolant accident.

Main steam isolation valve

A valve that closes to isolate the main steam line on a safety injection or high-radiation signal, preventing an uncontrolled reactor cooldown that would insert positive reactivity.

Effective multiplication factor

The ratio of neutrons produced in one generation to neutrons lost in the preceding generation; k equal to 1 is critical, below 1 subcritical, and above 1 supercritical.

Delayed neutrons

Neutrons emitted seconds to minutes after fission from decaying precursors; they constitute about 0.65 percent of U-235 fission neutrons and give the reactor a controllable response time.

Six-factor formula

The expression k-infinity equals epsilon times p times f times eta; these four factors account for fast fission, resonance escape, thermal utilization, and neutron reproduction in a thermal lattice.

Xenon-135

The strongest fission-product poison in thermal reactors, with a very large thermal absorption cross section; its iodine precursor causes a reactivity peak roughly 8 to 10 hours after shutdown.

Critical heat flux

The heat flux at which a boiling surface transitions from efficient nucleate boiling to film boiling, sharply reducing heat transfer and risking cladding overheating or failure.

Departure from nucleate boiling

The PWR thermal limit defined by critical heat flux; the ratio of CHF to local heat flux must stay above the design limit to protect fuel cladding.

Decay heat

Residual power generated by radioactive decay of fission products after shutdown; about 6.5 percent of full power one second later and still about 1 percent after an hour.

Reynolds number

A dimensionless group equal to density times velocity times diameter divided by viscosity; it determines whether pipe flow is laminar or turbulent and guides heat transfer correlation selection.

Sievert

The SI unit of equivalent and effective dose, equal to one joule per kilogram weighted for radiation type and tissue; one sievert equals 100 rem.

ALARA

The principle of keeping radiation doses as low as reasonably achievable, weighing economics, available technology, and social factors; a written program is required by 10 CFR 20.1101.

Half-value layer

The thickness of a shielding material that reduces photon intensity by half; it equals the natural logarithm of two divided by the linear attenuation coefficient.

Occupational dose limit

The US annual limit of 50 millisievert total effective dose equivalent under 10 CFR 20.1201, with separate limits for lens dose and extremity dose.

Separative work unit

A measure of the effort required to raise uranium enrichment; the amount depends on the feed, product, and tails assays rather than on the mass of uranium processed.

PUREX process

A solvent extraction method using tributyl phosphate in an organic diluent to separate uranium and plutonium from fission products in dissolved irradiated fuel.

Vitrification

Conversion of high-level radioactive liquid waste into a borosilicate glass matrix, producing a durable, leach-resistant solid suitable for long-term geologic disposal.

Spent fuel pool

A water-filled storage basin that removes decay heat through heat exchangers, shields workers from radiation, and uses dissolved boron and geometry to keep fuel subcritical.

Single failure criterion

The requirement that a safety system still perform its function assuming the worst single component failure, combined with the design-basis event being analyzed.

General Design Criteria

Appendix A to 10 CFR 50, containing criteria that establish minimum design requirements for nuclear power plant structures, systems, and components important to safety.

LOCA acceptance criteria

Under 10 CFR 50.46: peak clad temperature no more than 2200 F, clad oxidation no more than 17 percent, hydrogen generation no more than 1 percent, coolable geometry, and long-term cooling.

Emergency planning zone

The area around a nuclear plant, typically 10 miles for plume exposure, for which offsite notification, evacuation, sheltering, and protective action planning must be established.

Limiting condition for operation

A technical specification requirement defining the minimum equipment and performance needed for safe operation, together with the required actions and completion times if it is not met.

Surveillance test

A periodic test that demonstrates a safety-related system or component still meets its technical specification performance requirements, such as response time, flow, or stroke time.

Refueling outage

A planned shutdown to replace fuel and perform maintenance; core alterations demand a senior reactor operator, verified boron concentration, and adherence to the criticality checklist.

Type A leak test

An integrated containment leak rate test performed at design pressure to confirm that overall containment leakage does not exceed the technical specification acceptance limit.

Zircaloy

A zirconium alloy used for fuel cladding because it absorbs few neutrons and resists corrosion; at high temperature it reacts with steam exothermically and releases hydrogen.

Sensitization

Chromium carbide precipitation along grain boundaries in austenitic stainless steel after prolonged heating in a critical temperature range, leaving it prone to intergranular stress corrosion cracking.

Reactor protection system

Redundant, fail-safe instrumentation and logic that automatically trips the reactor when monitored parameters exceed their trip setpoints, typically using two-out-of-four coincidence.

Fission chamber

A neutron detector coated with fissile material that produces measurable ionization from fission fragments, used in source and intermediate range channels with good discrimination against gamma background.