NTN REACT flashcards

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

Multiplication factor k

Ratio of neutrons in one generation to those in the preceding generation. k = 1 is critical, k > 1 supercritical, and k < 1 subcritical.

Six-factor formula

k = ε·p·f·η·P_FNL·P_TNL. It multiplies fast fission, resonance escape, thermal utilization, reproduction, and fast and thermal non-leakage probabilities.

Reactivity in dollars

Reactivity ρ = (k−1)/k. Expressed in dollars, ρ/$ where $ equals β, the effective delayed neutron fraction, about 0.0065 for U-235.

Prompt criticality

A condition reached when reactivity equals or exceeds the delayed neutron fraction β. The reactor then becomes prompt critical and power can rise very rapidly.

Xenon-135 poisoning

A fission product with very high neutron absorption cross-section. Post-shutdown peak worth occurs roughly 8–10 hours after shutdown as iodine-135 decays.

Inverse count rate plot

A startup technique plotting 1/M against rod position or boron concentration. Extrapolation to zero indicates the criticality condition.

Shutdown margin

The reactivity worth of all control rods minus the highest-worth stuck rod, with the reactor at power and equilibrium poisons. It must remain positive.

Power defect

The reactivity change from zero to full power caused by Doppler, moderator temperature, and void feedback. Rod withdrawal compensates for it.

Moderator temperature coefficient

The change in reactivity per unit change in moderator temperature. A negative coefficient provides inherent load-following and shutdown feedback.

Differential rod worth

The change in reactivity per unit rod motion. It is largest near mid-core and smallest at the top and bottom of the core.

Equivalent dose

Absorbed dose multiplied by the radiation weighting factor w_R, expressed in sievert. Photons have w_R = 1; alpha particles have w_R = 20.

ALARA

As Low As Reasonably Achievable. Doses are minimized considering economic and social factors, and the principle is documented in radiation protection programs.

Half-value layer

The thickness of shielding material that reduces radiation intensity by half. Related to attenuation coefficient by HVL = ln2/μ.

Inverse square law

Dose rate from a point source falls with the square of distance. Doubling the distance reduces the dose rate to one quarter.

Derived air concentration

The concentration of a radionuclide in air that, if inhaled for a working year, would deliver the annual limit on intake. Used for airborne monitoring.

Emergency classification levels

A graded scale from Notification of Unusual Event through Alert and Site Area Emergency to General Emergency, based on actual or potential radiological impact.

Emergency action levels

Pre-defined measurable conditions or instrument readings that trigger each emergency classification level. They must be based on observable plant parameters.

ECCS acceptance criteria

Peak cladding temperature must not exceed 2200°F (1204°C), cladding oxidation must not exceed 17%, and a coolable geometry must be maintained.

Hydrogen flammability limit

Hydrogen concentration in containment must be kept below about 4% by volume to prevent deflagration. Recombiners or venting control post-accident hydrogen.

Critical safety functions

Reactivity control, reactor coolant inventory, heat removal, and containment integrity. Emergency procedures are symptom-based and address these functions.

Pressurizer function

Maintains primary system pressure using electric heaters to raise pressure and spray to lower it, and accommodates coolant volume changes during power maneuvers.

Steam generator tube boundary

The tubes separate primary and secondary coolant. Degradation is monitored by eddy current testing, and plugging reduces heat transfer area.

Residual heat removal system

Removes decay heat after shutdown and cools the refueling pool. It requires adequate coolant inventory and a correctly aligned flow path.

Safety injection

Injects borated water to restore primary inventory and provide reactivity control after a loss-of-coolant accident. High- and low-pressure systems operate at different pressures.

BWR direct cycle

Reactor coolant boils in the core at about 7 MPa. Steam separators and dryers produce high-quality steam that drives the turbine directly.

Source range detectors

Proportional counters sensitive to individual neutrons. They measure count rate during shutdown and startup, when neutron population is very low.

Intermediate range detectors

Compensated ion chambers that measure log power in decades per minute. High flux trip setpoints are typically in the 10–40% power range.

Axial offset

(Top power − bottom power)/(top + bottom power), derived from power range detector readings. It monitors core power distribution and is limited by technical specifications.

Reactor period

The time for reactor power to change by a factor of e. Period meters measure T = ln2/λ, and an 18-second period is a typical startup alarm threshold.

Coincidence voting logic

Safety instrumentation uses multiple independent channels with 2-out-of-4 voting. This reduces spurious trips while ensuring a trip occurs on genuine demand.

Limiting conditions for operation

Technical specification requirements that define the minimum equipment and performance needed to operate safely, including action statements and completion times.

Licensee event report

A written report required by 10 CFR 50.73 within 60 days of specified events. Immediate notification of certain events is required under 10 CFR 50.72.