HKIE Professional Assessment - Nuclear Discipline flashcards

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

Six-factor formula

k_inf = epsilon * p * f * eta * PFNL * PTRL, combining fast fission, resonance escape, thermal utilisation, reproduction factor and fast/thermal non-leakage probabilities to give infinite multiplication factor.

Reactivity in pcm

Reactivity rho = (k_eff - 1)/k_eff, expressed in pcm where 1 pcm = 1e-5. One dollar equals beta_eff, about 650 pcm for thermal U-235 systems.

Delayed neutron fraction

Beta_eff is about 0.0065 for U-235 thermal fission and 0.0021 for Pu-239. Operation below rho = beta keeps the reactor controllable by delayed neutrons.

Xenon-135 iodine pit

After shutdown, Xe-135 builds from I-135 decay for 6-10 hours because burnout stops. Its huge absorption cross-section (2.6e6 barns) depresses reactivity and restricts restart.

Doppler reactivity coefficient

Fuel temperature rise broadens U-238 resonance absorption, reducing resonance escape probability. This gives a prompt negative feedback of about -1 to -3 pcm/K in oxide fuel.

PWR operating conditions

Primary coolant at about 155 bar with cold leg near 290 C and hot leg near 325 C, remaining subcooled. Secondary side produces saturated steam at 60-70 bar to the turbine.

Departure from nucleate boiling

DNB is the critical heat flux condition in subcooled or low-quality PWR flow where a vapour blanket causes rapid cladding temperature rise. Design limit is typically DNBR of at least 1.3.

Decay heat fraction

Residual heat from fission products is about 6.5% of full power at 1 s, 1.3% at 1 hour and 0.4% at 1 day after shutdown, driving residual heat removal design.

LOCA acceptance criteria

Under 10 CFR 50.46, peak cladding temperature must stay below 1204 C, local oxidation below 17% of zirconium thickness, and hydrogen generation below 1% of the full reaction value.

Effective dose formula

Effective dose E equals the sum over tissues of tissue weighting factor w_T times equivalent dose H_T. ICRP 103 weights sum to 1.0, with lung 0.12 and gonads 0.08.

Occupational dose limits

ICRP recommends 20 mSv per year averaged over five years, with no more than 50 mSv in any single year. Lens of eye limit is 20 mSv per year.

Tenth-value layer

The thickness of shielding material that reduces gamma dose rate by a factor of ten. It equals ln(10)/mu, about 3.32 divided by the linear attenuation coefficient.

Neutron shielding principle

Fast neutrons are first moderated by hydrogenous material, then absorbed by boron or cadmium. Capture gamma rays of 2.22 MeV from hydrogen require an outer high-Z shield layer.

Defence in depth levels

Five IAEA levels: prevention of abnormal operation, detection and control, control of design basis accidents, severe accident management, and off-site emergency response. Each level has independent provisions.

IAEA safety standards hierarchy

Safety Fundamentals set principles, General Safety Requirements cover all facilities, and Specific Safety Requirements address NPPs (SSR-1, SSR-2), research reactors, waste, disposal and transport.

Periodic safety review

A comprehensive reassessment of plant safety, typically every ten years of operation, covering ageing, operating experience, safety analysis and modifications against current standards.

Very low level waste

IAEA GSG-1 classifies waste by activity level and half-life. VLLW needs limited containment and can go to near-surface disposal with simplified engineered barriers.

Geological disposal multi-barrier

HLW disposal at 500-1000 m depth uses vitrified waste, metal canister, bentonite buffer and host rock. Each barrier independently retards radionuclide release over long timescales.

Clearance of material

Regulatory release of material from control when activity concentration and total activity fall below IAEA RS-G-1.7 levels, verified by measurement and documented in a final survey.

Type B package tests

Type B transport packages must survive a 9 m drop onto an unyielding target, 1 m puncture, 800 C fire for 30 minutes, and 200 m water immersion.

Separative work unit

SWU measures enrichment effort. Mass balance F = P + T and F*xf = P*xp + T*xt apply; producing 4.5% U-235 at 0.25% tails needs roughly 5-6 SWU per kg.

PUREX reprocessing

Plutonium uranium reduction extraction uses tributyl phosphate in kerosene to separate uranium and plutonium from fission products, enabling MOX fuel fabrication and HLW vitrification.

Criticality safety margin

Fissile material operations maintain k_eff at or below 0.95, applying the double contingency principle so at least two independent unlikely failures are needed for criticality.

Reactor vessel embrittlement

Neutron irradiation raises the nil-ductility transition temperature of low-alloy steel. Surveillance capsules with test specimens monitor the RTNDT shift against pressure-temperature curve limits.

Reactor protection 2-out-of-4

Four independent measurement channels feed trip logic requiring at least two channels to exceed setpoint. This tolerates one failed channel and one channel in test.

Class 1E qualification

Safety-related electrical equipment must meet IEEE 323 for environmental qualification, IEEE 344 for seismic qualification and IEEE 384 for separation and independence.

Station blackout coping

Loss of offsite power plus emergency diesel failure. Plants must cope typically 4-8 hours using batteries, turbine-driven pumps or passive systems before AC power restoration.

Level 1 PSA output

Level 1 probabilistic safety assessment quantifies core damage frequency from initiating events, system fault trees and human error, using minimal cut sets and importance measures.

Fussell-Vesely importance

The fraction of total risk contributed by cut sets containing a component. It ranks contributors for risk-informed maintenance and design improvements in PSA models.

Risk-informed regulation criteria

RG 1.174 accepts changes when CDF increase stays below 1e-5/y and LERF increase below 1e-6/y, with defence in depth and safety margin maintained.

Urgent protective action zone

The UPZ extends typically 5-30 km, where urgent actions such as sheltering, evacuation and iodine thyroid blocking are planned based on projected dose averted.

Emergency action levels

EALs classify events as notification, alert, site area emergency or general emergency, based on plant parameters, radiation monitors and security conditions, triggering notification and response.

Engineer duty to report

Professional codes require engineers to report safety concerns through internal channels and to the regulator if unresolved, protected by just culture from retaliation for good-faith reporting.

Just culture

A framework distinguishing human error from at-risk or reckless behaviour. Honest mistakes are handled with learning; wilful violations face disciplinary action, encouraging reporting.