Basics Flashcards
What is the NCS objective?
To prevent accidental criticality during the handling, processing, and storage of fissile materials.
What are some consequences if NCS objective is not met?
- Radiation exposure leading to sickness, injury or death.
- Impact to site ops
- Loss of test data
- Loss of employment
- Contamination of facility and public
- Damage to public reputation
What is nuclear fission?
The process by which a neutron is absorbed into a fissile atom, splitting the nucleus and releasing energy, fission products and neutrons.
‘Slow’ neutrons are also called what? What are ‘slow’ neutrons more likely to do?
‘Thermal’ neutrons
Cause a fission reaction
In simple terms, what do you achieve if your Keff = 1?
Sustained criticality
What is criticality?
Condition in a system of nuclear material when a self-sustaining fission chain reaction is achieved.
What is fissile material?
Those isotopes that can support a self-sustaining fission chain reaction with thermal neutrons, simply by assembling enough material together.
What are the two ways to terminate a fission chain reaction?
- Neutron leakage from the system
- Neutron absorption by non-fissioning atoms
What are the criticality control parameters?
- Geometry
- Interaction
- Moderation
- Mass
- Enrichment
- Concentration
- Poison
- Reflection
What does a nuclear poison do? By adding a nuclear poison to a fissile system, does nuclear reactivity increase or decrease? the margin to criticality?
Absorbs thermal neutrons without fissioning.
Adding a poison to a fissile system will decrease reactivity, and increase margin to criticality.
What is the minimum critical mass?
Smallest quantity of a certain fissile material that could be made critical under specific optimized conditions
What is a reflector?
A material which bounces neutrons back into an arrangement of fissile material, preventing neutron leakage.
What are some examples of good reflectors?
Beryllium, natural/depleted uranium, thorium, concrete, water, lead, steel, graphite
What are the two primary criticality concerns with regard to natural and depleted uranium?
- Enriched uranium could be mislabeled as natural or depleted, and therefore the fissile mass of the system could be larger than expected
- Significant amounts of natural/depleted uranium materials in the vicinity of fissile material will increase neutron reflection to the fissile material.
What does FGE stand for? How many grams of U235 is 25 FGE?
Fissile grams equivalent.
25.
What is the main concern with geometry?
Fissile material that is subcritical in one configuration could be critical when placed in a different configuration
With regard to geometry; what provides the greatest margin to criticality, a low or high surface area to volume ratio?
High
What are some examples of good moderators?
water, heavy water, hydrides, plastics, polyethylene, hydrocarbons, beryllium hydride, pettrolatum, organics, oil
What 3 sectors must be in balance for the Nuclear Work Model to work effectively?
Engineering/processes, training, supervision
Name a few responsibilities of the fuel handler?
- Know and understand your FHA criticality safety rules and limits
- comply with your criticality safety requirements
- Stop fuel handling and report requirement deviations/potentially hazardous conditions to FHA management
- Prevent unauthorized personnel from handling fuel
- Prevent personnel from performing unauthorized work that may impact criticality safety
What is the DCC? Recit.
The double casualty criterion.
Nuclear fuel must be handled and equipment designed to ensure that an acceptable margin to criticality exists after the most limiting combination of two unlikely, independent and concurrent casualties.
In the DCC, what is meant by ‘unlikely’ casualties?
Events that are not expected to, but may occur during hte life of the facility.
In the DCC, what is meant by ‘independent’ casualty?
Means that one casualty is not caused by nor causes the other casualty.
In the DCC, what is meant by ‘acceptable margin to criticality’?
Measurable level of safety margin between the DCC condition and criticality.
What are some examples of ‘unlikely casualties’?
Overloading - violating mass limit
Moderation - violating controls on type or amount of moderator allowed
Reflection - violating controls on type or amount of reflector allowed
Geometry - changing from a safe geometry to an prohibited geometry
Poison - losing effectiveness of a strong neutron absorbing poison, which may be depended on for crit safety in certain systems.
What are some examples of times when a 4-step should be called?
- Control/limit violation
- KENS violation
- Unauthorized person handles fuel
- Unattended fissile material is discovered
- Mismatch between physical crit zone item location and LANMAS accountability records
- Lost item
What is the 4-step? Recite.
Response to potentially unsafe nuclear condition.
- Stop all activity within six feet of the noted abnormal condition
- Do not disturb any material in the affected area.
- Notify the area criticality custodian, who shall stop all activity in the FHA, and shall then notify NMM&CC and the FHA manager.
- The criticality custodian or NMM&CC shall also notify NRLFO
During the 4-step, what is the reasoning behind not ‘disturbing any material in the affected area’?
to prevent changing the environment around the abnormal condition, which could alter criticality safety parameters.
What must all FHAs have?
- A crit custodian and an alternate
- Clearly defined physical boundaries
- Documented NSP/CSE
- Posted crit board
What must all crit zones have?
- Identified boundaries
- Posted with a unique ID
- Maintain isolation from other crit zones
