RADIO Chemistry

Question 1

Describe the two mechanisms of fission product releases to the reactor coolant.

Answer 1

• Tramp Uranium - uranium oxide imbedded in fuel cladding; zircaloy also contains 0.1-1.0 ppm uranium “impurity.”
• Cladding Defect - pinholes, cracks, etc. through which fuel generated fission products can leave the fuel and enter the reactor coolant system.

Question 2

Describe two methods for monitoring fuel cladding integrity during power operations.

Answer 2

• Gross activity - or gross beta-gamma activity; a sample is taken, degassed and counted at exactly 20 minutes after sampling. This eliminates contribution or variance caused by short half life isotopes.
• Iodine 131/133 ratio - Because of the difference in half life between iodine 131 and 133 a “normal” ratio will develop. If iodine 133 increases with respect to iodine 131, it is likely that a “fresh” fuel leaker exists.

Question 3

Define Dose Equivalent I-131.

Answer 3

• Concentration of iodine-131 equivalent to the mixture of all radioiodines present;
• Concentration that would produce a thyroid dose as if all iodines were Iodine-131.
• Conversion factors of iodines reflect their half life and volatility, etc.

Question 4

Define Dose Equivalent Xe-133.

Answer 4

• Dose Equivalent Xe-133 is based on the acute dose to the whole body and considers the noble gases which are significant in terms of contribution to whole body dose

Question 5

Define CRUD and explain the CRUD cycle

Answer 5

CORROSION of out-of-core surfaces.
RELEASE of some portion of this corrosion.
DEPOSITION of some of the corrosion products on core surfaces.
ACTIVATION of these deposited corrosion products by neutrons.
RELEASE of some portion of these activated corrosion products.
DEPOSITION of these activated corrosion products on out of core surfaces.

Question 6

State the three major classifications of activation products, and list two examples of each.

Answer 6

Activation of corrosion products
Co-58, Co-60, Cr-51, Mn-54, Mn-56, Fe-59, Zn-65, Ag-110m
Activation of water and water impurities
N-16, N-17, O-19, Na-24, K-40, K-42, Ar-41
Activation resulting in tritium production
Neutron activation of H-2, Li-6, and B-10

Question 7

Describe the production of, and concerns associated with, Nitrogen-16

Answer 7

16O8 + 1η0 → 16N7 + 1p1

Very high-energy gamma emitter (6.13 Mev).

N-16 is the most abundant activation product and is the most limiting nuclide for shielding installations around any equipment carrying reactor coolant.

Fortunately, because of it’s short half-life (7.13 seconds), N-16 is not a radiological concern shortly after reactor shutdown

Question 8

Describe the hazards associated with tritium and the process responsible for the majority of the tritium in the reactor coolant.

Answer 8

10B5 + 1η0 → 3H1 + 24α2
(this accounts for 80% of all tritium production)

Tritium is not removed by filtration, ion exchange, or evaporation.

It is a low level beta emitter which becomes a radiological concern if it is inhaled, ingested, or absorbed through the skin.

It cannot be detected by a whole body count, only by urinalysis. It has a biological half-life of 8-14 days.