The following multiple choice questions test key concepts from the chapter on reprocessing and disposal.
Q1. Which of the following is NOT a purpose of reprocessing?
(a) Recovery of plutonium
(b) Recovery of uranium
(c) Concentration of fission product waste
(d) Decreasing the amount of active liquid waste
Answer: (d) — Reprocessing actually increases the total volume of liquid waste (through the various wash, scrub, and purification stages), although it reduces the volume of high-level waste. The primary purposes of reprocessing are to recover uranium (b) and plutonium (a) for reuse, and the fission products are concentrated into a smaller volume of HLW (c) through vitrification.
Q2. The generic process type used for nuclear fuel reprocessing is:
(a) OSE (Organic Solvent Extraction)
(b) BSE
(c) IX (Ion Exchange)
(d) CSE
Answer: (a) — The PUREX process is based on organic solvent extraction (OSE), using TBP diluted in odourless kerosene to selectively extract uranium and plutonium from an aqueous nitric acid solution containing the dissolved spent fuel.
Q3. Separation of Pu from U is normally achieved in THORP by:
(a) Transferring Pu to the aqueous phase and keeping U in organic phase
(b) Transferring U to the aqueous phase and keeping Pu in organic phase
(c) Forming insoluble Pu compounds and removal by centrifuging
(d) Forming insoluble U compounds and removal of U by centrifuging
Answer: (a) — In the U/Pu separation column (1BX), U(IV) is used to reduce Pu(IV) to Pu(III). Pu(III) has a very low distribution factor in TBP and therefore transfers back into the aqueous phase, while uranium (as UO₂^2+^) remains in the organic (TBP/OK) phase. The reaction is: U(IV) + 2Pu(IV) -> U(VI) + 2Pu(III).
Q4. The chemical process used at the THORP plant is:
(a) PUREX
(b) BUTEX
(c) Ralgex
(d) Radox
Answer: (a) — THORP uses the PUREX (Plutonium Uranium Refining by EXtraction) process, based on solvent extraction with TBP in odourless kerosene. BUTEX was the earlier process used at Windscale B-204.
Q5. Which of the following is NOT a criticality control method used in a reprocessing plant?
(a) Use of geometrically favourable vessels
(b) Batch control
(c) Use of Gd poison in active solutions
(d) Use of gravity feed rather than pumps where possible
Answer: (d) — Gravity feed is used to reduce the risk of mechanical failure and to simplify plant design (avoiding pumps, flanges, and valves), but it is not a criticality control method. The criticality control methods are: favourable geometry (a), batch control (b), neutron poisons such as gadolinium (c), and careful monitoring and accountancy of fissile liquors.
Q6. Cladding ‘hulls’ are classified as:
(a) High level waste
(b) Intermediate level waste
(c) Low level waste
(d) Very low level waste
Answer: (b) — Cladding hulls (the remains of the Zircaloy or stainless steel cladding after the fuel has been dissolved out in the chop-leach process) are classified as ILW. They contain residual contamination (approximately 0.1% of the original fuel) and activation products, requiring shielding but not generating significant heat.
Q7. Which of the following are isotopes discharged as gases from a reprocessing plant?
(a) Technetium and niobium
(b) Tritium and carbon dioxide
(c) Krypton and argon
(d) Xenon and krypton
Answer: (d) — The noble gas fission products xenon and krypton-85 are released as gases during dissolution of the fuel and are discharged to the atmosphere after treatment. Tritium and carbon-14 are also released but as HTO (tritiated water) and CO₂, not as elemental gases. Technetium and niobium are metals, not gases.
Q8. Tc-99 is an important isotope in reprocessing because:
(a) It is a fission product poison
(b) It has a long half-life and is hard to separate from actinides
(c) It is a noble gas hence is hard to contain
(d) It has a very high dose coefficient
Answer: (b) — Tc-99 has a half-life of approximately 211,000 years. It exists as Tc(VII) which is only weakly extractable by TBP, but it forms complexes with uranium, plutonium, and zirconium that are highly extractable, making it difficult to keep out of the product streams. It is definitely not a noble gas (c).
Q9. Criticality accidents in reprocessing facilities are less likely to produce fatalities than incidents in front-end processing because:
(a) The high activity of fission products means that heavy shielding is used in reprocessing
(b) Volumes of liquids are lower in reprocessing
(c) Liquids in reprocessing facilities contain fission product poisons
Answer: (a) — Because irradiated fuel contains extremely high activities of fission products, reprocessing plants are designed with heavy shielding (concrete, steel) around the active process areas and are operated remotely. If a criticality excursion were to occur, the heavy shielding already in place would protect workers from the radiation burst. In front-end processing (e.g., fuel fabrication), the materials are not highly radioactive and therefore heavy shielding is not typically present, meaning workers are closer and more exposed.
Q10. A 1 GWe plant produces approximately how much high level waste per year of operation?
(a) 3 tonnes
(b) 30 tonnes
(c) 300 tonnes
(d) 3000 tonnes
Answer: (b) — A typical 1 GWe nuclear power plant discharges approximately 25—30 tonnes of spent fuel per year. The fission product waste component (which becomes HLW after reprocessing) is approximately 4% of this by volume, but when discussing total HLW arising from the fuel (including the fuel matrix), the figure of approximately 30 tonnes per year is used. After vitrification, this would be equivalent to approximately 15 containers of vitrified glass.