Poo Metallurgy

When was the metallurgy of plutonium introduced to India?

The metallurgy of plutonium was introduced in India in 1961.

What was the initial achievement of the team that introduced plutonium metallurgy to India in 1961?

The team, consisting of a chemist, a chemical engineer, and a metallurgist, isolated milligram quantities of plutonium metal beads.

What method was first used in India to produce plutonium metal?

The calciothermic reduction of plutonium tetrafluoride was the first method used.

For India's nuclear energy program, what is the significance of plutonium?

Plutonium is significant because of India's limited uranium reserves and abundant thorium reserves, making it key to the three-stage nuclear program.

In what year was the first plutonium fuel reprocessing plant for recovering plutonium commissioned in Trombay, India?

The first plutonium fuel reprocessing plant was commissioned in 1964.

What is the primary reaction for generating energy in nuclear reactors from natural or low-enriched uranium?

Energy is derived from the fission of $^{235}U$ by slow or thermal neutrons.

Describe the nuclear reaction sequence that transforms fertile $^{238}U$ into fissile $^{239}Pu$.

A $^{238}U$ nucleus captures a neutron to become $^{239}U$, which then undergoes two successive beta decays to form $^{239}Np$ and finally $^{239}Pu$.

Besides $^{239}Pu$, what other isotopes of plutonium are formed by successive neutron captures in a reactor?

Other isotopes formed include $^{240}Pu$, $^{241}Pu$, and $^{242}Pu$ from $^{239}Pu$.

What factors influence the final isotopic composition of plutonium in spent nuclear fuel?

Factors include discharge burn-up of the fuel, neutron flux, neutron energy spectrum, fuel enrichment, and fuel-clad volume ratio.

What is the first step in the process of recovering plutonium from spent fuel elements after cooling?

The first step is the mechanical or chemical dejacketing of the fuel elements from their cladding material.

In the PUREX process, what chemical is used to dissolve the irradiated fuel?

The fuel is dissolved in nitric acid ($HNO_3$).

What is the function of solvent extraction in the PUREX process for plutonium recovery?

Solvent extraction is used to remove fission products from the aqueous solution containing uranium and plutonium.

What occurs during the 'partition' stage of the PUREX process?

In the partition stage, plutonium is separated from uranium.

After partitioning, how is the separated plutonium further purified in the PUREX process?

The separated plutonium is further purified by an ion-exchange process.

In what chemical form is plutonium obtained after the final purification step of the PUREX process?

Plutonium is obtained as plutonium nitrate.

How is plutonium nitrate solution converted into plutonium dioxide ($PuO_2$) powder for storage?

It is converted via oxalate precipitation followed by calcination in air at temperatures ranging from 400-700°C.

What are the three main safety considerations when handling plutonium?

The main considerations are its high radiotoxicity, specific biological behaviour, and fissile properties (criticality).

What is the primary concern for personnel handling plutonium in terms of biological hazards?

The primary concern is to prevent particulate matter containing plutonium from entering the body of the operator.

Why is inhalation of plutonium particles particularly hazardous?

Inhalation is hazardous due to the long biological half-life, high energy of emitted alpha particles, and selective localisation of plutonium in the bone.

What specialized equipment is essential for any plutonium handling laboratory to ensure containment?

A well-ventilated laboratory with confined and hermetically-sealed glove boxes is essential.

What atmospheric condition is maintained inside glove boxes used for handling plutonium?

The glove box is maintained under a slightly negative pressure in an inert gas atmosphere (like $N_2$, Ar, or He).

The external radiation hazard of plutonium is mainly from and radiations.

gamma, neutron

What isotope and its decay products are the main contributors to the gamma radiation dose rate from plutonium?

The beta emitting $^{241}Pu$ and its daughter product $^{241}Am$ are the main contributors.

What are the two sources of neutron emission from plutonium materials?

The sources are spontaneous fission of even-numbered isotopes (like $^{240}Pu$) and ($\alpha$, n) reactions with light element impurities.

To minimize radiation exposure, what is the guideline regarding the mass of plutonium that is handled at a time?

Restrictions are imposed on the mass of plutonium that is handled at a time, to minimize the neutron dose.

What is a 'criticality accident' in the context of fissile materials like plutonium?

A criticality accident is an uncontrolled, self-sustaining nuclear chain reaction.

The critical mass of plutonium and its compounds depends on what factors?

It depends on the geometry, the environment, and the surroundings of the fissile material.

What is the upper safe limit for handling fissile material in the plutonium metallurgy laboratory at Trombay, expressed as a percentage of the critical mass?

The upper safe limit is kept at 50% of the critical mass.

The average number of neutrons produced per neutron absorbed by a fissile nucleus is represented by what symbol?

It is represented by the Greek letter eta ($\eta$).

Which fissile nuclide, $^{233}U$, $^{235}U$, or $^{239}Pu$, has the highest $\eta$ value in a thermal neutron spectrum?

$^{233}U$ has the highest $\eta$ value in a thermal neutron spectrum.

For fast reactors, which fissile nuclide is considered the best fuel based on physics considerations?

Plutonium ($^{239}Pu$) is considered the best fuel for fast reactors.

The production of high purity, nuclear grade plutonium metal at Trombay was achieved using what general method?

It was achieved by the reduction of plutonium halides.

What is the specific chemical reaction for the calciothermic reduction of plutonium tetrafluoride ($PuF_4$) to produce plutonium metal?

$PuF4 + 2Ca \rightarrow Pu + 2CaF2$.

What is the purpose of adding a small amount of iodine as a 'booster' in the calciothermic reduction of $PuF_4$?

The iodine makes the reaction more exothermic and also lowers the melting point of the slag.

During the calciothermic reduction of $PuF_4$, what observation indicates the initiation of the reaction?

The start of the reaction is indicated by a sudden rise in temperature monitored by a thermocouple.

Why is melting and casting pure plutonium challenging?

It is challenging due to its extreme reactivity, high toxicity, low melting point, and the volume changes associated with its multiple phase transformations.

What type of crucible has been most widely used for melting plutonium, despite its slight contamination of the melt?

Magnesium oxide (MgO) crucibles have been widely used.

How are Aluminium-Plutonium (Al-Pu) alloys prepared, a technique particularly advantageous for plutonium alloy production?

They are prepared by the aluminothermic reduction of plutonium oxide ($PuO_2$).

What is the chemical reaction for the aluminothermic reduction of $PuO_2$ in the presence of excess aluminium and cryolite?

$3PuO2 + 4Al = 3Pu + 2Al2O_3$.

What is the primary advantage of the aluminothermic reduction technique for preparing Al-Pu alloys?

It eliminates costly steps of plutonium metal production, its handling in an inert atmosphere, and segregation issues.

Aluminium is considered an excellent inert carrier for plutonium fuel because it has a low parasitic _.

thermal neutron absorption cross-section

In dispersion type Al-Pu fuels, what is the advantage of having fissile particles (like $PuAl_4$) in a non-fissile matrix?

The advantage is that fission recoil damage is confined to the immediate area adjacent to the fissile particles, leaving the matrix largely undamaged.

Al-13 w/o U plate fuel elements, using 85% enriched $^{235}U$, were used as a substitute for imported fuel in which Indian reactor?

They were used in the Apsara Swimming Pool type reactor at BARC.

What is the primary application of Plutonium-Beryllium (Pu-Be) alloys?

They are used as low flux neutron sources to utilize the interaction of alpha particles from plutonium with beryllium atoms.

What is the nuclear reaction that generates neutrons in a Pu-Be source?

The reaction is $^9Be(\alpha, n)^{12}C$.

What is a major advantage of Pu-Be neutron sources regarding their stability?

Their neutron yield is stable with respect to time due to the long half-life of $^{239}Pu$ and the relatively small amount of low energy gamma radiation.

What intermetallic compound provides the maximum neutron yield in Pu-Be alloys?

The intermetallic $PuBe_{13}$ provides the maximum yield.

Why is unalloyed plutonium not generally tried as a nuclear fuel?

It is unsuitable due to its unfavorable metallurgical properties, including a low melting point and many allotropic transformations with large volume changes.

Which allotropic phase of plutonium is stable between 315 and 456°C and exhibits the highest ductility and best formability?

The delta ($\delta$) phase.

How can the ductile delta phase of plutonium be stabilized down to room temperature?

It can be stabilized by the small addition of alloying elements like Al, Ga, Ce, or In.

What are the desirable mechanical and metallurgical properties of delta-stabilised plutonium?

It is ductile, soft, has a hardness value of 40-45 kg/mm², and alloys have negligible volume change during working.

In India, the first major plutonium fuel fabrication job was for the complete core of which zero energy fast reactor?

It was for the PURNIMA fast reactor.

The core for the PURNIMA reactor consisted of 186 fuel pins containing around 25 kg of sintered _ pellets.

plutonium dioxide ($PuO_2$)

How were the $PuO_2$ pellets for the PURNIMA reactor core fabricated?

They were prepared from oxalate derived, sinterable $PuO_2$ powder by the powder metallurgy route of cold compaction and sintering.

Why is pure $PuO_2$ not suitable as a fuel in power generating reactors?

It fails to satisfy the reactor engineering and safety requirements of bigger reactors on its own.

What type of fuel, a mixture of uranium and plutonium oxides, is developed for liquid metal cooled fast breeder reactors (LMFBRs)?

Mixed oxide (MOX) fuel.

What was a significant problem observed with high-plutonium content MOX fuel, (U${0.3}$Pu${0.7}$)O$_{2-x}$, when it interacted with sodium coolant?

The interaction led to the formation of $Na3(U,Pu)O4$, which was accompanied by high swelling of the fuel.

To mitigate swelling from sodium interaction, what type of MOX pellet was developed?

Single-phase mixed oxide pellets of 70% $UO2$ - 30% $PuO2$ were developed.

In 1978, a decision was taken in India to explore fabricating MOX fuel as a substitute for what type of imported fuel?

It was to substitute for the imported enriched $UO_2$ fuel for the boiling water reactors (BWRs) at TAPS.

The pilot scale MOX fuel fabrication facility at Trombay has a capacity of how many sintered MOX pellets per day?

It has a capacity of 50 kg of sintered MOX pellets per day.

What is the effect on thermal conductivity when up to 5 w/o $PuO2$ is added to $UO2$?

The thermal conductivity is not significantly affected.

What is the effect on the melting point of $UO2$ when up to 5 w/o $PuO2$ is added?

The melting point decreases by 20°C.

Why are mixed carbide (UPu)C and nitride (UPu)N fuels considered more advanced than oxide fuels for fast reactors?

They have higher breeding ratios, higher specific power ratings, and much shorter doubling times.

What is a significant drawback of oxide fuels that limits their breeding ratio in fast reactors?

They have an inherent drawback of relatively low heavy atom density.

What is the primary method for synthesizing mixed uranium-plutonium carbides and nitrides?

They are synthesized by the carbothermic reduction of mechanically mixed $UO2$ and $PuO2$ powders.

Compared to uranium-rich carbides, what is an advantage of plutonium-rich (UPu)C in terms of sintering temperature?

Plutonium-rich (UPu)C has a sintering temperature that is 150-200°C lower.

The first stage of India's three-stage nuclear power program is based on what type of reactor?

It is based on natural uranium-fuelled Pressurised Heavy Water Reactors (PHWRs).

What is the role of the plutonium produced in the first stage of India's nuclear program?

This plutonium will be used to fuel the second stage of fast breeder reactors (FBRs).

The second stage of India's nuclear program involves fast breeder reactors that will use plutonium fuel and also breed more plutonium from what fertile material?

They will breed more plutonium from depleted uranium ($^{238}U$) and also produce $^{233}U$ from thorium ($^{232}Th$).

What is the fuel cycle for the third stage of India's nuclear power program?

The third stage is the self-sustaining Thorium-$^{233}U$ thermal breeder fuel cycle.

What is a promising alternative to the traditional powder and pellet fabrication route for plutonium-bearing fuels?

The 'gel-pelletisation route', which uses gel derived microspheres, is a promising alternative.

What is the primary advantage of the gel-pelletisation process for fabricating plutonium fuels?

It is a free flowing and dust-free process, which is ideally suited for remote fabrication of fuel pellets.

For safe handling of plutonium, operations are performed in hermetically-sealed glove boxes through _ gloves.

alpha-tight neoprene

The process of separating uranium and plutonium from fission products in an organic solvent is known as _.

solvent extraction

The plutonium-rich mixed oxide fuel (U${0.3}$Pu${0.7}$)O$_{2-x}$ was initially considered for which reactor technology in the 1970s?

It was considered for liquid metal-cooled fast breeder reactors (LMFBRs).

The addition of a small amount of to the $PuF4$-Ca charge serves as a chemical 'booster' in plutonium metal production.

iodine

Which phase of unalloyed plutonium is stable at room temperature?

The alpha ($\alpha$) phase, which is monoclinic.

What property of the alpha to beta phase transformation in plutonium makes it unsuitable for fuel use?

The transformation is accompanied by a large volume expansion of the order of 10%.

What is the crystal structure of the delta-stabilised plutonium phase?

It has a face-centred cubic (fcc) crystal structure.

The first MOX fuel experience in Trombay was acquired in 1972 with a test pin irradiation in which reactor?

The irradiation testing was done in the pressurised water loop (PWL) of the CIRUS reactor.

A prototype MOX fuel cluster of 6 pins was irradiated in the PHWR at RAPS starting in what year?

The irradiation started in December 1978.

What is the main advantage of (UPu)N fuel regarding its compatibility with sodium coolant?

(UPu)N has relatively good compatibility with sodium.

In the fabrication of mixed carbide fuels, what is the role of carbothermic reduction?

Carbothermic reduction of a powder mixture of $UO2$, $PuO2$, and graphite is the synthesis step to form the carbide.

What is a potential issue if the temperature for carbothermic reduction of mixed oxides is too high (above 1625°C)?

It can lead to the formation of the undesirable liquid phase PuC$_{1.5}$ by peritectic decomposition.

India's planned plutonium-fuelled prototype fast breeder reactor of 500 MW(e) capacity was scheduled for criticality around what year?

It was planned for criticality in the early 1990s.