Nuclear study provides major update on plutonium isotope fission

June 24, 2024
Posted by: OptimizeIAS Team
Category: DPN Topics

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Nuclear study provides major update on plutonium isotope fission

Sub: Science and tech

Sec: Nuclear Energy

Context:

On March 4, India advanced to the second stage of its nuclear power programme by starting core-loading of the prototype fast breeder reactor (PFBR) at Madras Atomic Power Station, Kalpakkam.

Details:

The first stage used uranium isotopes in heavy-water reactors to produce plutonium-239 (Pu-239) and energy.
The second stage focuses on plutonium fission, with Pu-239 capturing neutrons and becoming Pu-240 or undergoing fission.

Understanding Pu-240 Fission:

When Pu-240 captures a neutron, it can turn into Pu-241 or undergo fission, but predicting the energy of fission products is complex.
The prompt fission neutron spectrum (PFNS) measures neutrons emitted immediately after neutron capture by Pu-240.
Only two studies have measured PFNS in Pu-240; the latest used higher-energy neutrons and found significant deviations from theoretical predictions.

Implications and Uses of New Findings:

The PFBR uses plutonium from the CANDU reactor spent fuel, which contains Pu-240, making new data on Pu-240 behaviour relevant.
Pu-240, considered a contaminant in weapons-grade plutonium, is harder to separate from Pu-239 and accumulates predictably.
The recent study by researchers at Los Alamos Neutron Science Centre used a pure Pu-240 sample to measure neutron energies and fission products, identifying higher-than-expected second-chance fission rates.
- So far there has only been one study that attempted to study the PFNS of induced fission in Pu-240, where neutrons that bombarded the Pu-240 nuclei had an energy of 0.85 mega-electron-volt (MeV).

Impact on Nuclear Data Libraries:

Discrepancies between predicted and observed PFNS data suggest updates are needed in nuclear data libraries like ENDF, JEFF-3.3, and JENDL-5.0.
These libraries are crucial for reactor design, radiation shielding, nuclear medicine, and other applications.
The study found that only JENDL-5.0 included both multi-chance fission and pre-equilibrium neutron emission processes, highlighting areas for improvement in other libraries.

Important terms:

Prototype fast breeder reactor (PFBR)	It operates on the principle of using a breeder reactor mechanism, where it generates more fissile material (plutonium-239, Pu-239) than it consumes. In contrast to Pressurised Heavy Water Reactors (PHWRs) that utilize natural or low-enriched uranium-238 (U-238) and produce Pu-239 as a byproduct, the PFBR takes this produced Pu-239 and combines it with additional U-238 in a mixed oxide form. This mixture is then loaded into the reactor’s core along with a breeder blanket, a layer that interacts with the fission products to create more Pu-239. A distinctive feature of the PFBR is its use of fast neutrons (hence “fast” in the name), which are not moderated or slowed down, enabling certain fission reactions that contribute to the breeding process. The reactor uses liquid sodium as a coolant in two separate circuits for safety and efficiency. The primary circuit carries the coolant through the reactor core, absorbing heat and radioactivity, and then passes the heat (but not the radioactivity) to a secondary coolant circuit through heat exchangers. This secondary circuit then uses the transferred heat to generate electricity.
Pressurised Heavy Water Reactor (PHWR)	A PHWR is a nuclear reactor that uses heavy water (deuterium oxide D2O) as its coolant and neutron moderator. PHWRs frequently use natural uranium as fuel, but sometimes also use very low enriched uranium. The heavy water coolant is kept under pressure to avoid boiling, allowing it to reach higher temperature (mostly) without forming steam bubbles, exactly as for a pressurized water reactor. While heavy water is very expensive to isolate from ordinary water (often referred to as light water in contrast to heavy water), its low absorption of neutrons greatly increases the neutron economy of the reactor, avoiding the need for enriched fuel. The high cost of the heavy water is offset by the lowered cost of using natural uranium and/or alternative fuel cycles. As of the beginning of 2001, 31 PHWRs were in operation, having a total capacity of 16.5 GW(e), representing roughly 7.76% by number and 4.7% by generating capacity of all current operating reactors. Till now, the biggest reactor of indigenous design was the 540 MWe PHWR, two of which have been deployed in Tarapur, Maharashtra.
CANDU Reactors	The CANDU (Canada Deuterium Uranium) is a Canadian pressurized heavy-water reactor design used to generate electric power. The acronym refers to its deuterium oxide (heavy water) moderator and its use of (originally, natural) uranium fuel. CANDU reactors were first developed in the late 1950s and 1960s by a partnership between Atomic Energy of Canada Limited (AECL), the Hydro-Electric Power Commission of Ontario, Canadian General Electric, and other companies. By 2010, CANDU-based reactors were operational at the following sites of India: Kaiga (3), Kakrapar (2), Madras (2), Narora (2), Rajasthan (6), and Tarapur (2).

Source: TH