Thursday, March 15, 2012

Toward a Healthy Nuclear Mix

If the societies of both advanced and emerging nations are to generate a more abundant future, there is no getting around the need for safer, cleaner, more affordable nuclear power and heat. Both the UK and China are waking up to this fact, and will be turning away from unreliable and exorbitantly expensive green intermittent energy sources, toward more reliable nuclear plants.

There will be many approaches to fission reactors in the future. When taken together, the future mix of nuclear reactors are likely to generate far more power, with far less waste, far more safely. This will be true because the discarded "waste" from one type of reactor will actually be the valuable fuel for other types of reactors -- after which very little waste will remain.
Integral fast reactors (a new type of breeder reactor, so called because they can “breed” fuel) use almost 100% of the energy in uranium. Most of the world’s 440 commercial nuclear power plants are light water reactors using less than 1%.

According to University of Adelaide professor Barry Brook, this is because fast reactors use uranium 150 times more efficiently. For example, a 1GW light water reactor with a life span of 60- 80 years would need an initial loading of 60t-80t of uranium, 3%-5% of which would be enriched. Thereafter, for every year of its life, it would need 150t of fresh (mined) uranium and 20t of long- lived waste would be produced each year.

A fast reactor would also need 80t of uranium initially but would only need 1t of uranium a year from then on. And only 1t of waste would come out of it, which would be short-lived waste (it decays to normal levels of radioactivity in a few hundred years).

The even better news is that the reactors could take nuclear waste (the highly radioactive, long-lived type) and use it as a feedstock .

“If SA used fast reactors, the first step would be to consume all its current nuclear waste — that would last hundreds of years,” says Brook _fm
Whether using uranium or thorium, breeding fissile fuel from fertile fuel within a working reactor, is likely to be the most workable long-term approach to fission power and heat.

Another type of future breeder reactor is likely to be a hybrid fusion-fission reactor, where fusion is used as a neutron source, to breed fertile fuels such as thorium or U238 into fissile fuels such as U233 or Pu239.
...nuclear is often portrayed as a single, undifferentiated energy source. This is wrong and risks losing the opportunity to explore the role that new nuclear technologies can play.

Indeed, those who seek to write nuclear off completely are missing what could be remarkable developments on the horizon, with hybrid technologies potentially reshaping the way we think about nuclear energy.

...The long-term future of nuclear may therefore lie with combining nuclear fission (atoms splitting) and fusion (atoms merging) in a hybrid reactor. Governments, agencies and research institutes are already moving tentatively in this direction.

Hybrid fusion was first proposed by the American Nobel laureate, Hans Bethe, to enable more widely available reserves of nuclear fuels than uranium, such as thorium, to be used.

Hybrid could become a reality within the next two decades — the International Atomic Energy Authority has started a project on conceptual development of steady state compact fusion neutron sources, and the Institute of Plasma Physics in China is planning to build a hybrid fusion proof-of-principle prototype experiment by 2025. International experiments are under way into the critical fusion parts of such a system.

The basic principle is that neutrons generated by fusion in the plasma core stimulate fission in the outer blanket that contains uranium or other fissile materials (which could include nuclear waste).

Because there is relatively less energy extracted from the plasma than in pure fusion, continuous operation can be engineered more readily.

The fission is well below critical mass and operates only when there is a current flowing in the plasma, which can be switched off at a moment’s notice. This is why the system is safer, especially in regions where earthquakes and tsunamis can occur._BusinessDay
The hybrid fusion - fission reactor functions a lot like an accelerator-driven sub-critical reactor. But the hybrid reactor should prove to be more economical overall.

Other forms of "breeder reactors" will probably be adopted far sooner than hybrid designs can be perfected. Many of them will be of the small modular reactor (SMR) type, to provide increased scalability, affordability, reliability, and better siting options.

Besides a variety of breeder reactors, advanced light water reactors and gas-cooled high temperature reactors will round out the future mix, for greater versatility.

More on Oxford U. report recommending the UK turn away from expensive and unreliable green energy, to adopt more reliable nuclear power.

More on the Gen III and Gen IV nuclear reactor synergy



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