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Nuclear: what is a 4th generation reactor?

Isabelle Dumé, Science journalist
On March 31st, 2022 |
3 mins reading time
2
Nuclear: what is a 4th generation reactor?
Key takeaways
  • Several countries are investing in fourth generation nuclear reactors.
  • Generation IV nuclear power involves a system of fuel fabrication plants and reprocessing facilities that together would overcome some of the shortcomings of current nuclear power plants.
  • Plutonium is formed when uranium-238 captures neutrons from nuclear fission reactions. Most of these reactors need to be fuelled with uranium-235, but most fourth-generation reactors only need uranium-238 to operate.
  • The design of Generation IV reactors incorporates a number of technological advances to meet the criteria of sustainability, nuclear safety, economic competitiveness and resistance to nuclear proliferation

Sev­er­al coun­tries are invest­ing heav­i­ly in so-called fourth gen­er­a­tion nuclear reac­tors. But what are the char­ac­ter­is­tics of these new reactors?

Less energy-intense and safer

Gen­er­a­tion IV nuclear pow­er refers to a sys­tem of fuel fab­ri­ca­tion plants and repro­cess­ing facil­i­ties that togeth­er over­come some of the short­com­ings of cur­rent nuclear pow­er instal­la­tions. To be clas­si­fied as Gen­er­a­tion IV, a sys­tem must meet, or at least have the abil­i­ty to meet, the fol­low­ing cri­te­ria: (1) it is much more fuel-effi­cient than cur­rent plants; (2) it is designed in such a way that severe acci­dents are not pos­si­ble, that is, plant fail­ure or an exter­nal event (such as an earth­quake) should not result in radioac­tive mate­r­i­al release to the out­side world; (4) the fuel cycle is designed in such a way that ura­ni­um and plu­to­ni­um are nev­er sep­a­rat­ed (“diverged”) but only present in a mix and with oth­er ele­ments. This makes it more dif­fi­cult to cre­ate nuclear weapons.

“Generation” and “reactor technology”

In the nuclear indus­try, the term “gen­er­a­tion” is dis­tinct from “reac­tor tech­nol­o­gy”, and a gen­er­a­tion may com­prise sev­er­al types of tech­nol­o­gy. Dif­fer­ent gen­er­a­tions have spe­cif­ic require­ments at a giv­en point in time. The Gen­er­a­tion IV Inter­na­tion­al Forum 1, which is ded­i­cat­ed to future reac­tor research and was launched in 2001, has defined four gen­er­a­tions of nuclear fis­sion reac­tors, each with a cer­tain set of objec­tives. Most of the reac­tors cur­rent­ly in oper­a­tion are of the sec­ond and third gen­er­a­tion, but Chi­na suc­cess­ful­ly start­ed up a first fourth gen­er­a­tion reac­tor with its high-tem­per­a­ture gas-cooled mod­u­lar peb­ble bed (HTR-PM) demon­stra­tion project in late Decem­ber 2021.

In 2020, the aver­age age of the world’s nuclear fleet was 30 years, with 25% of the fleet being over 40 years old 2. Reac­tor oper­a­tors are there­fore endeav­our­ing to extend the oper­a­tion of this fleet through long-term invest­ments, with new stan­dards hav­ing been adopt­ed fol­low­ing the Fukushi­ma acci­dent. Anoth­er require­ment for Gen­er­a­tion IV reac­tors is that they must pro­duce more fuel than they con­sume as well as destroy the long-lived radioele­ments cre­at­ed in the reac­tor dur­ing operation.

Requires only uranium-238 to operate 

Ura­ni­um used in nuclear reac­tors is com­posed of two iso­topes: ura­ni­um-235, which can be used as fuel, and ura­ni­um-238, which makes up 99.3% of nat­ur­al ura­ni­um and which must be con­vert­ed to plu­to­ni­um before it can be used as fuel. Plu­to­ni­um is formed when ura­ni­um-238 cap­tures neu­trons from nuclear fis­sion reactions. 

Most “breed­er” reac­tors must be fuelled with ura­ni­um-235, but most fourth gen­er­a­tion reac­tors only need ura­ni­um-238 to oper­ate. There are huge reserves of this iso­tope in the world, as it has been set aside over the years as a by-prod­uct of the ura­ni­um-235 enrich­ment process that enrich­es this iso­tope to the con­cen­tra­tions required for today’s reactors. 

Even if nuclear pow­er gen­er­a­tion were to increase sig­nif­i­cant­ly, we would not need to extract addi­tion­al ura­ni­um for a very long time. If it were to remain at cur­rent lev­els, the mined ura­ni­um we already have would be suf­fi­cient to run reac­tors for sev­er­al thou­sand years.

As with Gen­er­a­tion II and III reac­tors, the non-reusable fis­sion prod­ucts, or waste, from Gen­er­a­tion IV reac­tors will also have to be dis­posed of safe­ly and stored per­ma­nent­ly. The same applies to the waste that will result from the decom­mis­sion­ing of these reac­tors at the end of their lives. A num­ber of coun­tries have invest­ed a lot of mon­ey in the devel­op­ment of Gen­er­a­tion IV reac­tors. While Europe has lagged behind Rus­sia, Chi­na, Japan and India, France has picked up the pace of invest­ment – notably with the gov­ern­men­t’s recent announce­ment to build new gen­er­a­tion nuclear reac­tors (see Box 1). The main objec­tive today in this con­text is to design reac­tors capa­ble of destroy­ing long-lived radioele­ments in spent fuel while pro­duc­ing new fuel.

1https://www.gen‑4.org/gif/
2 https://​www​.oecd​-nea​.org/​j​c​m​s​/​p​l​_​2​6​2​8​8​/​g​e​n​e​r​a​t​i​o​n​-​i​i​-​a​n​d​-​i​i​i​-​r​e​a​ctors