The NGNP Alliance recently published a thought provoking blog titled Energy Vs. Electricity and Why We Care that clearly explains the basis for their interest in using high temperature gas cooled reactors. That group of far-sighted organizations was formed in recognition that the energy market is far larger than just producing electricity.
They believe that higher temperature reactors offer a good path for enabling fission energy to serve needs in other segments of the energy market, bringing its energy density and emission free nature to applications like industrial process heat and enhanced resource recovery.
If we moved our electricity production to 100% carbon free sources, like nuclear, hydro, and renewables, we would reduce the use of carbon fuels by only 25%. Basically cutting most coal consumption and reducing natural gas by 30%. But we would still be left huge amounts of petroleum and natural gas being used for industrial and transportation purposes.
The NGNP Alliance is looking at a new kind of reactor, called a High Temperature Gas Reactor (HGTR) that can generate high temperature, high quality heat and do it with true inherent safety. That heat could replace coal, natural gas, and petroleum in many industrial processes including chemical and fertilizer manufacture and hydrogen and synthetic fuel production.
I’ve been interested in expanding atomic fission’s role in the energy market for almost as long as I can remember. My early experience in nuclear energy was in using it to propel ships around the world; electricity production was just an auxiliary task for the reactors I learned to operate.
I’ve never forgotten how the Navy’s propulsion reactors directly replaced diesel engines and large, oil burning steam turbines. That still seems to me to be a huge, untapped commercial opportunity, especially in a world that is so often made to tremble in the face of threats to continued oil abundance.
As I pointed out in a recent post welcoming the NGNP Alliance to the pro-nuclear blogging community, the group has recently opened the comment feature of its blog. That is a big step forward for the rather conservative, large-company members of the Alliance. Not only has the NGNP Alliance enabled comments, they have assigned a technically astute moderator who both keeps out the trolls and engages in thoughtful discussion.
I have taken advantage of the rare opportunity to participate in a publicly accessible conversation with people who are working on technology that has quite a bit more than a prayer of moving beyond the paper reactor stage of development. My latest contribution to the discussion thread was in response to a commenter who was concerned about the fact that helium is a difficult gas to contain. His concern is that a seemingly small leak rate could add up to a substantial issue over the life of the plants.
I understand NGNP’s decision to use helium, it has a number of attractive properties that resulted in its selection as the de facto coolant of choice for gas cooled reactors sometime in the late 1950s to early 1960s.
Up until that time, the favored gas was CO2, which was the design choice for the British Magnox and AGR reactors. Though no new CO2 cooled reactors have been built in 30 years, the UK still produces about 10-15% of its electricity each year with CO2 cooled reactors. By far, it is the coolant gas with the most run time in nuclear reactors.
There is one thing we already know about that alternative; CO2 breaks down at too low of a temperature to make it useful for the high temperature reactors that NGNP is planning. It’s maximum temperature limit is somewhere close to 600 C.
Designers looking for a better coolant gas selected helium for Peach Bottom, the AVR and for the Dragon HTR. There were promising results in those small reactors. The challenges associated with helium’s physical properties (monatomic gas with very low specific mass) did not make much of an impact until attempts were made to produce much larger machines and to consider using helium as the working fluid as well as the reactor coolant by directly coupling a gas turbine to the reactor heat source.
Then, factors like leakage and the challenge of completely redesigning turbines and compressors (and building up an entirely new supply chain) became much more important.
In my opinion, helium-related technical challenges have been a primary reason why gas cooled reactors have not had much commercial success, despite their promise and despite the fact that GA once had an order book of more than 10 large units, none of which were ever really started. Helium gas challenges are no more insurmountable than the challenge of using light water as a coolant at temperatures high enough to produce useful steam; the difference is that the LWR hill was climbed in the 1950s. That means there is a knowledge base and a supply chain.
I avoid climbing big hills. I’m a lazy cheap skate (actually, I am just not terribly wealthy, so I needed to find a cheaper way around the issues). Early in my Adams Engines days, I determined that nitrogen gas has “good enough” nuclear properties and with the advantage of having aerodynamic properties that are essentially identical to air. Using N2 allows atomic engine designers to take advantage of the vast technology and knowledge base associated with air breathing combustion turbines.
Aside: I discussed this decision in detail in a post titled Nitrogen (N2) Gas Cooling For a Closed Cycle Nuclear Heated Gas Turbine End Aside.
The market application I was interested in serving is different from the one that NGNP is aiming to serve. Their choice of helium makes perfect sense; there are nuclear related challenges with using nitrogen that cannot be solved, they must instead be mitigated. I think the mitigations will be effective; nitrogen’s inherent neutron absorption and activation issues discourage most nuclear engineers from even considering using it as a coolant gas.
In NGNP’s defense, the technical challenge of preventing leaks in a helium cooled reactor can be solved, my hope is that we have gained enough engineering and manufacturing experience in the 50 years since the ill-fated water cooled reactor coolant pump bearings so that NGNP has more success than Ft. St. Vrain.
I have selfish reasons for wanting NGNP to succeed. Not only do I want more nuclear fission power to replace fossil fuel combustion, but I also want regulatory acceptance and a supply chain to be established for TRISO coated fuel. Those tiny particles are a key building block that just might make it possible for another attempt at building Adams Engines sometime in the distant future.
(Note: I have made some minor edits since my original comment on the NGNP Alliance blog.)