March 24, 2023

French LEU Reactor & SSN Implications

French Anonymous made interesting comments on March 20, 2023. Pete has done some editing and Pete's additional comments are in [...] brackets. 

These are rumours from the Indian press but without any info from the French side..

In any case I am not sure what it means. 

The design and the deployment/military uses philosophies of the French SSN are quite different from the Russian or US views. The Chinese are using an approach to LEU that sounds similar to the French one apparently, without much public data. 

-       The LEU/HEU debate has been well documented. The French system is really an extension of their civilian PWR reducing hugely the cost, using the same critical civilian safety regulation and relying on the civilian fuel cycle assets and economics. The legal need to inspect an empty reactor every 10 years (using robots) allows the French Navy to have very compact designs with the steam generator within the reactor (a critical interface changed every 10 years, including in HEU system, anyway[??] )

[ Peter Lobner page 206 (of a large .PDF) reports regarding France’s K15 reactor used in the Barracuda SSN:

“Fuel: Much higher uranium enrichment than in the [outgoing Rubis-class SSNs] CAS-48 reactor (which is 7% enrichment). Some sources claim K15 uses HEU fuel at > 90% enrichment.”]

and to develop robots, facilities (as in Civilian PWR, changed every 2/3 years) to change the fuel quickly (2/3 weeks) and to allow easy dismantling

The USN on the contrary puts a huge premium on "sealed for life core" because they have a long positive learning curve/experience, they have still a large inventory of HEU (Nuclear weapons converted, the US stopped the production of HEU [but the US is reported to be restarting HEU enrichment at a new SILEX trial plant in Kentucky] and because most important this limits the number of USN facilities needed (equipment, people, political local sensitivities) worldwide to support the fleet as the USN cannot piggy back on the civilian (See US senate studies). 

This leads to much larger US SSNs (due to the need to deploy vertical rods to slow down or stop reactor fission, the heat exchanger is outside, there is limited U235 volumetric density/loading for obvious safety reasons, making reactors typically twice the size, much higher cost and larger nuclear engineer/technician/damage control crew needed. Once you have large assets you try to use them beyond a traditional sub mission and you incorporate more and more cruise missile for instance (leading to VLS in large numbers). 

-       The French deployment has the objective of having SSNs to protect French SSBNs, protect the French surface fleet and to intercept enemy naval assets.

-       This means emphasis on very silent French SSNs with the best sonars and torpedoes. They operate tactically in an electric mode with very large permanent magnet motors (4 to 10 MWe range) and the associated converter/drives. This is more difficult for larger US and UK SSNs, driven by steam turbines. The steam drives turbogenerators while the steam turbine is used essentially for quick strategic moves (deep and at 25+knots) in the Barracuda class SSNs.

By the way the French reactors can remain critical using natural cooling in the silent mode as reported (critical means that the neutrons level is constant, at any, very low or very high, power.). The French do not have the resources including human of having large boats 

[Australia, with the smallest population and GDP in the nuclear sub world has even less human resources than France. Yet Australia is buying Virginia SSNs that require more than twice the crew (135 men) than French Barracuda SSNs (60 men).]

Barracudas don’t have redundant cruise missile systems for land attack ([which may be just 6] MdCN missiles on a Barracuda, fired via the torpedo tubes. [Just 6] is a marginal amount compared numbers of land attack missiles on French surface ships or airforce platforms. France can’t afford US style inter-services rivalries [where the US Submarine Service (using its SSNs and SSGNs) competes bureaucratically to be permitted to launch more Tomahawk land attack missiles than US destroyers or cruisers, or more than US aircraft dropping missiles/bombs. For example, in the 2003 invasion of Iraq and 2011 invasion of Libya (for Libya see US "Forces Committed")]. 

In the case of Brazil, Brazil has developed an intermediate reactor solution of its own, using the highest level LEU (just under 20% U235) to contain costs while refueling its future SSN after 20/25 years. It is the electric drive mode that Brazil is buying from Naval Group to use an enlarged Scorpene hull for its future SSN (no pump-jet as far as I know). 

Is the Indian Navy interested in the electric propulsion that the Russian or the US have not explored as much? in the pump-jet? Does India want to move to a civilian compatible solution? Is this linked to an Indian civilian Nuclear strategy discussed with the French at the same time? [India and France propose to construct 6 French designed European Pressurised Reactors (EPRs) reactors at Jaitapur, India), where India would need to have a complete control of its fuel cycle if India is serious about civilian nuclear. 

It is not clear at all [about India's submarine and civilian power reactor sector integration plans] but these are interconnected to a large extent.

Is India to build or buy SSNs in the 10,000 tonne [Russian Akula SSN tradition] or in the [French Rubis SSN or large Scorpene hull style] 3,000/4,000 tonne ranges? [or some size in between?] 

PETE COMMENTS

On Chinese use of LEU reactors and any Australian compatibility to France's SSN setup will be sent to Donors next week.

6 comments:

Anonymous said...

Hi Pete
On the Steamgenerator exchange every 10 years,I do not have the source and this might be incorrect.However this the most crucial safety element as it is the only reactor cooling mean (clogging,corrosion,nominal flow ?..ect) , and it separates the primary "hot" to the secondary in the open area.Any leaks even minute (tritium for instance)will originate there.

In the civilian sector it is a critical procedureIn the Fr regulation the legal limit is at least one inspection (hydraulic higher pressure test for example) in less than 40 months).Framatome, now EDF, in its US NUC service changed 25 steam generators on 24 US PWR in the last 20years (lifes spanning from 4to 25years).I do not believe that you can tolerate a 33 years maintenance free steam generator.Somehow you have to get at it and better be organized and equipped

By the way I looked at the great monumental work of Peter Lobner (2018, On NUC prop, 1939/2016).The waiting time ,in 2017, in the USN for maintenance is 177 months !with on average 14.7 sub not available per year..(section 2A , page 132).So the lost operational time due to fuel change is not really a very strong argument..(if its automated and organized )

On the HEU story in K15, Peter mention "some sources" but is not affirmative(section 4 page 206).This does not make any sense
The transition from HEU to LEU started 40 years ago at least. HEU production was stopped in 1996 and the HEU plant in Pierrelatte dismantled (materials for 500 military devices produced out of which 290 are operationnal)
The reactors evolved over times incl K15 wich is a generic name. Over time the refueling schedule moved from 5 years on the aircraft carrier(2XK15) to 7 on the AMETHYSTE and to 10 on the Suffren/Barracuda.The progresses are achieved via increased U loading.Not that simple with U235 where very high spatial segregation is needed to prevent over critical situation (The critical mass is abouT 1 liter for HEU... may be 20 times more in a reactor..)

Why he French would do that?The idea that you can keep such info, involving at least several hundred people, for many years, secret,in a country like France, with strong political opponents to anything N, is not credible if not..childish
The core belief is that transparency in the N sector is critical for the public acceptance and by the way for the credibility of the deterrence

On the HEU

Anonymous said...

Another point on the HEU high rationality in the US,the disposal issue

Having a glut of HEU (up to 2064 according to Lobner in 2017, (less if more subs/sailing more)a smart mean to dispose it is not to store it in a repository underground but to use it as fuel and to dispose it after 35 year in a solid steel structure such as a sub section, in the same repository.So from an enviromental point of view it is better than to fabricate new LEU with the PU recycling (in MOX may be but not in the US) and its down processes.Highly rational
"The less we mess around with this N stuff the better we are,at the end put it in a deep cavern" (costs , competence ect) is what you read beeteween the line.It works well and change is costly, and we have the time
The US starting point is not the same as France or China.In the UK the fuel is coming from the US and the UK is not sure what to do..so far all the boats are floating storage waiting for a solution and a budget

The change of fuel lost time is a second order problem if any.The tactical impact is not material (or at least never documented )

Gessler said...

Hi Pete,

On the topic, it seems the S-2/SSBN-80 INS Arihant (the first Indian-built nuclear boat, commissioned in 2016) has come in for a dry-docking, the satellite image apparently being from November 2022:

https://ibb.co/RH3vdcj

It's not clear for exactly what purpose it's there. Some are speculating that the boat has come in for its first refit which includes reactor refueling. If so, given the Arihant's CLWR-B1 PWR had gone critical in mid-2013, it would imply a 9 or 10-year refueling interval on a reactor fueled with 40% enriched HEU. However, that is assuming there weren't any peculiarities/issues worth concern with the reactor (or the boat itself) necessitating the dry-docking, rather than anything to do with the fuel. Or perhaps just a regular maintenance refit...first-of-class boats often have issues that require taking a closer look.

I guess we'd know based on how long the boat remains in dock. Or maybe we won't...hard to say for sure given the Indian MoD keeps chatter on the SSBN program to a minimum.

Submarine expert H.I. Sutton had previously speculated that the reactors on the S-4 (3rd boat) could be of an 'improved' type. It's not clear what exactly he means but if the Arihant's recent dry-docking is indeed for a scheduled refueling, then for sure India would want its future reactors to have their refuel intervals closer to ~15 years at least, that would also imply a higher enrichment grade for the fuel.

All in all, it just goes to show that the India still has a lot of investments to make into its nuclear submarine program.

Cheers

Pete said...

RAN VIRGINIA AVAILABILITY BELOW

Hi French Anonymous at Mar 25, 2023, 2:21:00 AM and Mar 25, 2023, 4:57:00 AM

It looks like the accusation France has HEU submarine reactors is misinformed.

Thanks for Peter Lobner's Page 132 at https://lynceans.org/wp-content/uploads/2020/02/Marine-Nuclear-Power-1939-2018_Part-2A_USA_submarines.pdf

reference he low availability of US SSNs, specifically Lobner writes:

"In October 2017, the maintenance backlog was reported to have idled 15 SSNs for a total unplanned delay of 177 months (14.75 submarine years)."

So 15 of the USN's 50 SSNs are out of commission in maintenance at any one time.

RAN VIRGINIA AVAILABILITY

On that ratio, 1 of the 3 RAN Virginias of the 2030s will be out of commission at any one time

leaving only 2 Virginias, active in the RAN, for the odd A$120 Billion we would have spent by 2040!

Regards Pete

Pete said...

Hi again French Anonymous

A Nuclear Threat Initiative (NTI) 2010 paper makes some interesting points about HEU in USN sub reactors and LEU "Caramel"
fuel in French Navy SSNs. http://www.nti.org/analysis/articles/expanding-nuclear-propulsion-challenges/

"...Most civilian power reactors use uranium enriched to 3-5% levels.[5] The U.S. navy's nuclear program, formed under the direction of Admiral Hyman Rickover, favored HEU fuel over LEU, since the fuel volume can be smaller, and the vessel requires refueling less often.[6] Virginia-class attack submarines, for example, have HEU cores designed to last the lifetime of the submarine—an estimated 33 years.[7]..."

"...French nuclear vessels are able to extract more energy from LEU than are U.S. vessels by taking advantage of a more LEU-efficient fuel design. The French navy uses a uranium-dioxide composite embedded in a zirconium alloy grid, an arrangement known as "caramel" fuel.

CARAMEL fuel increases the efficiency of the burn-up of uranium-235 so that lower enrichment levels and/or smaller reactor volumes can be employed with a greater energy yield. Studies have shown that a design in which small spheres of uranium dioxide are embedded in a zirconium matrix can boost the efficiency of the fission reaction even further.[32]

Using this information, and basing their findings on a 1990 MIT nuclear engineering thesis by Thomas Ippolito Jr., Chunyan Ma and Frank von Hippel estimate that a submarine reactor utilizing

20-percent enriched caramel fuel could have a core life of 33 years at a 130 megawatt output

with a height of 1.7 meters and a diameter of 1.4 meters. The size of the reactor compartment of Virginia-class submarines is classified, but such a reactor could easily fit in the similarly-sized predecessor to the Virginia, the Los Angeles-class submarine.[33]

Ma and von Hippel's analysis suggests that the U.S. Navy could retrofit its fleet to achieve the flexibility afforded by the present HEU cores while still complying with an international norm against the use of HEU."..."

Separately

It is interesting France's 6 boat Redoubtable-class SSBNs used HEU reactors from 1971–2008 https://en.wikipedia.org/wiki/Redoutable-class_submarine_(1967) . From 1964, when the first Redoubtable was laid down, France was heavily producing HEU for its nuclear weapons - so HEU for sub reactors at that time made more economic sense.

After France's HEU production era ended the advantages of using civil-naval LEU reactors then must have become apparent.

Regards Pete

Pete said...

Hi Gessler

Refueling INS Arihant may be one reason for its dry-docking.

Additional or alternate reasons might be:

1. need to provide a 10 year service/replacement for Arihant's steam generator - see French Anonymouses comment above:

and/or

2. Arihant's 2017 flooding accident https://en.wikipedia.org/wiki/INS_Arihant#2017_accident

"In January 2018 it was reported that an aft hatch on the submarine was left open by mistake while the Arihant was docked in 2017, leading to saltwater flooding the propulsion area, rendering the submarine inoperative for ten months while corroding pipes were replaced."

So saltwater damaged pipes, electricals (perhaps some are now subject to shorting) and other components, might have further corroded and be in need of further replacement.

Yes India has a vast nuclear and conventional submarine to-do list.

Regards Pete