Taishan nuclear reactor Xenon problem

[etudiant]

TL;DR Summary

China EPR has high noble gas buildup in the primary cooling circuit.

French press reports indicate that the first of the two EPRs built at Taishan in Guangdong province has unusually high levels of radioactive noble gases in the primary cooling circuit, presumably as a result of defective fuel bundles.
https://www.lefigaro.fr/flash-eco/e...ntrale-nucleaire-chinoise-de-taishan-20210614

The reports suggest a burden of more than 1000 gigabequerels/ton of water, a level high enough to mandate shutting down the reactor within 8 hours under French rules. However, the responsible majority Chinese partners report no abnormality, having raised the acceptable limits and the reactors continue to run, as the region is very short on power. Possibly the problematic contaminants could be released over time, as the half life of the Xenon 133, the main contaminant, is only 9 hours. There was apparently one such release in April of this year.

What are the risks of such an approach? Presumably the main concern is that one or more fuel bundles fail more extensively, messing up the inside of the reactor.

 

[Astronuc]

The matter is covered here
https://www.world-nuclear-news.org/Articles/Chinese-EPR-experiences-performance-issue

Various media agencies are reporting based on the CNN story, which is based apparently on access to a confidential memo provided to the US DOE/NNSA. Basically, the CNN story contains false and misleading information, but it's not clear if CNN is reflecting their staff member's judgement or unofficial/unauthorized statements by someone at DOE. There was no claim of 'imminent radiological threat', except by CNN, and I suspect they simply wanted an sensational story. The safety authority did not change the offsite exposure limits, which is another false statement by CNN.

I prefer to read statements from Framatome and EdF. EdF has a 30% equity in the plant in question, and Framatome supplied the fuel.

I do not find the number of 1000 GBq/t, but I've seen a lower value. The French limit was restricted by IRSN in the early 2000s after Cattenom 3 had some severely degraded fuel with high coolant activity.

In France, more severe limits were imposed by French Safety Authorities after a multiple failure incident involving Cattenom 3 at cycle 8. For 1300 MW(e) nuclear power plants, new activity limits are set in terms of:
— Dose equivalent iodine (<20 GBq/t) ;
— The sum of noble gas with different limits as a function of burnup of failed rod estimates through caesium ratio during a power transient (<100 GBq/t if ¹³⁴Cs/¹³⁷Cs > 1.4 or <50 GBq/t if ¹³⁴Cs/¹³⁷Cs < 1.4);
— The increase in ¹³⁴I activity due to fuel failure after subtraction of ¹³⁴I activity due to uranium tramp (<1 GBq/t).

This indicator is used to limit the dissemination of new fuel material in primary coolant.

Ref: https://www-pub.iaea.org/MTCD/Publications/PDF/Pub1445_web.pdf
TABLE 3.5. INCIDENTS OF MULTIPLE FUEL FAILURES (≥10 FAILED FAs IN ONE CYCLE)
TABLE 3.6. INCIDENTS OF SIGNIFICANT, BUT NOT MASSIVE, FUEL FAILURES

The sum of noble gases refers to activities of ¹³³Xe+^133mXe+¹³⁵Xe+¹³⁸Xe+^85mKr+⁸⁷Kr+⁸⁸Kr

In 2001, Cattenom-3, Cycle 8 experienced 28 fuel assemblies (FAs) with failed fuel rods due to grid-to-rod fretting.
Also in 2001, Cattenom-4, cycle 8, experienced 7 FAs with failed fuel rods due to grid-to-rod fretting.
The two tables give some experience with relatively large numbers of failures during operation, so it is not unprecedented, not that unique, but happens less often these days that 10 or more years ago.

Ref: NEA/CSNI/R(2014)10 - Leaking Fuel Impacts and Practices, 2014
The limits on total fission gases in the coolant depend on the burnup of the fuel as evidenced by the ratio of ¹³⁴Cs/¹³⁷Cs.

I have more recent information from EdF that suggests the current limit is relaxed to 150 GBq/t, about 4 μCi/g.

In the current situation in Guangdong, the safety authority apparently raised the limit (of coolant activity) in order to continue operation of the plant. That is a rather poor practice, but it does not represent a threat to the public, as dose outside of the containment is within normal limits. It does mean potential and unnecessarily increased exposure of plant personnel, especially those who have to enter containment, such as when refueling and service the reactor and related systems.

If such an event happened in US, Europe, and most other regions, the utility would have shutdown already and removed the damaged fuel.

Summary:: China EPR has high noble gas buildup in the primary cooling circuit.

Presumably the main concern is that one or more fuel bundles fail more extensively, messing up the inside of the reactor.

There is an estimate of the numbers of failed rods, but we have to wait until the reactor shuts down to confirm the number of failures. I'm sure Framatome and EdF would prefer the local utility to shut down.

 

[etudiant]

Thank you, Astronuc, for a very enlightening summary.
The takeaway is that the reactor is fine to run still, but the staff has extra constraints.
The Figaro article did note that as of the end of May, the Taishan 1 level was in excess of 300 Gigabequerels per ton. It also noted the reactors fuel assemblies were made in France, so Framatome may be anxious about potential liability.
Apparently the problem was noted shortly after the reactor was refueled in Oct 2020, with the numbers deteriorating steadily subsequently. The operator requested an increase in the reactor shutdown limits in December, which the regulators subsequently granted
I do not understand the rationale for the French to approach the NRC given their prior experience with similar cases. They must be conscious that their Chinese partners would be furious.

 

[Astronuc]

It also noted the reactors fuel assemblies were made in France, so Framatome may be anxious about potential liability.

Yes. However, we will not know until the reactor is shut down and fuel removed. The primary concern would if the fuel experienced grid-to-rod fretting, especially if it is determined there is a flow instability with the fuel design and operating environment, or if there is some manufacturing flaw, which would represent a significant liability. Debris (foreign material from maintenance activities) would be another concern, as would some kind of corrosion (could happen with a combination of local power level and water chemistry anomaly).

The operator requested an increase in the reactor shutdown limits in December, which the regulators subsequently granted

That is the odd part. Utilities would not normally do that, and regulators (safety authorities) would not normally agree.

I do not understand the rationale for the French to approach the NRC given their prior experience with similar cases.

Framatome-US approached the DOE as they are required to do so based on 10 CFR 810. Framatome-US has to obtain a waiver, or otherwise get permission, from DOE to provide technical support the parties in certain foreign countries, in this case China.

https://www.energy.gov/nnsa/10-cfr-part-810

Part 810 of Title 10, Code of Federal Regulations (Part 810) implements AEA § 57 b.(2), pursuant to which the Secretary has granted a general authorization for certain categories of activities which the Secretary has found to be non-inimical to the interest of the United States – including assistance or transfers of technology to the “generally authorized destinations” listed in Appendix A to Part 810. Other activities within the scope of Part 810 -- including transfers of technology or provision of assistance to destinations not listed in Appendix A (“specifically authorized” destinations) – require a case-by-case specific authorization from the Secretary.

 

[etudiant]

Thank you, Astronuc, that does explain why the French went to the NRC, their existing US tech sharing agreement makes it mandatory. They probably are not thrilled by the resultant CNN publicity.

Your explanation of the potential sources for the fuel rod leakage makes total sense and I can see that the French would be doubly anxious to get to inspect the fuel elements, as it may be a combination of problems, manufacturing shortfalls causing the initial leaks, then exacerbated by reactor specific flow stability problems.
Presumably Taishan 2 should show similar trends once it gets comparable service time, although perhaps that reactor uses Chinese made fuel assemblies.

 

[Astronuc]

that does explain why the French went to the NRC

It is the US part of Framatome that went to DOE, since it relates to Export Control. The NRC only responsible for regulatory matters in the US, although the NRC does consult with safety authorities around the world.

 

[gmax137]

https://www.thedrive.com/the-war-zo...admits-fuel-rods-at-nuclear-plant-are-damaged

Why does nuclear power generate this kind of hyperbole?

Listen to this:

While there does not seem to be any consensus yet on the dangers posed by the damaged fuel rods at the Taishan Nuclear Power Plant, any type of radiological incident in close proximity to so many heavily populated urban areas could wreak havoc on the Chinese and Hong Kong public if any potential radioactive contamination grows to unsafe levels.

Translation: Unsafe levels are unsafe (especially nucular).

 

[etudiant]

https://www.thedrive.com/the-war-zo...admits-fuel-rods-at-nuclear-plant-are-damaged

Why does nuclear power generate this kind of hyperbole?

Listen to this:
Translation: Unsafe levels are unsafe (especially nucular).

I really don't know, but perhaps the problem is that nuclear processes cover so many orders of magnitude.
Going from a relatively safe background level to one many thousand times higher seems horrendous, even if it is quite modest in reality, partly because it is quite locally confined.
There are places in India and Brazil where the natural background radiation is a hundred times higher than US norms, with no visible ill effects, suggesting our norms are pretty reasonable.
Inside reactors however the radiation is quadrillions or much more times higher, really lethal levels, essentially the conditions inside a nuclear furnace.
That is difficult to translate into normal experience.

 

[etudiant]

It is the US part of Framatome that went to DOE, since it relates to Export Control. The NRC only responsible for regulatory matters in the US, although the NRC does consult with safety authorities around the world.

Seems clueless behavior by Framatome US. It pisses off the Chinese with no benefit afaik.
The NRC really does not know about the EPR or its fuel bundle behavior, plus they have no more recent experience with bad fuel bundles than Framatome.

More fundamentally, is this really a safety issue? Based on Astronucs earlier links, lots of reactors have operated with busted fuel assemblies. Should this one really make headlines?

 

[Astronuc]

Seems clueless behavior by Framatome US.

I'm not sure to what one is referring. Framatome US was simply complying with US law. They shared information with DOE that DOE should have retained as confidential. CNN falsely attributed statements to Framatome.

The NRC really does not know about the EPR or its fuel bundle behavior, plus they have no more recent experience with bad fuel bundles than Framatome.

The NRC is not involved in the matter with Taishan. However, they do know about the AFA-3G and AFA3G-LE.

Taishan has elevated coolant activity, which happens with fuel failures in LWR. The system is designed to handle it.

 

[Rive]

More fundamentally, is this really a safety issue?

While the event itself is absolutely in the manageable range (so far, as we know it): the handling of the event might point to some safety concerns.

 

[Astronuc]

World Nuclear News (WNN), July 23

Operator to decide on Taishan 1 outage, says EDF​

https://www.world-nuclear-news.org/Articles/Operator-to-decide-on-Taishan-1-outage-says-EDF

The decision to take unit 1 of the Taishan nuclear power plant in China's Guangdong province offline to investigate a fuel failure issue lies with the plant operator, EDF said yesterday. However, it said under its own operating procedures for its French units, operation of the EPR would be temporarily halted to carry out such inspections and take corrective measures. It noted the chemical composition of the primary circuit water at Taishan 1 remains within regulatory threshold limits.

EDF announced on 14 June it had been informed of an increase in the concentration of certain noble gases in Taishan 1's primary circuit. However, it noted this is "a known phenomenon, studied and provided for in the reactor operating procedures". The French company said that, as a shareholder of TNPJVC, it had requested the holding of an extraordinary meeting of the TNPJVC board of directors in order for management to "present all the data and the necessary decisions".

On 16 June, China's National Nuclear Safety Administration (NNSA) confirmed that an increase in the concentration of noble gases in the primary circuit of the Taishan 1 EPR was related to a few damaged fuel rods. The NNSA estimated that of more than 60,000 fuel rods in the core of Taishan 1, about five probably have damage to their cladding. The core of Taishan 1 contains 241 fuel assemblies, each of them made of 265 fuel rods.

"The proportion of damaged fuel rods is less than 0.01% of the total, which is much lower than the maximum damage of the fuel assembly assumed in the design proportion (0.25%)," it noted.

 

[Astronuc]

World Nuclear News - July 30, 2021

China General Nuclear (CGN) announced today it is taking unit 1 of the Taishan nuclear power plant in China's Guangdong province offline to replace damaged fuel rods. Last month, an increase in the concentration of noble gases in the primary circuit of the EPR was attributed to a few damaged fuel rods.

On 16 June, China's National Nuclear Safety Administration (NNSA) confirmed that an increase in the concentration of noble gases in the primary circuit of the Taishan 1 EPR was related to a few damaged fuel rods. The NNSA estimated that of the more than 60,000 fuel rods in the core of Taishan 1, about five probably have damage to their cladding. The core of Taishan 1 contains 241 fuel assemblies, each of them made from 265 fuel rods.

Following a meeting of TNPJVC's board of directors on 22 July, EDF said: "On the basis of the analyses carried out, EDF's operating procedures for the French nuclear fleet would lead EDF, in France, to shut down the reactor in order to accurately assess the situation in progress and stop its development. In Taishan, the corresponding decisions belong to TNPJVC."

CGN said today, "After full communication between Chinese and French technical personnel, TNPJVC insists on safety first and conservative decision-making in accordance with nuclear safety regulations and nuclear power plant operating procedures."

It added the fuel damage at Taishan 1 is "still within the allowable range of technical specifications and the unit can continue to operate stably". However, it said the reactor is being taken offline to carry out maintenance, find the cause of the fuel damage and replace the damaged fuel.

So about 6 weeks after the increase in activity, the utility CGN will shutdown the unit to remove and inspect the damaged fuel. I'm sure EdF and Framatome want to know the cause(s) of failure.