By Dr. Ian Fairlie
April 29. 2025

In April 2025, the headline of a BBC report stated “Hunterston B power station declared ‘nuclear free’” following the removal of nuclear fuel. https://www.bbc%5Bdot%5Dco.uk/news/articles/cyvq17enle8o

Unfortunately, this is wishful thinking.  No doubt the BBC reporter was seeking a ‘feelgood’ headline but he was ill-informed. The fact is that nuclear reactors remain dangerous for decades after they have been closed, even with their fuels removed.

This is because closed reactors continue to emit radioactive tritiated water vapour and discharge tritiated liquid water for decades. (Tritium is the radioactive isotope of hydrogen with a half-life of 12.3 years.) Some also emit radioactive gaseous carbon-14 as well.  (Carbon 14 is the radioactive isotope of carbon with a half-life of 5,760 years.)

In more detail, official UK emissions data reveal, for example, that the Trawsfynydd nuclear reactor which was closed in 1991 still emitted 13.6  billion Bq of tritium in 2023 more than 32 years later. And the same goes for  long-closed reactors at all closed Magnox and AGR stations. Another example is the Canadian NPD reactor at Rolphton, Ontario which was closed in 1988. Five years later, high residual concentrations of tritium up to 82,000 Bq/g were found in its concrete bioshields.  The tritium concentration was much higher than the  ~300 Bq/g for C-14  – the next highest nuclide (Krasznai, 1993).

Here is a table showing UK emission/discharge data for 2023 (the latest available year) from DEFRA’s annual RIFE report.

https://www.gov%5Bdot%5Duk/government/publications/radioactivity-in-food-and-the-environment-rife-reports.

(One becquerel (Bq) = one nuclear disintegration per second)

Annual HTO Releases (Bq)  from nuclear reactors in 2023 from tables A.1.1 and A1.2 of Appendix 1 of RIFE 29 (2023). GBq/a (billion Bq/a)

Nuclear Station	Year closed	tritiated water vapour	tritiated water	total tritium		Total C-14  gaseous
Winfrith	1995	4.56	0.36 + 0.07	4.99		0.13
Winfrith (waste treatment)		294	N/A	294		–
Berkeley	1989	5.57	0.07	5.6		1.52
Bradwell	2002	6.10	1.2	7.3		0.42
Chapelcross	2004	1,700	nil	1,700		NA
Dungeness  A	2006	54.9	1.87	56.8		0.39
*Dungeness  B	2018	95.4	1.71	97.1		9.32
Hinkley A	2000	17.2	3.47	20.7		0.53
*Hinkley B	2022	90.9	241	332		0.21
Hunterston A	1989	0.37	–	0.37		0.06
*Hunterston B	2022	95.3	2.85	98.2		21.5
Oldbury	2012	13.5	0.09	13.6		0.65
Sizewell A	2006	18.9	0.26	19.2		340
Trawsfynydd	1991	13.6	3.83	17.4		1.44
Wylfa	2015	52.0	0.06	52.1		0.86

*some fuel still being removed in 2023

Why is tritium (and some C-14) still being emitted from these old reactors?

The short answer is that much tritium (and some C-14) is created in the concrete and metal structures of nuclear reactors during their operating years, which later slowly oozes out for decades.

The longer answer (not widely acknowledged by nuclear utilities) is complicated.  During their operating years  tritium (H-3) is produced in all nuclear reactors as it is both an activation product and a tertiary fission product.  This happens in both water-cooled and gas-cooled reactors. In PWRs and BWRs, tritium from the cooling circuits (in the form of water and water vapour) enters the porous concrete matrices of the reactor shells and their containment structures during the ~30 year lifetimes of the reactors. In Magnox and AGRs, the hydrogen atoms in the hydration water of the chemical constituents of their concrete structures become activated. When all types of reactors are closed, tritium slowly oozes out of their concrete structures and containment shields for decades.

In more detail, the tritium concentrations in closed reactors are due to neutron activation of hydrogen, deuterium and Li-6 impurities in fuels, concrete structures, and metal structures . It also arises from tertiary fission (fission yield 0.01%) and diffusion from high levels of tritium in the cooling water and moderator in HWRs and LWRs (Kim et al, 2008). As stated by Kim ( 2009)

“During the lifetime of nuclear sites tritium becomes incorporated into the fabric of the buildings. When nuclear decommissioning works and environmental assessments are undertaken it is necessary to accurately evaluate tritium activities in a wide range of materials prior to any waste sentencing.”

Conventional computer models unfortunately give unreliable predictions of tritium concentrations in closed reactors. Older neutron codes alone (eg, ORIGEN-1 from Oak Ridge) incorrectly predict tritium levels. As stated by Kim et al (2008)

“Without an appreciation that two forms of tritium exist in concrete reactor bioshields, the H-3 content of samples may be severely underestimated using conventional analytical approaches”.

The two forms are strongly-bound and loosely-bound tritium. The former mainly originates from neutron capture on trace (1 part per 20,000) lithium (Li-6) within mineral phases, and requires temperatures in excess of 700 °C to achieve quantitative recovery. The weakly bound form of tritium can be liberated at significantly lower temperatures (100 °C) as HTO and is associated with dehydration of hydrous mineral components. ”

Kim et al (2008) added

“These findings exemplify the need to develop robust radioactive waste characterization procedures in support of nuclear decommissioning programs”. 

These high tritium concentrations diffuse out of concrete only very slowly with diffusion rates through concrete of ~2 cm² per year (Krasznai, 1993). This is confirmed by the evidence of continued high emissions of tritium from decommissioned reactors decades after their cessation.

Metals

In metals, tritium is retained by absorption of free water in the hydrated surface oxidation layer, by H ingress into bulk metal and also as lattice-bound tritium produced by neutron activation (Nishikawa M et al, 2006).

Croudace et al (2014) also found that significant tritium was incorporated in non-irradiated metals (eg stainless steel and copper), following prolonged exposure to tritiated water vapour (HTO) or tritium/hydrogen gas (HT) in nuclear facilities. In irradiated metals, an additional type of tritium was formed internally through neutron capture reactions. The amount formed depended on the concentration and distribution of trace lithium and boron in the metal. For example, steel containment vessels used for >20 years “exhibit tritium burdens greatly exceeding those predicted by simple gas solution in the parent metal” (Corcoran et al, 2017).

Investigation into the location of, and activity release from,  vessel materials indicate the existence of two major tritium sources:- (i) bulk metal where in-depth contamination arises from diffusion/solution; and (ii) a highly active surface layer, responsible for holding the main tritium inventory (Corcoran et al, 2017) .

Conclusions

The conclusions are that closed reactors are not just ugly, redundant, hulks on the landscape: they are dangerous ones too. The public should be alerted to the radioactive emissions from disused reactors. Also nuclear power utilities should re-examine the computer models used to predict nuclide emission rates from disused reactors.

References

Corcoran VJ, Campbell CA and Bothwell PB (2017) Decontamination and Decommissioning of UK Tritium Facilities. Fusion Technology Published online: 10 Aug 2017 http://www.tandfonline.com/doi/abs/10.13182/FST92-A29834

Croudace IW, Warwick PE, and Kim DJ (2014) Using Thermal Evolution Profiles to Infer Tritium Speciation in Nuclear Site Metals: An Aid to Decommissioning Anal. Chem., 2014, 86 (18), pp 9177–9185.

Kim DJ, Warwick PE and Croudace IW (2008) Tritium Speciation in Nuclear Reactor Bioshield Concrete and its Impact on Accurate Analysis. Anal. Chem., 2008, 80 (14), pp 5476–5480. http://pubs.acs.org/doi/abs/10.1021/ac8002787

Kim DJ (2009) PhD Thesis https://eprints.soton.ac.uk/72145/1/Kim_DJ_Thesis_2009.pdf

Krasznai JP (1993) The radiochemical characterization of regular- and high-density concrete from a decommissioned reactor. Waste Management.  Volume 13, Issue 2 1993, Pages 131-141 http://www.sciencedirect.com/science/article/pii/0956053X9390005H

Nishikawa M et al (2006)  Study on permeation behavior of gaseous tritium through concrete walls.  Fusion Science and Technology 50(4):521-527 https://www.researchgate.net/publication/286942566_Study_on_permeation_behavior_of_gaseous_tritium_through_concrete_walls

About Ian Fairlie

I’m an independent consultant on radioactivity in the environment living in London UK. I’ve studied radiation and radioactivity at least since the Chernobyl accident in 1986. I’ve a degree in radiation biology from Bart’s Hospital in London and my doctoral studies at Imperial College in London and (briefly) Princeton University in the US concerned the radiological hazards of nuclear fuel reprocessing. I formerly worked as a civil servant on the regulation of radiation risks from nuclear power stations. From 2000 to 2004, I was head of the Secretariat of the UK Government’s CERRIE Committee on internal radiation risks. Since retiring from Government service, I have been a consultant on radiation matters to the European Parliament, local and regional governments, environmental NGOs, and private individuals. My areas of interest are the radiation doses and risks arising from the radioactive releases at nuclear facilities.

https://www.ianfairlie.org/news/continued-radioactive-emissions-from-closed-nuclear-reactors/