CANDU: A Canadian horror story.
Here is a letter I sent to the Canadian Nuclear Safety Commission (CNSC) in December 2006:
In 2003 and 2005 I was an intervenor in the public hearings on the licensing of the four CANDU reactors at Pickering ‘A’ NGS. I felt compelled to participate in those hearings because of my first-hand knowledge of OPG’s nuclear operations and my concerns over the condition of the feeder pipes in Pickering ‘A’ Units.
These concerns were not alleviated by OPG’s announced intention of carrying out extensive feeder pipe inspections and only replacing degraded components where absolutely necessary. Indeed this merely guaranteed a major radiation dose commitment to the OPG employees and contract workers destined to carry out inspection work in the appalling conditions encountered close to the face of a large CANDU reactor. As it transpired the total dose to the individuals involved in the Pickering Unit 4 feeder pipe inspection was 271 mSv, a significant exposure when it is considered that the normal operation of a single CANDU Unit entails a radiation dose of about 700 mSv per year. Fortunately OPG eventually abandoned its plan to refurbish Pickering Units 2 and 3, even after the CNSC had granted OPG permission to proceed with such an ill-conceived plan.
Now, two years on from these events, I see that OPG wants to forge ahead with more refurbishments that will involve even more feeder pipe inspections and radiation exposures. However, the radiological consequences of OPG’s latest exercise in rebuilding near-defunct reactors, namely Units 5 - 8 at Pickering ‘B’, has the potential to endanger not only the station personnel involved in the task, but also the hapless residents of Pickering township and the local environments on the designated route from Pickering to the Bruce Waste Disposal Site. Why? Because the scope-of-work document issued by OPG lists replacement of steam generators and transportation of the associated waste as new and untested requirements for the refurbishment of Pickering ‘B’.
This immediately raises heightened concern about the Pickering ‘B’ refurbishment because of the simple fact that, after a CANDU reactor’s pressure vessel and in-core components such as the pressure and calandria tubes, the steam generators constitute the area within a nuclear power station that most effectively concentrates radioactivity. Furthermore, steam generator tubing is the thinnest barrier in a CANDU reactor heat transport circuit and therefore constitutes an area that is highly susceptible to the release of primary coolant and its associated radioactive contamination to the supposedly non-radioactive secondary side of the steam generator.
Two decades of operation of the four Pickering ‘B’ Units has resulted in the production and deposition of large quantities of activated corrosion/erosion products, fission product, uranium and transuranic isotopes from the neutron irradiation of pressure boundary materials and natural uranium. The transfer of radioactivity from the reactor core to the steam generators, mainly via the associated “sludge/crud” of corrosion metal oxides such as magnetite, has lead to many operational problems for OPG such as radiation field build up and loss of thermal efficiency through the fouling of steam generator tubes. Indeed, because of these problems, OPG has attempted from time to time, to chemically clean affected steam generators in Pickering ‘A’ and ‘B’ Units. As a result of these cleaning activities, a number of radioactive effluent solutions and particulate filters from Pickering “boiler-cleans” were subjected to chemical and radiochemical analyses by Kinetrics (Formerly OPT) in Toronto and AECL’s Whiteshell Laboratories in Pinawa, Manitoba.
These analyses showed that long-lived activation products from the irradiation of chromium, iron, cobalt, nickel, zinc and niobium, such as Fe-55, Fe-59, Co-60, Zn-65 and Nb-94 as well as fission products such as Ru-103, Ru-106, Sb-125, Cs-134, Cs-137, Ce-144, Eu-154 and the uranium and transuranic isotopes U-235, U-238, Pu-238, Pu-239, Am-241, Cm –242 and Cm-244 were present in substantial amounts in the analyzed samples. However, it should be noted that data on the long-lived species Cl-36, Ni-63, Sr-90 and I-129 are few and far between because of the difficulties, (and cost!), of measuring these pure beta-emitting radioisotopes.
Nevertheless, one of the most significant findings of the analytical studies of Pickering steam generator cleaning wastes is the fact that while these persistent and highly radio-toxic species are known to be present in all steam generator samples, it has proved to be next to impossible to convert the available data into meaningful steam generator inventories because of the great uncertainties involved in making such extrapolations. This is due to a number of factors:
(i)The variable distribution of deposited activity on steam generator surfaces, especially in inaccessible areas such as the “U-tubes”.
(ii)The highly uncertain efficiency of a chemical cleaning agent in removing a particular radioisotope from a steam generator deposit.
(iii)The nature of the samples, (i.e. un-quantified wash solutions and/or filters) from which the analytical data was derived.
If we focus only on the radiologically significant plutonium inventory in a Pickering steam generator we find that “guestimates” have in fact been made, but the uncertainties are acknowledged to be such that inventories as high as 10 times the quoted values are equally probable. And this raises a number of very serious concerns about the planned removal of steam generators from Pickering ‘B’ as I shall now explain.
The regulation of the Canadian nuclear industry is based on a probabilistic safety analysis approach in which the risk and radiological consequences of a potential nuclear accident are assessed. Typically the accident in question is assumed to involve the environmental release of a radionuclide and an associated radiation dose, via air or water-borne transport, to the population within a specified radius of the accident. In the present case, the accident scenario might involve damage, with breach of containment, to a steam generator through hard impact during its removal or transportation from Pickering ‘B’. Furthermore, the accident might be envisaged to result in the release of 1 % or more of the steam generator inventory of Pu-239 or, to follow standard CNSC practice in this regard, the release of a specific amount of this radionuclide, say 1 x 10^7 Bq of Pu-239.
Now herein resides the source of my concerns and the main reason for my intervention in the OPG proposals for the refurbishment of Units at Pickering ‘B’: as previously noted, all the Pickering steam generator’s Pu-239 inventories are highly uncertain. What is more, the radiation dose-to-Becquerel conversions used by OPG are also highly uncertain because of construction complexities and uneven crud composition/deposition patterns in the steam generator channel-head bowl, divider plate, tube sheet and tubes. Thus:
A meaningful probabilistic safety analysis of the proposed steam generator
removal operations at Pickering ‘B’ cannot presently be made.
I would also like to point out that OPG has a very poor track record in accurately predicting the condition of critical systems such as pressure tubes, feeder pipes and steam generators, in its nuclear reactors. An example of this may be seen in the information provided by OPG to British Energy in February 2003 regarding the fitness for service of the steam generators in Bruce Unit 8. It appears that OPG assured British Energy that the steam generators in question would be “in good condition, repair and proper working order, having regard for their use and age.” Unfortunately for all concerned, this turned out not to be the case. Indeed, when the Bruce Unit 8 steam generators were inspected during the first planned outage after the signing of the 2003 Purchase Agreement, their condition was such that British Energy immediately served a Statement of Claim on OPG seeking damages in the amount of $500,000,000 for the anticipated reduced operating life of Unit 8 steam generators.
This incident should make it perfectly clear to the CNSC that OPG cannot be trusted to provide a reliable assessment of the radiological conditions prevailing within the Pickering ‘B’ steam generators. And I hope the CNSC recalls how OPG previously misled the AECB with pronouncements that there was no carbon-14 on the pressure tubes at Pickering ‘A’, when, as it turned out, there was thousands of curies!
And we also need to consider OPG’s well-known reticence to share information with the public on the amount of “tramp” plutonium in its reactor systems as the following example shows: In my role as a research chemist for OPG, I used to analyze samples of irradiated fuel bay water from Pickering NGS. I typically found, in addition to the expected activated corrosion products, significant amounts of Pu-239. In the course of this research I became involved in an information exchange with U.S. nuclear industry researchers on issues connected with the long-term storage of nuclear fuel and I sought permission from my OPG manager to share my data with my American colleagues. My manager said I could provide the results of my Pickering fuel storage bay water analysis as long as the Pu-239 data were removed. When I asked the reasons for the exclusion of the plutonium data I was told: “We don’t want the whole world to know that we have plutonium in our fuel storage bays.”
With these facts in mind I am asking, indeed begging, the CNSC to acknowledge the reality that OPG is too secretive and too self-serving to be allowed to proceed with steam generator replacement activities without an independent audit and proper accounting of the radiological hazards involved. And OPG has already proven that it is more concerned with concealing its intentions with regard to the Pickering ‘B’ refurbishment than revealing the details of its work plans for this project. In fact OPG has gone so far as to deny the CNSC access to its Project Execution Plan (PEP) as reported in the CNSC Minutes of the Pickering ‘B’ Integrated Safety Review Meeting held on October 26 2006. This meeting also shows CNSC staff complaining about the impact of not having a PEP for Pickering ‘B’ on the CNSC’s business plan for 2007, rather than voicing any concerns over the potential radiological impact of OPG’s Pickering ‘B’ refurbishment operations!
Therefore, because it is well-known how the CNSC goes out of its way to cater to the wishes of OPG, I believe it would serve the best interests of the people of Ontario for the CNSC Commissioners to show real due diligence and insist that an independent consultant/auditor be contracted to provide a report that includes:
(i)A quantification of the Pu-239 and Sr-90 inventory in every Pickering ‘B’ steam generator slated for removal in the upcoming refurbishment.
(ii)A detailed description of how such data were derived.
(iii)An estimate of the predicted OPG employee and/or contract worker radiation exposure from involvement in the removal of the Pickering “B’ steam generators.
I am further requesting that the consultant/auditors report be produced before the CNSC grants perfunctory approval of the Pickering ‘B’ refurbishment operations so that the people of Ontario may understand the potential consequences of the high-risk activities OPG plan to undertake, supposedly for our benefit, before the inevitable problems arise.
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Needless to say I received no feedback on this from the CNSC....
