In February 1976, Nuclear Engineering International was blunt

Hope that the Dounreay Prototype Fast Reactor (PFR) would be brought up to full power in February will not now be fulfilled. The designed output of 250 MWe is not now likely to be achieved ‘for several months’.

The reactor continues to operate satisfactorily and with number 1 secondary (cooling) circuit in operation an electrical output of 40 MWe has been achieved with a thermal power of approximately 200 MW (of heat) … Work in preparation for recommissioning of number 3 secondary circuit is well advanced. The circuit has been filled with sodium and cleanup operations are in progress… It was expected that this circuit would be available for power operation during the next few weeks. On number 2 circuit, work on checking the superheater and to determine how best to operate has progressed well.

By September 1976 some of the news from Dounreay, as noted in Nuclear Engineering International, was at last genuinely good:

During most of August the 250 MWe PFR at Dounreay has been operating on all three of its coolant loops with all of the early heat exchanger problems now remedied. The maximum power reached so far is 500 MWt, but full power was expected to be reached by the first week in September.

The report continued, however, with additional news of a slightly more disconcerting kind:

Plans to replace all three types of heat exchanger with improved designs using austenitic steel and avoiding the thick tube plates where corrosion has occurred are still proceeding as scheduled for installation in 1979.

When this schedule for replacing major plant components with completely new ones had been decided, the magazine did not say. It was nevertheless a further indication that the PFR was a long way from demonstrating that fast breeders could fulfil the CEGB’s requirements that they be reliable, built on schedule and within budget. The AEA said that the replacement heat exchangers would be in service by 1979. They were not. Over the years, periodic questions in Parliament elicited monotonously similar answers: the cumulative capacity factor (output of electricity from the PFR as a fraction of its design capacity) remained stuck year after year at approximately 10 percent. In October 1984, the authoritative quarterly analysis published in Nuclear Engineering International gave the total lifetime capacity factor of the PFR in the first ten years after its startup as 9.9 percent.

On 23 March 1977 Lord Hinton, who had chosen the Dounreay site and supervised the early stages of construction of the DFR, threw the switch that consigned it to history. His reflective remarks on the occasion, reprinted in the AEA monthly Atom, were a tour de force of personal reminiscence interspersed with incisive views on the current state of the art, including the PFR:

I hope and believe that many lessons have been learned from PFR. At one of the early Fast Reactor Design Committee meetings Jim Kendal, whose feet were usually very firmly on the ground, put forward a complicated proposal for the design of the fast reactor and I remember saying to him, ‘Look Jim, that’s a very clever idea but I don’t pay you to be clever, I pay you to be successful’. Most of the mistakes (and fortunately they have been rectifiable) on PFR have been made because engineers have thought they were just that little bit more clever than any of us really are.

Hinton went on to endorse the proposal to build a full scale fast breeder "not later than the end of this year… the aim should be to commission it before 1985." Unfortunately, however, Hinton’s assumption about the ready rectification of the mistakes on the PFR was premature.

Another Dounreay mistake was to dump an assortment of discarded material, much of it uncatalogued and unrecorded, into a disused access shaft leading into a waste-disposal tunnel under the seabed offshore. On 10 May 1977 an explosion in the shaft blew its five-tonne concrete cap off and scattered debris in all directions. Investigations suggested that waste contaminated with sodium-potassium coolant had produced hydrogen in the shaft. The explosion happened less than a month before the opening of the intensely controversial public inquiry into the proposed

Thermal Oxide Reprocessing Plant (THORP) at what was then called Windscale. A key reason for THORP was to recover plutonium for the U. K.’s long-anticipated fast breeder power stations. Perhaps not surprisingly, almost no word about the Dounreay shaft explosion reached the media at the time.

The U. K. commitment to reprocessing was based on the assumed rapid commercialization of fast reactors. From the mid-1960s official U. K. opinion, led by the AEA, assumed that a rapid progression from the little DFR to the larger PFR to a series of full scale fast breeder power stations was not only natural but obviously desirable. The only possible constraint foreseen was a conceivable shortage of plutonium to fuel the full scale fast breeders. With that in mind, the reiterated policy of Government and AEA was to reserve all "civil" plutonium separated from U. K. spent fuel, against its imminent use to fuel the coming fast breeder power stations. Even in 1975, when the PFR had at long last gone critical only to manifest the sodium leaks that would cripple it, the official commitment remained unshaken.

A measure of this commitment could be seen from the AEA’s evidence to the Royal Commission on Environmental Pollution, chaired by Sir Brian Flowers. In September 1975, the AEA submitted a paper to the Flowers Commission taking as its premise a nuclear programme that would have a total of 104 GWe of nuclear power in operation by the year 2000, of which no less than 33 GWe would be fast breeders. At the time the total operative nuclear generating capacity in Britain was less than 5 GWe, the nuclear plant construction industry was in chaos and the PFR had yet to attain more than a modest fraction of its intended design output. Sir Brian Flowers, himself a part time board member of the AEA, was reported to have taken exception to this scenario as being utterly unreal. The AEA insisted that it was not a forecast, merely a "reference programme" to establish an upper limit on the scale of British nuclear involvement for purposes of weighing environmental impact. Be that as it might, the AEA clearly considered this "reference programme" as achievable.

Since the beginning of the 1970s, the AEA had been pleading for government permission to build its long-awaited Commercial Fast Reactor. Design teams from the AEA, the CEGB and the nuclear plant manufacturers had been busying themselves for years laying out their paper power plant, based on a 1.2 GWe fast breeder. By 1976, the AEA was spending close to £100 million a year in funding on research and development on the fast breeder. In 1976, confident rumour had it that the go-ahead for the CFR was at last imminent.

The rumour had received a boost from the suggestion that the Flowers Commission would be advocating the CFR. At the end of 1975, however, Sir Brian Flowers declared that this suggestion was "quite false." Flowers published letters he had exchanged with Prime Minister James Callaghan, asking that the Government hold off any decision "on whether to proceed with such a plant in collaboration with other European countries" until after the Commission published its report some months later. Failing such a postponement, the Commission wanted to see a clear distinction drawn between a single full scale demonstration fast breeder and a large continuing programme of such plants. The Commission conceded that, by building one full scale plant Britain might contribute significantly to resolving what the Commission called "the serious fundamental difficulties" associated with the fast breeder. No official body had for many years so much as hinted that the fast breeder could even raise "serious fundamental difficulties." Flowers indicated indirectly in his letter what these difficulties might be:

The demonstration site should be remotely sited; it should have its own fuel reprocessing and fabrication plant on site in order to remove the security risks of shipment of plutonium; it should be provided with every means of protection, including both physical devices and an armed security force; and experience of plutonium accountability and inspection should be designed into its system.