The regulatory taskforce has named this, which is useful. The harder question is what an operator, designer or developer does differently on Monday morning.
How the drift happens
Nobody decides to abandon proportionality. It erodes through a series of individually reasonable moves.
A safety case author facing a regulatory query finds it easier to adopt the additional measure than to construct and defend the argument for not adopting it. The additional measure costs the project money; the argument costs the author exposure. The incentive is obvious and it operates every time.
Precedent accumulates. Once a measure has been adopted on one plant, its absence elsewhere requires explanation, regardless of whether the circumstances are comparable. Over a few decades this ratchets in one direction only.
Disproportionality is rarely quantified. Gross disproportion is a genuinely demanding test, and demonstrating it requires cost estimates, risk reduction estimates and a defensible comparison. Projects frequently have none of these to hand at the point the question arises, so the argument cannot be made even where it would succeed.
And the consequences are asymmetric. An author who adds an unnecessary measure is rarely criticised. One who omits a measure that is later questioned is. Organisations get the behaviour they reward.
What recovering proportionality requires
Make the argument early, in writing. The optioneering stage is where proportionality decisions are cheapest to make and easiest to evidence. Recording why an option was discounted, with the cost and the risk reduction set out, creates a defensible position. Reconstructing that argument two years later, against a regulatory query, rarely works.
Quantify, even roughly. Quantified estimates can materially strengthen a gross-disproportion argument, although relevant good practice and qualitative evidence may provide an adequate demonstration. Risk reduction estimates do not need to be precise to be useful; an order-of-magnitude figure and a cost estimate with a stated basis support an argument that an unquantified assertion does not. Where a numerical comparison is needed, the absence of credible estimates can prevent the argument being made.
Distinguish the relevant good practice from the familiar. Relevant good practice has standing in an ALARP argument. What a previous project happened to do does not, unless it is genuinely applicable. Establishing which is which, and saying so, prevents precedent from operating as an unexamined requirement.
Separate the duty from the design preference. A measure may be desirable without being required. Safety cases that do not distinguish between the two end up defending preferences as duties, which is both expensive and corrosive of the argument’s credibility.
Resource the argument. A properly evidenced disproportionality case takes specialist time. Organisations that will not fund that time are choosing the additional measure by default, and should recognise that as a decision with a cost rather than an absence of one.
The regulatory relationship
A point that is often missed: the regulator is not the source of the drift. ONR’s framework has always been proportionate, and regulators have consistently said they will engage with a well-constructed ALARP argument. What they cannot do is construct it on the dutyholder’s behalf, or accept an assertion in place of evidence.
The behaviour that produces good outcomes is early, substantive engagement with the argument rather than late presentation of a conclusion. A dutyholder who brings the optioneering, the quantification and the reasoning to the regulator while decisions are still open is in a different conversation from one who arrives with a finished case and a request for acceptance.
It also helps to be honest about uncertainty. An argument that acknowledges the limits of its own evidence and explains how those limits were managed is more credible than one that implies a precision the analysis does not support.
Where it pays
The financial case for doing this properly is substantial and underappreciated. Unnecessary safety measures carry capital cost, operating cost, maintenance burden, outage time and, frequently, their own introduced hazards. A measure adopted to close an argument cheaply continues to cost money for sixty years.
There is also a programme argument. Proportionality disputes resolved late are a major source of schedule slip in nuclear projects, and they are particularly damaging because they arrive at the point of greatest commitment. Resolving them during optioneering, with the evidence assembled at the time, can reduce a category of late risk.
NCL supports clients with ALARP and BAT demonstration, optioneering and regulatory strategy, including the structured evidence that makes a proportionality argument hold. Get in touch to discuss your approach.