Office for Nuclear Regulation

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ONR’s regulation of nuclear submarine power range testing

10 August, 2012

Nuclear submarine HMS Ambush started power range testing in July following a formal agreement from ONR. It’s a significant step for the second in the Astute class of nuclear powered submarines to be built at Barrow-in-Furness.

Stephen Saunders, ONR Site Inspector for nuclear operations at the BAE Systems site at Barrow-in-Furness explains what this means, and the role that ONR have played in reaching this milestone.

As a nuclear submarine is built, a number of the individual elements that make up the vessel are tested individually, but ‘active commissioning’ is the first time that all those elements are tested together. Active commissioning of the reactor plant comprises several distinct stages. The first is referred to as initial criticality, which is when the reactor which powers the vessel is taken critical for the first time, starting off the chain reaction which generates the power. ‘Physics testing’ then confirms, in a controlled manner, that the performance of the reactor core is as expected. ‘Power range testing’ follows, which is the testing of the reactor up to full power. The final stage is termed ‘fast cruise’, in which the reactor and propulsion systems are tested at high power for a sustained period.  

It takes up to six years to reach this stage of the build, and active commissioning is the final stage of our involvement before sea trials and ultimately, handover to the Ministry of Defence, so it’s quite a significant milestone.

How does ONR regulate this?

ONR does not regulate the actual design or operation of the submarine or plant. This is regulated by DNSR – the Defence Nuclear Safety Regulator. Our role is to regulate the licensee’s arrangements for the protection of employees and the public by addressing site safety considerations.

So we look at things like management arrangements, control and supervision, training, procedures, (that is, do they have them and do they follow them?), and also facilities, maintenance… we review safety cases, target for inspection those activities we know from experience have a higher safety significance, and we sample the licensee’s compliance with licence conditions and the relevant legislation. We then ‘permission’ BAE, the licensee, to proceed through their build stages if the evidence they provide to us demonstrates their competency to do so.  

What sorts of issues arise?

We are striving for continual improvement, and encourage the industry to do the same, so there will always be issues – the real question is how significant they are and whether they realistically could affect safety. 

For example we attend annual exercises at which the licensee demonstrates their emergency response capability. In the course of preparing for active commissioning, BAE decided to improve their arrangements for accounting for personnel, but experienced a number of deficiencies in their software over a number of different attempts. At the latest exercise, before we permissioned power range testing, BAE successfully proved their new system. This is exactly what we would expect of them – to try out systems and processes and identify issues when they can present no safety risk.

A number of issues came to light in the course of this work, as in any process, but we were satisfied with the evidence that BAE offered us of their improvements.  

We have produced project assessment reports which detail those issues, what we did about them, and why we came to the conclusions that we did. In so far as is possible, we want to be open and transparent in all our work, and to help all of our stakeholders, including the public, understand it. You can read our reports online.

At the time of issue (8 August 2012) initial criticality, physics tests and power range testing has been successfully completed and preparations are being made to commence fast cruise.