Nuclear Operations

The Nuclear Operations capability consists of 4 capabilities providing technical support (commercial work, R&D, nuclear foresight & advice) to a wide range of customers including the UK government.

Safety, Security and Safeguards – Nuclear Safety

NNL provides a professional criticality and shielding safety assessment and related services to both our own facilities and a wide range of UK and international customers. Our technical expertise applies to a broad range of fissile isotopes and nuclear facilities, spanning all stages of the plant lifecycle.


NNL has extensive experience in producing criticality safety assessments for nuclear facilities and transport packages. Our aim is to produce ALARP, fit for purpose assessments. Our assessors are skilled in various criticality safety assessment methodologies and have even played a role in shaping them. Added to this, our team is experienced in hazard identification processes. They have all the expertise needed to carry out nuclear criticality safety analyses using criticality data handbooks, hand methods of calculation and Monte Carlo techniques.

Our specialists are further experienced in conducting independent peer review work for a wide variety of plants and processes, including Independent Nuclear Safety Assessment (INSA).

NNL has extensive experience of providing operational plant support to nuclear facilities. This operational support covers a broad range of areas, including:

  • Expert technical support to plant modifications
  • Focused job-specific training to non-criticality specialists
  • Technical support in response to non-routine plant conditions
  • Criticality compliance auditing and inspections
  • Independent safety representation on Management Safety Committees
  • Technical support to regulatory interactions

NNL has the capability to produce Criticality Incident Detection (CID) system omission cases and CID system placement assessments using hand calculation methods. Our assessors provide specialist input into emergency planning work and guidance through out-of-hours plant support and participation in criticality emergency exercises.

We provide training solutions for our facilities and customers, e.g., we run the UK Criticality Course and also teach on the equivalent course at the University of New Mexico, US.


NNL provides quality radiation shielding and dose rate assessments for its own facilities and for both UK and international customers. Our radiation shielding capability has a wide range of applications and covers the complete fuel cycle. This capability is enhanced with the latest nuclear codes capability, with nuclear codes such as MCBEND, MCNP® and ATTILA®, all of which can be run in parallel to aid enhanced quality of service to our customers in shorter timescales. In addition to these complex codes we can offer fit for purpose simplistic hand calculations or simple calculations using MICROSHIELD® for gamma radiation.

In addition, combined with other technical capabilities, such as Criticality, Reactor and Nuclear Physics within NNL, we can offer a complete integrated service. For example, fuel depletion calculations can be carried out in our FISPIN code or ORIGEN which can then feed directly into the above shielding codes.

Our services include:

  • Bulk shielding assessments for neutron (spontaneous fission + alpha n), gamma and capture gamma sources
  • Localised (penetration) shielding assessments for neutron (spontaneous fission + alpha n), gamma and capture gamma sources
  • Skyshine calculations
  • Radiation protection plans and ALARP assessments
  • Classification of areas and dose uptake assessments
  • Shielding design basis
  • Dose/shielding assessments for transportation of radioactive material in flasks/ships both in the UK and internationally (Japan, USA)
  • CIDAS placement assessment
  • Emergency planning criticality dose rate contours
  • Source inference calculations (adjoint calculations)

Customers: NNL Central Laboratory, NNL Preston Laboratory, NNL Windscale Laboratory.

SFL, SL, DSRL, NRG, LLWR, RWM – all in 2018/19.

UUK, CNS, RR – not currently, but in recent years (plus above list).

Minor work for numerous other UK and international organisations. We also act as a sub-contractor to other consultancies with projects/customers in the nuclear sector.

Indirectly through supporting facility work: e.g., SFL, UUK, UNS, DSRL, AWE, RR, MoD, EDF, NDA, IAEA, BEIS National Programmes – essentially, any customer work being carried out in our active facilities.

Skills: The combined team has experience in most areas of criticality and shielding safety, with particular individuals with internationally recognised as specialists.

Facilities: Team has access to specialist computational codes, including MONK, MCBEND, MCNP® and ATTILA® running on the Gemstone cluster (and standalone machines).

Collaborations: Sub-contract to Galson Sciences Ltd for RWM., On consortium for DSRL safety framework led by ARC., Representative on the UK Working Party on Criticality (WPC)., Vice-Chair of The Shielding Forum., IR&D project in collaboration with Lawrence Livermore National Laboratory.