Principal Mechanical Engineer

Amentum will inspire and empower you to deliver your best work so you can evolve, grow and succeed - today and into tomorrow. We offer an exciting range of opportunities to develop your career within a supportive and diverse team who always strive to do the right thing for our people, clients and communities.

People are our greatest asset, and we offer a competitive package to retain and attract the best talent.

In addition to the benefits you’d expect, UK employees also receive free single medical cover and digital GP service, family-friendly benefits such as enhanced parental leave pay and free membership of employee assistance and parental programmes , plus reimbursement towards relevant professional development and memberships. We also give back to our communities through our Collectively program which incorporates matched-funding, paid volunteering time and charitable donations.

About the Opportunity

We are currently recruiting for a Principal Mechanical Engineer to join our Energy business, which is entering an exciting phase of opportunity: supporting a key  client’s UK nuclear fleet through a business transformation; supporting new small modular reactor developers. Our work is varied, covering Licensing, New Build, Generation, Life Extension, and Defueling, and our capabilities are in demand across the nuclear sector. 

This role will be based at one of our Energy offices (Newcastle, Warrington, Glasgow, Gloucester, Stockton, Bristol or Knutsford).  

Your role will be to manage and deliver mechanical design solutions to time, cost and quality on projects of varying sizes. If you’re familiar with project delivery, you’ll know that they have lots of moving parts and complexity, which is why you’ll be working alongside our Operations Managers and Engineering Managers to enable delivery of maximum value. 

We put flexibility at the heart of what we do and we’re happy to consider flexible working patterns.

Role responsibilities:

• Take ownership of technical challenges, develop a strategy and implement the solution through engagement with internal and external stakeholders.

• Deliver technical solutions (analysis and design)

• Produce and review design deliverables (assumption notes, technical specifications and calculation notes, methodology plans etc).

• Work with international SMR developers to pass through the Office of Nuclear Regulation’s Generic Design Assessment process.

• Review and justify design decisions to the ONR.

• Fulfil and take ownership of CDM responsibilities.

Qualifications - External

• MEng, MSc, BEng or BSc in Mechanical Engineering or other relevant degree level qualification.

• Experience in relevant field of design of heavy infrastructure projects, nuclear or regulated industry

• Chartered with relevant institution (e.g., IMechE, MIET) or working towards Chartership.

• Ability to work within a design team, and also able to collaborate within multi-disciplinary teams.

• Previous experience in the design and/or construction of engineering solutions using American codes.

• Experience of designing pumps, valves, heat exchangers, tanks, filters or HVAC equipment as well as authoring datasheets

• Experience with CAD software AutoCAD, Inventor, Creo or Solidworks.

• Experience with authoring technical drawings to BS EN 8888 and Piping & Instrumentation Diagrams

• Familiar with safety cases in industrial enviroments

• Experience with Matlab and MathCAD would be beneficial

• Experience writing test plans for Equipment Qualification

• Knowledge and understanding of UK Nuclear Regulatory process in field of mechanical engineering is desirable.

Our Culture

Our values stand on a foundation of safety, integrity, inclusion and diversity. We put people at the heart of our business, and we genuinely believe that we all succeed by supporting one another through our culture of caring. We value positive mental health and a sense of belonging for all employees.   

We aim to embed inclusion and diversity in everything we do. We know that if we are inclusive, we’re more connected, and if we are diverse, we’re more creative. We accept people for who they are, regardless of age, disability, gender identity, gender expression, marital status, mental health, race, faith or belief, sexual orientation, socioeconomic background, and whether you’re pregnant or on family leave. This is reflected in our wide range of Global Employee Networks centered on inclusion and diversity. 

We partner with VERCIDA to help us attract and retain diverse talent. For greater online accessibility, please visit www.vercida.com to view and access our roles. As a Disability Confident employer, we will interview all disabled applicants who meet the minimum criteria for a vacancy. We welcome applications from candidates who are seeking flexible working and from those who may not meet all the listed requirements for a role. 

If you require further support or reasonable adjustments with regards to the recruitment process (for example, you require the application form in a different format), please contact the team. 

       

Compensation Details:

N/A

       

The compensation range or hourly rate listed for this position is provided as a good-faith estimate of what the company intends to offer for this role at the time this posting was issued. Actual compensation may vary based on factors such as job responsibilities, education, experience, skills, internal equity, market data, applicable collective bargaining agreements, and relevant laws.

 

Benefits Overview:

Our health and welfare benefits are designed to support you and your priorities. Offerings include:

• Health, dental, and vision insurance

• Paid time off and holidays

• Retirement benefits (including 401(k) matching)

• Educational reimbursement

• Parental leave

• Employee stock purchase plan

• Tax-saving options

• Disability and life insurance

• Pet insurance

 

Note: Benefits may vary based on employment type, location, and applicable agreements. Positions governed by a Collective Bargaining Agreement (CBA), the McNamara-O'Hara Service Contract Act (SCA), or other employment contracts may include different provisions/benefits.

       

Original Posting:

04/20/2026 - Until Filled

Amentum anticipates this job requisition will remain open for at least three days, with a closing date no earlier than three days after the original posting. This timeline may change based on business needs.

       

Amentum is proud to be an Equal Opportunity Employer. Our hiring practices provide equal opportunity for employment without regard to race, sex, sexual orientation, pregnancy (including pregnancy, childbirth, breastfeeding, or medical conditions related to pregnancy, childbirth, or breastfeeding), age, ancestry, United States military or veteran status, color, religion, creed,  marital or domestic partner status, medical condition, genetic information, national origin, citizenship status, low-income status, or mental or physical disability so long as the essential functions of the job can be performed with or without reasonable accommodation, or any other protected category under federal, state, or local law. Learn more about your rights under Federal laws and supplemental language at Labor Laws Posters.