Senior or Principal Mechanical Engineer

Sellafield; Butterwick; Hybrid; GBP 100,000 - 125,000; Full time

Job summary

A leading nuclear engineering firm is seeking a Senior or Principal Mechanical Engineer to join its MSSS-OBLM project in Butterwick. The position offers a hybrid working model with a mix of on-site collaboration in Warrington and remote work. Responsibilities include managing mechanical engineering tasks, ensuring compliance with safety requirements, and mentoring junior engineers. The role requires a strong background in nuclear or regulated industries and offers competitive pay of £51-£61/hour, emphasizing impactful safety-critical work.

Qualifications

• Experience operating at Senior or Principal Mechanical Engineer level.
• Background in nuclear or similarly highly regulated industries.
• Familiarity with Sellafield MSSS / OBLM design processes is highly advantageous.

Responsibilities

• Deliver and manage mechanical engineering tasks across MSSS-OBLM project scopes.
• Develop, review and approve designs and specifications.
• Provide technical leadership and mentoring to junior engineers.

Skills

Mechanical systems expertise

Strong technical capability

Task-based engineering delivery

Collaboration in multi-disciplinary teams

Job description

Are you an experienced Senior or Principal Mechanical Engineer looking to play a key role on one of Sellafield's most critical programmes? This opportunity sits within the MSSS-OBLM (Multi-Storey Seismic Stores - On-Balance Legacy Materials) projects, delivering essential mechanical engineering support to safety‑critical, legacy nuclear infrastructure.

You’ll provide technical leadership and delivery assurance across task‑based mechanical work packages, supporting the safe progression of complex designs within a highly regulated environment. The role offers a hybrid working model, balancing collaboration in Warrington with remote working flexibility.

Responsibilities

• Deliver and manage mechanical engineering tasks across MSSS-OBLM project scopes
• Develop, review and approve designs, calculations, specifications, and technical documentation
• Ensure compliance with Sellafield engineering standards, nuclear safety requirements, and site licence conditions
• Support design reviews, optioneering studies, risk assessments, and HAZOPs
• Provide technical leadership, mentoring and assurance to junior engineers
• Collaborate closely with multi-disciplinary teams to achieve safe, efficient project delivery

Qualifications

• Proven experience operating at Senior or Principal Mechanical Engineer level
• Background in nuclear or similarly highly regulated industries
• Strong technical capability across mechanical systems, structures, and process equipment
• Experience delivering task‑based engineering packages to programme, cost and quality requirements
• Familiarity with Sellafield MSSS / OBLM design processes and standards (highly advantageous)
• SC clearance preferred or the ability to obtain

Competitive £51‑£61/hour (Inside IR35). Long‑term opportunity on a high‑profile Sellafield MSSS-OBLM programme. Hybrid working with 3 days per week in Warrington. Technically complex, safety‑critical work with real national importance. Opportunity to influence design decisions and support the next generation of engineers.

Apply now to bring your mechanical engineering expertise to one of Sellafield’s most significant legacy infrastructure programmes.