Senior Security Software Engineer

About Valar Atomics At Valar Atomics, we're redefining what's possible in energy. Our mission is to make clean, high-temperature nuclear power scalable—unlocking abundant energy for industry, hydrogen, and next-generation manufacturing. We are a team of builders, engineers, and operators who believe nuclear energy should be fast to deploy, factory-made, and built for the real world. Our first pilot plant in Orangeville, Utah will demonstrate how advanced nuclear systems and fuel fabrication can power the future. Joining Valar Atomics means becoming part of a company where autonomy, ownership, and impact exist at every level. The Team As part of the Business organization, IT & Enterprise Software delivers the technology infrastructure, enterprise applications, and digital tools that power Valar's operations. The team ensures secure, reliable, and scalable technology solutions that support every function across the company. The Role We're looking for a Software Security Engineer to embed security into our software development lifecycle — from initial design through shipped code. This role is split across two key moments: early-stage design and planning reviews, where you'll help engineering teams make secure architectural decisions before code is written, and post-development code review, where you'll dig into implemented code to find and fix vulnerabilities before release. You'll work closely with engineering teams across our C#, Python, and React stack, along with our Postgres data layer, acting as a security partner rather than a late-stage gatekeeper. We strongly value candidates with backgrounds in large-scale technology organizations or the defense sector, where security rigor and compliance discipline are non-negotiable. Key Responsibilities Design & Planning Reviews • Participate in design and architecture discussions early, before implementation begins • Perform lightweight threat modeling on new features and services — identifying trust boundaries, data flows, and likely attack surfaces • Flag risky design patterns (auth schemes, data handling, third-party integrations, database access patterns) and recommend secure alternatives • Provide security requirements and acceptance criteria that get built into planning/ticketing, not bolted on afterward Code Review (Post-Development) • C#, Python, React: Perform manual and tool-assisted secure code review across all three • Postgres: Review queries and schema design for injection risks, access control issues, data exposure, and unsafe query patterns • React: Review front-end code for common web vulnerabilities (XSS, insecure state/data handling, unsafe use of dangerouslySetInnerHTML, client-side auth assumptions) • C#: Review backend code for issues like insecure deserialization, improper input validation, authorization flaws, and unsafe use of reflection/dynamic code • Provide clear, actionable remediation guidance directly to engineers — not just a list of flagged lines Compliance & Ongoing • CMMC 2.0: Support alignment with Cybersecurity Maturity Model Certification (CMMC) 2.0 practices where applicable to contracts and data handling requirements • Maintain and refine secure coding guidelines specific to our stack (C#/.NET, Python, React, Postgres) • Track recurring vulnerability patterns across reviews and feed them back into design guidance and developer training • Partner with engineering leads to balance security rigor against delivery timelines Basic Qualifications • Professional experience in application security, software security engineering, or a related security-focused engineering role • Strong proficiency reading and reasoning about C# and Python code • Working knowledge of React and common front-end/web security issues • Experience reviewing Postgres (or other relational database) queries and schemas for security issues • Demonstrated experience doing security reviews at both the design/planning stage and the code-review stage — this is a dual-mode role, not just one or the other • Familiarity with OWASP Top 10, secure design principles, and basic threat modeling (e.g., STRIDE) • Strong written and verbal communication — you'll need to explain security tradeoffs to engineers and, sometimes, non-technical stakeholders Preferred Skills and Experience • Experience at a large-scale technology company ("big tech") or within the defense industrial base • Familiarity with CMMC 2.0 requirements and how they translate into engineering and software practices • Experience working under DFARS, NIST 800-171, or similar federal/defense compliance frameworks • Software/application security certifications: CSSLP (Certified Secure Software Lifecycle Professional), GWAPT (GIAC Web Application Penetration Tester), or GSSP (GIAC Secure Software Programmer) • General security certifications: CISSP, OSCP, or Security+ Nice to Have • Experience with SAST/DAST tooling and integrating security checks into CI/CD • Experience with SBOM / software supply chain security • Familiarity with cloud environments (AWS/Azure/) What Success Looks Like • Security issues get caught in design discussions, before they're ever coded • Code review findings are specific, actionable, and rarely repeat the same root cause twice • Engineering teams bring you into planning conversations proactively, rather than security being an afterthought • The C#/Python/React/Postgres stack has clear, documented secure coding practices that teams actually follow • The organization maintains a clear path toward, or sustains, CMMC 2.0 compliance where required What We Offer • Competitive base salary • Equity ownership in a rapidly growing advanced energy company • Comprehensive medical benefits • Unlimited PTO • Free daily lunch and dinner provided onsite • Generous PPE stipend • High-impact startup environment with significant ownership and autonomy • Opportunities for rapid career growth and internal advancement • Direct collaboration with experienced operators, engineers, and industry leaders • The opportunity to help build and scale transformative energy technology from the ground up Equal Employment Opportunity Statement Valar Atomics is an equal opportunity employer. We consider all qualified applicants without regard to race, color, religion, sex, gender identity, sexual orientation, national origin, age, disability, veteran status, or any other protected status under applicable law. We are committed to providing a workplace free of discrimination and harassment and will provide reasonable accommodation as required by law. Applicants must be legally authorized to work in the United States as a U.S. citizen or lawful permanent resident (green card holder). Salary $175,000—$200,000 USD