Senior System Administrator

About Radiant

Radiant is an El Segundo, CA-based startup building the world’s first mass-produced, portable nuclear microreactors. The company’s first reactor, Kaleidos, is a 1-megawatt, fail-safe microreactor that can be transported anywhere power is needed and run for up to 5 years without refueling. Portable nuclear power with rapid-deploy capability can replace similar-sized diesel generators and provide critical asset support for hospitals, data centers, remote sites, and military bases. Radiant’s unique, practical approach to nuclear development leverages modern software engineering to rapidly deliver safe, factory-built microreactors that use existing, well-qualified materials. Founded in 2020, Radiant is on track to test its first reactor at the Idaho National Laboratory this summer, with initial customer deliveries beginning in 2028.

About the Role:

Radiant is seeking a Senior Systems Administrator to own the systems that keep the company running day-to-day within Microsoft 365 GCC High. You'll own the tenant, build our identity and access automation from the ground up in an Entra-native environment with no on-prem Active Directory or Group Policy, and manage the endpoint, email security, and SaaS infrastructure the business runs on. You'll implement and evidence the technical controls behind our CMMC assessment as part of the normal job, not a detour. This is a high-ownership seat in an interdisciplinary environment, advancing milestones toward commercializing the first mass-produced nuclear reactor.

Responsibilities and Duties:

• Own Microsoft 365 GCC High: Exchange Online, SharePoint, Teams, and the tenant configuration underneath them; be the authority on what's possible in this cloud and what has to be built in-house

• Own Entra end-to-end: conditional access, privileged access, app registrations, and single sign-on

• Build the IAM automation layer, the centerpiece of the role: joiner/mover/leaver lifecycle, entitlements driven by HR data, provisioning through Graph and SCIM, and access reviews that run themselves

• Own Windows and endpoint management through Intune, Autopilot, compliance policy, and update rings across the fleet, with no Group Policy underneath

• Own email security and information protection: Defender for Office, mail flow and anti-phishing posture, and Purview for DLP, labeling, and retention in an environment handling CUI

• Own SaaS administration and integration across the business application portfolio, including Box and Slack; some running today, some a project waiting for an owner

• Own the workloads, services, and licensing infrastructure running in AWS, in constant contact with the IT DevOps engineer who owns the account layer

• Take new platform projects from idea to deployed, integrated, and documented

• Implement and evidence the technical controls in these areas for the CMMC assessment ahead, as normal work rather than a detour

Required Qualifications and Skills:

• Bachelor's degree in Information Technology, Computer Engineering, Cybersecurity, or a similar field (4 years of work experience in lieu of a degree)

• 7+ years administering and engineering production systems

• Deep, hands-on experience across the responsibilities above: GCC High tenant administration, Entra, self-built IAM automation, Intune without Group Policy, email security and Purview, and SaaS/AWS administration

• Solid networking fundamentals: VLANs, routing, firewall policy, DNS/DHCP, VPN, wireless

• Treats compliance control implementation and evidence collection as normal work

• Service is the job; tier-1 handles day-to-day support, but nobody's too senior to help the person at their desk

Desired Qualifications and Skills:

• Purview depth: DLP, sensitivity labeling, retention, or eDiscovery

• CMMC or NIST 800-171 exposure; leading an assessment is not required

• Stood up identity governance tooling: Entra ID Governance, SailPoint, Okta Workflows, or equivalent

• Automation experience with PowerShell, Python, Microsoft Graph, and infrastructure as code (Terraform, Bicep, or similar)

• Written and maintained PowerShell modules other people use, not just scripts

• Deployed Box, Slack, or comparable platforms into a regulated environment and handled the data boundary questions

Additional Requirements

• Must be willing to work extended hours and weekends as necessary to accomplish our mission.

• Must work 100% onsite at El Segundo HQ.

Benefits and Perks

• Stock: Substantial incentive stock plan for all full-time employees.

• Medical: 100% up to base silver level plan for employee + 50% dependents, offers up to Platinum plans.

• One Medical: Sponsored memberships for employees and their dependents.

• Vision: 100% top tier plan coverage + 50% for dependents.

• Dental: 100% top tier plan coverage, orthodontia extra, 50% for dependents.

• Voluntary life, accident, hospital, critical illness, commuter and FSA/HSA are offered as employee contributed benefits.

• 8-weeks of paid parental leave for all parents. Additional paid pregnancy leave for CA employees.

• Daily catered lunch. Free snacks and drinks.

• Flexible PTO policy. Remote workday allocation.

• Company and team-bonding events, happy hours and in-person camaraderie.

• Beautiful El Segundo headquarters close to the Pacific Ocean.

Total Compensation and Benefits
Radiant compensates people for impact and invests in those who continue to raise the bar. Radiant’s new hire compensation package includes base salary, substantial equity grants, and comprehensive health benefits. Total compensation and level are determined through a rigorous evaluation of interview performance, experience, education, and qualifications, and are designed to support continued growth as scope, responsibility, and impact expand at Radiant.

The best of today’s advanced reactor builders don’t wait for job postings. They join the winning team. If that’s you, contact us directly for immediate opportunities: [email protected].

We are an equal opportunity employer and all qualified applicants will receive consideration for employment without regard to race, color, religion, sex, sexual orientation, gender identity or expression, pregnancy, age, national origin, disability status, genetic information, protected veteran status, or any other characteristic protected by law.

This position involves access to technology that is subject to U.S. export controls. Any job offer made will be contingent upon the applicant’s capacity to serve in compliance with U.S. export controls.