Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
ASME STP-NU-045-1-2012 — Roadmap to Develop ASME Code Rules for High Temperature Gas Cooled Reactors (HTGRs)
🗺️ ASME STP-NU-045-1-2012 is an ASME ST-LLC nuclear technology publication formally titled Roadmap to Develop ASME Code Rules for the Construction of High Temperature Gas Cooled Reactors (HTGRs). It was originally prepared by Robert Sims of Becht Engineering, revised by James Nestell of MPR Associates, and issued on June 30, 2012, with sponsorship from the U.S. Nuclear Regulatory Commission (NRC) and ASME ST-LLC. Its mission is to define a complete, phased roadmap for developing ASME Code rules for next-generation HTGRs — in particular the Next Generation Nuclear Plant (NGNP), funded by the U.S. Department of Energy and an industry alliance — setting priorities and schedules that align code development with the needs and publication cycles of plant owners, suppliers, and regulators.
💡 HTGR is the only Generation IV system combining helium cooling, graphite moderation, TRISO-coated fuel particles, and an all-ceramic core, with outlet temperatures of 750–950°C for both electricity generation and high-temperature industrial heat. Its containment, pressure boundary, and core components therefore require dedicated code rules.
1. Vision and Background 📌
The starting point is that current ASME Code rules do not completely cover HTGR design and construction. The report establishes a three-tier set of goals:
- Near term (Phase I): support NGNP design using existing Section III Subsection NH elevated-temperature rules, several high-temperature Code Cases, and the newly developed graphite component rules; this body of work was consolidated into the new Section III Division 5 as Phase I concluded.
- Intermediate (Phase II): complete NGNP support by extending temperature and time coverage and advancing design methods (improved inelastic analysis, wider allowable values).
- Long term: risk-based or system-based HTGR code rules, which the report explicitly treats as “very long term” activities beyond the scope of this roadmap.
⚠️ The roadmap emphasizes defining the boundary between “new construction” rules (BPV III-5) and “post-construction / inservice” rules (BPV XI-2) — one candidate transition point being the moment the ASME Certification Mark is applied. Without an agreed boundary definition, subsequent rule development will suffer overlaps, duplication, or gaps.
2. Phase I and Phase II Tasks 🔧
The roadmap divides a large body of code development work into “global” administrative and technical tasks spanning both phases, and specific code-rule tasks for Phase II. Global tasks include reaching consensus on a component classification system (for example, dividing pressure-boundary components into two or three categories based on probabilistic risk assessment results), obtaining alignment among BNCS, BPV III, BPV XI, the OM Committee, and regulators, and deciding how the new BPV III-5 and BPV XI-2 will directly incorporate or reference other Code Sections, Subsections, and Divisions — including non-nuclear sections such as Section VIII.
| Phase | Time Frame | Core Objective | Main Activities |
|---|---|---|---|
| Phase I (near term) | Support NGNP design review | Establish Section III Division 5 rules | Incorporate NH elevated-temperature rules, existing Code Cases, graphite component rules |
| Phase II (intermediate) | Code refinement around NGNP construction | Extend time-temperature coverage and advanced methods | New material qualification, improved inservice rules, OM/QME modifications, classification implementation |
| Long term (out of scope) | Further out | Risk/system-based code rules | Reserved as a future roadmap topic |
The report also defines the roles of stakeholders — plant owners, designers, equipment suppliers, regulators, standards organizations, universities, and laboratories — and lists the information required from HTGR designs (reactor geometry, operating transients, load spectra, material data) together with corresponding R&D tasks, plus the work items ASME ST-LLC itself should undertake, so that the technical basis for code development is available, reviewable, and traceable.
✅ The most important Phase I outcome was consolidating the dispersed Subsection NH high-temperature design rules, high-temperature Code Cases, and emerging ceramic graphite component rules into the new Section III Division 5, giving HTGR construction a unified code “home” — a core milestone the roadmap reports as largely completed at the time of publication.
3. Key Recommended Management Decisions 🛠️
- Committee coordination: BNCS should reach written agreement with BPV III, BPV XI, and regulators on the scope of new rules early, to avoid rework.
- Component classification: a PRA-based classification of pressure-boundary components should underpin the HTGR component and support classification scheme, rather than a simple transplant of LWR classes.
- References to non-nuclear sections: decide whether Division 5 directly adopts or references fabrication and examination rules from Section VIII and other non-nuclear sections, avoiding duplicated code text.
- Inservice and O&M: HTGR operation and maintenance (O&M) requirements should be assigned to the existing OM Code or a new section, avoiding overlap with BPV XI-2.
- Regulatory interfaces: the roles of committees such as NQA (quality assurance), QME (mechanical equipment qualification), and CNRM (nuclear risk management) in HTGR rules should be predefined.
💡 For engineering teams, the practical value of this roadmap is a checkable “code-readiness checklist”: designers can verify which rules their HTGR design depends on are already in Division 5, whether Code Cases are needed, and which inservice inspection programs should be prepared for the operations phase.
4. Frequently Asked Questions ❓
❓ Q: What is the relationship between Section III Division 5 and Subsection NH?
A: Division 5 is a new division of Section III created for high-temperature gas-cooled reactor applications. It absorbs the former Subsection NH rules for metallic components in elevated-temperature service and adds graphite and ceramic component rules, serving as the unified code entry point for HTGR construction.
A: Division 5 is a new division of Section III created for high-temperature gas-cooled reactor applications. It absorbs the former Subsection NH rules for metallic components in elevated-temperature service and adds graphite and ceramic component rules, serving as the unified code entry point for HTGR construction.
❓ Q: What is NGNP?
A: The Next Generation Nuclear Plant is a demonstration project funded by the U.S. Department of Energy and an industry alliance, intended to validate high-temperature hydrogen production and electricity generation using HTGR technology. The near-term goal of this roadmap is to provide code support for its design review.
A: The Next Generation Nuclear Plant is a demonstration project funded by the U.S. Department of Energy and an industry alliance, intended to validate high-temperature hydrogen production and electricity generation using HTGR technology. The near-term goal of this roadmap is to provide code support for its design review.
❓ Q: Must an HTGR design wait until all code rules are complete?
A: No. The roadmap permits a “Code Case first” approach: details not yet in the Code can follow a temporary compliance route through ASME Code Cases while data accumulate, and mature rules are eventually incorporated into Division 5.
A: No. The roadmap permits a “Code Case first” approach: details not yet in the Code can follow a temporary compliance route through ASME Code Cases while data accumulate, and mature rules are eventually incorporated into Division 5.
❓ Q: Why does this roadmap matter for nuclear regulation?
A: It gives regulators a predictable code evolution schedule, helps agencies such as the NRC arrange review resources in advance, and clarifies the new-construction/inservice boundary, reducing uncertainty in HTGR license applications.
A: It gives regulators a predictable code evolution schedule, helps agencies such as the NRC arrange review resources in advance, and clarifies the new-construction/inservice boundary, reducing uncertainty in HTGR license applications.
