HDPE piping in nuclear power plant systems

Use of HDPE in Nuclear Power Plant Piping Systems

Piping systems in U.S. nuclear power plants that are relied on for safe shutdown of the plant (i.e. “safety-related”) are typically constructed to Section III of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code. The materials allowed by the ASME B&PV Code have been limited to metallic materials only (Ref. Section III, NX-2121 and Section II, Part D). Due to the historical success of high density polyethylene (HDPE), power plants in the U.S. have expressed interest in using HDPE piping in ASME B&PV Code Class 3 safety-related applications.  In 2008, the first U.S. NPP was approved by the U.S. Nuclear Regulatory Commission (NRC) to install HDPE in a safety-related system (Ref Callaway SER). Since then, the rules for using HDPE have been integrated into the 2015 Edition of the ASME B&PV Code (Ref 2015 edition).  The NRC approval of the 2015 Edition is still pending (Ref 10CFR50.55a). 

History

·        1963 – Section III (Nuclear Power) of the ASME Boiler and Pressure Vessel Code – only allows for metallic materials.

·        2007 – Code Case N-755 issued for on behalf of Duke Energy for the use of Polyethylene Plastic Pipe for Class 3 applications.  HDPE fusing limited to butt-fusing (hot plate).

·        2008 – US. NRC grants Callaway Nuclear Power Plant permission to use HDPE in the Essential Service Water System based on Code Case N-755 and additional plant specific information. 

·        2009 - US. NRC grants Catawba Nuclear Power Plant permission to use HDPE in the Nuclear Service Water System based on Code Case N-755 and additional plant specific information.

·        2010 – First Revision to Code Case N-755 issued.

·        2013 – Second Revision to Code Case N-755 issued. 

·        2014 - U.S. NRC rejects Code Case N-755-0 for generic use due to unresolved issues concerning the joining procedure, degradation processes, and examination of joints (Ref Ref 1.193 r4). 

·        2015 - US. NRC grants Hatch Nuclear Power Plant permission to use HDPE in the Plant Service Water System.

·        2015 – Code Case N-755 incorporated into Mandatory Appendix XXVI of ASME Section III.

·        2017 – U.S. NRC rejects Code Case N-755-1 for generic use due to unresolved issues concerning the joining procedure, degradation processes, and examination of joints (Ref 1.193 R5).

Code Sections

ASME BPVC Section III – Rules for Construction of Nuclear Facility Components

Division 1 – Appendix XXVI – Rules for Construction of Class 3 Buried Polyethylene Pressure Piping (added in 2015 Edition)

·        Article XXVI-1000: General Requirements

·        Article XXVI-2000: Materials

·        Article XXVI-3000: Design

·        Article XXVI-4000: Fabrication and Installation

·        Article XXVI-5000: Examination

·        Article XXVI-6000: Testing

·        Article XXVI-7000: Overpressure Protection

·        Article XXVI-8000: Nameplates, Stamping, and Reports

·        Article XXVI-9000: Glossary

·        Mandatory Supplements I – III

·        Non-mandatory Supplements A - D

ASME BPVC Section IX – Welding, Brazing, and Fusing Qualifications

Part QF – Plastic Fusing

Application

The use of HDPE in U.S. nuclear power plants is limited to PE4710 since this was the material first identified in Code Case N-755 and reviewed by the U.S. NRC.  Code Case N-755 was initially limited to butt-fusing (hot plate) but electrofusion was included when incorporated into the ASME B&PV Code, Section III, Appendix XXVI.  (N-755 and Section III).  Both N-755 and Appendix XXVI limit the use of HDPE to Class 3 piping systems. 

Benefits

The carbon steel used in Service Water systems are often subjected to various forms of degradation including general corrosion, microbiological induced corrosion, tuberculation, and galvanic corrosion.  HDPE is typically impervious to these forms of degradation.  Additionally, nuclear power plants typically have robust seismic requirements and HDPE is very flexible which increases its ability to survive an earthquake.  (NRC presentation and tuberculation)

Challenges

The use of HDPE in nuclear power plants requires extensive qualification and testing efforts to demonstrate that the material is safe under all design basis conditions.  The U.S. NRC has raised concerns with the use of HDPE related to butt fusion joint integrity, the ability to detect flaws in joints, and the potential for slow crack growth (RG 1.193 r5 and Catawba).  Power plants can still request approval from the U.S. NRC on a case-by-case basis (i.e., relief request). 

Instructor Comments

The first topic is very good, so I went ahead and assigned it yo you. You might think of a better title. Also, you may find it to be very broad, and if that is the case, you could concentrate on HDPE Piping for Nuclear Plants including Butt Fusion and Electrofusion joining of these pipes.

Possible Topics:

1. Use of HDPE at Nuclear Power Plants (new article, would include regulatory history, ASME Code implications, and all uses to date based on publicly available submittals to the NRC)
2. HDPE Pipe
3. Horizontal Directional Drilling
4. Sliplining