FOCUS ON THE US | LIFE EXTENSION
Comanche Peak aims for 60-year life
One of the USA’s youngest nuclear plants has sought a renewed licence, which will extend its operating lifetime by 20 years. The application was recently published
VISTRA OPERATIONS COMPANY, THE OPERATOR of Comanche Peak nuclear power plant in Texas, has sought renewed operating licences for Comanche Peak 1 and 2. The company – acting both on its own behalf and on behalf of the plant owner, Comanche Peak Power Company – has submitted a formal application for licences that would add an additional 20 years to the plant lifetimes, bringing them up to 60 years each. The existing licences for unit 1 and unit 2 expire on
8 February 2030 and 2 February 2033, respectively. The application for licence renewal – which requires no physical plant alterations or modifications – was submitted to the Nuclear Regulatory Commission (NRC) in October and was recently made public. Comanche Peak 1 and 2 are sited 65 miles (108 km) southwest of Dallas-Fort Worth, Texas. Each unit is based on a four-loop Westinghouse Electric nuclear steam supply system. They are among the youngest of the USA’s fleet of nuclear stations – commercial operation began at Unit 1 on 13 August 1990 and Unit 2 on 3 August 1993. They were followed by Watts Bar 1 and 2. Each reactor was initially operated at a rated thermal power of 3411 MWt, but by 2008, the two units were each producing 3612 MWt after a series of upratings. As a consequence, electricity output has also been increasing; Unit 1 was uprated in autumn 2008 from 1,210 MWe to 1,259 MWe and Unit 2 was uprated in autumn 2009 from 1,208 MWe to 1,245 MWe. At that time it was thought that additional units could
potentially be built at the site. Vistra subsidiary Luminant formed a joint venture with Mitsubishi Heavy Industries for this purpose and in 2008 they jointly applied for a combined construction and operating licence from NRC, planning to build two 1,700 MW advanced PWRs of a Mitsubishi design. However, that application was suspended in 2013 when falling gas prices and the build out of wind in Texas hollowed out the financial case for expansion at the site. Meanwhile MHI shifted its focus to restarting its Japanese reactors following the Fukushima event. The application has not, however, been withdrawn although Vistra’s focus is now on gaining a new and substantially longer licence for the existing plant.
18 | December 2022 |
www.neimagazine.com
Preparing for the period of extended operation In order to prepare for the licence renewal application, the plant operator carried out a scoping and screening process to define which systems and structures were relevant for the renewed licence. These systems and structures were
grouped into the following areas: ● Reactor vessel, internals and reactor coolant system. ● Engineered safety features ● Auxiliary systems ● Steam and power conversion systems ● Containments, structures and component supports ● Electrical, instrumentation and control systems
Typical aging effects that require management in these groups of components are cracking, cumulative fatigue damage, change in dimension, loss of fracture toughness, loss of material, reduction of heat transfer or wall thinning. There are several general safety issues currently under
scrutiny by the US Nuclear Regulatory Commission (NRC) and designated as ‘active or unresolved’. Four of these that may apply to the units at Comanche Peak are as
follows: ● ‘Multiple steam generator tube leakage’ has been incorporated into the steam generator programme. It covers inspection requirements for steam generator tubes.
● ‘Fatigue evaluation of metal components for 60-year plant life’, concluded that licensees should address the effects of reactor coolant environment on component fatigue life as aging management programmes are formulated in support of licence renewal.
● ‘Assessment of debris accumulation on PWR sump performance’ addresses the potential for blockage of containment sump strainers that filter debris from cooling water supplied to the safety injection and containment spray pumps following a postulated loss of coolant accident. The issue is based on the identification of new potential sources of debris, including failed containment coatings, which may block the sump strainers.
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