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The Nuclear Electrical Engineer

An educational resource for electrical engineers in the nuclear power industry

Here you can find design tips on technical skills like cable and breaker sizing, short-circuit evaluations and more, PLUS deep-dive analysis of nuclear-specific topics like design basis, Tech Specs, UFSARs, and safety-related SSCs — built from primary source documents.

Licensing Basis · Feature

Nuclear power plant “modes” explained here

John Livingston
December 9, 2014 · 2 min read

The plant’s operating status is classified under one of several “modes.” These probably won’t be explained to you on your first day on the job . . . .

When a plant is “shut down,” there are actually different levels of how shut-down a plant is at any given time. These different steps are called modes. There are a different number of modes for a pressurized water reactor than there are for a boiling water reactor, and depending on the manufacturer of each. The two  tables below are taken from the generic tech specs from Westinghouse (for PWRs) and GE (BWRs). You will hear the “mode” designator often. These tables explain what they mean.

Table 1 – Westinghouse Pressurized Water Reactor Operation Modes

Mode Title Avg. Rx. Coolant Temp. (℉)
1 Power Operation N/A
2 Startup N/A
3 Hot Standby ≥ 350
4 Hot Shutdown 350 > TAVG > 200
5 Cold Shutdown ≤ 200
6 Refueling N/A

Table 2 – General Electric Boiling Water Reactor Operation Modes

Mode Title Avg. Rx. Coolant Temp. (℉)
1 Power Operation N/A
2 Startup N/A
3 Hot Shutdown > 200
4 Cold Shutdown ≤ 200
5 Refueling N/A

 

Both of these tables are published in the standard tech specs created by Westinghouse and GE. Here is the link to the NRC’s compilation of the latest versions of these two tech specs and more:

Link: http://www.nrc.gov/reactors/operating/licensing/techspecs/current-approved-sts.html

Here are the page numbers for quick referencing:

Westinghouse, Standard Technical Specifications, Volume 1: Specifications, Rev. 4, released as NUREG-1431, p. 1.1-7.

General Electric, Standard Technical Specifications, Volume 1: Specifications, Rev. 4, released as NUREG-1433, p. 1.1-7.

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