Analysis of instrument tube ruptures in Westinghouse 4-loop pressurized water reactors

Technical Report · Mon Dec 01 04:00:00 EST 1986

OSTI ID:6862310

Fletcher, C D; Bolander, M A

A recent safety concern for Westinghouse 4-loop pressurized water reactors (PWRs) is that, because of a seismic event, instrument tubes may be broken at the flux mapping seal table, resulting in an uncovering and heatup of the reactor core. This study's purpose was to determine the effects upon findings of a similar 1980 study if certain test variables changed. A 1980 US Nuclear Regulatory Commission (USNRC) analysis of PWR behavior used the RELAP4/MOD7 computer code to determine the effects of breaking instrument tubes at the reactor vessel lower plenum wall. The 1986 study discussed here was performed using RELAP5/MOD2, an advanced best-estimate computer code. Separate effects analyses investigated instrument tube pressure loss, heat loss, and tube nodalization effects on break flow. Systems effects analyses: (1) investigated the effects of changing the break location from the reactor vessel to the seal table, (2) compared RELAP4/MOD7 and RELAP5/MOD2 results for an identical transient, (3) verified a key finding from the 1980 analysis, and (4) investigated instrument tube ruptures in the Zion-1 PWR using best-estimate boundary and initial conditions. The outcome of these analyses permits adjustment of the 1980 analysis findings for instrument tube ruptures at the seal table and indicates the best-estimate response of a Washington PWR to the rupture of 25 small instrument tubes at the seal table.

• Research Organization: EG and G Idaho, Inc., Idaho Falls (USA); Nuclear Regulatory Commission, Washington, DC (USA). Div. of Reactor Systems Safety
• DOE Contract Number: AC07-76ID01570
• OSTI ID: 6862310
• Report Number(s): NUREG/CR-4672; EGG-2461; ON: TI87004485
• Country of Publication: United States
• Language: English

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