NS Savannah Nuclear Merchant Ship Design Review. Summary Report Page: 26 of 42
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20
is some possibility of gamma heating of the primary system piping adjacent to,
the reactor. However, since the pipe always contains water, gamma heating should
not cause abnormal thermal stresses.
For part (c), thermal insulation in contact with austenitic stainless steel
was investigated to establish the probability for failure stemming from stress
corrosion cracking. Stress corrosion cracks can occur in austenitic stainless steel
when it is exposed to a moist environment containing oxygen and as little as 5 parts
per million of chloride. Cracking has been observed in a temperature range of 650 F
down to -130 F in a time as short as 30 minutes and as long as 7 years. W.S. Savannah
insulation consists of commercial asbestos, fiberglas and other materials in which
small amounts of chloride ions may be present. In addition, the insulation fire-
resistive sealer, Benjamin Foster No. 30-72 contains 30 per cent chlorine. This
sealer forms a waterproof coating around the outside of the insulation. Quantities
of chlorine as an impurity in the insulation or as a major constituent in the
sealer are sufficient to form the corrosive agent in the presence of moisture. Since
the air temperature and humidity within the containment are controlled, no moisture
should collect on or penetrate the insulation, Therefore, the chance of stress
corrosion cracking occurring in normal operation is remote.
However, if moisture content should increase because of air conditioner failure,
water leakage, or other means and the insulation sealer should become ineffective,
stress corrosion may occur. Inspections within the containment should include exam-
ination of the insulation sealer, with removal and replacement of damaged portions
scheduled for the next maintenance shutdown. The probability that stress corrosion
cracking of the stainless steel will occur as a result of the above hypothesis is
remote, and the Benjamin Foster No. 30-72 Sealer appears to be one of the best sealers
available for this service.
For part (d), a review of B&W data and specified welding procedures for the
incidence of carbon migration and microfissures in weld heat afflicted zones for the
- reactor vessel and the primary loop was attempted.
However, since B&W welding procedures are proprietary company information
and so not available outside of the company, it was impossible for Ebasco to proceed
with the task.
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NS Savannah Nuclear Merchant Ship Design Review. Summary Report, report, June 30, 1960; United States. (https://digital.library.unt.edu/ark:/67531/metadc863057/m1/26/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.