Procedure to prevent temperature rise of primary upper shielding in high temperature engineering test reactor(HTTR)

In a non-nuclear heat up test of the high temperature engineering test reactor (HTTR), which was conducted in February 1997, the temperature of primary upper shielding as well as helium gas temperature inside standpipes of the reactor became much higher than expected. Because it was estimated that these temperatures should exceed design values at full power operation of the HTTR, countermeasures were considered and taken to prevent the temperature rise. After applying two countermeasure steps, confirmation tests to demonstrate the effect of the measures were performed. The test results and extrapolation by temperature analysis finally showed that the countermeasures are appropriate, and the design temperatures should be observed at full power operation.