Conference Proceedings Paper
Modified 37-Element Bundle Dryout
NURETH-14 - 2011 September 25-30
Ab Tahir (AMEC NSS)
Yuksel Parlatan (Ontario Power Generation)
Marc Kwee (Bruce Power)
Wie Liauw (Ontario Power Generation)
The Heat Transport Systems (HTS) of the Canadian nuclear reactors are ageing. One of the effects of ageing is the non-uniform change in the dimension of the reactor pressure tubes through the mechanism of diametral creep. The mechanism has the global effect of increasing channel flows and decreasing the reactor header-to-header pressure drop. However, the increased flow is not distributed uniformly through the fuel bundle cross-section because the bundle tends to settle at the bottom of the pressure tube leaving a crescent shaped space on the top. This portion experiences the bulk of the increased flow, as it offers the path of least hydraulic resistance. As a result of this flow bypass, the coolant flows through some of the interior-subchannels of the fuel bundle are reduced. For a given flow, inlet temperature and exit pressure, flow bypass in the top of the channel reduces flow from the interior subchannels and consequently reduces the Critical Heat Flux (CHF).
To recover some of the reduction in dryout power, OPG started a program in 2004 to examine possible modifications to the reference 37-element bundles that may result in an increase in dryout powers for the uncrept and crept pressure tube. Under accident conditions, where CHF is a concern, the ideal design is one where all fuel elements reach dryout at the same time. The ASSERT subchannel code  was used to explore potential modifications to the 37-element bundle that may result in increased dryout powers in an uncrept and crept pressure tube. In addition analysis of post-dryout tests in 37-element bundle  were examined to explore the potential of increasing the dryout power of the reference 37-element bundle by slightly modifying the bundle geometry. A small reduction of the centre element in the bundle was selected as an approach to enhance the dryout power of the bundle. CHF tests of the modified bundle were performed . The measurement confirmed that the modified bundle has higher dryout powers than the reference bundle.
Individual Conference-Paper Copies (Electronic Where Available):
- For CNS members, the first 5 copies per calendar year are free, and additional copies are $10 each.
- For non-members, the price is $25 for the first Conference-paper copy in a request, and $10 each for additional copies of papers in the same conference and in the same request.
- Contact the CNS office to order reprints.