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Title: TRACE/PARCS Analysis of ATWS with Instability for a MELLLA+BWR/5

A TRACE/PARCS model has been developed to analyze anticipated transient without SCRAM (ATWS) events for a boiling water reactor (BWR) operating in the maximum extended load line limit analysis-plus (MELLLA+) expanded operating domain. The MELLLA+ domain expands allowable operation in the power/flow map of a BWR to low flow rates at high power conditions. Such operation exacerbates the likelihood of large amplitude power/flow oscillations during certain ATWS scenarios. The analysis shows that large amplitude power/flow oscillations, both core-wide and out-of-phase, arise following the establishment of natural circulation flow in the reactor pressure vessel (RPV) after the trip of the recirculation pumps and an increase in core inlet subcooling. The analysis also indicates a mechanism by which the fuel may experience heat-up that could result in localized fuel damage. TRACE predicts the heat-up to occur when the cladding surface temperature exceeds the minimum stable film boiling temperature after periodic cycles of dryout and rewet; and the fuel becomes “locked” into a film boiling regime. Further, the analysis demonstrates the effectiveness of the simulated manual operator actions to suppress the instability.
Authors:
;  [1] ;  [1] ;  [1] ;  [1] ;  [2]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States)
  2. Nuclear Regulatory Commission, Washington, DC (United States)
Publication Date:
OSTI Identifier:
1239794
Report Number(s):
BNL--111742-2016-JA
Journal ID: ISSN 0029-5450; TRN: US1601634
Grant/Contract Number:
SC0012704
Type:
Accepted Manuscript
Journal Name:
Nuclear Technology
Additional Journal Information:
Journal Volume: 196; Journal Issue: 2; Journal ID: ISSN 0029-5450
Publisher:
American Nuclear Society (ANS)
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
Nuclear Regulatory Commission/Non-NUREG, Washington, DC (United States)
Country of Publication:
United States
Language:
English
Subject:
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS; 42 ENGINEERING BWR MELLLA+ operating domain; ATWS instability; TRACE/PARCS model of operator actions