Document: NUREG-0800
Document ID: 41b2cf88-b6dc-4005-939a-cf3fb1a561d2
Document Type: srp
Title: INADVERTENT DECREASE IN BORON CONCENTRATION IN THE REACTOR
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0703/ML070380222.pdf
Revision Date: 2023-06
Chapter: 15
Section ID: 15.4.6
CFR Part: 
CFR Title: 

Content:
COOLANT SYSTEM (PWR) REVIEW RESPONSIBILITIES Primary - Organization responsible for review of transient and accident analyses for PWRs/BWRs Secondary - None I. AREAS OF REVIEW Unborated water can be added to the reactor coolant system (RCS), via the chemical volume and control system (CVCS), to increase core reactivity. This may be inadvertent due to operator error or CVCS malfunction, and cause an unwanted increase in reactivity and a decrease in shutdown margin. A specific plant design may include other inadvert additions of unborated water to the RCS, like instrument flushing systems. During refueling, the RCS is an open system. An inadvertent addition of unborated water to the RCS is possible due to operator error or malfunction of systems not connected to the RCS. The operator must stop this unplanned dilution before the shutdown margin is eliminated. As sequences of events that may occur depend on plant conditions at the time of the unplanned moderator dilution, the review includes conditions like refueling, startup, power operation (automatic control and manual modes), hot standby, hot shutdown, and cold shutdown. 15.4.6-2 Revision 2 - March 2007 The specific areas of review are as follow: 1. The review of postulated moderator dilution events considers causes, initiating events, the sequence of events, the analytical model, the values of parameters in the analytical model, and predicted consequences of the event. 2. The sequence of events described in the applicant's safety analysis report (SAR) is reviewed. The reviewer concentrates on the need for the reactor protection system and required operator action to secure and maintain the reactor in a safe condition. 3. The analytical methods are reviewed for whether the mathematical modeling and computer codes have been accepted by the staff. If a referenced analytical method has not been previously reviewed, the reviewer initiates a generic evaluation of the new analytical model. 4. The predicted results of