SAFETY P R A C TIC E S - gnssn - International Atomic Energy Agency

This publication is no longer validPlease see http://www-ns.iaea.org/standards/Basis for acceptanceSafety Guide 50-SG-D7, paras 212-215, 507.Assessment questions(1) Are the connections of the EPS to the off-site power supplies of sufficientcapacity to provide reliable power and maintain adequate redundancy consideringthe on-site arrangements and design of the EPS?(2) Have provisions been included to minimize the probability of losing electricalpower to the EPS from any of the remaining power supplies as a result of, orcoincident with, one of the following: the loss of power generated by thenuclear unit, loss of power from the off-site supplies, or the loss of all powerfrom the on-site electrical power supplies?(3) Are the connections from the off-site grid designed and protected so as tominimize, to the extent practical, failures (or simultaneous loss) under operationalstates and postulated accident conditions? Do other lines cross theconnection? Are there any other structures or other hazards which by theirfailure can damage the connections, e.g. transmission towers, meteorologicaltowers, lightning shield wires or potential explosions?(4) If two circuits originate from a common switchyard does there exist any potentialcommon cause failure mode, physical or otherwise, which can affect bothcircuits, such as the effects from apparatus explosions and/or fires, interactionsof controls, electrical short circuits, inadequate protective relaying systemdesign or co-ordination, non-independence of control power or supportsystems for apparatus for the two circuits?(5) Do any common cause failure modes exist between the normally connectedcircuits to the grid and the stand-by power supplies such that power cannot berestored from the grid following the loss of either off-site circuit and a singlefailure in the EPS, in the time limits required to shut down the plant safely?(6) Is the electrical power from the connections of the EPS to the grid availablewithin specified time limits after a shutdown of the plant?(7) Where there are two or more circuits extending from the grid connection tothe EPS, have provisions been made to permit isolation of a failed circuit andthe energization of the alternative circuit within the time limits required tofulfil the safety function?(8) Do the components of the grid connections have sufficient capacity and capabilityto supply the loads which may be connected under operational states andaccident conditions, taking into account the pertinent transient conditions?7