AnsaldoEnergia

Divisione Nucleare
Progetto
Project
PDS-XADS
AnsaldoEnergia
Identificativo
Document no.
XADS 20 TRIX 009
Rev.
Rev.
1
Cl. ris.
class
Pagina
Page
49
of the two loops at any reactor power level (see Fig. 3.2-9), provided by centrifugal pumps
(one per loop). Due to the constant pump speed and to the absence of flow regulating
devices no increase of the oil flowrate is can take place in the system).
level 4 events description
The event [2.1.1.1] "DECREASE OF ORGANIC FLUID TEMPERATURE" can be attributed
to:
• malfunctions of the SCS Air Coolers that lead to reject to the external air more heat than
that removed from the primary system. It should be noted that, due to the performance
of the SCS system, this phenomenology appears to have a weak impact at nominal plant
power level; its impact becomes more and more significant for decreasing plant
operating power.
• malfunctions of the SCS Feed and Bleed System that lead to the decrease of oil storage
tank temperature.
level 5 events description
Considering the event [2.1.1.1.1] "INCREASED AIR COOLERS HEAT REMOVAL", the
MLD shows that it can derive from the malfunction that affect all Air Coolers of one SCS
loop (3 out of 3 SCS AIR COOLERS MALFUNCTION) or from the malfunction that affect
only one Air Cooler (1 out of 3 SCS AIR COOLERS MALFUNCTION).
It is noted here that the XADS primary and secondary coolant temperatures control strategy
is centered on the Air Coolers System which therefore is designed with a large degree of
flexibility and provided with several regulating devices including variable speed fans,
orientable fan valves, moving inlet and outlet louvers in each fan (see Fig 3.2-10).
The drawback of this flexibility is then the large variety of malfunctions that can be
postulated.
Considering the event [2.1.1.1.2] "SECONDARY COOLANT FEED and BLEED SYSTEM
MALFUNCTION", the MLD shows that it can derive from the malfunctions of the oil storage
tank heaters. This event however is considered of small significance.
DNU 020/1