Discussed below are the specific positive and negative effects of incorporating inherent and passive safety design features that, in view of the SMR designers, affect plant characteristics in areas other than safety.

4.1. WATER COOLED SMRS

Table 46 summarizes the positive and negative effects of the inherent and passive safety design features of pressurized water type SMRs in areas other than safety, based on inputs provided by SMR designers in Annexes I-V of this report.

As can be seen from Table 46, relying more on inherent and passive safety features and passive safety systems as compared to traditional solutions based on active safety systems is in all cases a trade-off regarding plant economy.

TABLE 46. SUMMARY OF POSITIVE AND NEGATIVE EFFECTS FROM INCORPORATION OF INHERENT AND PASSIVE SAFETY DESIGN FEATURES INTO PRESSURIZED WATER TYPE SMRs — AREAS OTHER THAN SAFETY

— Reduced operation and maintenance IRIS

costs resulting from simplified operation and maintenance;

-Higher capacity factor; IRIS

-Possibly reduced security costs IRIS

resulting from ‘inherent security’

-Certain economic benefits achieved CAREM-25,

via longer reactor pressure vessel IRIS

lifetime owing to a reduced fast neutron fluence

-Reduced plant costs resulting from CAREM-25,

simplification of certain safety IRIS

systems

Decrease in plant costs resulting from Certain deterioration of KLT-40S

Decrease in the operation costs KLT-40S

resulting from a decrease in the amount of radioactive waste

6 Reduced number of safety Improved plant economy owing to grade systems and simplified operation and maintenance

components requiring and reduced operation waste maintenance

Increase in plant construction and KLT-40S maintenance costs

Increase in plant construction KLT-40S and maintenance costs

9 All safety grade safety — Reduced operation and maintenance IRIS

systems are passive costs resulting from reduced

complexity and improved reliability of the plant;

-Added resilience to sabotage and other malevolent actions

Increased specific cost of reactor CAREM-25 pressure vessel; potentially increased complexity of reactor operation (startup, etc.)

Decrease in costs owing to simplified Increased specific cost of reactor SCOR operation and maintenance pressure vessel; potentially

increased complexity of reactor operation (startup, etc.)

Increased plant costs owing to MARS limited reactor power and energy conversion efficiency

the use of a passive emergency core cooling system with an infinite grace period, actuated upon flow rate decrease

a With a potential of being counteracted by modular construction of multiple units at a site. b Counteracted by reduced containment size and reduced plant footprint.

Regarding solutions intended to eliminate certain types of accidents or prevent their consequences through design features, see numbers 1-6 of Table 46. The commonly mentioned expected benefits are:

• Decrease in plant capital costs due to compact primary circuit and compact containment (except for the MARS);

• Decrease in plant capital costs due to simplicity of operation and maintenance, specifically due to a reduction of the number of systems requiring maintenance;

• Decrease in plant capital costs due to elimination or reduction of off-site emergency planning;

• Decrease in plant capital costs via an enhanced option to build several plants at a site or to use twin or multiple unit plants, owing to decreased core damage frequency and large early release frequency;

• Less concern regarding human actions of a malevolent character and, potentially, cost reduction resulting from ‘inherent security’ of the plant.

At the same time, the same solutions are expected to result in the following negative implications:

• Increased plant capital costs owing to the limited power of a single module (potentially counteracted by modular construction of multiple units at a site);

• Increased cost of a larger reactor pressure vessel (or additional pressure vessel in the case of the MARS design);

• Certain deterioration of burnup cycle characteristics (for example, when the liquid boron system is abandoned) or maintainability (for the compact modular design of the KLT-40S and for the MARS design with an additional pressure vessel).

In nearly all cases, the above mentioned benefits and disadvantages have a potential to counteract each other; for example, increased specific capital costs for a single unit plant could possibly be counteracted by modular construction of multiple units at a site; increased vessel costs could be counteracted by reduced containment costs; and certain deterioration of maintainability could be counteracted by a reduced number of systems needing maintenance.

Regarding positive and negative impacts resulting from the application of passive safety systems, the opinions of SMR designers may vary. For example, designers of the KLT-40S see only negative cost implications with use of passive safety systems, such as increased construction and maintenance costs; see numbers 7-8 of Table 46. Designers of the IRIS see only positive cost implications with use of passive safety systems, such as reduced operation and maintenance costs and enhanced resilience to sabotage; see number 9 of Table 46. Other designers mention both positive and negative features. The opinion of designers may also be conditioned by a specific passive safety system type, i. e., expectations might be different for, say, a gravity driven passively actuated shutdown system and a natural convection based decay heat removal system.