No major technical roadblocks prevent S’pore from storing nuclear waste, study with Swedish firm shows

SKB International is the firm behind the technology for Finland’s nuclear waste tomb called Onkalo – a 10km-long cavern within granite and gneiss rock.

The company performed the desktop study on various deep geological repository concepts based on publicly available data for Singapore, said EMA.

“The study did not indicate that there are technical showstoppers in any of the radioactive waste management options for Singapore. For example, the amount of radioactive waste generated is not expected to be prohibitive for a small country like Singapore,” said the agency.

The amount of waste produced depends on the type of reactor. A 1GW traditional large reactor, for instance, can produce enough energy to power about 700,000 homes a year.

It can produce about 370,000 litres of nuclear waste a year, which would fill about one-seventh of an Olympic pool. Of this, around 5 per cent is high-level waste, mainly used fuel.

In comparison, Singapore’s Semakau Landfill has the capacity of more than 11,000 Olympic-sized swimming pools.

The study concluded that existing approaches in managing radioactive waste from traditional nuclear power plants are feasible for small modular reactors – which are more advanced and safer reactors that Singapore has been monitoring.

Small modular reactors can have a power capacity of up to 300MW, a third of a 1GW conventional plant. The amount of waste produced by a small reactor depends on its design. Some studies have shown that a small modular reactor can produce as much waste as a large one for every unit of electricity produced.

“The risks of managing radioactive waste are low and can be mitigated through proper radiation shielding and containment measures,” said EMA.

However, to comprehensively assess the technical feasibility of hosting a deep geological repository in Singapore, additional surveys on the country’s geophysical environment will still need to be conducted, added the EMA.

“We will continue building our capabilities in this area, including collaborating with international experts to understand various waste management solutions and their suitability for Singapore,” said EMA.

Experts said Singapore’s granite rocks in the northern and central regions may be suitable to store used fuel and radioactive waste, but they must be unfractured and possess certain properties.

Granite is a preferred rock type for deep waste storage because it is hard, dense and relatively impermeable to groundwater, which can transport radiation-emitting particles, said Mark Lim, chairman of the Institute of Electrical and Electronics Engineers Nuclear and Plasma Sciences Society’s Singapore chapter.

“Singapore is fortunate to have well-characterised granitic formations, such as the Bukit Timah granite, which extends across Woodlands and Sembawang through Bukit Batok and down to the central part of Singapore. We also have granitic rock on Pulau Ubin,” added Lim.

The granite needs to be unfractured, or free of fault lines.

“In heavily fractured zones, groundwater can find pathways through the rock and this defeats the purpose of geological isolation,” he noted.

Further studies will need to scrutinise rock samples, monitor groundwater movement and look into environmental impacts before any site can be considered, he added.

Apart from the rock, a deep underground repository should have two other layers of defence, or barriers: a corrosion-resistant copper canister encapsulating the used fuel rods, and a buffer clay material that envelops the canister and swells when exposed to groundwater, to close up fissures in rock.

If one barrier is weaker, the other barriers can be enhanced to maintain the overall stability of a deep geological repository, EMA explained.

This enables such underground facilities to be safely built across a range of geological conditions, the agency said.

Instead of building a snaking underground cavern, Singapore could consider drilling a narrower, but deep borehole to store the waste, given the space constraints on land and underground, suggested Lim.

This is an emerging form of underground storage which involves placing fuel canisters at the bottom of a 5km-deep hole – far away from shallower groundwater aquifers. The waste will then be sealed with bentonite clay, cement and asphalt, making it impossible to retrieve.

Experts say that one key issue to navigate is the social perception towards having a nuclear waste storage site in Singapore. Globally, it has been tough to pin down disposal areas because neighbouring communities have concerns.

Matthew Chew, nuclear competency and strategy lead at engineering consultancy HY, noted that it took four decades for Finland’s Onkalo site to be built.

“It took almost 20 years for a site to be selected, after the Finnish government set up its nuclear waste policy, and with continuous public engagement. And even after ratification, it took another 20 years before operations will begin,” said Chew.

He added: “Given Singapore’s extremely unique considerations and geographical constraints, the public will need to be constantly engaged. We will need to engage the public on basic nuclear energy before we even talk about underground waste storage in Singapore.”

Lim added: “An underground disposal facility could be sited in an area well away from residential neighbourhoods. Potentially in a less densely developed part of Singapore, or on a suitable offshore island.”