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Accounts Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Accounts Receivable
Deferred DOE cost share liabilities	$ 10,237	$ 10,237	$ 0

X

- Definition

The carrying amount of deferred DOE cost share liabilities.

+ References

No definition available.

+ Details

Name:	svsvu_DeferredDoeCostShareLiabilities
Namespace Prefix:	svsvu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- References

No definition available.

+ Details

Name:	us-gaap_AccountsReceivableNetCurrentAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration